Download Inverted-U dopamine D1 receptor actions on prefrontal neurons

© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
ARTICLES
Inverted-U dopamine D1 receptor actions on prefrontal
neurons engaged in working memory
Susheel Vijayraghavan1, Min Wang1, Shari G Birnbaum1,3, Graham V Williams2 & Amy F T Arnsten1
Dopamine (DA) D1 receptor (D1R) stimulation in prefrontal cortex (PFC) produces an ‘inverted-U’ dose-response, whereby
either too little or too much D1R stimulation impairs spatial working memory. This response has been observed across species,
including genetic linkages with human cognitive abilities, PFC activation states and DA synthesis. The cellular basis for the
inverted U has long been sought, with in vitro intracellular recordings supporting a variety of potential mechanisms. The current
study demonstrates that the D1R agonist inverted-U response can be observed in PFC neurons of behaving monkeys: low levels
of D1R stimulation enhance spatial tuning by suppressing responses to nonpreferred directions, whereas high levels reduce
delay-related firing for all directions, eroding tuning. These sculpting actions of D1R stimulation are mediated in monkeys and
rats by cyclic AMP intracellular signaling. The evidence for an inverted U at the cellular level in behaving animals promises to
bridge in vitro molecular analyses with human cognitive experience.
The prefrontal cortex (PFC) is critical for higher order cognitive
functions, guiding our behavior, thoughts and emotions using representational knowledge; that is, working memory1. Stimulation of DA
D1–D5 receptors (D1Rs) in PFC produces an ‘inverted-U’ doseresponse on working memory whereby either too little or too much
stimulation impairs cognitive performance2. Unlike many other biological functions, in which the inverted U occurs at the extremes of
physiological conditions, the D1R inverted U occurs within the confines of normal physiology and may account for some of the
ordinary variability in higher cognitive abilities. This inverted-U
dose-response has been observed in mice3, rats2, monkeys4–6 and
humans7,8 performing PFC cognitive tasks. Recently, the inverted U
has been observed in regard to genetic alterations in catecholamine-Omethyltransferase (COMT), an enzyme that breaks down DA and
thus controls DA levels in PFC9–11. The impact of COMT polymorphisms in patients with schizophrenia12 highlights the significance of
prevailing PFC DA transmission to our understanding of human
cognitive disorders.
The cellular and molecular bases of the inverted U have long been
sought in animal studies. Important clues have arisen from intracellular
recordings of PFC neurons in slices from rat cortex. These studies have
shown that D1R stimulation may alter excitability and attenuate
information flow by altering input efficacy to PFC neurons13–15.
However, neurons in slices are necessarily in an altered state from
those in intact animals performing higher cognitive tasks. PFC neurons
in monkeys performing a spatial working memory task show taskrelated firing specific to each task epoch: some cells fire when the cue is
presented in specific spatial positions, some fire during the delay period
when spatial information is held in the absence of environmental
stimulation and some fire in relation to the response when the subject
makes an eye movement to the remembered spatial position. Neurons
firing during the delay period are usually spatially specific, firing more
to preferred directions (PDs) than nonpreferred directions (NPDs),
thus creating a spatially tuned memory field (Fig. 1a). This spatially
tuned delay-related activity is considered the electrophysiological
signature of spatial working memory. DA cells that project to
PFC fire during the cue period in spatial working memory tasks16.
Thus, endogenous DA is presumably released in PFC during
task performance.
Until now, our understanding of D1R effects on mnemonic
activity of PFC neurons has been limited to application of D1R
antagonists. Previous studies17,18 found that high levels of D1R blockade completely inhibited cell firing, whereas low levels of blockade
increased cell firing18. An inverted U dose-response was inferred based
on the cognitive data3,18, but direct evidence for an inverted U at the
cellular level would require experiments varying doses of D1R stimulation on single PFC neurons. This study provides these data, demonstrating D1R inverted-U effects on PFC neuronal firing in monkeys
performing a spatial working memory task. Low levels of D1R
stimulation enhanced spatial tuning by reducing firing to the
NPDs more, whereas high levels of D1R stimulation suppressed
delay-related firing for all directions, thus eroding tuning. The intracellular events underlying this suppression were also explored using
agents that inhibit either cAMP or protein kinase C (PKC) signaling.
Although D1Rs are generally coupled by Gs to activation of cAMP
signaling, they are also thought to couple to the phosphatidyl inositol
cascades19, and in vitro studies have shown D1R effects through both
signaling pathways.
1Department of Neurobiology, Yale Medical School, 333 Cedar Street, New Haven, Connecticut 06520-8001, USA. 2Department of Psychiatry, Yale University School of
Medicine, 300 George Street, Suite 901, New Haven, Connecticut 06511, USA. 3Present address: University of Texas Southwestern Medical Center, Department of
Psychiatry, NC6.102, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9070, USA. Correspondence should be addressed to A.F.T.A. ([email protected]).
Received 20 December 2006; accepted 12 January 2007; published online 4 February 2007; doi:10.1038/nn1846
376
VOLUME 10
[
NUMBER 3
[
MARCH 2007 NATURE NEUROSCIENCE
ARTICLES
a
F C
Fixation
F C
D
D
R
D
F C
R
D
F C
Time
F C
D
PD
D
D
NPD
R
80
0
0
F C
C
R
Saccade
2,500 ms
F
R
45
180
500 ms
D
PD
80
90
135
Delay
C
Control
R
Cue
500 ms
F
b
R
315
225
270
R
F C
D
F C
NPD
D
0
SKF 81297 at 10 nA
R
R
c
Firing rate (Hz)
80
1.6
Mean normalized
firing rate difference
(PD – NPD) (arbitrary units)
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
500 ms
1.4
*,†,**
1.2
0
80
0
SKF 81297 at 15 nA
80
80
1
0.8
0
0.6
0
SKF 81297 at 40 nA
0.4
80
80
0.2
0
Control
0 nA
Dose 1
10 nA
Dose 2
15 nA
Dose 3
40 nA
0
0
0.5
2.5
0
0
0.5
2.5
Time (s)
Figure 1 Inverted-U effects mediated by D1R agonists. (a) Left, a schematic of the ODR task, delineating the fixation (F), cue (C), delay (D) and saccaderesponse (R) epochs of the task with the target presentation profile (see Methods). Right, an example of a PFC delay cell that showed sustained activation
toward PDs only. (b) PSTHs and rastergrams of a PFC neuron with weak spatial delay tuning (first row). Application of D1R agonist SKF81297 at 10 nA
produced a slight reduction in delay-related activity (second row; P o 0.05, F3,100 ¼ 30.268, ANOVA). Further application at 15 nA caused more reduction
in activity with a larger reduction in the NPD (right panels) than the PD (left panels), leading to sculpting of spatial tuning in the neuron (third row, ANOVA,
P o 0.05; interdirectional, P o 0.05). Application of SKF81297 at 40 nA caused a more marked suppression of activity with a reduction in spatial tuning
(bottom row, ANOVA, P o 0.05). Rastergrams and histograms aligned to cue onset. (c) Inverted-U SKF81297 dose-response profile of spatial tuning for
neuron shown in b. The mean difference in spike rate normalized to baseline firing rate in the PD and NPD is plotted as a function of the condition. Control,
D1R agonist dose 1 (10 nA) and dose 3 (40 nA) did not differ significantly in the spatial tuning estimate. Dose 2 (15 nA) was significantly different from
control (*P o 0.001, t-test), dose 1 (wP o 0.001, t-test) and dose 3 (**P o 0.001, t-test). Error bars, s.e.m.
