GABA responses of rod bipolar cells in rabbit retinal slices

GABAergic responses of rabbit rod bipolar cells were reexamined by using whole-cell recordings in the superfused slice preparation to determine if there is GABA(C) receptor input to their axon terminal and to characterize the contribution that GABA(A) and GABA(C) receptors make to the total GABA current on the axon terminals of these cells. Pharmacological agents specifically blocking GABA(A) and GABA(C) receptor currents demonstrated that 37% of the GABA-activated current was blocked by either the GABA(A) antagonists bicuculline or SR-95531, whereas the remaining 63% of the GABA current was blocked by a mixture of bicuculline and the GABA(C) antagonist TPMPA. This indicated that GABA(C) receptors were present on the axon terminal of the rabbit rod bipolar cell and that they were responsible for mediating the bicuculline insensitive GABA current.