Substance P regulates the vasodilator activity of calcitonin gene-related peptide

The 37-amino-acid calcitonin gene-related peptide (CGRP) occurs as a result of alternative processing of mRNA from the calcitonin gene. The potency of CGRP as a vasodilator and the occurrence of the peptide in nerves associated with blood vessels suggest an important role for CGRP in the regulation of blood flow. The finding that CGRP induces protracted vasodilatation when administered extra-vascularly, to mimic release from nerves, has led us to investigate how the vasodilator activity of CGRP is controlled in vivo. CGRP is often co-localized with substance P in C-fibre nerves. Here, we demonstrate that injection of CGRP with substance P into human skin converts the long-lasting vasodilatation induced by CGRP into a transient response. Experiments in animals reveal that the phenomenon is dependent on the action of proteases from mast cells stimulated by substance P. The results reveal a new regulatory interaction between two neuropeptides and provide evidence for an in vivo role for mast cell proteases.     

Vanilloid receptors on sensory nerves mediate the vasodilator action of anandamide.

The endogenous cannabinoid receptor agonist anandamide is a powerful vasodilator of isolated vascular preparations, but its mechanism of action is unclear. Here we show that the vasodilator response to anandamide in isolated arteries is capsaicin-sensitive and accompanied by release of calcitonin-gene-related peptide (CGRP). The selective CGRP-receptor antagonist 8-37 CGRP, but not the cannabinoid CB1 receptor blocker SR141716A, inhibited the vasodilator effect of anandamide. Other endogenous (2-arachidonylglycerol, palmitylethanolamide) and synthetic (HU 210, WIN 55,212-2, CP 55,940) CB1 and CB2 receptor agonists could not mimic the action of anandamide. The selective 'vanilloid receptor' antagonist capsazepine inhibited anandamide-induced vasodilation and release of CGRP. In patch-clamp experiments on cells expressing the cloned vanilloid receptor (VR1), anandamide induced a capsazepine-sensitive current in whole cells and isolated membrane patches. Our results indicate that anandamide induces vasodilation by activating vanilloid receptors on perivascular sensory nerves and causing release of CGRP. The vanilloid receptor may thus be another molecular target for endogenous anandamide, besides cannabinoid receptors, in the nervous and cardiovascular systems.     

Arterial dilations in response to calcitonin gene-related peptide involve activation of K+ channels

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid peptide produced by alternative processing of messenger RNA from the calcitonin gene. CGRP is one of the most potent vasodilators known. It occurs in and is released from perivascular nerves and has been detected in the blood stream, suggesting that it is important in the control of blood flow. The mechanism by which it dilates arteries is not known. Here, we report that arterial dilations in response to CGRP are partially reversed by blockers of the ATP-sensitive potassium channel (K(ATP)), glibenclamide and barium. We also show that CGRP hyperpolarizes arterial smooth muscle and that blockers of K(ATP) channels reverse this hyperpolarization. Finally, we show that CGRP opens single K+ channels in patches on single smooth muscle cells from the same arteries. We propose that activation of K(ATP) channels underlies a substantial part of the relaxation produced by CGRP.     

Nitric oxide as an inhibitory non-adrenergic non-cholinergic neurotransmitter

Inhibitory non-adrenergic non-cholinergic (NANC) nerves are thought to be important in the autonomic innervation of the gastrointestinal tract and other organ systems. The nature of their neurotransmitter is still debated. Speculation that nitric oxide (NO), formed from L-arginine in neuronal structures and other cells, could act as a neurotransmitter, is not yet supported by demonstration of its release upon nerve stimulation. Using a superfusion bioassay, we report the release of a vasorelaxant factor upon stimulation of the NANC nerves in the canine ileocolonic junction. Several pieces of evidence, including the selectivity of the bioassay tissues, chemical instability, inactivation by superoxide anion and haemoglobin, inhibition by NG-nitro-L-arginine (L-NNA) and potentiation by L-arginine all indicated that NO accounted for the biological activity of this transferable NANC factor.     

