Substance P-like immunoreactivity in nerves associated with the vascular system of guinea-pigs

Substance P-like immunoreactivity was localized by an indirect immunohistochemical technique in whole mounts and sections of blood vessels from the guinea-pig. There was a widespread association of nerve fibres that had substance P-like immunoreactivity with blood vessels, extending into all vascular beds. The relative densities of supply of different vessels were assessed visually and a rating scale used to compare them. Large elastic arteries close to the heart had dense networks of immunoreactive nerves associated with them. The density decreased as more peripheral beds were approached, except that there was a particularly dense network of nerves with arteries of the splanchnic beds. Arteries to myocardial, central nervous system, renal, reproductive and skeletal muscle beds all had substance P-immunoreactive nerves associated with them to varying extents. The venae cavae near the heart were densely supplied, but there were few fibres with their more peripheral extensions. Some large veins (e.g. pulmonary, hepatic portal and superior mesenteric) had a few fibres with them, but veins of peripheral vascular beds had very few or no immunoreactive nerve fibres. Substance P-like immunoreactivity in vascular nerves was markedly reduced in guinea-pigs that were injected with capsaicin but was unaffected by the injection of 6-hydroxydopamine. It is concluded that the vascular substance P-immunoreactive nerves are likely to be of sensory origin.     

Sympathectomies lead to transient substance P-immunoreactive sensory fibre plasticity in the rat skin.

Research using animal models of neuropathic pain has revealed sympathetic sprouting onto dorsal root ganglion cells. More recently, sensory fibre sprouting onto dorsal root ganglion cells has also been observed. Previous work in our laboratory demonstrated persistent sympathetic fibre sprouting in the skin of the rat lower lip following sensory denervation of this region. Therefore, we applied immunocytochemistry to determine the effects of sympathectomies on the terminal fields of sensory fibres. The superior cervical ganglia were removed bilaterally and the effects on the innervation of the skin of the rat lower lip were observed 1, 2, 3, 4, 6 and 8 weeks post-surgery. Substance P and dopamine-beta-hydroxylase immunoreactivities were used to identify a subset of sensory and sympathetic fibres, respectively. We also assessed neurokinin-1 receptor immunoreactivity. Quantitative data was obtained with the aid of an image analysis system.In controls, the epidermis and upper dermis were innervated by substance P-immunoreactive fibres only and upper dermal blood vessels possessed the highest density of neurokinin-1 receptor immunoreactivity. Blood vessels in the lower dermis were innervated by both substance P- and dopamine-beta-hydroxylase-immunoreactive fibres. Following sympathectomies, substance P-immunoreactive fibres in the epidermis and upper dermis were more intensely labelled only 1 and 2 weeks post-surgery when compared to sham controls. The length of substance P-immunoreactive fibres in this region was also increased only on the second week. Neurokinin-1 receptor immunoreactivity in the upper dermis was slightly decreased 1 and 2 weeks post-surgery. In the lower dermis, substance P-immunoreactive fibres associated with blood vessels were more intensely labelled only 1 and 2 weeks post-surgery, and at all post-surgical time points studied, blood vessels in this region were devoid of dopamine-beta-hydroxylase-immunoreactive fibres. The length of substance P-immunoreactive fibres was increased from the first to the third week post-surgery in the lower dermis.These results indicate that sympathectomies lead to transient changes in substance P-immunoreactive fibre innervation and neurokinin-1 receptor expression in rat lower lip skin. The effects are most prominent in the lower dermis probably due to a greater local concentration of nerve growth factor in this region. The plasticity of the interactions between sensory and sympathetic fibres may prove important in the regulation of skin microcirculation and in the generation of painful sensations under normal conditions or following peripheral nerve injuries.     

