Cryoprecipitate prepared from plasma virally inactivated by the solvent detergent method

The newly discovered peptide nociceptin/orphanin FQ has been found to increase reactivity to pain and to influence locomotor activity after intracerebroventricular administration. This study investigated the possible role of hippocampal nociceptin/orphanin FQ in spatial learning and in spontaneous locomotion. Male rats were trained in the Morris water task after microinjection of 10 nmol nociceptin/orphanin FQ or artificial cerebrospinal fluid (as control) into the CA3 region of the dorsal hippocampus. Nociceptin/orphanin FQ was found to severely impair spatial learning without interfering with swimming performance. Intrahippocampal injection of nociceptin/ orphanin FQ markedly decreased exploratory locomotor activity including vertical movements (rearing). The data suggest that nociceptin/orphanin FQ is a potent modulator of synaptic plasticity within the hippocampus.     

Nocistatin, a peptide that blocks nociceptin action in pain transmission

Prolonged tissue damage or injury often leads to chronic pain states such that noxious stimuli evoke hyperalgesia and innocuous tactile stimuli evoke pain (allodynia). The neuropeptide nociceptin, also known as orphanin FQ, is an endogenous ligand for the orphan opioid-like receptor which induces both hyperalgesia and allodynia when administered by injection through the theca of the spinal cord into the subarachnoid space (that is, intrathecally). Here we show that the nociceptin precursor contains another biologically active peptide which we call nocistatin. Nocistatin blocks nociceptin-induced allodynia and hyperalgesia, and attenuates pain evoked by prostaglandin E2. It is the carboxy-terminal hexapeptide of nocistatin (Glu-Gln-Lys-Gln-Leu-Gln), which is conserved in bovine, human and murine species, that possesses allodynia-blocking activity. We have also isolated endogenous nocistatin from bovine brain. Furthermore, intrathecal pretreatment with anti-nocistatin antibody decreases the threshold for nociceptin-induced allodynia. Although nocistatin does not bind to the nociceptin receptor, it binds to the membrane of mouse brain and of spinal cord with high affinity. Our results show that nocistatin is a new biologically active peptide produced from the same precursor as nociceptin and indicate that these two peptides may play opposite roles in pain transmission.     

Nociceptin/orphanin FQ. A new opioid, a new analgesic?

Opioids form the major class of strong analgesics. Endogenous opioids and their receptors play important roles in central nervous system function. Thus, the discovery of a new opioid peptide, nociceptin or orphanin FQ, and its receptor, opioid receptor-like 1 (ORL-1) has caused considerable interest since this transmitter system appears to exhibit a number of key differences to the other opioids. Analgesia can be produced at spinal sites but there is compelling evidence that the peptide may also have 'anti-opioid' actions in the brain. Effects on auditory processing, pains from nerve injury coupled with an apparent lack of motivational effects have important implications for novel therapy. This review surveys the recent functional studies on this novel peptide.     

Carbachol, an acetylcholine receptor agonist, enhances production in rat aorta of 2-arachidonoyl glycerol, a hypotensive endocannabinoid

Orphanin FQ/nociceptin binds with high affinity to the orphan opioid receptor-like/K-3 (ORL1/KOR-3) clone, and stimulates feeding. The present study demonstrated that antisense oligodeoxynucleotides directed against either exons 1, 2 or 3 of the ORL1/KOR-3 clone reduced orphanin FQ/nociceptin-induced hyperphagia. A missense probe was ineffective. Naltrexone dose-dependently reduced orphanin FQ/nociceptin-induced hyperphagia. These data suggest that the receptor responsible for orphanin FQ/nociceptin-induced hyperphagia is encoded by the ORL1/KOR-3 clone.     

Expression and regulation of steroid 5 alpha-reductase in the genital tubercle of the fetal rat

Nociceptin/orphanin FQ is a heptadecapeptide which was recently isolated from brains. It induces hyperalgesia, in contrast to the analgesic effects of opioid ligands, although it and its receptor structurally resemble opioid peptides and opioid receptors, respectively. To investigate the molecular mechanism underlying nociceptin/orphanin FQ actions, we performed Xenopus oocyte expression assays, in situ hybridization histochemistry and electrophysiological analyses of neurons. We found that the nociceptin/orphanin FQ receptor is functionally coupled with the G-protein-activated K+ (GIRK) channel in Xenopus oocytes, and that the receptor mRNA and GIRK1 mRNA co-exist in various neurons, including hippocampal pyramidal cells. Furthermore, we found that nociceptin/orphanin FQ induces hyperpolarizing currents via inward-rectifier K+ channels in hippocampal pyramidal cells, suggesting that the nociceptin/orphanin FQ receptor couples with the GIRK channel in this region. We conclude that the nociceptin/orphanin FQ receptor couples with the GIRK channel in various neurons, including hippocampal pyramidal cells, thereby modulating neuronal excitability.     

