A comparison of some photoreceptor characteristics in the pineal and retina

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Abstract
A rod-specific antiserum was used to immunolabel elements within the retina and pineal of the adult Djungarian hamster and Welsh Mountain sheep. In the retina immunostaining was localized to the outer segments and perikarya of photoreceptor cells, while in the pineal limited numbers of labelled pinealocytes were scattered throughout the gland. An enzyme-linked immunosorbent assay (ELISA) was then used to obtain a quantitative measure of rod opsin in total eye and pineal extracts from the Djungarian hamster. Total rod opsin (±SEM) in the eye was measured by absorbance spectroscopy (1.88±0.10 nmoles opsin/eye) and by using the ELISA (1.75±0.02 nmoles opsin/eye). The opsin content from a total of 56 pineals gave a mean value of 0.34±0.01 pmoles opsin/pineal. Since a functional photopigment should be coupled in a 1∶1 ratio to a chromophore, we investigated whether we could identify 11 -cis and/or alltrans retinaldehydes in the pineal extracts by quantitative extraction and HPLC analysis as the oximes. No evidence of 11-cis or all-trans retinaloxime could be found, the chromatograms were indistinguishable from those produced by extracts of cortical brain tissue. We conclude that the opsin present within the adult hamster pineal is not coupled to the common vertebrate retinaldehyde chromophore, and as a result, is unlikely to be part of a functional photopigment.