Entrainment of methamphetamine-induced locomotor activity rhythm to feeding cycles in SCN-lesioned rats

Suprachiasmatic nuclei (SCN)-lesioned rats, showing a locomotor activity rhythm with a circadian period by chronic methamphetamine treatment, were subjected to the periodic food restriction (RF) of 4 h per every 27 h and 24 h. All rats were phase set by the feeding schedule of both 24-h and 27-h periods. Phase angle differences between the activity onset and food presentation were more positive under the RF with a period of 27 h than that of 24 h. Methamphetamine-induced locomotor rhythm showed a stable entrainment to RF of the 27-h period in all rats. Under the RF of the 24-h period, on the other hand, some rats showed circabidian rhythms, i.e., an activity band appeared at every second food presentation. After the termination of feeding schedule, the locomotor rhythm started to free-run from the phase set by the previous feeding schedule in all rats examined. Methamphetamine-induced locomotor rhythm was shown to be entrained by the RF with a predictable manner of an oscillation theory.