Cell type and conduction velocity of rat primary sensory neurons with substance P-like immunoreactivity

Cells in laminae III and IV of the rat spinal cord that possess the neurokinin-1 receptor and have dorsally directed dendrites receive a major synaptic input from tachykinin-containing primary afferents

Many neurons with cell bodies in laminae III or IV of the spinal dorsal horn possess the neurokinin 1 receptor and have dorsal dendrites that arborize in the superficial dorsal horn. We have performed a confocal microscopic study to determine whether these cells receive inputs from substance P-containing primary afferents. All neurons of this type received contacts from substance P-immunoreactive axons, and in most cases the contacts onto dorsal dendrites were very numerous. A great majority (90-100%) of substance P-immunoreactive varicosities in contact with these cells were also immunoreactive with antibody to calcitonin gene-related peptide, indicating that they were of primary afferent origin. The density of contacts from substance P-immunoreactive varicosities onto these cells was significantly higher than that seen on cholinergic neurons in lamina III (which do not possess the receptor). Electron microscopy revealed that synapses were present at points of contact between substance P-immunoreactive boutons and dorsal dendrites of cells with the neurokinin 1 receptor. Some cells of this type belong to the spinothalamic tract, and we therefore examined neurons with cell bodies in laminae III or IV that possessed the neurokinin 1 receptor and were labeled retrogradely after thalamic injection of cholera toxin B subunit. These cells also received contacts from substance P-immunoreactive axons on their dorsal dendrites. The results of this study indicate that neurons of this type are a major target for substance P-containing primary afferents.

The generation of neuronal heterogeneity in a rat sensory ganglion

Adult sensory neurons differ chemically, morphologically, and functionally, but the factors that generate their diversity remain unclear. For example, neuropeptides are generally found in small neurons, whereas abundant neurofilament is common in large neurons. Neurons containing the neuropeptides calcitonin gene-related peptide (CGRP) or substance P were quantified using immunohistochemistry in rat lumbar dorsal root ganglion (DRG) at times before and after sensory neurons contact central and peripheral targets in vivo. No neurons in the newly formed DRG expressed neuropeptide or neuropeptide mRNA, but neuropeptides were detectable about the time that axons connect with peripheral targets. To determine the requirement for target in neuropeptide regulation, embryonic DRG neurons were isolated at times before central and peripheral connections had formed, placed in culture, and immunocytochemically assayed for CGRP and substance P. Cultured neurons expressed neuropeptides with a time course and in proportions similar to those in vivo. Thus, some neurons in the embryonic DRG seem to be intrinsically specified to later express CGRP and substance P. The percentage of CGRP-immunoreactive neurons was not changed by cell density, non-neuronal cells, neurotrophins in addition to nerve growth factor (NGF), or antibody inactivation of neurotrophin-3 in the presence of NGF. To test the role of extrinsic cues on CGRP expression, DRG neurons were co-cultured with potential target tissues. Co-culture with a rat epidermal or smooth muscle cell line increased the proportion of CGRP-containing neurons, whereas primary skeletal muscle and 3T3 cells had no effects. Thus, multiple appropriate sensory neuron phenotypes arise in a regulated fashion in cultured neurons isolated before target connections have formed, and some candidate target tissues can modulate that intrinsic expression pattern.

Evidence for the existence of substance P autoreceptor in the membrane of rat dorsal root ganglion neurons

Substance P, a putative peptide neurotransmitter contained in primary sensory neurons, is suggested to play a major role in nociceptive transmission. In the present study, the existence of substance P autoreceptor in dorsal root ganglion neurons was identified with a method we developed recently and substance P-activated inward current in the dorsal root ganglion neurons and its ionic mechanism were also explored preliminarily. The majority of the cells examined (68/76, 89.5%) were sensitive to external application of substance P (0.01-10 microM) with a concentration-dependent inward current. This current was found to result from the opening of nonselective ion channel, preferring the Na+ channel. The substance P-activated current can be suppressed by Cd2+ (0.05 microM), which suggested Ca2+ may also be involved. Soon after the neurons had been identified to be endowed with substance P receptor with whole-cell patch-clamp technique, 17 cells were chosen for immunocytochemical staining to detect substance P-immunoreactivity. Seven neurons which were classified into small and intermediate size were found to reveal substance P-immunoreactivity. Using this method we have identified the existence of substance P autoreceptor in rat DRG neurons.

Differential roles of neurokinin 1 and neurokinin 2 receptors in the development and maintenance of heat hyperalgesia induced by acute inflammation

1. Following induction of acute inflammation by intraarticular injection of kaolin and carrageenan into the knee joint in rats, there was a significant decrease in the withdrawal latency to radiant heat applied to the paw (i.e. heat hyperalgesia), an increased joint circumference and increased joint temperature. 2. A neurokinin1 (NK1) receptor antagonist (CP-99,994, 10 mM) had no effect on the paw withdrawal latency when it was administered spinally through a microdialysis fibre before the induction of inflammation. Pretreatment with a NK2 receptor antagonist (SR48968, 1 mM) administered spinally through the microdialysis fibre prevented the heat hyperalgesia from developing in the early stages of the inflammation. 3. Post-treatment through the microdialysis fibre with the NK1 receptor antagonist (0.01-10 mM) was effective in reversing the heat hyperalgesia. In contrast, post-treatment spinally with the NK2 receptor antagonist (0.01-1 mM) had no effect on the heat hyperalgesia. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 4. Pretreatment systemically with the NK1 receptor antagonist (30 mg kg-1) had no effect on the heat hyperalgesia or pain-related behaviour ratings where 0 is none and 5 is non weight bearing and complete avoidance of limb contact. Pretreatment with a NK2 receptor antagonist (10 mg kg-1) systemically prevented the heat hyperalgesia and pain-related behaviour ratings from developing in the early stages of the inflammation. The inactive stereoisomers of NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 5. Post-treatment systemically with either the NK1 (0.1-30 mg kg-1) or the NK2 (0.1-10 mg kg-1) receptor antagonist resulted in a dose-dependent reversal of the heat hyperalgesia. Pain-related behaviour ratings were reduced by post-treatment only with the NK1 receptor antagonist. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the behavioural responses. 6. Direct pretreatment of the knee joint with either the NK1 (30 mg) or the NK2 (10 mg) receptor antagonist prevented the heat hyperalgesia from developing without affecting joint swelling. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 7. There appears to be a differential role for the spinal tachykinin receptors in the development and maintenance of the heat hyperalgesia associated with acute joint inflammation. The NK2 receptors appear to be activated early in the development of the heat hyperalgesia and NK1 receptors are involved in the maintenance of the heat hyperalgesia. 8. Peripherally, both NK1 and NK2 receptors are involved in the development of heat hyperalgesia and pain-related behaviour ratings induced by acute inflammation.

Localization of a metabotropic glutamate receptor, mGluR7, in axon terminals of presumed nociceptive, primary afferent fibers in the superficial layers of the spinal dorsal horn: an electron microscope study in the rat

It was examined electron microscopically in the rat if a metabotropic glutamate receptor, mGluR7, might be localized in axon terminals of nociceptive, primary afferent fibers in laminae I and II of the spinal dorsal horn. Nociceptive nature of axon terminals showing mGluR7-like immunoreactivity (mGluR7-LI) was indicated by binding to the isolectin I-B4 from Griffonia simplicifolia (I-B4), or by substance P-like immunoreactivity (SP-LI). Axon terminals labeled with immunogold particles indicating mGluR7-LI were usually filled with round synaptic vesicles and were in asymmetric synaptic contact with dendritic or somatic profiles; occasionally they contained pleomorphic vesicles and were in symmetric synaptic contact with somatic profiles in lamina II. The double-labeling studies revealed that most of axon terminals with I-B4 labeling as well as a small population of axon terminals with SP-LI, showed mGluR7-LI. About one-third or much smaller population of axon terminals with mGluR7-LI in laminae I and II were labeled, respectively, with I-B4 or SP-LI; these were in asymmetric synaptic contact with dendritic profiles.

