Pinealocyte

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

Measurement of tryptophan hydroxylase activity in rat pineal glands and pinealocytes using an HPLC assay with electrochemical detection.

Abstract: A method for measuring tryptophan hydroxylase activity by assaying the product 5-HTP using high-performance liquid chromatography (HPLC) with electrochemical detection is described. A nocturnal elevation (80%) in rat pineal gland tryptophan hydroxylase activity was detected. Experiments on isolated rat pinealocytes with the protein synthesis inhibitor cycloheximide indicate that tryptophan hydroxylase turns over rapidly in these cells. This method will be valuable in studies of the adrenergic mechanisms regulating pineal tryptophan hydroxylase activity.

Regional differences in the pineal gland of the cotton rat, Sigmodon hispidus: Light microscopic, electron microscopic, and immunohistochemical observations

Abstract: Light microscopic, electron microscopic and immunohistochemical observations of the various portions of the pineal gland of the cotton rat (Sigmodon hispidus) were made. The volume of the proximal half occupied about 30% of the whole organ, and pinealocytes were slightly smaller in size in the proximal portion than elsewhere. The distal and intermediate portions contained few interstitial cells and numerous astrocytes, but the proximal portion lacked interstitial cells and had more abundant astrocytes than elsewhere. Astrocytes, which were immunoreactive for glial fibrillary acidic protein, mainly lined the pericapillary spaces in the distal and intermediate portions, but in the proximal portion these cells often surrounded isolated or groups of pinealocytes. In the distal and intermediate portions, abundant sympathetic fibers and less numerous non-sympathetic, peptidergic fibers were mainly localized in the pericapillary spaces; these fibers were sparsely distributed in the parenchyma close to interstitial cells or astrocytes. In the proximal portion, non-sympathetic fibers were scarce and sympathetic fibers were distributed abundantly and almost exclusively in the parenchyma. Most of the sympathetic fibers were adjacent to astrocytes and, occasionally, made specialized contact with them. Fenestrae in the capillary endothelium were numerous in the distal portion but absent in the proximal portion. Thus, marked differences in structure existed between the distal and proximal portions of the pineal gland of the cotton rat, suggesting that both portions are functionally dissimilar. In addition, the present study indicates that the proximal portion of the cotton rat was well developed and showed morphological features similar to the deeply situated pineal glands of other mammals.

Identification of extraretinal photoreceptors in the teleost Phoxinus phoxinus

Abstract: Summary. The existence of cells capable of detecting changes of the photoperiod within the deep brain, the socalled deep brain photoreceptors, was proposed in the early years of the twentieth century. By using immunocytochemistry with antisera against phototransductory proteins on paraffin and vibratome sections, we have localized several positive areas in the brain of the teleost Phoxinus phoxinus. These areas were restricted to two encephalic regions: the epithalamus and the hypothalamus. Immunopositive (rod-opsin- and α-transducin-like) pinealocytes and parapinealocytes, as well as some sparse neurons in the habenula, were seen in the epithalamus. The immunoreaction of the hypothalamus was represented by α-transducin-like positive (magnocellular and parvicellular) neurons of the Nucleus Preopticus, as well as by α-transducin- and arrestin-like positive fibers corresponding to the hypothalamic-hypophyseal tract and a few fibers running towards the basal telencephalon. These findings corroborate the data published on other teleost fish and fully support the hypothesis of the presence of photosensitive cells in the encephalon of lower vertebrates. The labelling with antisera against different components of the phototransductory cascade also strengthens the idea that such cells employ a biochemical mechanism similar to that in the retinal visual photoreceptor cells, rods and cones. Although the function is still unclear, the detection of the photoperiod seems to be the most likely role for these extraretinal photoreceptors.

Morphometric investigations of the pineal gland after ganglionectomy and thyroidectomy under the aspect of circadian and seasonal variations.

Abstract: It is well established that the pineal gland is involved in the regulation of thyrotropin (TSH) secretion. Previous investigations in our laboratory showed that under hypothyroid conditions the nuclear size of pinealocytes was diminished while an increase in the size of nuclei was seen under hyperthyroid conditions. In the present study we confirmed these results while considering circadian and circannual oscillations. After ganglionectomy (GX, removal of the sympathetic superior cervical ganglia) the mean annual values of the nuclear size of pinealocytes, pineal weights and thyroxine (T4) levels were diminished, whereas the pituitary weights increased. Comparable, but more drastical reactions were found after thyroidectomy (TX). The diminution of the nuclear size of pinealocytes was more pronounced in the wintertime (December, L: D = 8: 16), the finding for the summertime (June, L: D = 16: 8) being similar. Under short-day conditions the nuclear size was larger than under long-day regimes. In the winter the enhancement of the nuclear size was accompanied by decreased pituitary weights and increased T4 levels while under long-day conditions lower size of pinealocytes and T4 levels were associated with higher weights of pituitary glands. The statistically significant circadian patterns of the nuclear size of pinealocytes showed that the largest nuclei occurred at the end of the light phase or at the onset of the dark phase. In June, the largest nuclei were found in the middle of dark (control) or in the early light phase (ganglionectomy). Considering the circadian patterns of pineal weights and T4 levels, these results underline the existence of a functional connection between the pineal gland and the thyroid axis.(ABSTRACT TRUNCATED AT 250 WORDS)

A negative regulatory element required for light-dependent pinopsin gene expression.

Abstract: In vertebrates, a variety of light-stimulated genes are distributed in the retina, the pineal gland, and the suprachiasmatic nucleus, but a cis-element(s) responsible for the light-dependent transcriptional regulation is left unexplored. Focusing on the pinopsin gene, a light-stimulated gene in the chick pineal gland, we performed a transcriptional analysis in the primary culture of the chick pineal cells that were transiently transfected with a luciferase reporter gene fused with various lengths of the 5' upstream region of the pinopsin gene. Light-dependent enhancer activity was detectable in the construct with the upstream region between -1156 and +31. Introduction of mutations within the 18 bp sequence at positions -1103 to -1086 (TGGCACGTGGGGTTCCTC), including a CACGTG E-box sequence, elevated the transcriptional activity in the dark and thereby abrogated the light dependency, suggesting that the 18 bp sequence is essential for a reduction of the transcriptional activity in the dark. In an electrophoretic mobility-shift assay, we identified a pineal nuclear factor(s) capable of binding to the 18 bp element in a sequence-specific manner. When a 49 bp fragment (-1122 to -1074) including the 18 bp sequence was placed upstream of the simian virus 40 promoter, the transcriptional activity was dramatically suppressed regardless of light conditions in the chick pineal cells, and a more pronounced repression was observed in nonpineal/nonphotosensory LMH and NIH 3T3 cells. These results suggest that the 18 bp element in the pinopsin promoter constitutes the binding site of a ubiquitous factor that serves for the transcriptional repression that is required, although not sufficient, for the light-dependent expression of pinopsin gene in the chick pinealocytes.