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Biomedical subjects

M J Kelly

Publications and source records attributed to M J Kelly.

At least 55 records · Page 3Linked to original sources
PubMed1999

Activation of an inwardly rectifying K+ conductance by orphanin-FQ/nociceptin in vasopressin-containing neurons.

The orphanin-FQ/nociceptin (OFQ/N) receptor (previously, ORL1, LC132) has been shown to be coupled to an inwardly rectifying K+ conductance in several neuronal populations. Although OFQ/N receptor mRNA is densely expressed in the supraoptic nucleus (SON), little is known about its coupling to effector system(s). The present study examined the effects of OFQ/N on guinea pig magnocellular neurons within the SON using intracellular recording from hypothalamic slices. In the presence of tetrodotoxin, OFQ/N hyperpolarized 48 of 48 SON magnocellular neurons, 24 of which were subsequently identified by immunocytochemistry as arginine vasopressin positive (AVP+). Nineteen of the 48 SON neurons, including 7 which were AVP+, responded to OFQ/N with an outward current that reversed at the K+ equilibrium potential (EK+) and a decrease in slope resistance consistent with the activation of an inwardly rectifying K+ channel. In 4 of these neurons, BaCl2 significantly attenuated both the hyperpolarization and the decrease in slope resistance induced by OFQ/N. Twenty-one SON neurons, 13 of which were AVP+, responded to OFQ/N with an increase in slope resistance which did not reverse at EK+. An additional 5 neurons (2 were AVP+) were treated with the gap junction blocking agent carbenoxolone (CARB). CARB induced a small hyperpolarization, increased slope resistance and significantly reduced the subsequent OFQ/N-induced hyperpolarization. However, when the CARB and CARB plus OFQ/N hyperpolarizations were summed in these 5 cells, they were no different than the OFQ/N hyperpolarization alone. The effect of two putative OFQ/N receptor antagonists was also evaluated. The kappa3-opioid antagonist naloxone benzoylhydrazone was without effect (n = 3), and the 13-amino-acid [Phe1Psi(CH2-NH)Gly2]OFQ/N(1-13)NH2 OFQ/N analog produced a small hyperpolarization on its own in addition to partially antagonizing the effects of OFQ/N (n = 3). Taken together, these results suggest that OFQ/N acts upon SON neurons through two mechanisms, one which hyperpolarizes the neuron by activating an inwardly rectifying K+ conductance, and another which may increase membrane resistance by closing the low-resistance gap junctions.

Animals↗
PubMed1998

A powerful GABA(B) receptor-mediated inhibition of GABAergic neurons in the arcuate nucleus.

We combined histofluorescence with in situ hybridization to identify GABAergic neurons in the arcuate nucleus (ARC) following electrophysiological recordings, using GAD65 as a marker. Intracellular recordings were made in hypothalamic slices prepared from ovariectomized guinea pigs. Over 90% of ARC neurons tested with the GABA(B) receptor agonist baclofen responded with a membrane hyperpolarization or an outward current. The hyperpolarization was dose-dependent, and the GABA(B) receptor antagonist CGP 35,348 produced a rightward shift in the agonist dose-response curve. Agonist potency was lower, and the efficacy greater, in GAD-positive neurons. The use of this novel technique for identifying GABAergic neurons thus reveals differences in the pharmacodynamics of GABA(B) receptor activation GABAergic and non-GABAergic ARC neurons.

Animals↗
PubMed1998

mu-Opioid agonist-stimulated [35S]GTPgammaS binding in guinea pig hypothalamus: effects of estrogen.

mu-Opioid receptors play a critical role in the regulation of the female reproductive cycle, and estrogen modulates the coupling of mu-opioid receptors to a potassium channel in the basal hypothalamus (BH) of the female guinea pig. Therefore, we ascertained the distribution of mu-opioid receptors in the BH with autoradiography using the mu-opioid selective agonist [3H]DAMGO. In addition, we investigated the effects of estrogen on DAMGO- or the GABAB receptor agonist baclofen-stimulated [35S]GTPgammaS binding in the BH. Based on the high density of mu-opioid receptors, but the lack of effects of estrogen on [35S]GTPgammaS binding, we conclude that mu-opioid receptor interaction with its G-protein is not the target of estrogen's actions.

