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.