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Department of Physiology, Faculty of Medicine and Health Science, University of Auckland, Auckland, New Zealand
A distinct subpopulation of neurons in
the rostral and ventrolateral part of the medulla oblongata (RVL) plays
a key role in controlling sympathetic vasomotor tone. To characterize
these neurons under conditions in which all cell-to-cell interactions are eliminated, RVL neurons were acutely dissociated from 13- to 19-day
old rats. Cells projecting to the upper thoracic segments were
retrogradely labeled with fluorescent beads. Fifty-two percent (17/33)
of examined spinally projecting neurons were catecholaminergic, as
demonstrated by single-cell reverse transcription-polymerase chain
reaction or immunocytochemistry. No spontaneous (capacitive) spikes
were revealed in the tight seal cell-attached configuration. Whole cell
recordings were made from 54 spinally projecting neurons using
Cs+- or
K+-containing pipettes. No
spontaneous firing was observed in current-clamp mode with
K+-based pipettes (membrane
potential, 
61.5 ± 2.3 mV). Step depolarizations (300- or 400-ms pulses, up to 100 pA) evoked regular firing or one to
four spikes. Several voltage-gated currents, resembling the transient
and persistent Na+, delayed
rectifier and low- and high-threshold
Ca2+, were revealed in
voltage-clamp mode. These results show that isolated spinally
projecting RVL neurons display no pacemaker-like activity. Because data
from the literature indicate that these neurons are capable of
generating such activity under different experimental conditions, the
factors responsible for different behavior need to be determined.
Dissociated RVL neurons provide a useful new model for studying
biophysical and other properties of neurons involved in blood pressure
control.
dissociated neurons; brain stem; medulla oblongata; C1 adrenergic cells; single-cell reverse transcription-polymerase chain reaction; immunocytochemistry; ion channels; cardiovascular control
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