Animals↗
PubMed1998

Proopiomelanocortin (POMC) mRNA expression: distribution and region-specific down-regulation by chronic morphine in female guinea pig hypothalamus.

There is compelling evidence that endogenous opioid peptides are regulated by exogenous opiates. Our previous studies have shown that the mu-opioid receptor protein and mRNA are down-regulated in the mediobasal hypothalamus of the female guinea pig following chronic morphine treatment. In addition, electrophysiological studies have shown that hypothalamic beta-endorphin (beta-EP) neurons express mu-opioid receptors that are uncoupled and down-regulated following chronic morphine treatment. Currently, we tested the hypothesis that chronic morphine, which produces down-regulation of mu-opioid receptors, causes a down-regulation of pro-opiomelanocortin (POMC, the precursor of beta-EP) mRNA expression in female guinea pig hypothalamus. Female guinea pigs were ovariectomized and implanted subcutaneously (s.c.) with 4 x 75 mg pellets for 2 days plus six more pellets of either morphine (n = 6) or placebo (n = 6) for another 5 days. Animals were sacrificed between 1000 and 1100 h on day 7. The expression of POMC mRNA were investigated using in situ hybridization histochemistry with a guinea pig specific 35S-labeled cRNA probe in hypothalamic tissue sections. POMC mRNA was localized to the arcuate nucleus (Arc) and median eminence (ME) of the medial basal hypothalamus. The distribution pattern was the same in both morphine and placebo control animals. However, the density of silver grains was less in morphine treated animals versus placebo control animals. Overall, the level of POMC mRNA was decreased by 22% in the Arc of morphine-treated guinea pigs as compared with the placebo controls (p < 0.05). This decrease in POMC mRNA expression was even greater in the caudal Arc (28%, p < 0.01) in morphine-treated animals. These results suggested that the biosynthetic activity of POMC neurons is down-regulated with chronic exposure to morphine.

Animals↗
PubMed1998

The limited role of myocardial fluorine-18 fluorodeoxyglucose imaging in candidates for cardiac transplantation: a planar imaging study.

This study compares the incidence and extent of hibernating myocardium (defined by myocardial perfusion/metabolism mismatch) in 28 cardiac transplant candidates with ischaemic cardiomyopathy and in 16 other patients with coronary artery disease (CAD) undergoing viability assessment. It then reviews the impact of myocardial perfusion metabolism imaging on management decisions in the transplant candidates at 6 months after scintigraphy. Each patient underwent a planar myocardial thallium-201 and fluorine-18 fluorodeoxyglucose scan on a modified gamma camera. Perfusion/metabolism mismatch was sized semi-quantitatively and each patient was assigned a global mismatch score. Transplant candidates had a lower left ventricular ejection fraction (LVEF) (P < 0.0002) and extent of hibernation myocardium (lower global mismatch score: P = 0.005) than other CAD patients but the difference in respect of mismatch frequency (8/28 vs 9/16 patients) did not reach statistical significance. Transplant candidates with LVEF < 20% had a lower global mismatch score (P < 0.02) than those with an LVEF > or = 20%. Interestingly two of three other CAD patients with LVEF < 20% had a moderate mismatch. Follow-up studies revealed the lack of impact of metabolic imaging as none of the three transplant candidates who eventually underwent revascularisation had hibernating myocardium and transplantation was offered to one of only two candidates with more than one minor mismatch. Thus metabolic imaging in potential transplant candidates may be of limited value because of the very low extent of hibernating myocardium, particularly if LVEF is below 20% and where clinical decisions are often based on many other factors.

Adult↗
PubMed1998

The peptide orphanin FQ inhibits beta-endorphin neurons and neurosecretory cells in the hypothalamic arcuate nucleus by activating an inwardly-rectifying K+ conductance.

