The response of rat spinal cord cells to unmyelinated afferents after peripheral nerve section and after changes in substance P levels

The histology, physiology, neurochemistry and circuitry of the substantia gelatinosa Rolandi (lamina II) in mammalian spinal cord

The substantia gelatinosa Rolandi (SGR) was first described about two centuries ago. In the following decades an enormous amount of information has permitted us to understand - at least in part - its role in the initial processing of pain and itch. Here, I will first provide a comprehensive picture of the histology, physiology, and neurochemistry of the normal SGR. Then, I will analytically discuss the SGR circuits that have been directly demonstrated or deductively envisaged in the course of the intensive research on this area of the spinal cord, with particular emphasis on the pathways connecting the primary afferent fibers and the intrinsic neurons. The perspective existence of neurochemically-defined sets of primary afferent neurons giving rise to these circuits will be also discussed, with the proposition that a cross-talk between different subsets of peptidergic fibers may be the structural and functional substrate of additional gating mechanisms in SGR. Finally, I highlight the role played by slow acting high molecular weight modulators in these gating mechanisms.

Development of a duration threshold for modulating evoked neuronal responses after nerve root compression injury

Cervical nerve roots are susceptible to compression injuries of various durations. The duration of an applied compression has been shown to contribute to both the onset of persistent pain and also the degree of spinal cellular and molecular responses related to nociception. This study investigated the relationship between peripherally-evoked activity in spinal cord neurons during a root compression and the resulting development of axonal damage. Electrically-evoked spikes were measured in the spinal cord as a function of time during and after (post-compression) a 15 minute compression of the C7 nerve root. Compression to the root significantly (p=0.035) reduced the number of spikes that were evoked over time relative to sham. The critical time for compression to maximally reduce evoked spikes was 6.6±3.0 minutes. A second study measured the post- compression evoked neuronal activity following compression applied for a shorter, sub-threshold time (three minutes). Ten minutes after compression was removed, the discharge rate remained significantly (p=0.018) less than baseline by 58±25% relative to sham after the 15 minute compression, but returned to within 3±33% of baseline after the three minute compression. Axonal damage was evident in the nerve root at day seven after nerve root compression only after a 15 minute compression. These studies demonstrate that even a transient mechanical insult to the nerve root is sufficient to induce sustained neuronal dysfunction and axonal pathology associated with pain, and results provide support that such minor neural tissue traumas can actually induce long-lasting functional deficits.

If substance P fails to fulfil the criteria as a neurotransmitter in somatosensory afferents, what might be its function?

In the first part of this paper, a series of examples are described where substance P content of afferent C fibres and responses which have been attributed to C fibre excitation vary independently. Thirteen sets of data fail to support the proposal that SP is an excitatory transmitter for noxious inputs. In the second part an alternative hypothesis is proposed in which C fibres would have functions in addition to impulse propagation. It is shown that C fibres are involved in establishing and maintaining the connection between afferent fibres and central cells and that transport mechanisms play a role in this connectivity control. Therefore it is proposed that the chemicals in C fibres should be examined for their possible action on regulatory mechanisms as well as for neurotransmitter action.

Neural plasticity after peripheral nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory and autonomic functions conveyed by the lesioned nerves to the denervated segments of the body, due to the interruption of axons continuity, degeneration of nerve fibers distal to the lesion and eventual death of axotomized neurons. Injuries to the peripheral nervous system may thus result in considerable disability. After axotomy, neuronal phenotype switches from a transmitter to a regenerative state, inducing the down- and up-regulation of numerous cellular components as well as the synthesis de novo of some molecules normally not expressed in adult neurons. These changes in gene expression activate and regulate the pathways responsible for neuronal survival and axonal regeneration. Functional deficits caused by nerve injuries can be compensated by three neural mechanisms: the reinnervation of denervated targets by regeneration of injured axons, the reinnervation by collateral branching of undamaged axons, and the remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of specificity in target reinnervation; plasticity in human has, however, limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain, hyperreflexia and dystonia. Recent research has uncovered that peripheral nerve injuries induce a concurrent cascade of events, at the systemic, cellular and molecular levels, initiated by the nerve injury and progressing throughout plastic changes at the spinal cord, brainstem relay nuclei, thalamus and brain cortex. Mechanisms for these changes are ubiquitous in central substrates and include neurochemical changes, functional alterations of excitatory and inhibitory connections, atrophy and degeneration of normal substrates, sprouting of new connections, and reorganization of somatosensory and motor maps. An important direction for ongoing research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, but are also able to modulate central nervous system reorganization, amplifying those positive adaptive changes that help to improve functional recovery but also diminishing undesirable consequences.

Selectivity of the central control of sensory information in the mammalian spinal cord

Afferent feedback from muscle proprioceptors, as well as movement-induced activation of skin receptors plays an important role in the patterning of motor activity for stepping and postural control. An important component in this control is the presynaptic GABAergic modulation of the synaptic effectiveness of muscle and cutaneous afferents, known to change in phase with the locomotor cycle, during the execution of voluntary movements, or after a peripheral nerve injury. Recent electrophysiological studies, together with ultrastructural observations, indicate that the distribution of GABAa synapses in the intraspinal arborizations of muscle spindle and tendon organ afferents is not homogeneous. Namely, that some collaterals are the targets of one, or more, GABAergic interneurones, while other collaterals of the same fibre receive no GABAergic connections. In addition, both PAD and inhibition of PAD have a local character. This allows, at least in principle, decoupling the information arising from common sensory inputs. A spatially restricted modulation of PAD could play a significant role in the adjustment of the synaptic effectiveness of Ia afferents at the onset of voluntary contractions in humans, during movement-induced stimulation of the skin, or during the compensation of motor activity following partial denervation of muscles. Changes in the synchronization of the PAD-mediating interneurones can also have a profound effect on the information transmitted by a given set of afferent fibres. Data are presented that in the anesthetized cat, variation in the spontaneous activity of a population of dorsal horn neurones in laminae III-VI, that respond to stimulation of low-threshold cutaneous afferents, produce correlated fluctuations of monosynaptic reflexes by means of pre- and postsynaptic mechanisms. It is suggested that correlated changes in the level of PAD can also play a significant role in the presynaptic adjustment of the synaptic effectiveness of the afferent fibres during specific motor tasks.

