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Chemistry
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2. Sedative hypnotic effect of phenobarbital is through? a) Increase the affinity of GABA for GABA receptors b) Decrease the affinity of GABA for GABA receptors c) a-inhibition d) f-inhibition​

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GABA receptors have been identified electrophysiologically and pharmacologically in all regions of the brain

Because GABA is widely distributed and utilized throughout the CNS, early GABAergic drugs had very generalized effects on CNS function. The development of more selective agents has led to the identification of at least two distinct classes of GABA receptor, GABAA and GABAB. They differ in their pharmacological, electrophysiological and biochemical properties. Electrophysiological studies of the GABAA-receptor complex indicate that it mediates an increase in membrane conductance with an equilibrium potential near the resting level of −70 mV. This conductance increase often is accompanied by a membrane hyperpolarization, resulting in an increase in the firing threshold and, consequently, a reduction in the probability of action potential initiation, causing neuronal inhibition. This reduction in membrane resistance is accomplished by the GABA-dependent facilitation of Cl− ion influx through a receptor-associated channel. On the other hand, increased Cl− permeability can depolarize the target cell under some conditions of high intracellular Cl−. This in turn potentially can excite the cell to fire or to activate Ca2+ entry via voltage-gated channels and has been proposed as a physiologically relevant event, especially in embryonic neurons.

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