Download Spinal NMDA Receptors Contribute to Neuronal Processing of Acute

Spinal NMDA Receptors Contribute to Neuronal Processing of
Acute Noxious and Nonnoxious Colorectal Stimulation in the Rat
YAPING JI1 AND RICHARD J. TRAUB1,2
1
Department of Oral and Craniofacial Biological Sciences, Dental School and 2Program in Neuroscience,
University of Maryland, Baltimore, Maryland 21201
Received 20 October 2000; accepted in final form 27 June 2001
It is becoming increasingly apparent that neuronal mechanisms involved in signaling visceral stimuli differ from somatic
mechanisms. For example, the majority of spinal primary afferent fibers that innervate hollow visceral organs encode mechanical stimulus intensities from the innocuous through the
noxious range in contrast to specific low-threshold mechanoreceptors and nociceptors that innervate somatic structures
(Bahns et al. 1987; Berkley et al. 1988, 1990; Blumberg et al.
1983; Haupt et al. 1983; Janig and Koltzenburg 1991; Ozaki et
al. 1999; Sengupta and Gebhart 1994; Sengupta et al. 1990).
Opioids affect somatic and visceral primary afferents differently and electrical stimulation of visceral nerves produces
significantly less windup of dorsal horn neurons than does
electrical stimulation of somatic nerves (Laird et al. 1995). The
postsynaptic dorsal columns-medial lemniscal pathway appears to be the major ascending route to the ventral posterolateral nucleus of the thalamus for noxious visceral stimuli
originating in the abdomen and pelvis, while the spinothalamic
tract is the major ascending pathway to the lateral thalamus for
noxious somatic stimuli (Al-Chaer et al. 1997a,b, 1998; Ness
2000a; Willis and Coggeshall 1991). These differences in
viscerosensory processing warrant further investigation into
mechanisms of visceral sensation and pain.
It is generally accepted that N-methyl-D-aspartate (NMDA)
ionotropic excitatory amino acid receptors contribute to spinal
neuronal hyperexcitability (central sensitization) and behavioral hyperalgesia following somatic tissue inflammation
(Coderre and Melzack 1992a,b; Dickenson and Sullivan 1990;
Haley et al. 1990; Ren and Dubner 1993; Ren et al. 1992a,b;
Woolf and Thompson 1991) but do not signal transient somatic
noxious stimuli or innocuous somatic stimuli (Dickenson and
Sullivan 1987; Haley et al. 1990; Nishiyama 2000; Olivar and
Laird 1999). However, since many visceral afferent fibers
encode noxious and nonnoxious stimulus intensities, the possibility exists that the same transmitters and receptors contribute to the signaling of both noxious and nonnoxious visceral
stimuli at primary afferent-dorsal horn neuron synapses. It has
been established that both NMDA and nonNMDA ionotropic
excitatory amino acid receptors contribute to colonic inflammation-evoked hyperalgesia and dorsal horn neuron hyperexcitability (Al-Chaer et al. 1996; Coutinho et al. 1996; Ide et al.
1997; Kolhekar and Gebhart 1994, 1996). NMDA receptors
also mediate the spinal processing of acute, noxious stimulation of the ureter in the absence of inflammation (Olivar and
Laird 1999). However, the role of NMDA receptors in transient
noxious and nonnoxious colorectal sensory processing is not
clear.
Colorectal distention (CRD) is widely used as a model for
visceral stimulation. It is generally accepted that 80-mmHg
Address for reprint requests: R. J. Traub, Dept. OCBS, University of
Maryland Dental School, 666 W. Baltimore St., Baltimore, MD 21201 (E-mail:
[email protected]).
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked ‘‘advertisement’’
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
INTRODUCTION
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0022-3077/01 $5.00 Copyright © 2001 The American Physiological Society
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Ji, Yaping and Richard J. Traub. Spinal NMDA receptors contribute to neuronal processing of acute noxious and nonnoxious colorectal
stimulation in the rat. J Neurophysiol 86: 1783–1791, 2001. The
present study investigated the role of NMDA receptors in the spinal
processing of acute noxious and nonnoxious colorectal stimulation
using extracellular single-unit recording in the rat. Fifty-three neurons
in the L6–S2 dorsal horn of the spinal cord were studied. Neurons were
identified using touch and light pinch of the ipsilateral perianal/scrotal
area and colorectal distention (CRD). All neurons had excitatory
responses to CRD. Thirty neurons were studied using a search stimulus of 80-mmHg CRD. The effects of a systemically administered
N-methyl-D-aspartate (NMDA) receptor channel blocker, dizocilpine
maleate (MK-801) (0.1, 0.5, 1.0, and 5.0 mg/kg), were tested on the
CRD-evoked responses of 13 neurons. The lowest dose had no effect
on the neuronal responses to CRD, while greater doses lowered the
CRD-evoked responses at all distention pressures tested (20, 40, 60,
and 80 mmHg). Similarly, spinal application of MK-801 (20, 50, 100,
and 200 nmol) attenuated CRD-evoked activity (n ⫽ 9). In addition,
a spinally administered competitive NMDA receptor antagonist,
2-amino-5-phosphonovaleric acid (APV) (30, 60, 120, and 240 nmol),
dose-dependently attenuated the CRD-evoked response at all distention pressures (n ⫽ 5). Systemically administered APV did not affect
neuronal responses to CRD (n ⫽ 3). Twenty-three neurons were
studied in animals that never received distention pressures exceeding
30 mmHg; the search stimulus ranged between 20- and 30-mmHg
CRD. These neurons were tested using 20-mmHg CRD. Systemically
administered MK-801 facilitated the response to 20-mmHg CRD in
three neurons and inhibited the response in five neurons, and the
response of five neurons was not affected. Spinally administered
MK-801 had no effect on neuronal responses to 20-mmHg CRD in six
neurons. However, spinally administered APV dose-dependently decreased the response to 20-mmHg CRD in four neurons. These results
are consistent with our previous observations that used Fos expression
as the index, suggesting that spinal NMDA receptors contribute to
processing of both noxious and nonnoxious CRD.
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METHODS
All experimental procedures were approved by the University of
Maryland Dental School Animal Care and Use Committee. Fifty-three
male Sprague-Dawley rats (Harlan) weighing 275–350 g were initially anesthetized with pentobarbital sodium (50 mg/kg ip). The left
jugular vein was catheterized for continuous infusion of pentobarbital
sodium at a rate of 5–10 mg 䡠 kg⫺1 䡠 h⫺1. The left carotid artery was
catheterized for continuous arterial blood pressure monitoring and
drug administration (pancuronium bromide, 0.2 mg 䡠 kg⫺1 䡠 h⫺1;
MK-801). A tracheal cannula was inserted for artificial ventilation
(2.5–3 ml stroke volume, 75– 80 strokes/min; adjusted so the mean
arterial blood pressure was maintained between 95 and 120 mmHg).