On the Role of Galanin, Substance P and Other Neuropeptides in Primary Sensory Neurons of the Rat: Studies on Spinal Reflex Excitability and Peripheral Axotomy

The interaction of intrathecally (i.t.) applied galanin (GAL) with substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), somatostatin (SOM) and C-fibre conditioning stimulation (CS) with regard to their effects on the spinal nociceptive flexor reflex was studied in decerebrate, spinalized, unanaesthetized rats with intact or sectioned sciatic nerves. SP, CGRP, VIP and SOM applied onto the surface of lumbar spinal cord or a brief CS train (1 Hz, 20 s) to the sural nerve facilitated the flexor reflex for several minutes in animals with intact or sectioned nerves. Pretreatment with GAL, which by itself had a biphasic effect on the flexor reflex in a dose-dependent manner, antagonized the reflex facilitation induced by sural CS before and after sciatic nerve section. SP-induced facilitation of the flexor reflex was antagonized by GAL in rats with intact sciatic nerves, but not after nerve section. In contrast, VIP-induced reflex facilitation was antagonized by GAL only after sectioning of the sciatic nerve. GAL was effective in antagonizing the facilitatory effect of CGRP under both situations, but had no effect on SOM-induced facilitation. A parallel immunohistochemical study revealed that after sciatic nerve section GAL-like immunoreactivity (LI) and VIP-LI are increased in the dorsal root ganglia and that these two peptides coexist in many cells. The present results indicate that GAL antagonizes the excitatory effect of some neuropeptides which exist in the spinal cord. This antagonism could explain the inhibitory effect of GAL on C-fibre CS-induced facilitation of the flexor reflex, which is presumably due to the release of some of these neuropeptides from the terminals of primary afferents. Furthermore, the interaction between GAL and other neuropeptides is altered by sciatic nerve section, paralleling changes in the levels of these neuropeptides in primary afferents and their pattern of coexistence after nerve section. It is proposed that SP and CGRP are important mediators of the spinal flexor reflex in intact rats. However, after axotomy VIP may replace SP in this capacity, paralleling the decrease in SP and marked increase in VIP levels. In general the study provides further support for involvement of peptides in sensory function.

Regulation of afferent connectivity in the adult spinal cord by nerve growth factor

During development, nerve growth factor (NGF) regulates the density and character of peripheral target innervation (Barde, Neuron, 2, 1525 - 1534, 1989; Ritter et al., Soc. Neurosci. Abstr., 17, 546.2, 1991); its role in adult animals is less well defined. Here we have asked if the availability of growth factors such as NGF in peripheral tissues can influence the pattern of primary afferent connections in the CNS. Using osmotic minipumps, we raised the levels of NGF in rat skeletal muscle in vivo, a tissue where the levels of this factor are normally very low (Korsching and Thoenen, Proc. Natl. Acad. Sci. USA, 80, 3513 - 3516, 1983; Shelton and Reichardt, Proc. Natl. Acad. Sci. USA, 81, 7951 - 7955, 1984; Goedert et al., Mol. Brain Res., 1, 85 - 92, 1986). After 2 weeks of treatment we asked if the sensory neurons innervating this tissue showed an altered strength and distribution of connections with dorsal horn neurons. The contralateral (vehicle-treated) muscle, and totally untreated animals, served as controls. In normal and vehicle-treated animals, electrical stimulation of muscle afferents excited relatively few neurons in the dorsal horn, and these generally showed only weak responses. In contrast, on the NGF-treated side many more dorsal horn neurons in the lumbar enlargement of the spinal cord were excited by muscle afferents. The increased responsiveness could not be explained by a generalized increase in dorsal horn excitability, since spontaneous activity was not enhanced, nor by a change in A-fibre-mediated inhibitions from the treated afferents. Thus, these afferents appeared to establish new synaptic connections or strengthened previously weak ones as a result of increased neurotrophic factor availability. The data suggest that, in the adult rat, the levels of growth factors in peripheral targets may be used to regulate an appropriate degree of afferent connectivity within the central nervous system.

A beta-fiber intensity stimulation of chronically constricted median nerve induces c-fos expression in thalamic projection neurons of the cuneate nucleus in rats with behavioral signs of neuropathic pain

This study was aimed to investigate the possible involvement of neurons in the cuneate nucleus (CN) in the processing of A beta afferent inputs evoked by electrical stimulation of constricted median nerve in rats with behavioral signs of neuropathic pain. Immunohistochemical localization of Fos protein was used to examine the neuronal activation, and the combination of Fos immunohistochemistry with the retrograde labeling of Fluoro-Gold (FG) injected into the ventrobasal complex of the thalamus was used to characterize the activated neurons. Two weeks after unilateral median nerve constriction injury, the rats exhibited behavioral signs of neuropathic pain in the affected forepaws. In rats after nerve injury but without electrical stimulation, some Fos-like immunoreactive (Fos-LI) neurons were detected in the dorsal horn of the seventh cervical segment (C7) but none was found in the CN. Similar features were also noted when the stimulation of the intact median nerve served as an additional control. After A beta-fiber intensity stimulation of the previously constricted median nerve, an increase in number of Fos-LI neurons occurred in the medial half of the ipsilateral C7 dorsal horn as well as in the ipsilateral CN. In the latter, the Fos-LI neurons were located in the median nerve projection territory throughout the nucleus. Most of the Fos-LI neurons were distributed in the middle region of the CN, with about 78% of them emitting FG fluorescence indicating that they were cuneothalamic projection neurons. The results of this study suggest that the dorsal column-medial lemniscal system may contribute to the transmission and modulation of A beta-fiber mediated neuropathic pain signals.

Effects of sciatic nerve injuries on delta -opioid receptor and substance P immunoreactivities in the superficial dorsal horn of the rat

The aim of the present study was to examine the effects of transection combined with tight ligation, and crush of the sciatic nerve on delta -opioid receptor and substance P immunoreactivities in the superficial spinal dorsal horn at different time points after injury. Both the delta -opioid receptor and substance P are primarily localised to primary afferent fibres and terminals. Seven days following transection and ligation, a slight decrease in both delta -opioid receptor and substance P levels was seen in laminae I and II. The maximal reduction appeared to take place around 4 weeks. Restoration of immunoreactivity was observed by 32 weeks, and by 1 year the levels were almost back to normal. Regarding crush injury, the reduction in both delta -opioid receptor and substance P immunoreactivities were less pronounced and recovery was faster than after transection injury. Already by 16 weeks, the levels were almost back to normal.These results show that peripheral nerve injuries dramatically reduce the levels of delta -opioid receptor and substance P immunoreactivities in the superficial dorsal horn after short survivals and demonstrate recovery after long survivals. Whether the marked reduction of delta -opioid receptors in the dorsal horn is involved in the decreased ability of opioid analgesics to alleviate neuropathic pain remains to be studied. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.

