Spinal control of erection by glutamate in rats

The lumbosacral spinal network controlling penile erection is activated by information from peripheral and supraspinal origins. We tested the hypothesis that glutamate, released by sensory afferents from the genitals, activates this proerectile network. In anesthetized intact and T8 spinalized (i.e., freed from supraspinal inhibition) male rats, the parameters of electrical stimulation of the dorsal penile nerve (DPN) that elicited intracavernous pressure (ICP) rises were determined. In T8 spinalized rats, DPN stimulations were applied in the presence of d(-)-2-amino-5-phosphonopentanoic acid (d-AP5), a competitive NMDA receptor antagonist, or of 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (NBQX), an AMPA-kainate receptor antagonist, injected intrathecally at the lumbosacral level. Both antagonists, alone or in combination, dose dependently decreased the ICP rise and increased its latency. In conscious rats, reflexive erections were depressed by d-AP5 and NBQX, as revealed by an increased latency of the first erection and by decreases of the number of rats displaying erections, of the number of erection clusters and of the number of erections per cluster. In anesthetized ats, the combined administration of the glutamatergic agonists NMDA and AMPA elicited ICP rises in the absence of DPN stimulation. In contrast, both agonists moderately decreased the ICP rise elicited by DPN stimulation but did not affect its latency. These results support our hypothesis that glutamate, released on stimulation of the genitals and acting at AMPA and NMDA receptors, is a potent reactivator of the spinal proerectile network.     

Vanilloid receptor VR1-positive primary afferents are glutamatergic and contact spinal neurons that co-express neurokinin receptor NK1 and glutamate receptors

The vanilloid receptor VR1 (TRPV1) is a temperature- and capsaicin-sensitive cation channel expressed by a class of primary afferents involved in nociception. To confirm the hypothesis that VR1-positive primary afferents are glutamatergic and contact spinal neurons that express the main classes of ionotropic glutamate receptors, we performed multiple immunofluorescent staining for VR1 and the glutamate transporter VGLUT2 (a specific marker for glutamatergic transmission) or AMPA and NMDA receptor subunits. VR1-positive cells in the dorsal root ganglion and boutons of their central afferent fibers in the dorsal horn expressed VGLUT2, and the latter contacted AMPA- or NMDA receptor-positive perikarya. Based on our previous observations of preferential targeting of VR1-positive primary afferents to spinal neurons that express the neurokinin receptor NK1 (Hwang et al., 2003), we further quantified the frequency of termination of VR1-positive afferents onto NK1-positive neurons co-expressing glutamate receptors. A larger fraction of NK1/NMDA receptors-positive than NK1/AMPA receptors-positive sites were contacted by VR1-positive boutons. We conclude that VR1-positive primary afferents in the rat use glutamate as neurotransmitter and contact postsynaptic sites that co-express NK1 and ionotropic glutamate receptors.     

Differential Roles of Phosphorylated AMPA Receptor GluR1 Subunits at Serine-831 and Serine-845 Sites in Spinal Cord Dorsal Horn in a Rat Model of Post-Operative Pain

