Involvement of NMDA receptors in Zif/268 expression in the trigeminal nucleus caudalis following formalin injection into the rat whisker pad

We investigated the involvement of N-methyl-D-aspartate (NMDA) glutamate receptor in the expression of the proteins Zif/268 and c-Fos elicited by painful stimuli. To this purpose, the effect of the administration of MK-801, an NMDA receptor antagonist, on Zif/268 and c-Fos expression following a noxious stimulus, represented by formalin injection into the whisker pad of rats, was examined in neurons of the trigeminal nucleus caudalis. Furthermore, the co-localization of formalin injection-evoked Zif/268 and c-Fos expression and subunit 1 of the NMDA receptor (NR1) was studied in this nucleus. Zif/268 or c-Fos immunoreactivity elicited by formalin injection was significantly reduced by pretreatment with MK-801 in the superficial layer of the trigeminal nucleus caudalis; more than 40% of the neurons expressing Zif/268 and c-Fos in this layer were also immunolabeled by NR1. On the other hand, there was little effect of MK-801 administration on Zif/268 and c-Fos immunoreactivity in the nucleus proprius and deep lamina V of the trigeminal nucleus caudalis, while most neurons expressing Zif/268 or c-Fos in these two regions were labeled by NR1. These results point out differences between the superficial and deeper layers of the trigeminal nucleus caudalis in the involvement of NMDA receptor in the mechanisms underlying the expression of protein products of immediate early genes induced by painful stimuli.     

Peripheral noxious stimulation induces phosphorylation of the NMDA receptor NR1 subunit at the PKC-dependent site, serine-896, in spinal cord dorsal horn neurons

The N‐methyl‐D ‐aspartate receptor (NMDAR) contributes to central sensitization in the spinal cord and the generation of pain hypersensitivity. NMDAR function is modulated by post‐translational modifications including phosphorylation, and this is proposed to underlie its involvement in the production of pain hypersensitivity in the spinal cord. We now show that a noxious heat stimulus applied to the rat hindpaw induces phosphorylation of the NMDAR NR1 subunit at a protein kinase C (PKC)‐dependent site, serine‐896, in superficial dorsal horn neurons. Phosphorylation of NR1 serine‐896 is essentially absent in the superficial dorsal horn laminae of naïve rats, but there is rapid (< 2 min) induction following a noxious but not innocuous heat stimulus. The number of pNR1‐immunoreactive neuronal profiles in the superficial dorsal horn peaks 30 min after noxious heat stimulation and persists for up to 1 h. pNR1serine896 induction occurs in the endoplasmic reticulum, suggesting that it contributes to trafficking of the receptor from intracellular stores to the membrane. The phosphorylation of the subunit is attenuated by intrathecal injection of the NMDAR antagonist, MK801, suggesting that the NMDAR is involved via a feed‐forward mechanism in its own phosphorylation. The pNR1serine896‐positive neurons are highly co‐localized with PKCdelta and only rarely with PKCgamma. These data provide evidence for an activity‐dependent NMDAR phosphorylation at the PKC‐dependent site, serine‐896, in spinal cord dorsal horn neurons initiated by peripheral noxious stimuli.     

Effects of MK-801 on rat primary afferent neurons and fibers

Recent evidence suggests that glutamate and its N-methyl-D-aspartate (NMDA) receptor may participate in regulating neurite morphology and peptide expression. A previous study from this laboratory showed that treatment with the NMDA receptor antagonist, MK-801, induced an apparent increase in the density of calcitonin gene-related peptide (CGRP)-immunoreactive primary afferent fibers in the dorsal spinal cord of the rat. The present study was undertaken to extend this work by: 1) quantifying the MK-801-induced increase in CGRP immunostaining in the dorsal grey commissure/medial dorsal horn region and 2) examining the effect of MK-801 on the number of CGRP-immunoreactive primary afferent cell bodies in lumbar dorsal root ganglia. Following 7 days of MK-801 treatment, a significant increase (p less than 0.001) in CGRP immunostaining was observed in the dorsal grey commissure/medial dorsal horn. However, after MK-801 treatment, no significant difference was noted in the numbers of CGRP-immunoreactive primary afferent cell bodies in dorsal root ganglia. These data suggest that MK-801 produces significant alterations in the intraspinal projection of CGRP-immunoreactive fibers without inducing immunocytochemically detectable CGRP within a new population of primary afferent neurons.     

