Comparative Gross and Fine Morphology of the Mammalian Pineal Gland

Abstract

Some knowledge of the structure of an organ is indispensable for the investigation and understanding of its function. This is also very evident in case of the mammalian pineal organ the structure of which clearly points to its endocrine function.Its classical name, and also its official one now, is "corpus pineale". This term was given to the structure by Galen (ca 130 -ca 200 A.n.) who observed that, in man, the organ is shaped like the cone of a pine tree. In general, however, the shape, size and also the location of the mammalian pineal greatly vary among mammals. Before dealing with this matter, a short survey of the principles of pineal embryology is necessary because the ontogenetic development of the organ elucidates much about its adult morphology and its relationship to neighbouring structures.Just like in other vertebrates, the mammalian pineal organ develops from the neuroepithelial layer which forms the roof of the dorsal part of the diencephalon, the epithalamus. In fetal stages, this layer, which is situated between the habenular commissure rostrally and the posterior commissure caudally, evaginates forming a sac-like structure. In the rat, this first indication of a pineal anlage is observed between the 12th and the 14ith day of fetal life (Gardner, 1949;Ariens Kappers, 1960;Vollrath, 1981, also for literature). Next, the pineal evagination deepens and its wall becomes thicker by cell proliferation. At days 16 and 17. the wall forllLs infoldings

Gene Duplication and Loss ofAANATin Mammals Driven by Rhythmic Adaptations

“…Surgical removal of the pineal gland in animals can abolish the circadian behavior and reduce sleep duration ( Kocher et al 2006 ; Trivedi et al 2016 ). During the mammalian evolution, four taxa (cetaceans, sirenians, pangolins, and xenarthrans) have been reported to lack of discernable pineal glands ( Ralph 1975 ; Kappers 1983 ), and correspondingly, independent inactivating mutations or missing of AANAT locus were identified in these four clades in the present study. This result may have been associated with their particular features in circadian rhythm to adapt to specific ecological niches.…”

“…The changing duration of melatonin provides a dominant time cue for seasonal behavioral cycles ( Bartness and Goldman 1989 ; Lincoln 2006 ). Additionally, the rhythmicity of pineal melatonin is a hallmarker of internal time in mammals, but some taxa such as cetaceans, sirenians, pangolins, and xenarthrans (i.e., anteaters, sloths, and armadillos) seem to lack pineal glands ( Ralph 1975 ; Kappers 1983 ; Panin et al 2012 ).…”

Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light

“…They detected both AANAT and ASMT proteins in brain nonsynaptosomal mitochondria, whereas these enzymes were virtually absent in the cytosol. In pinealocytes, as expected, the expression of AANAT protein exhibited a circadian rhythm, whereas no rhythm in AANAT expression was demonstrable in non- It was originally widely accepted that melatonin was synthesized in the cytosol [38], even though there was no solid data to support this opinion. The majority of the melatonin synthetic studies were carried out in the supernatants of the tissue or cell homogenates.…”

“…animals, melatonin may provide uncommonly elevated protection against ROS during high stress conditions (exercise, solar exposure, heat exhaustion, digestion, and anxiety attacks.) It was originally widely accepted that melatonin was synthesized in the cytosol [38], even though there was no solid data to support this opinion. The majority of the melatonin synthetic studies were carried out in the supernatants of the tissue or cell homogenates.…”