Body temperature was measured with a probe in the esophagus or a
thermacouple placed subcutaneously. The body temperature was kept
J Neurophysiol • VOL
within physiological limits (36 –38°C) with a heating pad and overhead lamp.
The rat was placed in a head holder and suspended with thoracic
vertebral and ishial clamps and the lower lumber/upper sacral spinal
cord was exposed by laminectomy of the L1–L2 vertebrae. The dura
matter was carefully cut and the spinal cord was bathed in warm
paraffin oil or artificial cerebral spinal fluid (ACSF). A 5- to 7-cm
balloon attached to Tygon tubing was inserted through the anus into
the descending colon and rectum. The distal end of the balloon was at
least 1 cm proximal to the external anal sphincter.
Tungsten microelectrodes (1–5 M⍀, Micro Probe, Potomac, MD)
were used for extracellular single-unit recording in the L6–S2 spinal
segments, 0 –1.5 mm lateral to midline, 500 –1,500 ␮m ventral to
spinal cord dorsum. Signals were amplified (A-M Systems, model
1800 AC amplifier) and passed through a dual time and voltage
window discriminator (BAK Electronics, DDIS-1) to isolate a single
unit. Data were collected with a CED 1401 plus and Spike2 for
Windows software (Cambridge Electronic Design, UK) on computer
for on- and off-line analysis. Colorectal distention was produced by
inflating the distention balloon with air. The pressure was monitored
and kept constant by a pressure controller/timing device (Bioengineering, University of Iowa).
The search stimulus consisted of touch and brief light pinch with
serrated forceps (on the rump and back area around the tail, the
scrotum and the pelvic belly) and CRD. When a neuron responsive to
the cutaneous stimuli was identified, the colon was distended for 10 s
to test whether the neuron was responsive to CRD. Two distention
pressures were used as for different purposes. In 30 animals the
distention pressure was 80 mmHg. For cells identified with this
stimulus as CRD responsive neurons, at least two increasing-stimulusintensity trials (20-, 40-, 60-, and 80-mmHg CRD, each lasting for
20 s with a 3-min interstimulus interval) were tested before drug
administration to establish the baseline response of the neuron. Since
repetitive 80-mmHg CRD (see INTRODUCTION) produces sensitization
in several independent measures of the response to CRD (Burton and
Gebhart 1995; Ness and Gebhart 1988b) and evokes protein plasma
extravasation in the colon measured with Evans blue (Zhai and Traub
1999), neuronal responses to distention were considered as occurring
in rats with a sensitized colon.
In separate animals (n ⫽ 23), the colorectal search stimulus did not
exceed 25 mmHg (n ⫽ 21) or 30 mmHg (n ⫽ 2). Repetitive 20-mmHg
CRD, sufficient to induce Fos in the spinal cord, does not evoke
plasma extravasation in the colon (Zhai and Traub 1999). In these
animals, the colons were considered not sensitized or normal so the
neuronal responses were considered a true measure of a nonnoxious
stimulus. At least five 20-mmHg distentions were used to obtain the
baseline response to this nonnoxious stimulus.
Drugs were administered systemically (intravenous; dose not adjusted for volume) or spinally. Only one neuron was studied in each
animal. MK-801 (Sigma-RBI) was predissolved in 0.9% saline when
it was used for intravenous injection. A cumulative dosing paradigm
(cumulative doses are reported) was used for MK-801 as it had a long
duration of action. For spinal application, MK-801 and APV (SigmaRBI) were predissolved in ACSF (in mM: 1.3 CaCl2 䡠 H2O, 2.6 KCl,
0.9 MgCl2 䡠 6H2O, 21 NaHCO3, 2.5 Na2HPO4, 125 NaCl, and 3.5
glucose). The APV was brought to a neutral pH. Drug was applied in
a 20 ␮l volume to the surface of the spinal cord. The drug was
removed by a tissue wick prior to application of the next dose. The
reported doses are the applied dose not a cumulative dose.
Neurons were classified according to the response to CRD (onset
latency and duration of response) as either short latency-abrupt (SLA),
short latency-sustained (SLS), or long latency (LL) (Ness and Gebhart
1987, 1988a). The response of the neuron to stimulation of the
convergent cutaneous receptive field was further used to describe
neurons as wide dynamic range (WDR; respond to brush and pinch)
or nociceptive specific (NS; respond to pinch only).
The response to distention was quantified as the total number of
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CRD is a noxious stimulus; this pressure is perceived as painful
by human beings (Munakata et al. 1997; Ness et al. 1990;
Ritchie 1973) and considered noxious in rats because they
learn to avoid this stimulus intensity in a passive-avoidance
behavioral paradigm (Ness and Gebhart 1988b; Ness et al.
1991; R. J. Traub, Q. Zhai, Y. Ji, and M. Kovalenko, unpublished observations). On the other hand, 20-mmHg CRD is
considered nonnoxious because it is not perceived as painful by
normal volunteers and rats do not avoid this stimulus in the
passive-avoidance paradigm (Lembo et al. 1994; Ness et al.
1990, 1991; Traub et al., unpublished observations). In addition, 60 80-mmHg distentions, but not 60 20-mmHg distentions, evokes plasma extravasation in the colon (Zhai and
Traub 1999) and produces macro- and microscopic tissue damage of the colon wall (Traub et al. 1992), suggesting repetitive
noxious colonic stimulation produces mild inflammation of the
colon. Indeed, several end points measuring responses to noxious CRD in animals and humans (e.g., blood pressure, visceromotor reflex, dorsal horn neuron discharge, visual analogue
scale) are facilitated over the first 5–10 stimulus presentations
(Burton and Gebhart 1995; Munakata et al. 1997; Ness and
Gebhart 1987, 1988b; Ness et al. 1990), suggesting the mild
inflammation sensitizes colonic afferents and facilitates the
response to noxious CRD. In contrast, repetitive innocuous
CRD (20 mmHg) does not facilitate the visceromotor reflex in
rats (Traub et al., unpublished observations).
