Tonic glutamate-mediated control of rostra1 ventrolateral medulla and sympathetic vasomotor tone

neurons in the rostra1 ventrolateral medulla (RVLM) play a key role in the tonic maintenance of resting arterial pressure. Removal of tonically active inhibitory inputs to the RVLM provided by the caudal ventrolateral medulla (CVLM) elicits a large increase in arterial pressure. The present study addresses the hypothesis that excitatory amino acids (EAA) provide the excitation of the RVLM responsible for the increase in arterial pressure that occurs after withdrawal of CVLM-mediated inhibition of the RVLM. In rats anesthetized with either or-chloralose or urethan, inhibition of the CVLM by local injection of muscimol markedly elevated arterial pressure. Subsequent injection of the EAA receptor antago-nist kynurenic acid into the RVLM caused arterial pressure to fall to levels comparable to those that occur with total autonomic blockade. In contrast, injection of kynurenic aci