Orphanin FQ (OFQ) is a novel heptadecapeptide whose structure resembles that of dynorphin A1-17. Its receptor shares appreciable homology with mu-, delta- and kappa-opioid receptors, and is highly expressed in the hypothalamus. The present study examined the effects of OFQ on neurons within the arcuate nucleus (ARC) of the mediobasal hypothalamus, using intracellular recordings from coronal slices. In current clamp, OFQ produced a hyperpolarization of ARC neurons, including those immunopositive for beta-endorphin, tyrosine hydroxylase and gonadotropin-releasing hormone. This hyperpolarization was dose-dependent, insensitive to antagonism by naloxone and was associated with a decrease in input resistance. In voltage clamp, OFQ produced an outward current associated with an increase in conductance. Varying the extracellular K+ concentration shifted the reversal potential for the OFQ response to the degree predicted by the Nernst equation. Furthermore, barium chloride markedly attenuated both the OFQ-induced hyperpolarization and decrease in input resistance. Administration of maximally effective concentrations of OFQ, followed by coadministration of maximal concentrations of either OFQ and the mu-opioid receptor agonist DAMGO or OFQ and the GABAB receptor agonist baclofen produced additive hyperpolarizations and outward currents. If DAMGO was applied first, followed by the coadministration of DAMGO and OFQ, then the responses were occluded. Taken together, these results indicate that OFQ inhibits beta-endorphin neurons, as well as A12 dopamine and GnRH neurosecretory cells, within the ARC by activating a subset of inwardly-rectifying K+ channels. This suggests that OFQ is not only an antiopioid peptide, but that it also modulates the hypothalamo-pituitary axis and, ultimately, reproductive behavior.

Animals↗
PubMed1998

Protein kinase A maintains cellular tolerance to mu opioid receptor agonists in hypothalamic neurosecretory cells with chronic morphine treatment: convergence on a common pathway with estrogen in modulating mu opioid receptor/effector coupling.

The present study examined protein kinase A (PKA) and protein kinase C (PKC) involvement in the maintenance of cellular tolerance to mu opioid receptor agonists resulting from chronic opiate exposure in neurosecretory cells of the hypothalamic arcuate nucleus (ARC). The possibility that the diminution of mu opioid receptor/effector coupling produced by acute 17beta-estradiol or chronic opiate exposures is mediated by a common kinase pathway also was investigated. Intracellular recordings were made in hypothalamic slices prepared from ovariectomized female guinea pigs. The mu opioid receptor agonist D-Ala2, N-Me-Phe4, Gly-ol5-enkephalin (DAMGO) produced dose-dependent hyperpolarizations of ARC neurons. Chronic morphine treatment for 4 days reduced DAMGO potency 2.5-fold with no change in the maximal response. This effect was mimicked by a 20-min bath application of the PKA activator cAMP, Sp-isomer, or the PKC activator phorbol-12,13-dibutyrate. A 30-min bath application of the broad-spectrum protein kinase inhibitor staurosporine completely abolished the reduced DAMGO potency seen in morphine-tolerant neurosecretory cells, including those immunopositive for gonadotropin-releasing hormone. The effect of staurosporine was mimicked by the PKA inhibitor cAMP, Rp-isomer, but not by the PKC inhibitor calphostin C. Finally, a 20-min bath application of 17beta-estradiol did not further reduce DAMGO potency in morphine-tolerant ARC neurons. Therefore, increased PKA activity maintains cellular tolerance to mu opioid receptor agonists in ARC neurosecretory cells caused by chronic morphine treatment. Furthermore, acute 17beta-estradiol and chronic opiate treatments attenuate mu opioid receptor-mediated responses via a common PKA pathway.

Analgesics, Opioid↗
PubMed1997

Cerebral noradrenaline spillover and its relation to muscle sympathetic nervous activity in healthy human subjects.

Studies using internal jugular vein blood sampling in human subjects have demonstrated the release of noradrenaline from the brain and have provided a link between central nervous system noradrenergic neuronal activity and renal, cardiac and total body sympathetic activity. The aim of this study was to further categorise the dependence of regional sympathetic nervous function on central nervous system noradrenergic neuronal processes by combining measures of internal jugular venous noradrenaline spillover, as an indicator of brain noradrenaline release, and cerebral blood flow scans with measures of the overall integrated neuronal firing rate for the body as a whole, the spillover of noradrenaline into the coronary sinus and with measurements of resting muscle sympathetic nerve activity. Positive veno-arterial plasma noradrenaline gradients were found across the brain, with the plasma concentration being 17 +/- 3% (p < 0.01) greater in the internal jugular vein. Linear regression analysis revealed a significant relationship between the degree of muscle sympathetic nerve activity and the spillover of noradrenaline from subcortical brain regions (y = 0.1 x + 16.0; r = 0.81, p < 0.02). The rate of spillover of noradrenaline for the body as a whole also bore a significant association with the rate of subcortical noradrenaline spillover (y = 0.01x + 2.33; r = 0.71, p < 0.05). Cortical noradrenaline spillover was not related to any of the sympathetic nervous system parameters measured in this study. The demonstration of a direct relationship between the rate of peroneal nerve firing and the spillover of noradrenaline from subcortical brain regions provides further support for the concept of central nervous system noradrenergic cell groups behaving in a sympathoexcitatory role.

