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C.E. Strang, J.M. Renna, F.R. Amthor, K.T. Keyser; Nicotinic Receptor Subtype Diversity in Rabbit Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4141.
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Purpose: α3 and ß2 nicotinic acetylcholine receptor (nAChR) subunits are expressed by amacrine and ganglion cells (GCs) in the rabbit retina (Keyser et al., 2002). Additional nAChR subunits have been shown by RT-PCR (Strang et al., 2002) and by physiology (Reed et al., 2002). The purpose of the project is to identify other nAChR subunit mRNA and to explore the contribution of pharmacologically identified nAChR subtypes to the response properties of physiologically distinct GCs. Methods: For RT-PCR analysis, total RNA was extracted from retinas. Subunit-specific primers were used to amplify nAChR message and the resulting products were sequenced. Standard recording techniques were used to record light responses of GCs in an isolated retina-choroid-epithelium preparation. Either 2 µM nicotine or 400 µM choline was applied together with the subtype-specific antagonist methyllycaconitine (MLA). After recording, sharp electrodes were used to fill the cells with fluorescent dye. The retinae were fixed, cryoprotected, sectioned, and incubated with an antibody that recognizes α1, α3 and α5 nAChRs (Lindstrom, 2000). Results: Message for α3, α6, α7 and ß4 nAChR subunits was expressed in rabbit retina. Application of nicotine and choline resulted in cell-type specific excitatory and inhibitory effects on both spontaneous and light-evoked activity. The effects of choline were completely blocked by 15 nM MLA, while MLA blocked only a portion of the nicotine effects. In addition, under synaptic blockade, GCs demonstrated both MLA-sensitive and MLA-insensitive responses to agonist application. Conclusions: The MLA-sensitive choline response is likely mediated by α7 nAChRs, but may also include heteromers containing α6 subunits. The MLA-insensitive responses may be mediated by α3ß2 nAChRs but may also include heteromeric nAChRs containing ß4 subunits.
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