Receptor for calcitonin gene-related peptide: localization in the dorsal and ventral spinal cord.

Although the distribution of calcitonin gene-related peptide has been extensively studied in the spinal cord, little is known about the precise subcellular localization of receptors for calcitonin gene-related peptide. The present study was undertaken to localize calcitonin gene-related peptide receptors in both the dorsal and ventral horns of the rat spinal cord. Immunocytochemical localization with specific monoclonal antibodies was performed at the light and electron microscopic levels. Calcitonin gene-related peptide receptor was expressed in neuronal but not glial elements. Discrete postsynaptic localization of receptor for the calcitonin gene-related peptide was evident in the cells and dendrites of the superficial dorsal horn. Some of the terminal endings apposing the stained synapses formed the central terminals of glomerular complexes. The endings were scallop shaped (Type I), typical of primary afferent terminations. Other dorsal horn structures with postsynaptic labeling were contacted by dome-shaped or elongated axonal endings. Presynaptic localization on some dorsal horn terminations may serve an autoreceptor function. Motoneurons, on the other hand, were contacted by axonal terminals with presynaptic calcitonin gene-related peptide receptors. These data suggest that (i) dorsal horn neurons are capable of direct primary afferent, calcitonin gene-related peptide receptor-mediated interactions and (ii) neuronal terminals contacting motor horn cells can be influenced through presynaptic paracrine-like calcitonin gene-related peptide receptor-mediated interactions. Thus, calcitonin gene-related peptide can have multiple modulatory effects on spinal cord neurons through site-specific receptors.     

大鼠脊髓P物质受体定位分布的免疫细胞化学研究

用免疫细胞化学技术对大鼠脊髓和脊神经节内Ｐ物质受体的定位分布进行了系统的研究。结果证明，Ｐ物质受体阳性胞体和树突主要密集地分布于脊髓全长的Ⅰ层，此外，还发现Ⅱ层的外侧部出现少量阳性胞体和树突，来自Ⅲ层的阳性树突穿过Ⅱ层后进入Ⅰ层；Ⅲ～Ⅳ和Ⅹ层也可见中等密度的阳性胞体和树突；Ⅵ层和Ⅶ层仅见少量阳性胞体和树突，但胸髓中间带外侧核、骶髓副交感运动核、骶髓后连合核内可见大量浓染的阳性胞体和树突；Ⅷ、Ⅸ层、Ｏｎｕｆ氏核、外侧颈核和外侧脊索核也有阳性胞体和树突．灰质内的阳性胞体的树突还伸向前索和外侧索，有时可达脊髓的边缘．此外，脊神经节内也可见少量散在且均匀分布的小型阳性胞体．     

大鼠脊髓后角浅层内六种肽类和5-羟色胺的来源及其功能探讨

分别切断大鼠一侧坐骨神经和半横切颈髓上段,用免疫组织化学技术观察了L_(4-6)后角浅层内SP、CCK、SOM、VIP、L-ENK、NT、5-HT等的量的改变。并半横切L_5节段的吻、尾侧,观察了NT在同节段内的含量改变。 1.切断坐骨神经后,术侧L_(4-6)后角浅层的坐骨神经占位区内SP、CCK、SOM、VIP有不同程度的脱失,SP、CCK最明显。结合文献,作者认为后根节中SP、CCK、SOM、VIP阳性神经元外周突部分分布于外周躯体神经。 2.半横切颈髓后,术侧L_(4-5)后角浅层的5-HT阳性反应物基本消失,而L_6后角浅层内有少量存留。CCK、L-ENK阳性反庆物在L_(4-6)节段背外侧索中明显减少,但后角浅层只有轻微减少。SOM在术侧后角浅层中也似有轻微减少。这些提示脑结构到脊髓后角浅层的下行纤维中除含有5-HT外还含有一些神经肽。 3.L—ENK阳性反应物在切断坐骨神经后轻度增高;SOM无论在切断坐骨神经或半横切劲髓例均变比不大;NT在此两组实验中均无变化,且在L_5节段吻、尾侧半切腰髓后L_5后角浅层内仍无变化。以上提示分布于后角浅层的某些肽类有一部分直接来自脊髓内甚至同节段内的固有神经元。     

Localization of serotonin- and substance P-like immunofluorescence in the caudal spinal trigeminal nucleus of the rat