Previous studies have demonstrated that the enhanced levels of phosphorylated α-amino-3-hydroxy-5-methy-4-isoxazole propionate (AMPA) receptor GluR1 subunits at Serine-831 (pGluR1-Ser-831) and Serine-845 (pGluR1-Ser-845) in the spinal cord dorsal horn are involved in central sensitization of inflammatory pain. However, whether the phosphorylatory regulation of AMPA receptor GluR1 subunits is implicated in the development and maintenance of post-operative pain remains unclear. The current study aims to examine the functional regulation of AMPA receptor GluR1 subunit through its phosphorylation mechanism during the period of post-operative painful events in rats. Our data indicated that the expression of pGluR1-Ser-831 in ipsilateral spinal cord dorsal horn increased significantly at 3 h after incision, then decreased gradually, and returned to the normal level 3 day post-incision. Meanwhile, the expression of pGluR1-Ser-845 and GluR1 in ipsilateral spinal cord dorsal horn remained unchanged. The cumulative pain scores increased at 3 h after incision, gradually decreased afterwards and returned to the baseline values at 4 day after incision and the trend was almost parallel to the expression changes of pGluR1-Ser-831 in spinal dorsal horn. Intrathecal injection of a calcium-dependent protein kinase (PKC) inhibitor, Gö6983 (10 μM), significantly reversed the incision-mediated over-expression of pGluR1-Ser-831 in spinal dorsal horn at 3 h after incision and decreased the cumulative pain scores as well. These results indicate that the phosphorylation of GluR1 subunits at Serine-831 and Serine-845 sites might be differentially regulated following surgical procedures and support a neurobiological mechanism of post-operative pain involved in phosphorylation of AMPA subunits GluR1-Ser-831, but not pGluR1-Ser-845. Our study suggests that the therapeutic targeting the phosphorylation regulation of AMPA receptor GluR1 subunit at Serine-831 site would be potentially significant for treating postoperative pain.

     

The glutamatergic nature of TRPV1-expressing neurons in the spinal dorsal horn

The transient receptor potential vanilloid receptor 1 (TRPV1) is expressed on primary afferent terminals and spinal dorsal horn neurons. However, the neurochemical phenotypes and functions of TRPV1-expressing post-synaptic neurons in the spinal cord are not clear. In this study, we tested the hypothesis that TRPV1-expressing dorsal horn neurons are glutamatergic. Immunocytochemical labeling revealed that TRPV1 and vesicular glutamate transporter-2 were colocalized in dorsal horn neurons and their terminals in the rat spinal cord. Resiniferatoxin (RTX) treatment or dorsal rhizotomy ablated TRPV1-expressing primary afferents but did not affect TRPV1- and vesicular glutamate transporter-2-expressing dorsal horn neurons. Capsaicin significantly increased the frequency of glutamatergic spontaneous excitatory post-synaptic currents and miniature excitatory post-synaptic currents in almost all the lamina II neurons tested in control rats. In RTX-treated or dorsal rhizotomized rats, capsaicin still increased the frequency of spontaneous excitatory post-synaptic currents and miniature excitatory post-synaptic currents in the majority of neurons examined, and this effect was abolished by a TRPV1 blocker or by non-NMDA receptor antagonist. In RTX-treated or in dorsal rhizotomized rats, capsaicin also produced an inward current in a subpopulation of lamina II neurons. However, capsaicin had no effect on GABAergic and glycinergic spontaneous inhibitory post-synaptic currents of lamina II neurons in RTX-treated or dorsal rhizotomized rats. Collectively, our study provides new histological and functional evidence that TRPV1-expressing dorsal horn neurons in the spinal cord are glutamatergic and that they mediate excitatory synaptic transmission. This finding is important to our understanding of the circuitry and phenotypes of intrinsic dorsal horn neurons in the spinal cord.     

AMPA and NMDA glutamate receptors are found in both peptidergic and non-peptidergic primary afferent neurons in the rat

Two distinct classes of nociceptive primary afferents, peptidergic and non-peptidergic, respond similarly to acute noxious stimulation; however the peptidergic afferents are more likely to play a role in inflammatory pain, while the non-peptidergic afferents may be more characteristically involved in neuropathic pain. Using multiple immunofluorescence, we determined the proportions of neurons in the rat L4 dorsal root ganglion (DRG) that co-express AMPA or NMDA glutamate receptors and markers for the peptidergic and non-peptidergic classes of primary afferents, substance P and P2X(3), respectively. The fraction of DRG neurons immunostained for the NR1 subunit of the NMDA receptor (40%) was significantly higher than that of DRG neurons immunostained for the GluR2/3 (27%) or the GluR4 (34%) subunits of the AMPA receptor. Of all DRG neurons double-immunostained for glutamate receptor subunits and either marker for peptidergic and non-peptidergic afferents, a significantly larger proportion expressed GluR4 than GluR2/3 or NR1 and in a significantly larger proportion of P2X(3)- than SP-positive DRG neurons. These observations support the idea that nociceptors, involved primarily in the mediation of neuropathic pain, may be presynaptically modulated by GluR4-containing AMPA receptors.     

