Effect of a light pulse on melatonin receptor density and mRNA expression in Siberian hamster suprachiasmatic nuclei

Melatonin receptors located in the suprachiasmatic nuclei (SCN) have been cloned in mammals hypothalamus. We previously reported a SCN melatonin receptor photic regulation in the rat. The present study's aim was to investigate whether a photic regulation of both melatonin receptor density and mRNA expression takes place in the SCN of a highly photoperiodic species, the Siberian hamster. To achieve this goal, we first set up an in situ hybridization protocol without RNase treatment to allow a highly sensitive and reproducible quantitative analysis of melatonin receptor mRNA expression. Results showed that a 1 h light pulse delivered during night-time did not affect SCN melatonin binding capacities while it induced a strong increase of the melatonin receptor mRNA expression in the SCN of pinealectomized animals.