A double immunofluorescence labeling method was used to study the localization of serotonin (5-HT)- and substance P (SP)-like immunoreactivities within neuronal fibers in the caudal spinal trigeminal nucleus of the rat. The 5-HT- and SP-immunoreactive fibers share extensive topographical overlap within the superficial laminae of the caudal trigeminal nucleus; however, the majority of stained fibers are immunoreactive for either 5-HT or SP, but not both simultaneously. A small population of fibers in which 5-HT and SP are co-localized is present and restricted to the marginal zone as well as the inner and outer layers of the substantia gelatinosa. The results of the present study suggest that fibers containing coexistent 5-HT and SP may be involved in the processing of nociceptive somatic sensation in the medullary dorsal horn of rat.     

日本猴脑内阿片μ-受体样免疫反应物质的分布:Ⅱ.颈、胸、腰、骶段脊髓及后根节(英)

通过应用识别大鼠阿片μ-受体（MOR）C末端30个氨基酸残基特异性位点的豚鼠抗体，本文对日本猴颈、胸、腰、骶段脊髓和背根节内MOR-样免疫反应物质的分布形式和特点进行了免疫组织化学研究。结果如下：强染色MOR－Li密集分布于脊髓吻尾全长的背角浅层，主要以Rexed第二层内侧部为主。在脊髓背角深层和中央导水管周围区域内也可见中到低等数量的MOR-Li标记。在脊髓背角浅层，MOR-Li广泛分布于Ⅰ、Ⅱ层内神经毯和神经元突起，但似乎只分布于第Ⅱ层神经元胞体。背角深层（Ⅳ－Ⅵ层）有些神经元的胞体和树突也有较强的MOR－Li染色。MOR－Li在背根入髓区和Lissauer's氏束中分布密集且染色强。在后根节，MOR－Li主要分布于中、小细胞，其中MOR－Li阳性小细胞约占65.71％（1018／1562），直径平均为29.50±0．11μm（17．31～34．88μm），中等细胞约占34．19％（534／1562），直径平均为39．04±0．14μm（24.01～49．86μm），而MOR－Li阳性的大细胞只占0．64％（10／1562），直径平均为59.00±2.35μm（51．09～71．39μm）。本结果揭示猴脊髓内阿片肽主要通过突触前和突触后两种方式发挥镇痛作用，除此之外，还可能通过作用于外周伤害性感受器部位的MOR发挥镇痛作用。     

Ontogeny and characterization of [125I]Bolton Hunter-eledoisin binding sites in rat spinal cord by quantitative autoradiography.

The distribution and characteristics of [125I]Bolton Hunter-eledoisin binding sites in rat lumbar spinal cord were studied during postnatal development by in vitro receptor autoradiography. At three, six and 10 days of age, specific [125I]eledoisin binding was distributed throughout the dorsal and ventral horns of the spinal cord. In contrast, from day 24 onwards, specific binding of [125I]eledoisin was confined to superficial layers of the dorsal horn, with negligible amounts of specific binding in the ventral horn. [125I]Eledoisin binding to neonatal (three day) and adult (eight to 12 weeks) spinal cord sections was characterized using tachykinin agonists. In both dorsal and ventral horns of neonatal spinal cord, the rank order of potency of agonists indicated that the majority (64%) of specific [125I]eledoisin binding was to neurokinin-3 binding sites. The identity of the non-neurokinin-3 sites labelled by [125I]eledoisin remains to be determined. In adult rat spinal cord, [125I]eledoisin appeared to bind exclusively to neurokinin-3 binding sites. These results suggest that major changes take place in the localization of neurokinin-3 receptors during postnatal ontogeny of the rat spinal cord. These changes may reflect an important role for tachykinins in neuronal plasticity of the developing spinal cord.     