C fiber responses of wide dynamic range neurons in the spinal dorsal horn

Responses of wide dynamic range neurons in the spinal dorsal horn to input from C fibers with various conduction velocities were analyzed. The wide dynamic range neurons studied were located in the laminae IV-VI of the spinal dorsal horn. The C fiber response to stimulation of the superficial peroneal nerve consisted of three components: early, middle, and late. The separation into three components was found to be caused by asynchronous volleys in three different classes of C fibers in the superficial peroneal nerve. The phenomenon of windup was observed to occur always in the late component, frequently in the middle component, and to a far lesser extent in the early component. The early component was augmented by sciatic nerve compression, indicating that the initial part of the C fiber response is suppressed within the spinal cord by an inhibitory effect of A fiber afferent volleys. An intravenous administration of a specific N-methyl-D-aspartate receptor antagonist, MK-801 hydrogen maleate, significantly suppressed the middle and late components of the C fiber response, although the effect on the early component was insignificant. Thus, one can infer that the hyperexcitability of wide dynamic range neurons to input from early components of cutaneous C fiber stimuli will yield hyperpathic symptoms such as paresthesia, hyperalgesia, and allodynia associated with damaged peripheral nerves, and that learning how to inhibit the hyperexcitability of wide dynamic range neurons to input from early components of C fiber stimuli will lead to the curative treatment for neuropathic pain.

Changes in PAD patterns of group I muscle afferents after a peripheral nerve crush

In the anesthetized cat we have analyzed the changes in primary afferent depolarization (PAD) evoked in single muscle spindle and tendon organ afferents at different times after their axons were crushed in the periphery and allowed to regenerate. Medial gastrocnemius (MG) afferents were depolarized by stimulation of group I fibers in the posterior biceps and semitendinosus nerve (PBSt), as soon as 2 weeks after crushing their axons in the periphery, in some cases before they could be activated by physiological stimulation of muscle receptors. Two to twelve weeks after crushing the MG nerve, stimulation of the PBSt produced PAD in all MG fibers reconnected with presumed muscle spindles and tendon organs. The mean amplitude of the PAD elicited in afferent fibers reconnected with muscle spindles was increased relative to values obtained from Ia fibers in intact (control) preparations, but remained essentially the same in fibers reconnected with tendon organs. Quite unexpectedly, we found that, between 2 and 12 weeks after crushing the MG nerve, stimulation of the bulbar reticular formation (RF) produced PAD in most afferent fibers reconnected with muscle spindle afferents. The mean amplitude of the PAD elicited in these fibers was significantly increased relative to the PAD elicited in muscle spindle afferents from intact preparations (from 0.08 +/- 0.4 to 0.47 +/- 0.34 mV). A substantial recovery was observed between 6 months and 2.5 years after the peripheral nerve injury. Stimulation of the sural (SU) nerve produced practically no PAD in muscle spindles from intact preparations, and this remained so in those afferents reconnected with muscle spindles impaled 2-12 weeks after the nerve crush. The mean amplitude of the PAD produced in afferent fibers reconnected with tendon organs by stimulation of the PBSt nerve and of the bulbar RF remained essentially the same as the PAD elicited in intact afferents. However, SU nerve stimulation produced a larger PAD in afferents reconnected with tendon organs 2-12 weeks after the nerve crush (mean PAD changed from 0.05 +/- 0.04 to 0.32 +/- 0.17 mV). The results obtained indicate that the PAD patterns of the afferent fibers reconnected with muscle spindle and tendon organ afferents are changed after crushing their axons in the periphery: stimulation of the bulbar RF appears to produce larger PAD in fibers reconnected with muscle spindles, and stimulation of cutaneous afferents produces larger PAD in fibers reconnected with tendon organs. It is suggested that these alterations in the patterns of PAD of muscle afferents result from central changes in the balance of excitatory and inhibitory influences acting on the segmental pathways mediating the PAD. Although the functional role of these changes has not been established, they may reflect compensatory changes aimed to adjust information arising from damaged afferents.

Ultrastructural studies on peptides in the dorsal horn of the rat spinal cord--III. Effects of peripheral axotomy with special reference to galanin

In this study co-localization of galanin- with calcitonin gene-related peptide (CGRP)-like immunoreactivity was examined in dorsal root ganglion neurons 14 days after sciatic nerve cut using a laser scanning confocal microscope. CGRP- and galanin-like immunoreactivities were also analysed in the dorsal horn of the spinal cord of these animals with immunofluorescence microscopy. The ultrastructural changes in galanin-immunoreactive, presumably primary afferent terminals in the superficial dorsal horn, were studied as well as the relationship between galanin-, substance P- and CGRP-like immunoreactivities in primary afferent terminals. Local galanin-positive neurons in lamina II were also analysed after peripheral axotomy. Under the confocal microscope, CGRP-like immunoreactivity was located in the perinuclear region, probably the Golgi complex, and in dot-like structures, probably representing large dense-core vesicles, in normal dorsal root ganglion neurons. However, after peripheral axotomy CGRP was mainly detected in dot-like structures. Only a slight decrease in percentage of CGRP neurons in dorsal root ganglion was seen after axotomy, and about 84% of the galanin-positive neurons contained CGRP. The field of galanin-positive nerve fibres in the superficial lumbar (L)4 and L5 dorsal horn expanded and the intensity of staining for CGRP was reduced in these regions 14 days after sciatic nerve cut. Using pre-embedding immunoelectron microscopy, several morphological changes were observed in galanin-positive terminals in laminae I and II ipsilateral to the lesion. Most importantly, the most frequently occurring type of galanin-positive terminals (type 1) showed distinct changes with a granular matrix, many immunoreactive, peripherally located large dense-core vesicles, empty large vesicles and synaptic vesicles which were displaced from the presynaptic zone. Other galanin-positive terminals underwent even more pronounced morphological changes, including extensive vesiculolysis, also of large dense-core vesicles, filamentous degeneration or formation of axonal labyrinths. An increased number of galanin-positive nerve terminals was observed in lamina III of the ipsilateral dorsal horn after axotomy. They did not form glomeruli and contained few large dense-core vesicles. Post-embedding immunocytochemistry combined with quantitative analysis revealed that significant changes occurred in a proportion of terminals also with regard to peptide content in large dense-core vesicles after axotomy. Thus, the percentage of galanin-positive large dense-core vesicles increased in several cases and that of substance P- and CGRP-immunoreactive ones decreased.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of an acute muscle nerve section on the excitability of dorsal horn neurones in the rat

