Effects of sciatic nerve resection on L7 spinal roots and dorsal root ganglia in adult cats

The size, distribution, and number of nerve fibers and neuronal perikarya in the L7 spinal roots and ganglia of adult cats were examined 35, 90, and 190 days after ipsilateral sciatic nerve resection. With increasing survival time the size spectra of myelinated ventral root nerve fibers showed a progressive flattening of the alpha peak. In the dorsal roots the myelinated fiber size distribution exhibited a marked shift toward smaller sizes. The reduction in the proportion of large myelinated axons was particularly evident in the dorsal roots. Less clearcut changes were found in the size distribution of spinal ganglion neuronal perikarya. No significant loss of axons could be detected in ventral or dorsal roots. There was, however, a marked reduction in the number of dorsal root ganglion neurons. This discrepancy suggested the possibility that an initial loss of dorsal root axons was concealed by recurrent sprouting of axons from the proximal nerve stump. However, neuroma excision 90 days after nerve resection did not lead to any reduction in dorsal root axon numbers. Thus, any ingrowth of new axons to the dorsal root should occur from levels proximal to the neuroma. In comparison with previous findings in kittens, peripheral nerve resection in adult cats had significantly smaller effects on sizes and numbers of spinal root nerve fibers as well as of dorsal root ganglion neurons. Therefore, the potential for restitution of the peripheral innervation by axon regeneration appeared to be basically greater in mature than in immature animals.     

Structural changes in kittens' ventral and dorsal roots L7 after early postnatal sciatic nerve transection

The number and size distribution of myelinated and unmyelinated axons were studied in spinal roots L7 of 19 kittens, 8 to 200 days after early postnatal left sciatic nerve transection. Ventral and dorsal roots on the side of transection were compared with corresponding contralateral roots. Three normal kittens were used as additional controls. On the control side the proportion of unmyelinated ventral root axons increased from about 15 to 30% between 3 and 7 months postnatally. In the ventral roots on the lesion side there was a loss of myelinated axons of all sizes (total loss 15 to 25%). The loss seemed to be somewhat greater in the gamma population. The number of unmyelinated ventral root axons increased markedly through sprouting. This increase was similar at different root levels. The persistence of such axonal sprouts in the proximal stump after ventral root division in one kitten indicated that they originate proximally in the ventral root or within the central nervous system. The dorsal roots on the lesion side showed a 30% deficit of both myelinated and unmyelinated axons. Signs of axonal sprouting were not observed. Both in ventral and dorsal roots the size spectra of myelinated axons were markedly shifted to the left on the lesion side due to a growth retardation of larger axons. With respect to the unmyelinated axons the size distribution was expanded toward larger sizes in the ventral roots and remained largely unaltered in the dorsal roots.     

Retrograde and transganglionic degeneration of sensory neurons after a peripheral nerve lesion at birth

The sciatic nerve of newborn rats (less than or equal to 16 h old) was crushed with a watchmaker forceps. During the first 4 weeks after the injury, examination of ipsilateral L4 through L6 dorsal root ganglia, their dorsal nerve roots, and the dorsal funiculus revealed the presence of degenerating myelin and axons. Chromatolysis was not observed. In the spinal cord, the degenerating argyrophilia was restricted to the medial part of the dorsal funiculus (fasciculus gracilis). This is interpreted as transganglionic degeneration of the central processes of the pseudounipolar cells. Twelve weeks after nerve crush, there was a noticeable reduction in the size of the leg, foot, and muscles innervated by the sciatic nerve as well as a substantial loss (P less than 0.001) of neurons and myelinated axons in ipsilateral spinal ganglia and their dorsal nerve roots. The reduction was most prominent among the larger sensory neurons (greater than 40 microns) and the larger myelinated axons. A total loss of about 60% of sensory neurons was found in the L4 through L6 spinal ganglia. About 58 and 64% of the myelinated axons were lost in L4 and L5 dorsal roots, respectively. The remaining perikarya and dorsal root axons were hypoplastic.     