Analgesic activity of orphanin FQ2, murine prepro-orphanin FQ141-157 in mice

Orphanin FQ/nociceptin (OFQ/N) is generated from a larger precursor peptide, prepro-orphanin FQ (ppOFQ). Within the sequence of murine ppOFQ is another putative heptadecapeptide, orphanin FQ2 (OFQ2), corresponding to murine ppOFQ141-157. OFQ2 was a potent analgesic given either supraspinally (ED50 0.5 microgram, i.c.v.) or spinally (ED50 0.7 microgram, i.t.). As with opioids and OFQ/N, OFQ2 analgesia was enhanced by blockade of sigma receptors with haloperidol, which increased the potency of the peptide over 10-fold. Supraspinal OFQ2 analgesia was readily reversed by naloxone, implying that it activated opioid systems. Spinal OFQ2 analgesia was insensitive to naloxone. OFQ2 also inhibited gastrointestinal transit. Together, these studies suggest that OFQ2 may be a relevant neuropeptide with important physiological actions.     

Molecular cloning and characterization of a novel form of neuropeptide gene as a developmentally regulated molecule

To examine the molecular basis controlling neuronal differentiation, subtraction library construction and differential screening were used to identify cDNAs whose mRNA levels are regulated in mouse NS20Y cells by dibutyryl cyclic AMP treatment. One of them, N27K, whose mRNA increases transiently during both neuronal differentiation in NS20Y cells and development in mouse brain. The deduced amino acid sequence of N27K comprises 212 amino acid residues and is a novel form of a precursor protein for a new neuropeptide nociceptin/orphanin FQ, which we independently cloned as N23K. That is, the putative protein encoded by N27K is 25 amino acids longer than that encoded by N23K. Using an antibody against a C-terminal peptide of the N27K protein that recognizes a 27-kDa protein in Western blot analysis, a punctate structure in the perinuclear region and areas near the tip of neurites is visualized in neurally differentiating NS20Y cells. The time of maximal expression correlates with periods of neurite extension, and expression decreases as the neuritic network develops. Immunohistochemistry of tissue sections of the mouse central nervous system revealed that reactivity for the anti-N27K protein antibody can detected in early generated neurons at embryonic day 14, in virtually all immature neurons at postnatal day 1, and in subsets of neurons of discrete brain regions such as the hypothalamus and spinal cord in adults. This remarkable redistribution suggests that N27K may be involved in a process in neurite outgrowth and nervous system development.     

Sprouting of primary afferent fibers after spinal cord transection in the rat

After spinal cord injury, hyper-reflexia can lead to episodic hypertension, muscle spasticity and urinary bladder dyssynergia. This condition may be caused by primary afferent fiber sprouting providing new input to partially denervated spinal interneurons, autonomic neurons and motor neurons. However, conflicting reports concerning afferent neurite sprouting after cord injury do not provide adequate information to associate sprouting with hyper-reflexia. Therefore, we studied the effect of mid-thoracic spinal cord transection on central projections of sensory neurons, quantified by area measurements. The area of myelinated afferent arbors, immunolabeled by cholera toxin B, was greater in laminae I-V in lumbar, but not thoracic cord, by one week after cord transection. Changes in small sensory neurons and their unmyelinated fibers, immunolabeled for calcitonin gene-related peptide, were assessed in the cord and in dorsal root ganglia. The area of calcitonin gene-related peptide-immunoreactive fibers in laminae III-V increased in all cord segments at two weeks after cord transection, but not at one week. Numbers of sensory neurons immunoreactive for calcitonin gene-related peptide were unchanged, suggesting that the increased area of immunoreactivity reflected sprouting rather than peptide up-regulation. Immunoreactive fibers in the lateral horn increased only above the lesion and in lumbar segments at two weeks after cord transection. They were not continuous with dorsal horn fibers, suggesting that they were not primary afferent fibers. Using the fluorescent tracer DiI to label afferent fibers, an increase in area could be seen in Clarke's nucleus caudal to the injury two weeks after transection. In conclusion, site- and time-dependent sprouting of myelinated and unmyelinated primary afferent fibers, and possibly interneurons, occurred after spinal cord transection. Afferent fiber sprouting did not reach autonomic or motor neurons directly, but may cause hyper-reflexia by increasing inputs to interneurons.     

