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)-synthesizing neurons in the hypothalamo-neurohypophyseal system (HNS) were lesioned in order to examine their role in regulating VP mRNA and OT mRNA levels in rats. There was no effect of unilateral sham-, 6-hydroxydopamine- (6-OHDA) or 5,7-dihydroxytryptamine- (5,7-DHT) lesions of the medial 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 dehydration. In dehydrated 6-OHDA-lesioned rats an increase was found only on the lesioned side, whereas on the non-lesioned side there was no change in VP mRNA and OT mRNA levels. Rats with a lesion of the subfornical 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 increases in these mRNA levels to dehydration. The results indicate that multiple pathways are involved in the osmotic regulation of VP and OT gene expression in the HNS, one may involve the catecholaminergic projection of the MFB. The parallel in responses of VP and OT neurons indicate that common neural pathways regulate the levels of VP mRNA and OT mRNA.