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Li YW, Bayliss DA, Guyenet PG: C1 neurons of neonatal rats: intrinsic beating properties and alpha 2-adrenergic receptors. Am J Physiol. 1995 Dec;269(6 Pt 2):R1356-69.
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 whether they have alpha 2-adrenergic inhibitory "autoreceptors." RVL bulbospinal cells (retrogradely labeled with microbeads) were recorded in thin slices from 3- to 7-day-old rats with patch electrodes containing Lucifer yellow. Forty-two of eighty-nine 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 plus bicuculline plus strychnine or with a low-Ca (2+)-high-Mg2+ medium failed to reduce their firing rate. The membrane trajectory consisted of one of two patterns interconvertible by injections of depolarizing or hyperpolarizing current: 1) depolarizing ramps leading to spikes or 2) slow oscillations (tetrodotoxin resistant but absent at hyperpolarized potentials) leading to spikes or repolarization. The cells had Ca (2+)-dependent afterhyperpolarizations, large transient outward currents, and a hyperpolarization-activated inward current activated at potentials less than -65 mV, blocked by CsCl, and presumably responsible for a large inward rectification. Of 27 TH-ir cells, 21 had inhibitory responses to alpha 2-adrenergic agonists. These were blocked by idazoxan (n = 9). alpha 2-Agonists activated an inwardly rectifying potassium conductance (KIR). We confirm that bulbospinal C1 cells have intrinsic pacemaker properties and demonstrate that they have alpha 2-adrenergic receptors (autoreceptors) coupled to KIR channels. |
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