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

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.

Relative contribution of sympathetic and sensory nerves to thermal nociception and tissue trophism in rats

Neonatal injection of 6-hydroxydopamine (420 mg/kg s.c.) lowered thermal nociceptive threshold (hot plate and tail immersion tests) and increased levels of substance P-like immunoreactivity in the skin (paws, tail, area of vibrissae) of Wistar rats. Chemical ablation of primary afferents, induced in either neonatal or adult rats by systemic administration of capsaicin, increased thermal nociceptive threshold (hot plate), irrespective of 6-hydroxydopamine pretreatment, and reduced substance P-like immunoreactivity in the hind-paw skin of either control or sympathectomized rats. Capsaicin pretreatment of neonatal but not adult rats produced antinociceptive effect in the tail-immersion test and completely reversed the hyperalgesic effect of sympathectomy, without affecting levels of substance P-like immunoreactivity in the tail skin. These findings indicate that sympathetic nerves and different subsets of capsaicin-sensitive primary afferents are involved in the processing of thermal nociceptive input. Corneal and cutaneous lesions were induced by neonatal sensory denervation with capsaicin. Sympathectomy afforded protection against the development of corneal pathology, while it did not affect the occurrence of cutaneous lesions. It appears that a balance in the neuronal activity between sympathetic neurons and trigeminal sensory neurons is critical for maintaining the normal trophism of the cornea, and that sensory neuropeptides play a key role in the maintenance of normal trophism of the skin.

Ultrastructural studies on peptides in the dorsal horn of the spinal cord--I. Co-existence of galanin with other peptides in primary afferents in normal rats

The aim of the present study was to investigate galanin-like immunoreactivity in primary afferent terminals and its relationship to other neuropeptides in laminae I and II of the fourth and fifth lumbar segments of normal rat spinal cord using immunofluorescence and pre- and post-embedding electron-microscopic immunocytochemistry. Triple-immunofluorescence staining showed that galanin-like immunoreactivity co-localized with substance P- and calcitonin gene-related peptide-like immunoreactivities in many nerve fibres and terminals in laminae I and II of the dorsal horn. At the ultrastructural level, using pre-embedding immunocytochemistry, galanin-like immunoreactivity was found in type I glomeruli with an electron-dense central terminal containing many densely packed synaptic vesicles and several large dense-core vesicles. Both the cytoplasm and the core of the large vesicles were immunoreactive. In type II glomeruli with an electron-lucent central terminal and loosely packed synaptic vesicles the large dense-core vesicles and the cytoplasm were only weakly galanin-positive. Post-embedding immunocytochemistry revealed that galanin-like immunoreactivity co-existed with substance P- and calcitonin gene-related peptide-like immunoreactivities in many terminals and in individual large dense-core vesicles in lamina II. These terminals were considered to represent primary afferents, since there is evidence that calcitonin gene-related peptide in the dorsal horn only occurs in nerve endings originating in dorsal root ganglia. Evidence was also unexpectedly obtained for the occurrence of several other peptides in calcitonin gene-related peptide-positive terminals, i.e. in presumably primary afferents. Thus galanin-like immunoreactivity sometimes also co-localized with cholecystokinin- and neuropeptide tyrosine-like immunoreactivities in calcitonin gene-related peptide-immunoreactive terminals and in some large dense-core vesicles in such terminals. A small number of calcitonin gene-related peptide immunoreactive, presumably primary afferent terminals contained enkephalin-, neurotensin- (and galanin-)like immunoreactivities. These results indicated that galanin can be co-stored with several other neuropeptides in large dense-core vesicles in primary afferent terminals and may presumably be released together with them in the superficial layer of the dorsal horn. Since various combinations of peptides, presumably at varying concentrations, occur in the large dense-core vesicles in a given nerve ending, it is likely that the individual large dense-core vesicles produced in a neuron are heterogenous with regard to peptide content and thus to the message that they transmit upon release.

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.

The effects of neurokinin receptor antagonists on mustard oil-evoked activation of rat dorsal horn neurons

Previous evidence indicated that brief nociceptive responses of neurons in laminae IV/V of both rat and cat dorsal horn are more readily inhibited by antagonists at NK2 rather than at NK1 neurokinin receptors. Further support for a role of spinal NK2 receptors in nociception has been provided from experiments assessing modulation of the nociceptive flexor reflex by tachykinins and activation of dorsal horn neurons by brief application of capsaicin to afferents. The present experiments were designed to compare the contribution of NK1 and NK2 receptors in dorsal horn to the sustained neuronal activity induced by peripheral application of the chemical algogen mustard oil (reported to be a selective activator of C afferents). In nearly all of the multireceptive laminae IV/V neurons tested, a selective NK2 receptor antagonist L 659,874 inhibited previously established mustard oil-induced activity. In contrast, two selective NK1 receptor antagonists L 668,169 and GR 82334 were only rarely effective. These results further underline the apparent importance of NK2 receptors in spinal nociceptive processing. NK1 receptors do not appear to play a major role in the present experimental protocol, but they may of course do so under different circumstances.

