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Ishikawa A, Ambroggi F, Nicola SM, and Fields HL
Presented by:
Andrew Burke
Mesocorticolimbic System
Medial Prefrontal
Cortex
mPFC
NAc
Nucleus Accumbens
VTA
BLA
Basolateral Amygdala
Ventral Tegmental
Area Dopamine Cells
For review: Wise (1996) Neurobiol of Addictio
Medial Prefrontal Cortex (mPFC)
Nucleus Accumbens Core &Shell
Cg
PrL
IL
Core
Shell



Cg = Cingulate Cortex
PrL = Prelimbic Cortex
IL = Infralimbic Cortex
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Medial Prefrontal Cortex (mPFC)
Nucleus Accumbens Core &Shell
Cg
PrL
IL
Core
Shell



Cg = Cingulate Cortex
PrL = Prelimbic Cortex
IL = Infralimbic Cortex

“Limbic-motor interface”
◦ Facilitates appropriate responding to rewardpredictive stimuli

Subpopulations of NAc neurons
◦ Excited/inhibited by discriminative stimuli (DSs)
 Predict reward availability

Source of cue-evoked firing of the NAc
Glu
◦ mPFC
Glu
◦ BLA
DA
◦ VTA
NAc

Inactivation of VTA by GABAB agonist, baclofen
◦ Reduced behavioral response to reward
associated cue
◦ Reduced NAc firing in response to reward
associated cue

Manipulating DA activity in the nucleus
accumbens (NAc) core and shell
◦ DAT blocker (GBR12909) increased behavioral
responding to a predictive stimulus
◦ D1 receptor antagonist decreased behavioral
responding to a predictive stimulus

Dopamine acts on NAc (GABA) neurons to
mediate responding to a cue for reward

Inactivation of BLA impaired behavioral
responding to predictive cues
◦ Also reduced cue-induced firing in NAc

Inactivation of dmPFC impaired behavioral
responding to predicitive cues
◦ ??

Inputs to the NAc contribute to cue-evoked
excitations of NAc neurons include
glutamergic inputs from the mPFC.

Adult Long-Evans rats
◦ ~350 g (n=9)
◦ Housed individually
◦ 1 week of restricted food and water before
training
 13 g food and 30 ml H2O during expts.
◦ Experiments conducted in the dark (12h
hours of dark per day)

Placed in operant chamber
◦ White noise 65dB and orange houselight ON always

Given 2 auditory stimuli
 Intermittent 6 kHz tone on 40 ms and off 50 ms (90
ms period)
 Siren-frequency ramped from 4 to 8 kHz and back
with 400 ms cycle period
Operant Chamber
White noise
(65 dB)
Auditory Stimuli
2 stimuli
(85 dB)

Auditory stimuli=tone cues were either:

Active lever and DS tone were counterbalanced

Pressing the active lever during DS tone = termination of
DS = 50 ml of 10% sucrose into reward receptacle

Cues presented on a variable interval schedule with
average interval of 30 s

The DS (on for up to 10 s) or NS (10 s) was randomly
presented at end of each interval
◦ Discriminative stimuli (DS) (AKA “incentive cue”) - predicted
reward delivery after correct lever press during DS presentation
◦ Nonrewarded stimulus (NS) - lever pressing did not trigger reward
delivery

Stage 1
◦ Introduced to chamber
◦ Entry into reward receptacle or pressing either lever
triggered delivery of 50 ml of a 10% sucrose solution
◦ 10 s timeout was imposed after reward delivery
when reward could not be delivered
◦ Trained until they learned to obtain 100 rewards in
<1 hr

Stage 2
◦ 2-lever fixed ratio (FR) 1 task
 Response on either lever triggered reward delivery
followed by 3 s timeout.
 Remained in this stage until they learned to obtain all
100 rewards in < 1 hr.

Stage 3
◦ One-lever FR task
 Pressing active lever during cue presentation triggered
reward delivery with 10 s timeout
 Cue presented at end of timeout and remained on until
an active lever press
 Lever pressing in absence of the cue was not rewarded
 Timeout increased from 10 s to 20 s then to 30 s when
rats obtained >100 rewards during the session
 Stayed in stage 3 until latency to press lever was <15 s
after DS cue presentation

Stage 4
◦ Trained on DS task until the
 Correct response to the DS occurred >90% of the time
 Incorrect responses to the NS only occurred about 20%
of the time
◦ When this criteria was met rats were rewarded with
brain surgery

Anesthetized with isoflurane

Implanted with bilateral guide cannula (27ga)
directed at the dmPFC


Bilateral recording electrode arrays
(consisting of 8 electrodes) were implanted
into the Nac core
Rats allowed to recover from surgery for 1
week before experiment began


Retrained on DS task for >6 days with recording
cables connected
Disabling the dmPFC
◦ Performed DS task for 60 min to obtain a baseline for
recording
◦ Removed from behavior/recording chamber
◦ Infused saline or M/B (mixed solution containing 25ng of
muscimol (GABAA agonist) and 50ng baclofen (GABAB
agonist) into dmPFC slowly (4 min total)

Returned to chamber immediately for a 2 h post
injection session for subsequent recording


“All 9 rats received bilateral injection of all drugs”
“unilateral injections of saline, 25 or 50 ng M/B were given to eight,
nine, and six rats, respectively”
◦ 8 of the 9 received Saline, 9=25ng, 6=50ng?

