Central neural respiratory drive and afterdischarge.

Different modes of stimulation of the carotid sinus nerve were used in anesthetized cats to study development of inspiratory neural activity and respiratory afterdischarge. Continuous and inspiratory-only stimulations produced rapid rises of activity; cessation led to equally rapid initial falls followed by slowly decaying afterdischarges. Expiratory-only stimulations produced more slowly rising and smaller increases of inspiratory activity and the offset led to no rapid fall of activity; nevertheless, the time course of the afterdischarge was similar to those of continuous and inspiratory runs. During alternate cycle stimulation, the developing pattern of activity of stimulated breaths resembled that of continuous or inspiratory stimulation, whereas that of unstimulated breaths was like expiratory. The findings support conclusions that the neural network causing the afterdischarge is separate from and does not require input from inspiratory neurons in the medulla. Both the activation and decay times of this neural mechanism are relatively long.