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Biomedical subjects

K A Sharkey

Publications and source records attributed to K A Sharkey.

At least 91 records · Page 5Linked to original sources
PubMed1994

c-Myc antigens in the mammalian enteric nervous system.

We have investigated the presence of c-Myc-like antigens in the enteric nervous system of the guinea-pig, rat, dog, sheep, monkey and human. c-Myc-like immunoreactivity was demonstrated by immunohistochemistry in the enteric nervous system of all animals tested, with one or more monoclonal antibodies raised against peptide sequences found in the human c-Myc protein. While in most cases the labelling was nuclear, cytoplasmic labelling was also observed. In the guinea-pig enteric nervous system, c-Myc-like immunoreactivity detected by two different antibodies remained detectable for up to 4 h in the presence of cycloheximide. The size and density of labelled nuclei in the ileal submucous plexus were consistent with exclusive neuronal labelling by one antibody and neuronal plus glial labelling by the other. Double-labelling with antiserum directed against vasoactive intestinal peptide revealed a subset of c-Myc-immunoreactive neurons that also contain this neuropeptide. Anti-c-Myc antibodies specifically immunoprecipitated proteins from guinea-pig myenteric plexus-longitudinal muscle preparations whose sizes were consistent with previous observations for c-Myc antigens and whose distribution was consistent with synthesis in the myenteric plexus. We conclude that c-Myc proteins are expressed in mammalian enteric neurons and that they have characteristics similar to those of c-Myc proteins in other nonproliferative cells.

Animals↗
PubMed1994

Modulation of ion channels in rod photoreceptors by nitric oxide.

Subcellular compartments in the outer retina of the larval tiger salamander were identified as likely sites of production of nitric oxide (NO), a recently recognized intercellular messenger. NADPH diaphorase histochemistry and NO synthase immunocytochemistry labeled photoreceptor ellipsoids and the distal regions of bipolar and glial cells apposing photoreceptor inner segments, suggesting a role for NO in visual processing in the outer retina. We investigated the actions of NO on several rod photoreceptor ion channels. Application of the NO-generating compound S-nitrosocysteine increased Ca2+ channel current and a voltage-independent conductance, but had no affect on voltage-gated K+ or nonspecific cation currents. Given the steep relation between voltage-dependent Ca2+ influx and photoreceptor synaptic output, these results indicate that NO could modulate transmission of the photoresponse to second order cells.

Amino Acid Oxidoreductases↗
PubMed1994

Beneficial effects of local or systemic lidocaine in experimental colitis.

Neuropeptides liberated from enteric neurons have been suggested to contribute to the inflammatory process in colitis. Based in part on this evidence, lidocaine enemas have recently been suggested as a treatment for ulcerative colitis, but their effects have yet to be fully characterized. We have assessed the effects of lidocaine on the development and maintenance of colitis induced by trinitrobenzenesulfonic acid (TNBS) in rats. In the initial experiments, rats were given lidocaine [5-100 mg/kg intrarectally] 30 min before TNBS administration, and the severity of colitis was assessed 6-24 h later. In subsequent experiments, rats received lidocaine intrarectally or subcutaneously 30 min before TNBS administration and once daily for 7 days. The severity of colitis was assessed by blind macroscopic scoring, measurement of myeloperoxidase activity, and histological evaluation. Lidocaine dose dependently reduced the severity of colitis and the infiltration of granulocytes at 24 h and 7 days post-TNBS. At the latter time point, lidocaine was also found to improve the histological appearance of the tissue and significantly reduce mucosal mast cell hyperplasia. Beneficial effects were also evident when intrarectal lidocaine treatment was initiated after induction of colitis or when lidocaine was given subcutaneously. Granulocyte infiltration into the colon could also be attenuated by a substance P receptor antagonist. These results suggest that lidocaine can exert anti-inflammatory effects in colitis, perhaps by virtue of its effects on intrinsic and/or extrinsic nerves.

Administration, Rectal↗
PubMed1994

Fos expression in ferret dorsal vagal complex after peripheral emetic stimuli.

