gamma-Aminobutyric acid receptors in brain postsynaptic densities.

Rat brain synaptic plasma membranes contain two receptorlike binding sites for the inhibitory transmitter gamma-aminobutyric acid. Postsynaptic junctional structures (postsynaptic densities) isolated from these membranes contain only the higher affinity site enriched more than sixfold compared to the membranes. The results provide the first direct evidence for the association of transmitter receptors with postsynaptic junctional sites in the brain.