etifoxine and tert-butylbicyclophosphorothionate

A disordered regulation of neuroactive steroids release in response to acute stress could induce GABAergic dysfunctions underlying anxiety disorders.. 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 5alpha-reductase inhibitor).. 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 microg/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.. 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.

Topics: Allosteric Regulation; Animals; Anxiety; Bridged Bicyclo Compounds, Heterocyclic; Clonazepam; Convulsants; Drug Interactions; Finasteride; Isoquinolines; Male; Mice; Mice, Inbred BALB C; Oxazines; Picrotoxin; Pregnanolone; Progesterone; Receptors, GABA-A; Restraint, Physical; Seizures; Stress, Psychological

We looked for an interaction between etifoxine and the neurosteroid allopregnanolone at central gamma-aminobutyric acid (GABA(A)) receptors. Etifoxine (2 microM) did not affect the affinity of allopregnanolone (IC(50)=108 nM) for its site in preparations of Sprague-Dawley rat cerebral cortex membranes, as determined by the inhibition of [(35)S] t-butylbicyclophosphorothionate binding, a specific ligand of the GABA(A) receptor chloride channel site. Etifoxine and allopregnanolone were anticonvulsants, blocking the clonic convulsions induced by bicuculline (an antagonist of the GABA(A) receptor) in CD1 mice. A combination of subactive doses of the two compounds showed additive anticonvulsant effects. These results suggest that etifoxine and allopregnanolone bind to distinct putative recognition sites at or near the chloride channel site. Functionally, their binding may have an additive effect by enhancing GABA(A) inhibitory transmission.

Topics: Allosteric Site; Animals; Anticonvulsants; Bicuculline; Bridged Bicyclo Compounds, Heterocyclic; Chloride Channels; Convulsants; Drug Interactions; GABA Antagonists; Male; Oxazines; Pregnanolone; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Sulfur Radioisotopes

We have investigated the effects of 2-ethylamino-6-chloro-4-methyl-4-phenyl-4H-3,1-benzoxazine hydrochloride (etifoxine) on GABA(A) receptor function. Etifoxine displaced [(35)S]TBPS (t-butylbicyclophosphorothionate) from GABA(A) receptors of rat cortical membranes with an IC(50) of 6.7+/-0.8 microM and [(3)H]PK11195 from peripheral (mitochondrial)-type benzodiazepine receptors (PBRs) of rat heart homogenates with an IC(50) of 27.3+/-1.0 microM. Etifoxine displayed anxiolytic properties in an anticonflict test in rats, and potentiated GABA(A) receptor-mediated membrane currents elicited by submaximal (5-10 microM) but not saturating (0.5 mM) concentrations of GABA in cultured rat hypothalamic and spinal cord dorsal horn neurones. In hypothalamic cultures, etifoxine induced a dose-dependent inward current for concentrations >1 microM which reflected the post-synaptic potentiation of a small ( approximately 20 pA) tonic and bicuculline-sensitive GABA(A) receptor-gated Cl(-) current. Etifoxine also increased the frequency of spontaneous and miniature GABAergic inhibitory post-synaptic currents without changing their amplitude and kinetic characteristics. Both effects of etifoxine were insensitive to flumazenil (10 microM), an antagonist of central-type benzodiazepine sites present at GABA(A) receptors, but were partly inhibited by PK11195 (10 microM) an antagonist of PBRs which control the synthesis of neurosteroids. Our results indicate that etifoxine potentiates GABA(A) receptor-function by a direct allosteric effect and by an indirect mechanism involving the activation of PBRs.

Topics: Animals; Behavior, Animal; Bicuculline; Binding, Competitive; Brain; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Dose-Response Relationship, Drug; Drinking Behavior; Flumazenil; GABA Antagonists; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Hypothalamus; Isoquinolines; Male; Membrane Potentials; Membranes; Neurons; Oxazines; Patch-Clamp Techniques; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptors, GABA-A; Sulfur Radioisotopes; Synaptic Transmission; Tetrodotoxin; Tranquilizing Agents

This study examined the nature of the interactions of etifoxine, an anxiolytic and anticonvulsant compound, with the GABA(A) receptor/chloride channel complex. In membrane preparations of Sprague-Dawley rat cerebral cortex, etifoxine competitively inhibited the binding of [35S]t-butylbicyclophosphoro-thionate (TBPS), a specific ligand of the GABA(A) receptor chloride channel site. In vivo studies demonstrated an anticonvulsant effect of etifoxine (50 and 75 mg/kg, i.p.) against the clonic convulsions induced by TBPS in CD1 mice. Flumazenil (10 and 40 mg/kg, i.p.), an antagonist of benzodiazepine sites at GABA(A) receptors, had no effect on the action of etifoxine. These findings suggest that etifoxine exerts its effect by interacting with the Cl- channel of GABA(A) receptors and probably by facilitating GABAergic inhibition.

Topics: Animals; Anticonvulsants; Binding, Competitive; Bridged Bicyclo Compounds, Heterocyclic; Cell Membrane; Cerebral Cortex; Chloride Channels; Convulsants; Flumazenil; GABA Modulators; Kinetics; Male; Mice; Oxazines; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, GABA-A