Dynorphin mRNA expression in dorsal horn neurons after traumatic spinal cord injury: temporal and spatial analysis using in situ hybridization

Dynorphin, an endogenous opioid, may contribute to secondary nervous tissue damage following spinal cord injury. The temporal and spatial distribution of preprodynorphin (PPD) mRNA expression in the injured rat spinal cord was examined by in situ hybridization. Rats were subjected to traumatic spinal cord injury at the T13 spinal segment using the weight-drop method. Motor function of these rats was evaluated by their ability to maintain their position on an inclined plane. Two double-labeling experiments revealed that increased PPD mRNA and dynorphin peptide expression were found exclusively in dorsal horn neurons. Neurons exhibiting an increase in the level of PPD mRNA were concentrated in the superficial laminae and the neck of dorsal horn within several spinal segments from the epicenter of the injury at 24 and 48 h after injury. A number of neurons showing increased PPD mRNA were found in gray matter adjacent to the injury areas. Segments caudal to the injury site exhibited a long-lasting elevation of PPD mRNA in neurons, compared to the rostral segments. The number of neurons expressing PPD mRNA in each rat was significantly positively correlated with its motor dysfunction. These findings suggest that increased expression of dynorphin mRNA and peptide in dorsal horn neurons occurs after traumatic spinal cord injury. This also supports the hypothesis that the dynorphin has a pathological role in secondary tissue damage and neurological dysfunction after spinal cord injury.     

Sensory axons are guided by local cues in the developing dorsal spinal cord

During development, different classes of sensory neurons establish distinctive central projections within the spinal cord. Muscle spindle afferents (Ia fibers) grow ventrally through the dorsal horn to the ventral cord, whereas cutaneous sensory collaterals remain confined to the dorsal horn. We have studied the nature of the cues used by Ia fibers in establishing their characteristic projections within the dorsal horn. An organotypic culture preparation of embryonic chicken spinal cord and sensory ganglia was used to test the influence of ventral spinal cord and local cues within the dorsal spinal cord on the growing Ia afferents. When the ventral half of the spinal cord was replaced with an inverted duplicate dorsal half, Ia fibers entering through the dorsal columns still grew ventrally within the host dorsal horn. After the fibers entered the duplicate dorsal half, they continued growing in the same direction. With respect to the duplicate dorsal tissue, this was in an opposite, ventral-to-dorsal, direction. In both cases, however, Ia collaterals remained confined to the medial dorsal laminae. Restriction to these laminae was maintained even when the fibers had to change their direction of growth to stay within them. These results show that cues from the ventral cord are not required for the development of correct Ia projections within the dorsal horn. Local, rather than long-range directional, cues appear to determine the pattern of these projections. When the ventral half of the spinal cord was left intact but sensory axons were forced to enter the dorsal gray matter growing rostrally or caudally, their collateral axons grew in random directions, further showing the absence of directional cues even when the ventral cord was present. Taken together, these observations suggest that Ia fibers are guided by local positional cues that keep them confined to the medial gray matter within the dorsal horn, but their direction of growth is determined primarily by their orientation and position as they enter the dorsal gray matter.     

Met-enkephalin-Arg6-Phe7 in spinal cord and brain following traumatic injury to the spinal cord: influence of p-chlorophenylalanine. An experimental study in the rat using radioimmunoassay technique

The possibility that trauma to the dorsal horn may affect the release and distribution of enkephalin was examined using the opioid peptide Met-Enk-Arg6-Phe7 (MEAP) as a marker in a rat model. The peptide content of samples of spinal cord and whole brain was measured using a radioimmunoassay (RIA) technique. In addition, the possible functional relation between this peptide and serotonin was evaluated using a pharmacological approach that included depletion of endogenous serotonin. A focal trauma to the right dorsal horn in the T10-11 segments (2 mm deep and 5 mm long) markedly modified the content of MEAP of the adjacent rostral and caudal segments of the cord, as well as the content of MEAP of the brain. Depletion of serotonin with p-CPA (an inhibitor of the synthesis of serotonin) significantly elevated the content of MEAP in the whole brain without affecting the regions of the spinal cord (except T9 level which showed a 25% decrease from an intact control group). Trauma to the spinal cord in the serotonin-depleted animals did not alter the content of MEAP further, as compared to a p-CPA-treated but untraumatized group. These results indicate that enkephalin (i) participates in the pathophysiology of spinal cord trauma and (ii) suggest that the peptide is somehow functionally related with serotonin.     

