The modulation of the dorsal immobility response in the adult male Wistar rat: the opposite effects of ACTH4-10 and [D-Phe7]ACTH4-10.

A series of experiments were conducted to determine the behavioral effect of ACTH4-10 and [D-Phe7]ACTH4-10 on the dorsal immobility response (DIR) in adult male Wistar rats. Both peripheral and central injections of ACTH4-10 attenuated the duration of DIR, whereas, peripherally injected [D-Phe7]ACTH4-10 resulted in the potentiation of this response. The effect of peripherally administered ACTH4-10 was dose dependent in the range of 0.2 to 20 micrograms. These results, in part, extend the prior findings on the modulation of various learned and species-typical behaviors by ACTH-related peptides to a complex state of behavioral inhibition and immobility.