Cardiovascular responses evoked from the fastigial region of the cerebellum in anaesthetized and decerebrate rabbits.

1. The rostral and caudal regions of the fastigial nucleus (f.n.) in both anaesthetized and decerebrate rabbits have been stimulated electrically while monitoring phrenic nerve activity, heart rate, blood pressure and blood flow to the kidney and hindlimb in addition to recording renal sympathetic nerve activity. 2. Stimulation of the rostral region of the f.n. in the anaesthetized and decerebrate rabbit produced a silencing of phrenic nerve discharge, either no change in heart rate or a vagally mediated bradycardia and a pressor response associated with vasoconstriction in both renal and femoral beds which resulted from an increase in sympathetic vasomotor tone. 3. Stimulation of the caudal region of the f.n. in the anaesthetized rabbit evoked apnoea and a bradycardia which was partially attenuated by vagal blockade. Also, a depressor response was obtained with no change in renal vascular resistance, a transient inhibition of renal sympathetic nerve discharge and a vasodilation in the hindlimb resulting from the withdrawal of sympathetic vasoconstrictor tone. In contrast, electrical stimulation of the same site in the unanaesthetized decerebrate rabbit evoked an increase in central inspiratory drive, a tachycardia and a pressor response with vasoconstriction in both vascular beds. The cardiac and vascular responses were abolished after sympathetic blockade. 4. Administration of a small dose of anaesthetic to the decerebrate preparation did not affect the direction of the cardiovascular or central respiratory responses evoked from the rostral f.n. but reversed the pattern of response elicited from the caudal f.n. to that seen in the intact anaesthetized rabbit. 5. The results of the present study suggest the existence of two separate regions associated with the f.n. which can influence the cardiovascular system in the rabbit. Furthermore, it would seem that the cardiovascular responses evoked from the vicinity of the caudal and rostral poles of the f.n. are mediated by two distinct pathways which might suggest two separate functional roles for the cerebellum in cardiovascular control in the rabbit.