In 4 rats bilateral injection was first

In 2 rats unilateral injection was first

The remaining 3 rats were given injections in random order

Doses were always given in random order

Two animals were implanted with movable electrodes that could be
deepened by 150 µm

Behavior analyzed
◦ DS response latency
◦ Rate of uncued responding on active levers
 Rate of responding in the absence of DS and NS
◦ DS and NS response ratios
 Proportion of these cues during which the animal made a response on
active lever

Effects of bilateral inj. analyzed with 1-way repeated
measures ANOVA

Effect of unilateral inj. analyzed with 1-way ANOVA

Post hoc test: Fisher’s PLSD



Raster plots were also used to visualize firing of
individual neurons
Incentive cue, operant and receptacle exit related
responses illustrated with a perievent time
histogram (PETH) (AKA, peristimulus time
histogram)
Mean firing increases or decreases and pre-DS
baselines were compared across neurons
between pre and post injection conditions using
the paired t test
Results indicate that the dmPFC is required for behavioral responding to
reward-predicative cues during the DS task.
Averaged PETHs (0.5 s bin width) of all recorded cue-excited
neurons before (black) and after (red) 25 ng M/B, 50 ng of M/B,
and saline injections.
Comparisons of DS-evoked excitations before
and after each drug injection.


Both excitatory and inhibitory neuronal
profiles in response to the reward associated
cue were reduced when dmPFC is inactivated
Previous study (Nicola, et al 2004) suggests
that incentive cue excitations AND inhibitions
are reduced when the animals fails to make
the appropriate response (press the lever)
Excitatory
Inhibitory
Reduction of incentive cue
excitation/inhibition after dmPFC
inactivation is at least in part
responsible for the reduction in
behavioral responding to the DS.
A, B: DS response ratio was significantly correlated with the magnitude of DS
excitation but not DS inhibition.
C: negative correlation between DS excitation and behavioral response latency
Suggest that reduced excitation of NAc core after dmPFC inactivation may be
the cause of impaired behavioral responses to the cue.
•Ipsilateral excitatory
projection from the
dmPFC to the NAc is
essential for appropriate
cue responding (E).
•Could be a contribution
to incentive cue
responding for the
contralateral inhibitory
effect (H)

M/B inactivation of the dmPFC
◦ Reduced operant behaviors in response to incentive cues
during this DS task
◦ Minimal effects on consumption behaviors
◦ Reduced magnitude of excitatory neuronal responses in
NAc Core
◦ Reduced the magnitude of inhibitory neuronal responses
in NAc Core
◦ Minimal effects on baseline firing in NAc Core


Dopamine alone does not directly excite NAc
neurons (Nicola, et al 2000, 2004)
Dopmaine manipulations altered responding
for cue (Nicola, et al 2005)
◦ The enhanced neuronal and behavioral responding
after DA release onto NAc and PFC may be caused
by increasing PFC glutamate excitatory afferents to
the NAc GABA neurons

dmPFC NAc core projection is implicated in the
reinstatement of drug seeking (Kalivas)

Authors suggest a parallel between present findings and
those of drug reward

Is the incentive salience of sucrose reward and drug the
same?
◦ Suggested that other areas, excluding mesolimbic DA system,
mediates incentive value of food rewards, also learning new
associations between unconditioned stimuli and reward (ie, TPP,
NAc opiod system)

Are the same pathways and mechanisms involved in both
drug reinstatement and palatable reward in food deprived
animals?
◦ “Dopamine systems are only implicated in reward when individuals
are in a state of physiological deprivation”
Discussed in Berridge & Robinson (1998)

Inactivating VTA reduced cue excitatory &
inhibitory (phasic) and baseline (tonic) NAc
activity, & reduced beh response (Yun, et al 2004)

Reduced DA in mPFC after VTA inactivation inactivates the mPFC and NAc
◦ Here, mPFC blockade is sufficient to reduce
behavioral response and blocks mostly phasic
activity
◦ It is the phasic responses, not tonic, that drive
this incentive cue behavior

mPFC Glu projection to NAc is excitatory and
should cause increased firing rate
◦ A direct ipsilateral projection is likely responsible for
the excitatory NAc response to the cue


Perhaps the projections responsible for
inhibitory responses in NAc derive from
polysynaptic connections
i.e., PFC(GLU+)NAc?(GABA-)NAc(GABA-)

Ambroggi F, Ishikawa A, Seroussi A, Fields HL, Nicola SM (2007) Evidence that dopamine
enhance nucleus accumbens responses to incentive cues by gating an excitatory input from the
basolateral amygdala. Soc Neurosci Abstr 33:310.8.

Berridge K, Rominson TE (1998) What is the role of dopamine in reward: hedonic impact,
reward learning, or incentive salience? Brain Research Rev 28:309-369.

Ishikawa A, Ambroggi F, Nicola SM, Fields HL (2007) Contrasting contributions of the prefrontal
cortex and amygdala to cue-evoked reward seeking behavior. Soc Neurosci Abstr 33:310.10.

McFarland K, Kalivas PW (2001) The circuitry mediating cocaine-induced reinstatement of
drug-seeking behavior. J Neurosci 21:8655– 8663.

Nicola SM, Surmeier J, Malenka RC (2000) Dopaminergic modulation of neuronal excitability in
the striatum and nucleus accumbens. Annu Rev Neurosci 23:185–215.


Nicola SM, Taha SA, Kim SW, Fields HL (2005) Nucleus accumbens dopamine release is
necessary and sufficient to promote the behavioral response to reward-predictive cues.
Neuroscience 135:1025–1033.
Yun IA, Wakabayashi KT, Fields HL, Nicola SM (2004b) The ventral tegmental area is required
for the behavioral and nucleus accumbens neuronal firing responses to incentive cues. J
Neurosci 24:2923–2933.