Adult↗
PubMed1997

Sports supplement drinks and dental health in competitive swimmers and cyclists.

AIM: To assess dental status and sports supplement uptake in swimmers and cyclists. To determine chemico-physical properties of the most popular sports drinks. DESIGN: Descriptive, prevalence study of tooth wear and caries experience. Questionnaire analysis of sports drinks usage. SETTING: Two public swimming pools in Liverpool and three cycle clubs in North West England. SUBJECTS AND METHOD: A convenience sample of swimmers and cyclists was examined for caries and tooth wear. A questionnaire ascertained which sports drinks were consumed and their pattern of consumption. pH and titratable acidity, concentrations of calcium, phosphate and fluoride, and viscosity were analysed. Salivary flow rate in response to these drinks and water was also determined. RESULTS: 25 swimmers and 20 cyclists participated. Caries experience and tooth wear into dentine (excluding incisally exposed dentine) was significantly more frequent among cyclists (P < 0.05). Cyclists had significantly more upper palatal wear (P < 0.001). Pattern of sport drink consumption between the two groups was significantly different (P < 0.001). pH range of the most popular sport drinks was 2.4-4.5. Salivary flow rate after a 1-minute rinse was significantly lower (P < 0.05) with one drink (0.47 ml/min) and water (0.41 ml/min) compared with the other drinks. CONCLUSIONS: An association between caries or erosive tooth wear and sport drink consumption was not found. However, the erosive potential of sport drinks is real and must be borne in mind as an aetiological factor for erosion in young people.

Adolescent↗
PubMed1997

Modulation of G protein-coupled receptors by an estrogen receptor that activates protein kinase A.

17beta-Estradiol (E2) rapidly (<20 min) attenuates the ability of mu-opioids to hyperpolarize guinea pig hypothalamic (beta-endorphin) neurons. In the current study, we used intracellular recordings from guinea pig hypothalamic slices to characterize the receptor and intracellular effector system mediating the rapid effects of E2. E2 acted stereospecifically with physiologically relevant concentration dependence (EC50 = 8 nM) to cause a 4-fold reduction in the potency of a mu-opioid agonist to activate an inwardly rectifying K+ conductance. Using Schild analysis to estimate the affinity of the mu-opioid receptor for an antagonist (naloxone), we found that estrogen did not compete for the mu-opioid receptor or alter the affinity of the mu receptor. Both the nonsteroidal estrogen diethylstilbestrol and the "pure" antiestrogen ICI 164,384 blocked the actions of E2, the latter with a subnanomolar affinity. The protein synthesis inhibitor cycloheximide did not block the estrogenic uncoupling of the mu-opioid receptor from its K+ channel, implying a nongenomic mechanism of action by E2. The actions of E2 were mimicked by the protein kinase A (PKA) activators forskolin and cAMP, Sp-isomer triethylammonium salt. Furthermore, the selective PKA antagonists cAMP, Rp-isomer triethylammonium salt and KT5720, which have different chemical structures and modes of action, both blocked the effects of E2. Thus, estrogen binds to a specific receptor that activates PKA to rapidly uncouple the mu-opioid receptor from its K+ channel. Because we have previously shown that gamma-aminobutyric acidB receptors are also uncoupled by estrogen, this mechanism of action has the potential to alter synaptic transmission via G protein-coupled receptors throughout the brain.

Analgesics↗
PubMed1997

Tolerance to mu-opioid receptor agonists but not cross-tolerance to gamma-aminobutyric acid(B) receptor agonists in arcuate A12 dopamine neurons with chronic morphine treatment.

