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M Connaughton

Publications and source records attributed to M Connaughton.

8 recordsLinked to original sources
PubMed1996

Ventricular arrhythmias induced by ischaemia-reperfusion are unaffected by myocardial glutathione depletion.

Reduced glutathione (GSH) is a major myocardial antioxidant. Since reperfusion phenomena such as ventricular fibrillation (VF) are associated with oxygen free radical production during ischaemia, myocardial GSH depletion might be expected to increase susceptibility to such phenomena. This possibility was tested in isolated rat hearts using diethylmaleate (DEM) or L-buthionine-SR-sulfoximine (BSO) to deplete myocardial GSH. High dose DEM (860 mg/kg) depleted myocardial GSH from a control mean of 7.64 +/- 0.73 to 3.18 +/- 0.56, low dose DEM (215 mg/kg) to 4.29 +/- 0.53 nmol/mg protein and BSO (4 mmol/kg) from a control mean of 6.94 +/- 0.54 to 2.18 +/- 0.14 nmol/mg protein. Hearts were perfused in the Langendorff mode at 37 degrees C with bicarbonate buffer (K+ = 4.3 mM). Regional ischaemia was induced for 5, 8.5, 10, 20 or 40 min (DEM groups: n = 10/treatment/time point) or 8.5 min only (BSO groups: n = 10/treatment) then hearts were reperfused for 5 min. Reperfusion VF incidence showed a classical "bell-shaped" curve, but there was no difference in VF incidence, VF time-to-onset, arrhythmia duration and "arrhythmia scores" between GSH-depleted and control hearts. Depleting myocardial GSH is not proarrhythmic for reperfusion-induced arrhythmias. It would appear GSH is not significantly involved in protecting against the oxidant stress of reperfusion, or conversely that the reserve of this redox system is so high only severe depletion might show an effect.

Animals↗
PubMed1987

Ultrastructure and distribution of substance P-immunoreactive sensory collaterals in the guinea pig prevertebral sympathetic ganglia.

A light and electron microscopic study has been made of the substance P-immunoreactive networks formed by sensory nerve fibres in the prevertebral sympathetic ganglia of the guinea pig to seek confirmation that these networks arise from collateral branches of sensory fibres passing through the ganglia and to explore the synaptic and other specialized relationships established by these networks. Slices from coeliac-superior mesenteric and inferior mesenteric ganglia of young adult males, perfusion-fixed by paraformaldehyde, were immunostained with a monoclonal antibody to substance P, and the immunolabelling was visualized by a peroxidase reaction. Immunolabelled fibres passing through the ganglia were seen by light microscopy to give off varicose collaterals that ramified in the ganglionic neuropil. Electron microscopy showed that the parent fibres were almost exclusively unmyelinated. Many collaterals ran directly beneath the basal lamina bordering the intraganglionic tissue spaces, and the varicosities either remained superficially exposed under the basal lamina or sank deeper into the supporting Schwann cells, becoming apposed to dendrites of the ganglionic neurones, upon which they formed synapses, or to other nerve terminals. The incidence of these specific associations was quantified, singly and in combination. Synapses could be situated at the same level as unlabelled synapses on the same dendrite, and exposed varicosities could lie within 0.5 micron of exposed, postsynaptic dendrites. These observations confirm a collateral, synaptic nature for the networks and suggest additional nonsynaptic modes of release and sites of transmitter action. They are consistent with the hypothesis that the system serves a nocifensor function of axon reflex type.

Animals↗
PubMed1986

Inputs to motoneurones in the hypoglossal nucleus of the rat: light and electron microscopic immunocytochemistry for choline acetyltransferase, substance P and enkephalins using monoclonal antibodies.

Light and electron microscopic peroxidase-antiperoxidase immunocytochemistry has been used to localize choline acetyltransferase, substance P and enkephalin in the hypoglossal nucleus of the rat. Choline acetyltransferase immunoreactivity was observed in motoneurone cell bodies and proximal dendrites, in large varicosities in the surrounding neuropil and in nerve terminals in synaptic contact with immunostained motoneurones. Most choline acetyltransferase immunostained terminals which made synaptic contact with motoneurone cell bodies and proximal dendrites possessed prominent subsynaptic cisterns and belong to the terminal type referred to in the literature as C or L. Substance P and enkephalin immunoreactivity did not occur in motoneurones but was seen in fibres and synaptic terminals. Substance P immunoreactive fibres made multiple axosomatic contacts while enkephalin immunoreactive terminals made synaptic contact mainly with large and small dendrites. C terminals were not stained for either substance P or enkephalin. This study provides immunocytochemical support for the classic identification of hypoglossal motoneurones as cholinergic and in addition shows that these neurones are innervated by a number of morphologically and chemically distinct terminal types. C terminals have previously been shown to contain cholinesterase and our demonstration that these terminals contain choline acetyltransferase thus provides additional evidence for their cholinergic nature and for a cholinergic innervation of hypoglossal motoneurones. The origin of the immunoreactive terminals was not identified in this study but possible candidates include the raphe nuclei for substance P. and propriobulbar interneurones for choline acetyltransferase.

Animals↗