We previously reported that repetitive noxious (80 mmHg)
and nonnoxious (20 mmHg) CRD induce Fos expression in the
lumbosacral spinal cord (Traub et al. 1992; Zhai and Traub
1999) although noxious CRD induces significantly more Fos
than nonnoxious CRD. Fos expression to both noxious and
innocuous stimuli was partially attenuated by a systemically
(Zhai and Traub 1999) or intrathecally (Traub et al., unpublished
observations) administered NMDA receptor antagonist, though
noxious CRD-induced Fos expression was more efficaciously
attenuated than nonnoxious CRD-induced Fos. These data suggest
the involvement of NMDA receptors in the signaling of visceral
stimuli. To further examine the involvement of NMDA receptors
in mediating the processing of innocuous and noxious visceral
stimuli, single-unit activity was recorded in the lumbosacral dorsal
horn and the effects of the noncompetitive NMDA receptor channel blocker dizocilpine maleate (MK-801) and the competitive
NMDA receptor antagonist 2-amino-5-phosphonovaleric acid
(APV) on neuronal responses to both noxious and nonnoxious
CRD were investigated. Part of these data have been reported in
abstract form (Ji and Traub 2000).
NMDA RECEPTOR INVOLVEMENT IN INNOCUOUS AND NOXIOUS CRD
action potentials during the 20 s (SLA neurons) or 40 s (SLS and LL
neurons) after the onset of distention minus spontaneous activity
during the 20 or 40 s prior to distention. The response to CRD was
normalized to the response to 80- or 20-mmHg CRD prior to drug
administration. The data were expressed as means ⫾ SE. For each
drug treatment group (see following text), the data at each distention
pressure were analyzed separately using one-way repeated-measures
ANOVA and Student-Newman-Keuls for multiple comparisons. P ⬍
0.05 was considered significant.
RESULTS
Classification of neurons according to CRD response type
and cutaneous receptive field
tentions so subsequent data analyses were on the first postdrug
series of distentions. Figure 1A shows an example of the
attenuation of the response of a single neuron following systemic administration of MK-801. The effect of 0.1 mg/kg
MK-801 was observed on two neurons, and no change in the
magnitude of the response was found. Increasing doses of
MK-801 (0.5, 1.0, and 5.0 mg/kg) attenuated the response to
CRD (Fig. 1B). One and 5 mg/kg, but not 0.5 mg/kg, MK-801
significantly attenuated the response to 40, 60, and 80 mmHg
of distention. At 20-mmHg CRD, there was a significant attenuation of the response to distention, but there was no dose
dependence. Five milligrams per kilogram MK-801 decreased
the response to 80-mmHg CRD by 47% compared with the
baseline response to 80-mmHg CRD. The response to 20mmHg CRD was decreased by 44% compared with the baseline response to 20-mmHg CRD.
Effect of systemic MK-801 on neuronal responses to
nonnoxious CRD
Thirteen neurons were studied to determine the effect of
systemically administered MK-801 on the response to nonnoxious CRD. The search stimulus used to find these neurons
never exceeded 25 mmHg (n ⫽ 11) or 30 mmHg (n ⫽ 2). At
no point during the experiment were these animals subject to
distention pressures greater than the search stimulus pressure.
Effect of systemic MK-801 on neuronal responses to
noxious CRD
The effects of systemically administered MK-801 on the
response to graded intensities of CRD were examined in 13
neurons. Ten were classified as SLA neurons, 2 were SLS
neurons, and 1 was a LL neuron. Four doses of MK-801 (0.1,
0.5, 1.0, and 5.0 mg/kg) were used in this study. Increasing
intensity trials were initiated 10 min and 40 min after each drug
administration. Most neurons had a monotonic stimulus response function to graded pressures of distention. The effect of
the drug was more pronounced during the first series of disJ Neurophysiol • VOL
FIG. 1. A: peristimulus time histograms showing the response to increasing
intensities of colorectal distention (CRD) of a short latency-abrupt (SLA)
neuron prior to drug administration (baseline) and following systemic administration of 5.0 mg/kg MK-801. The intensity and duration of each distention
is shown below each histogram. Each distention was 20 s in duration. B:
stimulus-response functions showing the mean responses to systemic application of MK-801. For each neuron the responses were normalized to 80 mmHg
CRD before MK-801 application. }, baseline; ■, 0.5 mg/kg; ●, 1.0 mg/kg; Œ
5.0 mg/kg. P values for 1-way repeated-measures ANOVA at each distention
pressure are shown across the top. *P ⬍ 0.05 vs. the baseline response at that
distention pressure.
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A total of 53 neurons showing excitatory responses to CRD
were recorded in the dorsal horn of the L6–S2 spinal cord
segments; 40 were SLA neurons, 12 were SLS neurons, and 1
was a LL neuron; neurons showing inhibitory responses to
CRD were not studied. Within each treatment group (see
following text), there were no differences in responses of SLA
and SLS neurons so the data were pooled.
The cutaneous receptive field was qualitatively examined.
Fifty neurons had a cutaneous receptive field around the ipsilateral scrotal/perianal area. Six neurons also responded to tail
movement. The three neurons for which no receptive field
could be found were excited by the CRD search stimulus when
another neuron with a cutaneous receptive field was tested. The
latter neuron did not respond to CRD and was not studied. The
CRD responsive neuron was isolated with the window discriminator and used in the study. Of the 23 neurons obtained using
the nonnoxious CRD search stimulus, 14 responded to both
noxious pinch and nonnoxious touch of the receptive field, 6
were only activated by noxious pinch and 2 only by nonnoxious touch. There was one neuron excited by noxious pinch but
inhibited by nonnoxious stimuli. The other 30 neurons were
obtained with 80 mmHg as the search stimulus. Ten responded
to both noxious and nonnoxious cutaneous stimuli, 11 were
only excited by noxious cutaneous stimuli, 3 by nonnoxious
cutaneous stimuli, and 3 were inhibited by pinch. The receptive
field could not be found for three neurons.
The mean spontaneous activity of the 53 neurons was
11.3 ⫾ 1.9 Hz. There was no difference in spontaneous activity
between neurons searched with 25-mmHg CRD and 80-mmHg
CRD (Mann-Whitney rank sum test, P ⫽ 0.971). Interestingly,
the mean response to 20-mmHg CRD prior to drug administration for neurons searched with the low-intensity distention
stimulus was significantly greater than the mean discharge to
20-mmHg CRD for neurons searched with 80-mmHg CRD
(Hz: 12.6 ⫾ 1.5 vs. 7.6 ⫾ 0.8, t-test, P ⫽ 0.003).
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Y. JI AND R. J. TRAUB
Effect of spinal MK-801 on neuronal responses to
noxious CRD
MK-801 was administered to the surface of the spinal cord
while recording from nine neurons to determine if the effect of
MK-801 occurred in the spinal cord or was supraspinally
and/or peripherally mediated. Six were SLA neurons and the
rest were SLS neurons. Two of the three SLS neurons were
inhibited by pinch of the cutaneous receptive field; the cutaneous receptive field of the other neuron was not found. Three
of the six SLA neurons responded to noxious and nonnoxious
cutaneous stimulation; the others were only activated by noxious pinch of the cutaneous receptive field.
