Incidence of dye coupling among magnocellular paraventricular nucleus neurons in male rats is testosterone dependent.

Recently published work in the rat has shown that: the incidence of electrical coupling, as measured by dye coupling, is decreased from control levels by 8 days of drinking hypertonic saline; an index of circulating testosterone, seminal vesicle weight, is also decreased by 8 days of saline drinking; and both plasma and urinary vasopressin levels are reduced in castrated males, but can be returned to normal with testosterone replacement. These findings have led to the hypothesis that dye coupling, particularly that involving vasopressinergic cells, may be affected by gonadal steroids. We have investigated the effects of castration and testosterone replacement on the incidence of dye coupling among the neurons of the predominantly vasopressinergic magnocellular lateral paraventricular nucleus in slices of male rat hypothalamus. Incidence of dye coupling in this nucleus of castrated rats was found to be decreased by 67% from sham castrated control levels. Testosterone-filled Silastic capsules (but not empty capsules) implanted subcutaneously at the time of castration abolished the effect of castration on dye coupling. We conclude that testosterone has a powerful influence upon coupling among PVN vasopressinergic neurons and may participate in the control of vasopressin release in intact animals.