大鼠脊髓后角内初级传入C纤维中δ阿片受体的免疫电镜定位

目的：观察大鼠脊髓后角浅层内δ阿片受体是否存在于初级传入Ｃ纤维内,为脑啡肽在痛觉切级传入调制中的突触前抑制提供更为可靠的形态学依据。材料与方法：应用双标（免疫）组织化学电镜护林在鼠脊髓后角浅层（Ⅰ～Ⅲ层）凝集素Ｉ－Ｂ们 和δ阿片受体。结果：大量轴突及轴突终末呈δ阿片受体阳性免疫反应,特别是在双标切片上,观察到约４０％的凝集素Ｉ－Ｂ４结合位点阳性纤维及其终末内也含有δ阿片受体。结论：脊髓后角浅层内的     

Characterization and localization of a putative morphine-modulating peptide, FLFQPQRFamide, in the rat spinal cord: biochemical and immunocytochemical studies

The bovine octapeptide Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (FLFQPQRFamide), originally detected by antisera raised against the invertebrate peptide, Phe-Met-Arg-Phe-NH2, is a neuropeptide which antagonizes the actions of endogenous and exogenous opiates. Using a sensitive radioreceptor assay, we show that rat spinal cord extracts were able to inhibit binding of FLFQPQRFamide, suggesting that a biologically active FLFQPQRFamide-like material exists in the rat spinal cord. We also raised antibodies against the peptide and used them, together with radioimmunological and immunohistochemical methods, to characterize this material further and analyse its cellular and subcellular localization in this area of the central nervous system. Radioimmunoassay showed that extracts from cervical and thoracolumbar levels contained measurable amounts of FLFQPQRFamide-immunoreactive material (about 3 ng/g tissue), present essentially in the dorsal horn. Analytical reverse-phase chromatography revealed that this material existed in several molecular forms. One of these fractions (about 20% of the total immunoreactivity) had the elution characteristics of synthetic FLFQPQRFamide. Light microscopic immunohistochemistry showed FLFQPQRFamide immunoreactivity at all spinal levels, localized mainly in a dense plexus of fibers in the superficial layers of the dorsal horn. Immunoreactive profiles were also seen in the lateral funiculi and around the central canal at all levels and in the intermediolateral columns; some rare immunoreactive fibers were also noted in the ventral horn at cervical and thoracic levels. FLFQPQRFamide-positive cell bodies were never detected in any of our sections. Electron microscopy of ultrathin sections of the dorsal horn and central gray treated with our antisera and a post-embedding immunogold procedure revealed that the immunoreactivity, at least within these areas, was restricted to dense-cored vesicles (90-120 nm in diameter) in axonal and terminal profiles. As seen by radioimmunoassay and immunohistochemistry, unilateral rhizotomy of all dorsal roots between segments C4 and T2 did not change the levels of FLFQPQRFamide immunoreactivity in the ipsilateral C6-C8 segments. Taken together with our recent data showing the existence of specific FLFQPQRFamide receptors at the spinal cord level, our present observations suggest that the dorsal horn of the rat spinal cord may be a site where vertebrate Phe-Met-Arg-Phe-like peptides, and in particular, FLFQPQRFamide, may exert opiate modulating activities.     

Substance P release in the cat spinal cord upon afferent C-fibre stimulation is not attenuated by clonidine at analgesic doses

In anaesthetized cats, antibody microprobes were used to measure the release of immunoreactive substance P (irSP) in the lumbar dorsal horn during electrical stimulation of primary afferent fibres at intensities suprathreshold for unmyelinated fibres. Release of irSP was detected in the region of the superficial dorsal horn. This evoked release was not reduced by clonidine hydrochloride, administered intravenously or by superfusion of the dorsal cord surface. Microprobes inserted during cord superfusion with lignocaine hydrochloride detected less irSP along their entire length, including in the region of evoked release. The results suggest that the analgesic action of clonidine does not involve reduced release of SP from the central terminals of nociceptors in the spinal cord.     

Diabetes affects the expression of GABA and potassium chloride cotransporter in the spinal cord: a study in streptozotocin diabetic rats