MK-801 reduces non-noxious stimulus-evoked Fos-like immunoreactivity in the spinal cord of rats with chronic constriction nerve injury

We investigated the role of N-methyl-D-aspartate (NMDA) receptors on non-noxious stimulus-induced pain by examining the effect of MK-801, a non-competitive NMDA receptor antagonist, on Fos-like immunoreactivity (FLI) in the spinal dorsal horn by non-noxious stimulation to rats with chronic constriction injury (CCI) of the sciatic nerve. In CCI rats that did not receive the non-noxious stimulus, FLI was significantly increased in laminae V/VI of the dorsal horn at the 7th and 14th days after surgery relative to sham rats. When CCI rats received non-noxious stimuli, rubbing the plantar of the hind paw, FLI in laminae I/II at the 14th day was significantly increased relative to CCI rats that did not receive the stimulation. In sham rats, the same stimulus significantly decreased FLI in laminae III/IV and V/VI at the 7th and 14th day. When MK-801 was administered intraperitoneally prior to non-noxious stimulation in CCI rats at the 14th day after surgery, the stimulus-induced FLI in laminae I/II in CCI rats was significantly reduced. This study indicates that NMDA receptor is involved in upregulating FLI in response to non-noxious stimulation of CCI rats.     

Increases in protein kinase C gamma immunoreactivity in the spinal cord of rats associated with tolerance to the analgesic effects of morphine

Our previous studies have indicated a critical role of protein kinase C (PKC) in intracellular mechanisms of tolerance to morphine analgesia. In the present experiments, we examined (1) the cellular distribution of a PKC isoform (PKCγ) in the spinal cord dorsal horn of rats associated with morphine tolerance by utilizing an immunocytochemical method and (2) the effects of theN-methyl-d-aspartate receptor antagonist MK-801 on tolerance-associated PKCγ changes. In association with the development of tolerance to morphine analgesia induced by once daily intrathecal administration of 10 μg morphine for eight days, PKCγ immunoreactivity was clearly increased in the spinal cord dorsal horn of these same rats. Within the spinal cord dorsal horn of morphine tolerant rats, there were significantly more PKCγ immunostained neurons in laminae I–II than in laminae III–IV and V–VI. Such PKCγ immunostaining was observed primarily in neuronal somata indicating a postsynaptic site of PKCγ increases. Moreover, both the development of morphine tolerance and the increase in PKCγ immunoreactivity were prevented by co-administration of morphine with 10 nmol MK-801 between Day 2 and Day 7 of the eight day treatment schedule. In contrast, PKCγ immunoreactivity was not increased in rats receiving a single i.t. administration of 10 μg morphine on Day 8, nor did repeated treatment with 10 nmol MK-801 alone change baseline levels of PKCγ immunoreactivity. These results provide further evidence for the involvement of PKC in NMDA receptor-mediated mechanisms of morphine tolerance.     

The effect of glutamate antagonists on c-fos expression induced in spinal neurons by irritation of the lower urinary tract

Chemical irritation of the lower urinary tract (LUT) of the rat increases the expression of c-fos in neurons in the dorsal horn, dorsal commissure and intermediolateral region of the spinal cord. The role of glutamatergic synapses in this response was examined using two glutamate receptor antagonists, MK-801 (an NMDA antagonist) and CNQX (an AMPA antagonist). In rats with an intact spinal cord, MK-801 (3.5 mg/kg, i.v.) administered 15 min before bladder irritation decreased (50–60%) the number of c-fos-positive cells in all regions of the cord. A smaller dose of MK-801 (0.8 mg/kg, i.v.) was ineffective. In spinal transected rats (4–7 days prior to the experiment) MK-801 (3.5 mg/kg, i.v.) decreased c-fos expression only in the medial dorsal horn. CNQX (1.2 mg/kg, i.v.) was ineffective in both preparations. These results indicate that activation of NMDA receptors at glutamate synapses in the central nervous system may play a role in the processing of nociceptive input from the LUT and may also be involved in reflex pathways mediating micturition.     

