Extra-Synaptic GABA_A Receptor Potentiation and Neurosteroid-Induced Learning Deficits Are Inhibited by GR3027, a GABA_A Modulating Steroid Antagonist

Objectives In Vitro: To study the effects of GR3027 (golexanolone) on neurosteroid-induced GABA-mediated current responses under physiological GABAergic conditions with recombinant human alpha 5 beta 3 gamma 2L and alpha 1 beta 2 gamma 2L GABAA receptors expressed in human embryonic kidney cells, using the response patch clamp technique combined with the Dynaflow (TM) application system. With alpha 5 beta 3 gamma 2L receptors, 0.01-3 mu M GR3027, in a concentration-dependent manner, reduced the current response induced by 200 nM THDOC + 0.3 mu M GABA, as well as the THDOC-induced direct gated effect. GR3027 (1 mu M) alone had no effect on the GABA-mediated current response or current in the absence of GABA. With alpha 1 beta 2 gamma 2L receptors, GR3027 alone had no effect on the GABA-mediated current response or did not affect the receptor by itself. Meanwhile, 1-3 mu M GR3027 reduced the current response induced by 200 nM THDOC + 30 mu M GABA and 3 mu M GR3027 that induced by 200 nM THDOC when GABA was not present. Objectives In Vivo: GR3027 reduces allopregnanolone (AP)-induced decreased learning and anesthesia in male Wistar rats. Rats treated i.v. with AP (2.2 mg/kg) or vehicle were given GR3027 in ratios of 1:0.5 to 1:5 dissolved in 10% 2-hydroxypropyl-beta-cyclodextrin. A dose ratio of AP:GR3027 of at least 1:2.5 antagonized the AP-induced decreased learning in the Morris Water Mase (MWM) and 1:7.5 antagonized the loss of righting reflex (LoR). GR3027 treatment did not change other functions in the rat compared to the vehicle group. Conclusions: GR3027 functions in vitro as an inhibitor of GABAA receptors holding alpha 5 beta 3 gamma 2L and alpha 1 beta 2 gamma 2L, in vivo, in the rat, as a dose-dependent inhibitor toward AP's negative effects on LoR and learning in the MWM.