Excitatory inputs to the RVLM in the context of the baroreceptor reflex

The central neural circuit mediating baroreceptor control of sympathetic vasomotor outflow involves an excitatory projection from arterial baroreceptors to nucleus tractus solitarius, an excitatory projection from nucleus tractus solitarius to the caudal ventrolateral medulla, an inhibitory projection from the caudal ventrolateral medulla to the rostral ventrolateral medulla (RVLM), and an excitatory projection from the RVLM to sympathetic preganglionic neurons in the spinal cord. For this circuit to be operational, the relevant neurons in the RVLM must be tonically active. Indeed, numerous studies have demonstrated that RVLM vasomotor neurons are tonically active; however, little is known regarding the nature of the tonic excitatory drive to these neurons. We present a model in which RVLM vasomotor neurons are tonically excited by inputs to the RVLM that can be blocked by the excitatory amino acid receptor antagonist, kynurenic acid, as well as an input from the caudal ventrolateral medulla that is not sensitive to kynurenic acid.