Ionotropic glutamate receptors contribute to maintained neuronal hyperexcitability following spinal cord injury in rats

In this study, we examined whether topical treatment of glutamate receptor antagonists attenuate hyperexcitability of lumbar spinal dorsal horn neurons following low thoracic hemisection spinal cord injury in rats. Four weeks after spinal hemisection, neuronal activity in response to mechanical stimuli applied on the peripheral receptive field was significantly increased in three different phenotypes of lumbar spinal dorsal horn neurons: wide dynamic range (WDR), low threshold (LT) and high threshold (HT). Topical application of MK-801 (NMDA receptor antagonist, 50 µg) significantly attenuated the activity of WDR, but not LT and HT neurons; whereas, NBQX (AMPA receptor antagonist, 0.5 and 1 µg) significantly attenuated neuronal activity in all three phenotypes of neurons (*p < 0.05). However, MCPG (group I/II metabotropic glutamate receptor antagonist, 100 µg) had no effect. The present study, in the context of previous work, suggests that ionotropic glutamate receptor activation play critical roles in the maintenance of neuronal hyperexcitability and neuropathic “below-level” pain behavior following spinal hemisection injury.     

Visualizing sensory transmission between dorsal root ganglion and dorsal horn neurons in co-culture with calcium imaging

Sensory information is conveyed to the central nervous system by primary afferent neurons within dorsal root ganglia (DRG), which synapse onto neurons of the dorsal horn of the spinal cord. This synaptic connection is central to the processing of both sensory and pain stimuli. Here, we describe a model system to monitor synaptic transmission between DRG neurons and dorsal horn neurons that is compatible with high-throughput screening. This co-culture preparation comprises DRG and dorsal horn neurons and utilizes Ca(2+) imaging with the indicator dye Fura-2 to visualize synaptic transmission. Addition of capsaicin to co-cultures stimulated DRG neurons and led to activation of dorsal horn neurons as well as increased intracellular Ca(2+) concentrations. This effect was dose-dependent and absent when DRG neurons were omitted from the culture. NMDA receptors are a critical component of synapses between DRG and dorsal horn neurons as MK-801, a use-dependent non-competitive antagonist, prevented activation of dorsal horn neurons following capsaicin treatment. This model system allows for rapid and efficient analysis of noxious stimulus-evoked Ca(2+) signal transmission and provides a new approach both for investigating synaptic transmission in the spinal cord and for screening potential analgesic compounds.     

Substance P and neurokinin A, two coexisting tachykinins stimulating the release of [3H]5-HT from rat cerebral cortical slices.

Noxious heat applied to the footpad evokes the expression offos protein-like immunoreactivity in the rat spinal cord lumbar dorsal horn. Electrical stimulation in the medullary nucleus raphe magnus (NRM) while not evokingfos-like immunoreactivity itself, reduced significantly the number of neurons (to 50% of control) in the dorsal horn demonstratingfos protein-like immunoreactivity in response to noxious heating of the footpad. Thus descending projections from the medullary NRM appear to have direct inhibitory effects on dorsal horn neurons that receive nociceptive input from cutaneous thermal nociceptors.     

Chronic Spinal Nerve Ligation Induces Changes in Response Characteristics of Nociceptive Spinal Dorsal Horn Neurons and in Their Descending Regulation Originating in the Periaqueductal Gray in the Rat

