[Delayed effect of exorphins on learning of albino rat pups].

The delayed effect of food-derived opioid peptides (exorphins) after chronic administration on postnatal days 1-14 on the learning of albino rat pups has been studied. Heptapeptide YPFPGPI (beta-casomorphin-7), pentapeptide YPLDL (rubiscolin-5) and pentapeptide YPISL (exorphin C) improved the development of the conditioned foraging reflex in a complex maze. Hexapeptide PFPGPI lacking the N-terminal tyrosine proved inefficient.

[Influence of acute and chronic administrations of beta-casomorphins on the maternal motivation in albino rats].

The influence of food-derived opioid peptides beta-casomorphines on the manifestation of nursing albino rats maternal behavior was investigated. It was shown that both acute and chronic (during the postnatal period) administration of beta-casomorphin-7 (Tyr-Pro-Phe-Pro-Gly-Pro), the typical representative of this group of peptides, decreases the level of the parental motivation. The effects of beta-casomorphin-7 were naloxone-dependent; N-terminal-reduced analogues had a significantly lesser activity.