α2-Adrenoceptor-mediated inhibition of bulbospinal barosensitive cells of rat rostral medulla

Abstract

Bulbospinal barosensitive neurons of the rostral ventrolateral medulla (RVLM cells; presumed sympathetic vasomotor premotor neurons) were recorded with iontophoretic electrodes in urethan-anesthetized rats. The majority of these cells were insensitive to intravenous clonidine (Clo; up to 20 μg/kg) and insensitive to iontophoretically applied Clo or α-methylnorepinephrine (α-MNE). These cells (n = 47 of 76) had a spinal conduction velocity of 4.1 ± 0.2 m/s and a mean firing rate of 20 ± 1 spikes/s. A second population (n = 29) was powerfully inhibited by intravenous Clo (5-10 μg/kg, activity decreased by 83 ± 11%), iontophoretically applied Clo (decreased by 51 ± 7%), and iontophoresis of α-M..