Pinealocyte

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

The role of the intracellular and extracellular serotonin in the regulation of melatonin production in rat pinealocytes.

Abstract: This study investigated whether the activation of pinealocyte beta-adrenergic receptors is involved in the regulation of serotonin (5-HT) synthesis and release, as it is for melatonin production. In addition, the role of the intra- and extra-cellular 5-HT in modulating the synthesis of melatonin induced by the beta-adrenergic agonist isoproterenol (ISO) was also studied. The incubation of dissociated pinealocytes with 0.1-10 microM ISO resulted in a concentration-dependent increase of melatonin synthesis. 5-HT release and intracellular 5-HT content were increased by 0.1 and 1 microM ISO but they were reduced after ISO 10 microM. Moreover, when incubated with the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA), the secretion of 5-HT as well as the intracellular 5-HT levels were markedly reduced in both ISO-stimulated and unstimulated conditions. Melatonin release was also inhibited by PCPA, although it responded in the expected manner to increasing concentrations of ISO. These data indicate that the release of 5-HT from pinealocytes depends on the availability of cytoplasmic 5-HT, which in turn is highly dependent on the tryptophan hydroxylase activity. In cells stimulated with moderate ISO concentrations, 5-HT release may be an important regulatory process of pineal 5-HT. After a large stimulation of N-acetyltransferase (NAT) activity by ISO, the synthesis of melatonin prevails on 5-HT release, whose decrease is associated to a deficit of intracellular 5-HT. On the other hand, the present study shows that the incubation of pineal cells with high concentrations of 5-HT or with a selective 5-HT2 receptor agonist, alpha-methyl-5-hydroxytryptamine, reverses partially the inhibitory effect of PCPA on the ISO-stimulated melatonin synthesis. In contrast the 5-HT2 antagonist, ketanserin, results in an inhibiton of the release of melatonin following ISO stimulation. These results suggest that released 5-HT may have a role in the full expression of the beta-adrenergically induced NAT activity and, thus, may contribute to the optimal melatonin synthesis at night.

Electron microscopy of the rabbit pineal organ in vitro. Evidence of norepinephrine-stimulated secretory activity of the Golgi apparatus.

Abstract: The results presented in this study show that the rabbit pineal organ cultured in vitro retained its in vivo fine structure for at least eight days. However, the Golgi complex in the light pinealocytes stopped forming dense core vesicles while vesicle-crowned ribbons increased in number. After addition of norepinephrine to the culture medium, the Golgi complex once more began the production of dense core vesicles. Terminals of light pinealocytic processes then often contained Golgi dense core vesicles in close contact with the cell membrane, suggesting the release of the vesicular content into the intercellular and perivascular spaces. A close topographical relationship between Golgi dense core vesicles and vesicle-crowned ribbons was observed.

[On axon-like endings, secretion and extrusion of the pinealocytes of the rabbit].

Abstract: Die hellen Pinealozyten des Kaninchens schicken lange, schmale, kolbenformig endigende Fortsatze in den perivaskularen Bindegewebsraum. Das Sekret der Zellen wird in typischer Weise ausgeschieden: Zahlreiche kleine Blaschen umgeben einen dichten Kern („Rosettenstruktur“). Die Ansammlung von Blaschen verschwindet, wahrend das dichte Material in den interzellularen oder perivaskularen Raum gelangt. Eine „postsynaptische Membran“ fehlt.

Tentative immunohistochemical demonstration of melatonin in the rat pineal gland.

Abstract: In the present study an attempt was made to demonstrate melatonin in the rat pineal gland by means of immunohistochemistry. The anti-body used was raised against 5-methoxy-N-acetyltryptophan which is chemically similar to melatonin. Specific fluorescence was demonstrable only in pineals from rats killed during the night, when melatonin formation is high. It was restricted to parenchymal cells lying in a marginal zone of the organ. These results are discussed in relation to a subdivision of the pineal parenchyma into cortical and medullary areas.

Modulation of Aanat gene transcription in the rat pineal gland.

Abstract: The main function of the rat pineal gland is to transform the circadian rhythm generated in the suprachiasmatic nucleus into a rhythmic signal of circulating melatonin characterized by a large nocturnal increase that closely reflects the duration of night period. This is achieved through the tight coupling between environmental lighting and the expression of arylalkylamine-N-acetyltransferase, the rhythm-controlling enzyme in melatonin synthesis. The initiation of Aanat transcription at night is controlled largely by the norepinephrine-stimulated phosphorylation of cAMP response element-binding protein by protein kinase A. However, to accurately reflect the duration of darkness, additional signaling mechanisms also participate to fine-tune the temporal profile of adrenergic-induced Aanat transcription. Here, we reviewed some of these signaling mechanisms, with emphasis on the more recent findings. These signaling mechanisms can be divided into two groups: those involving modification of constitutively expressed proteins and those requiring synthesis of new proteins. This review highlights the pineal gland as an excellent model system for studying neurotransmitter-regulated rhythmic gene expression.