Inhibition by NK2 but not NK1 antagonists of carrageenan-induced preprodynorphin mRNA expression in rat dorsal horn lamina I neurons

Previous evidence indicated that NK2 rather than NK1 receptors play a central role in mediating the electrophysiological responses of dorsal horn neurons to brief cutaneous stimuli such as noxious heat (but not noxious pinch) and moderately sustained stimuli such as mustard oil, topically applied over 10-20 min. The present experiments were designed to investigate, by in situ hybridisation histochemistry, a delayed genomic response in dorsal horn neurons (the expression of preprodynorphin mRNA induced by intraplantar carrageenan injection) and explore the role of NK1 and NK2 receptors in mediating this response. In anaesthetised rats with bilateral intraplantar injections of carrageenan, neurokinin receptor antagonists were administered unilaterally by prolonged ionophoresis into the superficial dorsal horn. The marked increase in preprodynorphin mRNA expression elicited by carrageenan was inhibited (both in terms of number of expressing cells and their level of expression) by NK2 but not NK1 antagonists.

Evidence for a role of tachykinin NK2 receptors in mediating brief nociceptive inputs to rat dorsal horn (laminae III-V) neurons

Since the NK2 receptor-selective tachykinin, neurokinin A is present in fine primary afferent neurons in addition to the NK1 receptor-selective tachykinin, substance P, we have addressed the relative role of NK1 and NK2 receptors in somatosensory processing in spinal dorsal horn. Recording extracellularly from rat laminae III-V neurons whilst ionophoresing drugs nearby, the selective NK1 receptor antagonists L 688,169, GR 82334 and [D-Pro4,D-Trp7,910Phe11]substance P-(4-11) failed to influence neuronal responses to cutaneous pinch or noxious heat but often enhanced responses to innocuous brush. In contrast, the highly selective NK2 receptor antagonist L 659,874 profoundly inhibited responses to noxious heat but not pinch or brush. Highly selective synthetic agonists for both NK1 and NK2 receptors ([N-acetyl-Arg6,Sar9,Met(O2)11]substance P-(6-11) and GR 64349, respectively) and also NKA showed the inverse effects on sensory responses to those brought about by their antagonists. At higher ionophoretic currents, both NK1 and NK2 receptor agonists increased spontaneous activity. This increased basal firing induced by GR 64349 and neurokinin A (but not that due to [N-acetyl-Arg6,Sar9,Met(O2)11]substance P-(6-11) appeared to partially pre-empt further excitatory responses to noxious heat. It is concluded that although both NK1 and NK2 receptors can clearly mediate excitation of dorsal horn neurons, it is not NK1, but rather NK2 receptors that are important as the physiological transducer of brief thermal nociceptive inputs in this model.

The effect of intrathecal administration of RP67580, a potent neurokinin 1 antagonist on nociceptive transmission in the rat spinal cord

The effect of intrathecal application of the selective neurokinin 1 (NK1) receptor antagonist RP67580 and its enantiomer RP68651 was studied on the responses of dorsal horn nociceptive neurones to formalin in the rat. The first and second phases of the formalin response were inhibited by RP67580 in a dose-related manner (1-10 micrograms), whereas RP68651 (5 micrograms) facilitated the second phase of the response. The same doses of RP67580 had minimal effects on the acute C-fibre responses. The NK1 receptor appears to play a role in prolonged nociceptive transmission in the spinal cord.

Effect of RP 67580, a non-peptide neurokinin1 receptor antagonist, on facilitation of a nociceptive spinal flexion reflex in the rat

1. In order to examine the contribution of neurokinin1 (NK1) receptors to facilitation of a spinal nociceptive reflex in the rat, we have investigated the effects of RP 67580 (3aR, 7aR)-7,7-diphenyl-2(1-imino-2-(2-methoxyphenyl/ethyl)perhydrois oindole)), a non-peptide neurokinin1 (NK1) receptor antagonist, selective for the rodent receptor sub-type, on the activity of individual motorunits. These results were compared with the effects of RP 68651, the inactive 3aS, 7aS enantiomer of RP 67580, as a control for non-specific activity. 2. Experiments were performed on 15 rats anaesthetized with a continuous i.v. infusion of alphaxalone/alphadalone and spinalized at T9-10. Single unit recordings of motorunit activity from biceps femoris/semitendinosus were made with a concentric needle electrode. In each experiment, a vehicle dose followed by 4 sequential rising doses of either RP 67580 or RP 68651 were given at 15 min intervals. High intensity electrical stimuli were applied to the hindlimb receptive field of the motorunit at a rate of 1 per 60 s throughout the experiment to establish a baseline. A conditioning stimulus (20 of these stimuli at 1 Hz) was delivered 5 min after each dose and the effect of the size of the baseline response examined. 3. The conditioning stimulus evoked a facilitation of the baseline at the start of all experiments (mean increase +/- s.e. mean = 151 +/- 20%). RP 67580 attenuated this facilitation, with an ID50 (+/- s.e. mean) of 2.5 +/- 4.2 micrograms kg-1, i.v., whereas RP 68651 at doses of up to 3 mg kg-1, i.v. did not. There was no statistically significant effect of drug on the baseline reflex, nor on the response to the conditioning stimulus. Doses of 300 and 3000 microg kg-1 of both RP 67580 and RP 68651 evoked small depressor effects on systemic arterial blood pressure.4. We conclude that the facilitation of a spinal flexor reflex by noxious conditioning stimuli in the rat is mediated by NK1 receptors whereas the baseline reflex is not. The results suggest that brain penetrantNK1 receptor antagonists may have central anti-nociceptive effects.