RESULTS
Dose-response profile of D1R stimulation
This study examined the effects of a range of D1R agonist doses on PFC
neurons engaged by a working memory task to determine evidence of
an inverted U at the cellular level. We recorded PFC neurons from
monkeys engaged in the oculomotor delayed response (ODR) task
(Fig. 1a; see Methods) a spatial working memory task dependent on the
PFC (area 46). Of 500 neurons recorded, 147 possessed task-related
activity and 106 units possessed spatially tuned delay-related activity.
We used subpopulations of these units in the series of experiments
described in this study, iontophoresing D1R agonists at various doses
on these neurons to assess the effects of D1R stimulation on the
neurons (see Methods). Figure 1b shows effects of successive applications of the full D1R agonist SKF81297 on a PFC unit showing weakly
tuned delay-related activity in the control condition (first panel).
Application of a very low dose (10 nA) of SKF81297 (second panel)
marginally reduced the neuronal firing rate (P o 0.05, F3,100 ¼ 30.268,
ANOVA). Subsequent application of 15 nA of SKF81297 (third panel)
attenuated the activity in the NPD more markedly; activity in the PD
was less reduced in comparison (P o 0.001, F1,48 ¼ 20.603, ANOVA on
percentage reduction, average –19% PD, –50% NPD), thereby increasing the spatial tuning of mnemonic activity of this neuron. Further
application of a high dose (40 nA) of the agonist significantly
suppressed delay-related activity of the unit in the PD as well (P o
0.001, t-test for PD), resulting in erosion of spatial tuning compared
with the low-dose condition. The spatial tuning of this cell showed an
inverted-U dose-response relationship, as assessed by the difference
NATURE NEUROSCIENCE VOLUME 10
[
NUMBER 3
[
MARCH 2007
between the mean normalized firing rate at the PD and NPD (Fig. 1c).
The spatial tuning rose at 10–15 nA agonist doses and decreased at the
40 nA dose. An eight-direction polar plot (Supplementary Fig. 1
online) of the unit in Figure 1b demonstrates that the low dose of
SKF81297 enhanced spatial tuning by suppressing activity for the
NPDs. Effects of SKF81297 at low doses (10–18 nA) were also observed
with a different D1R agonist, A68930. In 19 of 23 units tested with
either agonist, delay-related activity was suppressed, whereas activity of
four units increased upon agonist application. In 14 of the 19 units in
which activity was suppressed, tuning was enhanced through greater
suppression of response to NPDs. Figure 2a shows mean normalized
delay-related firing for these 14 units tested with low doses of either
agonist at all spatial locations. We aligned the PD of all units to y ¼ 01
and normalized activity by equalizing activity in PDs in both conditions to delineate effects on spatial tuning alone. Shown are the spatial
profiles of the activity of the units in the control and D1R agonist drug
condition. A comparison of the two curves shows constriction of the
width of the tuning profile of units in response to low doses of the
agonist, leading to sharper tuning of the mnemonic activity upon D1R
stimulation. D1R agonists at low doses significantly reduced spatial
spread of neuronal activity (t-test, P ¼ 0.008; see Supplementary
Fig. 2 online).
Further, we fitted the average firing rates in the delay period to a
modified von Mises function (see Supplementary Methods online) to
assess D1R low-dose effects on tuning width. We estimated tuning
curve widths from the von Mises fits and found that reduction in the
width of the tuning curve by D1R agonist application was correlated
377
ARTICLES
Figure 2 Effects of low doses of D1R agonists on
the tuning profile of PFC neurons. (a) Effect of
1
40
low (10–20 nA) doses of D1R agonists on
R = –0.683 n = 19
20
normalized activity across the spatial field for a
n =14
0
population of 14 units that showed enhancement
10
20
30
40
50
60
70
80
90 100
–20
of spatial tuning with reduction in width of the
Tuning width control
–40
tuning curve. Control (blue) and D1R agonist (red)
–60
traces are shown as a function of spatial angle (y)
0
–80
away from the PD (y ¼ 0). We normalized firing
–135
0 θ
180
rates for maximal firing rate in the PD in control
and drug epochs and obtained average curves.
These curves were smoothed and plotted. (b) The change in tuning width upon low dose (5–18 nA) D1R agonist application on 19 PFC neurons (ordinate)
plotted against tuning width in the control condition (abscissa). A linear relationship was observed between the tuning in control conditions and the change
of tuning width following D1R agonist application (R ¼ –0.68, P ¼ 0.005, y ¼ –0.99x + 65). Broadly tuned cells with larger control tuning widths (abscissa)
showed greater reduction in width (ordinate) upon agonist application, whereas cells that were better tuned under control conditions showed lesser narrowing
of tuning with D1R agonist application.
b
Change in tuning width
with how broadly tuned the cells were in the control condition
(Fig. 2b). Cells that were less tuned (broader tuning curves) in the
control condition had a greater propensity to tuning enhancement
due to D1R agonist suppression (Pearson’s coefficient R ¼ –0.683,
P ¼ 0.005, n ¼ 19). Neuronal spatial activation assessed by other
methods such as loop-vector analysis showed a similar dependence of
the effects of agonists on initial conditions of the units.
Suppressive effects of D1R stimulation and specificity
We examined the specificity of the D1R suppressive effects by (i) using
three different D1R agonists and (ii) challenging the D1R agonist
response with a D1R antagonist. We tested a population of cells at
20–100 nA with the full D1R agonists SKF81297 or A68930 or the
partial agonist SKF38393 (Fig. 3a). Most neurons (106 of 116) showing
task-related activities were suppressed at higher doses of D1R stimulation, albeit with variable latencies. This suppression was substantial,
with nearly complete loss of neuronal spatial information. Higher doses
(20–100 nA) of either SKF38393 (Fig. 3a, top panel, n ¼ 10) or A68930
a 10
Normalized firing rate
F
C
D
R
F
C
10
PD
0
0
10
10
0
0
10
10
0
R
NPD
Control
SKF38393 (25–50 nA)
n = 10
Control
A68930 (25–50 nA)
n = 11
Control
SKF 81297 (25–50 nA)
n = 12
0.5
3.0
0
Time (s)
b
0.5
3.0
Time (s)
1
n = 5 sites
Control
D1R agonist (20–100 nA)
0
–135
378
D
0
0
Normalized response
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
Normalized response
a
0
θ
180
(middle panel, n ¼ 11) suppressed neuronal activity in the PD
compared with control (right panel), rendering activity comparable
to that in the NPD (left panel) and detuning the population spatial
response. High doses of SKF81297 (Fig. 3a, 20–75 nA, bottom panel,
n ¼ 12) also suppressed cell firing; however, as these neurons had
higher firing rates in the NPD as well, suppression was observed for
both the PD and the NPD. In summary, we found that high doses of
D1R stimulation led to general suppressive effects with loss of cellular
spatial information, whereas low doses enhanced spatial tuning
through asymmetric suppression of firing to NPDs.
