NONPHOTIC PHASE-SHIFTING IN THE OLD AND THE COLD

When confined to novel running wheels or when given injections of tria zolam in their home cages, old hamsters do not become as active as you ng hamsters. Therefore, lack of nonphotic phase shifting following suc h manipulations may stem from insufficient activity or arousal. Phase advances can be obtained in some 10-month-old animals when wheel runni ng during the pulse is increased by the presence of females in estrous condition and in most 18-month-old hamsters by combining confinement to a novel wheel with triazolam injections. These data suggest that th ere is relatively little if anything wrong in aging hamsters with the nonphotic phase-shifting mechanism itself. The reason why in certain s ituations old hamsters do not shift appears to be because the nonphoti c inputs to these shifting mechanisms are not strong enough. However, when running in novel wheels is increased by carrying out the tests at cold temperatures, most old animals did not show subsequent phase shi fts. Evidently it is not running per se that is critical for phase shi fts, but probably the motivational context for such running.