J. Lincoln

MYENTERIC PLEXUS IN STREPTOZOTOCIN TREATED RATS. NEUROCHEMICAL AND HISTOCHEMICAL EVIDENCE FOR DIABETIC NEUROPATHY IN THE GUT

Adrenergic, cholinergic, and serotoninergic nerves were studied in the myenteric plexus of ileum and colon from streptozotocin-treated rats, an animal model of juvenile-onset diabetes. In view of clinical reports implicating diabetic autonomic neuropathy as the cause of gastrointestinal dysfunction in diabetes mellitus, neurochemical and histochemical techniques were used to study changes in the innervation of the gut. In the myenteric plexus of the ileum from diabetic animals, adrenergic nerves displayed signs of degeneration and the brightness of fluorescence in serotoninlike immunoreactive nerves was lower. Cholinergic nerves, however, did not display any signs of reduction in the ileum, and both choline acetyltransferase and acetylcholinesterase activities per centimeter were increased. In contrast, in the proximal colon 8 wk after induction of diabetes, neurochemical assays revealed significant increases in noradrenaline and serotonin levels as well as choline acetyltransferase activity, although no obvious changes in the pattern of innervation could be detected histochemically. The results indicate that changes do occur in the innervation of the gut of the streptozotocin-diabetic model shortly after the induction of diabetes, although they differ significantly in the ileum and colon; these may be of relevance to the types of gastrointestinal dysfunction displayed in human diabetes.

Ultrastructural localisation of substance P and choline acetyltransferase in endothelial cells of rat coronary artery and release of substance P and acetylcholine during hypoxia.

Substance P and choline acetyltransferase have been localised in a small proportion of endothelial cells of rat coronary arteries using electron microscopic immunocytochemistry. During a hypoxic period of 1 min, coronary vasodilatation was produced in the Langendorff heart preparation and increased levels of substance P and acetylcholine were released into the perfusate. The possibility that these substances are released from endothelial cells during hypoxia and contribute to the hyperaemic response is discussed.

Enteric nerves in diabetic rats: Increase in vasoactive intestinal polypeptide but not substance P

The distribution of vasoactive intestinal polypeptide (VIP) and substance P-like immunoreactivities was studied by immunohistochemistry in the myenteric plexus and circular muscle layer of the ileum and proximal colon of rats 8 wk after induction of diabetes with streptozotocin. A consistent increase was observed in fluorescence intensity of VIP-like immunoreactivity in the nerve fibers, and intensely stained cell bodies were significantly more frequent in the myenteric plexus of the ileum (p less than 0.001) from diabetic animals. Some varicosities of VIP-like immunoreactive fibers in the myenteric plexus appeared to be enlarged. Vasoactive intestinal polypeptide-like immunoreactivity was increased and VIP-like immunoreactive nerves appeared thicker in the circular muscle layer of both diabetic ileum and proximal colon. The VIP levels were measured biochemically in tissue consisting of the smooth muscle layers and myenteric plexus. A significant increase in the VIP content per centimeter of intestine was found in both the ileum (p less than and proximal colon (p less than 0.01) from diabetic rats. In contrast, no apparent change in substance P innervation was observed immunohistochemically in the myenteric plexus and circular muscle layer of either diabetic ileum or proximal colon when compared with controls. The results are discussed in relation to the symptoms of autonomic neuropathy of the gut in diabetes.

Serotonin as a neurotransmitter in cerebral arteries.

Abstract Evidence is presented for the existence of serotoninergic nerves in rabbit verterbral artery: the neurogenic vasoconstrictor response in isolated vessels was resistant to adrenoceptor and cholinoceptor blockede but was blocked by ketanserin, a serotonin (5-HT) antagonist; vertebral arteries contained high levels of 5-HT (over 0.5 μg/g wet weight) and its metabolite, 5-hydroxyindoleacetic acid (over 0.6 μg/g wet weight); and a 5-HT-immunoreactive nerve plexus was demonstrated. The possible role of these nerves is discussed.

Progressive changes in adrenergic, serotonergic, and peptidergic nerves in proximal colon of streptozotocin-diabetic rats

The effect of progression of diabetes on adrenergic, serotonergic, and peptidergic innervation of the proximal colon of the rat at 8, 16, and 25 wk after induction of diabetes with streptozotocin was investigated using immunohistochemical, biochemical, and immunochemical methods. Two different responses to diabetes emerged from the present study. The first response, which involves noradrenaline and vasoactive intestinal peptide, was characterized by a sign of degeneration, where there was an initial increase in tissue level and immunoreactivity of the transmitters followed by a decrease in tissue level and density of nerve fibers at 16 and 25 wk after induction of diabetes. The second response, which involves 5-hydroxytryptamine, substance P, and calcitonin gene-related peptide, was characterized by changes in tissue level and immunoreactivity of the transmitters with no evidence of degeneration. The third feature was one of resistance to change due to diabetes, which was demonstrated by neuropeptide Y-containing nerves, where there was neither a change in tissue level of neuropeptide Y nor a change in immunoreactivity. It seems likely that the overall changes described will have profound implications in the function of the gut in the streptozotocin-diabetic rat model that may have some parallels in diabetic humans.