A previous study of this laboratory showed that an acute myositis (which is associated with increased activity in slowly conducting muscle afferent fibres) is followed by marked excitability changes in the dorsal horn within a few hours. The present work addresses the question as to how the responsiveness of dorsal horn neurones changes when the same muscle nerve is transected. In anaesthetized rats, an axotomy of the gastrocnemius-soleus (GS) muscle nerves was performed and the electrical and mechanical excitability of single dorsal horn neurones in the lumbar spinal cord determined 2-8 h after the lesion. Axotomy led to a decrease in the proportion of neurones responding to A-fibre input from the cut nerve and to an increase in the efficacy of sural and peroneal nerve stimulation. The change in GS input became significant only 5-8 h after the lesion and could reflect the beginning of neuroplastic changes. The change in sural and peroneal input was most marked 2-5 h after axotomy and is probably due to fast neuronal processes. The efficacy of C-fibre input from the sural and peroneal nerves increased significantly in the lateral dorsal horn only. In comparison with the effects of an acute myositis, the axotomy had opposite effects with regard to the GS input, but similar effects with regard to the C-fibre drive from the other nerves. It is concluded that transection of a muscle nerve is similarly effective in inducing acute changes in dorsal horn excitability as is an increase in muscle nerve activity.

Ultrastructural studies on peptides in the dorsal horn of the rat spinal cord--IV. Effects of peripheral axotomy with special reference to neuropeptide Y and vasoactive intestinal polypeptide/peptide histidine isoleucine

Using immunofluorescence histochemistry and pre- and post-embedding immunoelectron microscopy the rat lumbar dorsal horn was analysed in normal rats and 14 days after unilateral transection of the sciatic nerve. A marked increase in neuropeptide Y-like immunoreactivity was observed in the ipsilateral, superficial dorsal horn, especially in laminae III and IV, of the lumbar 4-5 spinal cord segments after peripheral axotomy. In the ipsilateral lamina II two types of neuropeptide Y-immunoreactive, presumably primary afferent terminals could be identified at the ultrastructural level. The first type contained many large dense-core vesicles (100-155 nm in diameter), whereas a second, more common type had only a few and smaller large dense-core vesicles (80-100 nm in diameter), plus synaptic vesicles of varying diameter (50-85 nm), large empty vesicles and tubular structures. Only occasionally were neuropeptide Y-positive terminals in lamina II involved in the formation of axonal labyrinths. In the ipsilateral lamina III, the number of neuropeptide Y-positive nerve terminals markedly increased after axotomy, with a moderate increase in lamina IV. These neuropeptide Y-positive terminals were morphologically similar to the second type of neuropeptide Y-positive terminal in lamina II, i.e. contained many synaptic vesicles (45-50 nm in diameter), a few small large dense-core vesicles (80-100 nm in diameter), electron-dense granular matrix and a few tubular structures. Fusion of synaptic vesicles with the plasma membrane was often observed at these synapses. These terminals frequently formed glomeruli but were not involved in axonal labyrinths. With regard to local neurons, neuropeptide Y-like immunoreactivity was observed in many dendrite-like profiles mostly making synaptic contacts with neuropeptide Y-negative dendrites and only rarely contacting the central terminal of the glomeruli. Neuropeptide Y-positive nerve endings were mainly seen in lamina I and the outer third of lamina II. After peripheral axotomy the number of vasoactive intestinal polypeptide/peptide histidine isoleucine immunoreactive terminals was increased in laminae I and II. They contained many large dense-core vesicles (100-120 nm in diameter), and some of them were positive for vasoactive intestinal polypeptide/peptide histidine isoleucine. Morphologically, the terminals were characterized by a granular matrix, tubular structures, empty vesicles, reduction in synaptic vesicles and absence of postsynaptic densities. Vasoactive intestinal polypeptide/peptide histidine isoleucine-like immunoreactivities were often found in association with labyrinth formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasticity in spinal nociception after peripheral nerve section: reduced effectiveness of the NMDA receptor antagonist MK-801 in blocking wind-up and central sensitization of the flexor reflex

We have examined and compared the effects of systemically applied MK-801, an NMDA receptor/channel blocker, on the wind-up and facilitation of the flexor reflex during and after conditioning stimulation (CS) of C-afferents in rats with intact sciatic nerves or 13-16 days after axotomy. In rats with intact sciatic nerves, intravenous MK-801 (0.5 mg/kg) partially reduced wind-up and totally blocked reflex facilitation following C-fiber CS to the sural nerve. In contrast, 13-16 days after unilateral section of the sciatic nerve, the same dose of MK-801 failed to reduce the wind-up and reflex facilitation following C-fiber CS to the axotomized sural nerve, although the duration of reflex facilitation was significantly shortened. These findings indicate that the involvement of NMDA receptors in mediating activity-dependent spinal hyperexcitability is substantially reduced after peripheral nerve section, possibly reflecting a reduced release of glutamate by primary sensory afferents.

Distribution of c-fos expressing dorsal horn neurons after electrical stimulation of low threshold sensory fibers in the chronically injured sciatic nerve

The distribution of proto-oncogene c-Fos protein-immunoreactive cells in the spinal cord dorsal horn was studied after electrical stimulation at A alpha/A beta-fiber intensity of normal and previously injured sciatic nerves in urethane anesthetized rats. No or only occasional Fos protein-like immunoreactive cells were seen after stimulation of the normal uninjured nerve or after nerve transection without stimulation. Electrical nerve stimulation at 3, 12, and 21 days after sciatic nerve transection resulted in substantial increases in the numbers of Fos protein-like immunoreactive cell nuclei in each of Rexed's laminae I-V. Combined demonstration of Fos protein-like immunoreactivity and of glial fibrillary acidic protein-like immunoreactivity (astroglia) or OX-42 immunoreactivity (microglia), indicated that the observed Fos protein-like response was confined to neurons and not to astroglia or microglia. Combined demonstration in the spinal cord of Fos protein-like immunoreactive neurons and neurons labeled retrogradely with Fluoro-Gold from the gracile nucleus showed that some of the Fos protein-like immunoreactive neurons in Rexed's laminae III and IV contributed to the postsynaptic dorsal column pathway. The results indicate that stimulation at A alpha/A beta-fiber intensity of a previously injured nerve gives rise to an abnormally increased activation pattern of postsynaptic neurons in the dorsal horn, some of which contribute to the postsynaptic dorsal column pathway.

