Prevention of neuropathy in the pyloric sphincter of streptozotocin-diabetic rats by gangliosides

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Insulin resistance occurs in parallel with sensory neuropathy in streptozotocin-induced diabetes in rats: differential response to early vs late insulin supplementation

We investigated whether progressive sensory neuropathy was accompanied by changes in whole-body insulin sensitivity (WBIS) in rats made diabetic by streptozotocin (STZ). The effects of early and late insulin supplementation were also studied. The STZ-treated rats failed to gain weight and exhibited stable hyperglycemia and low plasma insulin levels with a decrease in nerve conduction velocity (NCV) measured in A and C fibers of the saphenous nerve. A decreased sensory neuropeptide (SNP) release such as that of substance P, somatostatin, and calcitonin gene-related peptide determined from organ fluid of tracheal preparations subjected to electrical field stimulation also occurred in diabetic animals. These features were accompanied by a decrease in WBIS measured by hyperinsulinemic-euglycemic glucose clamping and a decrease in insulin-stimulated glucose uptake in cardiac and gastrocnemius muscle. When insulin supplementation with slow-release implants (2 IU/d) was started 4 weeks after STZ injection, blood glucose level normalized. Both insulin sensitivity and sensory nerve function reflected in either NCV or SNP release completely recovered by the 12th post-STZ week. When the insulin implants were applied from the eighth post-STZ week, both WBIS and glucose uptake remained significantly decreased, with a seriously impaired NCV and SNP release with strong hyperglycemia. Late insulin supplementation, however, even by using double implantation from the 10th post-STZ week, was unable to restore blood glucose, WBIS, NCV, and SNP release by the 12th week. Insulin resistance occurs in parallel with sensory neuropathy in STZ-diabetic rats. Both can be improved by early but not late insulin supplementation.

Depletion of peptidergic innervation in the gastric mucosa of streptozotocin-induced diabetic rats

Autonomic neuropathy affecting the gastrointestinal system is a major presentation of diabetic neuropathy. Changes in the innervation of gastric mucosa or muscle layers can contribute to gastrointestinal symptoms. The present study investigated this issue by quantitatively analyzing the immunohistochemical patterns of the gastric innervation in rats with streptozotocin (STZ)-induced diabetes. In control rats, calcitonin gene-related peptide (CGRP) and substance P (SP) (+) nerve fibers appeared in the gastric mucosa and muscle layers. Double immunohistochemical staining showed that immunoreactivities for SP and CGRP were co-localized with a pan-neuronal marker protein gene product 9.5. Both SP (+) nerve fibers (p<0.001) and CGRP (+) nerve fibers (p<0.005) were decreased in the gastric mucosa within 4 weeks of diabetes; the reduction persisted throughout 24 weeks. Diabetic rats treated with insulin did not show decrease of SP or CGRP (+) fibers in the mucosa 4 weeks after STZ injection (p>0.05). There was no significant change in SP (+) nerve fibers (p>0.05) or CGRP (+) nerve fibers (p>0.05) of the gastric muscle layers. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression levels of SP and CGRP mRNA in the thoracic dorsal root ganglia were similar between diabetic and control animals (p>0.05). Qualitative and quantitative ultrastructural examinations on the gastric mucosa documented unmyelinated nerve degeneration. These results suggest the existence of gastric sensory neuropathy in STZ-induced diabetes, and this pathology provides a foundation for understanding diabetic gastropathy.

Botulinum toxin type A inhibits rat pyloric myoelectrical activity and substance P release in vivo

The effect of botulinum toxin type A (BTX-A) on rat pyloric myoelectrical activity in vivo and the content and distribution of substance P (SP) in pylorus were investigated, respectively, with electromyography, radioimmunoassay, and immunohistochemistry. A pair of electrodes for recording pyloric myoelectrical activity and a guide cannula for drug injection were implanted into the pylorus. The changes of pyloric myoelectrical activity were recorded followed vehicle, 10, 20, and 40 U/kg body mass of BTX-A injection. Pyloric tissues were dissected for radioimmunoassay and immunohistochemistry after recording. The 3 dosages of BTX-A injections caused the reduction of slow wave of pyloric myoelectrical activity in amplitude but not in frequency and the diminishment of spike activity in amplitude and spike burst. The inhibitory effect of 20 U/kg BTX-A was significantly different from that of 10 U/kg (p<0.05), but not from the effect of 40 U/kg administration (p>0.05). After BTX-A intrasphincteric injection, SP content was reduced in the pylorus, and cell number of SP-immunoreactivity was decreased more in myenteric nerve plexus of circular muscle and in mucosa of pylori. In conclusion, BTX-A inhibits pyloric myoelectrical slow activity in amplitude and spike activity and weakens pyloric smooth muscle contractility depending on threshold of dose or concentration. BTX-A-induced inhibition of pyloric myoelectrical activity implies a mechanism of inhibiting SP release from the autonomic and enteric nervous terminals in the pylorus.

