Host: The Physiological Society of Japan
The hypothalamic suprachiasmatic nucleus (SCN) is the master regulator of the systemic circadian organization. Many neurons in the SCN are capable to generate circadian output and are synchronized in a steady light:dark condition. However, light exposure during the night disrupts the synchrony. Previously, we demonstrated that the endogenous desynchrony in the SCN occurs after the rapid light:dark cycle shift in rats, which suggested that jet lag syndrome is caused by endogenous desynchrony in the SCN and that the aberrant peripheral circadian rhythm faithfully reflects the state of the central clock in the SCN. How does the SCN deliver its rhythm to the locomotor activity? SCN transplantation is an effective method to investigate the question. The transplanted SCN restored the circadian rhythms of locomotor in SCN-lesioned arrhythmic mice. Since the graft of the embryonic SCN in the third ventricle has a few number of neural connections to the surrounding brain tissues, it is assumed that the humoral factors from the SCN mainly deliver the rhythm of the master oscillator to the periphery in the SCN grafted animals. In our present analysis, some characteristics of the circadian rhythms in the locomotor activity and peripheral organs were not fully restored. The finding suggests that the humoral factor is able to evoke the peripheral circadian rhythm but neural projection from the SCN is also involved in the formation of the circadian peripheral rhythm. [J Physiol Sci. 2008;58 Suppl:S12]
