Day/night fluctuations in melatonin content, arylalkylamine N-acetyltransferase activity and NAT mRNA expression in the CNS, peripheral tissues and hemolymph of the cockroach, Periplaneta americana

Melatonin content in the hemolymph of the American cockroach is more than 12 times that in the brain under a light/dark cycle.

• Melatonin levels in the brain fluctuate with higher concentrations at night, a pattern sustained even in constant darkness.
• Activity of the enzyme arylalkylamine N-acetyltransferase (NAT) is also elevated at night in the brain.
• Melatonin levels in the retina are higher at night, although NAT activity does not significantly increase during this time.
• NAT mRNA is more abundant in the midgut, ovary, and female accessory glands compared to fat body and brain, indicating tissue-specific expression.
• The midgut shows higher NAT transcript levels at night, while ovary and female accessory glands exhibit the opposite pattern.
• NAT-like antigen is present in specific brain cells, suggesting multiple forms of NAT exist with varied functions across different tissues.

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