We studied whether a chronic neuropathy induced by unilateral spinal nerve ligation changes the response characteristics of spinal dorsal horn wide-dynamic range (WDR) neurons or their periaqueductal gray (PAG)-induced descending modulation. Experiments were performed in rats with behaviorally demonstrated allodynia induced by spinal nerve ligation and in a group of nonneuropathic control rats. The stimulus–response functions of WDR neurons for mechanical and thermal stimuli and the modulation of their peripherally evoked responses by electrical stimulation of the PAG were determined under pentobarbital anesthesia. The results showed that neuropathy caused a significant leftward shift in stimulus–response functions for mechanical stimuli. In contrast, stimulus–response functions for noxious heat stimuli in the neuropathic limb were, if anything, shifted rightward, although this shift was short of statistical significance. In neuropathic rats, PAG stimulation produced a significantly stronger attenuation of spinal neuronal responses induced by noxious heat in the unoperated than in the operated side. At the intensity that produced attenuation of noxious heat stimuli, PAG stimulation did not produce any significant change in spinal neuronal responses evoked by mechanical stimuli either from the operated or the nonoperated hindlimb of the neuropathic rats. Spontaneous activity of WDR neurons was higher in the operated side of neuropathic rats than in control rats. Afterdischarges evoked by peripheral stimuli were observed in 1/16 of the WDR neurons ipsilateral to spinal nerve ligation and not at all in other experimental groups. The WDR neurons studied were not activated by innocuous or noxious cold stimuli. The results indicate that spinal nerve ligation induces increased spontaneous activity and enhanced responses to mechanical stimuli in the spinal dorsal horn WDR neurons, whereas noxious heat-evoked responses are not significantly changed or if anything, attenuated. Moreover, the inhibition of noxious heat stimuli by PAG stimulation is attenuated in the neuropathic side. It is proposed that the observed changes in the response characteristics of the spinal dorsal horn WDR neurons and in their descending modulation may contribute to the neuropathic symptoms in these animals.     

c-Fos expression in NMDA receptor-contained neurons in spinal cord in a rat model of inflammation: a double immunocytochemical study

Double-labeling techniques were used to demonstrate the nociceptive activation of NMDA receptor-contained neurons in spinal dorsal horn by using c-Fos immunoreactivity as an indicator of this activation in a rat model of inflammation. About 25% and 55% of the c-Fos-immunoreactive neurons that were found in laminae I–II and lamina V showed NMDA receptor immunoreactivity, while about 4% and 11% of NMDA-receptor immunoreactive neurons in these two regions showed c-Fos immunoreactivity, respectively. The implication of the results was discussed.     

Enhanced Fos expression in rat lumbar spinal cord cultured with cerebrospinal fluid from patients with amyotrophic lateral sclerosis.

The etiology of amyotrophic lateral sclerosis (ALS) remains unknown although an existence of neurotoxic substances in cerebrospinal fluid (CSF) from ALS patients have been postulated. In order to investigate a possible effect of CSF from ALS patients on cellular signaling in spinal neurons, we compared Fos-like immunoreactivity (Fos-LI) in organotypic cultures of rat lumbar spinal cord after addition of CSF from ALS patients or another neurologic disease. Fos-LI was normally present predominantly in dorsal horn neurons, whereas only a few ventral horn neurons were positive for Fos-LI. The number of Fos-LI positive neurons significantly increased in dorsal horn with addition of CSF from ALS patients as well as glutamate at 100 microM. However, the increase was not observed with addition of CSF from other neurologic diseases. The increase in Fos-LI positive neurons in dorsal horn was reversed by a further supplement of MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, but not of CNQX, an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate antagonist. These results indicate that there may be substances in CSF from ALS patients that stimulate Fos expression in certain populations of spinal neurons via the NMDA receptors.     

Anticonvulsants suppress c-Fos protein expression in spinal cord neurons following noxious thermal stimulation

The expression of the nuclear immediate-early gene-encoded protein c-Fos in spinal cord dorsal horn neurons of the rat following noxious thermal stimulation was compared in carbamazepine-, valproate- and phenytoine-treated animals. Single intraperitoneal injection of carbamazepine (50 mg/kg), valproate (300 mg/kg) or intravenous injection of phenytoine (20 mg/kg) before noxious stimulation reduced the number of c-Fos immunoreactive neurons to 65–80% of control levels in superficial laminae and to 30–60% in deep laminae of the dorsal horn. Pretreatment with carbamazepine or valproate for 4 or 8 days combined with an injection immediately before noxious stimulation further significantly decreased the number of c-Fos neurons in the deep dorsal horn only in animals treated with valproate. The observation that activity-dependent gene expression in the spinal cord is effectively modulated by anticonvulsants discloses a novel therapeutic potential of these compounds. Presumably via an acute suppression of high-frequency repetitive firing and/or altered synaptic transmission of intraspinal or descending neurotransmitter systems these drugs gain access to neuroplastic mechanisms which might be relevant for the restoration of physiological levels of neuronal excitability in the central nervous system.     

