ENTRAINMENT OF CIRCADIAN WHEEL-RUNNING RHYTHMS OF THE NORTHERN BROWN BANDICOOT, ISOODON MACROURUS, BY DAILY RESTRICTED FEEDING SCHEDULES

Northern brown bandicoots (Isoodon macrourus) were subjected to restri cted feeding for 3 h in the middle of the light period of a 14:10 ligh t/dark cycle and immediately following this in constant dark. When fee ding was restricted to the middle of the light period of the light/dar k cycle, all bandicoots maintained a nocturnal activity rhythm. In add ition to the nocturnal rhythm, a few bandicoots showed meal-anticipato ry activity during the light period. In bandicoots that did not show m eal-anticipatory activity, diurnal activity was sometimes evident eith er during or shortly after the daily meal time. The observation of mea l-anticipatory activity in some bandicoots suggests that this species may have a mechanism separate from the light-entrainable mechanism tha t allows the daily anticipation of periodically available food sources . In the next stage of the experiment, which was in constant dark, the meal was presented at the same time of day as it had been in the prev ious stage. Tn all bandicoots, the previously light-entrained componen t of activity free-ran and was eventually affected by the restricted f eeding schedule to some degree. Bandicoots showed weak entrainment and relative coordination, suggesting that restricted feeding is a weak z eitgeber in this species. Evidence also suggesting that two separate b ut coupled pacemakers control the activity rhythms of the bandicoot wa s that (a) bandicoots simultaneously showed free-running light-entrain able rhythms and meal-entrained anticipatory rhythms; (b) in several b andicoots, the light-entrainable rhythm was phase advanced when it fre e-ran through the meal time; and (c) in one bandicoot, meal-entrained anticipatory activity was forced away from the meal time when the prev iously light-entrained component of activity free-ran through it.