C1 neurons of neonatal rats: intrinsic beating properties and
[alpha]2-adrenergic receptors.
Li, Yu-Wen, Douglas A. Bayliss, and Patrice G. Guyenet.
University of Virginia, Department of Pharmacology,
Charlottesville, Va 22908, USA
APStracts 2:0170R, 1995.
Tyrosine-hydroxylase-immunoreactive (TH-ir) neurons (C1 cells) of the
rostral ventrolateral medulla (RVL) control sympathetic tone and may
be inhibited by the hypotensive drug clonidine. The present study
seeks to describe some of the intrinsic properties of bulbospinal C1
cells and to establish if they have [alpha]2-adrenergic inhibitory
"autoreceptors". RVL bulbospinal cells (retrogradely labeled
with microbeads) were recorded in thin slices from P3-P7 rats with
patch electrodes containing Lucifer yellow. Forty-two of 89 cells
were recovered histologically and 69% were TH-ir. The properties of
TH-ir cells could not be distinguished from those of the other
bulbospinal cells. Most cells were spontaneously active (0.5-5
spikes/s). Blockade of fast postsynaptic potentials with kynurenic
acid + bicuculline + strychnine or with a low Ca++/high Mg++ medium
failed to reduce their firing rate. The membrane trajectory consisted
of one of two patterns interconvertible by injections of depolarizing
or hyperpolarizing current: i) depolarizing ramps leading to spikes
or ii) slow oscillations (tetrodotoxin-resistant but absent at
hyperpolarized potentials) leading to spikes or repolarization. The
cells had calcium-dependant AHPs, large transient outward (IA)
currents and an Ih-like current activating at <-65 mV, blocked
by CsCl and presumably responsible for a large inward rectification.
Of 27 Thir cells, 21 had inhibitory responses to [alpha]2-adrenergic
agonists. These were blocked by idazoxan (N=9). Alpha2 agonists
activated an inwardly rectifying potassium conductance (K+IR). We
confirm that bulbospinal C1 cells have intrinsic pacemaker properties
and demonstrate that they have [alpha]2-adrenergic receptors
(autoreceptors) coupled to K+IR channels.
Received 24 March 1995; accepted in final form 14 June 1995.
APS Manuscript Number R206-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.