Noninactivating,tetrodotoxin-sensitive Na+ conductance in peripheral axons

A noninactivating, persistent sodium current has been demonstrated previously in dorsal root ganglia neurons and in rat optic nerve. We report here that Na(+) channel blockade with tetrodotoxin (TTX) in isolated dorsal and ventral roots elicits membrane hyperpolarization, suggesting the presence of a persistent Na(+) current in peripheral axons. We used a modified sucrose-gap chamber to monitor resting and action potentials and observed a hyperpolarizing shift in the nerve potential of rat dorsal and ventral roots by TTX. The block of transient inward Na(+) currents was confirmed by the abolition of compound action potentials (CAPs). Moreover, depolarization of nerve roots by elevating extracellular K(+) concentrations to 40 mM eliminated CAPs but did not significantly alter TTX-induced hyperpolarizations, indicating that the persistent Na(+) currents in nerve roots are not voltage-dependent. Tetrodotoxin-sensitive persistent inward Na(+) currents are present in both dorsal and ventral root axons at rest and may contribute to axonal excitability.     

Hypoglycaemic neuropathy in diabetic BB/Wor rats treated with insulin implants affects ventral root axons but not dorsal root axons

It is believed that hyperglycaemia underlies diabetic neuropathy. However, low blood glucose values may also cause pathological changes in peripheral nerves and in neuronal perikarya. This study examined spinal roots, dorsal root ganglia and the ventral horn at the segmental level L5 in long-term insulin-treated eu-/hypoglycaemic diabetic rats with an obvious plantar nerve pathology. The purpose was to determine whether hypoglycaemic neuropathy affects sensory and/or motor neurons at root and/or perikaryal levels. Electron microscopic examination of dorsal roots from eu-/hypoglycaemic rats showed a normal qualitative morphology and normal numbers of unmyelinated and myelinated axons. In ventral roots the picture varied. Whereas two rats exhibited an essentially normal morphology, three rats presented moderate or marked signs of pathology such as clusters of small and medium-sized myelinated axons, medium-sized myelinated axons with abnormally thin sheaths, large unmyelinated axons and signs of past or ongoing axonal degeneration. Light microscopic examination of the L5 dorsal root ganglion and ventral horn showed a qualitatively normal picture in eu-/hypoglycaemic rats and the mean number of large ventral horn neurons per section was normal. These results suggest that the type of eu-/hypoglycaemia examined here affects ventral root axons but not dorsal root axons, that the degree of ventral root pathology is variable and that sensory and motor neuron perikarya do not appear to be affected. Received: 22 October 1999 / Revised, accepted: 4 January 2000     

Carbonic anhydrase activity in the normal and injured peripheral nervous system of the rat

The carbonic anhydrase reactivity of primary neurons and axons of the L4 and L5 lumbar levels was studied in rats before and after various surgical procedures including transection of the spinal cord, removal of dorsal root ganglia, and transection of ventral or dorsal roots or spinal nerves. In normal animals, carbonic anhydrase reactivity was confined to large and medium size neurons of the dorsal root ganglia, and was also present in a sizeable percentage of cells scattered throughout the thoracolumbar sympathetic chain and in the celiac ganglion. At root level, enzymatic staining could be detected in 48.7% of the dorsal root myelinated axons of most sizes, whereas in ventral roots, it was restricted to small myelinated axons, in a proportion much higher at the L4 than in the L5 level. Spinal motoneurons remained unlabeled, despite procedures aimed at increasing the somal concentration of carbonic anhydrase, such as ventral root ligation and blocking of the fast or slow axoplasmic transport using colchicine or iminodiproprionitrile. However, it is likely that reactive ventral root axons originate from neurons situated segmentally in the spinal cord, and do not constitute aberrant sensory fibers, as carbonic anhydrase activity remained unchanged in the L4 and L5 ventral roots after removal of the corresponding spinal ganglia, whereas it disappeared after damage to the spinal cord at the lumbar level, or at a site distal to a ventral root section. Enzymatic staining of neurons of the dorsal root ganglia was not modified by a dorsal rhizotomy, but showed a marked decrease after transection of the spinal nerve.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nerve growth factor receptor immunoreactivity in the neuronal perikarya of human sensory and sympathetic nerve ganglia

