Communication from the brain’s daily rhythm center to the pineal gland during light and dark: changes in key signaling molecules after melatonin injection

Melatonin injection (1 mg/kg) influenced Per2 mRNA levels in the pineal gland at specific time points during light and dark periods.

• AVP content in the SCN decreased during the light period, while no changes were observed in the PVN.
• Per2 mRNA levels in the SCN increased during both light and dark periods.
• In the PVN, Per2 mRNA decreased during the light period and increased during the dark period at 180 minutes after melatonin injection.
• Per2 mRNA in the pineal gland increased between 60 and 180 minutes after melatonin injection during the light period, but did not change significantly during the dark period.
• AA-NAT mRNA levels varied similarly to Per2 mRNA levels, suggesting a linked response.

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