Biomedical subjects

P Milner

Publications and source records attributed to P Milner.

At least 19 recordsLinked to original sources

PubMed1992

Differential vulnerability of neuropeptides in nerves of the vasa nervorum to streptozotocin-induced diabetes.

Neuropeptides in perivascular nerves of vasa nervorum supplying blood to rat optic, sciatic, vagus and sympathetic chain nerve trunks are differentially vulnerable to streptozotocin (STZ)-induced diabetes. Immunohistochemical analysis of epineurial/perineurial nerve sheaths showed that 8 weeks after induction of diabetes, the density of neuropeptide Y (NPY)-immunoreactive nerve fibres in optic nerve sheaths was increased, while it was decreased in sciatic, vagus and sympathetic nerve sheaths. Vasoactive intestinal polypeptide (VIP)-immunoreactivity was increased in vasa and nervi nervorum of optic, sciatic, vagus and sympathetic chain nerve sheaths. Immunoassay of NPY confirmed increased levels in optic nerve sheaths and showed that substance P and calcitonin gene-related peptide levels increased in sciatic but not optic nerve sheaths. Neuropeptide levels in the intrafascicular nerve fibres were unaffected. This provides further evidence for a disturbance in the autonomic control of blood flow to peripheral and cranial nerve trunks via vasa nervorum in STZ-induced diabetes, which may lead to ischaemic changes, alter local axon reflexes and contribute to the pathogenesis of the disease.

Animals↗

PubMed1992

Chronic hypoxia changes the ratio of endothelin to ATP release from rat aortic endothelial cells exposed to high flow.

Endothelial cells isolated from the thoracic aorta of normoxic and chronically hypoxic rats were perfused (0.5 ml min-1) and stimulated by increased flow rate (3.0 ml min-1). The release of ATP, endothelin and vasopressin was investigated. During periods of high flow rate, endothelial cells isolated from normoxic rats increased their release of ATP and endothelin. In comparison, in hypoxic rats, ATP release during the period of high flow rate was less, whereas endothelin release was greater. Vasopressin release was not increased during periods of stimulation in either group of animals. These results suggest that, under conditions of reduced arterial oxygen tension, a dynamic balance between ATP and endothelin release could regulate the response of vessels to shear stress.

Adenosine Triphosphate↗

PubMed1992

Flow-induced release of adenosine 5'-triphosphate from endothelial cells of the rat mesenteric arterial bed.

Adenosine 5'-triphosphate (ATP) was released into the perfusate of rat isolated mesenteric arterial beds during each of two consecutive increases in flow. There was no significant difference between the amounts of ATP released on each occasion. Substance P was also released into the perfusate by increased flow, although its release was more variable. Removal of the endothelium of the mesenteric vessels with sodium deoxycholate led to a significant reduction (74%) in the amount of ATP released compared with the release before the endothelium had been removed. This suggests that the ATP released into the mesenteric arterial perfusate during increased flow arises from endothelial cells.

Adenosine Triphosphate↗

PubMed1992

Guanethidine sympathectomy of mature rats leads to increases in calcitonin gene-related peptide and vasoactive intestinal polypeptide-containing nerves.

Changes in the innervation of the heart (right atrium), mesenteric blood vessels, vas deferens and superior cervical ganglia have been examined following long-term sympathectomy of the mature rat. Patterns of innervation were investigated by histochemical and immunohistochemical techniques, while levels of noradrenaline and neuropeptides were measured by neurochemical assays. Large doses of guanethidine (80 mg/kg) were given daily for four weeks to 12-14 week-old male rats which were killed at 18-20 weeks of age. Catecholamine-containing nerves were severely depleted or absent in all tissues, together with a reduction in noradrenaline content. Neuropeptide Y levels were depleted by 97% in vas deferens, 78% in mesenteric vein and 50% in right atrium and superior cervical ganglion. Increases in levels of calcitonin gene-related peptide were seen in the mesenteric vein (up seven-fold), superior cervical ganglia (up 11-fold) and vas deferens (prostatic portion up three-fold), which were also evident by assessment of immunolabelling of nerve fibres. Calcitonin gene-related peptide levels were not increased in the right atrium. In addition, an increase in vasoactive intestinal polypeptide-immunoreactive nerve fibre density was seen in the mesenteric artery and vas deferens, although no significant differences were observed in assays of vasoactive intestinal peptide levels in any tissue. No changes were seen in the innervation of any of the tissues by substance P-immunoreactive nerve fibres either by immunohistochemical or immunochemical assay assessment. This study indicates that there are selective changes in the mature nervous system in response to the loss of sympathetic nerves. Differences between these changes and the response of the developing nervous system to long-term sympathectomy are discussed.