Ganglionic axons in motor roots and pia mater

In addition to motor axons and preganglionic axons, ventral roots contain unmyelinated or thin myelinated sensory axons and postganglionic sympathetic axons. It has been said that ventral roots channel sensory axons to the CNS. However, it now seems that these axons end blindly, shift to the pia or loop and return towards the periphery and that these units reach the CNS via dorsal roots. Sensory ventral root axons project from a variety of somatic or visceral receptors; some of them are third branches of dorsal root afferents and some seem to lack a CNS projection. Many ventral root afferents contain substance P (SP) and/or calcitonin gene-related peptide (CGRP). These fibres are not affected by neonatal capsaicin treatment and they cannot induce radicular or pial extravasation. Some thin ventral root axons are sympathetic and relate to blood vessels. Afferents containing SP and/or CGRP and sympathetic axons also occur in the spinal pia mater. The sensory axons mediate pain. They might also have vasomotor, tissue-regulatory and/or mechanoreceptive functions. The motor roots of cranial nerves IV, VI and XI contain unmyelinated axons arranged like in ventral roots outside the autonomic outflow. However, the motor root of cranial nerve V channels some unmyelinated axons into the CNS. The occurrence of thin axons in ventral roots and pia mater changes during development and ageing. After peripheral nerve injury, ipsilateral ventral roots and pia are invaded by new sensory and postganglionic sympathetic axons.

Evidence for the presence of neurokinin-1 receptors on dorsal horn spinocerebellar tract cells in the rat

Dorsal horn spinocerebellar tract cells of adult rats were labelled by retrograde axonal transport with the B subunit of cholera toxin. Sections were prepared from lumbar and thoracic spinal segments and incubated with antisera which specifically recognise neurokinin-1 receptor protein and substance P. Labelled cells and immunoreactivity for the receptor and substance P were identified by using three different fluorophores and the relationships between them were assessed in single optical sections with three-colour confocal laser scanning microscopy. Forty-eight cells were examined and 23 of them displayed immunoreactivity for the receptor. Many substance P-immunoreactive profiles were present in lamina V and some formed contacts with spinocerebellar tract cells possessing neurokinin-1 receptor immunoreactivity. The evidence suggests that substance P may influence the activity of a subpopulation of dorsal horn spinocerebellar tract cells by acting through neurokinin-1 receptors.

Interganglionic segregation of distinct vagal afferent fibre phenotypes in guinea-pig airways

1. The present study addressed the hypothesis that jugular and nodose vagal ganglia contain the somata of functionally and anatomically distinct airway afferent fibres. 2. Anatomical investigations were performed by injecting guinea-pig airways with the neuronal tracer Fast Blue. The animals were killed 7 days later, and the ganglia were removed and immunostained with antisera against substance P (SP) and neurofilament protein (NF). In the nodose ganglion, NF-immunoreactive neurones accounted for about 98% of the Fast Blue-labelled cells while in the jugular ganglion they accounted for approximately 48%. SP and NF immunoreactivity was never (n = 100) observed in the same cell suggesting that the antisera labelled distinct populations. 3. Electrophysiological investigations were performed using an in vitro guinea-pig tracheal and bronchial preparation with intact afferent vagal pathways, including nodose and jugular ganglia. Action potentials arriving from single airway afferent nerve endings were monitored extracellularly using a glass microelectrode positioned near neuronal cell bodies in either ganglion. 4. The nodose ganglion contained the somata of mainly fast-conducting tracheal A delta fibres whereas the jugular ganglion contained equal numbers of C fibre and A delta fibre tracheal afferent somata. The nodose A delta neurones adapted rapidly to mechanical stimulation, had relatively low mechanical thresholds, were not activated by capsaicin and adapted rapidly to a hyperosmotic stimulus. By contrast, jugular A delta and C fibres adapted slowly to mechanical stimulation, were often activated by capsaicin, had higher mechanical thresholds and displayed a slow adaptation to a hyperosmotic stimulus. 5. The anatomical, physiological and pharmacological data provide evidence to support the contention that the vagal ganglionic source of the fibre supplying the airways ultimately dictates its neurochemical and physiological phenotype.

Prostaglandin E2 increases the proportion of neonatal rat dorsal root ganglion neurons that respond to bradykinin

Prostaglandins sensitize some nociceptors to noxious mechanical, thermal and chemical stimuli; however, not all nociceptors are sensitized by prostaglandins. We used cultures of dorsal root ganglion neurons from neonatal rats to determine whether prostaglandins differentially alter the responsiveness of populations of neurons to the chemical stimulus bradykinin. Groups of dorsal root ganglion neurons were defined by size of the cell soma and by the presence of immunoreactivity for substance P. An increase in the concentration of free intracellular Ca2+ was used as an indicator of responsiveness to bradykinin. Pretreatment (5 min) with prostaglandin E2 (100 nM) increased the proportion of intermediate-size neurons (somal areas of 240-320 microns2) that responded to 30 nM bradykinin by two-fold but did not alter the proportion of small-size neurons (somal areas of 160-239 microns2) that responded. Pretreatment with prostaglandin E2 had no effect on the maximum increase in free intracellular Ca2+ evoked by 30 nM bradykinin in either population of neurons, defined by size. Although pretreatment with PGE2 did not increase the proportion of intermediate-size neurons that responded to a lower concentration of bradykinin (3 nM), it did increase the concentration of free intracellular Ca2+ evoked by 3 nM bradykinin. Both results were consistent with a leftward shift in the stimulus-response relationship for bradykinin following pretreatment with PGE2. Small- and intermediate-size neurons that responded to bradykinin also differed in their expression of immunoreactivity for substance P. Furthermore, intermediate-size neurons that expressed immunoreactivity for substance P were more likely to respond to bradykinin after treatment with prostaglandin E2. These results support the hypothesis that prostaglandin E2 sensitizes some normally unresponsive primary afferent neurons to chemical stimuli. One population of neurons which becomes responsive to bradykinin after treatment with prostaglandin E2 can be defined based on cell size, and furthermore, these neurons are likely to express substance P. During inflammation, recruitment of primary afferent neurons that are immunoreactive for substance P would enhance the participation of substance P in central mechanisms that contribute to hyperalgesia.

Coexistence of calcitonin gene-related peptide- and substance P-like immunoreactivity in retrogradely labeled superior spermatic neurons in the dog

The coexistence of calcitonin gene-related peptide (CGRP) and substance P (SP) was determined in primary afferent neurons of the superior spermatic nerve of the dog. Testicular afferent neurons were visualized by retrograde labeling with the fluorescent dye fast blue. CGRP-like immunoreactivity (LI) was found in about 80% of testicular L1 and L2 dorsal root ganglion cells, and 81% of CGRP-positive neurons also contained SP. Conversely, SP-LI was found in 66% of testicular afferents, and 96% of SP-positive neurons simultaneously contained CGRP. Both CGRP- and SP-LI were observed in the whole size range of the testicular afferent neurons. No significant difference in the diameter was detected between CGRP- and SP-positive testicular afferent neurons. In contrast, the diameter of SP-positive cells was significantly smaller than that of CGRP-positive cells in the whole population of dorsal root ganglion (DRG) neurons. Compared to skin and muscle afferents, a larger population of the testicular afferents contain these peptides. This is considered to be one of the characteristic features of visceral afferents. Coexistence of CGRP and SP in testicular afferent neurons suggest a close functional relationship between these two neuropeptides in the sensory nervous system.

