Regional distribution of calcitonin gene-related peptide-, substance P-, cholecystokinin-, Met5-enkephalin-, and dynorphin A (1-8)-like materials in the spinal cord and dorsal root ganglia of adult rats: effects of dorsal rhizotomy and neonatal capsaicin

Cerebrospinal alterations of immunoreactive dynorphin A after unilateral dorsal rhizotomy in the rat

Possible alterations of immunoreactive dynorphin A (ir-dyn A) were investigated at different levels of the spinal cord and in discrete brain regions of male rats 10, 30 and 60 days after unilateral dorsal rhizotomy, i.e., during the development of deafferentation pain and autotomy behavior that follows afferent nerve interruption. Dorsal rhizotomy caused an increase of spinal ir-dyn A at 10 days in the cervical segment; subsequent assays showed a progressive increase in other spinal regions too. At the last observation, 60 days after rhizotomy, neuropeptide levels were still significantly higher than in sham-lesioned animals in the cervical, thoracic and lumbosacral spinal cord. The spinal ir-dyn A changes were both ipsi- and contralateral to the lesion. No alterations were found in the brainstem and midbrain and a not significant decrease was observed in the hypothalamus. In the striatum and cortex, however, there was a bilateral significant increase 30 days after surgery and a constant and significant elevation was detected in the hippocampus at all three intervals. These data cast additional light on the neurochemical changes caused by the interruption of afferent nerves, followed by development of the deafferentation pain syndrome in laboratory animals and human beings. They also support the concept of central neuroplasticity in pathological pain and indicate that the opioid neuropeptide dynorphin is involved.

A selective CCKB receptor antagonist potentiates, mu-, but not delta-opioid receptor-mediated antinociception in the formalin test

The endogenous peptides enkephalins and cholecystokinin appear to play an opposite role in the control of pain. In this work, the effect of the selective CCKB receptor antagonist PD-134,308 on antinociceptive effects induced by morphine or by a complete inhibitor of enkephalin-metabolizing enzymes, RB 101, was studied using the formalin test. In mice, s.c. injection of formalin into the dorsal surface of the hindpaw had a biphasic effect: an early nociceptive response followed by a late response. Morphine (2 mg/kg i.p.) caused naloxone (0.5 mg/kg s.c.) but not naltrindole (0.5 mg/kg s.c.) reversible antinociceptive responses in the early and late phases of the assay, suggesting a preferential involvement of mu-opioid receptors in these responses. In contrast, RB 101 (50 mg/kg i.p.) produced antinociceptive effects in the early and late phases which were both antagonized by the delta-selective opioid receptor antagonist naltrindole (0.5 mg/kg s.c.). The antinociceptive response elicited by morphine on the late but not the early phase of the formalin test was potentiated by the CCKB antagonist PD-134,308 (1 mg/kg i.p.). This compound was unable to facilitate the analgesic effects produced by RB 101 on both phases, in contrast to what was observed in the hot plate test with mice and the tail flick test with rats. Therefore, in the formalin test with mice, the facilitating effects of opiate-induced analgesia by CCKB receptor antagonists seem to be restricted to mu-opioid receptor-mediated responses.

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.

Mu and delta opioid receptors mediate opposite modulations by morphine of the spinal release of cholecystokinin-like material

The possible modulations by morphine and various opioids of the spinal release of cholecystokinin-like material (CCKLM) evoked by 30 mM K+ was studied in vitro, using slices of the dorsal part of the rat lumbar enlargement superfused with an artificial cerebrospinal fluid. Addition of the mu agonist, DAGO (0.1-10 microM), to the perfusing fluid produced a concentration-dependent decrease in the peptide release, which could be prevented by the preferential mu antagonist, naloxone. Complex modulations were induced by the delta agonist, DTLET, as this drug inhibited CCKLM release when added at 10 nM-3 microM to the perfusing fluid, but enhanced it at 10 microM. Both effects were preventable by the delta antagonists naltrindole and ICI 154129, suggesting that delta receptors, possibly of different subtypes, mediated the inhibition and stimulation by DTLET. Morphine also exerted a biphasic effect, as the alkaloid decreased CCKLM release at 0.01-0.1 microM and enhanced it at 10 microM. Morphine-induced inhibition was preventable by naloxone, whereas its stimulatory effect could be blocked by naltrindole and ICI 154129. Although inactive on its own on CCKLM release, the selective kappa 1 agonist U 50488H (1 microM) prevented the inhibitory effects of both DAGO (10 microM) and morphine (0.1 microM), suggesting the existence of interactions between kappa 1 and mu receptors within the dorsal zone of the rat spinal cord. These data indicate that low concentrations of morphine exert an inhibitory influence on spinal CCKergic neurons that depends on the stimulation of mu opioid receptors. The excitatory influence of 10 microM morphine likely results from the simultaneous stimulation of mu, delta and kappa receptors, as the inhibitory effect of mu receptor stimulation can be masked by that of kappa 1 receptors, allowing only the expression of a delta-dependent excitatory effect similar to that induced by 10 microM DTLET.