Multiple tachykinin pools in sensory nerve fibres in the rabbit iris

A population of sensory nerve fibres in the rabbit iris is known to contain calcitonin gene-related peptide and tachykinins, such as substance P and neurokinin A. In the presence of atropine and guanethidine, the isolated iris sphincter responded to electrical stimulation with a contraction that could be abolished by tachykinin antagonists. Capsaicin, known to release tachykinins from sensory fibres, evoked a long-lasting tachykinin-mediated contraction of the iris sphincter. Repeated application of capsaicin led to tachyphylaxis, possibly reflecting depletion of releasable neuronal stores of tachykinins. At this stage, electrical stimulation failed to elicit contraction. The capacity of capsaicin to release neuropeptides from sensory fibres was confirmed by determination of substance P- and calcitonin gene-related peptide-like immunoreactivity in the incubation medium and in the iris tissue. The concentrations of substance P and calcitonin gene-related peptide in the iris after capsaicin exposure were reduced by about 25%. Like capsaicin, bradykinin evoked a tachykinin-mediated contraction and tachyphylaxis. However, after development of tachyphylaxis to bradykinin, electrical stimulation or exposure to capsaicin still evoked tachykinin-mediated contraction, albeit a reduced one compared with the response before bradykinin. Hence, capsaicin completely depletes tachykinin stores releasable by prolonged electrical stimulation, whereas bradykinin exhausts only a sequestered pool. The possibility that tachykinins occur in several releasable pools in sensory nerves was investigated in yet another way: the iris sphincter muscle was stimulated electrically once every 2.5 min over several hours. The contractile response diminished gradually.(ABSTRACT TRUNCATED AT 250 WORDS)     

The nature of the substance P-containing nerve fibres in taste papillae of the rat tongue

The nature of the association of substance P (SP) with taste buds in the rat tongue was investigated by immunohistochemical and radioimmunoassay techniques. Both the circumvallate and fungiform papillae were found to receive a rich innervation by substance P-containing fibres. Although these fibres were closely associated with the taste buds in these structures, they assumed a perigemmal rather than an intragemmal location. Bilateral lesions of the glossopharyngeal nerve resulted in the depletion of taste buds from the vallate papilla and a large reduction in substance P immunoreactive fibres in this area. Lesions of the chorda tympani, which led to the degeneration of taste buds in fungiform papillae, had no effect on the immunohistochemical appearance of substance P in these papilla or on the substance P levels in the anterior part of the tongue. Lesions of the mandibular division of the trigeminal nerve or neonatal capsaicin treatment had no effect on the structural integrity of taste buds in fungiform papillae but led to the depletion of substance P-immunoreactive fibres from these papillae. Both of these procedures caused a 71% reduction in the substance P content of the anterior tongue, ipsilaterally after the nerve lesion and bilaterally after capsaicin treatment. The results are discussed in relation to the possible functional role of substance P-containing fibres within nerves supplying taste structures of the tongue.     

Time course of effect of capsaicin on ultrastructure and histochemistry of substance P-immunoreactive nerves associated with the cardiovascular system of the guinea-pig

Capsaicin, a neurotoxin which depletes substance P from primary afferent nerve fibres, was injected systematically into adult guinea pigs. The effects of capsaicin were studied by immunohistochemistry, electron microscopy and radioimmunoassay at times from 5 min to 1 year. Within 5 min after a single injection of capsaicin (50 mg/kg) substance P immunofluorescence appeared less intense and less homogeneous than normal (i.e. it appeared granular). Large nerve trunks remained evident, but there were fewer fine single nerve fibres. With increasing time there was a progressive decrease in the number of immunoreactive fibres; by 4 h there was a marked reduction in the number of fibres and by 24 h only an occasional fibre was evident. In animals sacrificed 2 or more hours after treatment large brightly fluorescent swellings were seen in many nerves. Depletion of substance P-immunoreactivity persisted for as long as 365 days after treatment. Electron microscopy revealed alterations in capsaicin-sensitive nerve fibres within 5 min after treatment. Many fibres appeared swollen and there was disruption of their internal morphology, e.g. loss of microtubules and filaments and presence of an amorphous flocculent material in the axons. With increasing time after treatment, electron-dense profiles, indicative of degenerating nerve fibres, were commonly seen associated with Schwann cells. These findings demonstrate that the effects of systemic administration of capsaicin to adult guinea pigs occur rapidly in capsaicin-sensitive nerve fibres. The long lasting depletion of substance P-containing fibres is due to their degeneration.     

