First evidence of a cDNA encoding for a melatonin receptor (mel 1b) in brain, retina, and testis of Pelophylax esculentus.

Melatonin, nocturnally secreted by the pineal gland, regulates a variety of physiological functions, including reproduction. Here, we investigated the evidence of melatonin binding sites in frog tissue (brain, retina, and testis) through saturation and competition binding experiments. In the frog, Pelophylax esculentus, our results confirm the presence of a single class of melatonin-specific binding sites in the brain and retina, but not in the testis. Further experiments have been done using biomolecular approaches (PCR analysis). Here, we report the isolation of a cDNA encoding for a melatonin receptor type (mel 1b) from brain, retina, and testis of the P. esculentus. PCR analysis revealed that melatonin expression is higher in the brain and retina, whereas it is lower in the testis. The presence of a melatonin receptor transcript in the frog testis corroborates our previous results obtained in in vitro experiments that suggest that melatonin might act directly in male vertebrate gonads, and indicates that the frog testis may be a suitable model to verify the role of indolamine in testicular activity.