We examined immunohistochemically the dorsal root ganglia, sympathetic ganglia, spinal cord, ventral and dorsal roots, and sciatic nerves obtained at autopsy from adult humans, using a monoclonal antibody against the human nerve growth factor receptor. We observed labelling in a granular pattern in the neuronal perikarya of dorsal root and sympathetic nerve ganglia. Ventral horn cells and axons were not labelled.     

Effect of sciatic neurectomy on neuronal number and size distribution in the L7 ganglion of kittens

The number and size distribution of neurons in the L7 dorsal root ganglia were studied bilaterally 80 and 200 days after left-side sciatic nerve transection in kittens aged 1 week. The results show that about one-third to half of the neurons were lost on the operated side. Size spectra of surviving neurons showed a marked shift toward smaller sizes, most probably due to a combination of cell loss and atrophy or growth retardation of surviving neurons. The proportion of cells with intermediate sizes seemed to be increased, but the proportion of small cells was essentially unaltered. Both on the experimental and control sides the number of dorsal root axons exceeded the number of neurons. The absolute neuronal and dorsal root axon loss showed good agreement, but the proportion of lost neurons was larger than the relative decrease in dorsal root axon number. These results indicate that peripheral nerve transection results in a substantial loss of neurons in immature spinal ganglia, with no preference for a particular size class.     

Functional connections are established in the deafferented rat spinal cord by peripherally transplanted human embryonic sensory neurons

Functionally useful repair of the mature spinal cord following injury requires axon growth and the re-establishment of specific synaptic connections. We have shown previously that axons from peripherally grafted human embryonic dorsal root ganglion cells grow for long distances in adult host rat dorsal roots, traverse the interface between the peripheral and central nervous system, and enter the spinal cord to arborize in the dorsal horn. Here we show that these transplants mediate synaptic activity in the host spinal cord. Dorsal root ganglia from human embryonic donors were transplanted in place of native adult rat ganglia. Two to three months after transplantation the recipient rats were examined anatomically and physiologically. Human fibres labelled with a human-specific axon marker were distributed in superficial as well as deep laminae of the recipient rat spinal cord. About 36% of the grafted neurons were double labelled following injections of the fluorescent tracers MiniRuby into the sciatic and Fluoro-Gold into the lower lumbar spinal cord, indicating that some of the grafted neurons had grown processes into the spinal cord as well as towards the denervated peripheral targets. Electrophysiological recordings demonstrated that the transplanted human dorsal roots conducted impulses that evoked postsynaptic activity in dorsal horn neurons and polysynaptic reflexes in ipsilateral ventral roots. The time course of the synaptic activation indicated that the human fibres were non-myelinated or thinly myelinated. Our findings show that growing human sensory nerve fibres which enter the adult deafferentated rat spinal cord become anatomically and physiologically integrated into functional spinal circuits.     