Commande nerveuse peripherique de l’erection

Local mechanisms causing penile erection and detumescence result from variation in tone of vascular and trabecular smooth muscles and in a lesser part of striated muscles around the crura penis. All these events are neurally mediated. We reviewed human and animal data concerning the functional peripheral neuroanatorny of erection. General organization of peripheral nervous system is recalled. Somatic efferents of the pudendal nerve, originating in the sacral spinal cord, innervate the striated musculature of the perineum. Somatic afferents of the penis are conveyed by the dorsal penile nerve, a branch of the pudendal nerve. Afferent terminations project into the spinal cord, their role is discussed. Parasympathetic pathways are involved in the reflexogenic erections. Sympathetic pathways destinated to the erectile structures are more complex. They are issued from thoracolumbar spinal cord and travel through the hypogastric nerve or the lumbosacral sympathetic chain. Sympathetic fibers originating in the sacral sympathetic chain are present in both pelvic and pudendal nerves. Inhibitory role on the erection of the sympathetic nervous system is well-known, it could be also responsible for psychogenic erections. Parasympathetic and sympathetic fibees are mixed in the pelvic plexus and the cavernous nerves which are described. Relations between the four sets of peripheral nerves (somatic efferents, penile afferents, thoracolumbar sympathetic sacral parasympathetic and sympathetic) are discussed.     

Speaking out of turn: a role for silent synapses in pain

Severe tissue or nerve injury can result in a chronic and inappropriate sensation of pain, mediated in part by the sensitization of spinal dorsal horn neurons to input from primary afferent fibers. Synaptic transmission at primary afferent synapses is mainly glutamatergic. Although a functioning excitatory synapse contains both alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the postsynaptic membrane, recent evidence suggests that dorsal horn neurons contain some "silent" synapses, which exhibit purely NMDA receptor-mediated evoked postsynaptic currents and do not conduct signals at resting membrane potential. Serotonin, which is released onto dorsal horn neurons by descending fibers from the rostroventral medulla, potentiates sensory transmission by activating silent synapses on those neurons, i.e., by recruiting functional AMPA receptors to the postsynaptic membrane. This phenomenon may contribute to the hyperexcitability of dorsal horn neurons seen in chronic pain conditions.     

Rat gustatory neurons in the geniculate ganglion express glutamate receptor subunits

Taste receptor cells are innervated by primary gustatory neurons that relay sensory information to the central nervous system. The transmitter(s) at synapses between taste receptor cells and primary afferent fibers is (are) not yet known. By analogy with other sensory organs, glutamate might a transmitter in taste buds. We examined the presence of AMPA and NMDA receptor subunits in rat gustatory primary neurons in the ganglion that innervates the anterior tongue (geniculate ganglion). AMPA and NMDA type subunits were immunohistochemically detected with antibodies against GluR1, GluR2, GluR2/3, GluR4 and NR1 subunits. Gustatory neurons were specifically identified by retrograde tracing with fluorogold from injections made into the anterior portion of the tongue. Most gustatory neurons in the geniculate ganglion were strongly immunoreactive for GluR2/3 (68%), GluR4 (78%) or NR1 (71%). GluR1 was seen in few cells (16%). We further examined if glutamate receptors were present in the peripheral terminals of primary gustatory neurons in taste buds. Many axonal varicosities in fungiform and vallate taste buds were immunoreactive for GluR2/3 but not for NR1. We conclude that gustatory neurons express glutamate receptors and that glutamate receptors of the AMPA type are likely targeted to synapses within taste buds.     