Painful diabetic neuropathy is associated to hyperexcitability and spontaneous hyperactivity of spinal cord neurons. The underlying pathophysiological mechanisms are not clear. Increases in excitatory neurotransmission at the spinal cord, involving glutamate and SP, seem to account for the abnormal neuronal activity, but inhibitory influences were never evaluated. This study aims to analyse the expression of GABA, its synthesizing enzyme glutamic acid decarboxylase (GAD) and the potassium chloride cotransporter (KCC2), in the spinal dorsal horn of streptozotocin (STZ)-induced diabetic rats. Four weeks after saline or STZ (60mg/kg) injection, animals were sacrificed and the spinal segments L2-L3 were removed and immunoreacted for GABA, GAD and KCC2, or processed for western blotting for KCC2. Densitometric quantification was performed in the superficial dorsal horn (laminae I, II and III) of immunoreacted sections and in the immunoblots. STZ rats presented a significant increase of GABA expression in laminae II and III when compared with control animals, while no differences were detected in GAD expression. A significant decrease in KCC2 expression was detected by immunohistochemistry in laminae I and II, which was confirmed by immunoblotting. Increased GABA levels, along with decrease in KCC2 expression, may underlie the abnormal neuronal activity detected in the spinal cord of diabetic rats. Reduction in KCC2 expression was shown to lead to increases in intracellular chloride concentration and, in such condition, GABA binding to GABA(A) receptor induces membrane depolarization, provoking neuronal excitation rather than inhibition. Based on these findings, we propose that a loss of GABA-mediated inhibitory tone at the spinal cord may result in neuronal hyperexcitability and spontaneous hyperactivity during diabetes.     

Visceral and somatic afferent origin of calcitonin gene-related peptide immunoreactivity in the lower thoracic spinal cord of the rat

The origin of calcitonin gene-related peptide in the thoracic spinal cord of the rat was investigated by radioimmunoassay and immunohistochemistry. In transverse sections from normal animals there was a dense staining of calcitonin gene-related peptide-immunoreactivity in laminae I, II and V of the dorsal horn. In parasagittal sections this was found to consist of rostrocaudally orientated fibres in laminae I and II and longitudinal bundles of fibres interspersed with a plexus of immunoreactivity in lamina V. After sectioning the thoracic spinal nerves there was a significant reduction in immunoreactivity in the dorsal horn of the spinal cord which was seen as a marked reduction of staining in lamina II and in the bundles of fibres in lamina V. Section of the splanchnic nerve slightly reduced staining in lamina I and virtually abolished the plexuses of immunoreactivity in lamina V. However, measurement of calcitonin gene-related peptide in samples from coeliac-ganglionized rats revealed an increase in immunoreactivity in regions of the spinal cord containing lamina V. These results provide evidence of a visceral and somatic afferent origin of calcitonin gene-related peptide in the thoracic spinal cord of the rat.     

Immunocytochemical evidence for calcitonin gene-related peptide-like neurons in the dorsal horn and lateral spinal nucleus of the rat cervical spinal cord

Calcitonin gene-related peptide (CGRP) in the dorsal horn of the rat spinal cord was assumed until now to be principally of primary afferent origin. It is shown here, on the basis of both light and electron microscopic immunocytochemical evidence, that some cell bodies of the dorsal horn and lateral spinal nucleus (LSn) of the rat cervical spinal cord contain a CGRP-like immunoreactivity. At the light microscopic level, immunoreactive cell bodies were observed in animals pretreated with colchicine injected intraventricularly, CGRP-like cell bodies were morphologically heterogeneous and distributed in the three superficial layers of the dorsal horn. They were very rare in lamina I and more numerous in laminae II and III. A group of immunoreactive cell bodies was also observed in the LSn. Using electron microscopic techniques, a few immunoreactive cell bodies were observed even in control animals. In addition, relatively numerous immunoreactive dendrites were observed in lamina II. The specificity of the reaction and the physiological implications of the results are discussed.     

Binding sites for 125I-cholecystokinin in primate spinal cord are of the CCK-A subclass

Cholecystokinin (CCK) receptor binding was measured in sections of human, monkey and rat spinal cord using autoradiographical techniques. In each species, high levels of specific 125I-Bolton-Hunter CCK binding were detected in the superficial layers of the dorsal horn (the substantia gelatinosa). In monkey and human but not rat spinal cord, 125I-CCK binding was dose-dependently inhibited by low concentrations of the selective CCK-A antagonist L-364,718. Binding of [3H]L-364,718, which was saturable (Bmax = 29.0 +/- 0.95 pmol/g wet wt.) and of high affinity (pKd) = 9.92 +/- 0.16) was also detected in sections of monkey spinal cord and had a similar localization to that of specific 125I-CCK binding. These data indicate that in striking contrast to CCK receptors in rat spinal cord, those in the primate cord are of the CCK-A receptor subclass.     

