The light/dark difference in meal size in the laboratory rat on a standard diet is abolished during REM sleep deprivation

Using a modified flowerpot technique, by which it was possible to use test animals as their own controls, the meal patterns of eight adult male rats were recorded before, during and after rapid eye movement sleep (REMs) deprivation. The results demonstrated that the prominent light/dark (LD) difference in meal size, typical of the baseline meal pattern, was abolished during REMs deprivation. This equalization was entirely due to reduction in meal size during the dark hours. After termination of REMs deprivation the size of the dark meals increased almost to the baseline level. However, the LD difference was not restored since the size of the light meals was also significantly increased. Changes in meal frequency were confined to the period of REMs deprivation. The possible role of REMs as a modulator of meal size in relation to the LD cycle of illumination is discussed.