Disfacilitation of glutamatergic drive to the preBötzinger Complex (preBötC). A: Phrenic neurogram (PNG) tracings show that bilateral microinjection of NBQX and subsequently AP5 caused tachypnea with decreased peak phrenic activity (PPA), which was followed by apnea. B-E: Pooled data for the sequential, bilateral injection of NBQX and AP5 in 13 animals. In 7 animals, NBQX (blue) was injected first (left-hand side of each panel), in 6 separate animals, AP5 (red) was injected first (righthand side of each panel). Peak phrenic activity was normalized to control. See text for details. Box plots (median, 25–75% range) plus individual data points. *: p<0.05, **: p<0.01, ***: p<0.001