Substance P-immunoreactivity in the dorsal medial region of the medulla in the cat: effects of nodosectomy

The distribution of substance P in the vagal system of the cat was studied by immunohistochemistry. Substance P-immunoreactive cell bodies and fibres were observed in the nodose ganglion. Numerous substance P-immunoreactive terminals and fibres were localized in their bulbar projection area, i.e. throughout the caudo-rostral extent of the nucleus of the solitary tract. Four subnuclei, among the nine forming the nucleus of the solitary tract, were strongly labelled: interstitial, gelatinosus, dorsal and commissural. The dorsal motor nucleus of the vagus nerve also exhibited numerous substance P-immunoreactive terminals, sometimes closely apposed on the somata of preganglionic neurons. To determine the substance P component of the vagal afferent system a nodose ganglion was removed on one side. The ablation triggered ipsilaterally a large decrease of substance P immunoreactivity in the four subnuclei strongly labelled on normal cats. These results suggest the involvement of substance P-containing vagal fibres in integrative processes of the central regulation of cardiovascular, digestive and respiratory systems, viscerotopically organized throughout these four subnuclei. The nodose ablation also resulted in a decrease of substance P immunoreactivity in the ipsilateral dorsal motor nucleus of the vagus nerve, suggesting monosynaptic vago-vagal interactions.     

The effect of intra-articular capsaicin on nerve fibres within the synovium of the rat knee joint

The aim of this study was to establish the effects of intra-articular capsaicin (pelargonic acid vallinylamide) on synovial innervation of the rat knee. Rats were sacrificed 1, 2, 4 and 7 days after intra-articular injection of capsaicin and joint tissues stained with either conventional haematoxylin and eosin (H and E) or with specific antibodies to the calcitonin gene-related peptide (CGRP), substance P (both of which are markers for primary afferent fibres), the C-flanking peptide of neuropeptide Y (CPON) (localised in postganglionic sympathetic fibres), or protein gene product 9.5 (a pan-neuronal marker). At lower concentrations (0.1% and 0.25%), capsaicin produced no change in peptide staining pattern or histological appearance. At 0.5% capsaicin, there was complete loss of nerve fibres showing positive staining for CGRP and substance P at all time points. Staining for CPON and protein gene product 9.5 was still present, but decreased, 1 and 2 days after treatment and virtually absent at 4 and 7 days. These findings provide evidence for partially selective denervation induced by 0.5% capsaicin, in contrast to 1% capsaicin which abolished staining for all peptide markers, indicating a total ablation of nerve fibres. A consistent but unexpected finding was the presence of a severe inflammatory response in joints treated with 0.5% and 1% capsaicin. An influx of polymorphonuclear leucocytes was found to occur within 4 h of injection, with progressive appearance of mononuclear cells after this time. We conclude that it is difficult to specifically deplete sensory nerve fibres from the synovium by means of local capsaicin injection. Although selective loss of staining for sensory nerve fibres could be achieved by injection of 0.5% capsaicin, there was progressive non-specific loss of post-ganglionic autonomic fibres which may be related to the severe inflammatory response provoked by the higher doses of capsaicin.     