Endogenous Interleukin-1β in Neuropathic Rats Enhances Glutamate Release from the Primary Afferents in the Spinal Dorsal Horn through Coupling with Presynaptic N-Methyl-d-aspartic Acid Receptors

Excessive activation of glutamate receptors and overproduction of proinflammatory cytokines, including interleukin-1β (IL-1β) in the spinal dorsal horn, are key mechanisms underlying the development and maintenance of neuropathic pain. In this study, we investigated the mechanisms by which endogenous IL-1β alters glutamatergic synaptic transmission in the spinal dorsal horn in rats with neuropathic pain induced by ligation of the L5 spinal nerve. We demonstrated that endogenous IL-1β in neuropathic rats enhances glutamate release from the primary afferent terminals and non-NMDA glutamate receptor activities in postsynaptic neurons in the spinal dorsal horn. Myeloid differentiation primary response protein 88 (MyD88) is a mediator used by IL-1β to enhance non-NMDA glutamate receptor activities in postsynaptic neurons in the spinal dorsal horn. Presynaptic NMDA receptors are effector receptors used by the endogenous IL-1β to enhance glutamate release from the primary afferents in neuropathic rats. This is further supported by the fact that NMDA currents recorded from small neurons in the dorsal root ganglion of normal rats are potentiated by exogenous IL-1β. Furthermore, we provided evidence that functional coupling between IL-1β receptors and presynaptic NMDA receptors at the primary afferent terminals is mediated by the neutral sphingomyelinase/ceramide signaling pathway. Hence, functional coupling between IL-1β receptors and presynaptic NMDA receptors at the primary afferent terminals is a crucial mechanism leading to enhanced glutamate release and activation of non-NMDA receptors in the spinal dorsal horn neurons in neuropathic pain conditions. Interruption of such functional coupling could be an effective approach for the treatment of neuropathic pain.     

Chronic opioid potentiates presynaptic but impairs postsynaptic N-methyl-D-aspartic acid receptor activity in spinal cords: implications for opioid hyperalgesia and tolerance

Opioids are the most effective analgesics for the treatment of moderate to severe pain. However, chronic opioid treatment can cause both hyperalgesia and analgesic tolerance, which limit their clinical efficacy. In this study, we determined the role of pre- and postsynaptic NMDA receptors (NMDARs) in controlling increased glutamatergic input in the spinal cord induced by chronic systemic morphine administration. Whole-cell voltage clamp recordings of excitatory postsynaptic currents (EPSCs) were performed on dorsal horn neurons in rat spinal cord slices. Chronic morphine significantly increased the amplitude of monosynaptic EPSCs evoked from the dorsal root and the frequency of spontaneous EPSCs, and these changes were largely attenuated by blocking NMDARs and by inhibiting PKC, but not PKA. Also, blocking NR2A- or NR2B-containing NMDARs significantly reduced the frequency of spontaneous EPSCs and the amplitude of evoked EPSCs in morphine-treated rats. Strikingly, morphine treatment largely decreased the amplitude of evoked NMDAR-EPSCs and NMDAR currents of dorsal horn neurons elicited by puff NMDA application. The reduction in postsynaptic NMDAR currents caused by morphine was prevented by resiniferatoxin pretreatment to ablate TRPV1-expressing primary afferents. Furthermore, intrathecal injection of the NMDAR antagonist significantly attenuated the development of analgesic tolerance and the reduction in nociceptive thresholds induced by chronic morphine. Collectively, our findings indicate that chronic opioid treatment potentiates presynaptic, but impairs postsynaptic, NMDAR activity in the spinal cord. PKC-mediated increases in NMDAR activity at nociceptive primary afferent terminals in the spinal cord contribute critically to the development of opioid hyperalgesia and analgesic tolerance.     

