Influence of short-term constant light on phase shift of mouse circadian locomotor activity rhythm induced by agonist and antagonist of serotonin

Abstract

Despite the large body evidence from a variety of studies, the role of the serotonergic projection in the circadian system is still unclear. Previous work suggested that 5-HT is involved in both the response of SCN neurons to light and the phase-resetting properties of nonphotic stimuli. In hamsters, short exposure to constant light potentiates circadian phase-shifting caused by nonphotic stimuli, and the 5-HT pathway may be connected with this effect. The aim of this study was to determine whether a similar effect obtains in mice. We examined brief light-potentiation of (R)-(+)-8-OH-DPAT (8–hydroxyl-2-[di-n-propyloamino]-tetralin) and WAY100635 phase resetting, and found that short constant light before administration of (R)-(+)-8-OH-DPAT significantly enhanced the delays of the phase shift of the locomotor activity rhythm as compared with NaCl-injected animals. The transition from short LL to DD caused a phase shift, and WAY100635 attenuated this effect.