EYE-SPECIFIC PATTERNING OF RETINO-GENICULATE TERMINATIONS IN THE MEDIAL GENICULATE NUCLEUS OF REWIRED MICE C.A. Ellsworth; A.W. Lyckman*; M. Sur Dept Brain & Cognitive Sci, MIT, Cambridge, MA, USA Previous work in mice (Lyckman et al, Soc Neurosci Abstr 25:2263) has shown that denervation of the medial geniculate nucleus (MGN) at birth induces retinal fibers to innervate the MGN (rewiring). Rewiring offers a novel opportunity to explore the relative contributions of afferents and targets to patterning. We have examined whether eye-specific zones form in the MGN as they do in a normal thalamic target of retinal projections, the lateral geniculate nucleus (LGN). Cholera toxin B-subunit conjugated to AF-488 or to AF-594 was injected into the ipsilateral or contralateral eyes, respectively, of unilaterally rewired, adult mice. By confocal microscopy, retinal projections from the two eyes were found to occupy separate zones in the MGN. The contralateral eye contributed most of the retinal innervation of MGN, though in 4 of 5 cases the relative contribution from the ipsilateral eye was greater than that found in the normal LGN. The eye-specific segregation in the MGN of rewired mice resembles that in rewired ferrets (Angelucci et al, J Neurosci 17:2040). Eye-specific segregation suggests that afferent-dependent mechanisms are important to patterning. The targets, the MGN and LGN, appear to differ in their receptivity towards ipsilateral versus contralateral retinal innervation. Supported by: March of Dimes & NIH EY11512