Effects of the antinociceptive dipeptide L-tyrosine-L-arginine (kyotorphin) on the motivation, anxiety, and memory in rats.

The endogenous dipeptide L-tyrosine-L-arginine (kyotorphin, KTP) is found in brain structures related to the processing of information for nociception, the control of emotions, and memory formation. Besides the antinociceptive effect of KTP, it has a mild protective activity against the deleterious influence of the brain hypoperfusion and streptozotocin on the behavior and memory. We aimed to study the effects of the intracerebroventricular injection of effective antinociceptive doses of KTP on the motivational behavior, memory, and blood and hippocampal levels of the carbonylated proteins in healthy male adult Wistar rats. We used a paw-pressure test for assessment of acute nociception, an open field test for assessment of exploration and habituation to a new environment, elevated plus maze test for the evaluation of anxiety-like behavior, and novel object recognition test for working memory. Carbonylated protein assay was used for the assessment of the oxidative impairment of the proteins. The results were analyzed by ANOVA. The present data showed that all single doses of KTP exerted an antinociceptive effect, but this effect was not observed after chronic administration. Only the highest dose of 100 µg was able to induce anxiolytic and motor inhibiting effects. None of the doses used showed effects on the recognition memory or the level of the carbonylated protein. Our results showed that KTP exerted its antinociceptive effect without affecting negatively the blood and brain carbonylated protein or basic behavioral parameters related to the exploration, motivation, and memory formation in healthy rats.

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