Pinealocyte

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

“Synaptic” ribbons and spherules of the guinea pig pineal gland: Inverse day/night differences in number

Abstract: The present study deals with the functionally enigmatic "synaptic" ribbons and spherules of guinea pig pinealocytes. Whereas the ribbons have been shown to exhibit a 24-hr rhythmicity with low numbers during the day and high numbers at night, very little of a definitive nature is known about the spherules. Sixteen male guinea pigs of the Hartley strain were perfusion fixed, 8 between 0900-1100 hr, and 8 between 2100-2300 hr. The ribbons and spherules were counted in the pineal parenchyma of the proximal, intermediate, and distal regions. In confirmation of earlier studies, it was found that "synaptic" ribbons are equally abundant in the proximal, intermediate, and distal regions of the gland, during both the day and the night, and that they increase significantly in number at night when compared with daytime values. The spherules, by contrast, are more abundant proximally and are present in greater numbers during the day than at night. As ribbons and spherules are usually not found in one and the same pinealocytic profile, and based on previous electrophysiological studies, it is proposed that the ribbons are morphological markers of nocturnally active pinealocytes, whereas spherules characterize diurnally active pinealocytes.

Endocrinology of the Amphibian Pineal

Abstract: McCord and Allen (1917) found that extracts of mammalian pineal glands contain a potent contracting agent of larval amphibian melanophores. Lerner and his co-workers determined the chemical structure of this principle and named it melatonin. This agent contracts dermal melanophores at a concentration as low as 10−10 g/ml. Both intact and eyeless larval amphibians blanch when placed in the dark, and the melanophore contraction which causes this lightening response is abolished by pinealectomy. The amphibian pineal contains photoreceptive elements similar to those found in the vertebrate lateral eyes, and these elements are inhibited by light but are stimulated in its absence. There is evidence for the presence of both HIOMT and melatonin the amphibian pineal. It has been proposed that the body-blanching response results from a direct stimulation of the pineal under conditions of darkness leading to a release of melatonin into the general circulation which is then responsible for a direct contracting effect on dermal melanophores. The cytophysiological effects of melatonin mimic those that take place in the body-blanching response. Since no other hormone or pharmacological agent duplicates this response, this is strong evidence that melatonin is a hormone that normally regulates body blanching. Other evidence for the support of this hypothesis is presented. Cytological features of both normal and melatonin-induced lightening indicate that the effects of melatonin are at the effector cell level rather than at either the hypothalamus or the pituitary. An inhibition of MSH-release by melatonin is not involved. Melatonin plays a normal role in young larvae to regulate the lightening response that takes place in darkness (the primary chromatic response). Neither melatonin nor the pineal play a role in the later (secondary stage) adaptive background responses of amphibians. As McCord and Allen first noted, the pineal may contain other substances which may have other physiological roles in amphibians as well as other vertebrates. These have been little studied.

Glial fibrillary acidic (GFA) protein-containing cells in the human pineal gland.

Abstract: The development of human pineal astrocytes was studied in a prospective autopsy series of 115 cases with an age range of 24 weeks of gestation to 91 years. Pineal glands selected from cases with postmortem intervals of one to 24 hours were fixed in Bouin's fluid and immunostained using the peroxidase-antiperoxidase technique and an antiserum against human glial fibrillary acidic (GFA) protein. In adults, scattered, mostly angular and strongly-positive cells and processes were present. A few primary processes emanated from each astrocyte which abruptly subdivided into several secondary ones, creating a pervasive interstitial network of fibers which surrounded almost every individual pinealocyte. Astrocytic endfeet formed a limiting lamina at the periphery of the gland and a barrier between perivascular spaces and the pineal parenchyma. At 24 weeks of gestation, occasional punctate staining, mainly around vessels, was present in the pineal body, while in the surrounding white matter there was already pronounced astrocytic differentiation. Around 32 weeks of gestation, well-formed astrocytes and a weakly staining network of their processes appeared in differentiated areas of the pineal gland. Both astrocytes and their interstitial network of processes became more prominent with advancing age. There was no astrocytic hypertrophy or hyperplasia around calcified deposits. Rosenthal fibers stained negatively for GFA protein. These findings emphasize the significance of the astrocytic participation in the structure of the human pineal gland throughout life.

Circadian rhythms in the pineal organ persist in zebrafish larvae that lack ventral brain

Abstract: Background: The mammalian suprachiasmatic nucleus (SCN), located in the ventral hypothalamus, is a major regulator of circadian rhythms in mammals and birds. However, the role of the SCN in lower vertebrates remains poorly understood. Zebrafish cyclops (cyc) mutants lack ventral brain, including the region that gives rise to the SCN. We have used cyc embryos to define the function of the zebrafish SCN in regulating circadian rhythms in the developing pineal organ. The pineal organ is the major source of the circadian hormone melatonin, which regulates rhythms such as daily rest/activity cycles. Mammalian pineal rhythms are controlled almost exclusively by the SCN. In zebrafish and many other lower vertebrates, the pineal has an endogenous clock that is responsible in part for cyclic melatonin biosynthesis and gene expression. Results: We find that pineal rhythms are present in cyc mutants despite the absence of an SCN. The arginine vasopressin-like protein (Avpl, formerly called Vasotocin) is a peptide hormone expressed in and around the SCN. We find avpl mRNA is absent in cyc mutants, supporting previous work suggesting the SCN is missing. In contrast, expression of the putative circadian clock genes, cryptochrome 1b (cry1b) and cryptochrome 3 (cry3), in the brain of the developing fish is unaltered. Expression of two pineal rhythmic genes, exo-rhodopsin (exorh) and serotonin-Nacetyltransferase (aanat2), involved in photoreception and melatonin synthesis, respectively, is also similar between cyc embryos and their wildtype (WT) siblings. The timing of the peaks and troughs of expression are the same, although the amplitude of expression is slightly decreased in the mutants. Cyclic gene expression persists for two days in cyc embryos transferred to constant light or constant dark, suggesting a circadian clock is driving the rhythms. However, the amplitude of rhythms in cyc mutants kept in constant conditions decreased more quickly than in their WT siblings. Conclusion: Our data suggests that circadian rhythms can be initiated and maintained in the absence of SCN and other tissues in the ventral brain. However, the SCN may have a role in regulating the amplitude of rhythms when environmental cues are absent. This provides some of the first evidence that the SCN of teleosts is not essential for establishing circadian rhythms during development. Several SCN-independent circadian rhythms have also been found in mammalian species. Thus, zebrafish may serve as a model system for understanding how vertebrate embryos coordinate rhythms that are controlled by different circadian clocks.