Cardiovascular and respiratory responses evoked from the posterior cerebellar cortex and fastigial nucleus in the cat.

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'.