Cerebellar role in the load-compensating response of expiratory muscle

The hypothesis that the cerebellum is involved in the load-compensating response of expiratory muscles to expiratory tracheal occlusion was tested in anesthetized cats. A continuous expiratory threshold load (ETL; 5 cmH2O) was applied to elicit consistent phasic baseline electromyographic activity in the transversus abdominis muscle (EMGab). Tracheal occlusion for single expirations (TOE) were applied, and the evoked responses were compared in the intact and decerebellate preparation. Cold blockade of the dorsal spinal column (C5-7) and bilateral vagal inactivation (cold blockade or transection) were employed to determine the role of afferents from the lung, airways, chest wall, and diaphragm in shaping the cerebellar involvement in the motor response. The results showed that 1) decerebellation increased the baseline amplitude of the integrated EMGab (fEMGab) activity (P < 0.05) with little change in expiratory duration, 2) TOE applied after decerebellation markedly increased the expiratory duration compared with the intact values (P < 0.05), with little effect on the peak fEMGab, 3) cooling the dorsal spinal columns (C5-7) did not significantly affect EMGab responses in the intact or decerebellate preparations, and 4) vagal inactivation in the intact or decerebellate preparation significantly eliminated the fEMGab responses to ETL and TOE. We conclude that the cerebellum is involved in the modulation of transversus abdominis activity during ETL and TOE. Vagal afferents provide the major sensory input for the cerebellar modulation of the expiratory loading response.