Differences in the action of avermectin B1a on the GABAA receptor complex of mouse and rat

The effects of avermectin B1a (AVM) on the gamma-aminobutyric acid (GABA) receptor-chloride ionophore complex of mouse and rat brain were determined using assays of basal and GABA-stimulated 36Cl-uptake by brain vesicles. In the mouse, AVM acted solely as a potent non-competitive inhibitor of GABA-dependent chloride uptake. In the rat, inhibition of GABA-dependent chloride uptake was potent but incomplete, and AVM applied in the chloride uptake medium stimulated chloride uptake in the absence of GABA. The data provide evidence for qualitative differences between the GABA receptor complexes of mouse and rat brain in their responses to AVM.