Substance P hyperpolarizes vagal sensory neurones of the ferret

1. Intracellular recordings were made in intact and in acutely dissociated vagal afferent neurones (nodose ganglion cells) of the ferret to investigate the effects of substance P(SP). 2. In current-clamp recordings, SP (100 nM) applied by superfusion hyperpolarized the membrane potential (7 +/- 0.7 mV; mean +/- S.E.M.; n = 105) and decreased the input resistance in 80% of the neurones. With voltage-clamp recording, SP produced an outward current of 3 +/- 0.2 nA (n = 10). 3. The SP current was concentration dependent with an estimated EC50 of 68 nM. The SP-induced hyperpolarization or current was mimicked by the tachykinin receptor NK1 agonist Ac-[Arg6, Sar9, Met(O2)11]SP(6-11) (ASM-SP; 100 nM; n = 10) and blocked by the NK1 antagonist CP-96,345 (10 nM; n = 6), but not by the NK2 antagonist SR48968 (100 nM; n = 4). No measurable change in membrane potential or input resistance was observed with application of either [beta-Ala8]neurokinin A or senktide, selective NK2 and NK3 receptor agonists, respectively (100 nM; n = 3 for each agonist). 4. The reversal potential (Erev) for the SP outward current was -85 +/- 2.5 mV (n = 4). The Erev for the SP response shifted in a Nernstian manner with changes in extracellular potassium concentration. Alterations in extracellular sodium or chloride concentrations had no significant effect on the Erev for the SP response (n = 3 for each ion). 5. Nominally Ca(2+)-free external solution abolished the SP response. Removal of magnesium from the extracellular solution had no effect on the response. 6. Caesium (100 microM), barium (1 mM), tetraethylammonium (TEA; 5 mM), apamin (10 nM) and 4-aminopyridine (4-AP; 4 mM) each completely prevented the SP response (n > or = 3 for each). 7. These results indicate that SP, via an NK1 receptor, can induce a Ca(2+)-dependent outward potassium current which hyperpolarizes the resting membrane potential of vagal afferent somata.

Spontaneous action potential activity in isolated dorsal root ganglion neurons from rats with a painful neuropathy

One of the physiological changes accompanying neuropathic pain from nerve injury is the spontaneous firing of primary afferent fibers. At least some of this activity is thought to arise from the dorsal root ganglion. We have investigated whether this activity is resident in the cell bodies of dorsal root ganglion neurons and if it is retained in vitro. Dorsal root ganglion neurons from rats with a chronic constriction injury (CCI) from 4 loose ligatures of chromic gut sutures around the sciatic nerve were used. Isolated neurons were studied using the whole cell patch technique in current clamp mode within 6 hours of preparation. Neurons from rats with CCI showed a significantly increased incidence of spontaneous action potential activity (18/88 vs. 1/36 neurons). Firing activity consisted of both random spikes and long trains of regular, rapid spikes, with random activity being the exclusive mode in most cells. Spontaneous resting potential fluctuations (up to 10 m V peak-to-peak) occurred in both control and CCI neurons, and triggered the spontaneous, random action potentials in neurons from CCI rats. Spontaneously firing neurons exhibited more negative action potential threshold (-34.8 mV) when compared to quiescent neurons from ganglia either after CCI (-18.7 mV) or controls (-20.5 mV). These findings show that spontaneous action potential activity after CCI is a property residing in the cell bodies of dorsal root ganglion neurons and is amenable to more detailed analysis using such an in vitro system, allowing better understanding of the cellular changes underlying neuropathic pain from nerve injury.

Role of a Ca(2+)-dependent slow afterhyperpolarization in prostaglandin E2-induced sensitization of cultured rat sensory neurons

To determine if inhibition of a Ca(2+)-dependent slow afterhyperpolarization (AHPslow) contributes to prostaglandin E2 (PGE2)-induced sensitization of DRG neurons, we have used patch-clamp electrophysiological techniques on cultured dorsal root ganglion (DRG) neurons from the adult rat. In support of a role for AHPslow in sensitization of DRG neurons, we demonstrate that: (1) AHPslow expression is restricted to a subpopulation of putative nociceptors; (2) burst duration is controlled by AHPslow in these neurons; and (3) in some neurons, PGE2 decreases AHPslow and produces a concomitant increase in the number of action potentials generated in response to depolarizing current injection. However, our results also demonstrate that AHPslow modulation is not sufficient to explain PGE2-induced sensitization in the majority of DRG neurons because: (1) the size of the population of DRG neurons expressing AHPslow is less than half the size of the population of DRG neurons sensitized by PGE2; (2) PGE2 produces a decrease in action potential threshold as well as an increase in the number of action potentials in response to current injection, while inhibition of AHPslow has little effect on threshold; and (3) the sensitizing effects of PGE2 are dissociated from its effects on AHPslow in more than half of neurons tested. We conclude that PGE2-induced sensitization must involve the modulation of ionic currents in addition to that underlying AHPslow.

Co-expression of nociceptor properties in dorsal root ganglion neurons from the adult rat in vitro

The cell body of sensory neurons in vitro has been used as a model to study the electrophysiological properties of afferent terminals. A limitation of this approach has been the ability to identify the function of the neuron studied. In the present study, we have tested the hypothesis that a putative nociceptor can be identified in vitro based on the expression of properties associated with nociceptors in vivo. A combination of patch-clamp electrophysiological and immunohistochemical techniques were used to describe the expression of nociceptor properties in acutely cultured dorsal root ganglion neurons from the adult rat. These properties include: a small cell body diameter; the presence of the neuropeptides substance P and calcitonin-gene related peptide; a shoulder (inflection) on the falling phase of the somal action potential, a response to the algogenic agent capsaicin, and sensitization in response to prostaglandin E2. Our results indicate that the frequency of expression of each of these properties varies in a manner consistent with that predicted from observations made in vivo, and that when one property is present in any given neuron, the other properties are also likely to be present. These data support the suggestion that the cell body of adult rat dorsal root ganglion neurons in vitro can be used to study the electrophysiological properties of nociceptors.

Electrophysiological properties of neurones with CGRP-like immunoreactivity in rat dorsal root ganglia

Intracellular voltage recordings and fluorescent dye injections were made in vitro in 107 neurons in lumbar dorsal root ganglia (DRGs) of 6- to 8-week-old rats. Calcitonin gene-related, peptide-like immunoreactivity (CGRP-LI) was examined in these neurones, which were divided into C-, A delta-, and A alpha/beta-fibre neurones on the basis of their conduction velocities (CVs). A-fibre neurones with CGRP-LI had significantly longer mean action potential (AP) and afterhyperpolarisation (AHP) durations than those without CGRP-LI. A delta neurones with CGRP-LI had significantly longer AHP durations, slower CVs and slower maximal fibre following frequencies than those without CGRP-LI. They also had longer AP durations (not significant). The largest A delta neurones were CGRP-LI negative, whereas the smaller cells were either positive or negative. A alpha/beta neurones with CGRP-LI also had longer mean APs (not significant) and AHPs (significant) than those without CGRP-LI, and the cell size distributions were similar for positive and negative neurones. Most A-fibre neurones with CGRP-LI had inflections on the falling phase of the somatic AP. Of the A-fibre neurones with such inflections (Ai neurones), those with CGRP-LI had longer AP durations (not significant) and longer AHP durations (significant) than Ai neurones without CGRP-LI, pointing to a functionally distinct subgroup of Ai neurones. There were no significant differences in electrophysiological properties or cell size measurements between C-fibre neurones with and without detectable CGRP-LI. The patterns of electrophysiological properties of A delta neuronal somata with CGRP-LI and of most, but not all, A alpha/beta neuronal somata with CGRP-LI are similar to those reported for cutaneous nociceptors with A fibres in rat (Ritter and Mendell [1992] J. Neurophysiol. 68:2033-2041). Because rat DRG neurones that express CGRP normally also express trkA (Averill et al. [1995] Eur. J. Neurosci. 7:1484-1494), the properties described here of neurones with CGRP-LI are probably the same as those of DRG neurones with trkA.