Two functionally distinct alpha2-adrenergic receptors regulate sympathetic neurotransmission

The sympathetic nervous system regulates cardiovascular function by activating adrenergic receptors in the heart, blood vessels and kidney. Alpha2-adrenergic receptors are known to have a critical role in regulating neurotransmitter release from sympathetic nerves and from adrenergic neurons in the central nervous system; however, the individual roles of the three highly homologous alpha2-adrenergic-receptor subtypes (alpha2A, alpha2B, alpha2C) in this process are not known. We have now studied neurotransmitter release in mice in which the genes encoding the three alpha2-adrenergic-receptor subtypes were disrupted. Here we show that both the alpha2A- and alpha2C-subtypes are required for normal presynaptic control of transmitter release from sympathetic nerves in the heart and from central noradrenergic neurons. Alpha2A-adrenergic receptors inhibit transmitter release at high stimulation frequencies, whereas the alpha2C-subtype modulates neurotransmission at lower levels of nerve activity. Both low- and high-frequency regulation seem to be physiologically important, as mice lacking both alpha2A- and alpha2C-receptor subtypes have elevated plasma noradrenaline concentrations and develop cardiac hypertrophy with decreased left ventricular contractility by four months of age.     

Involvement of nitric oxide in the reflex relaxation of the stomach to accommodate food or fluid.

The fundus of the guinea-pig stomach actively dilates in response to low increases in intragastric pressure. This physiological response, now called adaptive relaxation, accommodates the intake of liquid or food. It is independent of external innervation, resistant to ganglion blockade, but reflex in origin. The nerves involved are neither adrenergic nor cholinergic in nature. Non-adrenergic, non-cholinergic (NANC) nerves have now been recognized in many parts of the gastrointestinal tract and have recently been linked with release of nitric oxide (NO) on electrical stimulation. Here we show that adaptive relaxation in isolated stomach of the guinea pig is mediated by a NANC neurotransmitter substance indistinguishable from NO derived from L-arginine. This is substantiated by inhibition of adaptive relaxation by NG-monomethyl-L-arginine or N omega-nitro-L-arginine methyl ester, both inhibitors of NO synthesis, and by methylene blue, an inhibitor of soluble guanylate cyclase. There are two distinct neuronal pathways signalling NO-dependent adaptive relaxation, as evidenced by tetrodotoxin sensitivity. The first is a local reflex arc, the afferent fibres of which sense changes in intragastric pressure. The second is stimulated by an agonist for ganglionic nicotinic receptors. Thus, the functional significance of NO release from NANC nerves in the stomach is to bring about adaptive relaxation through a reflex response to increases in intragastric pressure.     

Axoplasmic transport of muscarinic receptors

The reality of axoplasmic transport is widely accepted; various neutrotransmitters, enzymes, labelled proteins and peptides are known to move rapidly along the axons of different nerve fibres. In the terminals of sympathetic nerves, noradrenaline release is controlled by various regulatory mechanisms which imply the occurrence of presynaptic receptors. In this regard, there is considerable indirect physiological evidence for the existence of muscarinic cholinergic receptors in the sympathetic nerve endings; the stimulation by acetylcholine of such presynaptic receptors elicits an inhibitory effect on noradrenaline release. We not provide direct biochemical evidence for the occurrence in dog splenic nerve of muscarinic receptors which seem to move along the axon as suggested by their rapid accumulation on either side of a ligature.     

Target size regulates calibre and myelination of sympathetic axons

Axons in vertebrate peripheral nerves are ensheathed by Schwann cells. For some axons, this sheath consists of a single layer of glial cell cytoplasm and plasma membranes; for other axons, Schwann cells form multilayered myelin. Whether or not a Schwann cell makes myelin is determined by a signal from the axon, but the nature of this signal is not known. Here I show that sympathetic postganglionic axons, which are normally not myelinated, become myelinated when their calibre is increased as a result of increasing the size of the peripheral target they innervate. This result implies that axon calibre, which is known to be correlated with myelination, is in fact the crucial determinant of whether an axon becomes myelinated. Furthermore, the finding that increasing or decreasing target size causes corresponding increases or decreases in axon size indicates that axon calibre is itself regulated by retrograde signals from peripheral target tissues.     

