Peptidergic transmission in the brain. V. Systemic correlates of central activation

Inhibition of the hippocampus by the medial amygdala is mediated by vasopressin-like peptide. Because vasopressin has action on the periphery as well as the brain, we conducted experiments to evaluate the relationship between possible peripheral actions and the central effects of the endogenous peptide. In the acutely anesthetized rat, peptide-mediated inhibition of the hippocampus is not associated with significant changes in heart rate, blood pressure or body temperature. Peripheral injections of peptide agonist fail to evoke the central inhibition, and peripheral injections of peptide antagonist fail to block the central inhibition. Stimulation of central nuclei that contain vasopressin or a similar peptide also fail to duplicate the effect of stimulating the amygdala. We conclude that the peptidergic transmission is independent of peripheral causes or correlates.