Inhibitory mechanisms control active expiration by limiting parafacial expiratory drive.

Activity of parafacial neurons that control active expiration is heavily dependent on tonic and CO/H-dependent excitatory and inhibitory inputs from yet poorly defined sources. Contrary to the idea that CO/H disinhibits parafacial expiratory neurons, the recent work of J. D. Silva et al. (Silva JD, Oliveira LM, Souza FC, Moreira TS, Takakura AC. 123: 1933-1943, 2020) suggests that GABAergic raphe neurons preferentially limit expiratory activity during high CO. Here, I discuss these findings and propose a model where GABAergic raphe neurons function as CO/H-dependent breaks on expiratory drive.