磷酸化钙/钙调蛋白依赖性蛋白激酶Ⅱ在大鼠脊髓背角C-纤维诱发电位长时程增强的诱导和维持中的作用

实验旨在探讨钙/钙调蛋白依赖性蛋白激酶II(calcium／calmodulin-dependent protein kinase Ⅱ,CaMKⅡ)在脊髓背角C-纤维诱发电位长时程增强(long—term potentiation,LTP)的诱导和维持中的作用。用Western blot技术分别检测LTP形成30min和3h脊髓背角(L4-L6)CaMKⅡ的含量及其磷酸化水平。同时观察脊髓局部给予CAMKⅡ选择性抑制剂KN-93后对脊髓背角LTP和CaMKII磷酸化的影响。观察结果如下：(1)诱导LTP后30min,CaMK Ⅱ的磷酸化水平明显高于对照组,而CaMKⅡ的总量无变化;诱导LTP后3h CaMKⅡ的磷酸化水平进一步升高。而且CaMKⅡ的总量也明显增加(n=4);(2)强直刺激前30min于脊髓局部给予CaMKⅡ的特异性抑制剂KN-93(100μmol/L),可阻断LTP的诱导,同时明显抑制CaMKⅡ的磷酸化水平;(3)诱导LTP后30min给予KN-93,可显著抑制LTP的维持,同时CaMKⅡ的磷酸化水平与未用药组相比也明显降低（n=3);(4)LTP3h后给予KN-93,LTP的幅值不受影响,磷酸化的CaMKⅡ的含量与用药前相比也无差别（n=3)。根据上述实验结果可以认为,CaMKⅡ的激活参与脊髓背角C-纤维诱发电位LTP的诱导和早期维持过程。     

Immunohistochemical studies of peptidergic neurons in the dorsal horn of the spinal cord

The indirect immunofluorescence technique was used to localize substance P, somatostatin, methionine--enkephalin, neurotensin, and oxytocin in the dorsal horn of the rat spinal cord. The unique distribution of each peptide is described and the relative amount of each peptide in laminae I--III of the dorsal horn and the dorsal part of the lateral funniculus qualitatively assessed. Colchicine treatment and dorsal rhizotomy were used to determine, in part, the origin of immunoreactive fibers and terminals observed in the dorsal horn.     

Sustained neurochemical plasticity in central terminals of mouse DRG neurons following colitis

Sensitization of dorsal root ganglia (DRG) neurons is an important mechanism underlying the expression of chronic abdominal pain caused by intestinal inflammation. Most studies have focused on changes in the peripheral terminals of DRG neurons in the inflamed intestine but recent evidence suggests that the sprouting of central nerve terminals in the dorsal horn is also important. Therefore, we examine the time course and reversibility of changes in the distribution of immunoreactivity for substance P (SP), a marker of the central terminals of DRG neurons, in the spinal cord during and following dextran sulphate sodium (DSS)-induced colitis in mice. Acute and chronic treatment with DSS significantly increased SP immunoreactivity in thoracic and lumbosacral spinal cord segments. This increase developed over several weeks and was evident in both the superficial laminae of the dorsal horn and in lamina X. These increases persisted for 5 weeks following cessation of both the acute and chronic models. The increase in SP immunoreactivity was not observed in segments of the cervical spinal cord, which were not innervated by the axons of colonic afferent neurons. DRG neurons dissociated following acute DSS-colitis exhibited increased neurite sprouting compared with neurons dissociated from control mice. These data suggest significant colitis-induced enhancements in neuropeptide expression in DRG neuron central terminals. Such neurotransmitter plasticity persists beyond the period of active inflammation and might contribute to a sustained increase in nociceptive signaling following the resolution of inflammation.     

Depletion of substance P and somatostatin in the upper dorsal horn after blockade of axoplasmic transport

Summary In the upper dorsal horn of the rat lumbosacral spinal cord, substance P and somatostatin are present in two distinct and different populations of primary central afferent terminals. Substance-P-positive terminals are mainly concentrated in lamina I, while somatostatin-positive terminals are confined to lamina II. Although these two populations of primary afferent terminals differ at light- and electron-microscopic level, they are equally affected by transganglionic degenerative atrophy (TDA) which is induced by the blockade of axoplasmic transport in the segmentally related, ipsilateral sensory nerve by the local application of Vinblastin, a microtubule inhibitor. In consequence, substance P and somatostatin are depleted in the medial and intermediate portions of the upper dorsal horn, while the lateralmost area, which represents the postaxial portion of the dermatome, remains virtually intact. Substance P and somatostatin in propriospinal elements and the axonal meshwork within the dorsolateral funicle are not affected by TDA. Neurotensine, a propriospinal neuropeptide, does not show any alterations in the affected spinal segments.This work was supported by research grant no. 06/4-01/449 from the Hungarian Ministry of Health and no. 375/82/3.2 from the Hungarian Academy of Sciences     