Six neurons were tested with several changes of ACSF, and
there was no change in the response to CRD in these neurons.
Four doses of MK-801 (20, 50, 100, and 200 nmol) were then
tested. The response to CRD after 20 nmol MK801 did not
differ from the baseline. Greater concentrations of MK-801
(50, 100, and 200 nmol) attenuated the response to CRD at
each distention pressure (dose-dependently at 40-, 60-, and
80-mmHg; Fig. 3). The highest dose of MK-801 decreased the
response to 80-mmHg distention by 39% compared with the
baseline response to 80-mmHg CRD. The response to 20mmHg CRD was decreased by 43% compared with the baseline response to 20-mmHg CRD.
FIG. 3. A: peristimulus time histograms showing the response to increasing
intensities of CRD of a SLA neuron prior to drug administration (baseline) and
following spinal application of 50, 100, and 200 nmol MK-801. The intensity
and duration of each distention is shown below each histogram. Each distention was 20 s in duration. To the right of each histogram is an example of one
action potential recorded during the 80-mmHg distention. B: stimulus-response
functions showing the mean responses to spinal application of MK-801. For
each neuron, the responses were normalized to 80-mmHg CRD before MK801 application. }, baseline; ■, 50 nmol; ●, 100 nmol; Œ, 200 nmol. P values
for one-way repeated-measures ANOVA at each distention pressure are shown
across the top. *P ⬍ 0.05 vs. baseline at that distention pressure; ⫹P ⬍ 0.05
vs. 200 nmol MK-801 at that distention pressure. Values for 20 nmol MK801
were left off the graph for clarity but were included in the ANOVA.
Effect of spinal MK-801 on neuronal responses to
nonnoxious CRD
The effect of spinally administered MK-801 was tested on
six neurons from rats that only received nonnoxious CRD.
Four were SLA neurons and two were SLS neurons. Four were
WDR neurons, while the other two were only activated by
pinch of the receptive field. No change in the response to CRD
was observed in these neurons after 100 nmol of MK-801 was
administered (Fig. 4).
Effect of spinal APV on neuronal responses to noxious CRD
FIG. 2. The mean response to nonnoxious CRD of the five neurons that had
significantly attenuated responses following systemic administration of MK801. *P ⬍ 0.05 vs. baseline (0 mg/kg). ⫹P ⬍ 0.05 vs. 5 mg/kg MK-801.
J Neurophysiol • VOL
To confirm the results from the MK-801 studies, the competitive NMDA receptor antagonist APV (30, 60, 120, and 240
nmol) was applied to the surface of the spinal cord and the
effects on neuronal responses to increasing intensities of CRD
were examined in five cells. Two were classified as SLS
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All but one neuron were classified as SLA neurons. Seven
neurons responded to both noxious and nonnoxious somatic
stimulation, four to only noxious stimulation, and two to only
nonnoxious stimulation. The change in response to 20-mmHg
CRD following systemic administration of MK-801 was variable. The response of five neurons was attenuated (response to
20-mmHg CRD following 5 mg/kg MK-801 was more than 2
SD from the mean baseline response to 20-mmHg CRD), two
showed increased responses and the remaining six cells
showed no change in response. Figure 2 shows the mean
dose-dependent effect of systemically administered MK-801
on the five neurons that had a significantly attenuated response
as described in the preceding text. In these five neurons, the
mean response to 20-mmHg CRD was decreased by 74%
compared with baseline when 5 mg/kg MK-801 was administered. However, when all the neurons in this treatment group
were considered, there was no significant change in the mean
response.
NMDA RECEPTOR INVOLVEMENT IN INNOCUOUS AND NOXIOUS CRD
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CRD, but not 20-mmHg CRD in the absence of more intense
stimuli, produces mild sensitization of the colon facilitating
responses to colorectal distention (see INTRODUCTION). We
therefore thought that the 20-mmHg stimulus, when given as
part of a graded intensity distention trial, was given to a
sensitized colon and would be a different stimulus than 20mmHg CRD given to animals that never received more intense
colorectal stimulation. Our data demonstrate that NMDA receptor antagonists attenuate spinal neuronal responses to innocuous CRD as well. These results suggest that NMDA receptors partially mediate spinal sensory processing in the lumbosacral
spinal cord of noxious and innocuous colorectal stimuli.
General considerations
FIG. 4. Effect of spinal MK-801 on the response to nonnoxious CRD.
MK-801 did not change the response to 20 mmHg CRD (ANOVA, P ⫽ 0.347).
In the present study, most CRD responsive neurons were
characterized as SLA neurons (76%), a small number (22%)
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neurons, and the other three were SLA neurons. Two neurons
responded to touch and pinch of the receptive field, one only to
pinch. The receptive field could not be found for two neurons.
APV dose-dependently attenuated the neuronal response to
CRD at each distention pressure (Fig. 5). The highest dose of
APV attenuated the response to 80-mmHg CRD by 62% compared with the baseline response to 80-mmHg CRD. The
response to 20-mmHg CRD was decreased by 86% compared
with the baseline response to 20-mmHg CRD.
An additional three neurons were tested with systemically
administered APV (5.0 mg/kg). No change in the response to
CRD was observed in these neurons, further suggesting that the
NMDA receptor antagonist had a spinal site of action.
Effect of spinal APV on neuronal responses to nonnoxious
CRD
The effect of spinally administered APV (30, 60, 120, and
240 nmol) on the response to nonnoxious CRD was tested in
four neurons. Two were SLA neurons and two were SLS
neurons. Three neurons responded to noxious and nonnoxious
cutaneous stimulation, and one responded only to pinch of the
receptive field. APV attenuated both the spontaneous activity
and CRD evoked response of the neurons. Figure 6 shows the
dose-dependent effect of APV on responses to 20-mmHg
CRD. APV (30 nmol) attenuated the response to 20-mmHg
CRD by 30% compared with baseline. Following application
of 240 nmol APV, the response to 20-mmHg CRD was decreased by 80% compared with baseline.
