Pontine-evoked inspiratory inhibitions after antagonism of NMDA, GABAA, or glycine receptor.

Single-shock stimulation of the pontine respiratory group (PRG) produces a transient short-latency inhibition of inspiratory motor activity. Stimulus trains delivered to the PRG can elicit a premature termination of inspiration. This study examined the involvement of N-methyl-D-aspartate (NMDA), gamma-aminobutyrateA (GABAA), or glycine receptors in these inhibitory responses. Experiments were conducted in decerebrate, paralyzed, and ventilated cats. Control responses to PRG stimulation were obtained from recordings of the left phrenic nerve activity. After systemic injection of MK-801, bicuculline, or strychnine (antagonists to NMDA, GABAA, or glycine receptors, respectively), responses to stimulation were again recorded. Inspiratory termination elicited by the PRG stimulation persisted after antagonism of NMDA, GABAA, or glycine receptors. The onset latency and duration of the transient inhibition were not changed after administration of bicuculline, but MK-801 administration did significantly prolong the duration of the transient inhibition. Strychnine significantly prolonged both the onset latency and the duration. These data suggest that none of the three receptor types is required in the inspiratory termination response elicited by electrical stimulation of the PRG region and that NMDA, GABAA, or glycine receptor-mediated neurotransmission is not solely responsible for the transient inhibitory response. However, the prolonged onset and duration of the transient inhibition after strychnine administration suggest that glycine does normally participate in this response.