Increased cholinergic sensitivity in the central nervous system has been postulated to account for some of the neuroendocrine abnormalities and sleep disturbances seen in human depressives. The Flinders Sensitive Line (FSL) rats, which exhibit increased sensitivity to cholinergic agents, have been shown to have REM sleep patterns similar to those seen in depressives, including shorter REM sleep latency and increased daily percentage of REM sleep. We studied the response of FSL and control rats to brief dark pulses administered during the normal light period (which are known to stimulate REM sleep in albino rats) and to brief light pulses during the normal dark period (which suppress REM sleep in albino rats) to determine whether these responses are affected by central cholinergic hypersensitivity. FSL rats showed REM sleep patterns indistinguishable from controls during light or dark pulses, which does not support the primary involvement of cholinergic systems in this mechanism of REM sleep regulation. We also examined REM and non-REM (NREM) sleep patterns in FSL rats and their controls to determine whether they show sleep continuity disturbances or decreased sleep intensity as seen in depression. In agreement with an earlier study, we found that FSL rats had more daily REM sleep and accumulated less NREM sleep between REM bouts than controls. Duration of NREM sleep bouts, total daily NREM sleep time, and EEG amplitude of NREM sleep did not differ between FSL and control rats, suggesting that the cholinergic abnormalities in FSL rats do not produce substantial NREM sleep changes.