DISCUSSION
The present study tested the hypothesis that NMDA receptors partially mediate spinal neuronal processing of transient
noxious colonic stimuli. This is contrary to the generally accepted hypothesis that NMDA receptors mediate persistent
nociceptive stimuli (inflammatory pain, neuropathic pain) but
not transient nociception or innocuous somatic stimuli. Our
data demonstrate that both the noncompetitive NMDA receptor
channel blocker MK-801 and the competitive NMDA receptor
antagonist APV attenuate spinal neuronal responses to noxious
CRD. In addition, we tested the effects of the NMDA receptor
antagonists on neuronal responses to innocuous CRD in rats
that never received more intense stimuli. Repetitive 80-mmHg
J Neurophysiol • VOL
FIG. 5. A: peristimulus time histograms showing the response to increasing
intensities of CRD of a SLA neuron prior to drug administration (baseline) and
following spinal application of 60, 120, and 240 nmol 2-amino-5-phosphonovaleric acid (APV). The intensity and time of each distention is the same for
the 4 histograms and shown at the bottom. Each distention was 20 s in duration.
B: examples of the spike trains recorded 5 s before, during, and 5 s after the
80-mmHg distention following each dose of APV. Arrows indicate the onset
(1) and termination (2) of the distention. C: stimulus-response functions
showing the mean responses of five neurons to spinal application of APV. For
each neuron, the responses were normalized to 80-mmHg CRD before APV
application. }, baseline; ■, 60 nmol; ●, 120 nmol; Œ, 240 nmol. P values for
one-way repeated-measures ANOVA at each distention pressure are shown
across the top. *P ⬍ 0.05 vs. baseline at that distention pressure; ⫹P ⬍ 0.05
vs. 240 nmol at that distention pressure.
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Y. JI AND R. J. TRAUB
FIG. 6. A: peristimulus time histograms showing the response of a SLS
neuron to 20-mmHg CRD prior to APV administration (baseline) and following spinal application of 60, 120, and 240 nmol APV. Each histogram shows
the response from 5 20-s, 20-mmHg distentions. To the right of each histogram
is an example of one action potential recorded during the 80-mmHg distention.
B: histogram showing the mean response to 20-mmHg CRD before and
following spinal administration of APV. For each animal, the data were
normalized to the baseline (0 nmol). ANOVA, P ⫽ 0.019; *P ⬍ 0.05 vs.
baseline.
were SLS neurons, and only one (2%) was a LL neuron. These
percentages are similar to studies reporting 60 –90% of CRDresponsive neurons were SLA neurons (Katter et al. 1996;
Kozlowski et al. 2000; Olivar et al. 2000) but different from
studies reporting 34% of CRD-responsive neurons were SLA
neurons, 46% were SLS neurons, and 20% were LL neurons
(Ness and Gebhart 1987) or 25/33 neurons (76%) were SLS
neurons and the remainder were SLA neurons (Kolhekar and
Gebhart 1996). These differences are likely due to the use of
different search stimuli between the different groups of investigators. For example, Ness used antidromic stimulation in the
contralateral cervical spinal cord and/or colorectal distention
(75– 80-mmHg) as search stimuli, while we identified neurons
using cutaneous stimuli (light pinch and touch) and subsequently tested for responses to noxious or innocuous CRD.
It has been suggested that SLS and SLA neurons belong to
different functional groups. It was recently reported that colorectal inflammation increased the activity (both spontaneous
and CRD-evoked activity) of SLS neurons significantly more
than SLA neurons in the lumbosacral spinal cord (Ness and
Gebhart 2000), although this contradicts reports that most SLA
neurons have increased responses to CRD after colorectal
inflammation (Al-Chaer et al. 1996, 1997b; Olivar et al. 2000).
However, lidocaine, clonidine, morphine, and kappa opioid
J Neurophysiol • VOL
NMDA receptors and CRD
It is generally accepted that somatic hyperalgesia caused by
inflammation is partly mediated by spinal NMDA receptors
(Chapman and Dickenson 1995; Haley et al. 1990; Ren et al.
1992a; Woolf and Thompson 1991), while acute somatic pain
is not blocked by NMDA receptor antagonists (Olivar and
Laird 1999; Ren et al. 1992b; Urban et al. 1994). Several lines
of evidence suggest that NMDA receptors also contribute to
the generation and maintenance of visceral hyperalgesia
(Birder and De Groat 1992; Kakizaki et al. 1996; Olivar and
Laird 1999; Rice and McMahon 1994) and play an important
role in the processing of persistent pain after colorectal inflammation. Intrathecal administration of NMDA increased visceromotor, pressor, and neuronal responses to CRD, and these
effects were blocked by APV (Kolhekar and Gebhart 1994,
1996). Additionally, APV and MK-801 attenuated visceral
(colonic) hyperalgesia induced by intracolorectal injection of
turpentine or zymosan (Coutinho et al. 1996; Ide et al. 1997).
It is still not clear, however, whether NMDA receptors contribute to the processing of transient or phasic noxious colonic
stimuli or innocuous colonic stimuli. We previously reported
that systemic MK-801 attenuated noxious and nonnoxious
CRD-induced Fos expression in the lumbosacral spinal cord
(Zhai and Traub 1999). From these data, it can be argued that
MK-801 acted on a supraspinal or peripheral site rather than in
the spinal cord (McRoberts et al. 2001). The present study
however, demonstrates that MK-801, administered spinally or
systemically, attenuates responses to transient noxious CRD.
Furthermore, APV attenuated the response to CRD when administered spinally, but not systemically, supporting our hypothesis that spinal NMDA receptors contribute to the process-
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receptor agonists attenuated the CRD-evoked responses of SLS
neurons to a greater extent than SLA neurons (Ness 2000b;
Ness and Gebhart 1989; Omote et al. 1994). Unfortunately, we
were not able to differentiate changes in the responses of SLA
from SLS neurons after drug administration, probably due to
the relatively small number of SLS neurons in our study.
It has been reported that the mean response threshold to
colorectal distention is near 20-mmHg, although thresholds for
individual neurons range from less than 10 to more than
50-mmHg CRD (Al-Chaer et al. 1996, 1997b; Kolhekar and
Gebhart 1996; Ness and Gebhart 1987; Olivar et al. 2000). We
found it was more difficult to find a neuron that responded to
CRD when the search stimulus was 25-mmHg compared with
the 80-mmHg CRD search stimulus. Using the nonnoxious
search stimulus, we recorded from neurons that had thresholds
to CRD less than 25 mmHg but would have missed neurons
with slightly higher thresholds or very small responses to the
search stimulus that would have been recorded using the 80mmHg search stimulus. However, since 80-mmHg CRD produces some sensitization of dorsal horn neurons, it is possible
that neurons that normally would have had thresholds more
than 25 mmHg would have small responses to 20 mmHg when
the colon was sensitized. Indeed the mean response prior to
drug administration to 20-mmHg CRD from rats that only
received nonnoxious CRD was significantly greater than the
mean response to 20-mmHg CRD from rats that received
noxious intensities of CRD.
