Fig. 1. Pontine transections decrease minimum alveolar concentration (MAC). Transections made in the pons or pontomedullary junction block multisegmental movement at sub-MAC isoflurane concentrations. (A ) Baseline biceps femoris electromyogram motor response to a 30-s tail clamp in an intact animal. R.BF = right biceps femoris; L.BF = left biceps femoris. (B ) Negative response in the same animal with pontine transection (indicated by dashed line in diagram). Mid-medullary transection minimally decreases MAC but prevents repetitive movement during tail clamp. (C ) Repetitive movement elicited by a 30-s noxious tail clamp in another intact animal (D ) Response to tail clamp in the same animal after transection of the mid-medulla at the rostral end of the medullary dorsal reticular nucleus (dashed line in upper right ). The transection did not change isoflurane MAC in this animal, but only single low-magnitude movements occurred at the onset and offset of the noxious tail clamp.