THE PINEAL COMPLEX OF REPTILES - PHYSIOLOGICAL AND BEHAVIORAL ROLES

The pineal complex of reptiles is a morphologically and functionally c onnected set of organs that originates as an evagination of the roof o f the diencephalon. It is formed by two structures: the pineal organ a nd the parietal eye. The pineal gland is present in Chelonia, Squamata and Rhynchocephalia, but not in Crocodilia. The parietal eye is prese nt in some species of lizards (Squamata) and in the tuatara (Rhynchoce phalia). Both the pineal gland and the parietal eye are photosensitive . In particular, the parietal eye is an highly organized photoreceptiv e structure, with a well-defined lens, cornea and retina. The most imp ortant (and studied) secretory product of this complex is the hormone melatonin which is synthesized by both organs (pineal and parietal eye ). The pineal organ is believed to be the neuroendocrine transducer of changes in photoperiod and environmental temperature and it has been demonstrated to have a functional role in many aspects of reptilian bi ology. Melatonin has an influence on the mechanisms controlling thermo regulation (behavioral and physiological), because its manipulation or removal may produce significant alterations of behavioral and physiol ogical thermoregulatory parameters. The reptilian pineal complex may a lso possess self-sustained circadian oscillators which are involved in the circadian organization of these animals and in their reproduction . It is believed that many of the roles played by the pineal complex a re mediated by the hormone melatonin, since exogenous administration o f melatonin may affect the animal's physiology and/or behavior. The pr esent paper will review the current knowledge about the neuroendocrino logy and functional roles of the reptilian pineal complex.