The nicotinic receptors a9 and a10 are particularly well characterized in the auditory system (Elgoyhen et al. 1994 (Elgoyhen et al. , 2001a Vetter et al. 1999 Vetter et al. , 2007 Katz et al. 2004; Morley 2005) . Comparing the expression of a7 GFP to the results from these studies of the sensory hair cells and the nonsensory cells of the cochlea indicate that there are significant spatiotemporal differences during development between the expression of a7 versus a9 and/or a10. The a9 KO mouse also exhibits auditory deficiencies that are not observed in the a7 KO mouse, which is largely devoid of a phenotype in this sensory system under normal physiological conditions (Liberman and Brown 1986; Simmons and Morley 1998; Morley 2005; Lustig 2006 ). The a7 GFP is not detected in IHCs, which is consistent with a9 nAChR being the principle target of alpha-bungarotoxin in this cell type (Uziel et al. 1981; Glowatzki and Fuchs 2000) . Collectively, this suggests that functional redundancy between these receptor subtypes is unlikely (see also . This is also supported by the extensive studies by the Morley group Morley 1998, 2004; Morley and Happe 2000; Simmons and Morley 2011) who showed that multiple receptor subtypes are expressed in the cochlear and central auditory systems, but each exhibits distinct spatiotemporal patterns that likely preclude substantial or sustained functional overlap.