Abstract
To clarify the role of brain histamine (HA) on the photic and non-photic entrainment of circadian behavioral rhythms, the formal properties in the histidine decarboxylase knock out mice (HDC-/-) of C57BL6CrSlc background were examined. Male adult mice were individually housed in a LD cycles. The spontaneous locomotor activity was continuously measured by thermal sensor. Then, animals were released into constant darkness (DD) for ca.4 weeks. Mean free-running period of spontaneous locomotor rhythm were in 23.88 h in HDC-/- mice (n=10) and 23.61h in control mice (n=10) (p<0.05). Phase responses to 60min ca.300lux light pulse were measured at different circadian phase. HDC-/- mice showed a PRC almost identical to that of the control. With an exception of smaller phase advance shifts at CT0 (HDC-/- 0.97h vs. +/+ 1.57 h, p<0.05). In order to examine whether the circadian behavioral rhythm in HDC-/- mice entrain to non-photic stimulus, after having shown stable free-running rhythm, they were transferred to a cage with a running wheel for 3h a day for 68 days in DD. Eight of ten control mice entrained to the schedule, and other two mice were showed a relative coordination during the schedule. Whereas, eight of ten HDC-/- mice showed entrainment to the schedule and other two mice showed a change of freer-running period. These results demonstrated that brain HA might affect the photic entrainment but not affect the non-photic entrainment in the mammalian circadian pacemaker. [J Physiol Sci. 2007;57 Suppl:S73]
