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Serotonin Agonist Quipazine Induces Photic-Like Phase Shifts of the Circadian Activity Rhythm and c-Fos Expression in the Rat Suprachiasmatic Nucleus

Department of Animal Physiology, Institute of Biology; Universität Stuttgart, Biologisches Institut, Abteilung für Tierphysiologie, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Andreas Kalkowski

Franziska Wollnik

Department of Animal Physiology, Institute of Biology, University of Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany

Nonphotic stimuli can reset and entrain circadian activity rhythms in hamsters and mice, and serotonin is thought to be involved in the phase-resetting effects of these stimuli. In the present study, the authors examined the effect of the serotonin agonist quipazine on circadian activity rhythms in three inbred strains of rats (ACI, BH, and LEW). Furthermore, they investigated the effect of quipazine on the expression of c-Fos in the mammalian circadian pacemaker, the suprachiasmatic nucleus (SCN). Quipazine reduced the amount of running wheel activity for 3 h after treatment, however, no long-term changes in and in the activity level were observed. More important, quipazine induced significant phase advances of the activity rhythm and c-Fos production in the SCN at the end of the subjective night (Circadian Time [CT] 22), whereas neither phase shifts nor c-Fos induction were observed during the subjective day. Quipazine injections also resulted in moderate phase delays at the beginning of the subjective night (CT 14). A similar phase-response characteristic typically can be observed for photic stimuli. By contrast, nonphotic stimuli normally produce phase advances during the subjective day. The present results suggest species differences between the hamster and the rat with respect to the serotonergic action on circadian timekeeping and indicate that serotonergic pathways play a role in the transmission of photic information to the SCN of rats.

Key Words: circadian rhythm • nonphotic stimuli • phase-response curve • c-Fos • locomotor activity • free-running period

Journal of Biological Rhythms, Vol. 14, No. 2, 131-140 (1999)
DOI: 10.1177/074873099129000524


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