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)

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.

Quantitative analysis of substance P and calcitonin gene-related peptide immunohistochemical staining in the dorsal horn of neuropathic MK-801-treated rats

An animal model of peripheral neuropathy resulting in a unilateral hyperalgesia has recently been developed. The N-methyl-D-aspartate (NMDA) antagonist MK-801 reduces the thermal hyperalgesia observed in this model. The goal of the present study was to determine whether the immunohistochemical changes in dorsal horn peptides shown by neuropathic animals could also be modified by MK-801. Changes in immunostaining densities of substance P (SP) and calcitonin gene-related peptide (CGRP) within the spinal cord of untreated (reference population) neuropathic rats and that of neuropathic rats treated for 7 days with MK-801 were quantified and compared. The reference neuropathic animals demonstrated thermal hyperalgesia and an ipsilateral decrease in SP staining density without an accompanying change in CGRP staining density. MK-801-treated animals showed a dose-dependent attenuation of the thermal hyperalgesia. The expected ipsilateral decrease in SP was prevented in neuropathic animals treated with a low dose (0.5 mg/kg) of MK-801, while a higher dose of MK-801 (1 mg/kg) resulted in an increase in SP staining ipsilateral to the injury. MK-801 treatment in naive rats caused a global increase in both SP and CGRP staining in the dorsal horn. However, this global increase failed to mask the changes in staining density in neuropathic animals following MK-801 treatment. The results suggest a functional interaction between excitatory amino acids (EAAs) and SP, with activation of NMDA receptors mediating depletion of SP in neuropathic animals. It is suggested that SP-containing interneurons are a target of the EAAs in the dorsal horn.

Detection of thyrotrophin releasing hormone in rat brain in vivo using novel antibody microprobes: effects of amphetamine

Antibody microprobes of novel design were used to monitor thyrotrophin releasing hormone (TRH) in rat brain before and after-parenteral administration of amphetamine. Specific antibodies to TRH were bound to the outside of glass microprobes by adsorption to a surface of activated charcoal embedded in epoxylite resin. In male Wistar rats anaesthetised with chloral hydrate a series of antibody microprobes were implanted in forebrain. Amphetamine (10 mg/kg i.p.) caused a highly significant decrease in the binding of 125I-TRH to microprobes, indicating an increase in extracellular TRH localised in the lateral septum. There was also evidence of TRH release in the septo-hypothalamic nucleus. Neither saline, nor amphetamine at 2 mg/kg were able to evoke changes in the release of TRH at any sites.

Use of non-peptide tachykinin receptor antagonists to substantiate the involvement of NK1 and NK2 receptors in a spinal nociceptive reflex in the rat

Non-peptide antagonists of the NK1 and NK2 receptors were tested as inhibitors of the reaction time in the rat tail-flick and on the decrease of reaction time induced by the intrathecal injection of the NK1 receptor selective agonist [Sar9,Met(O2)11]SP or of the NK2 selective agonist NKA-(4-10). The decrease in reaction time produced by the NK1 agonist lasted less than 11 min while that evoked by the NK2 agonist persisted 26 min after injection. When given intrathecally, CP-96,345 and its chloro analog, Cl-CP, blocked dose-dependently both the behavioral responses and the decreases of reaction time induced by 6.5 nmol of [Sar9,Met(O2)11]SP while they failed to modify the hyperalgesic response to 6.5 nmol NKA-(4-10); CP-96,345 was found more potent than Cl-CP and was also active as an antagonist when given intravenously. In contrast, SR 48968 (6.5 and 65 nmol) blocked the NKA-(4-10)-induced decreases in reaction time and was inactive against the hyperalgesic effect of [Sar9,Met(O2)11]SP. The three antagonists blocked in a reversible manner, were inactive on their own on reaction time and non-toxic. The results indicate that the non-peptide CP-96,345 readily crosses the blood brain barrier and acts as a selective antagonist on spinal NK1 receptors, while SR 48968 is selective on NK2 receptors in the rat spinal cord. Hence, CP-96,345 and SR 48968 highlight a functional role of NK1 and NK2 receptors in spinal sensory neurotransmission.

Contribution of central neuroplasticity to pathological pain: review of clinical and experimental evidence

Peripheral tissue damage or nerve injury often leads to pathological pain processes, such as spontaneous pain, hyperalgesia and allodynia, that persist for years or decades after all possible tissue healing has occurred. Although peripheral neural mechanisms, such as nociceptor sensitization and neuroma formation, contribute to these pathological pain processes, recent evidence indicates that changes in central neural function may also play a significant role. In this review, we examine the clinical and experimental evidence which points to a contribution of central neural plasticity to the development of pathological pain. We also assess the physiological, biochemical, cellular and molecular mechanisms that underlie plasticity induced in the central nervous system (CNS) in response to noxious peripheral stimulation. Finally, we examine theories which have been proposed to explain how injury or noxious stimulation lead to alterations in CNS function which influence subsequent pain experience.

