Effect of synthetic substance P on internal carotid artery blood flow in man

Hypoxic adaptation of the peptidergic innervation in the rat carotid body

The abundance of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, and neuropeptide Y (NPY)-immunoreactive nerve fibers in the carotid body was compared between normoxic and chronically hypoxic rats (10% O2 and 3.0-4.0% CO2 for 3 months). The immunoreactive fibers appeared as thin processes with many varicosities, and were distributed mainly around the vasculatures. In the normoxic control carotid body, NPY fibers were more numerous than VIP, CGRP, and SP fibers. In the chronically hypoxic rats, the carotid body was enlarged several fold, and the mean absolute number of VIP and NPY fibers was 3.88 and 2.22 times higher than in the normoxic carotid body, respectively, although that of SP and CGRP fibers was not changed. When expressed as density per unit area of the parenchyma, the density of SP and CGRP fibers in the chronically hypoxic carotid body decreased significantly to under 50%, the density of VIP fibers increased significantly 1.80 times, and the density of NPY fibers were unchanged. Immunoreactivity for four neuropeptides was not found in the glomus cells of normoxic or chronically hypoxic carotid bodies. These results suggest that altered peptidergic innervation of the chronically hypoxic carotid body is one feature of hypoxic adaptation. Because these neuropeptides are vasoactive in nature, altered carotid body circulation may contribute to modulation of the chemosensory mechanisms by chronic hypoxia.

Substance P- and calcitonin gene-related peptide-containing nerve fibers in the nasal mucosa of chronically hypoxic rats

The distribution of substance P-immunoreactive and calcitonin gene-related peptide-immunoreactive nerve fibers in the nasal mucosa was compared between normoxic and chronically hypoxic rats (10% O2 and 3.0-4.0% CO2 for 3 months). In the normoxic nasal mucosa, substance P- and calcitonin gene-related peptide-immunoreactive nerve fibers were found within and under the epithelium and around the glands and blood vessels in the lamina propria. These immunoreactive fibers have many varicosities. In the chronically hypoxic nasal mucosa, the relative density of intra- and subepithelial substance P-immunoreactive and calcitonin gene-related peptide-immunoreactive fibers and those in the lamina propria was higher than in normoxic mucosa. The length of substance P-positive fibers within the chronically hypoxic olfactory and respiratory epithelium was 1.66 and 2.45 times higher than within the normoxic epithelium, respectively. The length of calcitonin gene-related peptide-immunostained fibers within the chronically hypoxic olfactory and respiratory epithelium was 1.56 and 1.84 times higher, respectively. Because substance P and calcitonin gene-related peptide are the predominant signal peptides of primary sensory neurons, the increased number of these fibers may represent enhanced sensory mechanisms in the hypoxic nasal mucosa. In addition, considered together with the findings in chronically hypoxic tracheal mucosa, the increased density of intraepithelial fibers containing substance P and calcitonin gene-related peptide suggests that this is a predominant feature of hypoxic adaptation throughout the upper and lower respiratory tracts.

Neuropeptide-containing nerve fibres in the human parotid gland: a semiquantitative analysis using an antibody against protein gene product 9.5

The occurrence and distribution of neuropeptide-containing fibres in the human parotid gland were examined by the peroxidase-antiperoxidase method with attention to the quality of fixation and the condition of patients. Many fibres immunoreactive for neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) and a moderate number of galanin-positive (GAL) fibres were distributed around the acini. A moderate number of NPY and VIP fibres were distributed around the intercalated ducts. The semiquantitative mean densities (+/- SD) of periacinar NPY, VIP and GAL fibres expressed as a percentage of the total protein gene product (PGP) 9.5 immunoreactive fibres were 75.62 +/- 7.25%, 70.52 +/- 9.33% and 41.76 +/- 5.45%, respectively, whereas those of substance P (SP), calcitonin gene-related peptide (CGRP) and FMRF amide (FMRF) fibres were below 10%. The mean densities of NPY and VIP fibres around the intercalated ducts expressed as the percentage of PGP 9.5 fibres associated with these ducts were 52.37 +/- 6.19% and 59.62 +/- 7.02% respectively. Those of SP, CGRP, GAL, and FMRF fibres were below 10%. The densities of NPY, VIP, SP, CGRP, GAL and FMRF fibres around the striated and excretory ducts were also below 10%. In the vasculature, NPY fibres were the most prominent. Similarly, the mean density of perivascular NPY fibres was 93.76 +/- 2.03%. No somatostatin or leucine or methionine enkephalin immunoreactivity was detected around the acini, duct system or blood vessels. These findings suggest that, in this gland, the periacinar NPY, VIP and GAL fibres may participate in regulating the synthesis of saliva and its secretion and that perivascular peptidergic fibres, especially NPY fibres, may be involved in controlling local blood flow.

