Improved conditioned avoidance learning by oxytocin administration in high-emotional male Sprague-Dawley rats

Objective: To examine anti-stress-like properties of oxytocin as a means to improve conditioned avoidance learning in a low-performing, high-emotional , stock of Sprague-Dawley male rats. Methods: Adult male rats of two stocks of the Sprague-Dawley strain, designated Slack A and Stock B, were treated daily with oxytocin (1 mg kg(-1) s.c.) for 5 days preceding four daily con ditioned avoidance acquisition sessions (approximately 20 trials per 25 min session). The Stock B animals were previously characterized as high-emotio nal based on [1] elevated plasma corticosterone, and lowered plasma oxytoci n, levels and [2] decreased reaction time and an increased startle amplitud e to an acoustic stimulation. Finally, [3] these animals were unable to acq uire a conditioned avoidance response within 5 days of training. Results: T he Stock A animals rapidly and statistically significantly acquired the avo idance behaviour within 4 days of daily training, whereas Stock B animals d id not improve over this time period. The avoidance performance of Stock B animals was markedly and statistically significantly improved by the oxytoc in pre-treatment, whereas the performance of Stock A animals was not affect ed by the same oxytocin treatment. Conclusions: pre-treatment with oxytocin markedly improved avoidance learning in the Stock B high-emotional animals . It is suggested that the improvement is due to previously demonstrated an ti-stress-like properties of oxytocin, rendering the animals able to succes sfully cope with the demands of the conditioned avoidance situation. (C) 20 00 Elsevier Science B.V. All rights reserved.