Opioidergic control of the spinal release of neuropeptides. Possible significance for the analgesic effects of opioids

Several neuropeptides play a key role in the transfer (substance P, calcitonin gene-related peptide, etc) and control (enkephalins, cholecystokinin, etc) of nociceptive messages from primary afferent fibres to spino-thalamic neurones in the dorsal horn of the spinal cord. This first relay in nociceptive pathways has been shown to be a major target for opioids such as analgesic drugs, and the effects of exogenous (mainly morphine) and endogenous opioids on the release of neuropeptides within the dorsal horn are reviewed here for a better understanding of the cellular mechanisms responsible for their antinociceptive action. Complex modulations of the in vitro (from tissue slices) and in vivo (in halothane-anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid) release of substance P and calcitonin gene-related peptide by opioids have been reported, depending on the opioid receptor (mu, delta, kappa, and their subtypes) stimulated by these compounds. In particular, the inhibition by delta agonists of substance P release from primary afferent fibres, and that by the concomitant stimulation of mu and kappa receptors of the release of calcitonin gene-related peptide are very probably involved in the analgesic action of specific opioids and morphine at the level of the spinal cord. Furthermore, the negative modulation (through presynaptic opioid autoreceptors) by delta and mu agonists of the spinal release of met-enkephalin, and the complex inhibitory/excitatory influence of delta, mu and kappa receptor ligands on the release of cholecystokinin within the dorsal horn very likely also contribute to the antinociceptive action of these drugs and morphine. The reviewed data strongly support the existence of functional interactions between mu and kappa receptors within the spinal cord, and their key role in the analgesic action of non specific opiates (acting on mu, delta and kappa receptors) such as morphine.

Calcitonin gene-related peptide-like immunoreactivity in spinal cord and superior cervical ganglion of the Djungarian hamster (Phodopus sungorus)

The indirect immunofluorescent method was employed to investigate the distribution of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) in the spinal cord and superior cervical ganglion of the Djungarian hamster Phodopus sungorus. In cross-sections of the spinal cord, immunoreactive fibres and terminals were found in laminae 1 and 2 in high density, in the dorsolateral (Lissauer's) tract, in ventral and lateral horns, and in the area surrounding the central canal. A few CGRP-LI perikarya were seen in the ventral but not the dorsal horn. CGRP-LI was further observed in preganglionic sympathetic neurons which were labelled by retrograde axonal transport of fluoro-gold (FG) following injection of the substance unilaterally into the superior cervical ganglion. Preganglionic sympathetic neurons (PSN) were localized ipsilateral to the injection site mainly in the intermediolateral nucleus and the lateral funiculus of the upper thoracic segments. Most PSN exhibited CGRP-LI. Immunoreactive PSN were not seen contralaterally to the site of FG application nor in animals that did not receive injections. When the preganglionic fibres were ligated 4 days before perfusion, CGRP-LI cell bodies were found in preganglionic sympathetic neurons similar to the situation seen upon FG treatment. In the superior cervical ganglia of untreated hamsters, immunoreactive fibres were seen to enter the ganglion in which they terminated at non-immunoreactive principal ganglion cells. The present study, the first in a hamster species, describes the widespread distribution of CGRP in the spinal cord of P. sungorus and supports the view that considerable interspecies differences exist in occurrence and location of this neuropeptide.

Deafferentation-induced changes in neuropeptides of the adult rat dorsal horn following pronase injection of the sciatic nerve

The effect of deafferentation on the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), somatostatin (SS), and cholecystokinin (CCK) in the lumbar dorsal horn of the adult rat was examined by the indirect immunohistochemical method. Deafferentation was induced by injecting the sciatic nerve of anesthetized rats with proteolytic enzymes (20 mg pronase), which cause selective death of the nerve's ganglion cells and degeneration of their terminal arborization in the spinal cord. The density of immunolabel of each peptide was determined by using a computerized densitometry analysis system in two animal groups, i.e., short-term (10-13 days after injection) and long-term (4-9 months). In both groups, the deafferentation produced a significant ipsilateral depletion of CGRP, SP, CCK, and SS immunoreactivity. This depletion was limited to the area occupied by the sciatic terminals in the dorsal horn. In the long-term group, the loss of CGRP and SP staining was significantly less than that in the short-term animals, thus indicating partial recovery. A similar, but not statistically significant, trend was observed for CCK and SS. The large decrease in CGRP and SP seen in short-term animals reflects the large contribution of the sciatic nerve to the lumbar dorsal horn. The partial recovery of peptides demonstrates the plasticity of the nervous system and may parallel sprouting of primary afferents from other nerves, such as the saphenous nerve, as we have demonstrated in previous studies.