The aim of this study was to investigate neuronal activation in the dorsal vagal complex of the halothane-anesthetized ferret after peripheral emetic stimuli. Neuronal activity was studied by examining the distribution of the nuclear phosphoprotein Fos using immunohistochemistry. The emetic stimuli used were electrical stimulation of the supradiaphragmatic vagal communicating branch (SVCB) or intraduodenal injection of hypertonic saline. Electrical stimulation of the SVCB induced the densest Fos expression within the medial subnucleus of the nucleus of the solitary tract. After hypertonic saline injection, the greatest density of Fos-positive nuclei was observed within the area postrema and also in the medial subnucleus of the nucleus of the solitary tract. It was concluded that the emetic response to hypertonic saline involves neurons in both the area postrema and the nucleus of the solitary tract, especially the medial subnucleus, and that the medial subnucleus is important in the emetic response to SVCB stimulation.

Animals↗
PubMed1993

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies.

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.

Animals↗
PubMed1993

Involvement of L-arginine-nitric oxide pathways in neural relaxation of the sphincter of Oddi.

To evaluate if L-arginine-nitric oxide-pathways are involved in the neural relaxation of the sphincter of Oddi, we studied the effect of nitric oxide synthase inhibition on electrical field stimulation-induced relaxation of the sphincter of Oddi in the guinea pig in vitro. After incubation with atropine (1 microM), phentolamine (1 microM) and propranolol (1 microM), histamine (50 microM) and cholecystokinin-octapeptide (25 nM) produced similar increases in sphincter tone. Subsequent field stimulation induced sphincteric relaxation, that was significantly greater when the initial tone had been raised by cholecystokinin (5 Hz, 59 +/- 9%; 10 Hz, 79 +/- 9%) compared to histamine (5 Hz, 27 +/- 3%; 10 Hz, 40 +/- 7%). N-omega-Nitro-L-arginine methyl ester (L-NAME, 100 microM), which competitively inhibits nitric oxide synthase, markedly suppressed this relaxation. The subsequent addition of L-arginine (1 mM), but not D-arginine (1 mM), restored the relaxation. Hexamethonium (100 microM) did not affect the relaxation, but tetrodotoxin (1 microM) completely abolished it. Sodium nitroprusside caused a dose-dependent relaxation of the sphincter (ED50 13 nM), which was unaffected by L-NAME. In conclusion, endogenous nitric oxide synthase products represent a major transmitter of non-adrenergic non-cholinergic relaxation of the sphincter of Oddi in the guinea pig. This relaxation is partially facilitated by cholecystokinin.

Amino Acid Oxidoreductases↗
PubMed1993

Interleukin 1 beta-induced increase in substance P in rat myenteric plexus.

BACKGROUND: Substance P (SP) is increased in the inflamed intestine of Trichinella spiralis-infected rats, but the underlying mechanism is unknown. Interleukin 1 beta (IL-1 beta) messenger RNA and protein is expressed in the longitudinal muscle-myenteric plexus (LM-MP) of this model. Thus, the purpose of the study was to examine the ability of human recombinant IL-1 beta (hrIL-1 beta) to increase SP in LM-MP preparations from the intestine of noninfected rats. METHODS: LM-MP preparations were incubated with hrIL-1 beta, and immunoreactive SP (IR-SP) was assessed in the tissues by radioimmunoassay or immunohistochemistry. RESULTS: hrIL-1 beta increased IR-SP in the tissue in a time- and concentration-dependent manner, being maximal after 6 hours at a concentration of 10 ng/mL. The IR-SP could be depleted by scorpion venom, and immunohistochemistry revealed increased staining for SP within nerves of the LM-MP. The action of IL-1 beta was dependent on protein synthesis, was receptor mediated, and was not due to endotoxin contamination of the cytokine preparation. CONCLUSIONS: hrIL-1 beta stimulates the synthesis of SP in myenteric nerves of rat intestine.

Animals↗
PubMed1993

Capsaicin treatment blocks development of hyperkinetic circulation in portal hypertensive and cirrhotic rats.

