Role of cholinergic fibers in a center essential to animal hypnosis.

We previously found that the center from which animal hypnosis is controlled in the rabbit is located in the area that includes the brachium conjunctivum and locus coeruleus (LC-BC) of the brainstem. Microinjection was used to investigate functions of cholinergic fibers in this area in relation to animal hypnosis. The duration of animal hypnosis (DAH) induced by inversion was diminished to about 60% of the controls by microinjecting atropine into the LC-BC, whereas microinjection of carbachol prolonged the DAH to 3.5 times that of the controls. Flexor muscle contraction of the upper extremities, induced by electrical stimulation of the motor cortex (CFM), was enhanced by atropine and suppressed by carbachol. In normal rabbits; hard pressing on the ear base or the lumbar paravertebral area reduced CFM (pressing effect), and this effect was partially antagonized by atropine microinjected into the LC-BC. The results suggest that cholinergic fibers in the LC-BC modulate functions involved in animal hypnosis.