Cerebellar influence on the termination of inspiration by intercostal nerve stimulation

Stimulation of either the intercostal afferents or the anterior lobe of the cerebellum may terminate inspiratory activity. Since intercostal afferents are known to project to the cerebellum, the present study examined the possibility that this intercostal inhibition of inspiration is mediated through the cerebellum. Decerebrate, vagotomized, paralyzed, and artificially ventilated cats were used. The left T6 intercostal nerve was stimulated centrally with a 3 pulse train (0.1 msec duration, 200 Hz, 0.01-5.0 mA) delivered at 10 different intervals (Ti) after the onset of phrenic neural activity. At each delay the stimulus intensity (mA) was adjusted to the minimal current required to terminate inspiration Plots of mA versus Ti were obtained before and after cerebellectomy at both 4% and 5% end-expiratory CO2 levels. The results demonstrated that the threshold stimulus strength required for inspiratory termination is elevated by hypercapnia. Cerebellectomy, however, did not alter the threshold stimulus strength at either of the CO2 levels. Therefore, although cerebellar inputs may affect the pattern of respiration, this study has shown that the intercostal activation of the inspiratory 'off-switch' is not dependent on an intact cerebellum.