Comparative biochemistry and physiology. Part A, Molecular & integrative physiologySep 21, 2005

Nighttime patterns and increased melatonin breakdown in day-active rodents after weaning under short daylight

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 29, 2026

Abstract

P. obesus displays elevated body temperature and oxygen intake during the dark phase after weaning under short photoperiods.

Body temperature and oxygen intake were generally high during the light phase in the diurnal rodent.
After weaning, P. obesus showed a shift to elevated body temperature and oxygen intake during the dark phase under short photoperiods.
The urinary excretion of 6-sulfatoxymelatonin increased alongside the nocturnal activity of the enzyme responsible for melatonin synthesis.
The cDNA encoding P. obesus pineal AANAT shares 90.2% homology with rat AANAT and 83.8% with human AANAT.
AANAT-mRNA levels exhibited a robust diurnal rhythm, peaking at night, without enhancement in the post-weaning phase.

Simplified

The ontogeny of daily rhythms in body temperature (T(b)) oxygen intake (VO(2)) and urinary excretion of the major melatonin metabolite, 6-sulfatoxymelatonin (6SMT) was studied in the day-active rodent, Psammomys obesus. Generally, T(b) and VO2 were high during the light phase in this diurnal species. However, after weaning, and only under the short photoperiod, P. obesus individuals display elevated T(b) and VO2 levels during the dark phase, as in nocturnally active species. In parallel, 6SMT and nocturnal activity of pineal arylalkylamine N-acetyltransferase (AANAT) were greatly enhanced. The cDNA encoding P. obesus pineal AANAT was cloned and found to share 90.2% homology with rat and 83.8% with human AANAT, and based on homology modeling, to structurally resemble the ovine enzyme. A robust diurnal rhythm in P. obesus pineal AANAT-mRNA was found, with maximal levels at night. AANAT-mRNA levels were not enhanced in the post-weaning phase, suggesting post-transcriptional up-regulation of pineal AANAT activity. The photoperiod-dependent post-weaning change into nocturnal behavior and up-regulation melatonin production (as evidenced from the increase in both 6SMT and AANAT activity) represent a hitherto unobserved pattern of transition of a diurnal mammal into independent life. Possibly, this pattern may be physiologically important to facilitate T(b) maintenance in the cold nights of winter in the desert.

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Nighttime patterns and increased melatonin breakdown in day-active rodents after weaning under short daylight

Abstract

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