Intravascular substance P dilates cerebral parenchymal vessels through a specific tachykinin NK1 receptor in cats

The role of substance P in the cerebral parenchymal circulation was examined in 19 anesthetized cats. The local cerebral blood volume in the temporoparietal cortex was measured by our photoelectric method. Cerebral blood volume reflects the cumulative dimensions of the parenchymal microvessels. Intravenous injection of 0.01, 0.1, and 1 mg/kg FK888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl) carbonyl-L-prolyl]-N-methyl-N-phenylmethyl-3-(2-naphthyl)-L-alaninamide) , a selective tachykinin NK1 receptor antagonist, had no significant effects (compared to the vehicle, ethanol) on cerebral blood volume and mean arterial blood pressure. Intracarotid injection of 1, 10, 100 pmol/kg, and 1 nmol/kg substance P increased cerebral blood volume (P < 0.01) in a dose-dependent manner (maximal increase of 6.5% at 5 min). Following injection of 1 nmol/kg substance P, cerebral blood volume was initially reduced, possibly due to the marked fall in mean arterial blood pressure (P < 0.01). The cerebral blood volume increase elicited by 1 nmol/kg substance P was strongly blocked (P < 0.05) by prior injection of 1 mg/kg FK888. However, the depressor effect of 1 nmol/kg substance P (-24 +/- 4 mm Hg at 30 s, P < 0.01) was partially inhibited (P < 0.01) by FK888. We conclude that endogenous substance P may not have a significant role in the maintenance of resting tone of cerebral parenchymal vessels. Intravascular substance P, however, dilates the small microvessels through a specific tachykinin NK1 receptor and could be involved in the development of pathologic processes such as migraine headache.

Distribution of substance P and calcitonin gene-related peptide immunoreactive nerve fibers in the trachea of chronically hypoxic rats

The distribution of substance P and calcitonin gene-related peptide immunoreactive nerve fibers in the trachea was compared between normoxic and chronically hypoxic rats (at 380 mm Hg for 10 weeks). In the normoxic trachea, the immunoreactivity to either peptide was seen in the nerve fibers in four principal locations: a) within and b) under the ciliated epithelium, c) within the smooth muscle bundles in the posterior wall, and d) in the connective tissue and around blood vessels in the lamina propria and submucosa. These immunoreactive fibers within the epithelium and smooth muscle bundles, in the connective tissue, and around blood vessels were thin and displayed some varicosities, and those under the epithelium appeared as thick nerve bundles. When the distribution and density of immunoreactive fibers were compared between normoxic and chronically hypoxic tracheas, there was a difference in number of substance P and calcitonin gene-related peptide immunoreactive fibers penetrating into the epithelium, although there was no difference in the other three locations. The mean number of substance P and calcitonin gene-related peptide immunoreactive intraepithelial fibers per section of the chronically hypoxic trachea was significantly increased. Because substance P and calcitonin gene-related peptide are predominant signal peptides of primary sensory neurons, the increase of substance P and calcitonin gene-related peptide immunoreactive fibers suggests that altered airway reflexes may be a feature of hypoxic adaptation.