Autoradiographic localization of [125I-Tyr8]-bradykinin receptor binding sites in the guinea pig spinal cord

The present study aimed to localize and characterize [125I-Tyr8]-BK binding sites in all major segments of the guinea pig spinal cord using in vitro quantitative receptor autoradiography. [125I-Tyr8]-BK specific binding sites were localized predominantly in superficial layers of the dorsal horn, with lamina II depicting the highest labelling. The density of specific binding in laminae I and III was moderate, whereas in other areas, i.e., laminae IV-X, lower amounts of labelling were noticed. The B2 receptor antagonists D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140), D-Arg[Hyp3,D-Phe7,Leu8]-BK, Tyr0,D-Arg[Hyp3,D-Phe7,Leu8]-BK, D-Arg[Tyr3,D-Phe7,Leu8]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK, D-Arg[Hyp3,Leu8]-BK and D-Arg[Hyp3,Gly6,Leu8]-BK as well as unlabelled [Tyr8]-BK inhibited [125I-Tyr8]-BK binding with respective Ki values of 0.04, 12.4, 23.4, 34.5, 43.5, 33.5, 23.0, and 0.6 nM while B1 related molecules (Tyr0,des-Arg10-kallidin and [Leu8]-des-Arg9-BK) did not significantly inhibit [125I-Tyr8]-BK binding up to micromolar concentrations. These results indicate that the specific [125I-Tyr8]-BK binding sites present in the guinea pig spinal cord belong to the B2 receptor subtype. The high density of B2 binding sites in the substantia gelatinosa provides an anatomical evidence in favour of a role for BK as a modulator of nociceptive information.

Modulation of opioid antinociception by CCK at the supraspinal level: evidence of regulatory mechanisms between CCK and enkephalin systems in the control of pain

1. Much evidence in the literature supports the idea that cholecystokinin (CCK) interacts with opioids in pain mechanisms. In this work, we have investigated the supraspinal interactions between enkephalins and CCK, using the hot plate test in mice. 2. Intracerebroventricular (i.c.v.) administration of BDNL (a mixed CCKA/CCKB agonist) induced dose-dependent antinociceptive responses on both paw lick and jump responses. In contrast, using the same test, the i.c.v. injection of BC 264 (a selective CCKB agonist) induced a hyperalgesic effect, which was restricted to paw licking and occurred only at a high dose of 2.5 nmol. 3. In addition, i.c.v. administration of BDNL potentiated the antinociceptive effects of the mixed inhibitor of enkephalin degrading enzymes, RB 101 and of the mu-agonist, DAMGO, while BC 264 reduced these effects. 4. Furthermore, at a dose where it interacts selectively with delta-opioid receptors, the opioid agonist BUBU reversed the hyperalgesic responses of BC 264 (2.5 nmol) but was unable to modify the effects induced by BDNL. 5. Taken together, these results suggest the existence of regulatory mechanisms between CCK and enkephalin systems in the control of pain. These regulatory loops could enhance the antinociceptive effects of morphine allowing the opiate doses used to be reduced and thus, possibly, the side-effects to be minimized.

Increased in vivo release of calcitonin gene-related peptide-like material from the spinal cord in arthritic rats

Possible alterations in spinal systems containing calcitonin gene-related peptide (CGRP) due to polyarthritis were assessed in rats 3-4 weeks after an intradermal injection of Freund's adjuvant in the low back. The tissue levels of CGRP-like material (CGRPLM) were approximately 50% higher in the dorsal zone of the spinal cord and dorsal root ganglia at both the cervical and lumbar (but not thoracic) segments in polyarthritic rats than in age-paired control animals. In addition the rate of the spinal release of CGRPLM determined through an intrathecal perfusion procedure in halothane-anaesthetized animals was approximately 15-fold higher in polyarthritic rats than in controls. The blockade of mu-opioid receptors by intrathecal perfusion with 10 microM naloxone produced a larger increase in the spontaneous CGRPLM outflow in polyarthritic rats than in age-paired controls. Furthermore, the stimulation of mu-opioid receptors by intrathecal perfusion with 10 microM DAGO significantly inhibited the spinal outflow of CGRPLM only in polyarthritic rats. These data indicate that CGRP-containing primary afferent fibres are markedly activated in chronic suffering polyarthritic rats. This activation occurs in spite of an increased tonic inhibitory control by endogenous opioids acting at mu receptors.

Monoaminergic control of the release of calcitonin gene-related peptide- and substance P-like materials from rat spinal cord slices

The possible control by monoamines of the spinal release of substance P- and calcitonin gene-related peptide-like materials (SPLM and CGRPLM, respectively) was investigated in vitro, using slices of the dorsal half of the rat lumbar enlargement superfused with an artificial cerebrospinal fluid. Whereas the spontaneous outflow of SPLM and CGRPLM was changed by none of the agonists/antagonists of monoamine receptors tested, the overflow of both peptide-like materials due to 30 mM K+ was differentially affected by alpha 2-adrenoreceptor and dopamine D-1 receptor ligands. Noradrenaline (10 microM to 0.1 mM) and clonidine (0.1 mM) significantly reduced the K(+)-evoked overflow of SPLM, and both effects could be prevented by idazoxan (10 microM) and prazosin (10 microM) as expected from their mediation through the stimulation of alpha 2B-adrenoreceptors. In contrast, CGRPLM overflow remained unaffected by alpha 2-adrenoreceptor ligands. Dopamine D-1 receptor stimulation by SKF 82958 (10-100 nM) significantly increased the K(+)-evoked overflow of both SPLM and CGRPLM, and this effect could be prevented by the selective D-1 antagonist SCH 39166 (1 microM). Further studies with selective ligands of other monoamine receptors indicated that neither alpha 1- and beta-adrenergic receptors, dopamine D-2, nor serotonin 5-HT1A and 5-HT3 receptors are apparently involved in some control of the spinal release of CGRPLM and SPLM. These data are discussed in line with the postulated presynaptic control by monoamines of primary afferent fibres conveying nociceptive messages within the dorsal horn of the spinal cord.

