The origin of VIP-containing nerves in the urinary bladder of rat

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

Postnatal development of neuropeptide Y- and calcitonin gene-related peptide-immunoreactive nerves in the rat urinary bladder

The postnatal development of neuropeptide Y- and calcitonin gene-related peptide-immunoreactive (NPY-IR and CGRP-IR) nerve fibers in the rat urinary bladder was investigated using whole-mount preparations and cryostat sections. In newborn and 3-day-old rats, many NPY-IR nerve fibers were observed in the subserous and muscle layers. Many NPY-IR nerve cell bodies clustered at branching points of the subserous nerve bundles. Within 4 weeks after birth, these cell bodies drastically decreased in number and spread along the bundles, although the number of NPY-IR nerve fibers increased moderately. In contrast, CGRP-IR nerve fibers in newborn and 3-day-old rats were less developed, and no CGRP-IR nerve cell body was observed in any rat. However, CGRP-IR nerve fiber distribution in the urinary tissues conspicuously increased within 4 weeks after birth. Especially, an increase of the infraepithelial fibers showing a meshwork appearance was prominent in the fundus and corpus of the bladder. The infra- and intraepithelial CGRP-IR nerve meshwork of the ventral wall was more dense than that of the trigone. At 4 weeks, NPY-IR and CGRP-IR nerves were similar to those of the adult rat (8-12 weeks old). The present study suggests a correlation between the development of the peripheral nervous system in the urinary bladder and maturation of micturition behavior in the rat.

[125I]vasoactive intestinal polypeptide binding sites: quantitative autoradiographic distribution in the rat spinal cord

The quantitative autoradiographic distribution of [125I]vasoactive intestinal polypeptide (VIP) receptor binding sites was investigated in the rat spinal cord. [125I]VIP binding sites are discretely distributed, with a rostro-caudal gradient, along the longitudinal length of the cord; highest densities of sites being observed in its lumbar and sacral segments. In transverse sections, highest levels of [125I]VIP sites are present in laminae I and II, around the central canal, and in the parasympathetic lateral horn of the sacral segment. Moderate densities are seen along the medial border of the dorsal horn and the sympathetic lateral horn of the thoracic cord. Low amounts of labeling are observed in most structures of the ventral horn while white matter areas are apparently devoid of specific [125I]VIP binding. Thus, the distribution of spinal [125I]VIP receptor sites correlates well with that of VIP-like immunoreactive materials and support possible roles for this peptide in sensory neurotransmission and in the control of autonomic functions.

Regulatory peptides in the mammalian urogenital system

By immunocytochemistry a number of the gut/brain peptides have been demonstrated in nerve fibers of the mammalian urogenital tract. These peptides are localized to large vesicles in nerve terminals of afferent fibers or efferent nerves innervating blood vessels, non-vascular smooth muscle, lining epithelium and glands. There is evidence that some neuropeptides (VIP, NPY) participate in the local non-cholinergic, non-adrenergic nervous control of smooth muscle activity and blood flow, while other peptides (substance P, CGRP) seem to be sensory transmitters. It is likely that impaired function of the peptidergic nerves is involved in sexual dysfunction such as male impotence.

Bladder vasodilatation and release of vasoactive intestinal polypeptide from the urinary bladder of the cat in response to pelvic nerve stimulation

In the feline urinary bladder blood flow was determined by means of a direct blood flow measurement technique before and during pelvic nerve stimulation. Simultaneous sampling of venous blood from the bladder was performed, and the output of vasoactive intestinal polypeptide (VIP) was determined by means of radioimmunoassay. Maximal stimulation of the pelvic nerves led to a clearcut increase in intravesical pressure and a small but sustained increase of blood flow in the bladder wall. These changes were associated with a drastic increase in VIP output from the bladder, increasing from a control level of 0.2 fmol./min. to 15 fmol./min. during stimulation. The results suggest that VIP might be the neurotransmitter responsible for the vasodilatation in the feline urinary bladder in response to pelvic nerve stimulation. The discrepancy between the moderate blood flow increase and the pronounced increase in VIP-release might, however, indicate that VIP exerts its main effects elsewhere in the bladder than in the vascular bed, for instance the detrusor smooth muscle.

Neuropeptides in pelvic afferent pathways

Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.

An atropine-like inhibitory effect of DMPP on rat isolated urinary bladder

DMPP inhibits the nerve-mediated contractions of the rat isolated bladder, its effect being greater in preparations from newborn (2 day old) than adult animals. This effect of DMPP was unaffected by hexamethonium. In preparations from adult animals the effect of DMPP increased with frequency of stimulation and was fully prevented by the presence of atropine. In bladders from newborn rats low concentrations of furthrethonium (FHR) (10 nM) activated a series of rhythmic contractions which were unaffected by tetrodotoxin and abolished by DMPP through an hexamethonium-insensitive action. On the other hand DMPP did not affect rhythmic contractions produced by a low concentration of eledoisin (60 nM). In bladders from adult rats FHR (10 microM) and KCI (30 mM) produced contractures of comparable magnitude. DMPP inhibited, in concentration-related manner the FHR-induced tonic contraction but had little effect on that produced by KCI. These findings indicate that in the rat bladder, DMPP antagonizes selectivity cholinergically-mediated contractions through a mechanism which is unaffected by hexamethonium or tetrodotoxin. An "atropine-like' activity of DMPP should be considered.