α‐Synuclein pathology in the cranial and spinal nerves in Lewy body disease

Accumulation of phosphorylated α‐synuclein in neurons and glial cells is a histological hallmark of Lewy body disease (LBD) and multiple system atrophy (MSA). Recently, filamentous aggregations of phosphorylated α‐synuclein have been reported in the cytoplasm of Schwann cells, but not in axons, in the peripheral nervous system in MSA, mainly in the cranial and spinal nerve roots. Here we conducted an immunohistochemical investigation of the cranial and spinal nerves and dorsal root ganglia of patients with LBD. Lewy axons were found in the oculomotor, trigeminal and glossopharyngeal‐vagus nerves, but not in the hypoglossal nerve. The glossopharyngeal‐vagus nerves were most frequently affected, with involvement in all of 20 subjects. In the spinal nerve roots, Lewy axons were found in all of the cases examined. Lewy axons in the anterior nerves were more frequent and numerous in the thoracic and sacral segments than in the cervical and lumbar segments. On the other hand, axonal lesions in the posterior spinal nerve roots appeared to increase along a cervical‐to‐sacral gradient. Although Schwann cell cytoplasmic inclusions were found in the spinal nerves, they were only minimal. In the dorsal root ganglia, axonal lesions were seldom evident. These findings indicate that α‐synuclein pathology in the peripheral nerves is axonal‐predominant in LBD, whereas it is restricted to glial cells in MSA.     

Distribution of carbonic anhydrase activity in neurons of the rat

Certain neurons of dorsal root ganglia (DRG) and some fibers of the sciatic nerve contain histochemically demonstrable carbonic anhydrase activity. Since the distribution of this enzyme throughout the nervous system has not yet been evaluated systematically, we conducted a comprehensive histochemical survey focusing particularly on structures derived from the neural crest and nonneural crest ectoderm. In the peripheral nervous system, we observed carbonic anhydrase activity in some, but not all, neurons of dorsal root, trigeminal, celiac, and myenteric ganglia as well as in glial cells throughout the CNS. Some neurons of the nodose ganglion also showed carbonic anhydrase activity. In all first order sensory ganglia that were studied, the enzyme was found only in large (50 micron or above) and medium (20-50 micron) size neurons; in the case of spinal ganglia, the reactive neurons constituted approximately 30% of the total neuronal population. Of these reactive neurons, 56% were heavily stained and 44% were moderately stained. Several possible roles for neuronal carbonic anhydrase are considered.     

Cholecystokinin in Mammalian Primary Sensory Neurons and Spinal Cord: In Situ Hybridization Studies in Rat and Monkey

The peptide cholecystokinin (CCK) has been suggested to be involved in nociception, but its exact localization at the level of the spinal cord and in spinal ganglia has been a controversial issue. Therefore the distribution of messenger RNA (mRNA) for CCK was studied by in situ hybridization using oligonucleotide probes on sections of adult rat lumbar dorsal root ganglia following unilateral section of the sciatic nerve and on sections of untreated monkey trigeminal ganglia, spinal cord and spinal ganglia from all levels. For comparison, calcitonin gene-related peptide (CGRP) mRNA was also studied in the monkey tissue using the same techniques. Peripheral sectioning of the sciatic nerve in the rat resulted in the appearance of detectable CCK mRNA in up to 30% of remaining ipsilateral L4 and L5 dorsal root ganglion neurons 3 weeks after surgery, with a distinct but more limited appearance also in the contralateral ganglia. No cells, or only single cells, could be seen in normal control rat ganglia. In contrast, in the normal monkey, ∼20% of dorsal root ganglion neurons, regardless of spinal level, and 10% of trigeminal ganglia neurons expressed mRNA for CCK. CGRP mRNA was expressed at detectable levels in ∼80% of these monkey dorsal root ganglion neurons. In the monkey spinal cord, CCK mRNA was detected in the dorsal horn and in motoneurons, whereas CGRP mRNA was only seen in motoneurons. The present results suggest that CCK peptides can be involved in sensory processing in the dorsal horn of the spinal cord in normal monkeys and in rats after peripheral nerve injury, adding one more possible excitatory peptide to the group of mediators in the dorsal horn.     

