Caudal ventrolateral medulla. A region responsible for the mediation of vasopressin-induced pressor responses.

We localized glutamate-sensitive sites in the ventrolateral medulla of the rat with the spinal cord cut at C1. When unilaterally injected into a circumscribed region of the caudal ventrolateral medulla,l-glutamate (30–300 ng) elicited a dose-dependent increase in arterial pressure. The pressor response was accounted for by an increased release of vasopressin because it was abolished by the intravenous injection of a vasopressin antagonist. Bilateral microinjections of kainic acid (50 ng) into the ventrolateral glutamate-sensitive area markedly reduced a vasopressin-induced pressor response to kainic acid (30 ng), injected bilaterally into the nucleus tractus solitarii. It is concluded that the glutamate-sensitive neurons in the caudal ventrolateral medulla are involved in mediation of the vasopressin-induced pressor response arising from the nucleus tractus solitarii.