Postsynaptic action of endogenous GABA released by nipecotic acid in the hippocampus

Intracellular and whole-cell recording from CA1 pyramidal cells and dentate granule cells was used to study the release of endogenous GABA by nipecotic acid. Local application of nipecotic acid produced responses that could be entirely blocked by a combination of the GABA A receptor antagonist picrotoxin and the GABA B receptor antagonist CGP 35348. These responses were due to the heteroexchange release of endogenous GABA because they were blocked by low Na + which blocks the GABA transporter and by SKF 89976 which is a competitive antagonist of the GABA transporter. Local application of nipecotic acid could, depending on the location, evoke pure GABA A or pure GABA B responses supporting proposals that GABA A and GABA B receptors can be segregated at separate inhibitory synapses.