Expression of mt(1) melatonin receptor subtype mRNA in the entrained rat suprachiasmatic nucleus: a quantitative RT-PCR study across the diurnal cycle

Melatonin acts on specific receptors in the suprachiasmatic nuclei (SCN) to phase-dependently regulate the phase of the circadian clock. How the gatin g of melatonin's effect is restricted to particular times of day is not kno wn, but may be related to temporal differences in receptor availability. In the present study, we used a competitive reverse transcription-polymerase chain reaction (RT-PCR) method to determine if the expression of mt, melato nin receptor subtype mRNA in rat SCN varied across the 12:12 light-dark (LD ) cycle. Measurement of core body temperature using radiotelemetry confirme d that the male Wistar rats used exhibited a robust diurnal rhythm. mt, rec eptor mRNA was readily detected in reduced SCN slices at all times of day. However, there was no significant variation in the amount of mt(1) mRNA wit h time of day. Expression of MT2 melatonin receptor subtype mRNA in reduced SCN slices was confirmed by nested PCR. These results indicate that change s in the level of mt(1) mRNA do not underlie the diurnal and/or circadian v ariation in the response of the SCN circadian clock to the phase-resetting effects of melatonin. (C) 1999 Elsevier Science B.V. All rights reserved.