Neuronal and glial expression of the adhesion molecule TAG-1 is regulated after peripheral nerve lesion or central neurodegeneration of adult nervous system

Expression of the cell adhesion molecule TAG-1 is down-regulated in adult brain, with the exception of certain areas exhibiting structural plasticity. Here, we present evidence that TAG-1 expression persists also in adult rat spinal cord and dorsal root ganglia (DRG), and can be up-regulated after injury. On Western blots of adult tissue, TAG-1 is detected as a 135-kDa band, with an additional specific 90-kDa band, not present in developing tissue. TAG-1 expression is found both in DRG neurons and in Schwann cells, particularly those associated with the peripherally projecting DRG processes. Quantitative in situ hybridization revealed that TAG-1 expression is significantly higher in small neurons that give rise to unmyelinated fibers, than in large DRG neurons. The regulation of TAG-1 was then examined in two different lesion paradigms. After a sciatic nerve lesion, TAG-1 expression is not up-regulated in DRG neurons, but decreases with time. At the lesion site, reactive Schwann cells up-regulate TAG-1, as demonstrated by both immunohistochemistry and in situ hybridization. In a second paradigm, we injected kainic acid into the spinal cord that kills neurons but spares glia and axons. TAG-1 is up-regulated in the spinal neuron-depleted area as well as in the corresponding dorsal and ventral roots, associated with both target-deprived afferent fibers and with the non-neuronal cells that invade the lesion site. These results demonstrate a local up-regulation of TAG-1 in the adult that is induced in response to injury, suggesting its involvement in axonal re-modelling, neuron-glia interactions, and glial cell migration.     

Selective degeneration of dorsal root ganglia and dorsal nerve roots in methyl mercury-intoxicated rats: a stereological study

The components of the nervous system of rats that are most critically affected by methyl mercury are still a matter of debate. A recent stereological study of rats with typical symptoms resulting from methyl mercury intoxication demonstrated that the morphology of cerebellar granule cells and Purkinje cells were unchanged at the light microscopic level, even though there was pronounced degeneration of myelinated axons in dorsal nerve root nerves. In the present study, unbiased stereological methods were used to quantify morphological changes in the dorsal root ganglion, and dorsal and ventral nerve roots of the rats used in the previous study. The rats were treated with methyl mercury (2 mg daily/kg, per os) for a 19-day period that was followed by a 32-day period without treatment. The means of the total numbers of A-cell and B-cell perikarya in the dorsal root ganglion of the intoxicated rats were reduced by 60% and 24%, respectively. The mean volume of A-cell perikarya in rats of the experimental group was reduced by 22%, whereas the mean volume of B-cell perikarya was the same in the two groups. In the experimental group, the total number of myelinated axons in the dorsal nerve roots was reduced by 60%, whereas no difference was found in the ventral nerve roots. The areas of axon and myelin sheath, dorsal and ventral nerve roots were not affected. This study demonstrates that extensive loss of dorsal root ganglion cells and myelinated axons in dorsal nerve roots precedes light microscopical changes in the ventral nerve roots and the cerebellum of rats intoxicated with methyl mercury. Received: 16 January 1998 / Revised, accepted: 23 February 1998     

The Microtubular Pattern Changes at the Spinal Cord-Root Junction and Reverts at the Root-Peripheral Nerve Junction in Sensory and Motor Fibres of the Rat

In the rat, we studied the microtubular content of central nervous system (CNS) axons (pyramidal tract, dorsal funiculus, and intracord domain of motor axons), of radicular axons (ventral and dorsal roots), and of peripheral axons (sural and lateral gastrocnemius nerves). The microtubular density had an inverse relationship with the size of the axon. Within the CNS, values ranged from over 120 microtubules/microm2 for axons smaller than 0.1 microm2 of the pyramidal tract and dorsal funiculus to 24 for 3-microm motor axons (area, 7 microm2) in their spinal cord domain. Peripheral nerve and CNS axons of the same size had comparable microtubular densities. In contrast, the microtubular density of dorsal and ventral root axons was one half that of CNS or peripheral nerve axons of equal calibre. Considered along the axon, the microtubular density of motor and sensory fibres is high in the CNS domain, low in the root, and high again in the peripheral nerve domain. These observations are inconsistent with the notion that the cytoskeleton moves coherently away from the perikaryon. We conclude that the axonal microtubular content accords with the calibre of the fibre and with the anatomical region where it courses. We propose that axonal microtubules are regulated by local cues.     