5-HT3 receptors in the rat central nervous system are mainly located on nerve fibres and terminals

Autoradiographic and membrane binding studies with [3H](R,S)- or [3H](S)-zacopride were performed in combination with lesions using various neurotoxins in an attempt to identify which neuronal cell types are endowed with 5-HT3 receptors in the rat central nervous system. Lesions of noradrenergic (by DSP-4), dopaminergic (by 6-hydroxydopamine) and serotonergic (by 5,7-dihydroxytryptamine) systems had little effect generally on the density of 5-HT3 receptors labelled with [3H](R,S)- or [3H](S)-zacopride in various regions of the brain and the spinal cord. The only exception was the amygdala where a significant loss (approximately -20%) of 5-HT3 receptors labelled by [3H](R,S)-zacopride was associated with the selective lesion of serotonergic fibres by 5,7-dihydroxytryptamine. Microinjection of kainic or ibotenic acid into the dorsal and ventral hippocampus reduced the density of 5-HT1A receptors labelled with [3H]8-OH-DPAT (approximately -45%) as expected from their known location on intrinsic neuronal cell bodies and/or dendrites. In contrast, the same lesion did not affect 5-HT3 receptors, suggesting their location on fibres 'en passage'. At the spinal level, 5-HT3 receptors were found to exist on primary afferent fibres terminating within the superficial layers of the dorsal horn, as shown by the marked reduction in the local autoradiographic labelling by [3H](S)-zacopride after either dorsal rhizotomy (-81%) or neonatal capsaicin treatment (-72%). These data suggest that 5-HT3 receptors in the central nervous system are generally located presynaptically on nerve terminals or fibres of non-monoaminergic neurones.

Opioid control of the release of calcitonin gene-related peptide-like material from the rat spinal cord in vivo

The possible control by opioids of the spinal release of calcitonin gene-related peptide-like material (CGRPLM) was investigated in halothane-anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid. Morphine (20 mg/kg i.v.; or at 10-100 microM added to the perfusing fluid), the mu selective agonist DAGO (10 microM) and the kappa selective agonist U 50488 H (10 microM) did not affect the spontaneous outflow of the CGRPLM. In contrast, the selective delta agonist DTLET (10 microM) significantly increased CGRPLM release. The latter effect could be prevented by the selective delta antagonist naltrindole (10 microM) as expected from the involvement of this class of opioid receptors. However, the addition of naltrindole alone to the perfusing fluid did not modify CGRPLM outflow, indicating that endogenous opioids do not exert a tonic control of CGRP-containing fibers through the stimulation of delta receptors. In contrast, intrathecal perfusion with naloxone (10 microM) or nor-binaltorphimine (10 microM), a selective antagonist of kappa receptors, produced a marked increase in spinal CGRPLM release, suggesting that endogenous opioids acting at mu and kappa receptors, respectively, exert a tonic inhibitory control of CGRP-containing fibers. Indeed, a significant decrease in the spinal release of CGRPLM release could be evoked by the combined addition of U 50488 H (10 microM) plus DAGO (10 microM) to the perfusing medium, indicating that the simultaneous stimulation of both kappa and mu receptors is required for this negative control to occur. This could notably be achieved with morphine (10 microM) in the presence of naltrindole (10 microM) which also produced a significant reduction in the spinal release of CGRPLM. In conclusion, morphine per se did not change CGRPLM release because this drug triggers opposite positive (through the stimulation of delta receptors) and negative (through the concomitant stimulation of both kappa and mu receptors) control mechanisms within the rat spinal cord.

Cholecystokinin in mammalian primary sensory neurons and spinal cord: in situ hybridization studies in rat and monkey

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

Long-term effects of neonatal capsaicin on C-fiber excitability and dorsal horn C-input processing in the rat

The effects of neonatal capsaicin treatment (50 mg/kg, SC, at day 2 of postnatal life) on C-fiber excitability and dorsal horn C-input processing were studied through recording of a C-fiber-evoked spinal flexor reflex in 55-60-day-old rats, anesthetized with urethane (1.1 g/kg, IP) and spinalized at Th9-10. Neonatal capsaicin resulted in decreased C-fiber excitability, as revealed by increased chronaxie values determined in a strength-duration paradigm. Besides, capsaicin-treated rats exhibited a reduced potentiation of the C-reflex discharge in response to repetitive stimulation. The results indicate that capsaicin given to rats early in life leads to both functional disturbances of surviving C-fibers and altered temporal synaptic processing of the C-input in the spinal cord.