Messenger plasticity in primary sensory neurons following axotomy and its functional implications

Following peripheral axotomy, long-lasting changes in the expression of neuropeptides and their receptors in primary sensory neurons are observed. These changes involve the downregulation of the excitatory peptides substance P and calcitonin gene-related peptide and the upregulation of the inhibitory peptides neuropeptide tyrosine and galanin, resulting in a reduction of transmission in the dorsal horn. The changes observed are thought to represent adaptive responses to limit the consequences of peripheral nerve damage to the organism as a whole and to promote survival and recovery of the individual neuron.

GABA decreases in the spinal cord dorsal horn after peripheral neurectomy

A significant fall in the number of GABA-immunoreactive cells in laminae I-III of the rat spinal cord occurred in the somatotopic area of projection of the sciatic nerve after nerve transection. The decrease started at 2 weeks post-neurectomy, and at 4 weeks ipsilateral mean cell numbers were approximately 72% of contralateral control values. Similarly, the concentration of GABA in spinal homogenates was significantly reduced 4 weeks post-neurectomy. These data, together with our recent finding of an increase in spinal GABA during chronic inflammation of the hindlimb, suggest that the level of GABA in the dorsal horn is regulated by the amount of primary afferent input.

Pharmacology of spinal peptides affecting sensory and motor functions: dynorphins, somatostatins and tachykinins

In recent years, the pharmacological activity of dynorphins and somatostatins on spinal sensory transmission has been intensively investigated with a view to developing new agents for pain control. Similarly, a series of tachykinin-related peptides with apparent receptor antagonist activity on endogenous substance P and neurokinins has been investigated. However, a number of observations suggest that these peptides, injected intrathecally in laboratory animals, not only exert a direct effect on nociceptive transmission but also affect a broader range of spinal somatomotor and autonomic functions and may cause peculiar neurotoxic effects that are not elicited by a large number of peptides affecting spinal neurotransmission. This article makes a critical review of their pharmacological activity on spinal sensory and motor functions and briefly touches on their anatomical and functional organization in the spinal cord.

Primary afferent origin of substance P-containing axons in the superficial dorsal horn of the rat spinal cord: depletion, regeneration and replenishment of presumed nociceptive central terminals

Substance P-like immunoreactivity (SPLI) was localized in the superficial spinal dorsal horn of the rat by means of light and electron microscopic immunocytochemical techniques. Serial immunocytochemical sections were subjected to densitometric measurements with an electronic Image Analyser, and with aid of a computer program, a two-dimensional reconstruction of the fine neuroanatomical structure of the SPLI-active regions of the lumbosacral upper superficial spinal dorsal horn was obtained. SPLI activity in the superficial dorsal horn outlines four well-marked and distinctly differing regions, called, in the mediolateral sequence, areas A, B, C, and D, plus Cajal's noyeau interstitiel ("lateral spinal nucleus" = "nucleus of the dorsolateral fascicle," L). Lumbosacral dorsal rhizotomy results in an almost complete depletion of SPLI from ipsilateral areas A, B, C, and D; it induces decreased SPLI in the area of the lateral spinal nucleus (L), ipsi- or contralaterally in an alternating fashion. Transection of the segmentally related, ipsilateral peripheral nerve induces a marked depletion of SPLI from areas A, B, and C but only a slight decrease in area D and virtually none in the area of L. Whereas a simple crush of the peripheral nerve (axocompression) induces only a slight depletion of SPLI, if any, semiautomatic densitometric analysis of serial immunocytochemical sections proves that a controlled crush injury (axocontusion) results in depletion of SPLI from the upper dorsal horn, similar to transection of the peripheral nerve. Following regeneration of the ipsilateral, segmentally related peripheral nerve, the original immunocytochemical structure of the superficial dorsal horn is re-established by SPLI-positive axonal sprouts originating from previously damaged dorsal root axons.

Changes in spinal cord reflexes after cross-anastomosis of cutaneous and muscle nerves in the adult rat

Evidence exists that the specification of afferent nerves and their central connections in the embryo may depend in part on influences from the peripheral target innervated. We have now investigated whether such peripheral determination persists in the adult rat using the unmyelinated afferent system of C fibres, which differ chemically in the adult depending on their target. We have previously shown that if the cutaneous sural nerve and the muscle gastrocnemius nerve are cross-anastomosed so that they grow to each other's target, the A fibres establish functional endings and the C fibres change their chemistry to that which is appropriate for the new target. Here we report that in normal adult rats, a short train of stimuli to the cutaneous sural nerve produced a brief facilitation of the flexion reflex, lasting on average only 5 min, whereas similar stimulation of the gastrocnemius-muscle nerve enhanced this reflex for an average of 54 min. In cross-anastomosed animals, stimulation of the gastrocnemius nerve (innervating skin) induced a brief potentiation of the flexion reflex, lasting on average only 3 min. By contrast, stimulation of sural nerve (innervating muscle) produced a potentiation of this reflex lasting 57 min. Thus the ability of adult afferent nerves to potentiate the flexion reflex depends on the target with which they make contact. We propose that tissue-specific factors influence some of the central actions of primary afferent neurons in the adult.

Nerve section alters the interaction between C-fibre activity and intrathecal neuropeptides on the flexor reflex in rat

The hamstring flexor reflex evoked by C-fibre strength electric shocks to the sural nerve was recorded in unanaesthetised, decerebrate, spinalized rats with sciatic nerves intact or sectioned 14-21 days previously. The effect of a brief C-fibre strength conditioning stimulus (CS) train (20 s, 1 Hz) to the sural nerve or intrathecally applied neuropeptides substance P (SP), vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP) on reflex excitability were quantified. The sural CS and all of the neuropeptides caused a brief (1-5 min) facilitation of the test reflex with no concomitant changes in the amplitude of the monosynaptic reflex. A synergistic facilitatory interaction between the CS and SP, but not between the CS and VIP was observed in rats with intact nerves. In nerve-sectioned animals no synergism was found between CS and SP, but a very strong synergistic facilitation was seen with CS and VIP. Since SP and VIP both coexist with CGRP in separate populations of primary afferents, the interaction between SP plus CGRP and VIP plus CGRP was tested in animals with intact and sectioned nerves. In animals with intact nerves, SP and CGRP had a strong synergistic effect, whereas VIP and CGRP had a weak facilitatory interaction. In animals with sectioned nerves, SP and CGRP did not interact, whereas VIP and CGRP had a stronger facilitatory interaction. Since it has been shown that there are changes in peptide levels in primary afferents and dorsal horn interneurons following nerve section, it is proposed that such alterations may underly some of the physiological changes in spinal cord function after damage to peripheral nerves.

