Decline of vasopressin immunoreactivity and mRNA levels in the bed nucleus of the stria terminalis following castration

Vasopressinergic (VP) neurons in the bed nucleus of the stria terminalis (BNST) of the rat are regulated by gonadal steroids. Gonadectomy causes the projections of the BNST to lose their VP immunoreactivity gradually over a period lasting more than 2 months. Here we have compared the rate of decline of VP mRNA and VP immunoreactivity in the BNST of adult male rats following castration. In experiment 1, the peak number of VP-immunoreactive cells and the level of VP gene expression were compared in sham-operated controls and at 1, 3, or 8 weeks postcastration. The number of VP-immunoreactive cells was not decreased at 1 week postcastration but was significantly reduced (p < 0.0001) at 3 and 8 weeks postcastration. VP gene expression declined more rapidly, and both the total number of labeled cells (p < 0.0001) and the average number of grains per cell (p < 0.01) were significantly reduced by 1 week postcastration. No VP-expressing cells were detectable at 3 or 8 weeks. The difference in the rate of decline in the number of cells labeled by the two techniques following castration did not appear to be due to colchicine pretreatment. In experiment 2, VP mRNA in the BNST was compared in sham- operated controls or at 1, 3, or 7 d postcastration. A significant decrease (p < 0.01) in the average number of grains per cell was detectable by just 1 d following castration, and the number of labeled cells was significantly reduced (p < 0.001) by 3 d postcastration. These results indicate that the capacity of BNST cells to synthesize VP responds more dynamically to changes in gonadal steroid levels than do levels of VP immunoreactivity. This difference may reflect the delay between VP gene expression and the processing of VP precursor molecules. Alternatively, gonadal steroids may modulate the release of VP from cells in the BNST.