Mechanism of action of benzodiazepine is

Ans. is 'a' i.e., GABAA - BZD - Cl- channel stimulator Mechanism of action of benzodiazepines (BZDs)* Muscle relaxation is produced by action on medulla.* Ataxia is due to action on cerebellum.* BZDs acts on GABAA receptors.* GABAa receptor has 5 subunits a / b, b, a / g.* GABA binding site is on b. subunit, while BZDs binding site is on a / g subunit.* BZDs receptor increase the conductance of Cl channel.* BZDs do not themselves increase Cl conductance, i.e. they have only GABA facilitatory but no GABA mimetic action. (Barbiturates have both GABA facilitatory and GABA mimetic actions).Effect on CNS* In contrast to barbiturates, BZDs are not general depressant, but exert relatively selective anxiolytic, hypnotic, muscle relaxant and anticonvulsant effects.* The antianxiety action of BZDs is not dependent on their sedative property - with chronic administration relief of anxiety is maintained, but drowsiness wanes off due to development of tolerance.* Stage 2 sleep is increased, while REM, Stage 3 & 4 sleep are decreased.* Nitrazepam is the only benzodiazepine, which increases REM sleep.* Clonazepan and diazepam have more marked muscle relaxant property.* Clonazepam, diazepam, nitrazepam and flurazepam have more prominent anticonvulsant activity than other BZDs.* Diazepam (but not other BZDs) has analgesic action.* Diazepam produces short lasting coronary dilatation on i.v. injection.* Diazepam decreases nocturnal gastric secretion and prevents stress ulcers.