Final answer:
GABA is the main inhibitory neurotransmitter in the brain, regulating neuronal excitability through GABAA, GABAB, and GABAC receptors. It plays a crucial role in maintaining the excitation-inhibition balance, affecting functions such as cognition, mood, and sleep, and is involved in pathologies like epilepsy and schizophrenia.
Step-by-step explanation:
Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the central nervous system. It is synthesized from glutamate by the enzyme glutamic acid decarboxylase and functions through various mechanisms of release, including exocytosis and transporters in the cell membrane. GABA operates via GABAA, GABAB, and GABAC receptors, with each type contributing differently to the neuronal functions and inhibitory actions. GABAA receptors are ionotropic, allowing chloride ions to enter the cell and hyperpolarize it, which decreases neuron excitability. GABAB receptors, being metabotropic, activate second messenger systems and modulate ion channels. GABA's role extends beyond typical synaptic transmission, as it is also involved in the regulation of neuronal network activities and maintaining the excitation-inhibition balance critical to cognitive processes, mood regulation, sleep, and control of muscle action.
GABA has a significant role in protecting the brain during stressful conditions like cerebral ischemia and plays a part in the pathophysiology of epilepsy, where imbalances in excitatory/inhibitory neurotransmission are common. In the disease context, GABAergic dysfunctions are involved in conditions like schizophrenia, affecting the cognitive functions of the afflicted individuals. The overall effect of GABA is inhibitory, promoting a calming effect and preventing over-excitation within neural circuits.