Influences of dorsal and ventral hippocampus on hypothalamic self-stimulation

Abstract

The effects of concurrent stimulation or bilateral ablation of either dorsal or ventral hippocampus on hypothalamic self-stimulation were investigated. Moderate concurrent electrical stimulation of the dorsal hippocampus did not affect the rate of positive self-stimulation elicited from the lateral hypothalamus. Avoidance responses to electrical stimulation of medial or ventromedial hypothalamus were not affected by the dorsal hippocampus stimulation either. Bilateral lesions in the dorsal hippocampus did not change behavioral reactions elicited by the electrical stimulation of any site of the hypothalamus. Concurrent electrical stimulation of the ventral hippocampus did not change negative responses elicited from medial or ventro-medial hypothalamus, but sharply inhibited positive self-stimulation behavior in the lateral hypothalamic animals. Bilateral ablation of the ventral hippocampus had no effect on the positive behavioral responses, but if made in the animals with negative responses, it converted well expressed aversive behavior (escape, thumping etc.) into positive postural self-stimulation responses. Although the rate of the latter was below the lateral hypothalamic self-stimulation rates, nevertheless the acquired responses were perfectly stable. It is suggested that the ventral hippocampus exerts an inhibitory influence upon the hypothalamic motivational centers and the general meaning of this influence must be of protective nature.