A marked diurnal rhythm of melatonin ML1A receptor mRNA expression in the suprachiasmatic nucleus

Melatonin (ML1A) receptor binding in the suprachiasmatic nucleus (SCN) exhibits a diurnal rhythm, with significant increases during the daytime. In order to determine whether the diurnal variation in binding is reflected by a cycling of melatonin ML1A receptor mRNA levels, we utilized a semiquantitative reverse transcriptase-polymerase chain reaction procedure to examine receptor expression throughout the light-dark cycle. Here we report the first evidence of a significant diurnal variation in ML1A receptor mRNA levels within the SCN. Furthermore, this mRNA expression occurs approximately 3 h prior to, but is tightly correlated to the diurnal rhythm in high-affinity melatonin binding in the SCN.