No abstract

This study was designed to examine the effects of psychological stress and oxytocin treatment (5.8 or 11.6 IU/kg) on noradrenaline, dopamine and serotonin levels in the hypothalamus, hippocampus and brainstem. Results indicated that repeated exposure to the novelty stressor resulted in amine levels which did not significantly differ from those of control levels. In contrast, oxytocin treatment produced a significant elevation in serotonin levels in each of the three brain regions examined, while the effects for dopamine were confined to the hypothalamus. Furthermore, when oxytocin was administered immediately prior to unpredictable exposure to the novelty stressor, a significant increase in levels of noradrenaline in the hypothalamus and serotonin in the hippocampus and brainstem were observed. These results suggest that oxytocin may play an important role in modulating monoaminergic activity which is also apparent when the animal is exposed to a psychological stressor.

Recent evidence suggests that oxytocin modulates both ACTH and prolactin secretion. The present study was designed to investigate the possible role of oxytocin in the corticosterone and prolactin response to predictable and unpredictable novelty stress. These responses were examined in lactating females (Day 6 and Day 21 postpartum) which had received stress and oxytocin treatment during pregnancy. The results demonstrated that exposure to the novelty stressors during pregnancy resulted in a significant elevation in corticosterone levels of lactating females on Day 6 postpartum. A similar elevation was also observed on Day 21 postpartum for the unpredictable condition. Oxytocin treatment did not, however, significantly affect the corticosterone response to the psychological stressor. Furthermore, prolactin levels were not significantly affected on either Day 6 or Day 21 postpartum by either novelty stress or oxytocin treatment administered during pregnancy. It was suggested that the sustained elevation in corticosterone levels obtained following unpredictable exposure to the stressor had important implications for the lactation process.

No abstract

Six experiments are reported on the effects of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on two-way escape and avoidance learning. Rats were tested on either escape or avoidance learning at 80 days of age after chemical sympathectomy at birth or 40 or 80 days of age. Neonatal and chronic sympathectomy (at 40 days), but not acute sympathectomy (at 80 days), resulted in depressed escape learning. Avoidance learning was affected by neonatal sympathectomy and partially by acute sympathectomy. The results have implications for the role of the autonomic nervous system in escape-avoidance learning.