WHOLE-CELL PATCH-CLAMP STUDY OF PUTATIVE VASOMOTOR NEURONS ISOLATED FROM THE ROSTRAL VENTROLATERAL MEDULLA

A distinct subpopulation of neurons in the rostral and ventrolateral p art of the medulla oblongata (RVL) plays a key role in controlling sym pathetic vasomotor tone. To characterize these neurons under condition s in which all cell-to-cell interactions are eliminated, RVL neurons w ere acutely dissociated from 13- to 19-day old rats. Cells projecting to the upper thoracic segments were retrogradely labeled with fluoresc ent beads. Fifty-two percent (17/33) of examined spinally projecting n eurons were catecholaminergic, as demonstrated by single-cell reverse transcription-polymerase chain reaction or immunocytochemistry. No spo ntaneous (capacitive) spikes were revealed in the tight seal cell-atta ched configuration. Whole cell recordings were made from 54 spinally p rojecting neurons using Cs+- or K+-containing pipettes. No spontaneous firing was observed in current-clamp mode with K+-based pipettes (mem brane 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 persisten t Na+, delayed rectifier and low-and high-threshold Ca2+, were reveale d in voltage-clamp mode. These results show that isolated spinally pro jecting RVL neurons display no pacemaker-like activity. Because data f rom the literature indicate that these neurons are capable of generati ng 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 o ther properties of neurons involved in blood pressure control.