The influence of lobule IX of the cerebellar posterior vermis on the baroreceptor reflex in the decerebrate rabbit.

Stimulation of lobule IX (the uvula) of the cerebellar posterior vermis, either electrically or chemically, has been shown to evoke marked cardiovascular effects in both rabbit and cat. Recent experiments suggest that this stimulation can also reduce the responsiveness of neurons in the nucleus tractus solitarii to baroreceptor inputs. The aim of the present study was thus to determine whether the uvula exerts an influence on the baroreceptor reflex. In order to evoke a reflex bradycardia in decerebrate rabbits, blood pressure was increased by inflating a Swan-Ganz catheter positioned in the descending aorta, and in some rabbits the aortic nerve was also stimulated electrically. In most rabbits, following uvula removal, significantly larger reflex falls in heart rate were observed. In a second group of rabbits, a lesion of cerebellar lobules VI-VIII had no effect on reflex bradycardia. It is concluded that the uvula tonically depresses the cardioinhibitory component of the baroreceptor reflex in the rabbit. The possible functional implications of these results are discussed.