Regulation by angiotensin II of its receptors in resistance blood vessels

The sensitivity of blood vessels to the vasoconstrictor effects of the hormone angiotensin II appears to be modulated by the activity of the renin-angiotensin system. Elevation of circulating angiotensin II levels by sodium depletion or renal artery stenosis is associated with a diminished pressor response to infused angiotensin II (refs 1-3). Conversely, the vasocontrictor response to the hormone is enhanced when endogenous angiotensin II levels are reduced by sodium loading or nephrectomy. The mechanisms of these varying effects are not known, but physiological and pharmacological experiments suggest involvement of the vascular smooth receptor for angiotensin II (refs 5-8). Modification of the interaction between angiotensin II and its vascular receptor, resulting in altered responsiveness to the hormone, could occur either via 'prior occupancy' of receptors by elevated levels of endogenous angiotensin II resulting in fewer free receptors available to respond to circulating angiotensin II (ref. 5), or, elevated levels of angiotensin II could result in a decrease in receptor affinity for the hormone or a decrease in total receptor number in the vascular smooth muscle cell. We now report the first direct evidence, by radioligand binding assay, that angiotensin II regulates the number of its own receptors in resistance vasculature.     

Calcitonin gene-related peptide regulates calcium current in heart muscle

The influx of Ca2+ due to the transmembrane calcium current, ICa, has a fundamental role in cardiac pacemaker activity, in the action potential plateau and in excitation-contraction coupling. Both sympathetic and parasympathetic neurotransmitters can modulate ICa. Recent studies indicate that in both the cardiovascular and the central nervous systems, nerve varicosities exist that contain a novel non-adrenergic, non-cholinergic peptide--calcitonin gene-related peptide (CGRP). Although CGRP is known to exert strong positive inotropic and chronotropic effects, as well as to cause vasodilation, very little is known about the ionic mechanisms of these effects. Here we report that CGRP dramatically increases ICa in single heart cells. Although this CGRP-induced increase in ICa resembles the effect of beta-adrenergic agonists, our results demonstrate some significant differences between the effects of CGRP and these agonists: (1) the increase due to CGRP cannot be blocked by beta-adrenergic antagonists; (2) the CGRP-induced effect is transient; and, (3) CGRP can inhibit isoproterenol-stimulated ICa. Our results provide the first electrophysiological evidence that CGRP can significantly modulate ICa in the heart, and suggest a new additional mechanism for the neurogenic control of cardiac function.     

Peptidergic transmitters in synaptic boutons of sympathetic ganglia

In sympathetic ganglia of the bullfrog, a slow synaptic potential lasting for minutes--the late slow excitatory postsynaptic potential (e.p.s.p.)--was discovered. This slow response, unlike other previously known synaptic potentials in the autonomic nervous system, is not mediated by acetylcholine or monoamines. Similar non-cholinergic, non-adrenergic slow synaptic potentials have since been found in several other vertebrate autonomic ganglia. We found that the late slow e.p.s.p. is probably mediated by a peptide that is identical to, or closely resembles, mammalian luteinizing hormone releasing hormone (LHRH), because (1) when applied directly to sympathetic neurones, LHRH and its agonists elicit a slow depolarization, associated with similar changes in membrane conductance and excitability as those occurring during the late slow e.p.s.p. Furthermore, both peptide-induced and nerve-evoked responses are blocked by antagonists of LHRH; and (2) radioimmunoassays indicate that a chain of sympathetic ganglia contains 100-800 pg of a LHRH-like peptide. Its distribution among spinal nerves, the great reduction of this substance following denervation, and its release from ganglia following isotonic KCl treatment or nerve stimulation suggest that the LHRH-like material is contained in preganglionic nerve fibres. Here we report that immunohistochemical staining of sympathetic ganglia shows that LHRH-like immunoreactivity is indeed present in synaptic boutons. We also show that the two types of ganglion cells (B cells and C cells) receive strikingly different patterns of peptidergic innervation.     

