Alprazolam is a triazolobenzodiazepine,[8] that is, a benzodiazepine with a triazolo-ring attached to its structure. Benzodiazepines produce a variety of effects by modulating the GABA subtype of the GABA receptor, the most prolific inhibitory receptor within the brain. The GABA receptor is made up from 5 subunits out of a possible 19, and GABA receptors made up of different combinations of subunits have different properties, different locations within the brain and importantly, different activities in regards to benzodiazepines.
In order for GABA receptors to be sensitive to the action of benzodiazepines they need to contain an α and a γ subunit, where the benzodiazepine binds. Once bound, the benzodiazepine locks the GABA receptor into a conformation where the neurotransmitter GABA has much higher affinity for the GABA receptor, increasing the frequency of opening of the associated Chloride ion channel and hyperpolarising the membrane. This potentiates the inhibitory effect of the available GABA leading to sedatory and anxiolytic effects. As mentioned, different benzodiazepines can have different affinities for GABA receptors made up of different collection of subunits. For instance, benzodiazepines with high activity at the α1 are associated with sedation whereas those with higher affinity for GABA receptors containing α2 and/or α3 subunits have greater anxiolytic activity.
The binding site for benzodiazepines is distinct from the binding site for barbiturates and GABA on the GABA receptor.
There is some evidence for antidepressant treatment of clinical depression in out patient settings, evidence for inpatients is lacking;[9] other benzodiazepines are not known to have antidepressant activity.
