INTENSE VASOCONSTRICTION AND BRADYCARDIA EVOKED BY STIMULATION OF NEURONES WITHIN THE MIDBRAIN VENTRAL TEGMENTUM OF THE RABBIT

1. Electrical stimulation of sites in the midbrain ventral tegmental area (VTA) and the lateral hypothalamic area of the anaesthetized rabbit elicited intense vasoconstric-tion and profound bradycardia. 2. The same effects were elicited by microinjections of glutamate ions into the VTA but not the lateral hypothalamic area. 3. Following baroreceptor denervation, the bradycardic component of the response was greatly reduced, but the vasoconstrictor component was unaffected. 4. It is concluded that the cardiovascular response is generated by excitation of a cell group within the VTA, but within the hypothalamus the response arises from ex-citation of axons of passage. Key words: baroreceptors, central vasomotor pathways, ventral tegmental area