THE EFFECT OF LESIONS OF NEURAL INPUTS TO HYPOTHALAMIC MAGNOCELLULAR NEURONS ON THE EXPRESSION OF VASOPRESSIN AND OXYTOCIN GENES

Two important neural inputs with known influence on the electrical and secretory activity of vasopressin (VP)- and oxytocin (OT)-synthesizin g neurons in the hypothalamo-neurohypophyseal system (HNS) were lesion ed in order to examine their role in regulating VP mRNA and OT mRNA le vels in rats. There was no effect of unilateral sham-, 6-hydroxydopami ne- (6-OHDA) or 5,7-dihydroxytryptamine- (5,7-DHT) lesions of the medi al forebrain bundle (MFB) on the basal level of VP mRNA or OT mRNA in the supraoptic nucleus (SON) in euhydrated rats. In sham- and 5,7-DHT- lesioned rats, a normal increase in the levels of VP mRNA and OT mRNA was seen in the SON on the lesioned and non-lesioned side upon dehydra tion. In dehydrated 6-OHDA-lesioned rats an increase was found only on the lesioned side, whereas on the non-lesioned side there was no chan ge in VP mRNA and OT mRNA levels. Rats with a lesion of the subfornica l organ had the same levels of VP mRNA and OT mRNA in the HNS as sham- lesioned rats and responded similarly as sham-lesioned rats with incre ases in these mRNA levels to dehydration. The results indicate that mu ltiple pathways are involved in the osmotic regulation of VP and OT ge ne expression in the HNS, one may involve the catecholaminergic projec tion of the MFB. The parallel in responses of VP and OT neurons indica te that common neural pathways regulate the levels of VP mRNA and OT m RNA.