To investigate a possible role of primary afferent innervation in the pathogenesis of hyperkinetic circulation in cirrhosis or portal hypertension, we used capsaicin to denervate the primary afferent nerves. Rat pups were injected with capsaicin (50 mg/kg) or a vehicle and were allowed to grow. When they reached young adulthood, operations to induce portal hypertension by portal vein stenosis or cirrhosis by bile duct ligation were performed. A control group had sham operation. Cardiac output and regional blood flows were measured in unrestrained conscious rats by radioactive microspheres. Capsaicin-treated portal hypertensive and cirrhotic rats had cardiac output and systemic vascular resistance similar to sham-operated rats, whereas the vehicle-treated portal hypertensive and cirrhotic rats showed the hyperkinetic circulation. No hemodynamic effect of capsaicin on sham-operated rats was detected. Capsaicin-treated rats did not demonstrate a splanchnic or renal hyperemia, but the percentage of cardiac output in these vascular beds was similar to controls. These results suggest that capsaicin treatment blocked the generalized vasodilatation in cirrhotic and portal hypertensive rats. Arterial pressure and heart rate were not modified in any group. These results show that denervation of capsaicin-sensitive primary afferent nerves in cirrhotic and portal hypertensive rats blocked the expected development of hyperkinetic circulation. We conclude that primary afferent innervation may be important in the genesis of hyperdynamic circulation in portal hypertension and cirrhosis.

Analysis of Variance↗
PubMed1993

Substance P levels in experimental ileitis in guinea pigs: effects of misoprostol.

Substance P, a neuropeptide mediator of inflammation, was quantified during the evolution of trinitrobenzene sulfonic acid (TNBS)-induced ileitis in guinea pigs. Ileitis was induced by a single intraluminal injection of TNBS (30 mg/kg in 50% ethanol). Misoprostol, a prostaglandin E1 analogue, was administered parenterally (30 mg/kg sc twice daily) in a group of TNBS-treated animals. Control guinea pigs received intraluminal saline (sham) or 50% ethanol (TNBS vehicle). Guinea pigs were evaluated at day 1, 3, 7, 14, or 30 after ileitis induction for substance P content (radioimmunoassay) and distribution (immunohistochemistry), morphology, myeloperoxidase (MPO) activity, and protein leak into the gut lumen. TNBS administration caused an increase in ileal MPO activity that peaked at day 7 and increased mucosal leak of protein. Misoprostol attenuated the granulocyte infiltration (MPO) response to TNBS but exacerbated the mucosal leak of protein. Substance P levels in whole ileal segments were unaltered from baseline on day 1 in all groups. On day 3 a marked decrease in ileal substance P content was evident in the TNBS and TNBS + misoprostol groups. As early as day 1, immunohistochemistry suggested that the decreased substance P content was confined to the mucosa and submucosa, because myenteric plexus staining was not reduced. Loss of staining in the perivascular nerves was particularly marked. Substance P content and distribution returned to baseline by day 30 post-TNBS, although MPO activity remained slightly elevated. We concluded that TNBS ileitis is associated with a marked reduction in mucosal and submucosal substance P content in parallel with the inflammatory response. Although misoprostol attenuated granulocyte infiltration in this model, it did not prevent the disturbances in enteric substance P or mucosal protein leak.

Animals↗
PubMed1993

Neural mediation of cholera toxin-induced mucin secretion in the rat small intestine.

We examined the role of enteric nerves in cholera toxin (CT)-induced mucin secretion in proximal and distal regions of rat small intestine. Stimulation of intestinal loops with 120 micrograms (1.5 mumol) CT using an in vitro open-loop model resulted in an approximately four-fold increase in luminal mucin content over unstimulated controls in both regions of the gut. Prior treatment of loops with tetrodotoxin had no effect on the amount of mucin released in response to CT. However, permanent destruction of primary sensory afferent nerves by neonatal treatment of rats with capsaicin reduced the mucin response to CT to baseline levels in both regions. In normal animals, atropine resulted in approximately 40% inhibition of mucin secretion in both the proximal and distal small intestine. The atropine-sensitive secretory response appears to be a component of the capsaicin-sensitive response. These results suggest that choleraic mucin secretion is mediated primarily by a capsaicin-sensitive neurogenic pathway involving local activation of sensory nerves, which may then elicit mucin secretion through interaction with cholinergic nerves.

Animals↗
PubMed1992

Peptides in the gastrointestinal tract in human immunodeficiency virus infection. The GI/HIV Study Group of the University of Calgary.