Enkephalin and capsaicin-resistant substance P-like immunoreactivities in intra-ocular grafts of different fetal spinal cord areas

Fetal spinal cord tissue was grafted to the anterior chamber of the eye of adult rats in order to evaluate survival and distribution of substance P- and enkephalin-immunoreactive neurons. Capsaicin treatment was used to evaluate any possible contribution of host iris-derived substance P fibres to the innervation of the grafts and to check for capsaicin sensitivity of graft substance P-positive systems. Substance P- and enkephalin-immunoreactive nerve fibres were present in grafts of half-transverse segments of the spinal cord and were clearly co-distributed throughout the grafts. Areas with a high density of substance P- and enkephalin-positive fibres resembling substantia gelatinosa were seen. Grafts of the dorsal horn alone had a moderate to high density of substance P- and enkephalin-positive fibres, while ventral horn grafts contained a low amount of such fibres. Capsaicin eliminated the substance P innervation of the host iris and the dorsal root ganglion-derived substance P innervation of the host spinal cord, while sparing the intrinsic substance P innervation of both host spinal cord and spinal cord grafts. These experiments show that intra-ocular grafts of defined spinal cord areas express relatively organotypic amounts of substance P- and enkephalin-positive nerve fibres, and thus emphasize the importance of intrinsic genetic determinants for spinal cord development.     

Immunohistochemical evidence from co-localization and denervation studies for four types of substance P-containing nervous structures in the rat superior cervical ganglion

Four types of substance P-immunoreactive structures have been distinguished in the rat superior cervical ganglion by double-immunofluorescence microscopy: (1) A major population of mainly varicose fibres enmeshed singly-scattered neuronal perikarya, some of which contained vasoactive intestinal polypeptide-immunoreactivity. These substance P-immunoreactive fibres did not contain colocalized calcitonin gene-related peptide (CGRP) and were absent after transection of the cervical sympathetic trunk. (2) A rather small substance P-immunoreactive fibre population with colocalized calcitonin gene-related peptide-immunoreactivity was distributed in a patchy manner and disappeared after cutting the postganglionic branches. (3) Most of the intraganglionic small intensely fluorescent (SIF) cell clusters were intensely substance P-immunoreactive. SIF cells were not visibly changed in number and fluorescence intensity by either surgical procedure. (4) Immunoreactivity was not visible in principal ganglionic neurons of control ganglia, but occurred in cell bodies after pre- as well as after postganglionic nerve transection. Some of the substance P-immunolabelled perikarya in addition revealed immunostaining to antisera against the catecholamine-synthesizin enyzme tyrosine hydroxylase or against the neuropeptides leu-enkephalin and vasoactive intestinal polypeptide, respectively. The results strongly suggest that, in addition to a substance P-containing preganglionic input (1), and a supply by substance P-containing sensory axon collaterals (2), the superior cervical ganglion of the rat gives origin to a paraganglionic (3) and a postganglionic (4) substance P-immunoreactive intrinsic system, the latter becoming visible only after disconnection of the sympathetic pathway.     

Vagal origin of substance P-containing nerves in the guinea pig lung

This study reports on the possible origin and putative sensory nature of substance P-containing fibres in the lung. Following vagal ligation experiments, carried out on adult guinea pigs, the vagi, nodose ganglia and lungs were investigated by immunocytochemistry and radioimmunoassay. After ligation the lung showed a marked depletion of substance P-immunoreactivity; concomitantly there was an accumulation of immunoreactive material proximal to the ligature, indicating a peripheral direction of the peptide axonal flow. Several substance P-immunoreactive neuronal cell bodies were observed in the nodose ganglion. These results suggest that substance P-immunoreactive fibres in the lung might originate from primary sensory neurones in the nodose ganglion, which is compatible with other evidence that substance P has a sensory role.     

