The relationship between GABA-containing cells and the cholinergic circuitry in the rabbit retina

As a part of ongoing efforts to understand the cholinergic circuitry in the mammalian retina, we studied the coexpression of nicotinic acetylcholine receptors (nAChRs) and gamma-aminobutyric acid (GABA), the GABA transporter 1 (GAT-1), or choline acetyltransferase (ChAT) immunoreactivity in the rabbit retina. Double-label experiments with monoclonal antibody 210 (mAb 210) against nAChRs and antibodies against GABA revealed that several populations of GABA-containing amacrine, displaced amacrine, and ganglion cells displayed nAChR immunoreactivity. Some of them also exhibited ChAT immunoreactivity and were identified as the cholinoceptive starburst cells. Other GABAergic amacrine cells positive for mAb 210 were not cholinergic. Simultaneous visualization of mAb 210 and GAT-1 immunoreactivity revealed that 10% of GAT-1 immunoreactive amacrine cells contained nAChRs. Ninety-nine percent of the GAT-1 labeled cells demonstrated GABA immunoreactivity, but only 75% of the GABAergic cells were outlined by GAT-1 staining. Neither population of starburst cells exhibited GAT-1 immunoreactivity. Thus, mAb 210 expressing, GAT-1 positive cells in the rabbit retina constitute a noncholinergic subset of GABAergic amacrine cells. Taken together, our results suggest that some GABAergic amacrine cells are cholinoceptive, raising the possibility that ACh, acting through nAChRs, can modulate the release of GABA in the rabbit retina.