Location and axonal projection of early-onset decrementing expiratory neurons in the cat.

The location and axonal projection of early-onset decrementing expiratory (eE-DEC) neurons were studied in Nembutal-anesthetized, paralyzed, and artificially ventilated cats. The eE-DEC neurons started firing around the peak of phrenic activity and attained maximum firing at the transition from inspiration to expiration. The eE-DEC neurons were distributed in the dorsomedial border of the dense assembly of respiratory neurons of the ventral respiratory group and the Bötzinger complex. Antidromic microstimulation showed that the eE-DEC neurons projected mainly to the ipsilateral reticular formation medial and dorsal to the nucleus ambiguus at the level of the obex but rarely to the medullary respiration-related areas. Participation of these eE-DEC neurons in the inspiratory off-switch may not be possible.