Adrenal grafting for Parkinson's disease: a role for substance P

Parkinson's disease (PD) is a progressive neurodegenerative disorder in which the primary pathology is thought to be a loss of dopaminergic neurons in the substantia nigra (SN). The mainstay of treatment has been the use of the drug L-DOPA, a drug that crosses the blood-brain barrier and is converted to dopamine. Recently, intracerebrally implanted grafts of adrenal tissue to promote functional recovery in nigral-damaged recipient animals and patients have been successfully performed. The recovery in these cases is said to be due to the dopamine present in the grafted adrenal tissue. This explanation has several fallacies, however. It is the contention of this paper that substance P is the active agent in the grafted tissue. This raises the possibility of improving the treatment for PD by the use of grafted tissue that is a purer source of SP or SP agonists.

Cortical organization after treatment of a peripheral nerve with ricin: an evaluation of the relationship between sensory neuron death and cortical adjustments after nerve injury

The present study was designed to assess whether cortical changes after peripheral nerve damage are related to the degree of death of primary sensory neurons in the damaged nerve. The cytotoxin ricin was injected into the sciatic nerves of adult rats to kill primary sensory neurons with axons through the injection site. Following periods of 6-101 days, the S-I hindpaw map was evaluated with neurophysiological techniques and compared with the hindpaw maps of previously studied normal adult rats and adult rats that had undergone adult or neonatal sciatic section at a comparable level of the nerve. These comparisons allowed evaluation of cortical functional organization following different degrees of sensory neuron loss after sciatic nerve injury. There were three main results. 1) The comparison of ricin-treated and normal adult rats indicated that ricin treatment interrupted inputs from the sciatic skin territory on the hindpaw and caused a limited increase in the size of the cortical area that was activated by stimulation of hindpaw skin innervated by the remaining saphenous nerve. 2) The cortical maps of rats that had undergone adult ricin treatment (relatively large primary neuron loss) or section during adulthood (small to moderate primary neuron loss) were similar. In both groups, only the saphenous hindpaw skin was represented in cortex, and the cortical area that was activated by stimulation of the saphenous hindpaw skin had undergone a comparable limited enlargement. 3) The comparison of ricin-treated adult rats (relatively large primary neuron loss) and adult rats that had undergone neonatal section (relatively large primary neuron loss) indicated that cortical organization differed after these treatments. In particular, after ricin treatment the cortical area that was activated by stimulation of the saphenous hindpaw skin was larger than the comparable area in neonatal denervates, and the topographical progressions between the hindpaw and adjacent body representations were not as variable as after neonatal section. These findings indicate that cortical maps are altered after injection of ricin into a nerve. The similarity in cortical organization after ricin treatment (relatively large sensory neuron loss) and nerve section in adults (relatively small sensory neuron loss) and the differences in cortical organization after ricin treatment and nerve section in neonates (both relatively large sensory neuron loss) indicate cortical changes do not covary as a simple function of the degree of peripheral neuron death.

Cutaneous stimuli releasing immunoreactive substance P in the dorsal horn of the cat

In barbiturate-anaesthetized spinal cats, antibody microprobes were used to examine immunoreactive substance P (irSP) release at sites within the spinal cord following cutaneous stimuli. A basal level of irSP release was detected in the region of the substantia gelatinosa of the lumbar spinal cord. No increase in this irSP release was produced by non-noxious thermal or mechanical cutaneous stimulation. Noxious thermal, mechanical or chemical cutaneous stimuli all increased release of irSP in the region of the substantia gelatinosa and in the overlying pia mater. The results support a role for SP in the transmission of information from nociceptors to spinal neurones.

Diminished dorsal root GABA sensitivity following chronic peripheral nerve injury

The depolarizing effect of gamma-aminobutyric acid (GABA) on rat lumbar dorsal roots was studied in a sucrose gap chamber following axotomy or crush injury of the sciatic nerve or dorsal root. The mean depolarization elicited by GABA on normal dorsal roots (3.96 +/- 0.71 mV, N = 14) was significantly reduced following chronic sciatic axotomy (2.02 +/- 0.99 mV, N = 15). Chronic sciatic crush injury had no significant effect on dorsal root GABA sensitivity. The amplitudes of the dorsal root compound action potentials were the same from rats with normal and injured sciatic nerves, indicating that axons proximal to the sciatic nerve lesion did not undergo appreciable degeneration. A marked loss of dorsal root GABA sensitivity was also seen following dorsal root axotomy or crush injury (1.02 +/- 0.98 mV (N = 10) and 0.69 +/- 0.70 mV (N = 9), respectively). These results indicate that GABA sensitivity of dorsal roots is attenuated following peripheral nerve lesions in which regeneration and functional reconnection with peripheral targets are prevented. Previous work indicates that the primary afferent depolarization is reduced under similar conditions. The reduction in GABA sensitivity of dorsal root fibers described here may have a contributory role in the reduced primary afferent depolarization that follows peripheral nerve transection, which has pathophysiologic implications in chronic pain syndromes.

Opiates distinguish spinal excitation from inhibition evoked by noxious heat stimuli in the rat: relevance to theories of analgesia

1. Experiments were performed to test the hypothesis that a significant part of the action of opiates in reducing responses to noxious stimuli is a reduction in the release of neurotransmitter from primary afferent fibres. 2. The effects of locally and systemically administered opiates were examined on the excitatory and gamma-aminobutyric acid (GABA)-mediated inhibitory responses of spinal dorsal horn neurones to noxious heat stimulation in the anaesthetized rat: the inhibitions are thought to involve the same C-fibre afferents as the excitation. 3. Microionophoretically administered morphine reduced the excitatory response i a small proportion of the cells, reduced the background firing in a larger proportion but was ineffective on the inhibition. 4. Intravenously injected morphine (0.5-6 mg kg-1) or etorphine (0.1-2 micrograms kg-1) invariably attenuated the excitation of dorsal horn neurones by noxious stimuli but had no effect on the inhibition. 5. It was concluded that the data do not support the hypothesis that the production of analgesia is due mainly to a reduction in the release of transmitter from primary afferent fibres.