Nerve growth factor contributes to the up-regulation of growth-associated protein 43 and preprotachykinin A messenger RNAs in primary sensory neurons following peripheral inflammation

Peripheral inflammation induced in adult rats by an intraplantar injection of complete Freund's adjuvant results in a rapid (6 h) increase in the expression of the messenger RNAs for the neuronal growth-associated protein 43 and for preprotachykinin A, the precursor for substance P, in dorsal root ganglion sensory neurons innervating the inflamed area. This increase peaks at 48 h and then declines by five days. The changes are present in the dorsal root ganglion cells innervating the inflamed skin (lumbar 4 or 5) but no elevation was found in the third lumbar dorsal root ganglion which innervates neighbouring non-inflamed skin. The increased growth-associated protein 43 messenger RNA in the dorsal root ganglion is followed by a marked increase in growth-associated protein 43-like immunoreactive fibres in the epidermis of the inflamed skin. Systemic administration of neutralizing anti-nerve growth factor antibodies immediately prior to the inflammation prevents the increase in growth-associated protein 43 and preprotachykinin A messenger RNAs in the sensory neurons. A subcutaneous injection of nerve growth factor (200 ng) into the hindpaw elevates preprotachykinin A but not growth-associated protein 43 messenger RNA in the fourth lumbar dorsal root ganglion 48 h post-injection and this could be prevented by co-administration of the anti-nerve growth factor serum. The production of nerve growth factor in inflamed target tissues leads to alterations in the phenotype of responsive adult primary sensory neurons which include a change in the levels of a growth-related protein and a peptide neuromodulator.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasticity in the synthesis and storage of substance P and calcitonin gene-related peptide in primary afferent neurons during peripheral inflammation

Several indices of peptidergic, primary afferent neural transmission in rat at the level of the lumbar spinal cord exhibited differential changes over time in response to adjuvant-induced inflammation of the hindpaw. The indices were measurements of the production of messenger RNA encoding the precursors for substance P and calcitonin gene-related peptide in dorsal root ganglia, the storage of substance P and calcitonin gene-related peptide in the dorsal spinal cord and the release of the peptides evoked by application of capsaicin to the dorsal spinal cord. A 47% decrease in the content of immunoreactive substance P in the dorsal half of the lumbar spinal cord, as determined by radioimmunoassay, was measured at 6 h following the injection of complete Freund's adjuvant into the hindpaw. Decreased content of immunoreactive SP persisted for four days, but was no longer present at eight days after the adjuvant injection. The content of immunoreactive calcitonin gene-related peptide in the dorsal spinal cord was decreased by 29% at one day following the injection of adjuvant into the rat hindpaw and 43% at two days; the content then increased to a level greater than that of control animals at eight days. The amount of messenger RNA encoding preprotachykinin and prepro-calcitonin gene-related peptide in L4-L6 dorsal root ganglia was determined from northern blot analysis of the total messenger RNA extracted from the dorsal root ganglia. Each species of messenger RNA had increased compared to the control animals at two days following the injection of adjuvant into the rat hindpaws and remained elevated after eight days. Thus, an increase in the messenger RNAs encoding substance P and calcitonin gene-related peptide in the dorsal root ganglia preceeded the recovery of the content of the peptides in the spinal cord. Morphometric studies of calcitonin gene-related peptide-immunoreactive perikarya in the L4 dorsal root ganglia indicated that the increase in messenger RNA occurred in neurons of the size that normally express calcitonin gene-related protein. Radioimmunoassay of the superfusate of the dorsal half of the lumbar spinal cord was used to measure the release of immunoreactive substance P and immunoreactive calcitonin gene-related protein in vitro. Although the basal release of immunoreactive substance P and immunoreactive calcitonin-gene related protein from the dorsal spinal cord was constant throughout the time points examined, changes occurred in the release of peptide evoked by 10 microM capsaicin. The capsaicin-evoked release of immunoreactive substance P was decreased at 6 h and eight days post-injection of adjuvant.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinoparabrachial tract neurons showing substance P receptor-like immunoreactivity in the lumbar spinal cord of the rat

By using substance P receptor (SPR) immunofluorescence histochemistry combined with fluorescent retrograde labeling, SPR-like immunoreactive (SPR-LI) neurons sending their axons to the lateral parabrachial region were observed in the lumbar spinal cord of the rat. After injection of Fluoro-Gold into the lateral parabrachial region, retrogradely labeled neurons with SPR-LI were seen frequently in lamina I and the lateral spinal nucleus, and occasionally in laminae IV and V, with a predominantly contralateral distribution. Some of these neurons, especially those in lamina I, may convey nociceptive information to the lateral parabrachial region.

Substance P is a possible neurotransmitter in the rat spinothalamic tract

In order to shed some light on the neurotransmitters in the spinothalamic tract (STT), we examined, biochemically and immunohistochemically, the contents of various neurotransmitter candidates in the terminal field of the STT after cervical hemi-chordotomy (HC) and dorsal quadrant-chordotomy (dQC) in the rat. Substance P (SP), calcitonin gene-related peptide (CGRP), enkephalin, neuropeptide Y, neurotensin, oxytocin and dynorphin A were analyzed immunohistochemically. The contents of neuropeptides (SP, CGRP and cholecystokinin octapeptide) were measured by radioimmunoassay and those of amino acids (aspartic acid, glutamic acid, gamma-aminobutyric acid (GABA) and glycine) and noradrenaline were determined using high-performance liquid chromatography. Cervical hemi-chordotomy, but not dQC, caused significant decreases of the SP-like immunoreactivity in and SP content of the ventral thalamus on the ipsilateral side, compared with that on the contralateral side and of rats subjected to sham-operation. However, neither HC nor dQC resulted in any changes in the ventral thalamic contents of other putative neurotransmitters examined. These results suggest that, in rats, the STT contains SP and that SP-positive fibers run in the ventral half of the ascending spinal tract at the cervical level.

Intrathecal capsaicin enhances one-kidney renal wrap hypertension in the rat

Afferent renal nerves (ARN) have been implicated in the development of one-kidney renal wrap (1K-WRAP) hypertension. The role of renal nerves in desoxycorticosterone acetate-salt (DOCA) hypertension, a low-renin model of hypertension, is controversial. The present study was designed to determine if spinal substance P (SP) and/or calcitonin gene-related peptide (CGRP) in ARN affects the development of 1K-WRAP or DOCA hypertension in adult rats. Selective long-term partial depletion of spinal SP and CGRP within small primary afferent nerve fibers including unmyelinated ARN was achieved by intrathecal administration of capsaicin. After capsaicin treatment, 1K-WRAP hypertension was induced by removing the right kidney and wrapping the left kidney with a figure-8 ligature. In a second group of rats, DOCA hypertension was induced by subcutaneous application of desoxycorticosterone pellets after unilateral nephrectomy. Systolic arterial pressure was monitored for 8 weeks by tail cuff plethysmography after which direct blood pressure measurement was performed followed by immunohistochemistry. Intrathecal capsaicin administration had no significant effect on SP-ir and CGRP-ir of ARN soma located within thoracic dorsal root ganglia whereas immunoreactivity against these peptides was reduced by one third to one half in the dorsal horn, indicating effective long-term spinal depletion of these neuropeptides. Intrathecal capsaicin enhanced the development of 1K-WRAP hypertension, since arterial pressure was greater in the treated group. In contrast, DOCA hypertension was unaffected by capsaicin pretreatment. Considering the neurotoxic action of capsaicin for SP-ir and CGRP-ir unmyelinated primary afferent neurons, we hypothesize that spinal SP, CGRP and/or related peptides existing in ARN and other capsaicin-sensitive unmyelinated primary afferent neurons in the lower thoracic spinal cord may ameliorate 1K-WRAP hypertension, but not DOCA hypertension.

