Pinealocyte

About: Pinealocyte is a research topic. Over the lifetime, 1605 publications have been published within this topic receiving 55609 citations.

Components and connections of the circadian timing system in mammals

Abstract: The circadian timing system is a neural network consisting of the hypothalamic suprachiasmatic nucleus, aided by the retina, other hypothalamic nuclei, autonomic regions of the spinal cord, sympathetic ganglia and the pineal gland. Extensive studies conducted over the last two decades have unravelled the principal items of its functional neuroanatomy. The system is responsible for the generation of the circadian rhythm, its synchronization by environmental factors such as light, and its mediation with respect to morphological, physiological and biochemical parameters of mammals that exhibit distinct alterations throughout the 24-h cycle. This review characterizes the brain sites involved and the pathways responsible for the generation and maintenance of circadian rhythmicity.

Secretory processes in the mammalian pinealocyte under natural and experimental conditions.

Abstract: Publisher Summary In various recent reviews it has been concluded that the pineal body synthesizes a number of compounds and is an endocrine gland whose secretory products influence the development and function of the reproductive organs. It has been postulated that the pineal mediates certain environmental factors which regulate the function of the reproductive system. At present, no known pineal compound satisfies all of the classical criteria for a candidate hormone, that is, a substance produced exclusively in the pineal gland and having a specific functional influence on (a) distant target organ(s). In the light of the different concepts treated, the confused state of comprehension of pineal functions becomes more understandable. Only chemical identification of the different hormones synthesized in the pineal will permit the exact determination of pineal function. It is evident that one must think in terms of multiplicity of types of regulation in relation to the multiplicity of effects. Probably, the mammalian pineal gland is a synchronizer contributing to seasonal and probably also to circadian organization of functions. It is nonexclusively involved in different neuroendocrine mechanisms, which attunes the physiological adaptation of animals to their unique daily and annual patterns. When considering these points, most of the paradoxical and contradictory facts related to pineal function become less confusing.

Origin of cerebrospinal fluid melatonin and possible function in the integration of photoperiod

Abstract: Melatonin, which is synthesized at night by the pineal gland, is present in the cerebrospinal fluid (CSF), but its entry site and its role in this compartment are not known. Using several approaches, we tested the hypothesis that melatonin enters the CSF through the pineal recess, an evagination of the third ventricle. CSF melatonin concentrations are higher near the pineal gland than in the anterior part of the third ventricle, and decrease markedly (80%) after sealing off the pineal recess. Moreover, ultrastructure and permeability analyses of the pineal-CSF interface showed that melatonin could reach the CSF either via delivery in situ by protruding pinealocytes that make direct contact with the CSF or via extracellular secretion and interstitial fluid draining into the ventricular lumen. These data indicate that melatonin in the CSF probably originates from a few pinealocytes of the basal part of the pineal gland neighbouring the pineal recess. Melatonin carried to the brain by the blood appears to be able to mediate the effects of photoperiod on reproduction, but it is unclear whether melatonin in CSF may fine-tune this response both in terms of timing and amplitude. It is critical to determine which pathway, blood or CSF, allows melatonin to reach its central targets more efficiently.

The 2004 Aschoff/Pittendrigh lecture: Theory of the origin of the pineal gland--a tale of conflict and resolution.

Abstract: A theory is presented that explains the evolution of the pinealocyte from the common ancestral photoreceptor of both the pinealocyte and retinal photoreceptor. Central to the hypothesis is the previously unrecognized conflict between the two chemistries that define these cells-melatonin synthesis and retinoid recycling. At the core of the conflict is the formation of adducts composed of two molecules of retinaldehyde and one molecule of serotonin, analogous to formation in the retina of the toxic bis-retinyl ethanolamine (A2E). The hypothesis argues that early in chordate evolution, at a point before the genes required for melatonin synthesis were acquired, retinaldehyde--which is essential for photon capture--was depleted by reacting with naturally occurring arylalkylamines (tyramine, serotonin, tryptamine, phenylethylamine) and xenobiotic arylalkylamines. This generated toxic bis-retinyl arylalkylamines (A2AAs). The acquisition of arylalkylamine N-acetyltransferase (AANAT) prevented this by N-acetylating the arylalkylamines. Hydroxyindole-O-methyltransferase enhanced detoxification in the primitive photoreceptor by increasing the lipid solubility of serotonin and bis-retinyl serotonin. After the serotonin --> melatonin pathway was established, the next step leading toward the pinealocyte was the evolution of a daily rhythm in melatonin and the capacity to recognize it as a signal of darkness. The shift in melatonin from metabolic garbage to information developed a pressure to improve the reliability of the melatonin signal, which in turn led to higher levels of serotonin in the photodetector. This generated the conflict between serotonin and retinaldehyde, which was resolved by the cellular segregation of the two chemistries. The result, in primates, is a pineal gland that does not detect light and a retinal photodetector that does not make melatonin. High levels of AANAT in the latter tissue might serve the same function AANAT had when first acquired- prevention of A2AA formation.