Composition of the pelvic nerve

Surgical interruption of the pelvic nerve elevated immunoreactive vasoactive intestinal polypeptide in the major pelvic ganglion of the rat. Two changes were noted: (i) varicose and smooth fibers appeared in the neuropil and (ii) a small number of ganglion cells became highly reactive for the polypeptide. A more proximal transection of preganglionic parasympathetic fibers, at their origin from spinal nerves, had no effect on vasoactive intestinal polypeptide immunoreactivity. Ganglion cells were labeled when a dye was applied to the cut distal end of the pelvic nerve. We conclude that a population of vasoactive intestinal polypeptide-containing neurons in the major pelvic ganglion send their axons proximally in the pelvic nerve.

A VIP/PHI-containing pathway links urinary bladder and sacral spinal cord

Nerve fibres containing VIP and the co-produced PHI are found in the dorsal horn and autonomic centres of the sacral spinal cord and in pelvic organs. We have investigated the origin of these nerve fibres and a possible peptide-containing pathway linking pelvic viscera with the spinal cord of the cat and rat using neurochemical and neurosurgical procedures, retrograde tracing and immunocytochemistry. Cell bodies were located in the dorsal root ganglia (after colchicine injection), pelvic ganglia and bladder wall. Capsaicin treatment induced a loss of VIP/PHI from the dorsal horn. Retrograde tracing from the bladder revealed True Blue labelled cells in the dorsal root ganglia (L6, S1), parasympathetic nuclei and pelvic ganglia. Labelled cells were sequentially immunostained for VIP/PHI which were numerous in pelvic ganglia and scattered and weak in dorsal root ganglia. Pelvic nerve section induced a decrease of VIP/PHI immunoreactivity from the spinal cord and no change or a minimal increase in immunoreactive nerve fibers of the bladder. Thus pelvic visceral afferents with cell bodies in the dorsal root ganglia are a significant source of VIP/PHI-containing fibres in the sacral dorsal horn.

Vasoactive intestinal polypeptide and substance P in primary afferent pathways to the sacral spinal cord of the cat

An analysis of vasoactive intestinal polypeptide immunoreactivity (VIP-IR) and substance P-IR in the cat spinal cord has revealed marked differences in the distribution of the two peptides. While substance P-IR was located at all levels of the cord, VIP-IR was most prominent in the sacral segments in Lissauer's tract and lamina I on the lateral edge of the dorsal horn. VIP-IR was also present in the sacral cord in (1) laminae V, VII, and X, (2) a thin band on the medial side of the dorsal horn, (3) the dorsal commissure, (4) the lateral band of the sacral parasympathetic nucleus, and (5) in a few animals in Onuf's nucleus. In other segments of the spinal cord VIP-IR was much less prominent but was present in Lissauer's tract and laminae I, II, and X. Substance P-IR was more uniformly distributed at all segmental levels in laminae I-III, V, VII, and X and in the dorsal commissure. In ventrolateral lamina I of the sacral spinal cord both VIP-IR and substance P-IR exhibited a distinctive periodic pattern in the rostrocaudal axis. The peptides were associated with bundles of dorsoventrally oriented axons and varicosities spaced at approximately 210-micron intervals center to center along the length of the spinal cord. The bundles in lamina I continued into lamina V where they further divided into smaller bundles that extended medially through laminae V and VII. The most prominent bundles of VIP axons passed ventrally from lateral laminae V and VII to enter lamina X and the ventral part of the dorsal gray commissure. On the other hand the majority of substance P axons in lamina V turned dorsally to join with axons on the medial side of the dorsal horn and to pass into the dorsal part of the dorsal gray commissure. Rostrocaudal VIP axons were present not only in Lissauer's tract but also in dorsolateral lamina I, in the lateral funiculus and in the ependymal cell layer of the central canal. Following unilateral transection of the sacral dorsal roots (2 weeks-22 months) the density of VIP axons and terminals was markedly reduced in ipsilateral Lissauer's tract and lateral laminae I and V; however, no change was detected in lamina X. Sacral deafferentation reduced substance P-IR in the dorsal gray commissure and in lateral laminae I and V.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution and localization of regulatory peptides

A new group of modulatory substances present in both endocrine cells and central and peripheral nerves has been described in the past few years. These substances are biochemically recognized as peptides and their actions affect many bodily functions. They are now widely known as regulatory peptides. The development of new immunocytochemical techniques, closely allied to radioimmunoassay, has disclosed that the regulatory peptides are present either in cells or in nerves, in almost every tissue of the body. The presence of peptides (the classical hormones) in endocrine cells was already known at the beginning of the century, but the presence of similar substances in nerve fibers, where they probably act as neurotransmitters, is a recent and revolutionary discovery. More than 30 peptides (neuropeptides) have been found to be present in nerves, to which the term "peptidergic" has been applied, although it is now known that in certain cases a neuropeptide can be present in the same nerves as a classical neurotransmitter, for example acetylcholine with VIP, or noradrenaline with NPY. Little is known about the physiological role of these neuropeptides. It is not yet fully accepted that they act as neurotransmitters although there is strong evidence for this, particularly in the case of substance P and VIP. The investigation of the regulatory peptides is now in an initial phase. The involvement of new disciplines, such as molecular biology, in this field is producing new and very exciting discoveries, including the isolation of novel peptides and precursors, the study of which will further contribute to the understanding of the basic control mechanisms.