Animals↗

PubMed1992

Loss of sensory neuropeptides in the obstructed human bladder.

This is the first investigation of alterations in the innervation of the obstructed human bladder by nerves containing neuropeptides. The patient groups studied were those with stable detrusor function, those with unstable detrusor function, and those presenting with acute retention of urine. Specimens of bladder tissue were taken from the lateral wall of the bladder below the peritoneal reflection. A total of 23 patients was studied (control, n = 4; acute retention, n = 5; stable obstruction, n = 5; unstable obstruction, n = 9). Substance P, calcitonin gene-related peptide and vasoactive intestinal polypeptide levels in the bladder were quantified by immunoassay. The density of innervation of the bladder detrusor by nerves containing these neurotransmitters and by those containing neuropeptide Y and somatostatin was assessed using both semiquantitative and quantitative immunohistochemical techniques. A reduction in the density of innervation by vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and somatostatin-immunoreactive but not neuropeptide Y-immunoreactive nerve fibres was shown in the obstructed bladder. These findings, combined with the significant reduction in substance P content of the obstructed bladder and in particular of the acute retention bladder, indicate that there may be an afferent nerve dysfunction resulting from prostatic bladder outflow obstruction.

Aged↗

PubMed1992

X-irradiation attenuates relaxant responses in the rabbit ear artery.

1. The relaxant actions of acetylcholine, substance P and calcitonin gene-related peptide, and the levels of neuropeptide Y and calcitonin gene-related peptide were assessed in the rabbit central ear artery 1, 4 and 6 weeks after a single dose of 45 Gy X-irradiation, a dose similar to that used clinically in intraoperative radiotherapy. 2. Relaxant responses induced by acetylcholine and substance P (both endothelium-dependent) and calcitonin gene-related peptide (endothelium-independent) were reduced, and endogenous neuropeptide Y and calcitonin gene-related peptide levels were unaffected after X-irradiation. 3. The mechanism(s) by which a single dose of 45 Gy X-irradiation may selectively damage relaxant, but not direct, contractile responses of the smooth muscle (as we have shown previously) of the rabbit central ear artery are discussed.

Acetylcholine↗

PubMed1992

Effects of long-term laxative treatment on neuropeptides in rat mesenteric vessels and caecum.

In order to investigate the toxic effects of long-term treatment with anthraquinone laxatives, rats were fed either chocolate alone, or chocolate adulterated with senna or danthron (1,8-dihydroxyanthraquinone) for 5 months. Mesenteric blood vessels and the outer muscle layers of the caecum, together with the myenteric plexus, were examined using ultrastructural, histochemical, immunohistochemical and immunoassay techniques. There was no ultrastructural evidence of degeneration in either the mesenteric vessels or the caecum. In the mesenteric vessels, levels of neuropeptide Y were significantly reduced in the danthron-fed rats, but levels of substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) were unaffected by all treatments. In the caecum, VIP-, SP- and CGRP-immunoreactivity and catecholamine-fluorescence were unchanged by the laxative treatments.

Animals↗

PubMed1991

Differential effect of streptozotocin-induced diabetes on the innervation of the ileum and distal colon.

The effect of short-term and long-term streptozotocin-induced diabetes on the pattern of distribution and tissue content of adrenergic and peptidergic nerves in ileum and distal (descending) colon of the rat was examined using immunohistochemical, biochemical, and immunochemical techniques. The effect of short-term streptozotocin-induced diabetes on the level of noradrenaline compared with weight-restricted (starved) and untreated controls in the celiac (celiac-superior mesenteric ganglia complex) and inferior mesenteric ganglia, which supply the two regions of the intestine, was also compared. The pattern of change in the distribution of dopamine-beta-hydroxylase-, substance P-, calcitonin gene-related peptide-, and vasoactive intestinal polypeptide-like immunoreactive nerve fibres that was observed in the ileum from diabetic rats was not evident in the myenteric plexus of distal colon. In contrast to the ileum, there was no evidence of degenerative change in any of the nerve types investigated in the myenteric plexus of the distal colon. The level of vasoactive intestinal polypeptide in the diabetic rat ileum was significantly increased, whereas the level of noradrenaline was reduced; no such changes were observed in the distal colon. The tissue content of noradrenaline in the celiac ganglion, which projects to the ileum, was increased at 8-week diabetes compared with both weight-restricted and untreated controls, whereas the diabetic state had no effect on the levels of noradrenaline of the inferior mesenteric ganglion, which projects to the distal colon. It is concluded that there is a differential effect of streptozotocin-diabetes on different regions of the rat intestine. The adrenergic and peptidergic innervation of the distal colon were changed little compared with ileum. This may be explainable in terms of the different functional roles of these two regions of the intestine and/or by the difference in origin of the sympathetic nerves supplying the two regions of the intestine.

