Gasping is elicited by briefer hypoxia or ischemia following blockade of glycinergic transmission.

The 'switching model' for generation of respiratory rhythms holds that gasping represents the release of a rostral medullary pacemaker mechanism from the pontomedullary neuronal circuit that generates eupnea. In a perfused preparation of the decerebrate juvenile rat, exposure to ischemia or hypoxic-hypercapnia caused an alteration in integrated phrenic activity from the incrementing pattern of eupnea to the decrementing pattern of gasping. The time required to elicit gasping was not altered by multiple exposures to ischemia or hypoxic-hypercapnia. Furthermore, this time to gasping was not altered following addition to the perfusate of increasing concentrations of bicuculline or picrotoxin; both block GABA(A) receptors. Addition to the perfusate of strychnine, a glycine antagonist, significantly shortened the duration of ischemia or hypoxic-hypercapnia required to elicit gasping. These results support the concept that a loss of inhibitory glycinergic transmission is a critical factor in release of pacemaker mechanisms for gasping from the pontomedullary neuronal circuit for eupnea.