Distribution of galanin-immunoreactive nerve fibers in the carotid labyrinth of the bullfrog, Rana catesbeiana: Comparison with substance P-immunoreactive fibers

Immunoreactivity of galanin (GAL) was detected in the nerve fibers distributed within the intervascular stroma of the bullfrog carotid labyrinth. GAL-immunoreactive fibers are numerous, and some are close to the sinusoidal plexus. Most GAL fibers appear as thin processes with some varicosities. A combination of indirect double immunofluorescence labelling and image processing clearly demonstrated that the distribution pattern of GAL fibers is different from that of SP fibers. This indicates that GAL and SP do not coexist in the same nerve fibers. The role of GAL fibers may be different from that of previously reported neuropeptides (substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, and others) as a neuromodulator in controlling vascular tone of the labyrinth.

Localization of immunoreactive neuropeptides in the kidney of the bullfrog, Rana catesbeiana, by immunofluorescence

Indirect double immunofluorescence labelling for demonstrating nine neuropeptides in the kidney of the bullfrog, Rana catesbeiana, revealed for the first time the occurrence, distribution, and coexistence of certain neuropeptides in the kidney of the submammalian vertebrates. Substance P, neuropeptide Y, and calcitonin gene-related peptide were localized in nerve fibers distributed along the afferent arterioles connected with the glomeruli, and along the capillary network between uriniferous tubules. Neuropeptide Y and calcitonin gene-related peptide immunoreactive fibers were more numerous than substance P immunoreactive fibers. In these two regions, about one half of the neuropeptide Y or calcitonin gene-related peptide fibers contained substance P. No immunoreactivity of vasoactive intestinal polypeptide, somatostatin, FMRFamide, or leucine- and methionine-enkephalins was detected in the bullfrog kidney.

Coexistence of substance P, neuropeptide Y, VIP, and CGRP in the nerve fibers of the carotid labyrinth of the bullfrog, Rana catesbeiana: a double-labelling immunofluorescence study in combination with alternate consecutive sections

Double immunohistochemical staining with rhodamine- and fluorescein isothiocyanate (FITC)-conjugated antisera revealed the coexistence of substance P (SP) and neuropeptide Y (NPY), and SP and calcitonin gene-related peptide (CGRP) in most nerve fibers in the intervascular stroma of the carotid labyrinth of the bullfrog, Rana catesbeiana, although there were a few fibers which showed only SP- or NPY-immunoreactivity. Approximately one third of SP-immunoreactive fibers also showed coexistence with vasoactive intestinal polypeptide (VIP)-immunoreactivity, and a few fibers contained VIP without SP. The combination of the double immunofluorescence technique and alternate consecutive sections further demonstrated the possible coexistence of SP, VIP, NPY, and CGRP. This coexistence of four different peptides in the same nerve fibers was proved by the following two evident facts: 1) some SP fibers which demonstrated coexistence with NPY-immunoreactivity were assumed to be continuous with those showing VIP-immunoreactivity, and 2) almost all of the SP fibers showed coexistence with CGRP-immunoreactivity. By this reasoning, nearly one third of SP fibers may demonstrate coexistence with NPY-, VIP-, and CGRP-immunoreactivities. These multiple peptides might be involved in vascular regulatory function, which is a possible function of the amphibian carotid labyrinth.

Immunohistochemical coexistence of calcitonin gene-related peptide and substance P in the nerve fibers of the internal gills of bullfrog (Rana catesbeiana) larvae

A double-labelling immunofluorescence study of the internal gills of larval bullfrogs revealed coexistence of calcitonin gene-related peptide (CGRP) and substance P (SP) in the same nerve fibers in the gill tufts. More than about 95% of CGRP fibers showed coexistence of SP, although some fibers contained CGRP without SP. In the branchial muscle, all CGRP fibers demonstrated coexistence of SP. These findings suggest that both CGRP- and SP-containing fibers may use both peptides as neuromodulators of active ion transport and gill movements.

