ROLE OF ROSTRAL VENTROLATERAL MEDULLA IN CENTRALLY MEDIATED PRESSER RESPONSES

The region of the rostral ventrolateral medulla (RVLM) plays an important role in central nervous system regulation of cardiovascular function. The initial purpose of these studies was to determine whether synaptic activation of excitatory amino acid (EAA) receptors in the RVLM might mediate central presser responses. Blockade of EAA receptors in the RVLM with kynurenic acid abolished presser responses evoked by stimulation of sciatic nerve afferents but had no effect on increases in arterial pressure produced by stimulation of hypothalamic sites. To determine whether synaptic transmission in the RVLM, independent of EAA receptor activation, was a prerequisite for the production of hypothalamic presser responses, axonal conduction and/or synaptic transmission were pharmacologically interrupted in the RVLM. Blockade of synaptic transmission with muscimol or kainic acid attenuated, but did not eliminate, hypothalamic presser responses. Concurrent blockade of synaptic and axonal transmission in the RVLM with lidocaine produced the greatest reduction of hypothalamic presser responses. Collectively, these results suggest that central presser responses are not uniformly mediated by synaptic activation of neurons within the RVLM. Instead, a combination of synaptic transmission and axonal conduction within and possibly outside the region of the RVLM may be required for the production of many centrally mediated presser responses.