Circadian Phase Shifting Associated with Routine Cage Maintenance: A Retrospective Analysis

Abstract

Stimuli that evoke behavioral activation can phase-shift free-running circadian activity rhythms in Syrian hamsters. Activation-induced phase shifting is characterized by a phase-response curve (PRC) that is dissimilar to the PRC for photic phase shifting, and recent studies indicate that complex interactions may occur between photic and non-photic phase shifting. Since animals in the laboratory may be exposed to both photic and behaviorally activating stimulation during routine cage maintenance procedures, we performed a retrospective analysis of possible phase shifts associated with cage cleaning in individually housed hamsters maintained in either constant darkness (DD) or dim red light (RR) during the course of an ongoing study of drug-induced phase shifting. All cage cleanings were conducted under RR and were separated from drug treatments by at least one week. The results indicated that both photic and non-photic phase shifts could be induced by routine cage maintenance procedures, depending on the circadian timing of the procedure, on lighting conditions, and on the degree of evoked activity.