Human and rat primary C-fibre afferents store and release secretoneurin, a novel neuropeptide

Secretoneurin is a recently discovered neuropeptide derived from secretogranin II (SgII). Since this peptide could be detected in the dorsal horn of the spinal cord we studied whether it is localized in and released from primary afferent neurons. Secretoneurin was investigated with immunocytochemistry and radioimmunoassay in spinal cord, dorsal root ganglia and peripheral organs. SgII mRNA was determined in dorsal root ganglia. Normal rats and rats pre-treated neonatally with capsaicin to destroy selectively polymodal nociceptive (C-) fibres were used. Slices of dorsal spinal cord were perfused in vitro for release experiments. Immunocytochemistry showed a distinct distribution of secretoneurin-immunoreactivity (IR) in the spinal cord and, lower brainstem. A particularly high density of fibres was found in lamina I and outer lamina II of the caudal trigeminal nucleus and of the spinal cord. This distribution was qualitatively identical in rat and human post-mortem tissue. Numerous small diameter and some large dorsal root ganglia neurons were found to contain SgII mRNA. Capsaicin treatment led to a marked depletion of secretoneurin-IR in the substantia gelatinosa, but not in other immunopositive areas of the spinal cord and to a substantial loss of small (< 25 microns) SgII-mRNA-containing dorsal root ganglia neurons. Radioimmunoassay revealed a significant decrease of secretoneurin-IR in the dorsal spinal cord, the trachea, heart and urinary bladder of capsaicin-treated rats. Perfusion of spinal cord slices with capsaicin as well as with 60 mM potassium led to a release of secretoneurin-IR. In conclusion, secretoneurin is a neuropeptide which is stored in and released from capsaicin-sensitive, primary afferent (C-fibre) neurons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetic properties and stereospecificity of the monomeric dUTPase from herpes simplex virus type 1

The heptadecapeptide orphanin FQ or nociceptin (OFQ/N), the endogenous ligand for the orphan opioid receptor, has a complex pharmacology in mice, eliciting either an anti-opioid/hyperalgesic action or analgesia depending upon the dose and testing paradigm. Unlike mice, orphanin FQ/nociceptin fails to elicit hyperalgesia in the rat following intracerebroventricular injection. Both OFQ/N and a truncated version, OFQ/N(1-11), produce a robust analgesic response. OFQ/N analgesia is readily antagonized by the opioid antagonists naloxone or diprenorphine, despite their very poor affinity for the cloned orphan opioid receptor. Antisense studies revealed that probes targeting the second and third coding exon of the orphan clone significantly attenuate OFQ/N analgesia, while the exon 1 probe was inactive. These results indicate that OFQ/N elicits a naloxone-sensitive analgesia in rats similar to that previously reported in mice.     

Functional interactions between spinal cord grafts suggest asymmetries dictated by graft maturity

Fetal spinal cord tissue grafts have been advocated as a possible repair strategy for spinal cord injury. In the present study, we used intraocular spinal cord grafts to model the interactions which may occur between fetal and adult spinal cord after making such a graft and to study to which extent functional connections can be expected to occur between the host and graft tissue. We first grafted fetal spinal cord to the anterior chamber of the eye where it was allowed to mature. A second piece of fetal spinal cord was then sequentially grafted in contact with the first graft. Electrophysiological recordings made from the older graft while electrically stimulating the younger graft provided evidence for an excitatory innervation from the younger spinal cord graft to the mature spinal cord which appeared to be glutamatergic. However, we only rarely found excitatory inputs from the first, mature spinal cord graft to the younger graft. Fiber connections between the two spinal cord grafts were verified by retrograde tracing and neurofilament immunohistochemistry. In no case was a trophic influence on graft volume observed between spinal cord grafts regardless of whether the transplantations were performed sequentially or at the same time. Even the introduction of a second graft to immature spinal cord tissue was ineffective. In contrast, we found a marked trophic, neuron-rescuing effect of spinal cord grafts upon cografts of fetal dorsal root ganglia. This latter observation is consistent with the hypothesis that spinal cord tissue can exert a trophic effect on developing sensory ganglia and demonstrates that many sensory neurons can survive in the presence of a central target and in the absence of the appropriate peripheral target. These intraocular experiments predict that fetal spinal cord grafted to the injured adult spinal cord may develop effective excitatory inputs with the host, while host-to-graft inputs may develop to a considerably smaller extent. Our results also suggest that the adult spinal cord does not exert marked trophic effects on growth of fetal spinal cord, while it does exert a trophic influence on central projections of dorsal root ganglia.     

