Adrenergic receptors in the nucleus tractus solitarii of the rat.

The nucleus tractus solitarii (NTS) is an area of the medulla in which baroreceptor afferent fibers mediating an inhibition of vasoconstriction terminate. The NTS also appears to be a site at which alpha-adrenergic receptors may be involved in blood pressure control. alpha- and beta-adrenergic agonists and antagonists were injected into the NTS via stainless steel cannulae and the effects on blood pressure determined. Norepinephrine (NE) and isoproterenol (ISO) caused dose-related decreases in mean arterial blood pressure (MABP). Phentolamine (PH) and propranolol (PR) caused dose-related increases in MABP. PH pretreatment in the NTS blocked the effects of ISO, but not NE. The effect of increased baroreceptor impulses to the NTS, produced by altering perfusion of the carotid sinus was blocked by propranolol. These results indicate the presence of beta- as well as alpha-receptors in the NTS, and also suggest the existence of presynaptic beta-receptors which facilitate neurotransmission.