The results of studies examining a7 expression using in situ hybridization and functional measurements using electrophysiology have shown that this receptor is an important contributor to various nuclei of the central auditory system (Happe and Morley 1998; Vetter et al. 1999 Vetter et al. , 2007 Morley and Happe 2000; Morley 2005 ). The a7 GFP mouse system offers an excellent opportunity to view these central systems and their connections as shown in Fig. 7 . The connections between the SG and the cochlear nuclei were strongly identified at E18.5, presumably due to the dense projections from SG cells expressing a7 GFP that extend processes both to the IHC (Fig. 2 ) and the developing cochlear nuclei of the brainstem (Fig. 7A) .