Cerebrovascular changes following administration of gammaglobulins against substance P or calcitonin gene related peptide in monkey with subarachnoid haemorrhage

Cerebrovascular changes after intrathecal (ith) administration of gammaglobulins against substance P (SP) or calcitonin gene-related peptide (CGRP) were investigated before and following a simulated subarachnoid haemorrhage (SAH) in the squirrel monkey. The SAH was produced by injection of homologous blood into the interpeduncular fossa and the cisterna magna. The gammaglobulins were given both prior to the blood injections and daily in 5 days post-SAH. The effect of the gammaglobulins was examined by angiography pre-SAH and at 10 min and at 6 days post-SAH, i.e. the time points for maximal acute and late spasm in the present model. Cerebral blood flow (CBF) was measured under general anesthesia at day 6 post-SAH with an autoradiographic technique. Five of nine animals treated with CGRP antigammaglobulin died from respiratory failure. Four animals received SP antigammaglobulin and two control animals received normal globulin. SP antigammaglobulin per se had no effect on baseline arterial diameter, while CGRP antigammaglobulin significantly reduced the diameter of the arteries. SP antigammaglobulin prevented the occurrence of acute spasm and significantly reduced the degree of late spasm. Moreover, the reduction in CBF noted in the control SAH animals was significantly reduced. In contrast, CGRP antigammaglobulin treatment had no effect on the degree of spasm and did not cause any change in CBF as compared to controls. The finding that CGRP but not SP antigammaglobulin significantly reduces the arterial diameter in conjunction with our previous demonstration that a post-, but not preganglionic trigeminal lesion reduces the baseline arterial diameter, indicates that CGRP could be the transmitter involved in a peripheral axon reflex. The function of SP might be as a neurotransmitter conveying information to the brainstem. The transmitter role is supported by the effect of SP antigammaglobulin impairing SP containing neurons and, in that way, mimicking a bilateral trigeminal rhizotomy.

Ontogeny of substance P-, CGRP-, and VIP-containing nerve fibers in the amphibian carotid labyrinth of the bullfrog, Rana catesbeiana. An immunohistochemical study

The ontogeny of substance P, CGRP (calcitonin gene-related peptide), and VIP (vasoactive intestinal polypeptide) containing nerve fibers in the carotid labyrinth of the bullfrog, Rana catesbeiana, was examined by the peroxidase-antiperoxidase method. The time of appearance of these three peptides was different for each. First, CGRP fibers appeared in the wall of the carotid arch and external carotid arteries, and in a thin septum between these two arteries at an early stage of larval development (stage III). At stage V, substance P immunoreactive fibers appeared, and VIP fibers were detected at the early metamorphic stage (stage XXII). Up to the completion of metamorphosis, the number of these fibers remained low. From 1 to 5 weeks after metamorphosis, substance P, CGRP, and VIP fibers increased in number to varying degrees. By 8 weeks after metamorphosis, the distribution and abundance of these fibers closely resembled those of the adults. Some CGRP and VIP immunoreactive glomus cells were found at the stages immediately before and after the completion of metamorphosis. These findings suggest that substance P, CGRP, and VIP fibers during larval development and metamorphosis may be nonfunctional, and start to participate in vascular regulation only after metamorphosis. The transient CGRP and VIP in some glomus cells may be important for the development of the labyrinth, or may take part in vascular regulation through the close apposition of the glomus and smooth muscle cells (g-s connection).

Occipital nerve block in the management of headache and cervical pain

The origins of chronic headache and the role of the greater occipital nerve in headache syndromes are reviewed. The anatomical pathways and physiological basis of these headaches are discussed with a view to synthesizing some current concepts of headache generation. Studies of occipital nerve blockade for treatment of headaches of various types are assessed and a retrospective analysis of our own experience is presented.

