PONTINE MICROINJECTION OF CARBACHOL AND CRITICAL ZONE FOR INDUCING POSTURAL ATONIA IN REFLEXIVELY STANDING DECEREBRATE CATS

Pontine carbachol injection sites critically related to the induction of postural atonia were explored in reflexively standing acute decereb rate cats. Carbachol (4.0 mug/0.25 mu]) and atropine (2.0 mug/0.25 mul ) were focally injected into the pontomedullary reticular formation, a nd their effects on hindlimb extensor muscle tone were studied. The ef fective carbachol injection sites were concentrated in the region betw een P 1.5 and P 3.5, H -3.0 and H -5.0, and LR 1.2 and LR 2.5 (Horsley -Clarke coordinates). The effective sites corresponded to the dorsomed ial part of both the nucleus reticularis pontis oralis (NRPo) and the rostral portion of the nucleus reticularis pontis caudalis (NRPc). The mean latency to the beginning of carbachol-induced postural atonia wa s about 90 s (92 +/- 28 s; n=24).