Silent glutamatergic synapses and nociception in mammalian spinal cord

Neurons in the superficial dorsal horn of the spinal cord are important for conveying sensory information from the periphery to the central nervous system. Some synapses between primary afferent fibres and spinal dorsal horn neurons may be inefficient or silent. Ineffective sensory transmission could result from a small postsynaptic current that fails to depolarize the cell to threshold for an action potential or from a cell with a normal postsynaptic current but an increased threshold for action potentials. Here we show that some cells in the superficial dorsal horn of the lumbar spinal cord have silent synapses: they do not respond unless the holding potential is moved from -70 mV to +40 mV. Serotonin (5-hydroxytryptamine, 5-HT), an important neurotransmitter of the raphe-spinal projecting pathway, transforms silent glutamatergic synapses into functional ones. Therefore, transformation of silent glutamatergic synapses may serve as a cellular mechanism for central plasticity in the spinal cord.     

Down-regulation of mu-opioid receptors in rat and monkey dorsal root ganglion neurons and spinal cord after peripheral axotomy

To understand the role of opioids and their receptors in chronic pain following peripheral nerve injury, we have studied the mu-opioid receptor in rat and monkey lumbar 4 and 5 dorsal root ganglion neurons and the superficial dorsal horn of the spinal cord under normal circumstances and after peripheral axotomy. Our results show that many small neurons in rat and monkey dorsal root ganglia, and some medium-sized and large neurons in rat dorsal root ganglia, express mu-opioid receptor-like immunoreactivity. Most of these neurons contain calcitonin gene-related peptide. The mu-opioid receptor was closely associated with the somatic plasmalemma of the dorsal root ganglion neurons. Both mu-opioid receptor-immunoreactive nerve fibers and cell bodies were observed in lamina II of the dorsal horn. The highest intensity of mu-opioid receptor-like immunoreactivity was observed in the deep part of lamina II. Most mu-opioid receptor-like immunoreactivity in the dorsal horn originated from spinal neurons. A few mu-opioid receptor-positive peripheral afferent terminals in the rat and monkey dorsal horn were calcitonin gene-related peptide-immunoreactive. In addition to pre- and post-junctional receptors in rat and monkey dorsal horn neurons, mu-opioid receptors were localized on the presynaptic membrane of some synapses of primary afferent terminals in the monkey dorsal horn. Peripheral axotomy caused a reduction in the number and intensity of mu-opioid receptor-positive neurons in the rat and monkey dorsal root ganglia, and of mu-opioid receptor-like immunoreactivity in the dorsal horn of the spinal cord. The decrease in mu-opioid receptor-like immunoreactivity was more pronounced in the monkey than in the rat dorsal root ganglia and spinal cord. It is probable that there was a parallel trans-synaptic down-regulation of mu-opioid-like immunoreactivity in local dorsal horn neurons of the monkey. These data suggest that one factor underlying the well known insensitivity of neuropathic pain to opioid analgesics could be due to a marked reduction in the number of mu-opioid receptors in the axotomized sensory neurons and in interneurons in the dorsal horn of the spinal cord.     

Human dorsal root ganglion neurons from embryonic donors extend axons into the host rat spinal cord along laminin-rich peripheral surroundings of the dorsal root transitional zone

Following dorsal root crush, the lesioned axons regenerate in the peripheral compartment of the dorsal root, but stop at the boundary between the peripheral and the central nervous system, the dorsal root transitional zone. We have previously shown that fibres from human fetal dorsal root ganglia grafted to adult rat hosts are able to grow into the spinal cord, but were not able to specify the route taken by the ingrowing fibres. In this study we have challenged the dorsal root transitional zone astrocyte boundary with human dorsal root ganglion transplants from 5-8-week-old embryos. By tracing immunolabelled human fibres in serial sections, we found that fibres consistently grow around the dorsal root transitional zone astrocytes in laminin-rich peripheral surroundings, and extend into the host rat spinal cord along blood vessels, either into deep or superficial laminae of the dorsal horn, or into the dorsal funiculus. Human fibres that did not have access to blood vessels grew on the spinal cord surface. These findings indicate, that in spite of a substantial growth capacity by axons from human embryonic dorsal root ganglion cells as well as their tolerance to non-permissive factors in the mature mammalian CNS, these axons are still sensitive to the repellent effects of astrocytes of the mature dorsal root transitional zone. Furthermore, this axonal ingrowth is consistently associated with laminin-expressing structures until the axons reach the host spinal cord.     

