Daily rhythm genes in the rat brain's internal clock during late fetal and early newborn stages

At postnatal day (P) 1, rhythms in Per1, Bmal1, and arginine-vasopressin (AVP) gene expression are present in the rat suprachiasmatic nucleus (SCN).

• Rhythms in clock gene expression were not detectable at embryonic day (E) 19 but began to develop between E20 and P3.
• At E20, only Per1 expression showed signs of rhythmicity, while other clock genes and AVP expression did not.
• By P1, rhythmic expression of Per1, Bmal1, and AVP was observed, with a developing rhythm in Per2 and no rhythm in Cry1.
• The Per1 rhythm was only slightly pronounced, and the Bmal1 rhythm had an atypical shape compared to adult patterns.
• At P2, significant rhythms in Per1, Per2, and Bmal1 were present, alongside a forming rhythm in Cry1, but not in Clock.
• The findings suggest that the development of clock gene rhythms primarily occurs postnatally and may involve additional mechanisms for AVP gene expression.

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