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 conditioned avoidance acquisition sessions (approximately 20 trials per 25 min session). The Stock B animals were previously characterized as high-emotional based on [1] elevated plasma corticosterone, and lowered plasma oxytocin, levels and [2] decreased reaction time and an increased startle amplitude to an acoustic stimulation. Finally, [3] these animals were unable to acquire a conditioned avoidance response within 5 days of training. Results: The Stock A animals rapidly and statistically significantly acquired the avoidance behaviour within 4 days of daily training, whereas Stock B animals did not improve over this time period. The avoidance performance of Stock B animals was markedly and statistically significantly improved by the oxytocin pre-treatment, whereas the performance of Stock A animals was not affected 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 anti-stress-like properties of oxytocin, rendering the animals able to successfully cope with the demands of the conditioned avoidance situation. (C) 2000 Elsevier Science B.V. All rights reserved.