AMPA receptor-dependent clustering of synaptic NMDA receptors is mediated by Stargazin and NR2A/B in spinal neurons and hippocampal interneurons

Under standard conditions, cultured ventral spinal neurons cluster AMPA- but not NMDA-type glutamate receptors at excitatory synapses on their dendritic shafts in spite of abundant expression of the ubiquitous NMDA receptor subunit NR1. We demonstrate here that the NMDA receptor subunits NR2A and NR2B are not routinely expressed in cultured spinal neurons and that transfection with NR2A or NR2B reconstitutes the synaptic targeting of NMDA receptors and confers on exogenous application of the immediate early gene product Narp the ability to cluster both AMPA and NMDA receptors. The use of dominant-negative mutants of GluR2 further showed that the synaptic targeting of NMDA receptors is dependent on the presence of synaptic AMPA receptors and that synaptic AMPA and NMDA receptors are linked by Stargazin and a MAGUK protein. This system of AMPA receptor-dependent synaptic NMDA receptor localization was preserved in hippocampal interneurons but reversed in hippocampal pyramidal neurons.     

Slow and selective death of spinal motor neurons in vivo by intrathecal infusion of kainic acid: implications for AMPA receptor-mediated excitotoxicity in ALS

Excitotoxicity mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors has been proposed to play a major role in the selective death of motor neurons in sporadic amyotrophic lateral sclerosis (ALS), and motor neurons are more vulnerable to AMPA receptor-mediated excitotoxicity than are other neuronal subclasses. On the basis of the above evidence, we aimed to develop a rat model of ALS by the long-term activation of AMPA receptors through continuous infusion of kainic acid (KA), an AMPA receptor agonist, into the spinal subarachnoid space. These rats displayed a progressive motor-selective behavioral deficit with delayed loss of spinal motor neurons, mimicking the clinicopathological characteristics of ALS. These changes were significantly ameliorated by co-infusion with 6-nitro-7-sulfamobenso(f)quinoxaline-2,3-dione (NBQX), but not with d(-)-2-amino-5-phosphonovaleric acid (APV), and were exacerbated by co-infusion with cyclothiazide, indicative of an AMPA receptor-mediated mechanism. Among the four AMPA receptor subunits, expression of GluR3 mRNA was selectively up-regulated in motor neurons but not in dorsal horn neurons of the KA-infused rats. The up-regulation of GluR3 mRNA in this model may cause a molecular change that induces the selective vulnerability of motor neurons to KA by increasing the proportion of GluR2-lacking (i.e. calcium-permeable) AMPA receptors. This rat model may be useful in investigating ALS etiology.     

Subunit rules governing the sorting of internalized AMPA receptors in hippocampal neurons

Removal of synaptic AMPA receptors is important for synaptic depression. Here, we characterize the roles of individual subunits in the inducible redistribution of AMPA receptors from the cell surface to intracellular compartments in cultured hippocampal neurons. The intracellular accumulation of GluR2 and GluR3 but not GluR1 is enhanced by AMPA, NMDA, or synaptic activity. After AMPA-induced internalization, homomeric GluR2 enters the recycling pathway, but following NMDA, GluR2 is diverted to late endosomes/lysosomes. In contrast, GluR1 remains in the recycling pathway, and GluR3 is targeted to lysosomes regardless of NMDA receptor activation. Interaction with NSF plays a role in regulated lysosomal targeting of GluR2. GluR1/GluR2 heteromeric receptors behave like GluR2 homomers, and endogenous AMPA receptors show differential activity-dependent sorting similar to homomeric GluR2. Thus, GluR2 is a key subunit that controls recycling and degradation of AMPA receptors after internalization.     