NMDA RECEPTOR INVOLVEMENT IN INNOCUOUS AND NOXIOUS CRD
J Neurophysiol • VOL
efficacy in attenuating the neuronal responses to 80- and 20mmHg CRD.
Conclusions
The present data conclusively demonstrate that spinal
NMDA receptors contribute to processing of transient innocuous and noxious colorectal stimuli in the rat. The fact that
electrical stimulation of visceral nerves evokes considerably
less windup in the spinal cord compared with somatic nerve
stimulation (Laird et al. 1995) combined with the present data
support the concept that mechanisms involved in visceral sensory processing partially differ from somatic sensory processing in the spinal cord. Furthermore, there is no facilitation of
reflex responses to repetitive innocuous CRD (Traub et al.,
unpublished observations), suggesting innocuous CRD does
not induce central sensitization. It is interesting to speculate
that mechanisms that would increase activity of NMDA receptors during low-intensity colorectal stimulation and produce
central sensitization could evoke visceral hypersensitivity and
hyperalgesia, a common complaint of patients suffering from
irritable bowel syndrome (Lembo et al. 1999; Munakata et al.
1997; Ritchie 1973).
We thank Dr. Ke Ren for critical comments on the manuscript.
This work was supported by National Institute of Neurological Disorders
and Stroke Grant NS-37424.
REFERENCES
AL-CHAER ED, FENG Y, AND WILLIS WD. A role for the dorsal column in
nociceptive visceral input into the thalamus of primates. J Neurophysiol 79:
3143–3150, 1998.
AL-CHAER ED, LAWAND NB, WESTLUND KN, AND WILLIS WD. Pelvic visceral
input into the nucleus gracilis is largely mediated by the postsynpatic dorsal
column pathway. J Neurophysiol 76: 2675–2690, 1996.
AL-CHAER ED, WESTLUND KN, AND WILLIS WD. Nucleus gracilis: an integrator for visceral and somatic information. J Neurophysiol 78: 521–527,
1997a.
AL-CHAER ED, WESTLUND KN, AND WILLIS WD. Sensitization of postsynaptic
dorsal column neuronal responses by colon inflammation. Neuroreport 8:
3267–3273, 1997b.
BAHNS E, HALSBAND U, AND JANIG W. Response of sacral visceral afferents
from the lower urinary tract, colon and anus to mechanical stimulation.
Pflügers Arch 410: 296 –303, 1987.
BARBER A AND GOTTSCHLICH R. Opioid agonists and antagonists: an evaluation
of their peripheral actions in inflammation. Med Res Rev 12: 525–562, 1992.
BERKLEY KJ, HOTTA H, ROBBINS A, AND SATO Y. Functional properties of
afferent fibers supplying reproductive and other pelvic organs in pelvic
nerve of female rat. J Neurophysiol 63: 256 –272, 1990.
BERKLEY KJ, ROBBINS A, AND SATO Y. Afferent fibers supplying the uterus in
the rat. J Neurophysiol 59: 142–163, 1988.
BIRDER LA AND DE GROAT WC. The effect of glutamate antagonists on c-fos
expression induced in spinal neurons by irritation of the lower urinary tract.
Brain Res 580: 115–120, 1992.
BLUMBERG H, HAUPT P, JANIG W, AND KOHLER W. Encoding of visceral
noxious stimuli in the discharge patterns of visceral afferent fibres from the
colon. Pflügers Arch 398: 33– 40, 1983.
BURTON MB AND GEBHART GF. Effects of intracolonic acetic acid on responses
to colorectal distention in the rat. Brain Res 672: 77– 82, 1995.
CHAPMAN V AND DICKENSON AH. Time-related roles of excitatory amino acid
receptors during persistent noxiously evoked responses of rat dorsal horn
neurones. Brain Res 703: 45–50, 1995.
CODERRE TJ AND MELZACK R. The contribution of excitatory amino acids to
central sensitization and persistent nociception after formalin-induced tissue
injury. J Neurosci 12: 3665–3670, 1992a.
86 • OCTOBER 2001 •
www.jn.org
Downloaded from http://jn.physiology.org/ by 10.220.33.2 on June 17, 2017
ing of transient noxious colonic stimuli. This observation is
consistent with a study reporting that systemically administered NMDA receptor blockers ketamine and memantine dosedependently inhibited pressor responses evoked by acute noxious visceral stimuli (Olivar and Laird 1999), pretreatment
with intrathecally administered APV stabilized visceromotor
and pressor responses to repeated noxious CRD when used in
a very low dose (1 pmol) (Kolhekar and Gebhart 1994), and
spinally administered MK-801 or APV attenuated Fos expression and the visceromotor reflex evoked by transient noxious
CRD (Traub et al., unpublished observations).
The present data contradicts a recent report showing only a
non-NMDA rather than a NMDA receptor antagonist produced
inhibition of the CRD-evoked response on several SLA neurons in rats without colorectal inflammation (Kozlowski et al.
2000). The cause of the difference with the present results is
likely due to the fact that the highest dose they used was 0.3
mg/kg of MK-801. Our experiment showed only a larger dose
(ⱖ0.5 mg/kg) of MK-801 had a significant effect on responses
to CRD. It should be noted that the doses of MK-801 and APV
used in the present study are consistent with doses reported to
attenuate nociceptive responses evoked from somatic tissue
[MK-801: 0.5–2 mg/kg iv (Haley et al. 1990; Ren et al. 1992a);
MK-801: 6 –100 nmol it (Coderre and Melzack 1992; Ren et al.
1992a); APV: 50 nmol-1000 nmol it (Coderre and Melzack
1992; Haley et al. 1990; Ren et al. 1992b)] and visceral tissue
[MK-801: 3.5 mg/kg iv (Birder and De Groat 1992); MK-801:
10 – 40 nmol it (Coutinho et al. 1996); APV: 250 –1,000 nmol
it (Rice and McMahon 1994)].
The effect of NMDA receptor antagonists on spinal processing of nonnoxious colorectal stimuli (20-mmHg search stimulus) produced mixed results. Spinally administered APV dosedependently attenuated the response to nonnoxious CRD in
nonsensitized rats supporting a role for NMDA receptors in the
spinal processing of nonnoxious visceral stimuli. On the other
hand, spinally administered MK-801 did not attenuate the
response to nonnoxious CRD, although systemically administered MK-801 was partially effective. Furthermore, spinally
administered MK-801 attenuated the response to 20-mmHg
CRD in neurons when the search stimulus was noxious CRD.