The presence of immunoreactivity to the neuronal phosphoprotein B-50 and the peptides bombesin, calcitonin gene-related peptide, galanin, neurotensin, neuropeptide Y, somatostatin, substance P, and vasoactive intestinal polypeptide was examined in biopsy specimens from the duodenum and rectum of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative male homosexual patients. The distribution of B-50 and the peptides was correlated with HIV serology, number of CD4+ lymphocytes, and the presence of HIV in biopsy culture. There was a very low incidence of enteric pathogens in both groups of patients. It was found that HIV-seropositive patients had a greater incidence of abnormal patterns of immunoreactivity (reduced intensity and/or density of innervation) in enteric nerves and enteroendocrine cells than HIV-seronegative patients. A reduction of substance P immunoreactivity was significantly correlated with reduced CD4+ lymphocyte count and HIV status; a similar trend was also seen for somatostatin and vasoactive intestinal polypeptide. Using B-50 as a marker, it was found that both groups of patients had altered patterns of immunoreactivity in rectal nerves. The findings of this study suggest that some of the clinical symptoms associated with HIV infection may be caused by a specific HIV enteropathy that influences enteric nerve and/or enteroendocrine cell function by altering the density of peptide immunoreactivity.

Adult↗
PubMed1992

Differential sensitivities of the sphincter of Oddi and gallbladder to cholecystokinin in the guinea pig: their role in transsphincteric bile flow.

Cholecystokinin (CCK) is considered to simply contract the gallbladder and relax the sphincter of Oddi with meals. In this study, we examined this hypothesis by investigating the action of CCK on the sphincter of Oddi and gallbladder of the guinea pig. The experimental design used an in vitro preparation of the sphincter of Oddi to measure contraction of the circular muscle. CCK increased tone in both the gallbladder and the sphincter of Oddi in a concentration-dependent manner. The normalized concentration-response curves for CCK, however, revealed that the gallbladder had a greater sensitivity to CCK (ED50 7 nM) than the sphincter of Oddi (ED50 22 nM; p < 0.01). Conversely, the sphincter was more sensitive to bethanechol than was the gallbladder. When the sphincter of Oddi was stimulated maximally with CCK in the presence of atropine (10(-6) M) or tetrodotoxin (10(-6) M), the contractile response was significantly reduced (p < 0.05) although not abolished. Conversely, atropine completely abolished the responses to bethanechol (10(-3) M) and transmural field stimulation (70 V, 10 Hz, 1 ms, for 20 s). Transmural field stimulation of the sphincter that had been precontracted with CCK (26 nM) caused a transient, initial relaxation followed by contraction. Pretreatment with atropine augmented the duration of this relaxation, which could be completely abolished by tetrodotoxin. Thus, CCK contracts the sphincter of Oddi in the guinea pig by a direct (myogenic) and a neural (likely cholinergic) mechanism. Relaxation of the sphincter of Oddi also occurs in the guinea pig via noncholinergic inhibitory nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Nutritional status and food intake in human immunodeficiency virus infection. GI/HIV Study Group.

Nutritional status and food intake of HIV+ and HIV- homosexual men that were free from enteric pathogens were compared. Food intake (7-day weighed record), anthropometry, and D-xylose excretion were measured in 44 patients (9 HIV-, 35 HIV+). HIV+ patients were found to be thinner, based on anthropometric measurements of skinfold thickness (p < 0.05) and percentage body fat (p < 0.05), and they also tended to be lighter than the HIV- patients. No differences were observed in the arm muscle mass or the food intake of the two groups. In the HIV+ patients, regression analysis was used to correlate changes in nutritional status with progression of the disease, using CD4+ lymphocyte count as a measure of severity. A decrease in CD4 count positively correlated with a decrease in weight (r = 0.48, p < 0.01), body mass index (r = 0.41, p < 0.05), and arm muscle area (r = 0.42, p < 0.01). Energy intake (r = 0.67, p < 0.01), serum albumin (r = 0.52, p < 0.01), and D-xylose excretion (r = 0.57, p < 0.0001) also positively correlated with CD4 count. Multiple regression analysis revealed a relationship between CD4 count, weight, and energy intake, indicating that as the disease progresses, a decline in weight is seen parallel to a reduction in food intake. These data indicate that changes in body composition and nutritional status are present throughout the stages of HIV disease, though no causal relationships can be interpreted from this study. The initial changes appear to be due to loss of fat stores, as determined by anthropometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthropometry↗
PubMed1991

Distribution and function of brain natriuretic peptide in the stomach and small intestine of the rat.