Tachykinin systems in the spinal cord and basal ganglia: influence of neonatal capsaicin treatment or dopaminergic intervention on levels of peptides, substance P-encoding mRNAs, and substance P receptor mRNA

The aim of the study was to test whether the synthesis of substance P (SP) and that of its receptor (also known as NK1 receptor) are coordinately regulated after chronic pharmacologic intervention in two neural systems, the spinal cord and basal ganglia. In one set of experiments, capsaicin was administered subcutaneously during the early postnatal period (day 3 after birth) to induce degeneration of afferent sensory neurons in the spinal cord. In the other set of experiments, interruption of dopaminergic transmission was achieved by two methods: (a) The neurotoxin 6-hydroxydopamine was used to denervate dopaminergic neurons during the early postnatal period, and (b) haloperidol was used in adult animals to block dopaminergic transmission by receptor blockade. The spinal cord, striatum, or both were used for the quantification of tachykinin [SP and neurokinin A (NKA)] and opioid peptides [[Met5]-enkephalin (ME) and dynorphin A (1-8) (DYN)] by radioimmunoassays. The abundance of total SP-encoding preprotachykinin (PPT) mRNA and SP receptor (SPR) mRNA in spinal cord (C5 to T1 segments), striatum, or microdissected substantia nigra was determined by northern blot or solution hybridization analysis. Amines and their acid metabolites were quantified by HPLC. Capsaicin administration (subcutaneously) during the early postnatal period increased latency in a hot-plate test, decreased SP and NKA levels, increased levels of PPT mRNAs, and did not affect SPR mRNA levels in the spinal cord. Intraspinal SP systems may attempt to compensate for the loss of afferent SP input, whereas spinal cord receptor mRNA levels do not appear to be altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin concentrations and peptide immunoreactivity in the intact and deafferented medullary dorsal horn of the rat

To further address the hypothesis that cholecystokinin (CCK) in the medullary dorsal horn (MDH) arises from intrinsic or higher-order neurons, CCK-8-specific radioimmunoassay (RIA) and immunohistochemical (IHC) experiments were carried out in adult rats after trigeminal tractotomy. RIA of punches from deafferented superficial layers of the MDH revealed no significant change in CCK levels vs. the control right side. In this same area, IHC revealed modest reductions in CCK, gastrin, and substance P staining. Calcitonin gene-related peptide (CGRP) staining was reduced substantially. Gastrin immunoreactive cell bodies, present normally in inner lamina II, were reduced in number. RIA and IHC methods were also used to assess MDH CCK concentrations in adult rats subjected to left infraorbital nerve section at birth. The left medulla contained significantly higher levels of CCK than the control right medulla (1.27 +/- 0.19 vs. 0.97 +/- 0.11 ng/mg protein). IHC revealed a dense band of CCK-like staining in laminae I and II ipsi- and contralateral to the lesion. Thus, neonatal deafferentation elevates medullary CCK. To determine if the neonatal lesion-induced increase in medullary CCK is due to primary afferent or higher-order reorganization, RIA and IHC experiments were run after infraorbital nerve section at birth and trigeminal tractotomy in adulthood. RIA revealed no significant change in CCK levels caudal to the tractotomy, although they were higher than control levels in 9 of 12 cases. IHC revealed modest reductions in CCK, substance P, and gastrin staining that resembled the reductions observed in tractotomy-alone cases. These data suggest that 1) most MDH CCK is of non-primary afferent origin, 2) gastrin immunoreactivity in layer II probably originates in CCK-containing cells intrinsic to layer II, the expression of which is dependent upon trigeminal primary afferent input, 3) neonatal V deafferentation induces increased CCK in the superficial MDH, reflecting reorganized intrinsic or higher-order inputs, and 4) higher-order substance P in the MDH is robust.

CGRP-immunoreactive primary afferent nerve fibers in the rat urinary bladder: effects of dorsal rhizotomy and MK-801

A transection lesion of the suprasacral spinal cord results in a decreased density of calcitonin gene-related peptide (CGRP)-immunoreactive (I) primary afferent nerve fibers in the rat urinary bladder. The fiber density can be restored by postsurgical treatment with the N-methyl-D-aspartate receptor antagonist MK-801. We are attempting to determine the level of the primary afferent neuron at which MK-801 might have a restorative effect on CGRP immunostaining. Thus, the purpose of this study was to determine if MK-801 had a similar restorative effect on immunostaining for CGRP in bladder nerves after a direct lesion of the sacral afferent system, i.e., rhizotomy of the L6 and S1 dorsal roots. To assess the effect of the lesion, the mean length and number of bladder CGRP-I nerve fibers, as well as the number of CGRP-I perikarya in the L6 and S1 dorsal root ganglia (DRG), were measured following bilateral L6 and S1 dorsal rhizotomies. Both the mean length and the numbers of CGRP-I bladder fibers were significantly decreased by the lesion. However, the number of CGRP-I primary afferent perikarya in the L6 and S1 DRG was unchanged from control values. Rats which received rhizotomies and subsequent treatment with MK-801 did not exhibit restoration of the density of CGRP-I bladder fibers nor an alteration in the number of CGRP-I primary afferent perikarya. These data suggest that MK-801-induced restoration of bladder CGRP-I primary afferent nerve fibers may rely on an intact central process.

