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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.

1. In both anaesthetized and decerebrate cats the cerebellar cortex (lobules VI, VII, VIII, IX and X) and the fastigial nucleus (f.n.) have been stimulated electrically, and chemically, while recording changes in phrenic nerve discharge, heart rate, arterial blood pressure and renal and femoral blood flow. 2. Stimulation of lobules VI, VII, VIII and Xb failed to elicit any cardiovascular or respiratory changes. Activation of lobule IX (the uvula), and in some preparations sub‐lobule Xa, evoked cardiovascular and respiratory responses consistently. In the anaesthetized cat, electrical stimulation of the uvula evoked apnoea, a small bradycardia and a depressor response associated with vasodilatation in the hindlimb vascular bed. In contrast, stimulation in an equivalent region in a decerebrate preparation elicited an apneustic discharge, a pronounced tachycardia and a rise in arterial pressure with vasoconstriction in both renal and femoral vascular beds. In both the anaesthetized and decerebrate animals the pattern of response elicited by chemical activation was identical to that seen with electrical stimulation. 3. Electrical, or chemical, stimulation after administration of anaesthetic to the decerebrate cat then evoked an identical pattern of response to that seen in the 'intact' anaesthetized animal. This evidence suggests that the reversal in the pattern of the response in an effect of the anaesthetic agent and not the decerebration itself. 4. The only area of the f.n. to produce cardiovascular effects was the rostral region. Electrical stimulation of the rostral f.n. in both anaesthetized and decerebrate preparations inhibited central inspiratory activity and evoked tachycardia, along with a pressor response associated with vasoconstriction in both renal and femoral vascular beds. In contrast, chemical excitation of those sites in the rostral f.n. shown previously to produce pronounced cardiovascular and respiratory changes failed to elicit any changes in the recorded variables. 5. The present evidence suggests that there are two areas in the cat cerebellum which can exert pronounced cardiovascular and respiratory effects. The patterns of response elicited by electrical stimulation of the posterior cortex and rostral f.n. are mediated by two separate cerebellar‐brainstem pathways as judged by the two different effects of anaesthesia on the evoked responses. We suggest that the f.n. may not play a role in the control of the cardiovascular system since chemical excitation of cell bodies of the rostral f.n. failed to elicit the so‐called 'fastigial pressor response'.

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.