D1R agonists also enhanced tuning in background unsorted unit
activity representing neurons more distant from the electrode. Whereas
high-dose D1R stimulation completely suppressed activity of isolated
single units close to the electrode, D1R agonist levels would be expected
to taper to lower concentrations in the volume surrounding the
electrode, leading to lesser stimulation in the surrounding milieu.
High-dose D1R agonist application would thus be expected to enhance
tuning of background multiunit firing in a manner reminiscent of low
dose D1R stimulation of single units. The spatial profile of multiunit
spiking at five recording sites revealed that high doses of D1R stimulation enhanced delay tuning of distant units (Fig. 3b).
Antagonist effects and prevention of D1R agonist suppression
To further confirm that suppression was specific to D1R stimulation,
we tested whether D1R antagonist (SCH23390) coapplication could
block agonist effects. SCH23390 application with the D1R agonist
Figure 3 Suppressive effects of higher doses of D1R agonists. (a) Effects of
various high doses of D1R agonists on spatial mnemonic activity of PFC
neurons. Average normalized population responses of PFC neurons showing
delay period activity in the ODR task are shown for PDs (left panels) and
NPDs (right panels). Iontophoresis of D1R agonists SKF38393 (top row,
n ¼ 10), A68930 (middle row, n ¼ 11) and SKF81297 (bottom row,
n ¼ 12) at high doses (25–40 nA) suppressed the task-related activity of
PFC neurons. Control condition traces, blue; drug condition traces, red.
PSTHs of units showing significant spatially tuned delay-related activity
were normalized and averaged in control and drug conditions (see Methods).
(b) Effects of high-dose (20–100 nA) D1R agonist application on multiunit
delay activity in the PFC. We isolated average multiunit firing rates during
the delay from five recording loci and normalized them to the maximal
firing rate in the PD in the control (blue) and drug (red) conditions. We then
normalized these within-locus response curves across loci to obtain averaged
population curves shown. The D1R agonist at high doses (20–100 nA),
while completely suppressing well isolated units at the same site, suppressed
the multiunit activity in a spatially asymmetric manner, resulting in reduction
of the tuning curve width and increased tuning of the multiunit activity
surrounding the electrode.
VOLUME 10
[
NUMBER 3
[
MARCH 2007 NATURE NEUROSCIENCE
ARTICLES
a
F
C
b
R
D
Control
Firing rate (Hz)
Firing rate (Hz)
A68930 at 30 nA
C
D
Figure 4 Specificity of D1R agonist-mediated
suppression and effects of antagonists on spatial
tuning. (a) Rasters and PSTHs of a PFC neuron
during the control condition (top panel) and during
iontophoresis of A68930 at 30 nA together with
SCH 23390 at 30 nA (middle panel). Application
of SCH23390 at 30 nA prevented agonistmediated suppression (two-tailed t-test,
coapplication versus control; P 4 0.05). Bottom
panel, suppression of neuronal activity upon
subsequent application of A68930 alone (twotailed t-test, previous coapplication versus agonist
alone; P o 0.005). Only the PD is shown.
Rastergrams and histograms are aligned to cue
onset. (b) PSTHs and rasters in PD (left panels)
and NPD (right panels) for a moderately tuned
PFC delay cell in the control condition (top row)
and with application of SCH23390 (25 nA,
second row), SCH23390 (25 nA) together with
SKF81297 (25 nA) (third row) and SKF81297
alone at a lower dose (15 nA, bottom row). All
PSTHs are binned in 0.1-s bins.
R
NPD
60
0
60
0
0
SKF81297 at 25 nA + SCH23390 at 25 nA
60
0
F
60
3.0
0.5
Time (s)
0
SKF81297 at 15 nA
0
60
60
0
0
0
0.5
3.0
0
Time (s)
prevented agonist-induced suppressive effects in seven units tested.
Subsequent agonist application alone suppressed neurons. After a
control condition (Fig. 4a, first panel), application of SCH23390
(30 nA) with A68930 (30 nA; second panel) to a PFC unit with
delay-related activity prevented suppression of mnemonic activity
(t-test, control versus coapplication, P ¼ 0.99). Subsequent A68930
application alone at the same dosage resulted in the expected
F C
Control
D
PD
F
C
R
D
R
NPD
b
Firing rate (Hz)
40
R
F
C
D
NPD
R
c
F C
Control
0
0
Rp-cAMPS at 50 nA
50
D
PD
F
R
C
D
NPD
R
50
0 0.5
3.0
0 0.5
Time (s)
40
0
SKF 38393 at 40 nA
50
0
Rp-cAMPS at 50 nA + SKF 38393 at 40 nA
0
SKF 38393 at 40 nA + Rp-cAMPS at 50 nA
3.0
Time (s)
50
Correct responses
d
SKF 38393 at 40 nA alone
40
0
D
PD
50
0 Rp-cAMPS at 50 nA
0
C
50
40
0
F
Control
suppression of activity (t-test, coapplication versus agonist alone, P o
0.005), indicating that suppressive effects of D1R agonists were specific
to and dependent on D1Rs. SCH23390 application alone, at comparable doses, augmented activity in some PFC cells (Supplementary
Fig. 3 online). SCH23390 application (Fig. 4b, second panel) increased
mnemonic firing of a PFC cell, eroding spatial tuning by preferentially
increasing firing for the NPD (t-test, P o 0.005). Application of
Firing rate (Hz)
a
3.0
0.5
Time (s)
Firing rate (Hz)
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
R
D
60
25
0
PD
0
SCH23390 at 25 nA
SCH23390 at 30 nA
+A68930 at 30 nA
25
0
C
60
25
0
F
Control
80%
60%
Time (s)
0 0.5
*
0
0 0.5
3.0
Time (s)
40%
0 0.5
3.0
Time (s)
20%
0%
3.0
0 0.5
†
3.0
Time (s)
Rp VEH Rp+ SKF
SKF
Figure 5 cAMP signaling in D1R agonist effects. (a) Rp-CAMPS (50 nA) application together with SKF38393 (40 nA, third row) on a PFC unit after control
(top row) and Rp-cAMPS application alone (second row). Rp-cAMPS did not significantly change activity (P ¼ 0.356, F3,180 ¼ 1.08, ANOVA), nor did
SKF38393 and Rp-cAMPS coapplication (P 4 0.05, F3,180 ¼ 3.76, ANOVA). Subsequently, SKF38393 alone at 40 nA suppressed neuronal activity (bottom
row; ANOVA, P o 0.05). (b) Rp-CAMPS alone (bottom row) at 50 nA augmented (P o 0.001, F3,180 ¼ 27.67, ANOVA) activity of another unit. (c) SKF38393
application at 40 nA (middle row) suppressed delay activity of a unit (P o 0.001, F3,180 ¼ 14.23, ANOVA). Coapplication of Rp-CAMPS at 50 nA partially
reversed suppression (bottom row; P o 0.001, F3,180 ¼ 10.32, ANOVA). (a–c) Left panels, PD; right panels, NPD; gray ovals, trials with no spikes.