Demonstration of dynorphin A 1–8 immunoreactive axons contacting spinal cord projection neurons in a rat model of peripheral inflammation and hyperalgesia

Using a double-labeling technique, we evaluated the input of afferents immunoreactive for dynorphin peptide onto a population of lumbar spinal neurons contributing to the spinoparabrachial tract in rats with 1 inflamed hind paw. We found that the frequency and distribution with which dynorphin immunoreactive varicosities were in apposition to projection neurons varied according to neuron location. In particular, neurons in the superficial dorsal horn and neck of the dorsal horn receive a high degree of dynorphin input. We also determine that unilateral peripheral inflammation is associated with both an increase in the number of projection neurons receiving detectable DYN input and in the frequency of this input onto a given neuron, with the largest increase seen in the superficial dorsal horn. Since almost all superficial dorsal horn neurons contributing to the spinoparabrachial tract respond either exclusively or maximally to noxious stimulation, our data supports dynorphin's involvement in nociception.

Normal development and effects of neonatal infraorbital nerve damage upon the innervation of the trigeminal brainstem complex by primary afferent fibers containing calcitonin gene-related peptide

Immunocytochemistry was used to study the normal development and response to infraorbital nerve (ION) damage of the innervation of the trigeminal (V) brainstem complex by axons recognized by an antibody directed against calcitonin gene-related peptide (CGRP). CGRP-like immunoreactivity (CGRPLI) was present in axons that occupied the outer V spinal tract (TrV) at all levels of the V brainstem complex. Almost no fibers terminated within V nucleus principalis (PrV), but there was dense CGRPLI in the supratrigeminal nucleus. There was also very little CGRPLI within rostral V subnucleus oralis (SpO). However, in the caudal one-half of the nucleus, a dense elongated patch of immunoreactivity was consistently present just medial to TrV. Only occasional CGRP-positive axons could be seen within V subnucleus interpolaris (SpI), but the paratrigeminal nucleus contained dense immunoreactivity. Trigeminal subnucleus caudalis (SpC) also contained CGRPLI that was very dense in lamina I and the outer portion of lamina II. Scattered terminals were also present in layers III and IV and dense terminal clusters were in lamina V. CGRP-immunoreactive neurons were present in the V ganglion by embryonic (E-) day 16 and immunoreactive axons could be seen in the V brainstem complex on E-17. At birth, CGRP-positive axons in the V brainstem complex had achieved a distribution very similar to that in adult rats. The major difference between the patterns of labelling in neonates and adults was the presence of relatively large numbers of CGRP-positive fibers in ventral PrV and SpO of the former animals. The disappearance of these fibers was completed by the middle of the third postnatal week. Transection of the ION on the day of birth had little effect upon CGRP in SpO, SpI, and SpC, but it did result in an increase in CGRP-positive fibers in PrV ipsilateral to the damaged nerve. When considered together with previous findings, these results suggest that CGRP-positive axons express this peptide well after they have entered the V brainstem complex and that the central terminal field of these fibers is not substantially altered by a manipulation which results in the death of nearly 60% of all V primary afferent neurons.

In vivo release of calcitonin gene-related peptide-like material from the cervicotrigeminal area in the rat. Effects of electrical and noxious stimulations of the muzzle

The continuous perfusion with an artificial cerebrospinal fluid of the cervicotrigeminal area of the spinal cord in halothane-anaesthetized rats allowed the collection of calcitonin gene-related peptide-like material with the same immunological and chromatographic characteristics as authentic rat alpha-calcitonin gene-related peptide. The spinal release of calcitonin gene-related peptide-like material could be significantly increased by the local application of 60 mM K+ (approximately +100%), high-intensity percutaneous electrical stimulation (approximately +200%) and noxious heat (by immersion in water at 52 degrees C; approximately +150%) applied to the muzzle. By contrast, noxious mechanical (pinches) and chemical (subcutaneous formalin injection) stimulations and deep cooling (by immersion in water at 0 degrees C) of the muzzle did not alter the spinal release of calcitonin gene-related peptide-like material. In addition, low-intensity electrical stimulation, recruiting only the A alpha/beta primary afferent fibres, significantly reduced (approximately -30%) the release of calcitonin gene-related peptide-like material from the cervicotrigeminal area. These data suggest that among the various types of natural noxious stimuli, noxious heat may selectively excite calcitonin gene-related peptide-containing A delta and C primary afferent fibres projecting within the dorsal horn of the spinal cord, and that activation of A alpha/beta fibres reduces spontaneous calcitonin gene-related peptide-like material release possibly through an inhibitory presynaptic control of calcitonin gene-related peptide-containing A delta/C fibres.

