Investigation of the anticonvulsive effect of acute immobilization stress in anxious Balb/cByJ mice using GABAA-related mechanistic probes

Rationale A disordered regulation of neuroactive steroids release in response to acute stress could induce GABAergic dysfunctions underlying anxiety disorders. Objectives First, we conducted studies indicating that a short immobilization stress in anxious Balb/cByJ mice produced an anticonvulsive effect. Second, the effects of different positive allosteric modulators (etifoxine, progesterone, clonazepam, and allopregnanolone) of GABA_A receptors were compared in a mouse model mimicking the disruption of the acute stress-induced neuroactive steroids release with finasteride (types I and II 5α-reductase inhibitor). Results The acute stress-induced anticonvulsive effect, expressed by the threshold dose of t-butylbicyclophosphorothionate-producing clonic seizures, was time-dependent. The extent of the enhancement of acute stress-induced anticonvulsive effect was lowered in the presence of finasteride. The same effect was observed with PK11195, which behaves as an antagonist of the peripheral benzodiazepine receptor in the dose range used in this study. Picrotoxin reduced the acute stress anticonvulsive effect, proving that this effect operates through the GABA_A receptor. Contrary to progesterone (up to 30 mg/kg), etifoxine (50 mg/kg), allopregnanolone (10 mg/kg), and clonazepam (10 μg/kg) inhibited the finasteride effect in stressed animals. The effect of etifoxine was blocked in the presence of finasteride and picrotoxin combined in stressed animals. Conclusions These findings support the hypothesis suggesting an involvement of neuroactive steroids in the anticonvulsive effect of restraint stress. The dual and complementary mechanisms of action of etifoxine (directly on the GABA_A receptor and indirectly via the neuroactive steroids) may represent a therapeutic benefit in the treatment of various anxiety disorders with abnormal production of neuroactive steroids.