RESUMO
Anatomical and physiological studies have suggested that the pineal gland of neonatal mammals has a photoreceptive capacity. Using the golden hamster (Mesocricetus auratus) as our model, we applied biochemical approaches to look for a functional photopigment within the pineal during early development. Immunocytochemistry and enzyme-linked immunosorbent assay (ELISA) were used to localize and quantify opsin, and high-performance liquid chromatography (HPLC) to identify photopigment chromophore (11-cis and all-trans retinaldehyde) in the developing eye and pineal. For HPLC analysis, retinaldehydes were converted to their corresponding retinoid oximes. Eluted retinoids were identified by comparison with standard vitamin A1 retinoid oxime isomers on the basis of relative elution sequence and characteristic absorbance spectra. Both immunocytochemistry and ELISA suggested an increase in the opsin content of the pineal during the first week of life. In the eye, 11-cis retinaldehyde was first detected between days 3 and 5 after birth. In three separate extractions, and using a considerable excess of pineal tissue, we failed to identify chromophore within the pineal during the first week of postnatal development. The appearance of 11-cis retinaldehyde within the eye between postnatal days 3-5 is consistent with the hypothesis that retinol isomerase activity is coordinated with outer segment development. The failure to identify chromophore within the neonatal pineal suggests that this gland lacks a functional opsin-based photopigment. These data contradict physiological evidence suggesting that the neonatal pineal of mammals contains photoreceptors.
