Attenuation of the carotid body chemoreflex during the stimulation of the posterior vermis in the anaesthetised rabbit

The purpose of this study was to investigate the effects of electrical and chemical stimulation of the sub-lobule IX-b of the cerebellar uvula on the cardiorespiratory responses evoked on stimulation of the carotid chemoreceptors in the anaesthetised and paralysed rabbit. Recordings of arterial blood pressure, ECG, heart rate and phrenic nerve activity were evaluated. Sub-lobule IX-b was activated electrically (1 ms, 20 microA, 100 Hz, 4-s train) and stimulated chemically with sodium glutamate microinjections (2 mM, pH=7.4 +/- 0.1) using bipolar concentric or multibarrelled microelectrodes. Carotid body chemoreflexes were evoked by the retrograde injection of sodium cyanide (0.1%, 0.1 ml) into the blood supply of the carotid body through a cannula inserted in the external carotid artery. The interaction of uvula stimulation and the carotid chemoreceptor reflex was studied by following the chemoreceptor stimulus with a stimulus to the uvula. Electrical and chemical stimulation of the uvula evoked a characteristic bradycardia and a depressor response together with a decrease in phrenic nerve activity. Carotid body stimulation evoked a decrease in heart rate accompanied by an increase of both arterial blood pressure and phrenic nerve activity. However, simultaneous delivery of the two stimuli resulted in a depressor response together with a decrease of phrenic nerve activity and an increased bradycardia. These data suggest that stimulation of the cerebellar uvula exerts an inhibitory control of the chemoreflex efficacy as far as respiratory activity and blood pressure is concerned.