Animals↗

PubMed1991

Changes in sympathetic and endothelium-mediated responses in the rabbit central ear artery after acrylamide treatment.

The effect of acrylamide intoxication on the innervation and local control of the rabbit central ear artery was investigated. There was no difference in the noradrenaline, neuropeptide Y and calcitonin gene-related peptide tissue content between control and experimental animals. There was, however, a slight reduction in catecholamine histofluorescence. Although the contractile efficiency of the rabbit central ear artery as measured by responses to potassium chloride was unchanged, nerve-mediated contractile responses were significantly attenuated in acrylamide-treated animals. Contractile responses induced by exogenous alpha,beta-methylene ATP were markedly increased after acrylamide treatment, in contrast to contractions induced by exogenous noradrenaline which were attenuated at maximal concentrations. Modulatory effects of nerve-mediated contractile responses by neuropeptide Y were unaffected by acrylamide intoxication. It therefore appears that acrylamide intoxication damages sympathetic cotransmission, perhaps with preferential action on the purinergic component. Endothelium-dependent relaxant responses to acetylcholine and substance P were attenuated in acrylamide-treated animals, whereas relaxant responses mediated by calcitonin gene-related peptide (endothelium independent) were unaffected. The question of whether the damage to the endothelial cell action is a primary effect, or a secondary consequence of sympathetic nerve damage, is discussed.

Acrylamide↗

PubMed1991

Neuropeptide Y in non-sympathetic nerves of the rat: changes during maturation but not after guanethidine sympathectomy.

Non-sympathetic neuropeptide Y-containing nerves were demonstrated by their persistence after destruction of sympathetic nerve terminals by acute 6-hydroxydopamine treatment for 48 h. In order to examine whether these neuropeptide Y-containing nerves reinnervate tissues following the loss of sympathetic nerves we administered guanethidine sulphate to one-week-old rat pups for three weeks to produce a complete and long-lasting sympathectomy and we monitored the innervation of the superior cervical ganglion, mesenteric vein, vas deferens and urinary bladder by noradrenaline- and neuropeptide Y-containing nerves two and 16 weeks later (assay and histochemical observations). By two weeks the reduction in neuropeptide Y content of tissues was similar to the reduction after acute sympathectomy with 6-hydroxydopamine treatment, indicating that there was no early reinnervation by non-sympathetic neuropeptide Y-containing nerve fibres at a time when sensory transmitters increase. Furthermore, there was no reinnervation by neuropeptide Y-containing nerve fibres by the time these sympathectomized animals had reached maturity, 16 weeks after cessation of treatment. Neuropeptide Y levels increased in the superior cervical ganglion with normal maturation but decreased in the prostatic end of the vas deferens. A non-sympathetic source of neuropeptide Y demonstrated in the immature rat vas deferens was no longer evident in the mature animal.

Aging↗

PubMed1990

Endothelial cells cultured from human umbilical vein release ATP, substance P and acetylcholine in response to increased flow.

Cultured human umbilical vein endothelial cells superfused with Krebs' solution were used to investigate release of ATP, substance P and acetycholine with shear stress. ATP was consistently released when the cells were exposed to increased flow rate; release was rapid, had declined by 1 min and occurred upon a second exposure. Release of substance P and acetylcholine was more varied; increased shear stress led to release of substance P from 4 out of 16 endothelial-cell columns, whereas acetylcholine was released in 4 out of 12 columns. This is the first time that unequivocal evidence has been presented for release of these neurotransmitter substances from vascular endothelial cells. These findings have important implications about the mechanisms of local regulation of vascular tone.

Acetylcholine↗

PubMed1990

Rapid release of endothelin and ATP from isolated aortic endothelial cells exposed to increased flow.

Freshly harvested rabbit aortic endothelial cells on filters were exposed to two 3 min periods of a sixfold increase in flow rate of the perfusion buffer. This led to an increase in the levels of endothelin and ATP in the perfusate; arginine vasopressin remained at the basal level. Less ATP was released on the second exposure to high flow; however, endothelin release was not diminished. Using immunohistochemical techniques, endothelin and arginine vasopressin were localised in the same population of endothelial cells; endothelin and vasopressin were present in approximately 90% and 70% of endothelial cells, respectively, which suggests that there is some co-localisation. This is the first time that a stimulation has been shown to produce rapid release of endothelin.

