Vasopressin and oxytocin in brain areas of rats selectively bred for differences in behavioral performance

Wistar rats were selectively bred over 10 generations for differences in performance in a footshock-motivated brightness discrimination (BD) test in a Y-maze. High behavioral performance (Wis/HBP) and low behavioral performance (Wis/LBP) rat lines were obtained which differ significantly in all behavioral components tested: frequency of correct responses, number of trials to criterion, response latency (HBP less than LBP), and frequency of freezing behavior (HBP less than LBP), the latter suggesting differences in emotionality. In Wis/LBP rats, furthermore, the normal increase in behavioral performance between the training and the relearning session, which indicates the formation of a memory trace, disappeared during selection. In male breeders sampled during selection of the two lines (Wis/HBP: n = 17; Wis/LBP: n = 21), both arginine vasopressin (AVP) and oxytocin (OXT) contents were measured by radioimmunoassay in the motor cortex, septum/striatum, hippocampus, hypothalamus, medulla oblongata and posterior pituitary. Compared with the Wis/HBP rats, the Wis/LBP rats contained less AVP in the hippocampus (3.1 +/- 0.58 vs 8.3 +/- 1.4 pg/mg wet wt., mean +/- S.E.M., P less than 0.001), but more AVP in the medulla (1.7 +/- 0.20 vs 1.1 +/- 0.18 pg/mg, P less than 0.05). In contrast, no significant differences between the lines were detected with respect to OXT concentrations. In the Wis/LBP rats, moreover, the hippocampal AVP content decreased during selection (r = -0.645, P less than 0.01), while the acquisition response latency increased (r = 0.549, P less than 0.01). As a consequence, a significant, albeit weak, negative correlation (r = -0.483, P less than 0.05) was observed between the individual hippocampal AVP content and the response latency during acquisition. Thus, the results confirm the view that genetically determined differences in the hippocampal content of endogenous AVP may contribute to an individual's level of emotionality and behavioral performance.