Endocrine and behavioral traits in low-avoidance Sprague-Dawley rats

In the present series of experiments, we have examined the endocrine profil e of two stable colonies of Sprague-Dawley rats, here labeled Stock A, and Stock B, differing markedly in their ability to acquire a conditioned avoid ance response. On separate occasions, the animals were subjected to five da ily sessions (approximately 20 trials per 15 min session) of conditioned av oidance training, measurements of startle reactivity to an auditory stimula tion and open-field spontaneous locomotor activity observations. The experi ments were concluded by taking blood samples for later analysis of plasma g lucose and plasma levels of the following hormones: insulin, gastrin, CCK, glucagon, somatostatin, oxytocin and corticosterone. The low-performing Sto ck B animals were characterized by [1] being more reactive to sensory stimu lation: higher startle amplitude and shorter startle latency; [2] having hi gher plasma insulin and corticosterone levels, whereas plasma gastrin and o xytocin were significantly lowered and a strong tendency for a decrease als o in plasma CCK. There were no differences in spontaneous locomotor activit y between the two substrains. Taking total variability in avoidance perform ance into account, there was a statistically significant positive correlati on between plasma oxytocin, as well as gastrin, levels and avoidance perfor mance. The evidence obtained here, and in other laboratories, suggests that the Stock B animals display hormonal changes indicative of a submissive-de fensive reaction pattern. Thus, the avoidance acquisition deficits displaye d by the present Sprague-Dawley stocks A and B, are in all probability caus ed by emotional reactions when challenged with external stimuli requiring a ctive responding. (C) 1999 Published by Elsevier Science B.V. All rights re served.