(d) Rp-cAMPS (Rp) infusion into PFC 15 min before testing blocked effects of SKF81297 (SKF; infused immediately before testing) on delayed alternation
performance in rats. ANOVA showed no significant main effect of SKF81297 (F1,4 ¼ 0.01, P ¼ 0.9) or of Rp-cAMPS (F1,4 ¼ 0.8, P ¼ 0.4), but significant
interaction between SKF81297 and Rp-cAMPS (F1,4 ¼ 9.21, P ¼ 0.039). In vehicle (VEH)-pretreated rats, SKF81297 significantly impaired performance
(F1,4 ¼ 13.33, *P ¼ 0.02). Rp-cAMPS pretreatment variably and nonsignificantly tended to impair performance (F1,4 ¼ 5.68, P ¼ 0.08), but completely
prevented SKF81297-induced impairments (F1,4 ¼ 12.06, wP ¼ 0.02). Error bars, s.e.m.
NATURE NEUROSCIENCE VOLUME 10
[
NUMBER 3
[
MARCH 2007
379
ARTICLES
F
C
D
Control
R
Firing rate (Hz)
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
D
R
F
b
C
D
Control
R
F
20
0
0
A68930 at 20 nA + Chelerythrine at 10 nA
0
2.5
0.5
Time (s)
0
R
60
0
Chelerythrine at 15 nA
60
60
0
0
Chelerythrine at 10 nA + SKF81297 at 20 nA
20
20
D
NPD
0
0
A68930 at 20 nA
C
PD
60
20
20
0
C
NPD
20
0
F
PD
Firing rate (Hz)
a
60
0
0.5
2.5
Time (s)
60
0
0
0
3.0
0.5
Time (s)
0
0.5
3.0
Time (s)
Figure 6 Effects of PKC inhibition on D1R agonist-mediated neuronal suppression. (a) The PKC inhibitor chelerythrine applied at 10 nA with the D1R
agonist A68930 at 20 nA (bottom row) did not reverse (F3,160 ¼ 1.928, P ¼ 0.12, ANOVA) D1R agonist (at 20 nA)-mediated delay-related activity
suppression (middle row; P o 0.001, F3,160 ¼ 16.26 ANOVA) of delay-related activity of a PFC unit (control condition, top row). Similar doses of
chelerythrine successfully reversed the effects of a1-adrenoceptor agonist applications in a previous study47. (b) Chelerythrine application with D1R
agonist SKF81297 (bottom row) was unable to block D1R agonist-mediated suppression (F3,160 ¼ 55.90, P o 0.001, ANOVA) of delay activity of a
prefrontal cell (control condition, top row). Chelerythrine application alone (middle row) resulted in a small nonsignificant reduction in the unit’s activity
(P ¼ 0.06, F1,80 ¼ 3.46, ANOVA). PD, left panels, NPD, right panels.
SKF81297 with SCH23390 (third panel, 25 nA) decreased activity in
both the PD and the NPD without reinstating spatial tuning (t-test, PD
versus NPD, P 4 0.05). Finally, SKF81297 alone at a low dose (15 nA,
bottom panel) preferentially reduced firing for the NPD, reinstating
and enhancing spatial tuning of the unit (t-test, P o 0.05).
Many, but not all, PFC units recovered after termination of D1R
agonist application. We observed best recoveries with the partial D1R
agonist, SKF38393, whereas recovery with full agonists varied with dose
application duration (Supplementary Fig. 4 online shows recovery
from SKF81297 application at 10 nA). Long-lasting effects of D1R
stimulation may arise from irreversible second-messenger actions.
Signaling basis of D1R actions: cAMP and protein kinase C
We used iontophoretic pharmacology to investigate the signaling basis
of D1R stimulation-mediated suppression. We examined the role of
second-messenger signaling by determining whether inhibitors of
cAMP or PKC signaling could block or reverse the D1R response.
Blockade was tested by concomitant application of the inhibitor with
the D1R agonist, and reversal was tested by applying the inhibitor after
the D1R agonist induced suppression.
The cAMP inhibitor Rp-cAMPS (25–100 nA) blocked suppressive
effects of D1R agonist application (20–50 nA) in nine of ten units.
Initial pretreatment of a representative neuron (Fig. 5a) with RpcAMPS (50 nA, middle panel) led to no significant change from control
in neuronal activity (top panel; P ¼ 0.356, F3,180 ¼ 1.08, ANOVA).
Subsequently, application (third panel) of the cAMP inhibitor
Rp-cAMPS (25–80 nA) with SKF38393 (25–50 nA) prevented the
suppressive effects of the D1R agonist application (P 4 0.05,
F3,180 ¼ 3.76, ANOVA). Subsequent application of D1R agonist
alone suppressed mnemonic activity (bottom panel; P o 0.001,
F3,180 ¼ 58.29, ANOVA). Population analysis of six units with this
sequence of conditions, in which coapplication of Rp-cAMPS successfully prevented agonist-induced suppression at doses that were not
suppressive by themselves, is presented in Supplementary Figure 5
online. Rp-cAMPS (25–100 nA) application with the D1R agonist
380
(20–50 nA) in nine of ten units blocked the D1R stimulationdependent suppression. Rp-cAMPS application alone occasionally
resulted in augmentation of neuronal activity in PFC (Fig. 5b; P o
0.001, F3,180 ¼ 27.67, ANOVA), where 10 of 15 units examined showed
either increases or no change in activity. Because Rp-cAMPS alone, at
doses that did not substantially change activity, prevented D1R agonistmediated suppression (Supplementary Fig. 5), this blockade could not
be merely due to additive opponent effects of application of Rp-cAMPS
and D1R agonists.
Rp-cAMPS reversed effects of D1R agonists in a subset of neurons
tested. Iontophoresis of SKF38393 (25 nA; Fig. 5c, middle panel; P o
0.001, F3,180 ¼ 14.23, ANOVA) suppressed mnemonic activity of a unit
compared to control (top panel). Subsequent application of
Rp-cAMPS (50 nA, bottom panel) with the agonist partially reversed
SKF38393-induced suppression (P o 0.001, F3,180 ¼ 10.32, ANOVA).
This re-induction of neuronal activity was specific to the PD, with a
reconstitution of the neuron’s native firing profile. Rp-cAMPS
co-application reversed agonist-mediated suppression in 14 of
40 units tested; the rest could not be reversed.
In order to relate these findings at the cellular level to their impact on
spatial working memory performance, the effects of Rp-cAMPS on
D1R stimulation were examined in rats performing a delayed alternation task (5–15 s delay) in a T-maze. The delayed alternation task in
rodents is commonly used to test working memory function, as it
requires response inhibition and distraction suppression as well as
spatial working memory functions for successful performance. The
short delays used in this study are comparable with timescales in
working memory tasks. Infusions of the D1R agonist SKF81297
(0.1 mg, 0.5 ml) into the prelimbic PFC significantly impaired delayed
alternation performance, consistent with previous reports3. Infusion of
Rp-cAMPS (42 nmol, 0.5 ml) into the PFC completely prevented the
impairment induced by SKF81297 (Fig. 5d). Rp-cAMPS infusion by
itself tended to impair cognitive performance, consistent with previous
reports20. Thus, Rp-cAMPS blockade of the D1R agonist response
cannot have arisen from additive effects of the two compounds. Rather,
VOLUME 10
[
NUMBER 3
[
MARCH 2007 NATURE NEUROSCIENCE
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
ARTICLES
it appears that inhibition of cAMP actions protects cognitive performance from the detrimental effects of high levels of D1R stimulation.
