Question

If GABA is released at synapse, then what will happen?
A. Depolarization of neuron
B. Repolarization of neuron
C. Hyperpolarization of neuron
D. No effect

Answer 1

Hint: There are two types of neurotransmitters that release at the synapse – excitatory and inhibitory. The excitatory neurotransmitter includes acetylcholine, glutamate, catecholamine, histamines.
Inhibitory neurotransmitters include serotonin and GABA.

Complete answer: The inhibitory neurotransmitter when released at synapse from pre synaptic membrane, it hyperpolarizes the postsynaptic membrane of the neuron.
GABA or gamma amino-butyric acid when binds to its receptor that is present on the postsynaptic membrane, helps in the increased influx of chloride ions into the postsynaptic cells and decreased efflux of potassium ions from postsynaptic cell to the synaptic region, which decreases the membrane potential and inhibits it.

Additional information: Neurons that release GABA as neurotransmitters are known as GABAergic neurons. GABA is synthesized from an amino acid, glutamate.
The synthesis is catalyzed by the enzyme glutamate decarboxylase (GAD) with the help of a cofactor – pyridoxal phosphate (vitamin B6). This process converts glutamate (an excitatory neurotransmitter) into GABA (an inhibitory neurotransmitter).
The binding of GABA to its pre and postsynaptic receptors helps in the opening of ion channels that we discussed above.

So, the correct answer is option C. Hyperpolarization of neurons.

Note: Many drugs such as Neomycin and Polymyxin B inhibit the binding of GABA to its receptor, which results in some clinical conditions such as psychosis or seizures.
There are two GABA receptors that are present in vertebrates are –
1. GABAA - the receptor is a ligand-gated ion channel complex, and
2. GABAB – this is a G protein-coupled receptor.