Development of glomerular synaptic complexes and immunohistochemical differentiation in the superficial dorsal horn of the embryonic primate spinal cord

 Development of glomerular synapses in the superficial dorsal horn has been studied in the embryonic macaque spinal cord using light and electron microscopic techniques including Golgi impregnation, ³H-thymidine radioautography and pre-embedding immunohistochemistry of substance P (SP), calcitonin gene related peptide (CGRP), calbindin D-28 K (CB) and parvalbumin (PV). The study revealed that substantia gelatinosa cells of the primate dorsal horn are generated last, but unlike in rodents, synaptogenesis in this region starts at early embryonic (E) stages of the 165-day long gestation. Already by E30, both Type 1 (light) and 2 (dark) dorsal root axons and their growth cones are identifiable within the oval bundle of His, before they form synaptic contact with their final target cells. Subsequently they invade the dorsal horn and enter the bisecting interfaces formed by orderly programmed cell death. Each type of scalloped (sinusoid) central primary afferent terminal (i.e. DSA, RSV and LDCV) have well defined pre- and post-synaptic specializations already by E40. Among the neuropeptides studied, SP appears first at E67 and CGRP at E70 in the lateral position but within a few days both of them are spread to the entire superficial dorsal horn. Both SP and CGRP are present in the thin dorsal root axons and their growth cones, giving rise to scalloped and simple axon terminals. PV is transiently present in the entire length of the thick dorsal root afferents before becoming concentrated in the synaptic boutons. CB is displayed mainly in neurons of the lamina I and III. Dendrites of CB-immunoreactive cells establish synaptic connection with each type of dorsal root afferents, including glomerular synaptic complexes. These data reveal that the superficial dorsal horn in the primate spinal cord develops its characteristic synaptic complexes much earlier in gestation than in any other mammalian species studied. Furthermore, characteristic cytological features of the prospective glomerular complex emerge before establishment of the final synaptic contacts. Accepted: 20 July 1998     

The colocalization of CGRP receptor and AMPA receptor in the spinal dorsal horn neuron of rat: a morphological and electrophysiological study

Both the calcitonin gene-related peptide (CGRP) receptor and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor are involved in the transmission of sensory information from primary afferent to the spinal cord. The present study found that there was a colocalization of CGRP receptor and AMPA receptor in a single spinal dorsal horn neuron in rat determined by double immunofluorescence labeling image methods. Furthermore, our results showed that the evoked discharge frequency of the wide dynamic range (WDR) neuron, one type of the dorsal horn neurons, increased significantly after micro-iontophoretic delivery of CGRP or AMPA alone tested by extracellular recording, indicating a functional colocalization of CGRP receptor and AMPA receptor in a single spinal dorsal horn neuron. The results of the present study found a morphological and functional colocalization of the CGRP receptor and AMPA receptor in a single dorsal horn neuron that involved in the transmission and modulation of sensory information from primary afferent to the spinal cord in rats.     

Evidence for a visceral afferent origin of substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord

A visceral afferent origin of substance P-like immunoreactivity in lamina V of the lower thoracic spinal cord of the rat was investigated. In transverse sections from normal animals there was a moderately dense substance P-immunoreactive innervation of lamina V. In some sections there was a dorsoventrally orientated fibre bundle from the superficial dorsal horn entering lamina V. In parasagittal sections, substance P-immunoreactivity in lamina V was found arranged in clusters, with a periodicity in the rostrocaudal axis of 200-600 microns. In some cases these were seen to be continuous with a dorsoventrally orientated fibre bundle from the superficial dorsal horn. After section of the splanchnic nerve there was a consistent reduction in the density of the substance P-like immunoreactivity in lamina V, with fewer clusters on the operated side. Adult rats treated neonatally with capsaicin showed a substantial reduction of substance P-immunoreactivity in laminae I and II and the virtual abolition of staining in lamina V. These results provide evidence of a visceral origin for some of the substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord. In addition, they confirm that most of the substance P-immunoreactivity in the dorsal horn is of primary afferent origin.     