Intimate apposition of the glomus and smooth muscle cells (g-s connection) in the carotid labyrinth of juvenile bullfrogs

Intimate apposition of the glomus and smooth muscle cells (g-s connection) was found in almost all glomus cells of the carotid labyrinths in juvenile bullfrogs, Rana catesbeiana. There were three types of g-s connection: between thin processes (0.1-0.2 micron in width) without dense-cored vesicles of glomus cells and smooth muscle cells; between thick processes (1.0-1.5 microns in width) with dense-cored vesicles of glomus cells and smooth muscle cells; and between the tongue-like projections of smooth muscle cells and the flat surface of the glomus cell. In some cases, a single glomus cell made g-s connections with several smooth muscle cells. Exocytosis often occurs at the g-s connection. Afferent and efferent synapses were found on the glomus cells with g-s connections. Reciprocal synapses were also observed. On the basis of these findings, the second and third types of g-s connection are presumed to participate in vascular regulation.

Localization of substance P, CGRP, VIP, neuropeptide Y, and somatostatin immunoreactive nerve fibers in the carotid labyrinths of some amphibian species

Immunohistochemical localization of substance P (SP), CGRP, VIP, neuropeptide Y (NPY), and somatostatin (SOM) in the carotid labyrinth were compared in some species of amphibians using the peroxidase-antiperoxidase method. Immunoreactivity of SP, CGRP, VIP, and NPY was found in the nerve fibers distributed in the intervascular stroma of the carotid labyrinth. SP, CGRP, and VIP immunoreactive varicose fibers were densely distributed in the peripheral portion of the carotid labyrinth. Some SP-immunoreactive fibers were distributed similarly to CGRP-immunoreactive fibers. The density of NPY and SOM immunoreactive varicose fibers was low. No immunoreactivity of enkephalins was observed in the labyrinth. The intensities of these peptides were varied from species to species. No glomus cells showed immunoreactivity for any of the 7 peptides studied. These results suggest that the vascular regulatory function, which is one of the possible functions of the carotid labyrinth, is controlled by the peptidergic mechanisms in addition to regulation through intimate apposition of glomus and smooth muscle cells (g-s connection).

Influence of substance P on carotid sinus nerve baro- and chemoreceptor activity in rabbits

Substance P (SP) is abundant in the carotid sinus nerve (CSN) and has been implicated in baro- and chemoreceptor reflexes. We examined the effect of SP on blood pressure, heart rate, phrenic nerve activity, hindlimb perfusion pressure, and cardiac contractile strength in urethane-anesthetized rabbits with bilaterally cut cervical sympathetic, vagus, and aortic depressor nerves. Retrograde simultaneous injection of SP (0.5-2.7 micrograms/kg in 0.2-0.3 ml saline) into both carotid sinus areas via the internal carotid arteries decreased blood pressure (by 56%), heart rate (by 13%), cardiac contractility (by 25%) and phrenic nerve activity (by 77%). The effect on hindlimb perfusion pressure was variable. There was both a reflex effect and direct hindlimb vasodilation. In another group of rabbits, the carotid sinus areas were vascularly isolated and perfused with SP (0.19 micrograms/min dissolved in Locke's solution) or Locke's solution alone for 5 min. While carotid sinus perfusion pressure was maintained in the range of 80-120 mmHg, mean arterial blood pressure, heart rate, and unit activity from the CSN were recorded. SP increased the activity of 11 of 18 baroreceptor fibers and inhibited all of 20 chemoreceptor fibers. SP decreased mean arterial blood pressure and heart rate, but the changes were less than those obtained with injection of SP into nonisolated carotid sinus arteries because systemic effects of SP, which in some cases counteracted the reflex effects, were eliminated.

