Role of GABA-A and mitochondrial diazepam binding inhibitor receptors in the anti-stress activity of neurosteroids in mice.
Neuroactive steroidal modulation of immobilization-stress and possible involvement of GABA-A and mitochondrial diazepam binding inhibitor (DBI) receptors (MDR) has been investigated in mice. Immobilization of mice for 2 h induced intense antinociception, anxiety state, and associated with a fall in adrenal ascorbic acid levels. Pretreatment with high dose of progesterone (10 mg/kg), a precursor of neurosteroids, significantly decreased the stress-induced antinociception, anxiety and fall in adrenal ascorbic acid, while low doses (1 and 5 mg/kg) or hydrocortisone (10 and 100 mg/kg) were ineffective. In contrast, progesterone (1 mg/kg, for 9 days) produced a significant antistress effect, which was blocked by GABA-A antagonists picrotoxin (1 mg/kg) and bicuculline (1 mg/kg), but not by flumazenil (2 mg/kg), a specific benzodiazepine (BZD) antagonist. 4'-chlordiazepam (0.1 and 0.25 mg/kg), a specific high affinity MDR agonist, produced significant anti-stress effect in a flumazenil-insensitive manner, but was blocked by pretreatment with PK11195 (1.5 mg/kg), a selective partial agonist of MDR, and with bicuculline (1 mg/kg), a potent GABA-A receptor antagonist. At higher doses, progesterone and 4'-chlordiazepam which are effective in immobilization stress also reduced locomotion. However, lower doses of progesterone (6.5 mg/kg) neither affected locomotion, nor produced any motor toxicity on rota-rod test. At the lower doses, the MDR ligand 4'-chlordiazepam (50 micrograms/kg) decreased locomotor activity, without altering motor toxicity on rota-rod test. Further, the per se effects of these treatments on unstressed mice were not significantly different from those of untreated controls, except for plus-maze test. The antistress profile of progesterone may be attributed to the in vivo production of neurosteroid allopregnanolone, thus resembled that of BZDs. Furthermore, the antistress actions are flumazenil-resistant, reaffirming that there may be an increase in the levels of pregnane neurosteroids in vivo, which may act on a specific allosteric site on GABA-A receptors distinct from BZD site. Because 4'-chlordiazepam binds to MDRs and stimulate mitochondrial neurosteroidogenesis, the anti-stress effects of 4'-chlordiazepam may be imputed to its MDR-induced neurosteroids, which then act on GABA-A receptors. These data suggest a pivotal role for GABA-A and mitochondrial DBI receptors in the antistress actions of neurosteroids and reinforces their ameliorative effect in physiological stress.
Reddy
D S
DS
Department of Pharmacology, Panjab University, Chandigarh, India.
Kulkarni
S K
SK
D000704:Analysis of Variance; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D001522:Behavior, Animal / Q000187:drug effects; D001665:Binding Sites; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D003975:Diazepam / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005442:Flumazenil / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D009043:Motor Activity / Q000187:drug effects*; D010147:Pain Measurement / Q000187:drug effects*; D010852:Picrotoxin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011374:Progesterone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology; D013315:Stress, Psychological; D014229:Triazolam / Q000378:metabolism / Q000494:pharmacology
D001205:Ascorbic Acid; D003975:Diazepam; D005442:Flumazenil; D018756:GABA Antagonists; D018757:GABA Modulators; D007546:Isoquinolines; D010852:Picrotoxin; D011374:Progesterone; D012313:RNA; D011963:Receptors, GABA-A; D014229:Triazolam; C037850:PK 11195