Which neurotransmitter can inhibit the postsynaptic neuron?

Gamma amino butyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. Its main function is to reduce neuronal excitability throughout the nervous system. When GABA is released from a presynaptic neuron, it binds to GABA receptors on the postsynaptic neuron, leading to the opening of ion channels that allow the influx of chloride ions or the efflux of potassium ions. This process results in hyperpolarization of the postsynaptic membrane, making it less likely to generate an action potential in response to subsequent stimuli.

Acetylcholine, while an important neurotransmitter, can function as either an excitatory or inhibitory neurotransmitter depending on the type of receptor it binds to. Glutamate, on the other hand, is primarily a excitatory neurotransmitter and is the most abundant neurotransmitter in the brain. Para amino butyric acid, although it is similar in name, does not function as a neurotransmitter in the same context as GABA. Therefore, GABA is the only neurotransmitter among the options provided that has a clear and direct role in inhibiting postsynaptic neurons.