What GABA Is โ and What It Isn't
GABA is an amino acid โ it has both an amino group (โNHโ) and a carboxyl group (โCOOH). But it's not one of the 20 standard amino acids incorporated into proteins. The difference lies in the position of the amino group: in standard amino acids, the amino group is on the alpha carbon (adjacent to the carboxyl). In GABA, the amino group is on the gamma carbon โ three carbons away. This makes GABA a beta-amino acid's cousin, and it means no ribosome will ever incorporate it into a protein chain.
What GABA does instead is function as a neurotransmitter โ a chemical messenger between neurons. And not just any neurotransmitter: GABA is the primary inhibitory neurotransmitter in the vertebrate central nervous system. While glutamate is the main excitatory signal (telling neurons to fire), GABA is the main brake (telling them not to). The balance between these two systems determines the overall excitability of the brain.
๐งช Discovery: Found in Brain, Ignored for Years
GABA was first identified in the mammalian brain in 1950 by Eugene Roberts and Sam Frankel working at the City of Hope Medical Center in California, and independently by Jorge Awapara at the University of Texas the same year. Both groups found an unusual amino acid in brain tissue that didn't fit the standard set โ and traced it to the decarboxylation of glutamic acid.
For years, the significance wasn't clear. GABA was found in the brain in large concentrations โ far higher than most other free amino acids โ but its function was unknown. It took until the late 1950s and 1960s, when electrophysiological techniques allowed neuroscientists to apply GABA directly to neurons and observe that it inhibited their firing, that its role as an inhibitory neurotransmitter became clear. Today, GABA receptors are among the most important drug targets in all of pharmacology.
How GABA Works
GABA is synthesized from glutamate by a single enzyme: glutamate decarboxylase (GAD), which removes a carboxyl group from glutamic acid. The synthesis requires vitamin B6 (pyridoxal phosphate) as a cofactor โ which is why severe vitamin B6 deficiency can cause seizures (insufficient GABA synthesis leads to uncontrolled neuronal firing).
Released from one neuron into the synapse, GABA binds to receptors on the neighboring neuron. The main receptor type, GABA-A, is an ion channel: when GABA binds, the channel opens and chloride ions flow in, making the inside of the neuron more negative. This hyperpolarization makes the neuron less likely to fire. The effect is inhibition โ a quieting of neural activity.
The Pharmacological Target
GABA's receptor system is the target of a remarkable number of important drugs โ most of them working by enhancing GABA's inhibitory effect rather than replacing it:
GABA in Food and Fermentation
GABA is produced naturally by lactic acid bacteria during fermentation. Many fermented foods contain meaningful amounts of free GABA โ the bacteria produce it from glutamate using the same decarboxylase enzyme found in the brain.
Whether dietary GABA can actually cross the blood-brain barrier and affect brain function directly is debated โ the evidence in humans is limited. The blood-brain barrier is selectively permeable, and GABA has limited transport. But GABA in the gut may affect the enteric nervous system, and the gut-brain axis offers another potential route of influence.
GABA in Plants
GABA isn't only a mammalian neurotransmitter โ plants produce it too, in large amounts, particularly under stress conditions. When a plant is wounded, attacked by insects, or exposed to extreme temperature, GABA concentrations in plant tissue rise rapidly. In plants, GABA appears to act as a signaling molecule in stress responses and possibly as a nitrogen storage compound. Tea plants produce particularly high amounts, especially when leaves are processed under low oxygen โ the basis of deliberately high-GABA green teas marketed in Japan.
