INCREASED EXPRESSION OF MAGNOCELLULAR ARGININE-VASOPRESSIN MESSENGER-RNA IN PARAVENTRICULAR NUCLEUS OF STRESS-INDUCED DEPRESSION-MODEL RATS

Exposure of rats to long-term intermittent walking stress results in a persistent inactive behavior in the subsequent two weeks in about 50% of rats (depression-model rats) while the activity returns gradually toward baseline in other rats (spontaneous recovery rats). To explore the role of hypothalamic-pituitary-adrenal (HPA) axis in these depress ion-model rats, we examined changes in the gene expression of corticot ropin-releasing factor (CRF) and arginine vasopressin (AVP) in the par aventricular nucleus (PVN) of the hypothalamus using in situ hybridiza tion histochemistry. We imposed the intermittent walking stress for tw o weeks in male Wistar rats, then compared the response of the depress ion-model rats and spontaneous recovery rats. The expression of CRF mR NA in PVN increased significantly by 60% and 80% compared to controls, in the model and the recovery rats, respectively. The magnocellular A VP mRNA in PVN increased significantly in the model rats by 60% compar ed to controls. The concentration of plasma ACTH increased in the mode l rats, but no significant change in plasma corticosterone or AVP leve l was noted in all three groups. Our results suggest that increased ma gnocellular AVP in PVN prays an important role in the regulation of HP A axis of the depression-model rats induced by long-term walking stres s.