Increased staining of immunoreactive dynorphin cell bodies in the deafferented spinal cord of the rat

This study examined the distribution of immunoreactive dynorphin neurons in the lumbar dorsal horn of unilaterally deafferented, colchicine-treated rats. Ipsilateral to a multiple dorsal rhizotomy there was a significant increase both in the number and intensity of staining of dynorphin-immunoreactive cells in laminae I, outer II and V. A comparable change was seen in animals that were deafferented by sciatic nerve section. Enkephalin immunoreactivity was not altered under these conditions. These results indicate that many forms of injury, not all of which result in increased nociceptive input, can increase the level of dynorphin in spinal cord neurons.

Noxious heating of the skin releases immunoreactive substance P in the substantia gelatinosa of the cat: a study with antibody microprobes

Using a new method, the antibody microprobe technique, the release of immunoreactive substance P (SPiR) in the dorsal horn in response to noxious heating of the skin, was studied in barbiturate anaesthetized spinal cats. Release of SPiR was not produced by immersing the ipsilateral hind paw in water at 37 degrees C. With water at 50 and 52 degrees C, however release was consistently detected in the region of the substantia gelatinosa. These results directly show a central release of SPiR with excitation of nociceptors by heat.

Excitatory amino acids increase glycogen phosphorylase activity in the rat spinal cord

Glycogen phosphorylase is present in nervous tissue in an active and inactive form. Using a histochemical technique, an investigation into which putative neurotransmitters have the capacity to modify the activity of the enzyme, has been performed on the rat spinal cord. Intrathecal injections of L-glutamate and L-aspartate elevate glycogen phosphorylase activity in the dorsal horn, while substance P has no effect and only high doses of adenosine triphosphate (ATP) increase the enzyme activity. In addition the N-methyl-D-aspartate receptor antagonist, 5-amino-phosphonovaleric acid was found to block the elevation of glycogen phosphorylase activity in the dorsal horn produced by the peripheral activation of chemo-sensitive primary afferents. Excitatory amino-acid neurotransmitters can therefore, acting via second messengers and protein kinases, modify glycogen metabolism in the spinal cord.

Regulatory mechanisms for substance P in the dorsal horn during a nociceptive stimulus: axoplasmic transport vs electrical activity

Substance P (SP) is believed to be a neuromediator of nociception in the dorsal horn of the spinal cord. SP precursor is synthesized in the dorsal root ganglia (DRG) and transported via axoplasmic transport to the nerve terminal where it is stored and released as SP. The chemical nociceptive stimulus, formalin, when injected into the hindpaw causes an increase in the level of SP in the dorsal horn. This increase in SP may be the result of increased electrical activity due to activation of free nerve endings or the transport of some chemical or trophic signal to the DRG or to the central terminal. This study investigates the mechanism of the SP increase during the formalin stimulus. Rats were anesthetized and a laminectomy performed. In some experiments the sciatic nerve was exposed. Agar gel pads containing either colchicine or tetrodotoxin (TTX) were applied to the dorsal root or sciatic nerve prior to the injection of 5% formalin or saline into the hindpaw. Electrical activity across the dorsal root distal to the gel pad was monitored to determine the effects of colchicine and TTX on the nerve. Sixty min after the injection into the hindpaw, the animal was perfused and the lumbar spinal cord removed. Ten-micron frozen sections were stained for SP. It was found that the formalin-evoked increase in SP could be partially blocked by either colchicine or TTX applied to the dorsal root and completely blocked by the application of both agents together. TTX or colchicine applied to the sciatic nerve completely blocked the formalin-evoked increase in SP.(ABSTRACT TRUNCATED AT 250 WORDS)

Exocytosis from large dense cored vesicles outside the active synaptic zones of terminals within the trigeminal subnucleus caudalis: a possible mechanism for neuropeptide release

It has been hypothesized that chemical interactions between neurons in the central nervous system can occur in the absence of well defined synaptic complexes, but morphological correlates have been difficult to find. The present study demonstrates exocytotic release from large (70-130 nm) dense cored vesicles at structurally nonspecialized areas along the plasmalemma of structurally different categories of terminals and occasionally from dendrites and axons within the neuropil of the trigeminal subnucleus caudalis. In rats, the marginal (lamina I) and substantia gelatinosa (lamina II) layers contain the central terminals of primary afferent fibers from the infraorbital nerve that supply the skin and whiskers (vibrissae). Different types of interneurons are also present and may modify the input being relayed to higher centers. While exocytotic profiles were present in control animals, they increased significantly (P less than 0.01) on the ipsilateral side 1-24 h after a unilateral skin lesion in the vibrissae area. A second increase (P less than 0.001) occurred 14-15 days after the lesion. Virtually all examples of large vesicle exocytosis were observed at structurally nonspecialized sites while those at the active synaptic zones involved small clear vesicles. Substance P-like immunofluorescence, present in controls and on the ipsilateral side during the first 6 days, subsequently declined until 4 weeks after surgery when some recovery was noted. The increase in large vesicle exocytosis and the decrease in substance P are interpreted to reflect functional adjustments of different neurons in response to the lesion. The exocytosis involving large dense cored vesicles may serve to deliver transmitters and/or neuropeptide modulators to appropriate receptors in a wider area than release into a specialized synaptic cleft would allow.

Substance P and Parkinson's disease: a causal relationship?

Parkinson's disease (PD) is a common condition that is thought to result from a marked degeneration of dopaminergic neurones of midbrain origin. Here I present evidence to show that PD may result from a primary loss of active tachykinin, probably substance P (SP) in the substantia nigra (SN), and that this loss leads to a secondary degeneration of the dopaminergic neurones. This raises the possibility of treating and curing patients with PD by giving them SP agonsts.

