Dorsal hippocampus: a site of action of neuropeptides on avoidance behavior?

Vasopressin and ACTH 4-10 induce a dose dependent long-term, respectively short-term inhibition of extinction of a pole jumping avoidance response in animals with sham lesions in the antero-dorsal hippocampus. Small lesions, causing a restricted damage in this area of the brain, partly inhibit the behavioral effect of vasopressin. Extensive lesions in the antero-dorsal hippocampus completely prevent the inhibitory effects of vasopressin and of ACTH 4-10 on extinction of the avoidance response. The extensive lesions in the dorsal hippocampus complex do not interfere with the rate of extinction, but acquisition of the response is retarded. These observations do not allow the conclusion that the hippocampal complex is the locus of action of neuropeptides in relation to avoidance behavior; it is more likely that this brain region is but one site of behavioral action of these hormones, and that the limbic system needs to be intact to permit the neuropeptides to exert their behavioral effects.