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Gamma-aminobutyric acid (GABA)
Gamma-aminobutyric acid (GABA) is one of the most common neurotransmitters found in mammals, where it acts as an inhibitor.
GABA, as a general inhibitor and plays an important role in regulation, preventing over-excitation of neuronal channels. It does this by opening ion channel that allow inflow of Cl- or outflow of K+ ions, leading to hyperpolarization.
It is important in brain development, particularly before glutamate synapses arise.
GABAA and GABAC are ionotropic receptors, whilst GABAB are metabotropic receptors. GABAA receptors accepts various drugs including benzodiazepines, barbiturates, ethanol, inhaled anaesthetics and neuroactive steroids.
In spastic diplegia, GABA absorption by some nerves becomes damaged, leading excessive muscular tensing.
Unrestricted synaptic excitation across the brain causes a seizure. It is thought that GABA is implicated in epilepsy.
Muscimol (derived muscarine) is a direct agonist.
Dicuculline blocks a GABA binding site and is a direct antagonist.
Benzodiasepines, including diazapam (Vallium) and chlorodiazepoxide (Librium) act as tranquillizers, binding to a GABAA site, reducing anxiety, relaxing muscles and promoting sleep. Alcohol is believed to bind with this site too.
Another GABAA site binds with barbiturates whilst another binds with steroids which are used as general anesthetics. In lower doses, barbituates are calming. In increasingly higher doses they cause difficulty in walking and talking, then unconsciousness, coma and death.
Picotoxin (a shrub-derived poison) binds to yet another site and inhibits GABAA. In high doses it causes convulsions.
Baclofen acts on GABAB as an antagonist, thus acting as a muscle relaxant.