A possible explanation for these discrepancies may be the
mechanism of action of the spinally administered MK-801 and
APV. APV is a competitive NMDA receptor antagonist, while
MK-801 is a noncompetitive NMDA receptor channel blocker
(Dingledine et al. 1999). While both have high affinity for
NR1/NR2A and NR1/NR2B subunits, which are abundant in
the spinal cord (Sucher et al. 1996), MK-801 acts by blocking
the open channel of activated NMDA receptors. It is possible
that the afferent drive from 80 mmHg of distention maintains
the channel in an open state to a greater degree than 20-mmHg
CRD facilitating access to MK-801. This suggests that neurons
that undergo 80-mmHg CRD were sensitized and that the
attenuation of the response to 20-mmHg CRD by MK-801 was
due to blocking the receptor on a sensitized neuron. In nonsensitized rats, the NMDA channel may not be in a state
readily accepting MK-801. APV on the other hand binds to a
ligand recognition site preventing channel activation by glutamate and would be an available mechanism under both stimulus conditions. The different mechanisms of APV and MK801 in blocking the channel likely contribute to the different
1789
1790
Y. JI AND R. J. TRAUB
J Neurophysiol • VOL
NESS TJ AND GEBHART GF. Characterization of neuronal responses to noxious
visceral and somatic stimuli in the medial lumbosacral spinal cord of the rat.
J Neurophysiol 57: 1867–1892, 1987.
NESS TJ AND GEBHART GF. Characterization of neurons responsive to noxious
colorectal distention in the T13–L2 spinal cord of the rat. J Neurophysiol 60:
1419 –1438, 1988a.
NESS TJ AND GEBHART GF. Colorectal distention as a noxious visceral stimulus: physiologic and pharmacologic characterization of pseudaffective responses in the rat. Brain Res 450: 153–169, 1988b.
NESS TJ AND GEBHART GF. Differential effects of morphine and clonidine on
visceral and cutaneous spinal nociceptive transmission in the rat. J Neurophysiol 62: 220 –230, 1989.
NESS TJ AND GEBHART GF. Acute inflammation differentially alters the activity
of two classes of rat spinal visceral nociceptive neurons. Neurosci Lett 281:
131–134, 2000.
NESS TJ, METCALF AM, AND GEBHART GF. A psychophysiological study in
humans using phasic colonic distention as a noxious visceral stimulus. Pain
43: 377–386, 1990.
NESS TJ, RANDICH A, AND GEBHART GF. Further evidence that colorectal
distention is a noxious visceral stimulus in rats. Neurosci Lett 131: 113–116,
1991.
NISHIYAMA T. Interaction among NMDA receptor-, NMDA glycine site- and
AMPA receptor antagonists in spinally mediated analgesia. Can J Anaesth
47: 693– 698, 2000.
OLIVAR T, CERVERO F, AND LAIRD JM. Responses of rat spinal neurones to
natural and electrical stimulation of colonic afferents: effect of inflammation. Brain Res 866: 168 –177, 2000.
OLIVAR T AND LAIRD JM. Differential effects of N-methyl-D-aspartate receptor
blockade on nociceptive somatic and visceral reflexes. Pain 79: 67–73, 1999.
OMOTE K, KAWAMATA M, IWASAKI H, AND NAMIKI A. Effects of morphine on
neuronal and behavioural responses to visceral and somatic nociception at
the level of spinal cord. Acta Anaesthesiol Scand 38: 514 –517, 1994.
OZAKI N, SENGUPTA JN, AND GEBHART GF. Mechanosensitive properties of
gastric vagal afferent fibers in the rat. J Neurophysiol 82: 2210 –2220, 1999.
REN K AND DUBNER RD. NMDA receptor antagonists attenuate mechanical
hyperalgesia in rats with unilateral inflammation of the hindpaw. Neurosci
Lett 163: 22–26, 1993.
REN K, HYLDEN JLK, WILLIAMS GM, RUDA MA, AND DUBNER R. The effects
of a non-competitive NMDA receptor antagonist, MK-801, on behavioral
hyperalgesia and dorsal horn neuronal activity in rats with unilateral inflammation. Pain 50: 331–344, 1992a.
REN K, WILLIAMS GM, HYLDEN JLK, RUDA MA, AND DUBNER R. The intrathecal administration of excitatory amino acid receptor antagonists selectively attenuated carrageenan-induced behavioral hyperalgesia in rats. Eur
J Pharmacol 219: 235–243, 1992b.
RICE AS AND MCMAHON SB. Pre-emptive intrathecal administration of an
NMDA receptor antagonist (AP-5) prevents hyper-reflexia in a model of
persistent visceral pain. Pain 57: 335–340, 1994.
RITCHIE J. Pain from distention of the pelvic colon by inflating a balloon in the
irritable colon syndrome. Gut 14: 125–132, 1973.
SENGUPTA JN AND GEBHART GF. Characterization of mechanosensitive pelvic
nerve afferent fibers innervating the colon of the rat. J Neurophysiol 71:
2046 –2060, 1994.
SENGUPTA JN, SAHA JK, AND GOYAL RK. Stimulus-response function studies
of esophageal mechanosensitive nociceptors in sympathetic afferents of
opossum. J Neurophysiol 64: 796 – 812, 1990.
SENGUPTA JN, SU X, AND GEBHART GF. Kappa, but not mu or delta, opioids
attenuate responses to distention of afferent fibers innervating the rat colon.
Gastroenterology 111: 968 –980, 1996.
SIMONIN F, VALVERDE O, SMADJA C, SLOWE S, KITCHEN I, DIERICH A, LE MEUR
M, ROQUES BP, MALDONADO R, AND KIEFFER BL. Disruption of the kappaopioid receptor gene in mice enhances sensitivity to chemical visceral pain,
impairs pharmacological actions of the selective kappa-agonist U-50,488H
and attenuates morphine withdrawal. EMBO J 17: 886 – 897, 1998.
STEIN C. The control of pain in peripheral tissue by opioids. N Engl J Med 332:
1685–1690, 1995.
SU X, SENGUPTA JN, AND GEBHART GF. Effects of opioids on mechanosensitive
pelvic nerve afferent fibers innervating the urinary bladder of the bat.
J Neurophysiol 77: 1566 –1580, 1997.
SUCHER NJ, AWOBULUYI M, CHOI YB, AND LIPTON SA. NMDA receptors: from
genes to channels. Trends Pharmacol Sci 17: 348 –355, 1996.
TRAUB RJ, PECHMAN P, IADAROLA MJ, AND GEBHART GF. Fos-like proteins in
86 • OCTOBER 2001 •
www.jn.org
Downloaded from http://jn.physiology.org/ by 10.220.33.2 on June 17, 2017
CODERRE TJ AND MELZACK R. The role of NMDA receptor-operated calcium
channels in persistent nociception after formalin-induced tissue injury.