Sensory neuropeptide effects in human skin

1 Neuropeptides released from sensory nerves may account for cutaneous flare and wheal following local trauma. In 28 normal subjects we have studied the effects of four sensory neuropeptides given by intradermal injection on the forearm or back. 2 All peptides caused a flare distant from the site of injection, presumably due to an axon reflex. Substance P (SP) was the most potent (geometric mean dose causing 50% of maximum flare, 4.2 pmol). Neurokinin A (NKA) was the next most potent with neurokinin B (NKB) and calcitonin gene-related peptide (CGRP) the least. The distant flare response to SP, NKA and NKB was maximal at 5 min and disappeared within 2 h. 3 CGRP caused a local erythema over the site of injection at doses above 0.5 pmol which at higher doses lasted for up to 12 h. 4 SP, NKA and NKB caused wheals at doses above 5 pmol with SP and NKB being the most potent. CGRP (up to 250 pmol) did not consistently cause wheal formation. There was no significant effect of coinjection of CGRP upon the response to SP although there was a tendency for an enhancement of the wheal response. 5 The H1-histamine antagonist terfenadine (60 mg orally) significantly inhibited the wheal and distant flare response to histamine (5 nmol) and NKA, but not that caused by NKB. The distant flare of CGRP was also reduced but the local erythema was unaltered. 6. Aspirin (600 mg orally) significantly inhibited the distant flare response to SP, NKA and CGRP, but not that caused by NKB or histamine; the local erythema induced by CGRP was unaffected by aspirin. Aspirin also inhibited the wheal formed by NKA but not the wheal induced by the other substances. 7. These results suggest that tachykinins cause a distant flare response partially via the release of histamine and cyclo-oxygenase products, but cause a wheal by a direct effect on the skin microvasculature. The order of potency SP > NKB > NKA suggests that an SPp or NK, receptor is involved in the wheal response. CGRP by contrast has a direct vasodilator effect which is very prolonged.

Mechanism of "substance P": on mesenteric blood flow; interactions with opioid peptides

The effects of close intra arterial injection of substance P (SP) and the interaction of SP with opioid peptides, have been studied on mesenteric blood flow in the anaesthetized dog. Injection of SP into the superior mesenteric artery caused a dose dependent increase in mesenteric blood flow. This effect was enhanced by pretreatment with the alpha 2 adrenergic antagonist yohimbine. The action of SP was significantly reduced by pretreatment with muscarinic and nicotinic cholinergic, dopamine and histamine (H1) receptor antagonists. Beta adrenergic, histamine (H2) and opiate receptor antagonists did not influence the action of SP. Pretreatment with tetrodotoxin partially inhibited the effect of SP, indicating that as well as a neurogenic action, it has a direct action on the vascular smooth muscle. The effect of SP was enhanced by D-Met2-NleS5-enkephalinamide, a delta opiate receptor agonist. The actions of D-Met2-NleS5-enkephalinamide were abolished by pretreatment with hexamethonium, partially abolished by naloxone but were unaffected by atropine. The mu opiate receptor agonist, D-Met2-Pro5-enkephalinamide, inhibited the effects of SP.

Peptides in the mammalian cardiovascular system

Ample immunocytochemical evidence is now available demonstrating that several peptides are present in the mammalian cardiovascular system where they are localised to nerve fibres and myocardial cells. The neuropeptides (neuropeptide Y, calcitonin gene-related peptide, tachykinins and vasoactive intestinal polypeptide) are localised to large secretory vesicles in subpopulations of afferent or efferent nerves supplying the heart and vasculature of several mammals, including man. Although they often exert potent pharmacological effects on the tissues in which they occur their physiological significance has still to be established. They may act directly via specific receptors and/or indirectly by influencing the release and action of other cardiovascular transmitters. In marked contrast, atrial natriuretic peptide is produced by cardiac myocytes and considered to act as a circulating hormone.

The distribution and origin of calcitonin gene-related peptide-containing nerve fibres in feline dental pulp. Relationship with substance P-containing nerve fibres

The origin and distribution of calcitonin gene-related peptide (CGRP)-like immunoreactivity in feline dental pulp were studied using indirect immunofluorescence. Nerve fibres with varicosities exhibiting CGRP-like immunoreactivity were observed to enter the pulp with blood vessels. Many CGRP-containing nerve fibres were found to extend along blood vessels in the central pulp, and some of these fibres exhibited a network arrangement in the walls of dental pulp blood vessels. However, some of fibres were apparently not associated with blood vessels. Some thin, CGRP-containing nerve fibres formed a part of the nerve plexus in the subodontoblastic area and penetrated into the odontoblastic layer. In animals that had undergone transection of the inferior alveolar nerve, no CGRP-containing nerve fibres were observed. Application of a double-immunofluorescence staining technique also revealed that the distribution of CGRP-containing nerve fibres is very similar to that of substance P-containing nerve fibres.

