Possible inspiratory off-switch neurones in the ventrolateral medulla of the cat.

The location and axonal projection of a type of respiratory neurones (termed bIE neurones), which show burst firing at the time of phase transition from inspiration to expiration, were studied in Nembutal-anaesthetized, paralysed and artificially ventilated cats. The bIE neurones showed maximum firing at the sharp decline of inspiratory activity. All of the bIE neurones tested projected to medullary respiration-related areas of the ventral respiratory group (VRG), the dorsal respiratory group (DRG), and the Bötzinger complex (BOT). The bIE neurones were distributed in the dorso-medial border of the main assembly of respiratory neurones of the VRG and BOT. The possibility that these bIE neurones participate in inspiratory termination is discussed.