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M.B. Feller, C.L. Torborg, K.A. Hansen; Connexin36 Deficient Mice Have Disrupted Retinal Waves and Normal Segregation of Retinogeniculate Afferents into Eye-Specific Layers . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1662.
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Purpose: During development, spontaneously generated action potentials in retinal ganglion cells (RGCs) drive the segregation of retinogeniculate afferents into eye-specific layers. These spontaneous action potentials are highly correlated, propagating as waves across the developing ganglion cell layer. To elucidate the role of gap junctions in this activity-dependent process, we studied the correlations induced by spontaneous activity in RGCs and eye-specific layer formation in mice lacking Connexin36 (Cx36, Deans et al, Neuron, 2001). Methods: Multielectrode array (MEA) recordings were conducted on acutely isolated whole-mount retinas from WT and Cx36-/- mice. Intraocular injections of Alexa Fluor-488 or –594 conjugated ß-choleratoxin were used to visualize axon terminals in dLGN sections. Results: Cx36 reporter expression in the retina was detected using Xgal staining as early as postnatal day 2 (p2), with increasing expression until p14. Using an MEA, we found that the percentage of time that a given RGC bursts was greater in Cx36-/- than WT at both p4/5 (7.5±1.4% (n=62) for Cx36-/-; 4.3±0.2% (n=33) for WT) and p10/11 (22.4±1.9% (n=162) for Cx36-/-; 6.6±1.7% (n=81) for WT). This finding implies that Cx36-/- mice have an increased probability of retinotopically matched RGCs from the two eyes firing simultaneously. In addition, cross-correlations between RGC pairs at p4/5 in Cx36-/- mice showed longer time delay to the peak correlation, consistent with a slower propagation velocity of retinal activity. By p10/11, correlations were significantly lower between pairs of Cx36-/- RGCs. Despite these dramatic differences in firing patterns between WT and Cx36-/- mice, the size of the ipsilateral projection and the amount of segregation of the retinogeniculate afferents from the two eyes was indistinguishable. Conclusions: These findings indicate that although Cx36 plays a role in establishing normal firing patterns of retinal waves, these precise spatiotemporal properties may not be instructive in the activity-dependent formation of eye-specific layers.
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