Behavioral evidence for a cholinoceptive pontine inhibitory area: descending control of spinal motor output and sensory input.

Earlier studies have shown that microinjection of the cholinergic agonist carbamylcholine (carbachol) into the rostral pontine tegmentum of the cat elicits postural atonia. However, conflicting reports exist regarding other concomitant behavioral changes. The present study has demonstrated that a variety of functions supporting animals' responsiveness to external stimuli including postural somatomotor, sympathetic visceromotor and nociceptive somatosensory functions are differentially affected depending upon the injection sites. Sites associated with maximal effects on each of these functions are clustered in the dorsal pontine tegmentum, i.e. cholinoceptive pontine inhibitory area (CPIA). In a medial area of CPIA, which corresponds to an area caudal to the ventral tegmental nucleus of Gudden and ventromedial to the principal nucleus of locus coeruleus, postural somatomotor and sympathetic visceromotor functions were maximally suppressed. In a laterally adjacent area ventral to the principal nucleus of locus coeruleus, somatomotor function was predominantly suppressed. Nociceptive somatosensory function was primarily suppressed following microinjections into a more lateral area surrounding the lateral half of the brachium conjunctivum. Several lines of evidence suggest that each of these phenomena ultimately involves descending influences on the spinal motor output and/or sensory input. There was no correlation between maximal suppression of these spinal cord functions and signs of desynchronized sleep such as rapid eye movement. Carbachol microinjection into wide areas of CPIA also suppressed orienting behaviors. Taken together, these data suggest that CPIA is a system which primarily regulates animals' responsiveness to external stimuli, in part by influencing segmentally organized behaviors.