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 r eceptors (nAChRs) and gamma-aminobutyric acid (GABA), the GABA transporter 1 (OAT-I), or choline acetyltransferase (ChAT) immunoreactivity in the rabb it retina. Double-label experiments with monoclonal antibody 210 (mAb 210) against nAChRs and antibodies against GABA revealed that several population s of GABA-containing amacrine, displaced amacrine, and ganglion cells displ ayed nAChR immunoreactivity. Some of them also exhibited ChAT immunoreactiv ity and were identified as the cholinoceptive starburst cells. Other GABAer gic amacrine cells positive for mAb 210 were not cholinergic. Simultaneous visualization of mAb 210 and CAT-I immunoreactivity revealed that 10% of GA T-1 immunoreactive amacrine cells contained nAChRs. Ninety-nine percent of the GAT-1 labeled cells demonstrated GABA immunoreactivity, bur 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 sub set of GABAergic amacrine cells. Taken together, our results suggest that s ome GABAergic amacrine cells are cholinoceptive, raising the possibility th at ACh, acting through nAChRs, can modulate the release of GABA in the rabb it retina.