Adenosine Triphosphate↗

PubMed1990

Pregnancy reduces noradrenaline but not neuropeptide levels in the uterine artery of the guinea-pig.

Using histochemical, immunohistochemical and biochemical techniques, noradrenaline-, neuropeptide Y-, vasoactive intestinal polypeptide-, substance P- and calcitonin gene-related peptide-containing nerve fibres were studied in the uterine artery of virgin, progesterone-treated and pregnant guinea-pigs. Morphological changes following hormone treatment or in pregnancy were also evaluated in a quantitative study on semithin sections of the uterine artery. In late pregnancy, the number of noradrenaline-containing nerve fibres, which formed the densest plexus in virgin animals, was significantly decreased, a finding supported by a significant reduction in noradrenaline levels. This reduction was not mimicked by systemic progesterone treatment. In contrast, the innervation of the uterine artery by neuropeptide Y-containing nerve fibres was increased in pregnancy, while the other peptidergic nerves and peptide levels were unchanged after progesterone treatment and in pregnancy. These changes led to a predominance of innervation by neuropeptide Y- rather than noradrenaline-containing nerve fibres in late pregnancy. No morphological changes were detected following progesterone treatment, but pregnancy led to a marked increase in the cross-sectional area of the vessel accompanied by an increase in the thickness of the media.

Animals↗

PubMed1990

Vasoactive intestinal polypeptide levels in sigmoid colon in idiopathic constipation and diverticular disease.

The distribution in the bowel wall of vasoactive intestinal polypeptide-, neuropeptide Y-, and substance P-containing nerve cell bodies and nerve fibers has been described in human sigmoid colon by immunohistochemical examination. In patients with chronic idiopathic constipation, diverticular disease, and in controls (of tissue taken from patients with carcinoma, from a site distant from the tumor that appeared macroscopically normal), the concentrations of vasoactive intestinal polypeptide, neuropeptide Y, and substance P have been measured by immunoassay in the following preparations of sigmoid colon: mucosa, whole colonic wall with mucosa dissected away, circular muscle, and taenia coli. In idiopathic constipation, the vasoactive intestinal polypeptide content of the whole wall minus mucosa was reduced when compared with controls (P less than 0.05) but was unaltered in the mucosa, circular muscle, and taenia coli. In diverticular disease, the vasoactive intestinal polypeptide content of the mucosa and whole wall minus the mucosal layer was increased when compared with control tissue (P less than 0.05 and P less than 0.02, respectively) but was unaltered in the circular muscle and taenia coli. Substance P and neuropeptide Y levels in all layers of colonic wall were unaltered in these two diseases. The disturbances in the normal neural content of vasoactive intestinal polypeptide in the bowel wall in idiopathic constipation and diverticular disease may initiate or contribute to the functional changes seen in these disorders.

Colon, Sigmoid↗

PubMed1990

Neuropeptide immunoreactivity and choline acetyltransferase activity in the mouse urinary bladder following inoculation with Semliki Forest Virus.

The effect of Semliki Forest Virus, a known central demyelinating agent and a proposed model for multiple sclerosis, on the innervation of the mouse urinary bladder has been examined 3, 6, 9 and 12 weeks after inoculation. Three weeks after Semliki Forest Virus inoculation, vasoactive intestinal polypeptide content of the bladder was reduced and the density of vasoactive intestinal polypeptide-immunoreactive nerves was decreased in the smooth muscle, but not in the mucosa. Choline acetyltransferase activity and neuropeptide Y and substance P content was normal, as was the pattern of innervation by acetylcholinesterase-containing and neuropeptide Y- and substance P-immunoreactive nerve fibres. Six weeks after Semliki Forest Virus inoculation, the choline acetyltransferase activity was significantly reduced. Between 6 and 9 weeks the level of vasoactive intestinal polypeptide in the bladder of Semliki Forest Virus-infected mice significantly increased, so that at 9 weeks it was higher than the control value. However, by 12 weeks both choline acetyltransferase activity and vasoactive intestinal polypeptide content were normal. At this time, the substantial age-related increase in substance P content of the bladder was more pronounced in the Semliki Forest Virus-treated animals. Thus there are transitory changes in the innervation of the mouse bladder by vasoactive intestinal polypeptide-containing and cholinergic nerve fibres after exposure to a central demyelinating agent which may reflect changes in bladder dysfunction seen in multiple sclerosis patients.

