DIFFERENCES IN THE RETINOHYPOTHALAMIC TRACT IN ALBINO LEWIS VERSUS BROWN NORWAY RAT STRAINS

Differences in sleep-wake patterns in response to light-dark stimulati on have been observed between albino Lewis and pigmented Brown Norway strains of rats, which may be associated with albinism.1,16 Since seve ral anatomical differences have been demonstrated in the visual pathwa ys of albino and pigmented mammals, the present study was undertaken t o determine whether additional differences in visual pathways of these rat strains exist that might account for their behavioral differences . Using anterograde tracing techniques and image analysis, we have inv estigated the retinal projections of Lewis and Brown Norway rats. Our results demonstrate that the distribution of retinal terminals in the hypothalamic suprachiasmatic nucleus extends over a greater area in Le wis compared to Brown Norway rats. This zone of termination correspond s to a cyto-architectonically definable ventrolateral subdivision of t he suprachiasmatic nucleus (SCN),22 which is also greater in Lewis tha n in Brown Norway rats. These results may have implications for behavi ors related to the SCN.