ROLE OF ROSTRAL VENTROLATERAL MEDULLA IN CENTRALLY MEDIATED PRESSER RESPONSES

The region of the rostral ventrolateral medulla (RVLM) plays an import ant role in central nervous system regulation of cardiovascular functi on. The initial purpose of these studies was to determine whether syna ptic activation of excitatory amino acid (EAA) receptors in the RVLM m ight mediate central presser responses. Blockade of EAA receptors in t he RVLM with kynurenic acid abolished presser responses evoked by stim ulation of sciatic nerve afferents but had no effect on increases in a rterial pressure produced by stimulation of hypothalamic sites. To det ermine whether synaptic transmission in the RVLM, independent of EAA r eceptor activation, was a prerequisite for the production of hypothala mic presser responses, axonal conduction and/or synaptic transmission were pharmacologically interrupted in the RVLM. Blockade of synaptic t ransmission with muscimol or kainic acid attenuated, but did not elimi nate, hypothalamic presser responses. Concurrent blockade of synaptic and axonal transmission in the RVLM with lidocaine produced the greate st reduction of hypothalamic presser responses. Collectively, these re sults suggest that central presser responses are not uniformly mediate d by synaptic activation of neurons within the RVLM. Instead, a combin ation of synaptic transmission and axonal conduction within and possib ly outside the region of the RVLM may be required for the production o f many centrally mediated presser responses.