EXPERIMENTALLY-INDUCED VISUAL PROJECTIONS TO THE AUDITORY THALAMUS INFERRETS - EVIDENCE FOR A W CELL PATHWAY

We have previously reported that following specific neonatal brain les ions in ferrets, a retinal projection is induced into the auditory tha lamus (Sur et al., Science 242:1437, '88). In these ''rewired'' ferret s, a novel visual pathway is established through auditory thalamus th e medial geniculate nucleus (MGN)! and primary auditory cortex (Al); c ells in both MGN and Al are visually responsive and exhibit properties similar to those of visual cells in the normal visual pathway. In thi s paper, we use three approaches-physiological, anatomical, and develo pmental-to examine which of the retinal ganglion cells project to the MGN in these rewired ferrets. We find that: 1) physiological response properties of postsynaptic visual cells in the MGN are W-like; 2) reti nal ganglion cells back-filled from the MGN are small and similar to s oma sizes of subsets of the normal retinal W cell population; and 3) s ubpopulations of these small cells can be preferentially rerouted to t he MGN in response to different surgical manipulations at birth, consi stent with differential W cell projection patterns in normal animals. These data suggest that retinal W cells come to project to the MGN in rewired animals. These findings not only provide a basis on which to i nterpret functional properties of this novel visual pathway, but also provide important information about the developmental capabilities of specific retinal ganglion cell classes and the regulation of their pro jections by target structures in the brain during development. (C) 199 3 Wiley-Liss, Inc.