Together, the electrophysiological and behavioral evidence described
above implies that high levels of D1R stimulation impair working
memory performance by suppressing mnemonic spatial tuning,
whereas Rp-cAMPS may protect cognitive performance by blocking
D1R-mediated activation of cAMP, restoring spatially tuned mnemonic
firing (for example, Fig. 5a).
In contrast to Rp-cAMPS, application of a PKC inhibitor, chelerythrine, did not reverse effects of D1R stimulation on PFC cell firing
(Fig. 6a, last panel versus middle panel; P ¼ 0.12, F3,180 ¼ 1.928,
ANOVA): 11 of 11 units tested with chelerythrine (10–20 nA) did not
show reversal of D1R agonist effects. Additionally, chelerythrine
application could not block SKF81297-mediated suppression of neuronal activity (Fig. 6b, bottom versus top panel; F3,160 ¼ 55.90, P o
0.001, ANOVA). Chelerythrine application alone resulted in either no
changes or a nonsignificant suppression of activity (Fig. 6b, middle
panel; P ¼ 0.06, F1,80 ¼ 3.46, ANOVA). Further, chelerythrine could
not reverse D1R agonist suppression in cells in which Rp-cAMPS was
unable to reverse agonist effects (eight of eight units tested), indicating
that PKC blockade was also ineffective when cAMP blockade could not
restore activity. Thus, in this paradigm, suppression of PFC mnemonic
activity due to D1R stimulation depended on the cAMP, rather than the
PKC, signaling pathway.
DISCUSSION
This study reports that D1R agonists had suppressive effects on firing of
PFC neurons engaged in a working memory task and that the
physiological consequences of these suppressive actions were dose
dependent: moderate levels of suppression preferentially reduced firing
to NPDs, leading to an enhancement in spatial tuning, whereas at
higher levels of D1R stimulation, physiological suppression became
overwhelming, leading to losses in spatial information capacity and
detuning of spatial memory-related information. This D1R stimulation-mediated suppression thus provides a physiological mechanism
that could constitute the underlying basis of a widely proposed view of
D1R function, the inverted-U response2. D1R stimulation at low doses
occasionally led to excitation of neurons, but overwhelmingly, inhibition was the most common occurrence. These findings are consistent
with previous results showing that low doses of D1R blockade can
increase delay-related firing in PFC neurons with presumed excessive
endogenous D1R stimulation18. The previous study showed that the
antagonist, at low doses, induced spatially asymmetric firing in PFC
cells. We believe these cells probably received excessive endogenous
dopaminergic tone, which suppressed spatially specific input to the cell,
and thus the antagonist unmasked their memory field by reducing D1R
signaling. In this study, we recorded both weakly tuned noisy cells,
which were likely to have had insufficient endogenous D1R stimulation, and neurons with strong spatial tuning, which were likely to have
had optimal endogenous D1R stimulation. Consistent with this
hypothesis, iontophoresis of a low dose of D1R agonist on weakly
tuned cells unmasked spatial activity by suppressing noisy spontaneous
activity. In contrast, in strongly tuned cells, spatial selectivity was less
improved or even worsened by application of the D1R agonist. Further,
in moderately tuned cells with presumed intermediate dopaminergic
tone, D1R blockade increased firing for the NPD and eroded spatial
tuning, whereas D1R stimulation decreased firing for the NPD and
augmented spatial tuning. This model of D1R function is schematically
illustrated in Supplementary Figure 6 online, wherein we hypothesize
that the effects of antagonists or agonists on spatial tuning depend on
the initial state of the cell in terms of the inverted U. The efficacy of D1R
NATURE NEUROSCIENCE VOLUME 10
[
NUMBER 3
[
MARCH 2007
stimulation is also likely to be a function of the inputs to the cell: a
neuron receiving broad inputs may benefit from D1R stimulation more
than a neuron with narrow spatial inputs. The effects of D1R agonists
in the current study were blocked by the D1R antagonist SCH23390,
indicating that these effects were due to D1R stimulation. Similarly, the
electrophysiological and behavioral effects of D1R were prevented by
pretreatment with Rp-cAMPS, consistent with signaling by means of
the G-protein Gs-cAMP cascade.
It is noteworthy that there was considerable variability in the efficacy
of recovery from D1R agonist application and antagonist-mediated
reversal of these effects. Thus, whereas pretreatment with D1R antagonist was always effective in preventing the D1R response, reversal of an
ongoing D1R agonist response was not always successful. This variability may arise from two factors: (i) D1R stimulation may have elicited
second-messenger actions that were further downstream of cAMP
actions and thus not amenable to reversal and (ii) D1R stimulation
may have lead to receptor internalization20, which is triggered concomitantly with physiological effects of receptor signaling. As D1R
antagonists at very high doses also lead to suppression of PFC
neurons18, effects of internalization of the receptor may be indistinguishable from the physiological effects of the agonist in our paradigm.
However, the current findings imply that suppressive effects of D1R
agonists result from stimulation of D1Rs, and not just from receptor
internalization, as (i) there were many instances of immediate recovery
from agonist-mediated suppression (see Supplementary Fig. 4),
(ii) SCH23390 was often able to prevent an ongoing response and
(iii) most importantly, cAMP inhibition partially restored normal
firing after suppression and prevented suppression when engaged
with D1R stimulation, arguing that the physiological effects of D1R
are also suppressive. Thus, although an irreversible component of the
response may have resulted from receptor internalization, a significant
portion of the inhibition appears to result from the reversible actions at
D1Rs. This interpretation is also consonant with the behavioral results:
Rp-cAMPS fully blocked the working memory impairment induced by
D1R agonist infusions.
Dorsolateral PFC in monkeys is speculated to encode spatial working
memory in a topological fashion: PFC neurons are thought to be
mnemonotopically organized in columns representing space discretely,
and intracolumnar neuronal connectivity is thought to form a functional microcircuit whose reverberatory activity sustains firing during
the delay period1. The spatial selectivity is likely to be mediated by a
variety of factors: for example, both input specificity to columns and
inhibition from GABAergic interneurons in neighboring columns are
hypothesized to shape and sculpt the spatial mnemonic receptive fields
of PFC cells21,22. The current data indicate that DA D1R neuromodulation also contributes to this sculpting process, and probably does so
through influences on effective neuronal connectivity and physiology
in these columns.
In vitro recordings have supported a number of mechanisms by
which D1R stimulation may influence PFC responsiveness. Extensive
work on intrinsic neuronal currents indicates that D1R stimulation
may have important excitatory influences on PFC pyramidal
neurons23–27. These excitatory actions of D1R are likely to be fully
engaged by endogenous DA in PFC neurons in the current study, and
thus not evident with further D1R agonist application. In vitro studies
have also observed evidence of D1R suppressive actions that are likely
to contribute to the sculpting actions observed in the current study.