Growth of nerve fibres into murine peritoneal adhesions

Adhesions in the peritoneal cavity have been implicated in the cause of intestinal obstruction and infertility, but their role in the aetiology of chronic pelvic pain is unclear. Nerves have been demonstrated in human pelvic adhesions, but the presence of pain-conducting fibres has not been established. The purpose of this study was to use an animal model to examine the growth of nerves during adhesion formation at various times following injury and to characterize the types of fibres present. Adhesions were generated in mice by injuring the surface of the caecum and adjacent abdominal wall, with apposition. At 1-8 weeks post-surgery, adhesions were processed and nerve fibres characterized histologically, immunohistochemically, and ultrastructurally. Peritoneal adhesions had consistently formed by 1 week after surgery and from 2 weeks onwards, all adhesions contained some nerve fibres which were synaptophysin, calcitonin gene-related peptide, and substance P-immunoreactive, and were seen to originate from the caecum. By 4 weeks post-surgery, nerve fibres were found to originate from both the caecum and the abdominal wall, and as demonstrated by acetylcholinesterase histochemistry, many traversed the entire adhesion. Ultrastructural analysis showed both myelinated and non-myelinated nerve fibres within the adhesion. This study provides the first direct evidence for the growth of sensory nerve fibres within abdominal visceral adhesions in a murine model and suggests that there may be nerve fibres involved in the conduction of pain stimuli.     

Co-localization of tachykinins and calcitonin gene-related peptide in capsaicin-sensitive afferents in relation to motility effects on the human ureter in vitro

Tachykinin- and calcitonin gene-related peptide (CGRP) immunoreactivities were localized by immunohistochemistry in the same nerves of the kidney, renal pelvis and ureter as well as in spinal ganglion cells of both the guinea-pig and man. The tachykinin and CGRP-immunoreactive nerves in the ureter were present within the smooth muscle layers, around blood vessels, close to and within the lining epithelium. The levels of neurokinin A-, substance P- and CGRP-like immunoreactivity per tissue weight, as determined by radioimmunoassay, were about 30-100-fold higher in the guinea-pig than in the human ureter, which was in good agreement with the relative density of immunoreactive nerve fibres, as seen by immunohistochemistry. Capsaicin treatment caused an almost total disappearance of both neurokinin A-, substance P- and CGRP-immunoreactive nerve fibres in the guinea-pig ureter and a 90% depletion of neurokinin A, substance P- and CGRP-like immunoreactivity, further supporting a sensory origin of these nerves. Reversed-phase high performance liquid chromatography of water extracts of the human ureter revealed the presence of neurokinin A- and eledoisin-like material using antiserum K12, which does not cross-react with substance P. Most of the CGRP-like immunoreactivity in human ureter extracts co-eluted with synthetic human CGRP. Capsaicin both caused inhibition of spontaneous motility of the human ureter in vitro and initiated contractions in some preparations. Neurokinin A and neuropeptide K potently initiated phasic contractions of the ureter, while substance P had only minor contractile effects. CGRP inhibited both spontaneous and neurokinin A-induced ureteric contractions. In conclusion, peptides with potent opposite motility effects are present in the same, presumably sensory nerves of the ureter in both the guinea-pig and man. It will be of importance to determine whether local release of neuropeptides can account for ureteric motility changes accompanying sensory nerve activation upon ureteral obstruction, by e.g. renal calculi.     

Substance P neurones in medullary baroreflex areas and baroreflex function of capsaicin-treated rats. Comparison with other primary afferent systems