GABA, acting at both GABAA and GABAB receptors, inhibits the release of cholecystokinin-like material from the rat spinal cord in vitro

Superfusion of slices of the dorsal zone of the lumbar enlargement of the rat spinal cord with an artificial cerebrospinal fluid allowed the collection of cholecystokinin-like material (CCKLM) whose Ca(2+)-dependent release could be evoked by tissue depolarization with 30 mM K+. Studies on the possible influence of GABA and related agonists on this process showed that the amino acid, the GABAA agonist, muscimol, and the GABAB agonist, baclofen, inhibited the K(+)-evoked release of CCKLM from the rat spinal cord in a concentration-dependent manner. Maximal inhibition did not exceed -40% with either agonist. Furthermore, the effects of GABAA and GABAB receptor stimulation were not additive. Whereas the effects of muscimol (10 microM) and baclofen (1 microM) could be completely antagonized by bicuculline (1 microM) and phaclofen (10 microM), respectively, complete blockade of the inhibition by GABA (1 microM) could only be achieved in the presence of both antagonists. These data indicate that both GABAA and GABAB receptors are involved in the negative influence of GABA onto CCK-containing neurones within the dorsal horn of the rat spinal cord. Apparently, these receptors are not located on CCK-containing neurones themselves, since the inhibitory effect of GABA on the K(+)-evoked release of CCKLM could be completely prevented by tetrodotoxin (1 microM). As CCK acts centrally as an endogenous opioid antagonist, such a GABA-inhibitory control of spinal CCK-containing neurones might participate in the analgesic action of the amino acid via the intrathecal route.

gamma-Aminobutyric acid, through GABAA receptors, inhibits the potassium-stimulated release of calcitonin gene-related peptide- but not that of substance P-like material from rat spinal cord slices

Superfusion of slices of the dorsal zone of the lumbar enlargement with an artificial cerebrospinal fluid was used to investigate the possible modulation by GABA receptor ligands of the in vitro release of calcitonin gene-related peptide- and substance P-like materials (CGRPLM and SPLM) from the rat spinal cord. Whereas the spontaneous outflow of both peptides remained unaffected, the K+ (30 mM)-evoked overflow of CGRPLM could be partially inhibited (approx. -30%) by GABA (1 microM-0.1 mM) and muscimol (10 microM-0.1 mM) but not by baclofen (1-10 microM). Bicuculline methiodide (1 microM) completely prevented the inhibition by GABA (1 microM) and muscimol (10 microM) as expected from an action through GABAA receptors. By contrast, the K(+)-evoked SPLM overflow was altered neither by GABA nor muscimol and baclofen. These data further support that GABA exerts a presynaptic inhibitory control of (CGRP-containing) primary afferent fibres within the rat dorsal horn.

Increased calcitonin gene-related peptide- and cholecystokinin-like immunoreactivities in spinal motoneurones after dorsal rhizotomy

Possible changes in neuropeptides within the ventral horn of the spinal cord were investigated after unilateral dorsal rhizotomy at the lumbar level (L1-L6) in adult rats. Ten days after the surgery, immunohistochemical observations and radioimmunological determinations confirmed a marked loss of calcitonin gene-related peptide (CGRP)- and substance P (SP)-like immunoreactivities within the superficial layers of the deafferented dorsal horn, as expected from the degeneration of primary afferent fibres containing these peptides. A concomitant increase in immunohistochemical staining and levels of CGRP (+296%) and CCK (+71%)-like immunoreactivities was observed in the ipsilateral ventral horn where both peptides are located in motoneurones. In contrast, substance P-like immunoreactivity that is confined to fibres and terminals within the ventral horn, was not altered by dorsal rhizotomy. These data indicate that the expression of neuropeptides in spinal motoneurones can be influenced by primary afferent inputs.

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.

Cholecystokinin (CCK)-like material and CCK mRNA levels in the rat brain and spinal cord after acute or repeated morphine treatment

The effects of a single or repeated administrations of morphine on the tissue levels of cholecystokinin-like material (CCKLM) and pre pro cholecystokinin mRNA (CCK mRNA) were examined in various brain and spinal cord regions (cerebral cortex, cerebellum, hippocampus, septum, substantia nigra, lumbar enlargement) in adult rats using a specific radioimmunoassay and 'Northern blot' analysis, respectively. Although a clear parallelism existed between the regional distribution of CCKLM (septum greater than cerebral cortex greater than or equal to hippocampus much greater than lumbar enlargement, dorsal zone greater than substantia nigra greater than lumbar enlargement, ventral zone much much greater than cerebellum) and that of CCK mRNA, some mismatch was found notably in the septum where CCK mRNA levels were less than in other regions except the cerebellum. Neither CCKLM nor CCK mRNA levels were altered one hour after an acute administration of morphine (5 mg/kg i.p.). Similarly, morphine addiction after a four-day treatment with this drug was not associated with any change in the tissue levels of CCKLM and CCK mRNA. These data indicate that the previously reported modulatory action of opioids on central CCKergic systems could occur without affecting the preproCCK gene transcription and the tissue peptide concentrations.

