The SC and the dLGN are the dominant targets of retinal projections in mammals. Despite its relatively small size in rodents, RGC projections to the dLGN are segregated with respect to eye of origin and display sharp retinotopic organization (Lund et al., 1974, Godement et al., 1984 and Pfeiffenberger et al., 2006). We examined retinotopy and eye segregation in the dLGN of β2(TG) mice and observed conditions analogous to that in the SC. In particular, we found that the retinotopy of projections to the dLGN from the dorsal monocular zone of the retina are normal (Figures 4A and 4B; 12% ±

14%, mean ± SD for WT; 29% ± 11%, mean ± SD for β2(KO); 17% ± 9%, mean ± SD for β2(TG); p < 0.001 for comparison between β2(KO) and both WT and β2(TG)), but RGC projections from the ventral-temporal binocular zone of the retina remain unrefined Metabolism inhibitor (Figures 4C and 4D; 18% ± 5%, mean ± SD for WT; 40% ± 10%, mean ± SD for β2(KO); 41% ± 9%, mean ± SD for β2(TG); p < 0.001 for comparison between WT and both β2(KO) LY294002 and β2(TG)),

unless binocular competition is removed through monocular enucleation (Figures 4E, 4F, and S4; 22% ± 5%, mean ± SD for WT; 42% ± 8%, mean ± SD for β2(KO); 25% ± 8%, mean ± SD for β2(TG); p < 0.001 for comparison between β2(KO) and WT; p = 0.005 between β2(KO) and β2(TG); p = 0.52 for comparison between β2(TG) and WT). Eye-specific segregation is also completely disrupted in the dLGN of β2(TG) mice, like in β2(KO) mice (Figures 4G–4K; Rossi et al., 2001, Muir-Robinson et al., 2002, Grubb et al., 2003, Pfeiffenberger et al., 2005 and Pfeiffenberger et al., 2006). These

data demonstrate that normal levels of spontaneous neuronal activity and “small” retinal waves are not sufficient to mediate the segregation of retinal afferents with respect to eye of origin in the dLGN and SC but are sufficient to mediate normal retinotopy (in the absence of binocular competition) throughout the dLGN and SC. We tested whether the abnormal spatiotemporal properties of waves in the β2(TG) mice are responsible for their visual map defects by manipulating β2(TG) retinal waves pharmacologically in vivo. Spontaneous retinal activity, retinal wave dynamics, and size are modulated by cAMP levels (Stellwagen and Shatz, 2002, Stellwagen et al., 1999 and Zheng Dichloromethane dehalogenase et al., 2006). Acute application of CPT-cAMP and other cAMP signaling agonists increases retinal wave size and frequency (Stellwagen and Shatz, 2002 and Stellwagen et al., 1999). Daily binocular intravitreal injection of CPT-cAMP, a nonhydrolyzable membrane-permeable analog of cAMP, beginning at P2 in β2(TG) mice significantly improves eye-specific segregation in both the dLGN and SC in comparison to saline (control) injections (Figure 5). This strengthens the assertion that the altered spatiotemporal properties of retinal waves in β2(TG) mice are responsible for their visual map defects, and demonstrates that expression of β2-nAChRs in the dLGN and SC is not necessary for eye-specific RGC axon segregation.