Regional distribution of immunoreactive-thyrotrophin-releasing hormone and substance P, and indoleamines in human spinal cord

The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3, and 4; thoracic groups T1-3, T4-6, T7-9, and T10-12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of the age of the patient, the postmortem time interval, and freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spinal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 65 and 90 years. Freezing the tissue (-80 degrees C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intrathecal and subepineural capsaicin on thermal sensitivity and autotomy in rats

In 79 Sprague-Dawley rats, we determined the effect of either intrathecal or subepineural capsaicin injection on: latency of withdrawal of the hind foot to a nociceptive thermal stimulus (50 +/- 1 degree C hot plate) and the onset and severity of putative behavioral evidence of chronic pain in the rat (autotomy) which commonly appears following sciatic nerve section. Capsaicin (50 micrograms) was suspended in 5 microliters of vehicle (10% Tween-80 in 0.9% saline) then injected either intrathecally at the level of the L4-5 vertebral interspace or subepineurally in the sciatic nerve at the level of the midfemur. Subepineural capsaicin consistently and efficiently produced thermal analgesia in the rat, while intrathecal capsaicin had no significant analgesic effect. In chronically denervated rats, both subepineural and intrathecal capsaicin decreased the latency to onset of first autotomy, and intrathecal capsaicin increased the severity of this behavior significantly. These data are consistent with the hypothesis that autotomy is the rat's response to abnormal sensations perceived in the denervated hind limb. Deafferentation of dorsal horn neurons appears to be of paramount importance in the production of autotomy while the relevance of peripherally originating spontaneous neuroma discharges to autotomy behavior is questioned.

The brief and the prolonged facilitatory effects of unmyelinated afferent input on the rat spinal cord are independently influenced by peripheral nerve section

Single C-fibre strength stimuli applied to the sciatic nerve in the decerebrate spinal rat evoke three separate bursts of activity in posterior biceps/semitendinosus flexor alpha motorneurones which are associated with the arrival in the spinal cord of volleys in the A-beta, A-delta and C-afferent fibres. Repetitive stimulation of the sciatic nerve at 1 Hz for 20 s generates a progressive wind-up of response and an after-discharge lasting up to 10 s. Twelve to fourteen days after section of the sciatic nerve, stimuli applied central to the section evoke a larger than normal response in the posterior biceps/semitendinosus flexor motorneurones and repetitive stimulation (1 Hz, 20 s) produces an after-discharge which is four times longer than that produced by stimulation of the intact nerve. In addition to the direct excitatory effects of sciatic nerve stimulation on the flexor motorneurones which lasts for seconds, conditioning stimuli to the sciatic nerve at C-fibre strength (1 Hz, 20 s) produce a facilitation of the flexor reflex evoked by a standard pressure stimulus to the ipsilateral and contralateral toes which lasts for 70 min. However, although the direct excitatory effects of stimulating a sectioned sciatic nerve on the posterior biceps/semitendinosus flexor motorneurones are exaggerated, the facilitation of the cutaneous flexion reflex evoked by stimulating sectioned sciatic nerves (1 Hz, 20 s) only lasts for 17 min. These results show that the mechanism which produces the rapid effects of sciatic nerve stimulation on the flexor reflex circuit can be separated from the mechanism which produces the prolonged facilitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative electron histochemistry of thiamine monophosphatase and substance P in the upper dorsal horn

The genuine marker enzyme of primary nociceptive neurons, thiamine monophosphatase (TMPase) has been localized in the substantia gelatinosa of the rat spinal cord by means of light-and electron microscopic histochemistry; localization of substance P has been studied by light-and and electron microscopic immunohistochemical methods. It has been shown that TMPase and substance P are located in two, regionally and structurally different populations of axon terminals. Substance P is contained both in A delta and in drC axons. In the postero-lateral funiculus of the white matter, substance P-positive axons establish axo-somatic synaptic contacts with large multipolar neurons of Cajal's interstitial nucleus.

Autotomy in rats after peripheral nerve section: lack of effect of topical nerve or neonatal capsaicin treatment

The influence of capsaicin on autotomy was studied in adult rats in which the sciatic and saphenous nerves were sectioned. Capsaicin was administered subcutaneously to neonatal rats or applied topically to the sciatic and saphenous nerves in adult animals. Quantification of neurogenic plasma extravasation in skin areas subserved by these nerves and of the number of small type B neurones in lumbar sensory ganglia were used to confirm the effectiveness of capsaicin-induced lesions of unmyelinated sensory nerves. Neonatal capsaicin treatment significantly reduced neuronal numbers in ganglia and, compared to control responses, plasma extravasation was nearly abolished after both neonatal and peripheral nerve treatment with capsaicin. Despite these deficits in sensory neurones function, no differences in any parameters of autotomy were observed between animals receiving both capsaicin treatment and nerve section and those given nerve section alone. Animals in both control and experimental groups exhibited high autotomy scores. These results suggest that capsaicin-sensitive primary sensory neurones do not have a significant role in precipitating autotomy characterized by high incidence and severity.

Nerve growth factor counteracts the neurophysiological and neurochemical effects of chronic sciatic nerve section

The sciatic nerve was sectioned unilaterally in rats and nerve growth factor (NGF) applied locally to the nerve stump for the following 10-14 days using an indwelling osmotic pump. The aim of the experiment was to test whether NGF had any effect on the previously reported neurophysiological and neurochemical events that occur central to a peripheral nerve lesion. The method of application allowed the sciatic nerve on the other side to be used as a control. Primary afferent depolarization fell, as expected, to 13% of its control value after chronic nerve section but if NGF was administered it fell to only 43.5% of control. Chronic nerve section is also known to result in expansion of the receptive fields of deafferented dorsal horn cells. NGF treatment reduced the number of such large receptive fields by 50%. The normal depletion of fluoride resistant acid phosphatase from the cut nerve terminals in the dorsal horn did not occur following NGF treatment. Radioimmunoassay of substance P revealed that the 30% reduction in dorsal horn levels that follows chronic sciatic nerve section did not occur when NGF was applied and that the accompanying 60% decrease in dorsal root ganglion levels was changed to a 64% increase by NGF. The results show that chronic NGF treatment of a cut sciatic nerve does partially reverse the central changes that normally follow deafferentation.

Lectin binding: a genuine marker for transganglionic regulation of human primary sensory neurons

Medium-sized human dorsal root ganglion cells and their central terminals in the upper dorsal horn exert preferential affinity for Ulex europaeus I lectin. Lectin binding of glycoconjugates outlines lamina III (+IIi) and disappears after peripheral neurotomy, which renders it a useful marker to study transganglionic regulation in man.