These suppressive influences include presynaptic inhibition28, reduction in excitatory synaptic drive14, blockade of apical dendritic-somal
interaction13, changes in intrinsic currents29 and increased GABAergic
inhibition15,30–33. D1R stimulation could also have hitherto unreported
381
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
ARTICLES
effects on other neuronal currents, such as Ih, which is cAMP dependent and can modulate dendritic integration34. These effects could
mediate suppression at higher D1R stimulation levels, when excitatory
effects are saturated. It is likely that many factors contribute to these
suppressive actions, and it is possible that they have distinct effects on
firing for the PD versus NPDs. For example, the suppression of firing to
the NPD may involve D1R enhancement of GABAergic tuning
mechanisms22,35, whereas the suppression of firing to the PD might
result from the collapse of persistent firing due to the opening of Ih
channels by way of cAMP34. Exploring the interactions between
phenomena observed at the intracellular and extracellular levels will
be a fertile area for future research.
The current study found that the cellular and behavioral effects of
D1R stimulation could be blocked by the cAMP inhibitor, Rp-cAMPS.
In contrast, the PKC inhibitor, chelerythrine, did not prevent the
suppressive effects of D1R agonist application. These data indicate
that the actions of cAMP, but not of PKC, contribute to the D1R effects
observed in the current study. However, it should be noted that the
current study is limited in its use of adult, highly trained animals under
nonstressful conditions, and that PKC actions might be engaged under
other conditions (for example, stress, advanced age or drug abuse).
Furthermore, the role of inositol-1,4,5-trisphosphate (IP3) signaling
was not tested in the present study, as currently available IP3 receptor
antagonists are not compatible with iontophoretic application. Thus,
the selectivity of cAMP mechanisms should be viewed within
these confines.
The present results predict that the effects of dopaminergic drugs on
cognition will depend both on the endogenous levels of DA D1R
stimulation and on the informational state of the neuron. Thus,
animals36 or humans7 with optimal levels of endogenous DA D1R
stimulation would have good spatial tuning, strong working memory
abilities and little beneficial effect of D1R agonist administration,
whereas those with poor working memory owing to insufficient DA
would show enhanced performance with additional D1R stimulation.
Such dichotomous effects of D1R agonists have also been observed in
tasks involving longer timescales, where D1Rs presumably exert an
influence on retention of working memory information in longer term
storage37. Furthermore, the optimal level of D1R stimulation may be
different depending on the signal-to-noise demands of a cognitive task.
This conclusion is consistent with reports that infusion of a D1R
agonist in rat PFC can simultaneously improve or impair working
memory depending on task demands38. The present results indicate
that D1R stimulation may be especially helpful when the task demands
precise rather than broad tuning and the subject must suppress
irrelevant information (‘noise’) for optimal performance. The reduction in processing of ‘noise’ by D1R stimulation seen in the current
study is consonant with results observed in imaging studies of human
subjects performing working memory tasks, whereby cognitionenhancing doses of stimulant medication actually reduce the area of
PFC activated by task demands, thus enhancing the efficiency of the
BOLD response9,39. The current results also have implications for why
loss of DA—for example, with advancing age or possibly in schizophrenia—leads to increased susceptibility to interference40,41 and,
conversely, why high-dose stimulant medication can lead to excessive
focus and impaired mental flexibility42. The collapse in PFC neuronal
firing under conditions of high D1R stimulation may also explain
the rapid and marked loss of PFC cognitive abilities and the worsening of neuropsychiatric symptoms following exposure to uncontrollable stress6,43.
The inverted-U dose-response observed with PFC D1R stimulation
in animals has now been observed in regard to cognitive performance
382
and genetic alterations in humans. Both adults and children with native
COMTval/val have poorer working memory and attentional abilities and
less efficient PFC activation than those subjects with genetic alterations
(Met/Met polymorphisms) that weaken COMT and thus increase DA
availability in PFC9,10,44. Subjects with weaker COMT were recently
shown to have less demand for DA synthesis in the midbrain under
basal conditions11. Interestingly, conditions that increase DA release
(amphetamine, stress) improve working memory in subjects with
native COMT, but impair working memory in those with altered
COMTand thus excessive DA9, consistent with the inverted U observed
at the cellular level in the current study. These results may be of
relevance to a range of neuropsychiatric disorders, including schizophrenia12 and schizotypal personality disorder45. COMT genotype
has also been associated with reduced PFC volume and cognitive
function and the development of psychosis in children with 22q11.2
deletion syndrome46. Thus, understanding DA D1R actions at the
cellular level will be key for developing effective cognitive enhancers
that rectify the delicate balance in neuromodulation of our highest
cognitive functions.
METHODS
For details, see Supplementary Methods.
Behavioral training, surgery and electrophysiology were performed as
described previously22,47; they were in accordance with US National Institutes
of Health guidelines and were approved by the Yale University Institutional
Animal Care and Use Committee.
Neuronal physiology in rhesus macaques. The ODR task. Studies were
performed on two adult male rhesus monkeys (Macaca mulatta) trained on
the spatial ODR task as previously described1. This task requires the subject to
make a memory-guided saccade to a remembered visuospatial target (Fig. 1a).
After a three-second intertrial interval, a central light appeared as the fixation
target on a screen. A trial began when the subject fixated at the central spot for
0.5 s (fixation period). Subsequently, a cue was illuminated for 0.5 s (cue
period) at one of eight peripheral targets located at an eccentricity of 131 with
respect to the fixation spot. After cue extinguishment, a 2–2.5 s delay period
followed. The fixation spot remained during the cue and delay periods and the
subject was required to maintain central fixation throughout both periods. At
the end of the delay, fixation spot extinguishment instructed the subject to
make a memory-guided saccade to the location where the cue had been shown.
Recording locus. Recording loci were determined using magnetic
resonance images of the brain in subject H or stereotaxically in subject
M. Recordings were performed around the principal sulcus in Walker’s area
46. Recording loci in subject M were further confirmed with histology
(Supplementary Fig. 7 online).
Iontophoresis, physiology and data acquisition. SKF38393, SKF81297, A68930,
chelerythrine and SCH23390 (Sigma-RBI) were dissolved in triple-distilled
water (adjusted with HCl or H3PO4 to pH 3.5–4.0, 0.01 M) and stored in 50-ml
aliquots at –70 1C. Rp-CAMPS (Sigma-RBI; Tocris Cookson) was dissolved in
water at pH 6–8 (adjusted with NaOH) and stored at –70 1C. Iontophoretic
recordings were performed as described previously47. Retention currents of 3 to
8 nA were cycled with opponent polarity (1 s on, 1 s off) when not applying
drugs. The drug barrels of these electrodes have very high impedances (typically
B100 MO and above). Current balancing was not employed in the iontophoretic manipulations employed in this study. In order to ensure that the
effects reported here were not artifacts due to unbalanced currents, a series of
control experiments using Na+ ejection were performed. Comparable currents
employing Na+ ejection had no effects on neuronal activity (see Supplementary Methods and Supplementary Figs. 8 and 9 online).
Extracellular voltage was amplified using a custom low-noise preamplifier
(SKYLAB) and band-pass filtered (180 Hz–6 kHz, 20 dB gain, four-pole
Butterworth; Kron-Hite). Signals were digitized (20.83 kHz, micro 1401,
Cambridge Electronics Design) and acquired using the Spike2 software (CED).
