Pineal arylalkylamine N‐acetyltransferase gene expression is highly stimulated at night in the diurnal rodent, Arvicanthis ansorgei

Aa-nat gene sequences between the diurnal grass rat and nocturnal Wistar rat are 86.6% identical.

• In the diurnal grass rat, melatonin synthesis is marked by increased Aa-nat gene expression at the beginning of the night, leading to higher AA-NAT activity and melatonin levels.
• At the end of the night, the decline in AA-NAT activity and melatonin levels occurs before the decrease in Aa-nat mRNA levels.
• A beta-adrenergic agonist administered during the day can mimic the nocturnal activation of melatonin synthesis.
• Conversely, a beta-adrenergic antagonist given at night reduces AA-NAT activity and melatonin synthesis, regardless of Aa-nat mRNA levels.
• The regulation of melatonin synthesis in the diurnal grass rat resembles that of the nocturnal Wistar rat, suggesting that differences in melatonin production are influenced by evolutionary rather than behavioral factors.

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