Testosterone Induces an All-or-None, Exponential Increase in Arginine Vasopressin mRNA in the Bed Nucleus of Stria Terminalis of the Hypogonadal Mouse.

The bed nucleus of the stria terminalis (BNST) in rodents contains arginine vasopressin (AVP) neurons which project to the lateral septum (LS) and habenula (LH) and are thought to be important for social recognition or memory. In previous studies we demonstrated that AVP immunoreactivity in the LS and LH is absent in the hypogonadal (hpg) mouse and that AVP immunoreactivity in the LH and LS of this mutant can be induced by testosterone. The aim of the present study was to determine whether this action of testosterone was due to the induction of AVP gene expression in BNST neurons and if so the time taken for testosterone to exert its effect. We found that exposure to supraphysiological concentrations of testosterone for 6-12 days caused an exponential, 50-fold increase in the number of cells that expressed AVP mRNA in the BNST in hpg mice. The action of testosterone is "all-or-none" in that the level of AVP mRNA in the AVP-positive cells was similar at all times after testosterone implantation and also similar or less than that in the few AVP-positive cells in animals not treated with testosterone. The relatively long time taken for testosterone to exert its effect on AVP mRNA in BNST neurons is comparable to its effects on AVP immunoreactivity in the LH and LS and on behaviour and suggests that the action of testosterone may be mediated by indirect or slow intracellular transduction mechanisms.