Tissue-specific abolition of Per1 expression in the pars tuberalis by pinealectomy in the Syrian hamster

Melatonin secretion by the pineal gland transduces photoperiod into a neuro endocrine signal. In the pars tuberalis (PT), we have shown that photoperio d modifies the amplitude of the clock gene Perl. The aim of this study was to test whether the endogenous melatonin signal is required for rhythmic ex pression of Perl in the PT. Male Syrian hamsters housed in long days (LD, 1 6:8 h light:dark) were pinealectomized and Perl mRNA expression studied by in situ hybridization. Pinealectomy abolished the rhythm of Perl expression in the PT, but had no effect on Perl expression in the suprachiasmatic nuc leus (SCN), or the ventromedial nucleus (VMH) of the hypothalamus. Interest ingly, a single night-time injection of melatonin (25 mug) given to pineale ctomized animals, failed to restore Perl expression in the PT. These data d emonstrate that Perl expression in the PT is driven by melatonin, and that the features of the endogenous signal through which the Perl expression is achieved cannot be reproduced by a single melatonin injection. NeuroReport 12:579-582 (C) 2001 Lippincott Williams & Wilkins.