Noxious mechanical stimulation of the hind paws of the anaesthetized rat fails to elicit release of immunoreactive beta-endorphin in the periaqueductal grey matter

As a test of the hypothesis that an animal responds to a severe peripheral painful stimulus by a central release of beta-endorphin, antibody microprobes were inserted stereotactically into the midbrain of urethane anesthetized rats. These microprobes bore antibodies to beta-endorphin immobilized to their outer surfaces. While microprobes were in the brain for periods of 10 to 30 min either no stimulus was delivered or alligator clamps were applied to both hind paws. Microprobes were then incubated with 125I-beta-endorphin. Quantitative image analysis of microprobe autoradiographs showed no differences between the no-stimulus and noxious-stimulus groups. Thus these experiments found no evidence for beta-endorphin release following a severe peripheral painful stimulus.

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.

Emerging relationships between cytochemical properties and sensory modality transmission in primary sensory neurons

Primary sensory neurons have been categorized according to a variety of characteristics, including modality responsiveness, somal size, cytology, cytochemistry, and the organization of their central axon collateral arborizations. A major aim in the study of primary afferents has been to determine the relationships between dorsal root ganglia neuronal physiology, anatomy, and chemistry that could provide a basis for a classification scheme more directly relevant to function. Here we briefly review these relationships and examine the utility of specific histochemical and immunohistochemical markers representative of distinct populations of neurons that may transmit particular sensory modalities. In addition, we discuss some of our observations suggesting that one population of dorsal root ganglia neurons contains high levels of cytochrome oxidase, carbonic anhydrase, parvalbumin, and calbindin D28k, while a separate population contains fluoride-resistant acid phosphatase, calcitonin gene-related peptide, and displays immunoreactivity with an antibody that labels the central arborization of a specific class of unmyelinated afferents in the dorsal horn. This may have implications for the combinations of substances contained within neurons with distinct sensory functions.

Nociceptive responses to intrathecally administered substance P and somatostatin in diabetic mice

Male ICR mice were rendered diabetic by i.v. injection of streptozotocin. The nociceptive behavioral responses to i.t. injection of somatostatin (SST) but nor substance P (SP) were attenuated in diabetic mice compared with that in non-diabetic mice. Spantide, a SP receptor antagonist, enhanced the nociceptive response induced by i.t. SST in diabetic mice. Pretreatment of mice with SP reduced the SST-induced nociceptive response in non-diabetic mice. These results suggest that a endogenous antinociceptive system may exist which links SP with SST-mediated nociceptive transmission in the spinal cord. Furthermore, this endogenous antinociceptive system may be enhanced in diabetic mice.

Release of immunoreactive neuropeptide Y from brainstem sites in the cat during isometric contractions

Fatiguing isometric contractions of the left hind-limb muscles in cats anesthetized with alpha-chloralose caused mean arterial pressure to increase by 82 +/- 18 mmHg above resting and post-contraction levels and heart rates to increase by 15 +/- 5 beats/min. Contractions were performed by stimulating the tibial nerve via a microprocessor-controlled stimulator. Glass microprobes, coated with antibody specific for neuropeptide Y (NPY) were inserted bilaterally into the periaqueductal grey (P 0.5-1.0, LR 2.0 mm) or into the right ventrolateral medulla (3.0 mm rostral to obex; LR 3.5 mm) prior to, during and following fatiguing contractions to determine whether immunoreactive NPY was released. No release of immunoreactive NPY was detected from the site in the ventrolateral medulla. Immunoreactive NPY was released from the contralateral but not the ipsilateral periaqueductal grey during the isometric contractions, suggesting that NPY-like substances maybe involved with the integration of muscle afferent input into this area of the brainstem.

Release and depletion of substance P by capsaicin in substantia gelatinosa studied with the antibody microprobe technique and immunohistochemistry

Using an antibody microprobe technique, we have detected substance P release from the region of the substantia gelatinosa of the cat during the first, but not the second, 30 min of topical application of capsaicin (1-3%) to the tibial nerve. Immunohistochemical analysis also showed that substance P-like immunoreactivity was markedly reduced in the superficial layer of the dorsal horn 30 min after application of capsaicin. These results indicate that substance P is released and then depleted from primary afferent central terminals following acute application of capsaicin to the peripheral sensory nerve.

Kappa-/mu-receptor interactions in the opioid control of the in vivo release of substance P-like material from the rat spinal cord

The possible involvement of mu and kappa receptors in the opioid control of the spinal release of substance P-like material was assessed in vivo, in halothane-anaesthetized rats whose intrathecal space was continuously perfused with an artificial cerebrospinal fluid supplemented with various opioid receptor agonists and antagonists. Whereas the intrathecal perfusion with the mu agonist DAGO (10 microM) significantly enhanced (approximately + 50%) the spontaneous release of substance P-like material, that with the kappa agonist U 50488 H (10 microM) produced no change in the peptide outflow. The respective antagonists naloxone (10 microM) for the mu receptors and nor-binaltorphimine (10 microM) for the kappa receptors did not affect the spontaneous release of substance P-like material, indicating that endogenous opioids acting at mu and kappa receptors do not exert a tonic control on substance P-containing neurons in the spinal cord of halothane-anaesthetized rats. However, as expected from the involvement of mu receptors, the stimulatory effect of DAGO on the peptide outflow could be prevented by naloxone but not norbinaltorphimine. Furthermore, instead of an increase with DAGO alone, a significant decrease in the spinal release of substance P-like material was observed upon the intrathecal perfusion with DAGO plus U 50488 H. Additional experiments with the respective mu and kappa antagonists naloxone and nor-binaltorphimine demonstrated that this effect actually resulted from the simultaneous stimulation of mu and kappa receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Neurokinin A-like immunoreactivity in articular afferents of the cat