After unit isolation and stabilization, a control condition was obtained with
approximately eight trials at each of eight cue locations. The control condition
VOLUME 10
[
NUMBER 3
[
MARCH 2007 NATURE NEUROSCIENCE
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
ARTICLES
was followed by successive drug applications. Around eight trials per location
were collected for each condition for statistical analysis.
Data analysis. We constructed poststimulus time histograms (PSTHs)
aligned to cue onset to assess the neuronal activity profile across space and
in different drug conditions. Memory cells with delay activity were subsequently identified. Subsets of these cells were then employed in individual
experiments; these subsets often overlapped for various experiments. Activity
was classified based on the activation patterns and analyzed for spatial and
drug-related effects using ANOVAs, t-tests and nonparametric tests. Neuronal
activity was normalized variously where appropriate. Subtraction of baseline
activity before analysis did not alter the results presented here (see Supplementary Fig. 10 online).
Average curves of firing rates in all directions were fitted to a modified von
Mises function, the circular analog of the Gaussian function. Fitting parameters
were optimized for best fits using nonlinear least-squares fitting with the
Levenberg-Marquardt algorithm implemented in MATLAB. Please see Supplementary Methods for more details.
Rat pharmacology. Subjects. Male Sprague-Dawley rats (Taconic) weighing
240–280 g when received (approximately two months old) were fed a limited
diet of Purina rat chow (16 g per rat daily) immediately following behavioral
testing. Subjects were given chocolate chips as reward during testing.
Cognitive testing. Rats were trained and tested on the delayed alternation task
in a T maze, using methods described previously47. The delay was raised as
needed to maintain each individual rat’s performance at stable baseline
performance of approximately 70% correct. Typically, the delays used in this
study were in the 5–15 s range, which is consistent with the general temporal
scales of working memory tasks. This baseline allowed for detection of either
improvement or impairment in performance following drug administration.
Cannula implantation in rats. All surgical procedures were carried out as
previously described (ref. 47, Supplementary Methods). Cannulas were
implanted into the medial PFC and pharmacological procedures were carried
out after the subjects reached stable postimplantation baselines.
Drug administration and data analysis. SKF81297 (Sigma-RBI; 0.1 mg, 0.5 ml)
and Rp-cAMPS (Sigma-RBI; 42 nmol, 0.5 ml) were infused (0.25 ml min–1) into
the PFC. Cognitive testing began 15 min after the infusion procedure. All
animals received (i) vehicle + vehicle, (ii) SKF81297 + vehicle, (iii) Rp-cAMPS
+ vehicle and (iv) SKF81297 + Rp-cAMPS. Data were analyzed with a two-way
ANOVA with repeated measures. Planned comparisons were made with test of
effects using Systat software.
URLs. MATLAB, http://www.mathworks.com.
Note: Supplementary information is available on the Nature Neuroscience website.
ACKNOWLEDGMENTS
We would like to thank G. Leydon for help with Spike2 scripts and C.J. Bruce for
assistance with surgical procedures and guidance with the research. We would
like to thank S. Wilson, J. Carlson, M. Horn, L. Ciavarella, S. Johnson and
T. Sadlon for veterinary assistance and help with surgeries. This research was
supported by P50MH068789 to A.F.T.A.
AUTHOR CONTRIBUTIONS
S.V. performed the D1R agonist dose-response experiments and secondmessenger experiments. S.V. and M.W. performed the D1R high-dose
experiments. S.G.B. provided the rat behavioral data. G.V.W. initiated the pilot
experiments with D1R agonists. S.V. and A.F.T.A. wrote the manuscript. A.F.T.A.
supervised the project.
COMPETING INTERESTS STATEMENT
The authors declare competing financial interests (see the Nature Neuroscience
website for details).
Published online at http://www.nature.com/natureneuroscience
Reprints and permissions information is available online at http://npg.nature.com/
reprintsandpermissions
1. Goldman-Rakic, P.S. Cellular basis of working memory. Neuron 14, 477–485 (1995).
2. Zahrt, J., Taylor, J.R., Mathew, R.G. & Arnsten, A.F. Supranormal stimulation of D1
dopamine receptors in the rodent prefrontal cortex impairs spatial working memory
performance. J. Neurosci. 17, 8528–8535 (1997).
NATURE NEUROSCIENCE VOLUME 10
[
NUMBER 3
[
MARCH 2007
3. Lidow, M.S., Koh, P.O. & Arnsten, A.F. D1 dopamine receptors in the mouse prefrontal
cortex: immunocytochemical and cognitive neuropharmacological analyses. Synapse
47, 101–108 (2003).
4. Cai, J.X. & Arnsten, A.F. Dose-dependent effects of the dopamine D1 receptor agonists
A77636 or SKF81297 on spatial working memory in aged monkeys. J. Pharmacol. Exp.
Ther. 283, 183–189 (1997).
5. Arnsten, A.F., Cai, J.X., Murphy, B.L. & Goldman-Rakic, P.S. Dopamine D2 receptor
mechanisms contribute to age-related cognitive decline: the effects of quinpirole on
memory and motor performance in monkeys. Psychopharmacology (Berl.) 116, 143–
151 (1994).
6. Arnsten, A.F. & Goldman-Rakic, P.S. Noise stress impairs prefrontal cortical cognitive
function in monkeys: evidence for a hyperdopaminergic mechanism. Arch. Gen.
Psychiatry 55, 362–368 (1998).
7. Gibbs, S.E. & D’Esposito, M. A functional MRI study of the effects of bromocriptine, a
dopamine receptor agonist, on component processes of working memory. Psychopharmacology (Berl.) 180, 644–653 (2005).
8. Callicott, J.H. et al. Physiological characteristics of capacity constraints in working
memory as revealed by functional MRI. Cereb. Cortex 9, 20–26 (1999).
9. Mattay, V.S. et al. Catechol O-methyltransferase val158-met genotype and individual
variation in the brain response to amphetamine. Proc. Natl. Acad. Sci. USA 100, 6186–
6191 (2003).
10. Blasi, G. et al. Effect of catechol-O-methyltransferase val158met genotype on attentional
control. J. Neurosci. 25, 5038–5045 (2005).
11. Meyer-Lindenberg, A. et al. Midbrain dopamine and prefrontal function in humans:
interaction and modulation by COMT genotype. Nat. Neurosci. 8, 594–596 (2005).
12. Goldberg, T.E. et al Executive subprocesses in working memory: relationship to catecholO-methyltransferase Val158Met genotype and schizophrenia. Arch. Gen. Psychiatry 60,
889–896 (2003).
13. Yang, C.R. & Seamans, J. Dopamine D1 receptor actions in layers V-VI rat prefrontal
cortex neurons in vitro: modulation of dendritic-somatic signal integration. J. Neurosci.
16, 1922–1935 (1996).
14. Urban, N.N., Gonzalez-Burgos, G., Henze, D.A., Lewis, D.A. & Barrionuevo,
G. J. Physiol. (Lond.) 539, 707–712 (2002).
15. Gorelava, N., Seamans, J. & Yang, C.R. Mechanisms of dopamine activation of fastspiking interneurons that exert inhibition in rat prefrontal cortex. J. Neurophysiol. 88,
3150–3166 (2002).
