INVOLVEMENT OF PONTILE NMDA RECEPTORS IN INSPIRATORY TERMINATION IN RAT

We evaluated the hypothesis that N-methyl-D-aspartate (NMDA) receptors in the rostral pens mediate the off-switch of inspiration in the adul t rat. Experiments were performed on decerebrate, vagotomized, paralyz ed and ventilated animals. Activity of phrenic nerve was recorded. Sma ll volumes (10 nl) of NMDA antagonists, MK-801 and AP-5, or non-NMDA a ntagonists, CNQX and DNQX, were injected into the rostral pens. We fou nd that injections of MK-801 reversibly increased the duration of neur al inspiration (TI), and the increase was dose-dependent. Injections o f AP-5 also increased TI. Injections of the DNQX and CNQX in these sam e loci resulted in no significant changes in the duration of neural in spiration, expiration or peak phrenic activity (PNA). However, injecti ons of kainic acid (KA, 4.7 mM) in the loci increased TI and decreased PNA. We conclude that neurons regulating the off-switch mechanism are located in the rostral pens. Further, the binding of NMDA receptors i n the rostral pens is involved in this off-switch mechanism.