Interferon-γ receptors are expressed at synapses in the rat superficial dorsal horn and lateral spinal nucleus

Summary Interferon-γ can facilitate the spinal nociceptive flexor reflex and elicit neuropathic pain-related behavior in rats and mice. Immunoreactivity for the interferon-γ receptor (IFN-γR) occurs in the superficial layers of the dorsal horn and the lateral spinal nucleus in the rat and mouse spinal cord, as well as in subsets of neurons in the dorsal root ganglia. The aim of the present study was to examine the cellular localization and origin of the IFN-γR in the spinal cord. As viewed by confocal microscopy, the immunopositivity for the IFN-γR was co-localized with that of the presynaptic marker synaptophysin and with neuronal nitric oxide synthase in the lateral spinal nucleus, whereas only a minor overlap with these molecules was observed in laminae I and II of the dorsal horn. There was no co-localization of the IFN-γR with markers for astrocytes and microglial cells. Ultrastructurally, the IFN-γR was found predominantly in axon terminals in the lateral spinal nucleus but also at postsynaptic sites in dendrites in laminae I and II. The IFN-γR expressed in neurons in dorsal root ganglia was transported in axons both centrally and peripherally. Hemisection of the spinal cord caused no reduction in immunolabelling of the IFN-γR in the dorsal horn or the lateral spinal nucleus. Since rhizotomy does not effect the immunolabelling in the lateral spinal nucleus, our observation indicates that the presynaptic receptors in this nucleus are derived from intrinsic neurons. The localization of the IFN-γR in the spinal cord differed from that of the AMPA glutamate receptor subunits 2 and 3 and the substance P receptor (NK1). Our results, showing localization of IFN-γR to pre- and postsynaptic sites in the dorsal horn and lateral spinal nucleus indicate that IFN-γ can modulate nociception at the spinal cord level.     

脊髓背角痛觉传递和调制的一些化学解剖学观察

本实验研究了脊髓背角内Ｃ纤维末梢的分布和突触学特征及其一些神经递质化学构筑;定量观察了急性痛引起背角的递质变化;显示了初级传入Ｃ纤维,抑制性中间神经元和背角伤害性感受神经元三者之间的突触关系,并探讨它们在痛觉信息传递和调制中的作用。     

Developmental characteristics of AMPA receptors in chick lumbar motoneurons

Ca2+ fluxes through ionotropic glutamate receptors regulate a variety of developmental processes, including neurite outgrowth and naturally occurring cell death. In the CNS, NMDA receptors were originally thought to be the sole source of Ca2+ influx through glutamate receptors; however, AMPA receptors also allow a significant influx of Ca2+ ions. The Ca2+ permeability of AMPA receptors is regulated by the insertion of one or more edited GluR2 subunits. In this study, we tested the possibility that changes in GluR2 expression regulate the Ca2+ permeability of AMPA receptors during a critical period of neuronal development in chick lumbar motoneurons. GluR2 expression is absent between embryonic day (E) 5 and E7, but increases significantly by E8 in the chick ventral spinal cord. Increased GluR2 protein expression is correlated with parallel changes in GluR2 mRNA in the motoneuron pool. Electrophysiological recordings of kainate-evoked currents indicate a significant reduction in the Ca2(+)-permeability of AMPA receptors between E6 and E11. Kainate-evoked currents were sensitive to the AMPA receptor blocker GYKI 52466. Application of AMPA or kainate generates a significant increase in the intracellular Ca2+ concentration in E6 spinal motoneurons, but generates a small response in older neurons. Changes in the Ca(2+)-permeability of AMPA receptors are not mediated by age-dependent changes in the editing pattern of GluR2 subunits. These findings raise the possibility that Ca2+ influx through Ca(2+)-permeable AMPA receptors plays an important role during early embryonic development in chick spinal motoneurons.