Time course analysis of sensory axon regeneration in vivo by directly tracing regenerating axons

Most current studies quantify axon regeneration by immunostaining regeneration-associated proteins,representing indirect measurement of axon lengths from both sensory neurons in the dorsal root ganglia and motor neurons in the spinal cord.Our recently developed method of in vivo electroporation of plasmid DNA encoding for enhanced green fluorescent protein into adult sensory neurons in the dorsal root ganglia provides a way to directly and specifically measure regenerating sensory axon lengths in whole-mount nerves.A mouse model of sciatic nerve compression was established by squeezing the sciatic nerve with tweezers.Plasmid DNA carrying enhanced green fluorescent protein was transfected by ipsilateral dorsal root ganglion electroporation 2 or 3 days before injury.Fluorescence distribution of dorsal root or sciatic nerve was observed by confocal microscopy.At 12 and 18 hours,and 1,2,3,4,5,and 6 days of injury,lengths of regenerated axons after sciatic nerve compression were measured using green fluorescence images.Apoptosis-related protein caspase-3 expression in dorsal root ganglia was determined by western blot assay.We found that in vivo electroporation did not affect caspase-3 expression in dorsal root ganglia.Dorsal root ganglia and sciatic nerves were successfully removed and subjected to a rapid tissue clearing technique.Neuronal soma in dorsal root ganglia expressing enhanced green fluorescent protein or fluorescent dye-labeled microRNAs were imaged after tissue clearing.The results facilitate direct time course analysis of peripheral nerve axon regeneration.This study was approved by the Institutional Animal Care and Use Committee of Guilin Medical University,China(approval No.GLMC201503010)on March 7,2014.     

Characterization of forms of immunoreactive somatostatin in sensory neuron and normal and deafferented spinal cord

In order to determine the contribution made by primary sensory afferents and supraspinal projections to the immunoreactive somatostatin (IRS) content of the spinal cord, measurements were made of the concentration of IRS in the dorsal and ventral halves of the cord in cats subjected to unilateral lumbosacral dorsal rhizotomy (L1-S3) alone or combined with spinal cord transection. The molecular forms of IRS (characterized by gel chromatography) in L7 lumbar spinal cord, L6-S1 dorsal roots, ventral roots and dorsal root ganglia, and sciatic nerve were also determined. S14 was the predominant form in all tissues examined, but two additional molecular forms corresponding to S28 and S11.5 kdalton were present in dorsal root ganglia and spinal cord; S28 but not S11.5 kdalton was detected in both dorsal roots and sciatic nerves. These results indicate that S14 and S28 and S28 are transported along the central and peripheral processes of dorsal root ganglia, but that spinal cord S11.5 kdalton originates in the central nervous system. IRS in the dorsal horn was reduced by ca. 40% following dorsal root section. Neither disruption of descending pathways by spinal transection nor surgical isolation of the lumbar segements lowered cord somatostatin content below that produced by dorsal root section, indicating that most of the somatostatin within the cord arises from the dorsal root and from neurons in local spinal segments. Although the total content of IRS in the dorsal horn was reduced by ca. 40% following dorsal rhizotomy, the pattern of molecular forms was not changed accordingly. Since S14 and S28 but not S11.5 kdalton are transported via the dorsal root, the dorsal root section would be predicted to produce a relatively greater decrease in S14 and S28 than in S11.5 kdalton. Therefore, failure to find a selective loss of S14 and S28 suggests that dorsal rhizotomy affects dorsal horn IRS content not only by removing afferent input but possibly also by modifyinh the processing of IRS by the remaining somatostatinergic neurons.     