Changes in sensory neuropeptides in dorsal root ganglion and spinal cord of spontaneously diabetic BB rats. A quantitative immunohistochemical study

This study examined the expression of the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously diabetic BB rats and non-diabetic controls using quantitative immunohistochemical analysis. In both animal groups immunoreactivities for CGRP and SP were widely distributed within the neurons of DRG and in nerve fibres of the dorsal spinal cord. Image analysis of each neuropeptide subpopulation in the DRG showed that in diabetic rats the cell diameter of immunostained CGRP neurons was significantly decreased compared with controls, while no difference could be found for SP-immunoreactive (IR) neurons. The decrease in the CGRP-IR cell diameter appeared to occur mainly in medium to large neurons (30-50 microns diameter; 2.2% controls, < 1% diabetes), this change being parallel to an increased frequency of small-size neurons (< 20 microns diameter) in diabetic rats (62% controls, 69% diabetes; P < 0.05). However, there was no statistical difference in the total number of cells immunostained for either CGRP or SP between control and diabetic rats. The ratio of CGRP or SP neurons compared to total cells in the ganglion was similar in control and diabetic groups. No difference could be observed for peptide immunoreactivity in the dorsal and ventral horns of either control or diabetic animals. The observed changes of perikaryal size in diabetic rats might relate to the reduced axonal calibre and conduction velocity observed in these animals, and indicate that subpopulations of sensory neurons are affected differently by diabetes.

The development of cutaneous afferent pathways in fetal sheep: a structural and functional study

In this study we have examined the functional and structural development of cutaneous afferent pathways in the fetal sheep hindlimb from 67 to 143 days of gestation. The earliest age at which extracellular discharges could be evoked in dorsal root ganglia and in dorsal horn cells by natural cutaneous stimulation was 75 days. The majority of cells responded to light stroking or indentation of the skin (low threshold) although some cells responded to intense squeezing (high threshold). With increasing gestational age, the majority of cells continued to respond to low threshold stimuli with cells responding to intense mechanical stimuli being recorded less frequently. Dorsal root ganglion cells responding to the cutaneous application of noxious heat (> 45 degrees C) were first observed at 107 days. We have also shown that fibres projecting from dorsal horn cells and presumably entering the spinothalamic tract carry signals at least as far as the mid thoracic spinal cord by 104 days. Ultrastructural studies of the skin revealed bundles of unmyelinated axons located to blood vessels throughout the dermis at 68 days. Innervation of the skin was first observed by silver staining at 75 days when fibres could be seen running along blood vessels in the dermis. With increasing gestational age fibres were seen traversing the dermis to innervate the epidermis as free nerve endings. Wool/hair follicle innervation was first evident at about 100-106 days with only a few follicles being innervated at this age. By 115 days, nerve endings had begun to form circumferential wrappings around follicles and by 134 days lanceolate terminals were observed around the base of the follicles. Biocytin-labelled afferent fibres entered the dorsal horn at 56 days. This initial innervation was sparse but by 76 days there was a marked increase in both the number of afferent fibres entering the dorsal horn and in the extent of their arborisation. Ultrastructural studies revealed that terminals immunoreactive for calcitonin gene-related peptide were present in lamina I as early as 61 days. The period of maximal synaptogenesis and synaptic maturation of this group of terminals appeared to occur between 87-128 days. Therefore the commencement of activation of dorsal horn cells by natural cutaneous stimulation occurs by mid gestation (75 days) in the fetal sheep. This is at the same time or just after peripheral nerves first innervate the skin and about 2 weeks after primary afferent terminals can be identified in the dorsal horn.

Substance P, neurofilament, peripherin and SSEA4 immunocytochemistry of human dorsal root ganglion neurons obtained from post-mortem tissue: a quantitative morphometric analysis

Immunocytochemical studies on lumbar dorsal root ganglia obtained at routine postmortem 24-36 h after death were carried out, and neuronal cross-sectional areas measured. The subjects were elderly (76-81 years), of both sexes, had died from heart attack or haemorrhage, and had no clinical evidence of clinical neuropathy or of disease known to be associated with neuropathy. The data were consistent between ganglia from the three subjects. There were striking similarities with data from other species. Two populations of cell profiles with overlapping size distributions were distinguished with an anti-neurofilament antibody, neurofilament-rich (45% of cell profiles) with a large mean area and neurofilament-poor with a smaller mean area. Anti-substance P and anti-peripherin antibodies both labelled a population with a small mean area, with extensive co-localization between them. There were also some differences between these human dorsal root ganglia and dorsal root ganglia from some other species. More neuronal profiles were labelled for substance P in humans (44%) than in rat (20%). More neuronal profiles were labelled for SSEA4 (stage specific embryonic antigen 4) in human (40.5%) than in rat dorsal root ganglia (10%), and the SSEA4-positive profiles were relatively smaller in human than in rat. No selective accumulation of lipofusin in profiles of large cells was apparent. This study also shows that quantitative morphometric analysis of immunocytochemically labelled dorsal root ganglion neuronal profiles can be carried out successfully on human sensory ganglia obtained at post-mortem. This is the first demonstration of the two main subgroups of dorsal root ganglia neurones with neurofilament-rich and poor somata in human tissue. The size distributions of neurons with neurofilament, substance P and peripherin are consistent with these neuronal populations having similar functional properties to those described in other species. From the known sensory and fibre loss with aging, it is speculated that the loss of some large diameter neurones with myelinated fibres and low mechanical thresholds, might account for the high percentage of neurones expressing substance P.

Altered tachykinin expression by dorsal root ganglion neurons in a rat model of neuropathic pain

The experiments described in the present study approached nerve injury from both a biochemical and anatomical perspective by monitoring changes in expression of preprotachykinin (PPT) mRNA encoding the prototypic tachykinin substance P and related peptide species in neurons of the rat dorsal root ganglia (DRG) following unilateral chronic constriction injury of the sciatic nerve. In situ hybridization histochemistry (ISHH) analyses in conjunction with computer-assisted image processing were employed to quantify levels of PPT mRNA distributed in DRG neurons. Injury-induced changes in PPT mRNA expression by affected DRG neurons included: (1) at early postoperative times, generally increased levels of PPT mRNA associated with small and intermediate-size B cells exhibiting normal morphology, (2) at late postoperative times, markedly decreased levels of PPT mRNA associated with degenerating B cells, and (3) induction of PPT gene expression by large A cells which is highly correlated with degenerative morphological changes. The significant aspects of these changes are discussed with special emphasis on the contribution of altered transmitter expression by DRG neurons to the pathophysiology of causalgia. In particular, the induction of PPT gene expression by many of the large neurons undergoing degenerative changes may represent an important biochemical parameter which is associated with the development and persistence of experimental allodynia.

Neurotransmitters in subcortical somatosensory pathways

Investigations during recent years indicate that many different neuroactive substances are involved in the transmission and modulation of somesthetic information in the central nervous system. This review surveys recent developments within the field of somatosensory neurotransmission, emphasizing immunocytochemical findings. Increasing evidence indicates a widespread role for glutamate as a fast-acting excitatory neurotransmitter at different levels in somatosensory pathways. Several studies have substantiated a role for glutamate as a neurotransmitter in primary afferent neurons and in corticofugal projections, and also indicate a neurotransmitter role for glutamate in ascending somatosensory pathways. Other substances likely to be involved in somatosensory neurotransmission include the neuropeptides. Many different peptides have been detected in primary afferent neurons with unmyelinated or thinly myelinated axons, and are thus likely to be directly involved in primary afferent neurotransmission. Some neurons giving rise to ascending somatosensory pathways, primarily those with cell bodies in the dorsal horn, are also immunoreactive for peptides. Recent investigations have shown that the expression of neuropeptides, both in primary afferent and ascending tract neurons, may change as a result of various kinds of peripheral manipulation. The occurrence of neurotransmitters in intrinsic neurons and neurons providing modulating inputs to somatosensory relay nuclei (the dorsal horn, the lateral cervical nucleus, the dorsal column nuclei and the ventrobasal thalamus) is also reviewed. Neurotransmitters and modulators in such neurons include acetylcholine, monoamines, GABA, glycine, glutamate, and various neuropeptides.

Sparse substance P-like immunoreactivity in intervertebral discs. Nerve fibers and endings in the rat

I studied rat lumbar intervertebral discs using a monoclonal antibody to substance P, which revealed immunoreactivity in the periosteum and ligaments adjacent to the intervertebral disc. Fibers containing substance P-like immunoreactivity were also found penetrating and terminating within the annulus fibrosus of both the anterior and posterior intervertebral disc. The maximum depth of penetration was 5 lamellae (annular rings) or approximately one sixth of the depth of the annulus. The terminal structures were not encapsulated (free-nerve endings) and were either branched, looped or both. The majority of fibers were varicose in appearance. Substance P-like immunoreactivity was very minor.

