SYNAPTIC INPUTS TO GABA(A) AND GABA(B)RECEPTORS ORIGINATE FROM DISCRETE AFFERENT NEURONS

Gamma-Aminobutyric acid (GABA) inhibits neurons by acting at GABA(A) and GABA(B) receptors but it is not known whether the two receptors are associated with discretely separate afferent inputs or whether GABA released from a single presynaptic neuron activates both receptors. Intracellular recordings were used to show that, in the lateral amygdala and ventral tegmental area of the rat, distinct sets of GABA-containing neurons provide the synaptic input to GABA(A) and GABA(B) receptors. Synaptic potentials resulting from GABA(A) receptor activation (blocked by bicuculline) and from GABA(B) receptor activation (blocked by 2-hydroxysaclofen) occurred spontaneously but as unrelated events, Furthermore, the two components of evoked synaptic potentials were differentially inhibited by agonists acting presynaptically (muscarine and 5-hydroxytryptamine). The finding that GABA acting at GABA(A) and GABA(B) receptors originates from distinct acts of presynaptic fibers suggests that two groups of GABA-containing neurons might be generally distinguishable in the mammalian nervous system.