J Neurosci 12: 3671–3675, 1992b.
COUTINHO SV, MELLER ST, AND GEBHART GF. Intracolonic zymosan produces
visceral hyperalgesia in the rat that is mediated by spinal NMDA and
nonNMDA receptors. Brain Res 736: 7–15, 1996.
DICKENSON AH AND SULLIVAN AF. Evidence for a role of the NMDA receptor
in the frequency dependent potentiation of deep rat dorsal horn nociceptive
neurones following C fibre stimulation. Neuropharmacology 26: 1235–
1238, 1987.
DICKENSON AH AND SULLIVAN AF. Differential effects of excitatory amino
acid antagonists on dorsal horn nociceptive neurones in the rat. Brain Res
506: 31–39, 1990.
DINGLEDINE R, BORGES K, BOWIE D, AND TRAYNELIS SF. The glutamate
receptor ion channels. Pharmacol Rev 51: 7– 61, 1999.
HALEY JE, SULLIVAN AF AND DICKENSON AH. Evidence for spinal N-methylD-aspartate receptor involvement in prolonged chemical nociception in the
rat. Brain Res 518: 218 –226, 1990.
HAUPT P, JANIG W, AND KOHLER W. Response pattern of visceral afferent
fibres, supplying the colon, upon chemical and mechanical stimuli. Pflügers
Arch 398: 41– 47, 1983.
IDE Y, MAEHARA Y, TSUKAHARA S, KITAHATA LM, AND COLLINS JG. The
effects of an intrathecal NMDA antagonist (AP5) on the behavioral changes
induced by colorectal inflammation with turpentine in rats. Life Sci 60:
1359 –1363, 1997.
JANIG W AND KOLTZENBURG M. Receptive properties of sacral primary afferent
neurons supplying the colon. J Neurophysiol 65: 1067–1077, 1991.
JI Y AND TRAUB RJ. MK-801attenuates spinal neuron responses to noxious and
nonnoxious colorectal distention. Soc Neurosci Abstr 26: 2191, 2000.
JOSHI SK, SU X, PORRECA F, AND GEBHART GF. kappa-Opioid receptor agonists
modulate visceral nociception at a novel, peripheral site of action. J Neurosci 20: 5874 –5879, 2000.
KAKIZAKI H, YOSHIYAMA M, AND DE GROAT WC. Role of NMDA and AMPA
glutamatergic transmission in spinal c-fos expression after urinary tract
irritation. Am J Physiol Regulatory Intgrative Comp Physiol 270: R990 –
R996, 1996.
KATTER JT, DADO RJ, KOSTARCZYK E, AND GIESLER GJJ. Spinothalamic and
spinohypothalamic tract neurons in the sacral spinal cord of rats. II. Responses to cutaneous and visceral stimuli. J Neurophysiol 75: 2606 –2628,
1996.
KOLHEKAR R AND GEBHART GF. NMDA and quisqualate modulation of visceral nociception in the rat. Brain Res 651: 215–226, 1994.
KOLHEKAR R AND GEBHART GF. Modulation of spinal visceral nociceptive
transmission by NMDA receptor activation in the rat. J Neurophysiol 75:
2344 –2353, 1996.
KOZLOWSKI CM, BOUNTRA C, AND GRUNDY D. The effect of fentanyl, DNQX
and MK-801 on dorsal horn neurones responsive to colorectal distension in
the anaesthetized rat. Neurogastroenterol Motil 12: 239 –247, 2000.
LAIRD JMA, DE LA RUBIA PG, AND CERVERO F. Excitability changes of somatic
and viscero-somatic nociceptive reflexes in the decerebrate-spinal rabbit:
role of NMDA receptors. J Physiol (Lond) 489: 545–555, 1995.
LEMBO T, MUNAKATA J, MERTZ H, NIAZI N, KODNER A, NIKAS V, AND MAYER
EA. Evidence for the hypersensitivity of lumbar splanchnic afferents in
irritable bowel syndrome. Gastroenterology 107: 1686 –1696, 1994.
LEMBO T, NALIBOFF B, MUNAKATA J, FULLERTON S, SABA L, TUNG S, SCHMULSON M, AND MAYER EA. Symptoms and visceral perception in patients with
pain-predominant irritable bowel syndrome. Am J Gastroenterol 94: 1320 –
1326, 1999.
MCROBERTS JA, COUTINHO SV, MARVIZON JC, GRADY EF, TOGNETTO M,
SENGUPTA JN, ENNES HS, CHABAN VV, AMADESI S, CREMINON C, LANTHORN
T, GEPPETTI P, BUNNETT NW, AND MAYER EA. Role of peripheral n-methyld-aspartate (NMDA) receptors in visceral nociception in rats. Gastroenterology 120: 1737–1748, 2001.
MUNAKATA J, NALIBOFF B, HARRAF F, KODNER A, LEMBO T, CHANG L,
SILVERMAN DH, AND MAYER EA. Repetitive sigmoid stimulation induces
rectal hyperalgesia in patients with irritable bowel syndrome [published
erratum appears in Gastroenterology 113: 1054, 1997]. Gastroenterology
112: 55– 63, 1997.
NESS TJ. Evidence for ascending visceral nociceptive information in the dorsal
midline and lateral spinal cord. Pain 87: 83– 88, 2000a.
NESS TJ. Intravenous lidocaine inhibits visceral nociceptive reflexes and spinal
neurons in the rat. Anesthesiology 92: 1685–1691, 2000b.
NMDA RECEPTOR INVOLVEMENT IN INNOCUOUS AND NOXIOUS CRD
the lumbosacral spinal cord following noxious and non-noxious colorectal
distention in the rat. Pain 49: 393– 403, 1992.
URBAN L, THOMPSON SWN, AND DRAY A. Modulation of spinal excitability:
co-operation between neurokinin and excitatory amino acid neurotransmitters. Trends Neurosci 17: 432– 438, 1994.
WILLIS WD JR AND COGGESHALL RE. Sensory Mechanisms of the Spinal Cord.
New York: Plenum, 1991.
1791
WOOLF CJ AND THOMPSON SWN. The induction and maintenance of central
sensitization is dependent on N-methyl-D-aspartic acid receptor activation;
implications for the treatment of post-injury pain hypersensitivity states.
Pain 44: 293–299, 1991.
ZHAI QZ AND TRAUB RJ. The NMDA receptor antagonist MK-801 attenuates
c-Fos expression in the lumbosacral spinal cord following repetitive noxious
and nonnoxious colorectal distention. Pain 83: 321–329, 1999.
Downloaded from http://jn.physiology.org/ by 10.220.33.2 on June 17, 2017
J Neurophysiol • VOL
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