A role for mitogen-activated protein kinase in the spindle assembly checkpoint in XTC cells

A prominent role for phagocytic cells in the regenerative response to CNS or PNS injury has been suggested by numerous studies. In the present work we tested whether increasing the presence of phagocytic cells at a spinal cord injury site could enhance the regeneration of sensory axons from cut dorsal roots. Nitrocellulose membranes treated with TGF-beta or coated with microglial cells were cotransplanted with fetal spinal cord tissue into an injured adult rat spinal cord. Cut dorsal roots were apposed to both sides of the nitrocellulose. Four weeks later, animals were sacrificed and spinal cord tissue sections were processed for immunocytochemical detection of calcitonin gene-related peptide (CGRP-ir) to identify regenerated sensory axons. Adjacent sections were processed with the antibody ED-1 or the lectin GSA-B4 for detection of macrophage/microglial cells in association with the regrowing axons. Qualitative and quantitative data indicate a correlation between the pattern and extent of axonal regeneration and the presence of phagocytic cells along the nitrocellulose implant. Axonal regeneration could be experimentally limited by implanting a nitrocellulose strip treated with macrophage inhibitory factor. These results indicate that increasing the presence of activated macrophage/microglial cells at a spinal cord injury site can provide an environment beneficial to the promotion of regeneration of sensory axons, possibly by the release of cytokines and interaction with other nonneuronal cells in the immediate vicinity.     

Partial and complete sciatic nerve injuries induce similar increases of neuropeptide Y and vasoactive intestinal peptide immunoreactivities in primary sensory neurons and their central projections

Partial nerve injury is more likely to cause neuropathic pain than complete nerve injury. We have compared the changes in neuropeptide expression in primary sensory neurons which follow complete and partial injuries to determine if these might be involved. Since more neurons are damaged by complete injury, we expected that complete sciatic nerve injury would simply cause greater increases in neuropeptide Y and vasoactive intestinal peptide than partial injury. We examined neuropeptide Y and vasoactive intestinal peptide immunoreactivities in L4 and L5 dorsal root ganglia, the dorsal horn of L4-L5 spinal cord, and the gracile nuclei of rats killed 14 days after unilateral complete sciatic nerve transection, partial sciatic nerve transection and chronic constriction injury of the sciatic nerves. In all three groups of rats, neuropeptide Y- and vasoactive intestinal peptide-immunoreactive neurons were increased in the ipsilateral L4 and L5 dorsal root ganglion when compared with the contralateral side. Most neuropeptide Y-immunoreactive neurons were of medium and large size, but a few were small. Neuropeptide Y-immunoreactive axonal fibers were increased from laminae I to IV, and vasoactive intestinal peptide-immunoreactive axonal fibers were increased in laminae I and II, of the ipsilateral dorsal horn of L4-L5 spinal cord. The increases of neuropeptide Y and vasoactive intestinal peptide immunoreactivities in the dorsal horn were similar among the three groups. However, only after constriction injury were some vasoactive intestinal peptide-immunoreactive neurons seen in the deeper laminae of the ipsilateral dorsal horn. Robust neuropeptide Y-immunoreactive axonal fibers and some neuropeptide Y-immunoreactive cells were seen in the ipsilateral gracile nuclei of all three groups of animals, but neuropeptide Y-immunoreactive cells were more prominent after constriction injury. Contrary to our expectations, partial and complete sciatic nerve injuries induced similar increases in neuropeptide Y and vasoactive intestinal peptide in lumbar dorsal root ganglion neurons and their central projections in the dorsal horn and the gracile nuclei two weeks after injury. Some neurons whose axons were spared by partial injury may also increase neuropeptide Y or vasoactive intestinal peptide expression. Altered neuropeptide release from these functional sensory neurons may play a role in neuropathic pain.