Pinealocyte

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

Delivery of pineal melatonin to the brain and SCN: role of canaliculi, cerebrospinal fluid, tanycytes and Virchow–Robin perivascular spaces

Abstract: Historically, the direct release of pineal melatonin into the capillary bed within the gland has been accepted as the primary route of secretion. Herein, we propose that the major route of melatonin delivery to the brain is after its direct release into the cerebrospinal fluid (CSF) of the third ventricle (3V). Melatonin concentrations in the CSF are not only much higher than in the blood, also, there is a rapid nocturnal rise at darkness onset and precipitous decline of melatonin levels at the time of lights on. Because melatonin is a potent free radical scavenger and antioxidant, we surmise that the elevated CSF levels are necessary to combat the massive free radical damage that the brain would normally endure because of its high utilization of oxygen, the parent molecule of many toxic oxygen metabolites, i.e., free radicals. Additionally, the precise rhythm of CSF melatonin provides the master circadian clock, the suprachiasmatic nucleus, with highly accurate chronobiotic information regarding the duration of the dark period. We predict that the discharge of melatonin directly into the 3V is aided by a number of epithalamic structures that have heretofore been overlooked; these include interpinealocyte canaliculi and evaginations of the posterodorsal 3V that directly abut the pineal. Moreover, the presence of tanycytes in the pineal recess and/or a discontinuous ependymal lining in the pineal recess allows melatonin ready access to the CSF. From the ventricles melatonin enters the brain by diffusion and by transport through tanycytes. Melatonin-rich CSF also circulates through the aqueduct and eventually into the subarachnoid space. From the subarachnoid space surrounding the brain, melatonin penetrates into the deepest portions of the neural tissue via the Virchow–Robin perivascular spaces from where it diffuses into the neural parenchyma. Because of the high level of pineal-derived melatonin in the CSF, all portions of the brain are better shielded from oxidative stress resulting from toxic oxygen derivatives.

The Mel1a melatonin receptor gene is expressed in human suprachiasmatic nuclei.

Abstract: The pineal hormone melatonin influences circadian rhythmicity in many vertebrate species. The circadian effects of melatonin in humans have led to its use to treat jet lag and circadian-based sleep disorders. Melatonin is thought to influence circadian rhythmicity by acting in the suprachiasmatic nuclei (SCN). The recent cloning of two melatonin receptor subtypes with high affinity for melatonin allows molecular analysis of melatonin receptors in human SCN. We report that Mel1a receptor mRNA is detectable in neonatal human SCN by in situ hybridization. Mel1b and melatonin-related receptor mRNAs were not detected. The presence of Mel1a receptor mRNA in human SCN supports the hypothesis that the Mel1a receptor is responsible for the circadian effects of melatonin in humans.

Regulation of melatonin secretion in a photoreceptive pineal organ: an in vitro study in the pike.

Abstract: The pineal organ (or pineal) of a teleost fish, the pike, contains typical (cone-like) and modified photoreceptor cells. Both are involved in indole metabolism, including melatonin production. How photoperiod controls melatonin biosynthesis in organs containing mainly photoreceptor cells, remains unclarified. To tackle this question we have used cultured pike pineal organs to investigate the variations in (1) the activity of the arylalkylamine-N-acetyltransferase (NAT), which is involved in the biosynthesis of melatonin, in static culture and (2) melatonin release in a perifusion system. Serum melatonin was also quantified in pike kept under a 24 hr light/dark (LD) cycle. Under LD conditions, NAT activity, melatonin release, and serum melatonin levels were high during the scotophase and low during the photophase. High-amplitude rhythms in NAT activity and melatonin release were maintained during three 24 hr cycles in constant darkness and a low-amplitude rhythm of NAT persisted in constant illumination. Midnight illumination induced a dramatic decrease of NAT activity and melatonin release. Darkness at midday did not induce a rise of the melatonin release, which occurred only at the onset of the subjective scotophase. From the present data it is strongly suggested that the pineal of the pike contains a circadian oscillator--synchronized by the photoperiod--which generates the rhythms of NAT activity and of melatonin release. Melatonin release, which reflects the rhythmic activity of NAT, might largely contribute to the melatonin circulating levels. The circadian oscillations observed under constant conditions suggest that the oscillator might behave differently in the pike, compared with intrapineal oscillators of 2 other species (lizard and chicken) under investigation.(ABSTRACT TRUNCATED AT 250 WORDS)