Fastigial nucleus stimulation and concurrent activation of cardiovascular receptors; differentiate effects on arterial pressure, heart rate and vasopressin release.

The integrated effects of stimulation of fastigial nucleus (FN) and of concurrent activation of baroreceptors on arterial pressure (AP), heart rate (HR) and vasopressin (VP) release in anaesthetized, paralysed, artificially ventilated rats were investigated. Stimulation of FN blocked the fall in AP and HR elicited by afferent vagal stimulation. It also abolished the atropine-sensitive bradycardia occurring at the peak of the stimulus-elicited pressor elevation in 6-hydroxydopamine treated rats. Sinoaortic denervation plus vagotomy left the cardiovascular responses to FN stimulus unmodified but facilitated FN elicited VP secretion. Vagotomy alone was ineffective. After high spinal cord transection more VP than in the intact condition was secreted after FN stimulation: simultaneous afferent vagal stimulation did not affect the facilitated VP release. Therefore FN stimulation can inhibit the reflex effects on AP and HR from baroreceptors, while the high-(but not the low-) pressure receptors can partly inhibit the VP release elicited by FN stimulation.