Relation of rat brain acetylcholine levels to duration of self-stimulation and escape behavior

Total brain acetylcholine (ACh) was assayed in groups of animals after various periods of operant responding maintained by electrical stimulation of the lateral posterior hypothalamus or of escape behavior induced by electrical stimulation of the midbrain tegmentum. Different groups of trained rats were placed in identical Skinner boxes for periods of 1 to 24 hr. The following groups were studied: controls, self-stimulators receiving electrical stimulation, escapers from brain stimulation or peripherally applied aversive stimulation, self-stimulators not receiving electrical stimulation prior to decapitation, tubocurarine-paralyzed respired rats with electrodes in the posterior-lateral hypothalamus not receiving stimulation, and a group of tubocurarine-paralyzed, respired rats receiving electrical stimulation automatically. It was found that brain stimulation decreased total brain ACh, regardless of whether the stimulation was positive, as during self-stimulation behavior, or negative, as during escape behavior. Animals that receivied positive stimulation while being paralyzed showed similar decreases in total brain ACh, but the change in ACh was smaller. No changes occurred in animals that were paralyzed that recieved no electrical stimulation. It is concluded that brain usage produced by electrical stimulation of discrete functional pathways causes a reduction of total ACh, but this is unrelated to the specific motivational properties of the electrical stimuli.