Time-dependent changes in Bolton-Hunter-labeled 125I-substance P binding in rat spinal cord following unilateral adjuvant-induced peripheral inflammation

Time-dependent changes in Bolton-Hunter-labeled 125I-substance P binding occurred in the dorsal horn of the spinal cord following unilateral adjuvant-induced inflammation in the hindpaw of the rat. Inflammation was characterized by measures of edema and hyperalgesia. Edema and hyperalgesia were both present 6 h after induction of inflammation. However, by eight days, hyperalgesia had dissipated while edema persisted. Six hours after the induction of inflammation, widespread decreases in Bolton-Hunter-labeled 125I-substance P binding occurred on both sides of the dorsal horn of spinal level L4 in comparison to the control group. However, by two days, widespread increases in Bolton-Hunter-labeled 125I-substance P binding occurred on both sides of the spinal cord at level L4 compared to the control group. The increase in radioligand binding was primarily due to a 10-fold increase in affinity of neurokinin-1 receptors for substance P. At later time-points of four and eight days, Bolton-Hunter-labeled 125I-substance P binding remained increased only in laminae I/II on the side of the spinal cord ipsilateral to inflammation. The changes in Bolton-Hunter-labeled 125I-substance P binding suggest that alterations in substance P synaptic transmission in the spinal cord may contribute to the increased excitability of spinal neurons that accompanies adjuvant-induced peripheral inflammation.

Calretinin-immunoreactive neurons in the trigeminal and dorsal root ganglia of the rat

The cell body size of primary neurons were measured in the trigeminal (TG) and lumbar dorsal root ganglia (DRG) monochrome-stained for calretinin (CR)-like immunoreactivity. A trichrome stain for CR, carbonic anhydrase (CA) and tachykinin (TK) was also employed to estimate possible overlap of cellular distribution of these substances. In the DRG, the cell size spectrum of CR-positive cells was clearly bimodal; a greater proportion (84.1%) of CR-positive cells was distributed in the range > or = 800 microns2 with a mode between 1,500-1,600 microns2, while a smaller proportion (14.8%) < 700 microns2 with a mode of 400-500 microns2. They were evenly distributed throughout the DRG. Although CR-positive TG neurons were smaller than similar DRG neurons, a bimodal distribution pattern remained unchanged. 94.6% of CR-positive cells measured 100-1,400 microns2 with peak ranges of 200-300 microns2 and 400-500 microns2. Most of CR-positive cells in the ophthalmic division were 400 microns2 or larger and small CR-positive cells (< 400 microns2) were concentrated in the maxillary and mandibular divisions. Most of CR-positive DRG cells showed CA activity (76.5%), while those with TK-immunoreactivity were rare (7.2%). In the TG, 38.4% of CR-positive cells were TK-positive. They were mostly smaller than 800 microns2. On the other hand, CA was detected in 43.4% of CR-positive TG cells. Most of the TG cells co-expressing CR and CA were 400 microns2 or larger. Simultaneous co-expression of TK and CA by the CR-positive cells was negligible.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of immunoreactivity for calcitonin gene-related peptide, substance P and glutamate in primary sensory neurons, and for serotonin in the spinal cord of fetal sheep

In this study we have described the ontogeny of immunoreactivity for calcitonin gene-related peptide, substance P and glutamate in primary sensory neurons, and for serotonin in the sacral spin cord, of fetal sheep (n = 37) from 56 to 140 days of gestation (term = 146 days). A few fine, varicose fibres immunoreactive for calcitonin gene-related peptide were present in Lissauer's tract, the dorsolateral funiculus and in laminae I and V in the dorsal horn of the spinal cord at 56-61 days of gestation. At this age, two groups of intensely staining immunoreactive cells were present in the motoneuron pool in laminae VIII and IX in the ventral horn of the spinal cord. By 77 days, immunoreactive fibres were also present in laminae II and X. With advancing gestational age, an increase in the intensity of staining was observed throughout the cord to term, with the exception of laminae VIII and IX, where a decrease was seen. Intense staining of cells in the motoneuron pool was evident until c. 128 days, after which time staining became very faint. Fine fibers immunoreactive for substance P were present in Lissauer's tract and lamina I of the spinal cord at 56-61 days of gestation. They were also present throughout laminae IV-VI and X as well as throughout the entire ventral horn. Immunoreactive fibres in lamina II were evident by 77 days. The staining increased in density but remained similar in distribution with increasing gestational age to term in the dorsal horn, but decreased markedly in the ventral horn. Cells immunoreactive for substance P were evident from 56 days, particularly on the border of laminae II and III, until late in gestation. Ultrastructural studies showed that axon terminals immunoreactive for calcitonin gene-related peptide and for substance P were present in lamina I by 61 days. Immunoreactivity for glutamate was evident at 83 days in dorsal root fibers and also in lamina I and II, where it was more prominent in cells than in fibres. At all ages examined, the dorsal horn stained more intensely than the ventral horn. Immunoreactivity for glutamate and neuropeptides appeared in the cells and fibres of dorsal root ganglia at 97-100 days. In the skin, immunoreactivity for calcitonin gene-related peptide and substance P was present at 85 days, some time after its appearance in the cord. Fibres immunoreactive for serotonin appeared in lamina I, at the neck of the dorsal horn and in the ventral horn at 83 days of gestation.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological and membrane properties of young rat lumbar and thoracic dorsal root ganglion cells with unmyelinated axons

Membrane and morphological properties of thoracic (Th9-13) and lumbar (L2-5) dorsal root ganglion cells have been investigated in an in vitro dorsal root ganglion (DRG) preparation from 14-day-old rats using intracellular recordings and the intracellular injection of Neurobiotin. The passive and active membrane properties of 47 DRG cells with conduction velocities (CV) less than 0.81 m/s were studied, which were considered to possess unmyelinated axons. The action potentials elicited by the stimulation of peripheral nerves or the dorsal roots were characteristic of C-cells, with long duration, inflexion on the falling phase and long lasting after hyperpolarization. Input resistance of the C-cells varied between 16 and 158 M omega and were significantly higher in thoracic than in the lumbar ganglia. Cells in the more cranial levels also tended to be smaller than those in the caudal levels with a mean cross sectional area of 301 +/- 32.5 microns2. Twenty-five percent of the cells from both regions showed an inward rectification. The distribution of CVs, input resistances and cross sectional areas were non-normal. While a weak correlation was found between the conduction velocity and input resistance of the cells, no correlation was present between the size of the perikarya and conduction velocity or the input resistance. These results show that by the 14th day of postnatal development membrane and morphological parameters approach those of adult rats. They also suggest that in cells with unmyelinated fibres, the size of the perikaryon does not predict the thickness of the axon, and that this cell population is heterogeneous.

Ultrastructural morphology, synaptic relationships, and CGRP immunoreactivity of physiologically identified C-fiber terminals in the monkey spinal cord

The spinal cord terminations of two electrophysiologically identified single C-fibers (one identified as a C-nociceptor) were intra-axonally labeled with horseradish peroxidase and analyzed with both light and electron microscopy. Serial section ultrastructural analysis and postembedding immunocytochemical techniques for calcitonin gene-related peptide (CGRP), substance P (SP), and GABA were used to study the synaptology, and neuropeptide content. All C-terminal synapses were in laminae I and II. The terminals sampled (n = 73) from these two C-fibers rarely established glomerular synaptic complexes, but rather, simple terminals, usually measuring 1-4 microns in length and 1-3 microns in diameter. They most often established 1 or 2 (range 1 to 5) quite large asymmetric axodendritic synaptic contacts. Postsynaptic structures included dendritic spines and shafts with and without vesicles. C-terminals were filled with small round synaptic vesicles (45-60 nm) and also contained variable numbers of large dense-core vesicles (LDCVs, 80-110 nm). LDCVs inside identified C-terminals frequently displayed CGRP immunoreactivity. We were unable to detect SP immunoreactivity inside our sample of C-fiber LDCVs. C-terminals were never found postsynaptic to other profiles. Thus, the C-fiber terminals sampled in this study have simple synaptology, do not receive presynaptic control and contain CGRP immunoreactivity. They differ greatly from the terminals of A delta nociceptors studied previously by our group that had glomerular endings, often received presynaptic input and did not contain CGRP immunoreactivity. This suggests the existence of different processing mechanisms, at the level of the first synapse, for nociceptive inputs arriving to lamina I and II through different types of primary afferents.

