Strain differences in the sleep of rats

Sleep was measured in two inbred rat strains (Lewis and Brown Norway) and their F1 hybrids to investigate patterns of inheritance and to provide a starting point for future studies of F2 and recombinant rats. Recordings from chronically implanted electrodes were quantified and scored by a computerized system; results were evaluated by an analysis of variance with pairwise comparisons by the Tukey HSD test. Brown Norway rats had the highest paradoxical sleep (PS) percentages; Lewis rats had the lowest. Hybrid rats had PS percentages intermediate between parent strains and significantly different from both. These results suggest codominance or multigenic transmission of PS amounts. There were no group differences of number of PS bouts; Brown Norway and hybrid rats had longer bouts than Lewis rats. Lewis and hybrid rats had similar amplitudes of the diurnal rhythm of PS, which were higher than those of Brown Norway rats; single gene transmission remains possible for diurnal rhythm amplitude. Thus, inheritance of PS percentage and rhythm amplitude appear independent. No group differences in PS latency were found.