The distribution and function of brain natriuretic peptide (BNP) was studied in the rat stomach and jejunum. BNP-like immunoreactive nerves were found in the myenteric plexus, circular muscle, submucosa and in the crypt region of the jejunum. In the stomach, BNP-like immunoreactivity was found in the myenteric plexus, circular muscle, submucosa and at the base of the gastric glands. In the submucosa, BNP-like immunoreactivity was often associated with blood vessels. In segments of rat jejunum mounted in Ussing chambers, serosal exposure to rat BNP caused a concentration-dependent increase in short circuit current. A maximal effect of 18 +/- 4 microA/cm2 was observed with 1 microM BNP. The effect was quantitatively and qualitatively similar to that elicited by serosal exposure to equimolar atrial natriuretic peptide. The response to BNP was reduced by 88% in chloride free Kreb's buffer, by 83% in tissues pretreated with cinanserin, an antagonist of the 5-HT2 subtype of the 5-hydroxytryptamine receptor, and by 96% in tissues pretreated with tetrodotoxin, a blocker of axonal conduction. These results are consistent with a physiological role for BNP as a neuromodulator of gastrointestinal electrolyte transport.

Animals↗
PubMed1991

Capsaicin-sensitive vagal stimulation-induced gastric acid secretion in the rat: evidence for cholinergic vagal afferents.

1. The effects of electrical vagal stimulation on frequency-dependent gastric acid secretion were investigated in urethane-anaesthetized rats in vivo. 2. Stimulation at 4, 16 or 32 Hz was performed in rats treated with atropine (1 mg kg-1, i.v.), hexamethonium (10 mg kg-1, i.v. bolus and 1 mg kg-1 min-1, i.v. infusion) or atropine and hexamethonium (doses as above); in some experiments pentagastrin (1.2 micrograms kg-1 h-1, i.v. infusion) was infused prior to stimulation. 3. Maximal acid secretion occurred at 16 Hz. This was significantly reduced but not abolished by atropine or hexamethonium and completely abolished after atropine and hexamethonium. In the presence of pentagastrin, the acid secretory response to 16 Hz stimulation was augmented, atropine or hexamethonium reduced stimulated secretion by about 70%, whereas atropine and hexamethonium completely abolished stimulated secretion. 4. In rats in which the vagus nerve was pretreated with capsaicin 10-14 days before experimentation there was a significant reduction (by about 40%) in stimulated acid secretion at 16 Hz, which was virtually abolished by atropine treatment. After acute treatment of the vagus nerve with capsaicin (at the time of experimentation) maximally stimulated acid secretion was significantly reduced by about 50%. 5. Taken together, these results indicate that capsaicin-sensitive afferent fibres contribute to the acid secretory response induced by electrical vagal stimulation in the rat. Based on pharmacological evidence, the capsaicin-sensitive afferent fibres may be cholinergic, since atropine and hexamethonium totally abolish vagal stimulation-induced acid secretion.

Animals↗
PubMed1990

Distribution of growth-associated protein, B-50 (GAP-43) in the mammalian enteric nervous system.

The presence of the growth-associated protein, B-50 (also known as GAP-43) was investigated in the adult mammalian enteric nervous system. The small intestine of rat, ferret and human was examined by immunohistochemistry. Dense B-50-like immunoreactivity was localized in nerves throughout the wall of the rat, ferret and human small intestine, notably in the myenteric and submucous plexuses, where in the ferret ileum it co-localized with vasoactive intestinal polypeptide-immunoreactive fibre groups. Material with the biochemical and immunological characteristics of rat B-50 was extracted from the rat ileum. In-situ hybridization demonstrated that enteric neurons express B-50. These findings are consistent with a role for B-50 in the documented plasticity of the adult enteric nervous system.

Animals↗