Effect of Amputating the Tail on the Circadian Rhythm of Serum Melatonin Level in Mice

Objective To investigate the effect of amputating the tail on the circadian rhythm of serum melatonin level in mice.Methods The distal 2.5 cm length of the tails in female mice were removed.72 normal and 72 tail-amputated female mice were divided into 6 groups randomly,with 12 mice in each group.All the mice were feeded under a standard light-dark rhythm(light phase 6:00-18:00;light:dark=12:12 h) for two weeks.Then they were decollated at 4:00,8:00,12:00,16:00,20:00 and 24:00,respectively,and the blood was drawn quickly to study the circadian rhythm of serum melatonin level by ELISA.Results Significant circadian rhythm of normal mice′s serum melatonin level was found.The serum melatonin level was lower in the day-time and higher at night.The melatonin level at night is about 2.5 times as that in the day-time.Similar circadian rhythm of serum melatonin level in tail-amputated mice was found.The serum melatonin level at night was about 1.8 times as that in the day-time.Conclusion Both normal and tail-amputated mice had significant circadian rhythms of serum melatonin level.Compared with normal mice,serum melatonin level of tail-amputated mice in the day-time was significantly increased and fluctuated obviously.