Modulated expression of c-Fos in the spinal cord following noxious thermal stimulation of monoarthritic rats

Peripheral noxious stimulation evokes functional and biochemical changes in the spinal cord which results in central sensitization and hyperalgesia, but at the same time also induces the activation of inhibitory control systems. The purpose of the present study was to investigate whether the adaptive changes induced by ongoing peripheral inflammation influence the spinal cord expression of c-Fos (a commonly used marker of neuronal activity) following an additional acute noxious stimulus. Therefore, the spinal expression of c-Fos was immunohistochemically investigated following noxious thermal stimulation of a rat monoarthritic hindpaw at various time points (1, 4, 8, 21 days) after induction of monoarthritis. Compared to normal rats, c-Fos expression following ipsilateral noxious thermal stimulation of monoarthritic rats was strongly modified in the deep laminae of the dorsal horn depending on the time course of inflammation. At 1 day of monoarthritis, an enhanced ipsilateral expression (135% and 208% of normal rats in laminae III–VI and VII, respectively) and at 3 weeks a reduced expression (38% and 23% of normal rats in laminae III–VI and VII, respectively) was detected. The amount of c-Fos-positive neurons in the ipsilateral superficial laminae I and II was unchanged at all time points investigated. To assess excitability changes on the contralateral side at an early stage of inflammation, a group of monoarthritic rats received a contralateral noxious stimulus at day 1 of monoarthritis. This resulted in a potentiated expression of c-Fos ipsilateral to the acute noxious stimulus (i.e., contralateral to the monoarthritic hindpaw) restricted to lamina II (137% of normal rats) of the dorsal horn. The data showed that changes in c-Fos expression depended on the time point of noxious heat stimulation (NHS) of monoarthritic rats, and differed in the ipsi- and contralateral side of the spinal cord. In addition to a possible habituation of c-Fos expression, it may be speculated that the time course-dependent changes reflect laminae-specific modulations of excitatory and inhibitory mechanisms during monoarthritis. Further studies are necessary in order to provide more insights into the contribution of these mechanisms on noxious stimulus-evoked c-Fos expression. J. Neurosci. Res. 53:203–213, 1998. © 1998 Wiley-Liss, Inc.     

Involvement of N-methyl-d-aspartate (NMDA) receptors in a rat model of visceral hypersensitivity

N-Methyl-d-aspartate (NMDA) is known to be involved in the transmission of nociceptive information. In the present study, we investigated the effect of peripheral and central NMDA receptor antagonist MK-801 in visceral hypersensitivity. In an animal model of colorectal distension (CRD), administration of both intrathecal MK-801 (1.5 nmol) and intraperitoneal MK-801 (0.15 mg/kg) completely abolished the CRD-induced visceral hypersensitivity of noxious and innocuous stimuli. Thus, the results from this experiment demonstrate the efficacy of MK-801 in blocking the visceral hypersensitivity mediated by central and peripheral mechanisms.     