The present study examined the potential for cross-tolerance development between mu-opioid and gamma-aminobutyric acidB receptor agonists, in hypothalamic arcuate neurons, resulting from chronic morphine treatment. Intracellular recordings were made in hypothalamic slices prepared from ovariectomized female guinea pigs. The mu-opioid receptor agonist D-Ala2,N-Me-Phe4,Gly-ol5-enkephalin and the gamma-aminobutyric acidB receptor agonist baclofen produced dose-dependent membrane hyperpolarizations of arcuate neurons. The reversal potential for both agonist-induced hyperpolarizations was near -95 mV, indicative of the activation of an underlying K+ conductance. Coadministration of maximally effective concentrations of D-Ala2,N-Me-Phe4,Gly-ol5-enkephalin and baclofen produced a response that was not additive, indicating a convergence onto a common K+ channel. In arcuate neurons, including a subset that was immunopositive for tyrosine hydroxylase, chronic morphine treatment for 4 to 7 days produced a 3.2-fold reduction in the potency, with no change in the efficacy, of D-Ala2,N-Me-Phe4,Gly-ol5-enkephalin. In contrast, it affected neither the potency nor the efficacy of baclofen. Therefore, chronic morphine exposure does not produce cross-tolerance between mu-opioid and gamma-aminobutyric acidB receptor agonists in A12 dopamine neurons, suggesting that convergence upon a common effector is not a sufficient criterion for the development of cross-tolerance between receptor systems.

Animals↗
PubMed1997

TUR syndrome and endoscopic transanal resection: no evidence for a clinically important association in 38 procedures.

BACKGROUND: The TUR syndrome is well described after transurethral resection of the prostate. Endoscopic transanal resection (ETAR) is increasingly used to remove rectal lesions. METHODS: A prospective study of 38 ETARs in 21 patients was carried out over 2 years. Each patient was observed for symptoms and signs of TUR syndrome, and each had serial venous blood sampling and subsequent biochemical and haematological analysis during the perioperative period. RESULTS: No symptoms or signs typical of TUR syndrome were recorded. However, analysis of the biochemical variables using the Kruskal-Wallis one-way analysis of variance showed that there were statistically significant (P < 0.05) subclinical changes during the 24 h following the procedure affecting levels of serum sodium, potassium, total protein, albumin, lactate dehydrogenase, glycine, ammonia and serum osmolality. CONCLUSION: The changes in the electrolyte concentrations, although statistically significant, were not of the same magnitude as described previously in the TUR syndrome. The risk of a TUR-type syndrome in ETAR is small and serial blood tests, as detailed above, may safely be omitted.

Adenoma↗
PubMed1996

Downregulation of mu-opioid receptor mRNA in the mediobasal hypothalamus of the female guinea pig following morphine treatment.

Ribonuclease protection assays were performed on the basal hypothalamus (BH), the preoptic area (POA) and the thalamus (THAL) from female guinea pigs that were ovariectomized and implanted with morphine (n = 8) or placebo (n = 8) pellets for 1 week. An antisense [32P]rUTP labeled riboprobe, representing a 280 bp fragment of the guinea pig mu-opioid receptor gene (spanning putative TM II through eight residues of TM IV), protected a single RNA band of 280 bp. In contrast to the rat, the guinea pig THAL expressed less mu-opioid receptor mRNA than both POA and BH. Morphine treatment caused a significant decrease (15.6 +/- 5.8%) in mu-opioid receptor mRNA expression in the BH, while POA and THAL were not different from placebo controls. Therefore, in conjunction with our previous findings of a downregulation of mu-opioid receptors, mu-opioid receptor mRNA is downregulated in the mediobasal hypothalamus of female guinea pigs following chronic morphine treatment.

Analgesics, Opioid↗
PubMed1996

An unusual presentation of intestinal lymphangiectasia.

Intestinal lymphangiectasia is a rare disorder, usually presenting with protein-losing enteropathy leading to oedema and ascites. We describe a case that presented as an acute surgical emergency with pain and a mass in the right iliac fossa, which was successfully treated by resection of the involved segment of ileum.

Abdomen, Acute↗