In an adult brain, the neurotransmitter GABA is inhibitory. When neurons are stimulated with GABAa receptor agonists, it causes the opening of the GABAa receptor coupled chloride channels and hyperpolarization.
Interestingly, in the embryonic brain, GABA is an excitatory neurotransmitter. When GABAa receptor agonists are applied to embryonic neurons, it causes their depolarization.
What happens during development that causes GABA to switch from excitation to inhibition?