Unmyelinated primary afferent fiber stimulation depletes dynorphin A (1-8) immunoreactivity in rat ventral horn

The present study demonstrates many dynorphin (DYN)-immunoreactive fibers and presumed presynaptic terminals in rat lumbar ventral horn. The fibers and terminals seem to arise largely from DYN-containing intrinsic neurons in the dorsal horn. The majority of the presumed terminals closely surround a subpopulation of motoneurons that tend to be located in flexor motoneuron columns. Acute C fiber, but not A fiber, primary afferent stimulation depletes the ventral horn DYN immunostaining. We interpret these findings to indicate that the spinal DYN neurons are well positioned to serve both as modulators of nociceptive input and as interneurons in motor reflexes. We further hypothesize that the depletion of DYN-immunoreactivity that follows either acute C fiber stimulation or intense nociceptive stimuli may be the trigger for the upregulation in spinal cord DYN that occurs in models of chronic pain states.

Cholecystokinin-like immunoreactivity in the rat spinal cord: effects of thoracic transection

A study of cholecystokinin-like immunoreactivity in the lumbar (L1-L5) spinal cord segments of rats was realised 24-48 hours after complete thoracic transection (T6-T8). A comparison was made with corresponding spinal cord segments from control and sham-operated animals. The immunocytochemical study with light microscopy showed cholecystokinin-like immunoreactive cell bodies in laminae VII and X at L1-L5, caudal to the transection. In addition, the immunoreactivity was greatly enhanced in bundles of the dorsolateral funiculus compared to sham-operated animals. Our results suggest that part of cholecystokinin-like cell bodies of laminae VII and X send projections to supraspinal sites. Some of these supraspinal projections would go through the dorsolateral funiculus. In the lumbar dorsal horn of operated animals, the immunoreactivity was greatly enhanced in lamina I, while it was slightly decreased in lamina II, compared to control animals. Using electron microscopy, in lamina I, the immunoreactivity localized in different neurites was generally very intense. Moreover, axon terminals showed swelling: their mean size was 0.8-1.8 microns (0.5-1.2 in control animals). This result suggests that some cholecystokinin-like neurons also project to lamina I of rostral cervical segments. In lamina II, numerous degenerating axons were observed (24 hours after thoracic spinal transection). This would suggest that part of descending cholecystokinin-like projections terminate in lamina II.

In vivo tonic inhibition of spinal substance P (-like material) release by endogenous opioid(s) acting at delta receptors

Although numerous data support the existence of a presynaptic inhibitory control by opioids of substance P-containing primary afferent fibres entering the dorsal horn of the spinal cord, the exact nature of the opioid receptor involved in this control is still a matter of debate. In the present study, the potential role of delta opioid receptors was investigated by looking for the possible effects of selective delta ligands on the in vivo release of substance P-like material from the whole spinal cord in halothane-anaesthetized rats. Perfusion of the intrathecal space allowed the collection of substance P-like material that was released at a constant rate of approximately 0.65 pg substance P equivalents/min for at least 135 min. The addition of Tyr-D-Thr-Gly-Phe-Leu-Thr (10 microM) or dermenkephalin (10 microM), two selective delta agonists, to the perfusing fluid produced a marked reduction (-50-65%) in substance P-like material outflow which could be prevented by the selective delta antagonist naltrindole (10 microM) but not by naloxone (10 microM), which acts preferentially on mu opioid receptors. Furthermore, naltrindole alone (or the association of this antagonist plus dermenkephalin) enhanced the outflow of substance P-like material (+ 170%) as expected from the blockade of a tonic inhibitory control due to the stimulation of delta receptors by endogenous opioids.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin-like immunoreactivity in the dorsal horn of the rat spinal cord: an attempt to analyse contradictory results between immunocytochemistry and radioimmunoassay

This study investigated the nature of the cholecystokinin-like immunoreactivity (CCKLI) in the dorsal horn of the rat spinal cord. Indeed, using the same antiserum, no variation of radioimmunoassayable CCKLI in the dorsal horn of rats treated neonatally with capsaicin could be seen, whereas the density of immunoreactive CCKLI fibres was greatly reduced in immunocytochemistry (IC). By comparing the technical conditions used in IC and radioimmunoassay (RIA), it could be concluded that the contradictory results obtained by the two techniques were very unlikely due to the fixation of the tissues, but rather to the concentration of the antiserum. First, CCKLI levels in extracts from fresh or 4% paraformaldehyde fixed tissues were not significantly different. Second, glomerular terminals, which are typical terminals of the fine primary afferents were immunoreactive at the surface of the block but unlabelled in its depth, where the concentration of antiserum might gradually reach a value closer to that used in radioimmunoassay. High pressure liquid chromatography analyses of acidic extracts of the dorsal part of the lumbar spinal cord of control rats revealed the presence, besides two major peaks coeluting with sulphated and non-sulphated CCK8, of two minor peaks '1' and '2' accounting for 23% of total CCKLI. Capsaicin treatment resulted in the disappearance of peak 2 and a marked reduction in the proportion of CCKLI in peak 1. Reported data suggested that the CCKLI material present in capsaicin-sensitive neurons, accounting for only about 10% of radioimmunoassayable CCKLI but for a much higher proportion of that detected in IC, was distinct from both genuine CCK and CGRP.