体外反搏提高舒张压在心、脑及小肠系膜动脉中的不同表现

通过观察体外反搏提高舒张压在心、脑及肠系膜动脉中的不同表现，发现体外反搏更能有效提高冠状动脉及脑动脉灌注压，而在小肠系膜动脉中压力则表现波动性较大．结果表明体外反搏更有利于提高心脑血管的灌注．     

VIP occurs in intrathyroidal nerves and stimulates thyroid hormone secretion

Vasoactive intestinal polypeptide (VIP) is known to have powerful effects on the secretion from several endocrine and exocrine glands, and occurs in nerves with a ubiquitous distribution in the body. This infers that neuronal VIP may be a regulator of such secretion, and there is evidence that it is involved in the regulation of exocrine pancreatic function. Previous studies have shown that adrenergic and cholinergic nerves participate in the regulation of thyroid hormone secretion. We describe here combined immunohistochemical and immunochemical studies which show that the thyroid of several species is supplied with VIP-containing nerve fibres that surround blood vessels and run between and along thyroid follicles and that in the mouse neuronal VIP participates in the regulation of thyroid hormone secretion through a mechanism that is mediated by cyclic AMP.     

Positioning of follicular dendritic cells within the spleen controls prion neuroinvasion

Peripheral infection is the natural route of transmission in most prion diseases. Peripheral prion infection is followed by rapid prion replication in lymphoid organs, neuroinvasion and progressive neurological disease. Both immune cells and nerves are involved in pathogenesis, but the mechanisms of prion transfer from the immune to the nervous system are unknown. Here we show that ablation of the chemokine receptor CXCR5 juxtaposes follicular dendritic cells (FDCs) to major splenic nerves, and accelerates the transfer of intraperitoneally administered prions into the spinal cord. Neuroinvasion velocity correlated exclusively with the relative locations of FDCs and nerves: transfer of CXCR5-/- bone marrow to wild-type mice induced perineural FDCs and enhanced neuroinvasion, whereas reciprocal transfer to CXCR5-/- mice abolished them and restored normal efficiency of neuroinvasion. Suppression of lymphotoxin signalling depleted FDCs, abolished splenic infectivity, and suppressed acceleration of pathogenesis in CXCR5-/- mice. This suggests that prion neuroimmune transition occurs between FDCs and sympathetic nerves, and relative positioning of FDCs and nerves controls the efficiency of peripheral prion infection.     

Modulation of the response of a photosensitive muscle by beta-adrenergic regulation of cyclic AMP levels

The light-induced constriction of the irises of some vertebrates is mediated by photosensitive pupillary sphincter cells, which have rhodopsin molecules in their sarcolemmas. Light-induced isomerization of these rhodopsin molecules leads to the release of Ca2+ from an internal pool, which in turn activate the contractile proteins. A central nervous reflex is therefore not essential for the light responsiveness of these irises, but they do appear to be innervated. The photosensitive iris of the toad receives sympathetic (adrenergic) innervation. Stimulation of sympathetic nerves to the eye or application of adrenergic agonists to the iris cause pupillary dilation due to relaxation of the sphincter muscle. We show here that beta-adrenergic stimulation of toad sphincter cells modulates their photoresponses by elevating the intracellular levels of cyclic AMP. However, cyclic AMP does not appear to be involved in the transduction event but rather alters the availability of Ca2+ for contraction.     

Localization of nitric oxide synthase indicating a neural role for nitric oxide.

Nitric oxide (NO), apparently identical to endothelium-derived relaxing factor in blood vessels, is also formed by cytotoxic macrophages, in adrenal gland and in brain tissue, where it mediates the stimulation by glutamate of cyclic GMP formation in the cerebellum. Stimulation of intestinal or anococcygeal nerves liberates NO, and the resultant muscle relaxation is blocked by arginine derivatives that inhibit NO synthesis. It is, however, unclear whether in brain or intestine, NO released following nerve stimulation is formed in neurons, glia, fibroblasts, muscle or blood cells, all of which occur in proximity to neurons and so could account for effects of nerve stimulation on cGMP and muscle tone. We have now localized NO synthase protein immunohistochemically in the rat using antisera to the purified enzyme. We demonstrate NO synthase in the brain to be exclusively associated with discrete neuronal populations. NO synthase is also concentrated in the neural innervation of the posterior pituitary, in autonomic nerve fibres in the retina, in cell bodies and nerve fibres in the myenteric plexus of the intestine, in adrenal medulla, and in vascular endothelial cells. These prominent neural localizations provide the first conclusive evidence for a strong association of NO with neurons.