Adult rats (age 13–17 weeks) treated 20 h after birth with capsaicin (50 mg/kg s.c.) showed a 50% loss of substance P-immunoreactive nerve terminals in the thoracic substantia gelatinosa as revealed by quantitative immunohistochemistry and radioimmunoassay. Other spinal substance P systems were unchanged. A similar decrease of immunoreactive substance P axons and nerve terminals was observed in medullary primary afferent systems, namely in IX and X rootlets, tractus spinalis nervi V, tractus solitarius and substantia gelatinosa nervi V. Other medullary substance P fibres, e.g. in the reticular formation, nucleus motorius nervi X and XII, inferior olive and area postrema, were not obviously changed. The nucleus tractus solitarii receiving, among others, IX and X primary afferents, e.g. from baroreceptors and chemoreceptors, showed a particular pattern of depletion: although the substance P axons penetrating from the tractus solitarius mainly into the intermediate and caudal nucleus tractus solitarii were markedly reduced in capsaicin-treated rats, the total number of substance P nerve terminals in the intermediate and caudal nucleus tractus solitarii was only moderately decreased and appeared normal in the cranial portion of the nucleus. The number of substance P-immunoreactive cells in the nucleus tractus solitarii was unchanged. Radioimmunoassay of substance P levels showed a 60% decrease in the microdissected substantia gelatinosa nervi V, but only insignificant decreases (by 20%) in microdissected divisions of the nucleus tractus solitarii and reticular formation.Thus, capsaicin destroyed a considerable part of primary spinal and medullary substance P afferents. In the entire nucleus tractus solitarii most of substance P is contained in a capsaicin-insensitive, probably intrinsic system. However, the intermediate and caudal divisions contain, in addition, primary afferent IX and X substance P terminals which were partly destroyed by capsaicin. In view of a recent proposal that substance P is the transmitter released from baroreceptor afferents, blood pressure and baroreflex function were measured in capsaicin-treated (50 and up to 600 mg/kg) rats; neither differed from controls. While, at first sight, this finding militates against a transmitter role of substance P in the baroreceptor reflex pathway, incomplete destruction of primary substance P afferents in the nucleus tractus solitarii by capsaicin and the possible development of compensatory mechanisms during growth of the animals have to be considered as alternative explanations. Furthermore, in the same rats, tests on the function of other primary afferents yielded, in part, incongruent results. The threshold for nociceptive chemical stimuli, as determined with capsaicin and formalin, was increased. On the other hand, threshold to nociceptive heat was unchanged in the tail-flick, but increased in the hot plate test.     

The mechanism of action of capsaicin on sensory C-type neurons and their axons in vitro

The selective excitant and neurotoxic action of capsaicin on vagal sensory neurons in the rat has been investigated in vitro using three techniques: extracellular recording of compound spike potentials from the whole nerve; intracellular recording from ganglion cells using single-electrode current and voltage clamp; and electron microscopy of the nerve and nodose ganglion. Capsaicin (0.1-10 microM) depolarized vagal sensory C fibres and cell bodies, and produced an increased conductance. The conductance increase appeared to be due to an increased permeability to sodium and calcium, plus a secondary increase in potassium (and perhaps chloride) conductance consequent upon calcium entry. The early entry of calcium seems to be a significant priming event in the neurotoxic process, since dramatic ultrastructural changes take place within a few minutes of capsaicin application, which are minimized by removing extracellular calcium ions. The observations indicate that in sensory C neurons capsaicin opens a conductance of limited specificity and that a resultant large calcium entry is closely involved in the rapid development of cell injury.     

Effects of capsaicin on myenteric neurons of the guinea pig ileum

The effects of capsaicin on the electrophysiological behavior of myenteric neurons were investigated with intracellular recording techniques in the isolated guinea pig ileum. Capsaicin evoked a marked long-lasting slow depolarization associated with increased input resistance, during which the cells spiked repeatedly or displayed anodal break excitation. Capsaicin did not produce the slow depolarizing action on myenteric neurons in Ca2(+)-free media (with 0.1 mM ethylenediaminetetraacetic acid) or in the mesenteric denervated ileum. This action of capsaicin on myenteric neurons seems to be mediated via a release of substance P, possibly from sensory nerve endings.     

Capsaicin and its effects upon meal patterns, and glucagon and epinephrine suppression of food intake

The neurotoxin capsaicin has been shown to selectively interfere with unmyelinated sensory fibers, as well as leading to depletions of substance P and other peptides. Meal pattern analysis was performed both before and after treatment with capsaicin in twelve adult male Sprague-Dawley rats. Capsaicin treatment only briefly altered feeding patterns. No long term effect on body weight was noted. These same animals were then tested for the appetite suppressing effects of IP injections of glucagon (125 micrograms/kg) and epinephrine (30 micrograms/kg). Capsaicin treated rats decreased their intake of sweetened condensed milk during a 30 minute test in response to glucagon and epinephrine. Controls failed to suppress intake in response to glucagon, but drank less milk after epinephrine than did capsaicin treated rats. Efficacy of capsaicin treatment was obtained using similarly treated animals subject to histological evaluation within 2 days of capsaicin treatment. These results suggest that peripherally generated information relayed to the CNS via small-diameter sensory neurons is not a necessary component of the normal hunger/satiety sequence, nor body weight regulation.     