Enhanced Fos expression in rat lumbar spinal cord cultured with cerebrospinal fluid from patients with amyotrophic lateral sclerosis

Abstract

School, Okayama, Japan The etiology of amyotrophic lateral sclerosis (ALS) remains unknown although an existence of neurotoxic substances in cerebrospinal fluid (CSF) from ALS patients have been postulated. In order to investigate a possible effect of CSF from ALS patients on cellular signaling in spinal neurons, we compared Fos-like immunoreactivity (Fos-LI) in organotypic cultures of rat lumbar spinal cord after addition of CSF from ALS patients or another neurologic disease. Fos-LI was normally present predominantly in dorsal horn neurons, whereas only a few ventral horn neurons were positive for Fos-LI. The number of Fos-LI positive neurons significantly increased in dorsal horn with addition of CSF from ALS patients as well as glutamate at 100 μM. However, the increase was not observed with addition of CSF from other neurologic diseases. The increase in Fos-LI positive neurons in dorsal horn was reversed by a further supplement of MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, but not of CNQX, an a-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA)/kainate antagonist. These results indicate that there may be substances in CSF from ALS patients that stimulate Fos expression in certain populations of spinal neurons via the NMDA receptors. [Neurol Res 1999; 21: 309-312]     

MOR-1-immunoreactive neurons in the dorsal horn of the rat spinal cord: evidence for nonsynaptic innervation by substance P-containing primary afferents and for selective activation by noxious thermal stimuli

A direct action of mu-opioid agonists on neurons in the spinal dorsal horn is thought to contribute to opiate-induced analgesia. In this study we have investigated neurons that express the mu-opioid receptor MOR-1 in rat spinal cord to provide further evidence about their role in nociceptive processing. MOR-1-immunoreactive cells were largely restricted to lamina II, where they comprised approximately 10% of the neuronal population. The cells received few contacts from nonpeptidergic unmyelinated afferents, but many from substance P-containing afferents. However, electron microscopy revealed that most of these contacts were not associated with synapses. None of the MOR-1 cells in lamina II expressed the neurokinin 1 receptor; however, the mu-selective opioid peptide endomorphin-2 was present in the majority (62-82%) of substance P axons that contacted them. Noxious thermal stimulation of the foot induced c-Fos expression in approximately 15% of MOR-1 cells in the medial third of the ipsilateral dorsal horn at mid-lumbar level. However, following pinching of the foot or intraplantar injection of formalin very few MOR-1 cells expressed c-Fos, and for intraplantar formalin injection this result was not altered significantly by pretreatment with systemic naloxone. Although these findings indicate that at least some of the neurons in lamina II with MOR-1 are activated by noxious thermal stimulation, the results do not support the hypothesis that the cells have a role in transmitting nociceptive information following acute mechanical or chemical noxious stimuli.     

MK-801, an NMDA receptor antagonist, in the rostroventromedial medulla attenuates development of neuropathic symptoms in the rat.

Segmental ligation of spinal nerves in the rat induces a long-lasting hyperalgesia and allodynia that mimicks neuropathic conditions in humans. In the present study we attempted to determine whether supraspinal NMDA receptors contribute to the induction of the long-lasting hypersensitivity to noxious and innocuous mechanical stimulation following segmental ligation of spinal nerves in the rat. MK-801, an NMDA receptor antagonist, was microinjected into the rostroventromedial medulla (RVM) 15 min before or 25 min after the ligation of spinal nerves and mechanical hypersensitivity was assessed at various time points following surgery by determining the hindlimb withdrawal threshold to noxious and innocuous mechanical stimulation. A single dose of MK-801 administered prior to nerve ligation into the RVM significantly attenuated the development of mechanical hypersensitivity throughout the 2 week postoperative observation period, whereas corresponding administration of MK-801 immediately after the nerve ligation attenuated the development of mechanical hypersensitivity only during the first postoperative day but not later. The results indicate that NMDA receptors in the RVM are involved in triggering the enhanced sensitivity to mechanical stimulation induced by a nerve injury.     