Primary sensory neurones: neurofilament, neuropeptides, and conduction velocity

This paper reviews and provides new data on the relationship of the peptide content in rat dorsal root ganglion (DRG) neurons to a) the neurofilament content of the soma and b) the conduction velocities of the fibres. The latter involved intracellular recordings made in vitro followed by dye injection and immunocytochemistry. Because neurofilament-poor DRG neurones have C-fibres, and A-fibre neurones are neurofilament rich, the soma neurofilament content of peptide containing neurones allowed predictions to be made about their conduction velocity ranges. Substance P-like immunoreactive (SP-LI) neurones were mostly small, neurofilament poor, but a few (15%) were neurofilament rich. From conduction velocity measurements, about half the C-fibre neurones studied and 10% of A delta-neurones but no A alpha/beta-neurones showed SP-LI. CGRP-LI neurones were also mainly neurofilament poor neurones, but 32% were neurofilament rich, including small, medium, and large neurones. Fibres of CGRP-LI neurones conducted in the C, A delta or A alpha/beta ranges. Neurones with somatostatin-LI (SOM-LI) were all neurofilament poor; preliminary data is consistent with SOM-LI neurones having C-fibres.

Autoradiographic analysis of 125I-substance P binding in rat spinal cord following chronic constriction injury of the sciatic nerve

Using receptor binding and autoradiographic techniques, changes in Bolton-Hunter labeled 125I-substance P (125I-BH-SP) binding were determined in laminae I/II, V and X of rat lumbar spinal cord after chronic constriction injury (CCI) of the sciatic nerve. When compared to the sham-operated side of the control group, SP binding significantly increased ipsilateral to the CCI in laminae I/II at 5, 10 and 20 days after injury and in lamina V at 5 days after injury. Scatchard analysis was performed on the 125I-BH-SP binding to the NK1 receptor in laminae I/II of rats 5 days after generation of the CCI. A significant decrease in the Kd of 125I-BH-SP binding was observed in laminae I/II ipsilateral to CCI when compared with the control side (ipsilateral to sham surgery). There was no significant change in the Bmax in laminae I/II ipsilateral to CCI. The changes in 125I-BH-SP binding in the rat spinal cord that occurred after CCI were found in areas of the spinal cord that receive terminations of nociceptive primary afferent fibers. The increased affinity of the NK1 binding site that we report could result in an increase in SP receptor activation in laminae I/II. Such central changes in SP binding may contribute to the neuropathic pain syndrome observed in rats with the CCI.

Trigeminal ganglion neurons which project by way of axon collaterals to both the caudal spinal trigeminal and the principal sensory trigeminal nuclei

Employing a combination of fluorescent retrograde double labeling and immunofluorescence histochemistry, we found that some single neurons in the trigeminal ganglion of the rat projected by way of axon collaterals both to the caudal spinal trigeminal nucleus and to the principal sensory trigeminal nucleus, and that about 40% or 57% of these neurons showed respectively substance P- or calcitonin gene-related peptide-like immunoreactivity.

The actions of capsaicin applied topically to the skin of the rat on C-fibre afferents, antidromic vasodilatation and substance P levels

1. Single applications of solutions of capsaicin were made to the intact skin of anaesthetized rats and the effects on cutaneous blood flow and the firing of C-nociceptor afferents determined. Blood flow was measured by laser-Doppler flowmetry. C-fibre activity was recorded from filaments dissected from the saphenous nerve. 2. Following the application of a capsaicin solution (concentration > or = 1 mM) to rat saphenous skin, low frequency firing occurred in C-polymodal nociceptors that sometimes continued for > 10 min. At the some time, large increases in skin blood flow occurred exceeding 300% in some instances. 3. After the initial excitation, some C-polymodal nociceptors lost their sensitivity to pressure whilst their sensitivity to heat was lost or enhanced depending on the vehicle used. 4. Sensitivity of C-polymodal nociceptors to heat recovered in < 1 day following a single application of 33 mM capsaicin. Thresholds to mechanical pressure, however, were still significantly elevated by 123% on day 1, but had recovered on day 2. 5. Vasodilatation in response to saphenous nerve stimulation ('antidromic vasodilatation') was significantly reduced by 35%, 2 days after a single application of 33 mM capsaicin, but was normal at 4 days. 6. Following a single application of 33 mM capsaicin, skin substance P levels fell to only half the normal value at day 1 and remained at this level throughout the 4 day period examined. 7. It is suggested that the ability of relatively low concentrations of capsaicin to desensitize C-fibre nociceptors may underlie the analgesic action of topical capsaicin in man.

Retrograde labelling of dorsal root ganglion cells in the rat: a quantitative and morphological comparison of Fluoro-Gold with horseradish peroxidase labelling

We have compared retrograde labelling of rat primary sensory neurons using Fluoro-Gold (FG) and horseradish peroxide conjugated with wheat germ agglutinin (HRP-WGA). Fluoro-Gold 2.5% after 48 h transit time and FG 5% after 24 and 48 h retrogradely labelled similar numbers of cell profiles as HRP-WGA (P greater than 0.1% Student's t-test). The calculated cell size distribution for the above FG groups were similar to those for the HRP-WGA. However, FG 2.5% after a 24 h transit time labelled significantly fewer cells (P less than 0.001 Student's t-test). FG retrograde transport may be used to identify the same population of DRG cells as HRP-WGA.

Distribution of neurokinin B in rat spinal cord and peripheral tissues: comparison with neurokinin A and substance P and effects of neonatal capsaicin treatment

In the present study, highly specific radioimmunoassays were developed and used to measure neurokinin B, neurokinin A and substance P in the rat spinal cord and various peripheral tissues. The results are as follows. (1) Neurokinin B and neurokinin A were distributed all along the rostrocaudal axis of the spinal cord, as is substance P, and were more concentrated in the dorsal than in the ventral region. (2) Substance P was more abundant in the central and peripheral nervous tissues than neurokinin A, while in certain peripheral organs, neurokinin A was more abundant than substance P. In the spinal cord, neurokinin B concentrations were lower than those of the other two tachykinins. (3) In contrast to neurokinin A and substance P, neurokinin B was not detected in any of the peripheral tissues examined. (4) Capsaicin treatment reduced by half neurokinin A and substance P concentrations in the dorsal region of the spinal cord, the dorsal root ganglia and the sciatic nerve, but was without effect on neurokinin B concentrations in the spinal cord. Neurokinin A, like substance P, may therefore have an important function in the transmission of sensory information, particularly in nociceptive transmission from the periphery to the spinal cord and in peripheral neurogenic inflammation. In contrast, since neurokinin B was not found in the sensory neurons, it is not likely to have these functions, but may perhaps control them.

