The endogenous rhythm of plasma melatonin and its regulation by light in the highveld mole-rat (Cryptomys hottentotus pretoriae): a microphthalmic, seasonally breeding rodent: Melatonin rhythm in C. hottentotus pretoriae (original) (raw)

The day and night levels of plasma melatonin were measured in adult male and female highveld mole-rats, Cryptomys hottentotus pretoriae. This study assessed whether melatonin secretion in this nocturnal, strictly subterranean but seasonally breeding rodent has a day-night rhythm and whether that rhythm is circadian and can be modified by photoperiod. In experiment 1, a day-night rhythm of plasma melatonin was found in all animals housed on a 12L:12D schedule, with significantly higher concentrations in the dark compared with the light phase. The increment of plasma melatonin concentration at night was the same on days 1 and 2 for animals in the control group and those transferred to constant dark. The animals transferred to constant light significantly reduced the amplitude of the melatonin rhythm on day 2. This indicates that the endogenous melatonin rhythm in C. h. pretoriae has a circadian pattern that can be synchronized by photoperiod and inhibited by exposure to light at night. Experiment 2 demonstrated that the concentration of plasma melatonin in animals kept under long (14L:10D) and short (10L:14D) day conditions differed significantly, supporting the notion that C. h. pretoriae is sensitive to changes in day length.