Neurohypophyseal hormones, analogs, and fragments: their effect on puromycin-induced amnesia.

Neurohypophyseal hormones and several of their analogs, as well as N-terminal and C-terminal fragments, have been studied for their ability to attenuate puromycin-induced amnesia in mice. [8-Lysine]vasopressin, [8-arginine]vasopressin, and the analogs des-9-glycinamide-[8-lysine]vasopressin, [1-beta-mercaptopropionic acid, 8-lysine]vasopressin, [1,6-aminosuberic acid, 8-lysine]vasopressin, [4-leucine, 8-lysine]vasopressin, glycyl-glycyl-glycyl-[8-lysine]vasopressin, [1-beta-mercaptopropionic acid, 8-D-arginine]vasopressin, and [1,6-aminosuberic acid, 8-arginine]vasopressin are active. [8-Arginine]oxytocin as well as oxytocin and all of its other analogs tested are inactive with the striking exception of glycyl-glycyl-glycyl-oxytocin. The structural aspects of the neurohypophyseal hormones which appear to be important for significant activity in memory consolidation include the combination of a cyclic moiety containing the Tyr and Phe residues along with a basic residue in position 8. Another series of active compounds comprises C-terminal neurohypophyseal peptides and analogs thereof, including the naturally occurring Pro-Leu-Gly-NH2 and, most surprisingly, Leu-Gly-NH2, as well as its derivatives D-Leu-Gly-NH2 and the diketopiperazine, cyclo(-Leu-Gly-).