Substance P innervation of the rat and cat thalamus. II. Cells of origin in the spinal cord

Evidence in the preceding paper suggests that fibers and terminals immunopositive for substance P (SP) in somatosensory thalamic nuclei are part of the spinothalamic tract (STT). In this paper, more direct evidence on this point is provided by immunocytochemistry for SP on the cervical spinal cord, alone or combined with the retrograde transport of colloidal gold-labeled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase (WGAapoHRP-Au). In cats and rats pretreated with colchicine and/or anterolateral chordotomy (to increase SP content in cell bodies), many small to large cell bodies are SP-immunopositive especially in laminae I and V, but also in more ventral laminae of the upper cervical cord. SP neurons are also present in the dorsolateral funiculus (in the lateral spinal nucleus, LSN, in rats) but not in the lateral cervical nucleus or in the internal basilar nucleus. In both species there is a considerable degree of overlap in the distribution of SP-positive neurons and that of STT neurons. SP immunocytochemistry in rats after WGAapoHRP-Au injection in the somatosensory thalamus reveals SP-positive STT neurons in LSN, in lamina I and in lamina V, and, to a lesser extent, in more ventral laminae. These results demonstrate that SP is a marker and/or neuromediator for some STT neurons. Together with the evidence discussed in the preceding paper, the results also suggest that SP-positive neurons may be involved in the transmission of nociceptive input.

Specific temporal and spatial distribution of JUN, FOS, and KROX-24 proteins in spinal neurons following noxious transsynaptic stimulation

We present the first comparative investigation of the basal and transsynaptically induced expression of c-JUN, JUN B, JUN D, c-FOS, FOS B, and KROX-24 proteins in the spinal cord, using immunocytochemistry with specific antibodies. We demonstrate that electrical stimulation of the sciatic nerve at A delta/C-fiber (not A alpha/beta-fiber) intensity strongly induces the expression of these immediate-early gene-encoded proteins. Basal immunoreactivity was found for c-JUN in motoneurons, for JUN D in almost every cell of the gray matter, and for KROX-24 in the superficial dorsal horn. One hour after electrical stimulation of the sciatic nerve at A delta/C-fiber intensity, expression of all proteins except JUN D reached its maximum. Initially immunoreactivity was restricted to the ipsilateral dorsal horn, but after 4 hours appeared contralaterally. Expression of JUN D was increased only after 4 hours. Within the dorsal horn, the expression of c-JUN, JUN B, FOS B, and KROX-24 was mainly restricted to the superficial layers. Immunoreactivity decreased to basal levels between 8 and 16 hours. c-FOS and JUN D were expressed in both the superficial and deep dorsal horn; in the latter, c-FOS and JUN D persisted longer. Induced JUN D was present the longest and was still visible after 32 hours. In motoneurons of the ipsilateral ventral horn, c-JUN, JUN D, and c-FOS appeared after 8 hours. Surgical exposure of the sciatic nerve evoked a strikingly prolonged expression of all proteins compared to that following electrical stimulation of the sciatic nerve. Our results demonstrate that stimulation of nociceptive A delta- and C-fibers induces early and late expression of proteins encoded by immediate-early genes with a specific temporal and spatial distribution of the expression of each protein. Furthermore, the extent of protein expression reflects the intensity of noxious stimulation.

Sensory pharmacology

During the last decade, evidence has been accumulated to demonstrate that a subpopulation of peptide-containing primary afferent neurones serve a dual sensory-efferent function. Considerable effort has been put into the development of pharmacological tools to modulate the release and/or the postjunctional effects of transmitters of primary afferents. This commentary summarizes the different approaches designated to achieve this goal, which, if successful, will lead to true 'sensory pharmacology'.

Biosynthesis and release of tachykinins from rat sensory neurons in culture

A long-term culture system of dissociated rat dorsal root (DRG) and trigeminal ganglion cells with high cell density has been developed. Two to 3 weeks after plating, the cultures consist of a nearly pure population of sensory neurons, which can be kept for more than 2 months in culture. Cultured neurons synthesize and release the tachykinins substance P (SP) and substance K (SK, neurokinin A) with a time course similar to that observed in vivo. High-pressure liquid chromatography (HPLC) analysis of peptides extracted from neuronal cultures and synthetic tachykinins revealed identical retention characteristics. Northern blot analysis of mRNAs from cultured cells with a specific tachykinin-probe demonstrated that the preprotachykinin-gene is expressed in preparations of both DRG and trigeminal ganglia cells. Depolarizing stimuli such as high potassium (47 mM) evoked a peptide release from cultured neurons in a strictly Ca(++)-dependent manner. Capsaicin, a compound known to stimulate nociceptive sensory neurons, dose-dependently released tachykinins in concentrations as low as 10(-9) M. Only total absence of Ca++ ions from the incubation medium abolished the capsaicin-induced peptide release. Nifedipine, a blocker of voltage-dependent L-type Ca++ channels, completely blocked the potassium-induced release of SP but did not reduce the capsaicin-evoked release. Mediator substances of pain and inflammation, such as bradykinin, serotonin, and histamine, triggered the release of tachykinins from sensory neurons in vitro. These results clearly demonstrate that the neurons characterized express properties similar to those of sensory neurons in vivo and provide model systems for detailed studies of the biosynthesis and release of neuropeptides as well as the participation of sensory neurons in pain and inflammatory reactions.

Neurofilament protein triplet immunoreactivity in the dorsal root ganglia of the guinea-pig

Immunoreactivity for the neurofilament protein triplet was investigated in neurons of the dorsal root ganglia of the guinea-pig by using a battery of antibodies. In unfixed tissue, nearly all neurons in these ganglia demonstrated some degree of neurofilament protein triplet immunoreactivity. Large neurons generally displayed intense immunoreactivity, whereas most small to medium-sized neurons showed faint to moderate immunoreactivity. Double-labelling immunofluorescence demonstrated that most antibodies to the individual subunits of the neurofilament protein triplet had the same distribution and intensity of labelling in sensory neurons. Increasing durations of tissue fixation in aldehyde solutions selectively diminished neurofilament protein triplet immunoreactivity in small to medium-sized neurons. Double-labelling with neurofilament protein triplet antibodies in combination with antibodies to other neuronal markers, such as neuron-specific enolase, substance P and tyrosine hydroxylase, showed that tissue processing conditions affect the degree of co-localization of immunoreactivity to the neurofilament protein triplet and to these other neuronal markers. These results indicate that, with a judicious manipulation of the duration of tissue fixation, neurofilament protein triplet immunoreactivity can be used in combination with other neuronal markers to distinguish groups of neurons according to their size and chemical coding.

Populations of rat spinal primary afferent neurons with choleragenoid binding compared with those labelled by markers for neurofilament and carbohydrate groups: a quantitative immunocytochemical study

A quantitative comparison was made of the population of L5 dorsal root ganglion neurons that bind choleragenoid and the population of neurons labelled by RT97, an anti-neurofilament antibody, SSEA3, an antibody to a globoseries carbohydrate group and 1B2, an antibody to a lactoseries carbohydrate group. Neurons with choleragenoid binding formed a population of 37% of all the cells and 94% of these were also immunoreactive to RT97. The choleragenoid-and RT97-positive groups of cells showed the same size distribution. Two small populations of cells existed which were choleragenoid negative/RT97 positive and choleragenoid positive/RT97 negative. SSEA3 immunoreactivity was found in 8% of the dorsal root ganglion neurons which were of all sizes. The 1B2 immunoreactivity was found in 32% of the dorsal root ganglion cells, the majority of which were in the small size range. More than half of the SSEA3-positive cells but only a few of the 1B2-positive neurons were labelled for choleragenoid. These results demonstrate that choleragenoid labels the majority of the light (RT97-positive) cell population and that light cells unlabelled by choleragenoid are small in number and spread across a wide size range.

Immunocytochemical localization of neuromedin K (neurokinin B) in rat spinal ganglia and cord

Specific antisera directed against substance P and neuromedin K (neurokinin B) have been used in double-label immunofluorescence studies to unambiguously localize these two neuropeptides of the tachykinin family in single tissue sections of rat spinal cord and dorsal root ganglia. Substance P-like immunoreactivity (SPLI) is present but neuromedin K-like immunoreactivity (NMKLI) is undetectable in dorsal root ganglia. Both peptides are present in the spinal cord, but NMKLI is largely restricted to the dorsal gray while SPLI shows a broader distribution. In the spinal gray, NMKLI coexists with SPLI in some, but not all, fibers. While substance P in the dorsal spinal cord is largely of primary afferent origin, neuromedin K appears to originate largely from intrinsic spinal neurons.