Withdrawal from 3α-OH-5α-pregnan-20-one using a pseudopregnancy model alters the kinetics of hippocampal GABA(A)-gated current and increases the GABA(A) receptor α4 subunit in association with increased anxiety

In the present study, we have characterized properties of steroid withdrawal using a pseudopregnant rat model. This paradigm results in increased production of endogenous progesterone from ovarian sources and as such is a useful physiological model. 'Withdrawal' from progesterone induced by ovariectomy on day 12 of pseudopregnancy resulted in increased anxiety, as determined by a decrease in open arm entries on the elevated plus maze compared to control rats and pseudopregnant animals not undergoing withdrawal. Similar findings were obtained 24 hr after administration of a 5α-reductase blocker to a pseudopregnant animal, suggesting that it is the GABA(A)-modulatory 3α-OH-5α-pregnan-20-one (3α,5α-THP) that produces anxiogenic withdrawal symptoms. Twenty-four hours after steroid withdrawal, the time constant for decay of GABA(A)-gated current was also reduced sixfold, assessed using whole-cell patch-clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. Thus, 3α,5α-THP withdrawal results in a marked decrease in total GABA(A) current, a possible mechanism for its anxiogenic, proconvulsant sequelae. In addition, 3α,5α- THP withdrawal resulted in insensitivity to the normally potentiating effect of the benzodiazepine lorazepam (LZM) on GABA(A)-gated Cl^- current. This withdrawal profile is similar to that reported for other GABA(A)-modulatory drugs such as the benzodiazepines (BDZs), barbiturates, and ethanol. These changes were also associated with significant two and threefold increases in both the mRNA and protein for the α4 subunit of the GABA(A) receptor, respectively, in hippocampus. The pseudopregnancy paradigm may be a useful model for periods of endogenous 3α,5α-THP withdrawal such as premenstrual syndrome and postpartum or postmenopausal dysphoria, when increased emotional lability and BDZ insensitivity have been reported.