Circadian rhythmicity in serotonin transporter knockout mice

Abstract

AimsSerotonin transporter knockout (5-HTT KO) mice exhibit elevated basal extracellular serotonin, increased depressive-like behaviors and increased rapid eye movement sleep. Because abnormalities of circadian rhythms are associated with mood disorders, we tested the hypothesis that 5-HTT KO mice would have altered circadian rhythmicity. Main methodsHomecage locomotor activity was recorded in wild-type (WT) and KO mice under a standard 12:12 light–dark cycle. After 4weeks of recording, mice received a one-hour light pulse at circadian time (CT) 14 and then were kept under constant darkness for 3weeks. Key findingsThere were no significant differences in amplitude, period, acrophase or total home cage locomotor activity between WT and KO mice during the 12:12 light–dark cycle or during constant darkness. The mean phase delay to a CT 14 light pulse was significantly attenuated in KO compared to WT mice. SignificanceAcute increases in serotonin have been reported to attenuate photic phase shifts. The current study demonstrates that this effect is maintained in the face of a lifelong absence of 5-HTT.