Feeble bronchomotor responses in diabetic rats in association with decreased sensory neuropeptide release

Type I diabetes is associated with a low incidence of asthma. We tested whether a decrease in sensory neuropeptide release is associated with an attenuated bronchoconstrictive response to field stimulation (FS; 100 stimuli, 20 V, 0.1 ms, 20 Hz) in streptozotocin (STZ)-induced diabetes. The organ fluid of the preparations were also tested for substance P, calcitonin gene-related peptide (CGRP), and somatostatin concentrations by RIA. Preparations were from either normal rats or those pretreated with 50 mg/kg STZ iv 8 wk before experiment. A group of STZ-treated animals was supplied with insulin delivery (4 IU/day sc) implants between 4 and 8 wk. A subgroup was formed to study the effect of capsaicin desensitization. The atropine-resistant contraction was attenuated by diabetes without capsaicin-sensitive relaxation response. Exogenous CGRP and substance P potentiated, whereas somatostatin inhibited (1 nM-10 microM) the FS-induced contractions in rings from either group. FS released somatostatin, CGRP, and substance P from 0.17 +/- 0.024, 0.15 +/- 0.022, and 1.65 +/- 0.093 to 0.58 +/- 0.032, 0.74 +/- 0.122, and 5.34 +/- 0.295 in preparations from normal, and from 0.19 +/- 0.016, 0.11 +/- 0.019, and 0.98 +/- 0.116 to 0.22 +/- 0.076, 0.34 +/- 0.099, and 1.84 +/- 0.316 fmol/mg wet wt in preparations from diabetic rats. Insulin supplementation restored neuropeptide release in rings from STZ-treated rats. The results show that the decreased FS-induced contractions occurred with a decrease in sensory neuropeptide release in STZ-diabetic rats.

Impairment of neurogenic inflammatory and anti-inflammatory responses in diabetic rats

The effect was studied of a primary (preconditioning) neurogenic inflammatory challenge induced by electrical stimulation of the peripheral stump of the sciatic nerve (20 V, 0.5 ms, 5 Hz, for 5 min) on neurogenic oedema (5 min later) induced by stimulation of the contralateral sciatic nerve. Plasma extravasation due to the second stimulation was decreased by 52.7+/-3.1% (P<0.01) in normal animals and by 29.7+/-2.2 and 18.1+/-1.5% with 50 mg/kg streptozotocin pretreatment i.v. 4 and 8 weeks previously, respectively. Subsequently, bilateral sciatic nerve stimulation increased baseline plasma somatostatin levels from 6.4+/-0.3, 11. 7+/-1.4, and 16.8+/-3.8 to 28.3+/-2.9 (P<0.01), 17.9+/-3.7, and 25. 1+/-1.7 pmol/l in normal, and 4- and 8-week diabetic animals, respectively. We conclude that experimental diabetes impairs the capability of a preconditioning neurogenic inflammatory episode to elicit a systemic anti-inflammatory effect. This is accompanied by a deficiency in elevation of the plasma somatostatin level in response to nerve stimulation, although the baseline plasma somatostatin level increases proportionally to the duration of experimental diabetes.