Large Calibre Primary Afferent Neurons Projecting to the Gracile Nucleus Express Neuropeptide Y after Sciatic Nerve Lesions: an Immunohistochemical and In Situ Hybridization Study in Rats

Using immunohistochemistry and in situ hybridization, we studied changes in expression of some neuropeptides in large and medium-sized neurons in lumbar 4 and 5 rat dorsal root ganglia projecting to the gracile nucleus, in response to peripheral axotomy. Fourteen days after unilateral sciatic nerve transection, many large neurons and some medium-sized neurons in ipsilateral dorsal root ganglia were strongly neuropeptide Y-positive. Galanin-, vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-like immunoreactivities coexisted with neuropeptide Y-like immunoreactivity in some of these neurons. After axotomy numerous large and medium-sized cells contained neuropeptide Y mRNA in the ipsilateral ganglia, whereas no hybridization was seen in the contralateral or control ganglia. Cross-sectioned, large neuropeptide Y-positive fibres were observed in a somatotopically appropriate zone within the ipsilateral gracile fasciculus. A dense network of neuropeptide Y-immunoreactive, large nerve fibres and terminals was seen in the ipsilateral gracile nucleus. A small number of galanin- and VIP/PHI-like immunoreactive nerve fibres and terminals were also observed in adjacent sections. Neuropeptide Y-like immunoreactivity colocalized with galanin- or VIP/PHI-like immunoreactivity in some nerve fibres. None of these neuropeptide immunoreactivities could be detected in nerve fibres and terminals in the control or contralateral gracile nucleus. These findings suggest that neuropeptides, in addition to their role in small dorsal root ganglion neurons, may have a function in large and medium-sized dorsal root ganglion neurons projecting to laminae III and IV in the dorsal horn as well as to the gracile nuclei, as a part of their response to peripheral axotomy.     

The distribution and origin of a novel brain peptide, neuropeptide Y, in the spinal cord of several mammals

The distribution of neuropeptide Y [NPY]-immunoreactive material was examined in the spinal cord and dorsal root ganglia of rat, guinea-pig, cat, marmoset, and horse. Considerable concentrations of NPY and similar distribution patterns of immunoreactive nerve fibres were found in the spinal cord of all species investigated. The dorsal root ganglia of the cat and the horse contained numerous immunoreactive nerve fibres, but in these species, as in the other three studied [rat, guinea-pig, marmoset], no positively stained cell bodies were found. Neuropeptide Y-immunoreactive nerves were observed at all levels of the spinal cord, being most concentrated in the dorsal horn. In the rat, guinea-pig, and marmoset, there was a marked increase of NPY-immunoreactive fibres in the lumbosacral regions of the spinal cord, and this was reflected by a considerable increase of extractable NPY. Estimations of NPY-immunoreactive material in the various regions of the rat spinal cord were as follows: cervical, 13.8 +/- 1.0; thoracic, 21.1 +/- 2.5; lumbar, 16.3 +/- 2.9; sacral, 92.4 +/- 8.5 pmol/gm wet weight of tissue +/- SEM. In the ventral portion of the guinea-pig spinal cord they were as follows: cervical, 7.1 +/- 1.2; thoracic, 8.2 +/- 3.6; lumbar, 22.6 +/- 7.0; sacral, 36.7 +/- 9.5 pmol/gm wet weight of tissue +/- SEM. Analysis of spinal cord extracts by reverse phase high performance liquid chromatography [HPLC] demonstrated that NPY-immunoreactive material elutes in the position of pure NPY standard. No changes in the concentration and distribution of the NPY-like material in the rat spinal cord were observed following a variety of surgical and pharmacological manipulations, including cervical rhizotomy, sciatic nerve section and ligation, and local application of capsaicin [50 mM] to one sciatic nerve. It is therefore suggested that most of the NPY-immunoreactive material in the spinal cord is derived either from intrinsic nerve cell bodies or from supraspinal tracts.