Cytological aspects of pineal development in rats and hamsters

Abstract

Evidence has been accumulating which supports the hypothesis that through phylogenetic evolution, the mammalian pinealocyte has evolved from the pineal photoreceptor-cell which is characteristic of certain lower vertebrates. In the present study, developing pineal glands in fetal rats and hamsters were studied at light and electron microscopic levels to determine whether or not the ontogenetic development of pineal cells affords clues to their phylogenetic origin. Pineal development in fetal rats occurs during the last eight days of gestation (14-22) and in fetal hamsters, during the last five days of gestation (11-16). The pineal gland exhibits many similarities in the two species as it develops from a tubular evagination of the diencephalic roof into a compact cellular mass. Different cellular types could not be readily distinguished in fetal material from either species. In both animals, as long as lumina persist, cells bordering on these lumina exhibit surface modiiications reminiscent of developing photoreceptor-cells, i.e., an "ellipsoid-like" apical cytoplasmic bulge which often contains one or two centrioles and bears a ciliary derivative exhibiting a 9 + 0 tubular configuration. As pineal tissue proliferates, the lumina and ciliumlike structures disappear. The findings, when considered with phylogenetic studies, strengthen the hypothesis that the mammalian pineal gland contains cells derived from the photoreceptor-cell line.

Development of the Photoreceptor Outer Segment-like Cilia of the CSF-Contacting Pinealocytes of the Ferret (Putorius furo).

“…On the other hand, mammalian pinealocytes are morphologically dissimilar to glandular cells and-as already mentioned by WOLFE (1965)-they exhibit some cytological characteristics of photosensory cells. Similar results were obtained for mammalian pinealocytes by CLABOUGH (1973) and ZIMMERMANN and Tso (1975).…”

Influence of Photoperiod on Reproductive Development in the Golden Hamster

“…photoreception (Wetterberg et a!., 1970) and, in addition, the pinea! gland may be capable of processing light information, since photoreceptor-like cells are present during the early development of the gland and after birth in rats and hamsters (Clabough, 1973 blinded as well as sighted hamsters. From 7 to 13 weeks of age, intact hamsters on 6L:18D cycles displayed no decline in sex accessory organ size and for the males, only partial gonadal regression.…”

Induction of photosensitivity in neonatal rat pineal gland

“…Pinealocytes of neonatal but not adult rats have photoreceptor-like morphology (19,20). Furthermore, in vitro studies by Araki and colleagues (21)(22)(23)(24) have shown that if neonatal rat pineals are dissociated and cultured, some cells express photoreceptor properties such as rhodopsin immunoreactivity and synthesis of rhodopsin transcript.…”