Dorsal root ganglion cells with axons innervating the cat's knee joint via the medial articular nerve were retrogradely labelled with Fast blue. Neurokinin A-like immunoreactivity was found in 4.5 +/- 1.1% (mean +/- S.D. of 5 nerves and 695 cells) of the articular afferents. Colchicine treatment of the ganglia increased the percentage of immunopositive cells to 8.5 +/- 0.7% (mean +/- S.D. of 6 nerves and 554 cells) after 3-22 h. The diameter distribution of the immunopositive somata ranged from 20 to 50 microns with a maximum at 26-30 microns. Comparing the proportions of neurokinin A-immunopositive cells with those of substance P, it can be calculated on the basis of mRNA encoding that neurokinin A is synthetized in about half of the substance P-containing primary articular afferents.

Intrathecal CP-96,345 blocks reflex facilitation induced in rats by substance P and C-fiber-conditioning stimulation

We have examined the effects of intrathecally (i.t.) administered CP-96,345, a non-peptide NK1 receptor ligand, on the spinal nociceptive flexor reflex and on the facilitation of this reflex evoked by i.t. substance P (SP), neurokinin A (NKA) and electrical conditioning stimulation of cutaneous C-afferents. CP-96,345 i.t. at 24 pmol-2.4 nmol had no significant effect on flexor reflex excitability. At the highest dose tested (24 nmol), CP-96,345 caused a brief facilitation of the flexor reflex, which was similar to the effect of the vehicle used at this drug concentration. CP-96,345 did not depress the flexor reflex at any dose. In rats with chronically implanted i.t. catheters, CP-96,345 at 24 nmol caused neither motor impairment nor morphological damage to the spinal cord. Pretreatment with CP-96,345 dose dependently and similarly antagonized facilitation of the flexor reflex induced by 7 pmol i.t. SP or by a 20-s, 1-Hz conditioning stimulus train applied to cutaneous C-fibers in the sural nerve innervation area. The vehicle had no effect. The antagonistic effect of CP-96,345 on the SP- and C-fiber reflex facilitation induced by conditioning stimulation became maximal only 20-30 min after the i.t. injection and lasted 3-4 h at the highest dose. CP-96,345 did not significantly block the facilitatory effect of 7 pmol i.t. NKA on the flexor reflex. These results demonstrate that CP-96,345 is a potent, long-lasting and selective antagonist of SP in rat spinal cord. Furthermore, facilitation of the flexor reflex (central sensitization) induced by conditioning stimulation of cutaneous C-afferents is mediated by NK1 tachykinin receptors, but the NK1 receptor may not be involved in the transmission of the flexor reflex. CP-96,345 is thus useful in experimental studies of the role of SP in the central nervous system.

Potentiated expression of FOS protein in the rat spinal cord following bilateral noxious cutaneous stimulation

A noxious mechanical or chemical stimulus to the ventral skin of one hindpaw induced the expression of FOS proteins ipsilaterally in the spinal dorsal horn neurons in the rat. The number of FOS-labelled cells reached a maximum at 2-3 h, and decayed to basal levels within 6 h after the stimulus. When a first noxious stimulus was applied to the contralateral hindpaw 1-1.5 h prior to this stimulus, the number of FOS-labelled cells increased, over all laminae, to 153% (mechanical) and 164% (chemical) compared to the number produced by a single stimulus. This effect of a prior stimulus in increasing the number of FOS-labelled cells produced by a contralateral stimulus persisted for several hours after the first stimulus. The results are interpreted as a sensitization of dorsal horn neurons induced by peripheral noxious stimuli, which is manifest at the molecular biological level.

The effects of A- and C-fiber stimulation on patterns of neuropeptide immunostaining in the rat superficial dorsal horn

The present study determines the effects of sciatic nerve stimulation at intensities that activate A-fibers alone or both A- and C-fibers on immunostaining for substance P (SP), cholecystokinin-octapeptide (CCK-8), galanin (GAL), dynorphin (DYN) and vasoactive intestinal polypeptide (VIP) in the superficial dorsal horn of the rat spinal cord. The goal of this study is to provide a more precise spatial localization of the sites of release or accumulation of these compounds in relation to specific types of stimuli. Following A-fiber stimulation, there was no significant change in immunostaining for any of these compounds. However, A- and C-fiber stimulation resulted in major changes. For SP, CCK-8, GAL and DYN there was a large and significant loss of immunostaining in medial regions of the dorsal horn. This is the area where sciatic nerve primary afferent fibers terminate and the depletion is probably correlated with activity in these fibers. By contrast, VIP immunostaining is increased in the lateral part of the superficial cord, which is outside of the central sciatic afferent fiber terminations. This indicates that the increase is not in the fine sciatic sensory axons that are directly stimulated. As a final point, the fact that C-fiber but not A-fiber stimulation causes marked changes in the immunocytochemical distribution of all these compounds is further evidence, albeit indirect, that they are involved in nociceptive information processing.