Animals↗

PubMed1990

Marked increases in calcitonin gene-related peptide-containing nerves in the developing rat following long-term sympathectomy with guanethidine.

Changes in the innervation of the cardiovascular system, urinogenital tract and sympathetic and non-sympathetic ganglia have been examined following long-term sympathectomy. Patterns of innervation were investigated using histochemical and immunohistochemical techniques, while levels of noradrenaline and neuropeptides were measured by neurochemical assays. Large doses of guanethidine (50 mg/kg) were given daily for 3 weeks to 8-day-old rat pups, which were killed at 6 or 20 weeks of age. In both age groups noradrenergic nerves were severely depleted or absent, while in some regions dramatic increases of calcitonin gene-related peptide levels were demonstrated. This was revealed by an increase in the density of nerve fibres and in calcitonin gene-related peptide content (up to 18-fold), most notably in the right atrium and superior cervical ganglion. No changes in substance P- or vasoactive intestinal polypeptide-immunolabelled nerves were seen. Conversely, short-term sympathectomy by 6-hydroxy-dopamine treatment caused a depletion of noradrenaline which was not accompanied by an increase in the number or content of calcitonin gene-related peptide-immunolabelled nerves. The possibility that nerve growth factor is involved in the mechanism of hyperinnervation by calcitonin gene-related peptide-containing sensory nerves following long-term sympathectomy is discussed.

Adrenergic Fibers↗

PubMed1990

Long-term chemical sympathectomy leads to an increase of neuropeptide Y immunoreactivity in cerebrovascular nerves and iris of the developing rat.

Short-term (surgical) and long-term (chemical) sympathectomy have revealed the presence of a population of neuropeptide Y-like immunoreactive nerve fibres which do not degenerate in parallel with noradrenaline-containing nerves supplying cerebral vessels and the iris of the rat. Two days after bilateral removal of the superior and middle cervical ganglia of 7-week-old rats, noradrenaline-containing nerves could not be detected along any of the arteries of the rat circle of Willis or of the iris, but 18-32% of neuropeptide Y-like immunoreactive nerves remained. Long-term treatment (6 weeks) with guanethidine commencing in developing 1-week-old rats caused degeneration of the sympathetic neurons in cervical ganglia and disappearance of 5-hydroxydopamine-labelled nerves (that showed dense-cored vesicles at the electron microscope level) from rat cerebral vessels, but did not significantly change the density of neuropeptide Y-like immunoreactive axons on the vessels. Furthermore, whilst in control rats neuropeptide Y-like immunoreactivity was localized largely within 5-hydroxydopamine-labelled cerebrovascular nerves, after long-term sympathectomy with guanethidine, neuropeptide Y-like immunoreactivity was seen only in nerves lacking small dense-cored vesicles. A small number of catecholamine-containing nerves appeared along the internal carotid and anterior cerebral arteries after long-term sympathectomy; these may arise from neurons of central origin. These results suggest that as a consequence of long-term sympathectomy with guanethidine, compensatory changes occur, involving an increase in the expression of neuropeptide Y-like immunoreactivity in non-sympathetic axons in cerebrovascular nerves and iris of the rat. In contrast, the neuropeptide Y-like immunoreactive nerves in the dura mater appear to be entirely sympathetic, since none were present after short-term sympathectomy and none appeared after long-term sympathectomy.

Adrenergic Fibers↗

PubMed1990

Cerebral vessel stenosis in sickle cell disease: criteria for detection by transcranial Doppler.

Ischemic stroke is a common and disabling complication of sickle cell disease (Hb SS). Most infarctions occur in the presence of intracranial stenotic lesions of the large vessels of the circle of Willis. Transcranial Doppler (TCD), by measuring flow velocity in these arterial segments, can detect focal stenosis on the basis of elevated flow velocity. We report the preliminary results of a prospective study to develop criteria for detection of stenotic lesions based on TCD and identification of patients with Hb SS at risk for stroke. Comparing the TCD findings from six patients with lesions demonstrated by angiography to those from 115 Hb SS children without stroke, we conclude: (a) middle cerebral (MCA), anterior cerebral (ACA), or internal carotid (ICA) artery mean velocities greater than 190 cm/s strongly suggest focal stenosis; (b) MCA or ACA mean velocities of 150 to 190 cm/s suggest abnormality but at present cannot be considered diagnostic of stenosis; (c) mean velocities up to 150 cm/s are possibly due to the effects of low hematocrit and/or young age, and cannot as yet be distinguished from velocity elevations due to vessel stenosis.

Adolescent↗