Immunocytochemistry and calcium cytochemistry of the mammalian pineal organ: A comparison with retina and submammalian pineal organs

Abstract

Morphologically the mammalian pineal organ is a part of the diencephalon. It represents a neural tissue histologically ("pineal nervous tissue") and is dissimilar to endocrine glands. Submammalian pinealocytes resemble the photoreceptor cells of the retina, and some of their cytologic characteristics are preserved in the mammalian pinealocytes together with compounds demonstrable by cyto- and immunocytochemistry and participating in photochemical transduction. In our opinion, the main trend of today's literature on pineal functions--only considering the organ as a common endocrine gland--deviates from this structural and histochemical basis. In mammals, similar to the lower vertebrates, the pinealocytes have a sensory cilium developed to a different extent. The axonic processes of pinealocytes form ribbon-containing synapses on secondary pineal neurons, and/or neurohormonal terminals on the basal lamina of the surface of the pineal nervous tissue facing the perivascular spaces. Ribbon-containing axo-dendritic synapses were found in the rat, cat, guinea pig, ferret, and hedgehog. In the cat, we found GABA-immunoreactive interneurons, while the secondary nerve cells, whose axons enter the habenular commissure, were GABA-immunonegative. GABA-immunogold-labeled axons run between pinealocytes and form axo-dendritic synapses on intrapineal neurons. There is a similarity between the light and electron microscopic localization of Ca ions in the mammalian and submammalian pineal organs and retina of various vertebrates. Calcium pyroantimonate deposits--showing the presence of Ca ions--were found in the outer segments of the pineal and retinal photoreceptors of the frog. In the rat and human pineal organ, calcium accumulated on the plasmalemma of pinealocytes and intercellularly among pinealocytes. The formation of pineal concrements in mammals may be connected to the high need for Ca exchange of the pinealocytes for their supposed receptor and effector functions.

GABAergic system of the pineal organ of an elasmobranch (Scyliorhinus canicula): a developmental immunocytochemical study

“…Our results in the dogfish also suggest that the GABA-ir cells of the pineal organ are intrinsic neurons. Small intrinsic GABA-ir neurons have furthermore been observed in the pineal gland of the cat (Vigh-Teichmann et al 1991;Vigh-Teichmann and Vigh 1992). Moreover, there is some physiological evidence of GABA actions on melatonin secretion and ganglion cell spike discharge in the pineal organ of the trout (Meissl and Ekström 1991;Meissl and Yáñez 1996;Brandstätter and Hermann 1996).…”

“…Immunocytochemical evidence exists for the presence of GABA-immunoreactive (-ir) neurons in the pineal organs of rainbow trout , frog (Ekström et al 1990), and lamprey Meléndez-Ferro et al 2002b), and physiological studies have explored the actions of GABA in the trout pineal organ (Meissl and Ekström 1991;Meissl and Yáñez 1996;Brandstätter and Hermann 1996). Mammals have been reported to possess small GABAergic neurons (cat: Vigh-Teichmann et al 1991;Vigh-Teichmann and Vigh 1992) and pinealopetal fibers of central origin (rodents and Tupaia: Sakai et al 2001).…”

Fibrous Calcareous Concretions in the Capsules of Human Pineal Glands

“…Non-fibrous calcareous concretions in the pineal matrix of some mammals [1][2][3] and humans [2][3][4][5][6][7][8][9][10][11] are formed by a fine lamination of alternating organic-rich and mineral-rich materials 1,11 . These matrix concretions, known also as psammoma bodies or brain sands, show a mulberry-shaped overall appearance 4,6,10 with the characteristic scallop-shaped laminations 1,3,8,10,11 .…”

“…However, such structures or their components remain to be identified in humans, although the presence of concretions in the pineal capsule was reportedly observed by optical microscopy 5,8 .…”

“…The coincident presence of these masses did not correlate with aging, but there tended to be a low negative correlation between their mineralized volumes assessed by microradiography. Human pineal glands containing a large number of matrix concretions also occasionally contain encapsulated masses 8 , although these are smaller than the matrix concretions 5,8 .…”