Release of immunoreactive enkephalinergic substances in the periaqueductal grey of the cat during fatiguing isometric contractions

Antibody-coated microprobes were used to determine whether immunoreactive enkephalins were released in response to fatiguing isometric contractions of the hind-limb muscles in cats anesthetized with alpha-chloralose. Contractions were performed by stimulating the tibial nerve via a microprocessor-controlled stimulator. Microprobes were inserted into the periaqueductal grey (P 0.5-1.0 mm) prior to, during and following fatiguing contractions. During fatiguing contractions, mean arterial blood pressure increased by 76 +/- 9 mmHg above resting and recovery levels. Levels of immunoreactive enkephalins were elevated in the dorsolateral periaqueductal grey during the isometric contraction when compared to resting levels. It is possible that isometric muscle contraction causes the release of Met-enkephalin-like substances in the periaqueductal grey.

Effect of peptidase inhibition on the pattern of intraspinally released immunoreactive substance P detected with antibody microprobes

Antibody microprobes bearing antibodies to the C-terminus of substance P (SP) were used to measure release of immunoreactive (ir) SP in the dorsal horn of barbiturate anaesthetized spinal cats. Electrical stimulation of unmyelinated primary afferents of the ipsilateral tibial nerve produced a relatively localised release of ir SP in the superficial dorsal horn. Prior microinjection of the peptidase inhibitors kelatorphan and enalaprilat in the dorsal horn resulted in ir SP being detected over the whole of the dorsal horn and the overlying dorsal column. This pattern had previously been observed with evoked release of ir neurokinin A and supports the proposal that a slow degradation results in a neuropeptide accessing many sites remote from sites of release.

Effects of intrathecal antibodies to substance P, calcitonin gene-related peptide and galanin on repeated cold stress-induced hyperalgesia: comparison with carrageenan-induced hyperalgesia

Rats exposed to a cold environment (4 degrees C) for 30 min every 1 h during the day and at night show a gradual decrease in the nociceptive threshold for pressure stimulation. Such hyperalgesia, referred to as repeated cold stress (RCS)-induced hyperalgesia, is stable for at least 4 h and maintained for 3 days only by exposing to cold overnight; thus, no adaptation to RCS is apparent. Hyperalgesia gradually returns over 4 days after cold exposure ceases. To determine whether three neuropeptides, substance P (SP), calcitonin gene-related peptide (CGRP) and galanin (GAL), which are present in the superficial dorsal horn including primary afferent terminals, would be responsible for RCS-induced hyperalgesia, we examined the effects of intrathecal injections of their antibodies (used as inhibitors of neuropeptide-mediated synaptic transmission) on the nociceptive threshold of RCS rats, and compared this with the antibody effect on carrageenan-induced hyperalgesia. An intrathecal injection of anti-SP antibody significantly inhibited the hyperalgesia of RCS rats as well as carrageenan-induced hyperalgesia, and slightly increased the nociceptive threshold of non-RCS rats. Anti-CGRP antibody produced an improvement in the hyperalgesia of RCS rats as well as carrageenan-induced hyperalgesia without having an effect on the nociceptive threshold of non-RCS rats. Although anti-GAL antibody significantly inhibited carrageenan-induced hyperalgesia, it did not affect the nociceptive threshold of RCS and non-RCS rats. The present results suggest that enhancement of synaptic transmission mediated by SP and CGRP, but not GAL, in the spinal dorsal horn is, at least in part, involved in RCS-induced hyperalgesia.

Prolonged potentiation of transmission through a withdrawal reflex pathway after noxious stimulation of the heel in the rabbit

The sural-gastrocnemius reflex of the spinalized rabbit was potentiated to an average of 3-6 times control levels after the application of noxious mechanical, thermal or chemical stimuli to the skin of the heel. Facilitation of the reflex was maximal within 1 min of the noxious stimulus, and in many cases persisted for more than 1 h. Prolonged increases in the excitability of the sural-gastrocnemius reflex were not seen after innocuous mechanical or thermal stimulation of the heel. Repetitive electrical stimulation of the sural nerve (100 shocks given at 0.5 Hz) caused persistent facilitation of the reflex when small myelinated A delta fibres or non-myelinated C-fibres were recruited by the conditioning stimulus. Such protracted increases in the excitability of the sural-gastrocnemius pathway would enhance the protective functions of this reflex. The mechanisms described here have probably evolved to provide a high level of reflex protection to the heel after tissue damage has occurred at that site.

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.

Substance P-mediated slow excitatory postsynaptic potential elicited in dorsal horn neurons in vivo by noxious stimulation

The original proposal that substance P is involved in the regulation of nociceptive information at the first sensory synapse in the spinal cord has been substantiated by a wide range of evidence, but definitive support has been lacking, due primarily to the lack of evidence that a specific nociceptive response in the dorsal horn can be blocked by a substance P antagonist. Here, we present evidence that CP-96,345, a specific substance P (NK-1) receptor antagonist, selectively blocks a slow, prolonged excitatory postsynaptic potential following noxious cutaneous stimulation or a train of intense electrical stimuli to sensory nerves but does not affect the response to innocuous input or the brief response to single electrical stimuli to C fibers. These results indicate the specific involvement of substance P in the mediation of a prolonged after-excitation to noxious stimulation. This may have important implications for the etiology and treatment of chronic pain and for plastic changes in nociceptive pathways.

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.