Increase in nitric oxide synthase and NADPH-diaphorase in the adrenal gland of streptozotocin-diabetic Wistar rats and its prevention by ganglioside

Levels of nitric oxide synthase (NOS) and NADPH-diaphorase in adrenal glands of streptozotocin-diabetic rats of 8 and 12 weeks' duration compared with control rats were assessed with histo-chemical and biochemical techniques. Adrenal glands from streptozotocin-diabetic rats of 8 weeks' duration treated with ganglioside were examined also. In the adrenal medulla of 8-weeks- and 12-weeks-diabetic rats, NOS-immunoreactive nerve fibres were increased and decreased, respectively; additional NOS-immunoreactive and NADPH-diaphorase stained cells, which appeared to be cortical cells, were located in medulla and cortex compared with controls. Increased intensity in NADPH-diaphorase staining of the cortical cells of diabetic rats was observed also. Ganglioside treatment of the 8-weeks-diabetic rats prevented the diabetic-induced increase in NOS-immunoreactive nerve fibres. Also, it reduced most of the increase in the NOS-immunoreactive and NADPH-diaphorase stained cells and the intensity of NADPH-diaphorase staining of cortical cells. With biochemical assay, a significant increase in NOS activity was found in the adrenal glands from 8-weeks-diabetic rats, and this increase was reduced by ganglioside treatment in four out of six diabetic rats. In summary, streptozotocin-induced diabetes causes an initial increase in the levels of NOS and NADPH-diaphorase in the adrenal gland of rat, which was prevented by ganglioside treatment.

The absence of autonomic perivascular nerves in human colorectal liver metastases

The peptidergic/aminergic innervation of normal liver and tumour blood vessels was investigated in order to determine vascular control with a view to improving the efficacy of hepatic arterial cytotoxic infusion in the treatment of colorectal liver metastases. Selected areas of liver metastases and macroscopically normal liver from resection specimens (n = 13) were studied using light microscope immunohistochemistry for the presence of protein gene product 9.5 (PGP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P (SP) and tyrosine hydroxylase (TH). The ultrastructure of blood vessels supplying liver metastases and their perivascular innervation were also examined by transmission electron microscopy. In the normal liver, perivascular immunoreactive nerve fibres containing PGP, NPY and TH were observed around the interlobular blood vessels and along the sinusoids and the central vein of the hepatic lobule. The greatest density of immunoreactive nerve fibres was seen for PGP, followed (in decreasing order) by NPY and TH. VIP, SP and CGRP immunoreactivity was observed only in nerve bundles associated with the large interlobular blood vessels. In contrast, no perivascular immunoreactive nerves were observed in colorectal liver metastases. Electron microscopy confirmed the absence of perivascular nerves in liver metastases. In addition, it showed that the walls of these blood vessels were composed of a layer of endothelial cells surrounded by an incomplete or, very rarely in the periphery of the tumour, a complete, layer of synthetic phenotype of smooth muscle-like cells. These results imply that the blood vessels supplying liver metastases are bereft of normal neuronal regulation; whether there is a role for endothelial cell control of blood flow in these vessels is not yet known.

Innervation of the rat gastrointestinal sphincters: changes during development and aging

The effect of age on the adrenergic and peptidergic innervation of the lower oesophageal, pyloric and ileocaecal sphincters of the rat was investigated using immunohistochemical techniques. The distribution of nerve fibres containing the neuronal protein, growth associated protein-43, was also studied to determine the integrity of the enteric nervous system during development and aging. The four age groups examined were 2-3 days, 6 weeks, 3 months and 25 months old rats. Using protein gene product 9.5 antibody (a non-specific general neuronal marker), it was revealed that the myenteric ganglia in all sphincter regions were compactly arranged and were smaller in size at neonatal stage getting more spaced out and larger in size with age. There was no obvious change in the structure of the neutral elements with age. In the lower oesophageal sphincter, calcitonin gene-related peptide- and substance P-like immunoreactive nerve fibres showed notable changes in density and fluorescence intensity with age, decreasing and increasing, respectively, with no obvious change in vasoactive intestinal polypeptide- and growth-associated protein-like immunoreactivity. A slight increase in dopamine-beta-hydroxylase-like immunoreactivity was seen in old age. In the pyloric sphincter, there was an increase in calcitonin gene-related peptide- and substance P-like immunoreactivity with a less notable increase in dopamine-beta-hydroxylase-like immunoreactivity. A decrease in vasoactive intestinal polypeptide- and growth-associated protein-43-like immunoreactivity in the circular muscle of the sphincter was seen in old age. In the ileocaecal sphincter there was a marked increase in growth associated protein-43-, vasoactive intestinal polypeptide-, dopamine-beta-hydroxylase and substance P-like immunoreactivity. There was a decrease in the density of calcitonin gene-related peptide-like immuno-reactive nerve fibres in old age. In summary, two main conclusions can be drawn from the results of the present study. First, there was an age-related differential change in the density of immunoreactive nerve fibres containing various neuroactive substances. This indicates a level of plasticity of the various enteric nerve types and may reflect the degree of importance of the different neurotrasmitters in the physiological activities of the specific sphincter.(ABSTRACT TRUNCATED AT 400 WORDS)

