Presynaptic [alpha]2-adrenoceptors inhibit excitatory glutamatergic
synaptic transmission in rat dorsal motor nucleus of the vagus.
Bertolino, Maria, Stefano Vicini, Richard Gillis, and Alberto
Travagli.
Department of Pharmacology, Department of Physiology and
Biophysics, Georgetown University School of Medicine, Washington,
D.C. 20007, Department of Physiology, West Virginia University School
of Medicine, Morgantown, WV 26506
APStracts 3:0222G, 1996.
The synaptic connection between the commissural portion of the nucleus
tractus solitarius (ComNTS) and the dorsal motor nucleus of the vagus
(DMV) was studied in rat brainstem slices using the patch clamp
technique. The excitatory postsynaptic currents (EPSCs) evoked by
stimulation of the ComNTS were blocked by kynurenic acid (1 mM) and,
in Mg++-free solution, were sensitive to both the NMDA receptor
blocker CPP (20 [mu]M) and the non-NMDA receptor blocker NBQX (5
[mu]M). Norepinephrine (NE) (1-100 [mu]M) inhibited the EPSCs and the
inhibition was attenuated by the [alpha]2-adrenoceptor antagonists
idazoxan (1 [mu]M) and yohimbine (10 [mu]M), but not by the [beta]
-adrenoceptor antagonist nadolol (50 [mu]M). The NE releasing agent
tyramine (100 [mu]M) reduced the EPSCs and the inhibition was
attenuated by 1 [mu]M idazoxan. NE (30 [mu]M) did not affect the
membrane input resistance but reduced the paired pulse depression
demonstrating that NE acts on presynaptic [alpha]2-adrenoceptors. The
results indicate the existence of a glutamatergic pathway from the
ComNTS to the DMV neurons modulated by presynaptic NE receptors. This
pathway might be a component of the vagovagal reflex regulating
gastrointestinal function.
Received 26 April 1996; accepted in final form 10 October 1996.
APS Manuscript Number G161-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996