Expression of Alpha 7 Nicotinic Acetylcholine Receptors by Bipolar, Amacrine, and Ganglion Cells of the Rabbit Retina

Abstract

Cholinergic agents affect the light responses of many ganglion cells (GCs) in the mammalian retina by activating nicotinic acetylcholine receptors (nAChRs). Whereas retinal neurons that express β2 subunit-containing nAChRs have been characterized in the rabbit retina, expression patterns of other nAChR subtypes remain unclear. Therefore, we evaluated the expression of α7 nAChRs in retinal neurons by means of single-, double-, and triple-label immunohistochemistry. Our data demonstrate that, in the rabbit retina, several types of bipolar cells, amacrine cells, and cells in the GC layer express α7 nAChRs. At least three different populations of cone bipolar cells exhibited α7 labeling, whereas glycine-immunoreactive amacrine cells comprised the majority of α7-positive amacrine cells. Some GABAergic amacrine cells also displayed α7 immunoreactivity; α7 labeling was never detected in rod bipolar cells or rod amacrine cells (All amacrine cells). Our data suggest that activation of α7 nAChRs by acetylcholine (ACh) or choline may affect glutamate release from several types of cone bipolar cells, modulating GC responses. ACh-induced excitation of inhibitory amacrine cells might cause either inhibition or disinhibition of other amacrine and GC circuits. Finally, ACh may act on α7 nAChRs expressed by GCs themselves.