EFFECT OF A LIGHT-PULSE ON MELATONIN RECEPTOR DENSITY AND MESSENGER-RNA EXPRESSION IN SIBERIAN HAMSTER SUPRACHIASMATIC NUCLEI

Melatonin receptors located in the suprachiasmatic nuclei (SCN) have b een cloned in mammals hypothalamus. We previously reported a SCN melat onin receptor photic regulation in the rat. The present study's aim wa s to investigate whether a photic regulation of both melatonin recepto r density and mRNA expression takes place in the SCN of a highly photo periodic species, the Siberian hamster. To achieve this goal, we first set up an in situ hybridization protocol without RNase treatment to a llow a highly sensitive and reproducible quantitative analysis of mela tonin receptor mRNA expression. Results showed that a 1 h light pulse delivered during night-time did not affect SCN melatonin binding capac ities while it induced a strong increase of the melatonin receptor mRN A expression in the SCN of pinealectomized animals. (C) 1997 Elsevier Science Ireland Ltd.