ABSTRACT
Arterial baroreceptor afferent nerve fibers arising from neurons in the nodose and petrosal ganglion project into the brain where they terminate primarily in the nucleus tractus solitarii (NTS) in the medulla oblongata. Numerous putative transmitters have been identified both in the NTS and in the primary sensory ganglia, but few of those chemical agents have sufficiently met criteria to be considered potential transmitters or modulators in the baroreceptor reflex arc. Two such putative transmitters are glutamate and acetylcholine. Both spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats responded to injection of glutamate with robust decreases in arterial pressure and heart rate. While dose-related responses of arterial pressure were shifted to the right in SHR compared to those in WKY rats, dose-related responses for heart rate in the two strains were similar. Microinjection of either glutamate or acetylcholine into the NTS of anesthetized rats elicits depressor and bradycardiac responses that mimic those following activation of the baroreceptor reflex.
