GABAB1a

GABAB1a is a splice variant of the GABA-B receptor subunit 1, encoded by the GABBR1 gene in humans. It forms a functional GABA-B receptor through heterodimerization with the GABA-B2 subunit (GABBR2), and together these subunits mediate slow, G-protein-coupled inhibitory neurotransmission in the central nervous system. The GABA-B receptor is activated by the neurotransmitter GABA and modulates neuronal excitability by modulating ion channels and downstream signaling pathways.

GABAB1 has several isoforms produced by alternative promoter usage, among which GABAB1a and GABAB1b are the best characterized. GABAB1a contains a longer N-terminal extracellular region compared with GABAB1b, a difference that influences receptor trafficking, localization, and potentially functional roles at synapses. The distinct N-termini contribute to differences in subcellular distribution, with evidence of variant-specific localization patterns in various brain regions.

Functionally, GABA-B receptors couple to Gi/o proteins, leading to inhibition of adenylyl cyclase, decreased cyclic AMP production, activation of G-protein–gated inwardly rectifying potassium (GIRK) channels, and reduced voltage-gated calcium channel activity. These actions decrease postsynaptic excitability and presynaptic neurotransmitter release, contributing to the net inhibitory tone in neural circuits. The B1a/B1b isoforms influence receptor localization and regulation of neurotransmission, with ongoing research into their precise roles in synaptic plasticity and network activity.

GABAB1a is widely expressed in the brain, including regions such as the hippocampus, cortex, and cerebellum, and is implicated in learning, memory, and behavior. Dysfunction or altered expression of GABA-B receptor components has been associated with neurological and neuropsychiatric conditions, making the GABAB1a-containing receptor a potential target for therapeutic intervention.