Ultrastructural study of post-hatching development in the pineal gland of the Japanese quail.

The pineal gland of the Japanese quail (Coturnix coturnix japonica) retained numerous follicular structures, each of which was composed mostly of pinealocytes and supporting cells radially arranged around the follicular lumen during the first 6 weeks of age. In the pinealocytes, paraboloids and regular stacks of lamellar disks, which were demonstrated at 1 day of age in a previous study [14], rapidly decreased in number after 1 week of age. From 1 to 6 weeks of age, the pinealocytes had more developed lamellar whorls in the follicular lumen with the increased numbers of mitochondria in their apical protrusions and synaptic ribbons in their basal processes. In addition to these photosensory elements, pigment-containing cells occasionally accumulated in the basal side of the follicular structure. Their pigment granules, which were considered as melanin, gradually became larger and more roundish in shape after 1 week of age. The histological elements associated with the secretory function of the quail pineal were dense-cored vesicles and lysosomes in the pinealocytes and dense bodies in the supporting cells. The synaptic ribbons and the dense-cored vesicles in the pinealocytes rapidly increased in number at 1 week of age, scarcely exhibiting distinct changes thereafter. Thus, it is clarified that the foregoing photosensory and secretory elements change during the post-hatching development. Furthermore, it is suggested that, in respect of these elements, the pineal gland of the quail assumes more active appearances than that of the chicken.