Nipecotic acid enhances synaptic transmission in the frog optic tectum by an action independent of GABA uptake inhibition.

In the frog optic tectum maintained in vitro at 7 degrees C to depress gamma-aminobutyric acid (GABA) transport systems the GABA uptake inhibitor nipecotic acid reversibly enhanced field potentials evoked by optic nerve stimulation. This effect was dose dependent and picrotoxin sensitive. Responses to low concentrations of GABA agonists were not affected by nipecotic acid, whereas responses to the maximal muscimol concentration were depressed. It is suggested that in addition to its well known inhibitory action on GABA uptake systems, nipecotic acid can evoke GABA mimetic effects whose precise origin is presently unclear.