Biochemical and anatomical observations on the degeneration of peptide-containing primary afferent neurons after neonatal capsaicin

Administration of a single dose of capsaicin (50 mg/kg; sc) to two-day-old rats resulted in a loss of between 85 to 95% of the small diameter unmyelinated primary afferent fibres from lumbar dorsal roots. The numbers of myelinated fibres in the dorsal roots were not significantly affected. The substance P and somatostatin contents of the dorsal roots were decreased by 85 to 95%. The extent of depletion of these peptides from the dorsal horn of the spinal cord was somewhat less; substance P was decreased by 55% and somatostatin by 19%. Histochemical studies showed that fluoride-resistant acid phosphatase was virtually absent from the dorsal horn of capsaicin-treated animals. There was also a conspicuous absence of substance P-positive fibres from layers I and II of the dorsal horn and of fibres traversing these layers to deeper regions.Colchicine pretreatment revealed the presence of substance P-containing perikarya within layers III–IV. The plexus of substance P-positive elements which normally surrounded these neurons was absent after capsaicin treatment, suggesting that they receive a substance P-containing primary afferent innervation.The neurotoxicity of capsaicin after a single dose of 50 mg/kg in neonatal animals appears to be restricted largely to unmyelinated primary afferent fibres. The present results suggest that both substance P and somatostatin are contained in primary afferent sensory neurons which give rise to unmyelinated fibres. It can be further concluded that about 50% of substance P and only about 20% of the somatostatin in the dorsal horn appears to be of primary afferent origin.     

Distribution of capsaicin-sensitive nerve fibres containing immunoreactive substance P in cutaneous and visceral tissues of the rat

Treatment of newborn rats with capsaicin causes a selective and permanent degeneration of unmyelinated sensory fibres, some of which contain immunoreactive substance P (ISP). Following treatment of newborn rats with capsaicin (50 mg/kg), the ISP content was decreased by 66-75% in various skin areas and in the oral and nasal mucosae as measured at the age of 3-4 months. There was no significant depletion of ISP in the mucosa of the tongue. The ISP content of trachea, lungs, myocardium, hepatic duct, ureter and urinary bladder, was decreased by 60-84%. The ISP concentrations in stellate and mesenteric ganglia were reduced by 54 and 81%, respectively. These results indicate a widespread innervation of cutaneous and visceral tissues by sensory nerve fibers containing ISP.     

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum were investigated. Capsaicin produced a contraction followed by a relaxation of the circular muscle. Both responses were easily desensitized. As the late relaxation response was not sufficiently intense to be analyzed, the inhibitory effect of capsaicin on substance P-induced contractions was explored. Capsaicin abolished the substance P-induced contractions. This inhibitory effect was not affected by tetrodotoxin, and the effect was desensitized. Therefore, all effects of capsaicin on circular muscle motility seem to be due to the release of sensory neuropeptides, similarly to those elicited in the longitudinal muscle.     

Substance P-immunoreactivity in the developing human retinogeniculate pathway

Substance P has been immunohistochemically localized in the human optic nerves and lateral geniculate nuclei during the prenatal period from 13-14 to 37 weeks of gestation. Substance P-immunoreactive fibres were present in the optic nerves and lateral geniculate nuclei in all these ages thereby providing direct evidence of this undecapeptide being associated with the retinogeniculate pathway. At 16-17 weeks, greater numbers of fibres were observed than in the later ages. It is likely that the reduction in number of optic nerve fibres seen quantitatively during prenatal life may partly be due to the loss of substance P fibres.