Enhancement of spinothalamic neuron responses to chemical and mechanical stimuli following combined micro-iontophoretic application of N-methyl-D-aspartic acid and substance P

A role for sensitization of nociceptors in the generation of primary hyperalgesia is well documented. More recent work has begun to define a role of an increased excitability of neurons within the spinal cord in the generation of secondary hyperalgesia. The present study demonstrates increased responses of primate spinothalamic neurons following co-administration of N-methyl-D-aspartic acid (NMDA) and substance P (SP) by micro-iontophoresis. Wide dynamic range and high threshold STT neurons in laminae I-VI showed an increased frequency of discharges following application of NMDA which was characterized by a slow onset to peak discharge rate and a slow return to background levels of discharge. Combined application of NMDA with SP resulted in an enhancement of responses to NMDA that often long outlasted the administration of SP. This increase in response of the cells to NMDA was not produced by repeated application of NMDA alone or following combined application of NMDA with an SP analog. NMDA responses were reduced or prevented in all cases by co-application of an NMDA-receptor antagonist. Finally, long-lasting potentiation of NMDA responses by SP was paralleled by enhanced responses to mechanical stimulation of skin. It is proposed that a mechanism involving the combined synaptic release of excitatory amino acids and peptides leads to secondary hyperalgesia.

Involvement of substance P in hyperalgesia induced by intrathecal galanin

Previously we have demonstrated that an intrathecal injection of galanin (GAL) decreases the nociceptive threshold for mechanical stimulation without effect on thermal nociceptive responses. The present experiments were conducted to determine whether substance P (SP) would be involved in such a decrease in the nociceptive threshold produced by GAL. An intrathecal injection of anti-SP monoclonal antibody inhibited the nociceptive threshold-decreasing effect of intrathecal GAL (0.1 nmol/rat). This antibody significantly suppressed the contractile action of SP (3 nM) on the longitudinal muscle and that of neurokinin A (3 nM) to a lesser degree. Binding of [125I]Tyr8-SP to this antibody was inhibited by SP in a concentration-dependent manner in the range 0.1-33 nM without suppression by GAL at a concentration of 3300 nM. In addition, an intrathecal injection of the anti-SP monoclonal antibody increased the nociceptive threshold for mechanical stimulation in carrageenin-inflamed rats without effect on thermal nociceptive behaviors. The capsaicin (0.5 microM)-evoked release of immunoreactive SP from dorsal-half slices of the spinal cord was increased by galanin (1 microM, but not 0.1 microM) without effects on basal release. An intrathecal injection of GAL did not produce aversive responses (biting, licking and scratching) at doses of 0.1 and 1 nmol/rat. GAL (0.1 nmol/rat) did not affect biting/licking behaviors evoked by SP (1 nmol/rat), but inhibited SP-evoked scratching behavior. These results suggest that the nociceptive threshold-decreasing action of intrathecal GAL is at least in part mediated by SP, and that GAL may act on primary afferent terminals to increase the release of SP evoked by stimulation.

Analgesic doses of morphine do not reduce noxious stimulus-evoked release of immunoreactive neurokinins in the dorsal horn of the spinal cat

1. Antibody microprobes were used to detect immunoreactive neurokinin A release in the dorsal spinal cord of barbiturate-anaesthetized spinal cats. 2. Noxious mechanical stimulation of the ipsilateral hind paw and electrical stimulation (suprathreshold for unmyelinated primary afferent fibres) of the ipsilateral tibial nerve evoked immunoreactive neurokinin A release. 3. Systemic morphine, 5 mg kg-1, i.v., did not block immunoreactive neurokinin A release in response to these stimuli. 4. Subsequent naloxone administration, 0.5 mg kg-1, i.v., did not alter this stimulus-evoked release. 5. Basal levels of immunoreactive neurokinin A were unaltered by morphine or naloxone. 6. These results suggest that the analgesic effects of morphine at the spinal cord level are not brought about by activation of presynaptic opiate receptors on neurokinin A containing afferent terminals.

Streptozotocin-induced diabetes in mice reduces the nociceptive threshold, as recognized after application of noxious mechanical stimuli but not of thermal stimuli

We report herein that streptozotocin (STZ)-induced diabetes selectively alters the nociceptive threshold with respect to noxious mechanical stimuli. Mice were rendered diabetic by an injection of STZ (200 mg/kg, IV). In the tail-pinch test, the latency of the biting response to forceps was significantly decreased in animals with diabetes of 2 weeks and 8 weeks duration as compared to that in age-matched controls. However, the nociceptive threshold, as determined by the tail-flick test, was not significantly altered. The level of substance P in the spinal cord was significantly increased in mice that has been diabetic for 2 weeks, while, there was a significant decrease, as compared to control levels, in level of substance P in mice diabetic for 8 weeks. However, the level of somatostatin was not significantly altered in mice diabetic for either 2 weeks or 8 weeks. These data suggest that STZ-induced diabetes selectively alters a neuronal system that involves substance P but not somatostatin in the spinal cord.

Prenatal development of cutaneous afferent connections in the spinal cord of fetal sheep. A physiological and neurochemical study

In this study we have examined the physiological and neurochemical development of the cutaneous afferent pathways from the hindlimb to the spinal cord in fetal sheep. We have shown that somatosensory input from the hindlimb evokes activity in DRG neurons at 87d gestation and in cells in the dorsal horn at 92d (term, 146d). There is evidence of immunoreactivity for substance P, calcitonin gene-related peptide and glutamine several days prior to this at 77-80 days. The implication of these findings are discussed.