Localization of neurones expressing the gap junction protein Connexin45 within the adult spinal dorsal horn: a study using Cx45-eGFP reporter mice

Connexin (Cx) proteins localized to neuronal and glial syncytia provide the ultrastructural components for intercellular communication via gap junctions. In this study, a Cx45 reporter mouse model in which the Cx45 coding sequence is substituted for enhanced green fluorescent protein (eGFP) was used to characterize Cx45 expressing neurones within adult mouse spinal cord. eGFP-immunoreactive (eGFP-IR) cells were localized at all rostro-caudal levels to laminae I–III of the dorsal horn (DH), areas associated with nociception. The neuronal rather than glial phenotype of these cells in DH was confirmed by co-localisation of eGFP-IR with the neuronal marker NeuN. Further immunohistochemical studies revealed that eGFP-IR interneurones co-express the calcium-binding protein calbindin, and to a lesser extent calretinin. In contrast, eGFP-IR profiles did not co-localize with either parvalbumin or GAD-67, both of which are linked to inhibitory interneurones. Staining with the primary afferent markers isolectin-B4 (IB4) and calcitonin gene-related peptide revealed that eGFP-IR somata within laminae I–III receive close appositions from the former, presumed non-peptidergic nociceptive afferents of peripheral origin. The presence of 5-HT terminals in close apposition to eGFP-IR interneuronal somata suggests modulation via descending pathways. These data demonstrate a highly localized expression of Cx45 in a population of interneurones within the mouse superficial dorsal horn. The implications of these data in the context of the putative role of Cx45 and gap junctions in spinal somatosensory processing and pain are discussed.     

Characterization of nestin expression in the spinal cord of GFP transgenic mice after peripheral nerve injury

Many studies have shown that activation and increase in the number of astrocytes and microglia in the spinal cord participate in the initiation and maintenance of neuropathic pain, but little attention has been paid to the responses of neural progenitor cells to peripheral nerve injury. Nestin, a class VI intermediate filament protein, is expressed both in neuronal and glial progenitors as well as in their common precursors; and nestin-positive cells appear in the brain and spinal cord following various forms of damage to these regions. To clarify the responses of neural progenitor cells to nerve injury, we applied L5 spinal nerve transection (L5-SNT) to nestin-promoter GFP (pNestin-GFP) transgenic mice to narrow the target to them. While pNestin-GFP expression was strongly retained in the ependyma lining the central canal of the transgenic spinal cord even in adulthood, it was markedly reduced in the dorsal horn during postnatal development by day 7. Increases in pNestin-GFP expression and labeling by the proliferation marker 5-bromodeoxyuridine were broadly found in the dorsal horn of adult mice on day 3 after L5-SNT. On the other hand, the activation and increase in number of microglia and astrocytes are restricted to the superficial layer of the dorsal horn, the central terminal of injured primary afferent fibers. Purinergic P2X agonist α, β-MeATP increased [Ca²⁺]i in nestin-positive cells in the superficial layer ipsilateral to nerve injury and P2 receptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2,4-disulphonic acid (PPADS) blocked the expression and elongation of pNestin-GFP fibers in the slice culture of the spinal cord. These results with pNestin-GFP transgenic mice demonstrate that nestin-positive cells proliferate in the dorsal horn in response to peripheral nerve injury and suggest that ATP may contribute to the expression of nestin and activation of neural progenitor cells after nerve injury.     

Nerve growth factor receptors in rat spinal cord: an autoradiographic and immunohistochemical study

The distribution of nerve growth factor receptors in the lumbar spinal cord of the rat was studied with autoradiographic and immunohistochemical techniques: [125I]nerve growth factor and specific monoclonal antibody (Mab 192) against nerve growth factor receptor were used to localize nerve growth factor binding sites. The distributions of nerve growth factor binding sites with highest density within the superficial layers (laminae I and II) of the dorsal gray matter were virtually identical as demonstrated by these two ligands; this suggests that Mab 192 can be used as a specific probe to identify nerve growth factor receptors in rat nervous system. Nerve growth factor receptor binding sites, as demonstrated by autoradiography, were also found in longitudinal bundles of fibers running dorsolaterally in the lateral funiculus. However, no immunoreactivity was detected in these areas by immunohistochemistry. No specific binding was found in the dorsal horn when [125I]nerve growth factor was co-injected with unlabeled nerve growth factor or after incubation with nonspecific monoclonal antibody. Dorsal root section produced a complete loss of nerve growth factor-specific labeling pattern throughout laminae I-II of the spinal cord. This suggests that nerve growth factor receptors are localized on the nerve terminals of primary afferent fibers which synapse in the region of the spinal cord. The presence of nerve growth factor binding sites in the dorsal horn of the spinal cord is consistent with the possibility that nerve growth factor, or a nerve growth factor-like substance, derived from the central nervous system, may have a role in trophic support of dorsal root ganglion neurons.