All act through GABA receptors except
Ans is 'd' i.e. Promethazine Gamma Aminobuturic acid (GABA) is the most important inhibitory transmitter in the central nervous system.GABA ergic neurons are widely distributed in the C.N.S. but are virtually absent outside the brain and spinal cord.GABA controls the state of excitability in all brain areas and the balance between excitatory inputs (mostly glutaminergic) and inhibitory GABA ergic activity determines the prevailing level of neuronal activity.If the balance swings in favour of GABA. then sedation, amnesia, muscle relaxation and ataxia appear and nervousness and anxiety are reduced.The mildest reduction of GABA ergic activity elicits arousal, anxiety, restlessness, insomnia, exaggerated reactivity.Mechanism of action of Drugs on GABAThe inhibitory neurotransmitter GABA acts on GABA receptors. When GABA binds with GABA receptors the permeability of the GABA receptors for the chloride ion increases allowing more ions into the neurons and decreasing excitability.Benzodiazepenes attach with GABA receptors.The resulting Benzodiazepene GABA receptor complex enhance the effectiveness of GABA by lowering the concentration of GABA required for opening the chloride channel thus enabling GABA ergic circuits to produce a larger inhibitory effect.Simply remember, Benzodiazepenes increase the frequency of channel-opening, thus leading to inhibition.Barbiturates also act on GABA receptors to cause sedation.But in contrast to benzodiazepenes they appear to increase the duration of GABA gate chloride channel opening.Zolpidem is a newer hypnotic that also modify GABA receptors.
Benzodiazepine
Barbiturates
Zopiclone
Promethazine.
C.N.S