Morphometric analysis of photoreceptive, neuronal and endocrinal cell differentiation of avian pineal cells: an in vitro immunohistochemical study on the developmental transition from neuronal to photo-endocrinal property.

Little is known about the developmental origin, determination and differentiation of different pineal immunoreactive cells in the avian group, and an experimental establishment is then required to explain the differentiation of cell types (i.e. photosensory, neural and secretory types). The present in vitro study suggests that the avian pineal organ is made up of multiple types of cells with different immunoreactivity at the ontogenic state (from embryonic day 9 to day 14), before it acquires the final photoendocrinal nature of the mature state. The morphometric analysis suggests that the developmental changes in the morphology of the quail pinealocytes appear to represent a condensed expression of the phylogenic development in the ontogeny. Several types of immunoreactive cells from a neuronal line were suppressed with maturation of developing pineal glands, while other cell types such as photoreceptive and endocrinal lines became more prominent. The melatonin level in the culture medium presented a high value up to 72 hr of culture, followed by a decrease as well as dampening of the level at the end of the culture possibly because the cultures were maintained in dark. The results of the present study, a combined analysis of morphometry and RIA, open a new line for research into the pineal development and cell differentiation.