Firing properties of identified parasympathetic cardiac neurons in
the nucleus ambiguus recorded with perforated patch clamp
techniques.
Mendelowitz, D.
Department of Physiology and Biophysics, University of Tennessee,
894 Union Ave., Memphis, TN 38163
APStracts 3:0249H, 1996.
This study tests the hypothesis that identified parasympathetic
cardiac neurons in the nucleus ambiguus possess pacemaker-like
activity, or alternatively, whether these neurons are inherently
silent. To test this hypothesis, and examine the firing properties of
these neurons, parasympathetic cardiac neurons were identified by the
presence of a fluorescent tracer previously applied to their
terminals surrounding the heart. Perforated patch clamp
electrophysiological techniques were used to study the spontaneous
and depolarization evoked firing patterns of these identified
parasympathetic cardiac neurons in an in-vitro brainstem slice.
Parasympathetic cardiac neurons were silent. Upon injection of
depolarizing current, however, these neurons fired with little delay
and spike frequency adaptation. Hyperpolarizing prepulses elicited a
significant delay prior to depolarization evoked firing. The calcium
activated potassium channel blocker apamin, but not carybdotoxin,
increased the depolarization activated firing frequency of these
neurons and inhibited the afterhyperpolarization. In summary,
parasympathetic cardiac neurons do not have pacemaker like
properties, but do possess discharge characteristics that would
enable them to closely follow excitatory synaptic activation closely
for prolonged periods.
Received 28 March 1996; accepted in final form 5 June 1996.
APS Manuscript Number H295-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96