The cardiovascular responses elicited from the posterior cerebellar cortex in the anaesthetized and decerebrate rabbit.

1. In this study the posterior cerebellar cortex has been electrically stimulated and changes in heart rate, arterial blood pressure, regional blood flows and renal sympathetic nerve discharge have been recorded in both the anaesthetized and the decerebrate unanaesthetized rabbit. 2. Specifically, lobules VII, VIII, IX and X of the posterior cerebellar vermis were stimulated but the only region which elicited cardiovascular changes was lobule IX (the uvula). The responsive area of the uvula was localized to the medial regions of sublobules a, b and c and was identical in both anaesthetized and decerebrate animals. 3. Under urethane anaesthesia, uvula stimulation evoked a small bradycardia, a fall in arterial pressure, a transient inhibition of renal sympathetic nerve activity, with no change in renal vascular conductance, and an increase in femoral vascular conductance. 4. Stimulation of an identical area in the decerebrate rabbit evoked a marked tachycardia, an increase in blood pressure, maintained increase in renal sympathetic nerve discharge, and decreases in both renal and femoral conductances. 5. The response evoked from the decerebrate rabbit could be reversed by a small dose of anaesthetic to a pattern of response which was essentially identical to that seen in the urethane-anaesthetized rabbit. 6. This influence of anaesthetics on the pattern of cardiovascular responses that may be elicited from the cerebellar cortex indicates that caution should be exercised when making physiological inferences on the basis of stimulation experiments in anaesthetized preparations. 7. In the light of the cardiovascular changes that may be evoked from the uvula, and recent neuroanatomical and neurophysiological data concerning afferent and efferent connexions of this cerebellar region, we discuss the possibility that the uvula plays a role in the alerting reaction of the rabbit.