Pineal transducers in the course of evolution: molecular organization, rhythmic metabolic activity and role.

Data on the cell biology of pineal transducers (chief cells: typical and modified photoreceptors, pinealocytes) which belong to the paraneuron family, are reviewed in the vertebrate series. In spite of major changes throughout phylogeny, it is proposed that pineal chief cells share a common feature: they somehow transform the information derived from the light/dark cycle into daily rhythms of neural (an excitatory neurotransmitter) and/or hormonal (melatoninergic) output and appear invariably involved in the temporal organization of physiological and behavioral processes.