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N.A. Dmitrieva, K.T. Keyser; Identification of Retinal Cholinoceptive Neurons Containing alfa 7 Nicotinic Acetylcholine Receptors . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5422.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Nicotinic cholinergic agents can affect the light–evoked responses of many ganglion cell types (GC) in the mammalian retina. We evaluated the expression of α7 nicotinic acetylcholine receptors (nAChRs) in different populations of rabbit retinal neurons. Methods: Rabbit retinas were fixed in 1% paraformaldehyde/L–lysine/sodium m–periodate, cryoprotected, frozen, sectioned perpendicularly to the vitreal surface, treated with 1% 2–mercaptoethanol and processed for immunohistochemistry. Goat polyclonal antibody against the carboxyl terminus of α7 subunit of nAChR (sc–1447, Santa Cruz Biotechnology, Inc) was used in conjunction with commercially available antibodies against calbindin, protein kinase C (PKC), parvalbumin, GABA, and glycine (provided by Dr. David Pow, University of Brisbane, Australia). Sc–1447 antibody specificity was tested by Western blot analysis and in studies with blocking peptide. Results: The sc–1447 antibody labeled a 56 kDA band which corresponds to the α7 nAChR subunit. Preabsorbtion of the sc–1447 antibody with blocking peptide abolished staining. The somata and processes of many bipolar and amacrine cells and a subset of ganglion cells were α7 immunoreactive. At least three different populations of bipolar cells expressed α7 nAChRs: calbindin–positive cells, glycine–positive calbindin–negative cells, and calbindin–glycine–negative bipolar cells. Glycine–labeled amacrine cells comprised the majority of α7– positive amacrine cells. Some GABAegic amacrine cells also displayed for α7 immunoreactivity. α7 labeling was never detected in the neurons of the rod pathway. Conclusions: Our data suggest that the activation of α7 nAChRs by acetylcholine (ACh) can affect the responses of ganglion cells through multiple pathways. ACh may affect glutamate release from different types of cone bipolar cells, enhancing ganglion cell responses. ACh–induced excitation of inhibitory amacrine cells might cause either inhibition or disinhibition of other amacrine and ganglion cells. Finally, ACh may act on α7 nAChRs expressed by the ganglion cells themselves.
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