|| Checking for direct PDF access through Ovid
We investigated the neurotropic activity of the following opioid peptides: fragments of gluten, Rubisco, and cytochrome b. Exorphin C and rubiscolin-5, which exhibited relative δ-selectivity, were shown to exert similar effects on the behavior of white newborn rats. Acute injections had weak influence on experimental animals, but chronic postnatal administration (1-14 days after birth) of these peptides decreased the anxiety level and improved the learning ability in a food-reinforced maze. The influence of cytochrophin-4 was very similar to that of β-casomorphin-5 (a short μ-selective fragment of β-casein). Both peptides exhibited an anxiolytic effect after acute injections, but their effects following chronic administration quickly weakened with the maturation of the newborn brain.