Peculiarities of Behavior and Emotional Reactions of Old Rats under Conditions of Brain Self-Stimulation Combined with Injections of Melatonin

Abstract

We studied the peculiarities of emotional reactions and behavior of old rats in the open field test under conditions of self-stimulation of the ventrolateral and ambivalent zones of the ventromedial hypothalamus either provided in isolation or combined with injections of melatonin. Isolated selfstimulation and self-stimulation combined with introduction of melatonin (six sessions) exerted mostly activating influences on the system of positive emotional reactions. Chronic self-stimulation exerted activating effects on the cerebral mechanisms responsible for negative emotional behavior and increased the levels of motor excitation and emotionality (autonomic behavior manifestations) in animals in the open field test, i.e., induced manifestations of emotional stress in experimental rats. Hypothalamic selfstimulation and injections of melatonin exerted modulating inhibitory effects on the system of negative reinforcement, i.e., decreased psychomotor excitation. The indices of orientation/searching (vertical) activity and the number of episodes of grooming increased, while the latency of coming out from the field center decreased. The data obtained indicate that melatonin possesses anxiolytic and antistress properties mediated by its influence on the reinforcing cerebral systems.