SNL大鼠L5 脊髓背角c-Fos的表达与谷氨酸不同投入途径的关系

1. We examined the effects of L-Glutamic acid (Glu), a NMDA receptor antagonist, D-2-amino-5-phosphonopentanoate (D-AP5) as well as a selective Group I mGluR antagonist, 7-Hydroyiminocyclo propan[a]chromen-1a- carboxylic acid ethyl ester (cpccoEt ), on c-fos-like immunoreactivity (c-fos LI) within the L5 spinal cord dorsal horn of urethane anaesthetized Sprague-Dawley rats, in which L5-L6 nerves were ligated to produce neuropathic pain model (SNL model), two weeks after the operation, rats were adopted. 2. In SNL rats, nerve ligation with no drug use resulted in an increase in the level of c-Fos expression in two sides of spinal cord, particularly, in III/IV of ligated side. Intraplantar or intrathecal administration of saline significantly increased the c-Fos labeled neurons in I/II of ligated side compared with ligated group without saline administration, there was no difference between intraplantar and intrathecal administration of saline in I/II of ligated side. 3. On the other hand, either intraplantar or intrathecal administration, glutamate (5 mol) could significantly increase the number of c-Fos positive neurons compared with saline group value in intact, sham-operated and SNL rats; when intrathecal administration of glutamate into SNL rats, the number of c-Fos positive neurons in I/II of ligated side was three times higher than that induced by intraplantar administration; however, there was no difference between in I/II of ligated and of unligated side in the level of c-Fos expression induced by intrathecal administration. In addition, the number of c-Fos positive neurons in I/II of ligated side induced by intrathecal administration of glutamate in SNL rats was two times higher than in sham-operated rats. 4. There was no difference among saline group, D-AP5 (50 nmol) group and cpccoEt (250 nmol) group in the number of c-fos LI cells either in sham-operated or in SNL rats, respectively; In addition, the number of c-Fos positive neurons in I/II ipisilateral side induced by saline or D-AP5 in SNL rats was three times higher than that in sham-operated rats, by cpccoEt in SNL rats was two times higher than that in sham-operated rats. However, glutamate (5 mol) combined with D-AP5 (50 nmol) or cpccoEt (250 nmol), intrathecal administration, the number of c-Fos positive neurons either in sham-operated or SNL rats was less than glutamate group value, thus, D-AP5 significantly reduced labeled cells in I/II layer induced by glutamate by a maximum of 69.5% in the left side and 72.1% in the right side in sham-operated rats, of 71.6% in ligated side and 70.6% in unligated side, respectively; cpccoEt significantly decreased the number of c-fos LI cells by glutamate by a maximum of 71.8% in the left side and 71.7% in the right side in sham-operated rats, of 72.4% in the ligated side and 90.1% in the unligated side, respectively. 5. Taken together, c-Fos expression may be associated with different pass-way of excitation of nerve. These results suggest that nerve ligation might be able to influence c-Fos expression; saline and glutamate progressively promote the c-Fos expression in SNL rats; blockade of NMDA receptors, group I mGluRs decrease the response of peripheral and spinal cord neurons to glutamate.     

Differential inhibition produced by peripheral conditioning stimulation on noxious mechanical and thermal responses of different classes of spinal neurons in the cat

The effect of conditioning stimulation of a peripheral nerve on responses of spinal neurons (dorsal horn cells and motoneurons) was studied in 16 decerebrate-spinal cats. The activity of dorsal horn cells was recorded with a microelectrode at the lumbosacral spinal cord and the single-unit activity of motoneurons was recorded from a filament of ventral rootlet divided from either the L7 or S1 ventral root. The responses of spinal neurons were evoked by noxious and innocuous mechanical stimuli and by noxious thermal stimuli applied to the receptive fields. The peripheral conditioning stimulation was applied to the tibial nerve with repetitive electrical pulses (2 Hz) at an intensity either suprathreshold for A delta or C fibers for 5 min. Applying conditioning stimulation to a peripheral nerve produced a powerful inhibition of the responses elicited by noxious stimuli, suggesting this inhibition is an antinociceptive effect. The inhibition produced by peripheral conditioning stimulation was differentially greater on the responses to noxious than to innocuous stimuli. Based on the results obtained from conditioning stimulation with graded strengths, afferent inputs from both myelinated and unmyelinated fibers seem to contribute to the production of the antinociceptive effect. The magnitude of the antinociceptive effect is bigger for the responses to noxious thermal than to mechanical stimuli. Furthermore, the reflex activity recorded in motor axons seemed to be more sensitive than in dorsal horn cells to the antinociceptive effect.