16. Schultz, W., Apicella, P. & Ljungberg, T. Responses of monkey dopamine neurons to
reward and conditioned stimuli during successive steps of learning a delayed response
task. J. Neurosci. 13, 900–913 (1993).
17. Sawaguchi, T., Matsumara, M. & Kubota, K. Effects of dopamine antagonists on
neuronal activity related to a delayed response task in monkey prefrontal cortex.
J. Neurophysiol. 63, 1401–1412 (1990).
18. Williams, G.V. & Goldman-Rakic, P.S. Modulation of memory fields by dopamine D1
receptors in prefrontal cortex. Nature 376, 572–575 (1995).
19. Zhen, X., Goswami, S. & Friedman, E. The role of the phosphatidyinositol-linked D1
dopamine receptor in the pharmacology of SKF83959. Pharmacol. Biochem. Behav.
80, 597–601 (2005).
20. Arnsten, A.F., Ramos, B.P., Birnbaum, S.G. & Taylor, J.R. Protein kinase A as a
therapeutic target for memory disorders: rationale and challenges. Trends Mol. Med.
11, 121–128 (2005).
21. Schwartz, M.L., Zheng, D.S. & Goldman-Rakic, P.S. Periodicity of GABA-containing
cells in primate prefrontal cortex. J. Neurosci. 8, 962–970 (1988).
22. Rao, S.G., Williams, G.V. & Goldman-Rakic, P.S. Destruction and creation of spatial
tuning by disinhibition: GABAA blockade of prefrontal cortical neurons engaged by
working memory. J. Neurosci. 20, 85–94 (2000).
23. Henze, D.A., Gonzalez-Burgos, G.R., Urban, N.N., Lewis, D.A. & Barrionuevo, G.
Dopamine increases excitability of pyramidal neurons in primate prefrontal cortex.
J. Neurophysiol. 84, 2799–2809 (2000).
24. Tseng, K.Y. & O’Donnell, P. Dopamine-glutamate interactions controlling prefrontal
cortical pyramidal cell excitability involve multiple signaling mechanisms. J. Neurosci.
24, 5131–5139 (2004).
25. Seamans, J. & Yang, C.R. The principal features and mechanisms of dopamine
modulation in the prefrontal cortex. Prog. Neurobiol. 74, 1–58 (2004).
26. Gorelova, N. & Yang, C.R. Dopamine D1/D5 receptor activation modulates a persistent
sodium current in rat prefrontal cortical neurons in vitro. J. Neurophysiol. 84, 75–87
(2000).
27. Yang, C.R., Seamans, J. & Gorelova, N. Electrophysiological and morphological properties of layers V-VI principal pyramidal cells in rat prefrontal cortex in vitro. J. Neurosci.
16, 1904–1921 (1996).
28. Gao, W.J., Krimer, L.S. & Goldman-Rakic, P.S. Presynaptic regulation of recurrent
excitation by D1 receptors in prefrontal circuits. Proc. Natl. Acad. Sci. USA 98,
295–300 (2001).
29. Maurice, N., Tkatch, T., Meisler, M., Sprunger, L.K. & Surmeier, D.J. J. Neurosci. 21,
2268–2277 (2001).
30. Yan, Z. & Surmeier, D.J. D5 dopamine receptors enhance Zn2+-sensitive GABAA currents
in striatal cholinergic interneurons through a PKA/PP1 cascade. Neuron 19,
1115–1126 (1997).
31. Trantham-Davidson, H., Neely, L.C., Lavin, A. & Seamans, J.K. Mechanisms underlying
differential D1 versus D2 dopamine receptor regulation of inhibition in prefrontal cortex.
J. Neurosci. 24, 10652–10659 (2004).
32. Seamans, J.K., Gorelova, N., Durstewitz, D. & Yang, C.R. Bidirectional dopamine
modulation of GABAergic inhibition in prefrontal cortical pyramidal neurons. J. Neurosci. 21, 3628–3638 (2000).
383
© 2007 Nature Publishing Group http://www.nature.com/natureneuroscience
ARTICLES
33. Zhou, F.M. & Hablitz, J.J. Dopamine modulation of membrane and synaptic properties of
interneurons in rat cerebral cortex. J. Neurophysiol. 81, 967976 (1999).
34. Luthi, A. & McCormick, D.A. H-current: properties of a neuronal and network pacemaker.
Neuron 21, 9–12 (1998).
35. Constantinidis, C., Williams, G.V. & Goldman Rakic, P.S. A role for inhibition in shaping
the temporal flow of information in prefrontal cortex. Nat. Neurosci. 5, 175–180 (2002).
36. Granon, S. et al. Enhanced and impaired attentional performance after infusion of D1
dopaminergic receptor agents into rat prefrontal cortex. J. Neurosci. 20, 1208–1215
(2000).
37. Floresco, S.B. & Phillips, A.G. Delay-dependent modulation of memory retrieval by
infusion of a dopamine D1 agonist into the rat medial prefrontal cortex. Behav. Neurosci.
115, 934–939 (2001).
38. Chudasama, Y. & Robbins, T.W. Dopaminergic modulation of visual attention and
working memory in the rodent prefrontal cortex. Neuropsychopharmacology 29,
1628–1636 (2004).
39. Mehta, M.A. et al. Methylphenidate enhances working memory by modulating discrete
frontal and parietal lobe regions in the human brain. J. Neurosci. 20, 65 (2000).
40. Chao, L.L. & Knight, R.T. Prefrontal deficits in attention and inhibitory control with
aging. Cereb. Cortex 7, 63–69 (1997).
384
41. Franke, P. et al. Attentional abilities and measures of schizotypy: their variation and
covariation in schizophrenic patients, their siblings, and normal control subjects.
Psychiatry Res. 54, 259–272 (1994).
42. Robbins, T.W. & Sahakian, B.J. ‘‘Paradoxical’’ effects of psychomotor stimulant drugs in
hyperactive children from the standpoint of behavioural pharmacology. Neuropharmacology 18, 931–950 (1979).
43. Nuechterlein, K.H. et al. Developmental processes in schizophrenic disorders:
longitudinal studies of vulnerability and stress. Schizophr. Bull. 18, 387–425
(1992).
44. Diamond, A. Genetic and neurochemical modulation of prefrontal cognitive functions in
children. Am. J. Psychiatry 161, 125–132 (2004).
45. Minzenberg, M.J. et al. Catechol-O-methyltransferase Val158Met genotype variation
is associated with prefrontal-dependent task performance in schizotypal
personality disorder patients and comparison groups. Psychiatr. Genet. 16, 117–124
(2006).
46. Gothelf, D. et al. COMT genotype predicts longitudinal cognitive decline and psychosis
in 22q11.2 deletion syndrome. Nat. Neurosci. 8, 1500–1502 (2005).
47. Birnbaum, S.G. et al. Protein kinase C overactivity impairs prefrontal cortical regulation
of working memory. Science 306, 882–884 (2004).
VOLUME 10
[
NUMBER 3
[
MARCH 2007 NATURE NEUROSCIENCE