Origins and distribution of calcitonin gene-related peptide-containing nerves in the wall of the cerebral arteries of the guinea pig with special reference to the coexistence with substance P

The origins and overall distribution of calcitonin gene-related peptide-like immunoreactivity (CGRPI) in the wall of the cerebral arteries were investigated in the guinea pig by using whole-mounts. Two types of CGRPI fibers were seen; one forming dense fiber bands, located among the periadventitial nerves, and the other forming a meshwork. CGRPI fibers in the periadventitial nerves often leave these nerves to form a meshwork, of a density that varies according to the diameter or location of the blood vessel. The present study showed that CGRPI fibers in the walls of the carotid arterial system originated from the trigeminal ganglion, and those in the vertebrobasilar arterial system from other origins besides the trigeminal ganglion. We also examined the coexistence of this peptide with substance P-like immunoreactive (SPI) structures in a single neuron system. Double staining immunocytochemistry showed that the patterns of the running of CGRPI and SPI fibers in the wall of the cerebral arteries were similar, and this method also demonstrated the presence of neurons containing both CGRPI and SPI structures in single cells of the trigeminal ganglion, which is the major origin of these fibers in the cerebral arteries.

Neurotensin and substance P immunoreactive nerve endings in the guinea pig carotid sinus and their ultrastructural counterparts

The carotid sinus of the guinea pig was analysed immunohistochemically for the occurrence of neuropeptides. Immunoreactivity (IR) for neurotensin (NT) and substance P (SP) is distributed in two different populations of nerve endings and varicosities. NT-IR fibers penetrate deeply into the tunica media of the elastic segment of the carotid sinus and form the large, branched lanceolate nerve terminals. Electron-microscopic investigations have revealed that the NT-IR varicosities correspond to the large afferent baroreceptor endings containing abundant mitochondria. SP-IR fibers are located mainly at the media-adventitial border. They seem to be correlated to dense-core, vesicle-containing varicosities identified in the electron microscope. Therefore, these fibers may constitute afferent and efferent perivascular plexus regulating the vascular tone of the carotid sinus wall.

Substance P: its distribution, pharmacological actions and possible physiological role in sensory neurons

The undecapeptide substance P (SP) is a normal constituent of most tissues, particularly the central and peripheral nervous system. SP-immunoreactive cell bodies and terminal networks are distributed in most areas of the brain. Particular interest has been focused on the presence and function of SP in the primary sensory neuron. SP is released from both the central and peripheral part of the sensory neuron following stimulation of the dorsal roots and peripheral sensory nerves. Evidence is given for a transmitter role of SP in the sensory neurons and for the hypothesis that SP is involved in the vascular effects induced by sensory stimulation, referred to as the axon reflex. SP is present in large amounts in the gastro-intestinal tract. By immunohistochemistry SP is demonstrated within nerve cell bodies and terminals of the intramular plexuses but also in extrinsic neurons. It is released both from intrinsic sensory neurons of the gut and from the gastro-intestinal lumen in response to vagal stimulation. SP stimulates motor activity and is ascribed a regulatory role for both the intestinal motility and blood flow. SP has numerous pharmacological effects, the most obvious being excitation of spinal motoneurons, vasodilation and stimulation of salivary and pancreatic secretion. It is a normal constituent of blood plasma but there is no evidence that SP acts as a circulating hormone.

Perivascular substance P: occurrence and distribution in mammalian pial vessels

Nerve fibres containing immunoreactive substance P (SP) were demonstrated in the wall of cerebral blood vessels of several mammalian species. Pial arteries of cat and guinea-pig were richly supplied with SP nerve fibres, while those of rat, rabbit, pig, and man had a moderate number. SP fibres were more numerous in pial vessels belonging to the rostral parts of the circle of Willis as compared to more caudally located blood vessels. In cat and guinea-pig, blood vessels in the choroid plexus were surrounded by few SP nerve fibres; also spinal cord blood vessels of cat contained few such fibres.