Disordered gastric motor function in diabetes mellitus

The application of novel investigative techniques has demonstrated that disordered gastric motility occurs frequently in diabetes mellitus. Gastric emptying is abnormal in about 50% of diabetic patients and delay in gastric emptying of nutrient-containing meals is more common than rapid emptying. The blood glucose concentration influences gastric motility in diabetes. In IDDM patients, gastric emptying is retarded during hyperglycaemia and may be accelerated by hypoglycaemia. Gastroparesis therefore does not necessarily reflect irreversible autonomic neuropathy and blood glucose concentrations must be monitored when gastric motility is evaluated in diabetic patients. There is a poor relationship between gastric emptying and gastrointestinal symptoms and the mechanisms by which abnormal motility causes symptoms are unclear. The introduction of new gastrokinetic drugs has improved therapeutic options for the management of symptomatic patients with gastroparesis considerably. The contribution of disordered gastric emptying to poor glycaemic control is unclear, but the demonstration that the rate of gastric emptying is a major factor in normal blood glucose homeostasis suggests that this is likely to be significant.

Impaired sensory-motor nerve function in the isolated mesenteric arterial bed of streptozotocin-diabetic and ganglioside-treated streptozotocin-diabetic rats

1. Adult male Wistar rats were treated with streptozotocin (65 mg kg-1, i.p.) to induce diabetes. Subgroups of age-matched control and streptozotocin-treated rats were given daily injections of mixed brain bovine gangliosides (60 mg kg-1 body weight, i.p.). At eight weeks after treatment mesenteric arterial beds from rats in each of the four groups were isolated and perfused and the function of perivascular nerves (sympathetic and sensory-motor), endothelium and smooth muscle was assessed. 2. Values for basal tone of mesenteric beds from diabetic and diabetic-ganglioside rats were significantly lower than those of the control and control-ganglioside-treated rats. Perfusion pressures at basal tone were 25.55 +/- 0.8 (n = 11), 22.58 +/- 1.5 (n = 12), 28.42 +/- 1.6 (n = 12) and 30.67 +/- 1.9 (n = 12) mmHg for diabetic, diabetic-ganglioside, control and control-ganglioside-treated rats respectively. 3. There was no difference between the groups with respect to vasoconstrictor responses to sympathetic nerve stimulation, or to doses of noradrenaline. Vasoconstrictor responses to potassium chloride were also similar between the groups. 4. Perivascular nerve stimulation in the presence of the sympathetic blocker guanethidine (3 microM), with tone of the preparation raised with methoxamine (3-100 microM), elicited frequency-dependent vasodilatation of mesenteric arterial beds due to transmitter release from sensory-motor nerves. Sensory-motor nerve-induced vasodilator responses of mesenteric arterial beds from streptozotocin-diabetic and ganglioside-treated diabetic rats were significantly smaller than those of mesenteric beds from the controls (untreated and ganglioside-treated). Vasodilator responses to exogenously applied calcitonin gene-related peptide, the principal vasodilator transmitter released from these nerves, were not different between the groups. Vasodilator responses to the sensory neurotoxin capsaicin were also not different between the groups.5. Endothelium-dependent vasodilator responses to acetylcholine were similar between the groups as were those to the endothelium-independent vasodilator sodium nitroprusside.6. These results indicate that streptozotocin-induced diabetes produces marked impairment of sensory motor nerve function in the rat mesenteric arterial bed. The significantly lower basal perfusion pressures of mesenteric beds from diabetic rats compared to controls may be a reflection of sympathetic dysfunction, but no differences were apparent from the vasoconstrictor responses produced when sympathetic nerves were electrically stimulated. There was no evidence for changes in endothelial vasodilator function, or smooth muscle vasodilator and vasoconstrictor function. Ganglioside treatment did not modify any aspect of vascular function of mesenteric beds from streptozotocin-diabetic or control rats.