Sustained isometric contraction of skeletal muscle results in release of immunoreactive neurokinins in the spinal cord of the anaesthetized cat

Antibody microprobes were used to study release of immunoreactive neurokinins in the dorsal horn of the anaesthetized spinal cat following sustained isometric contraction of ipsilateral hindlimb muscles. Microprobes had immobilized antibodies to neurokinin A (NKA) on their outer surfaces and bound a proportion of released molecules when inserted in the central nervous system. Bound molecules were detected in autoradiographs as zones of reduced binding of 125I-NKA in which microprobes were incubated after withdrawal from the spinal cord. The left hindlimb was immobilized using an epoxy bandage splint and isometric contraction of muscles induced by intermittent tetanic stimulation of a ventral root. A basal presence of immunoreactive neurokinins was detected and this was increased by sustained isometric muscle contraction. It is probable that ergoreceptors contain and release neurokinins.

Substance P- and calcitonin gene-related peptide immunoreactivity in primary afferent neurons of the cat's knee joint

The distribution of substance P and calcitonin gene-related peptide was determined in primary afferent neurons of the medial and posterior articular nerve of the cat's knee joint. Perikarya of articular afferents were visualized by retrograde labelling with the fluorescent dye Fast Blue which was applied at the transected end of the peripheral nerves. Substance P was found in about 17% of labelled medial articular afferents and in about 16% of labelled posterior articular afferents, respectively, whereas calcitonin gene-related peptide was present in about 35 and 32% of the medial and posterior articular nerve cells, respectively. Taking into account that these neuropeptides are known to be co-localized, probably not more than one-third of the joint afferents contain substance P and/or calcitonin gene-related peptide. Quantification of cell diameters revealed that substance P was found only in small- or intermediate-sized perikarya (less than 50 microns) indicating that this peptide is predominantly found in unmyelinated neurons. Calcitonin gene-related peptide was present mainly in small- and intermediate- but also in some large-sized neurons (greater than 50 microns) providing evidence that this peptide is found in unmyelinated and to a lesser extent in myelinated neurons. This is consistent with previous studies that show that substance P and calcitonin gene-related peptide are present primarily in unmyelinated and thinly myelinated primary afferents. When the portion of substance P-positive neurons of the medial articular nerve is compared to the number of articular afferents displaying a nociceptive function as determined in earlier electrophysiological studies, it can be calculated that at most 30% of the nociceptive-specific articular afferents contain this neuropeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraspinal release of substance P and calcitonin gene-related peptide during opiate dependence and withdrawal

The antibody microprobe technique was used to study the release of immunoreactive substance P and immunoreactive calcitonin gene-related peptide within the lower lumbar spinal cord of anaesthetized spinalized cats pretreated twice daily for 3.5 days with increasing doses of morphine hydrochloride (2-20 mg/kg, i.p.). Both peptides were released in the region of the substantia gelatinosa during noxious cutaneous thermal stimulation or high-intensity electrical stimulation of a hind limb nerve. Intravenous administration of naloxone increased the nociceptive excitation of lumbar dorsal horn neurons, but did not alter the evoked release of immunoreactive substance P or immunoreactive calcitonin gene-related peptide in the superficial gray matter dorsal to these neurons. In addition, the release of both peptides was not significantly different to that detected under similar experimental conditions in opioid-naive cats. The results suggest that alterations in neuropeptide release from the central terminals of nociceptive primary afferent neurons do not occur during states of opiate dependence and withdrawal, and thus do not contribute to the characteristic signs of these phenomena in dependent animals.

On the role of NK-2 tachykinin receptors in the mediation of spinal reflex excitability in the rat

The effects of intrathecal administration of neurokinin A, substance P and [Tyr5, D-Trp6,8,9 Arg10]neurokinin A-(4-10) (Men 10207), a specific NK-2 receptor antagonist, on the spinal nociceptive flexor reflex were studied in decerebrate, spinalized, unanesthetized rats. Intrathecal neurokinin A and substance P facilitate the flexor reflex in a similar manner. The reflex facilitation to intrathecal neurokinin A, but not substance P, is dose-dependently blocked by pretreatment with Men 10207. The NK-2 receptor antagonist by itself facilitates the flexor reflex with a potency about 10 times less than that of neurokinin A, indicating a partial agonistic property. Reversible depression of the flexor reflex, which is not due to nonspecific spinal blockade, is observed after 700 pmol Men 10207. Further increasing the dose of Men 10207 to 7 nmol for 20 s at an intensity that activates unmyelinated (C) fibers stimulation of peripheral nerves at 1 Hz for 20 s at an intensity that activates unmyelinated (C) fibers facilitates the ipsilateral flexor reflex. The duration of the facilitation after conditioning stimulation of the cutaneous sural nerve is several minutes and about 1 h after conditioning stimulation of the gastrocnemius muscle nerves. Pretreatment with Men 10207 (70-700 pmol) has no effect on facilitation by the sural nerve conditioning stimulation, but effectively blocks the long-term reflex facilitation to the gastrocnemius nerve stimulation. The present results indicate a distinct role for NK-2 tachykinin receptors in mediation of spinal reflex excitability in the rat. Neurokinin A may be involved in the long-term increase of spinal reflex excitability after activation of unmyelinated fibers innervating muscle.