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.

Serotonin and 5-Hydroxyindoleacetic Acid Are Increased in the Sigmoid Colon in Severe Idiopathic Constipation

The distribution of serotonin and dopamine beta-hydroxylase was examined in sigmoid colon specimens from patients with severe idiopathic constipation and control patients with carcinoma of the rectum or colon. Specimens were divided into three regions: (a) the mucosa; (b) the myenteric and submucosal plexuses with the longitudinal and circular smooth muscles; and (c) the circular smooth muscle, for biochemical analysis of serotonin and 5-hydroxyindoleacetic acid (total indoles) and noradrenaline. In both groups of patients, serotonin- and dopamine beta-hydroxylase-like immunoreactivity was localized in nerves in the myenteric and submucosal plexuses, and a sparse innervation was observed in the circular muscle. In addition, intense serotonin-like fluorescence was present in a large number of enterochromaffin cells in the mucosa. Total indole levels were significantly increased in the mucosa (p less than 0.02) and circular muscle (p less than 0.05) of the constipated patients. In contrast, no changes in noradrenaline levels were observed in any of the regions studied. Altered levels of total indoles may thus contribute to severe idiopathic constipation. Analysis of biopsy specimens could be a useful tool in clinical diagnosis and future investigations of diseases of the gut.

Lack of release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation of enteric nerves in streptozotocin-diabetic rats.

The simultaneous release of endogenous acetylcholine, serotonin, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide was measured during electrical field stimulation of isolated preparations of rat ileum from control and 8-wk streptozotocin-treated diabetic rats. Electrical field stimulation of the control rat ileum caused a significant increase in the release of all the above substances from the enteric nerves. The electrically evoked, but not the basal, release of these substances was inhibited by tetrodotoxin. In the diabetic rat ileum, however, there was no increase in the release of vasoactive intestinal polypeptide and calcitonin gene-related peptide during electrical stimulation, whereas endogenous release of acetylcholine, serotonin, and substance P was unaffected by the diabetic state. This was surprising in view of the increased fluorescence intensity and tissue content of vasoactive intestinal polypeptide-like immunoreactivity in the same tissue reported previously. The lack of increase in evoked release of vasoactive intestinal polypeptide in the diabetic preparations might be due to an impaired mechanism of release at the terminal site or to defective axonal transport of the peptide, whereas in the case of calcitonin gene-related peptide, it might be the result of the low level of the peptide present in the enteric nerve fibers of the diabetic rat ileum. The differential effect of diabetes on enteric nerves is discussed.

Vasoactive Intestinal Polypeptide-like Immunoreactive Nerves in Diabetic Penis: A Comparison Between Streptozotocin-treated Rats and Man

Vasoactive intestinal polypeptide (VIP) has been demonstrated by immunofluorescence histochermistry in nerves in human and rat penile tissue. A reduction in VIP-like immunoreactivity in nerves was revealed in tissue from streptozotocin-diabetic rats and a human diabetic with impotence. These results suggest that an impairment in the VIP-ergic innervation in penile tissue may be an important factor in the development of impotence in diabetes. They also support the view that the streptozotocin-treated rat is a useful experimental model for diabetic autonomie neuropathy.

Increased density of perivascular nerves to the major cerebral vessels of the spontaneously hypertensive rat: differential changes in noradrenaline and neuropeptide Y during development.

Fluorescence and immunohistochemical techniques were used to study the pattern and density of perivascular nerves containing noradrenaline (NA) and neuropeptide Y (NPY) supplying the major cerebral arteries of 4-, 6-, 8- and 12-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar (WIS) controls. Levels of NA and NPY in the superior cervical ganglia were measured. The density of nerves containing NA and NPY was greater in the hypertensive animals at all ages studied. However, the developmental changes in the density of innervation showed similar trends in both SHR and WIS groups. With few exceptions, there was a significant increase in the density of nerves containing NA from 4 to 6 weeks and from 8 to 12 weeks of age. This was in contrast to a low expression, and in some vessels a significant decrease in the number of NPY-containing nerves from 4 to 6 weeks. The density of nerve fibres containing NPY increased significantly in almost all vessels between 6 and 8 weeks of age and then stabilized. Thus there is a differential time course for the appearance of NA and NPY during development. Furthermore, the hyperinnervation of cerebral vessels in SHR by nerves containing NA and NPY precedes the onset of hypertension and associated medial hypertrophy. High-performance liquid chromatography and enzyme-linked immunosorbant assays show that the NA and NPY contents of the superior cervical ganglion do not reflect the changes in innervation pattern seen in the terminal fibres in the cerebral arteries. This tends to support the view that a local neurovascular mechanism is involved in the maintenance of hypertension. The possibility that increase in NPY as well as NA in cerebral perivascular nerves of hypertensive animals is involved in the protection of the blood-brain barrier against oedema and cerebral haemorrhage is raised.