Pinealocyte

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

Sensory receptors as a special class of hormonal cells.

Abstract: Classically, sensory receptors are specialized cells which detect specific environmental disturbances and send out neural signals for the integration, control and/or regulation of effector organs. Recently, a special class of sensory receptors called sensori-hormonal cells which employ hormones as their means of flux of biological information has been proposed. These sensori-hormonal cells are capable of detecting and transducing environmental signals directly into the secretion of hormones within the same cells. Theoretically, all sensory receptors may have examples capable of direct sensori-hormonal transduction. However, only one group of sensori-hormonal cells, the photoendocrine cells, have so far been studied. The photoendocrine cells including the photoreceptors of fish retinas and pinealocytes of bird pineals are capable of detecting light and/or darkness and transducing the electromagnetic radiation energy into a hormonal output. Generally, light suppresses and darkness stimulates the biosynthesis and secretion of melatonin by these photoendocrine cells. Contrary to many hormonal systems which employ principally the feedback mechanism for regulation, the sensori-hormonal cells are predominantly controlled by the feedforward mechanism. However, other factors may serve as additional means of regulation by influencing the system and affecting the transduction processes and/or the synthesis and secretion of the hormone. The ability of sensori-hormonal transduction is suggested to be important for the survival of the organism itself and/or its species and sensori-hormonal cells or their equivalent should appear early in the course of animal evolution. It is further suggested that the sequence of appearance of melatonin functions in the course of evolution would be: hormone--humoral factor--neuromodulator--neurotransmitter.

CSF-contacting pinealocytes in the pineal recess of the Mongolian gerbil: a correlative scanning and transmission electron microscope study.

Abstract: The pineal recess of the Mongolian gerbil was studied using correlative scanning and transmission electron microscopy. The surface of the pineal recess can be subdivided into three distinct zones: (1) central, (2) transitional, and (3) peripheral. In the gerbil, the deep pineal gland is located deep to the central and transitional zones. The ependyma of the peripheral zone is densely ciliated and resembles that of the main ventricular lining. Ependymal cells of the transitional zone are sparsely ciliated but possess numerous microvilli on their apical surfaces. Supraependymal neurons were identified in the transitional zones. These cells appear to make a synaptic-like contact with the underlying ependymal cells. Of the three zones, the central zone demonstrated the greatest amount of morphological variability. Although a number of supraependymal structures could be identified in the central zone, the most remarkable feature was the presence of protruding cells that possessed no significant surface features. Employing correlative transmission electron microscopy, the protruding cells were shown to be CSF-contacting pinealocytes. The number of CSF-contacting pinealocytes present in the central zone varied from one cell to large clusters that covered the entire zone. The results of this investigation demonstrate the presence of a direct contact and the potential for interaction between the deep pineal gland and the CSF of the pineal recess in the gerbil.

Effects of blinding on the ultrastructure of mouse pinealocytes with particular emphasis on the dense-cored vesicles.

Abstract: The mammalian pineal is thought to produce an antigonadotropic principle under conditions of reduced photoperiod, constant darkness or blinding by optic enucleation. A number of previous studies on mammalian pineals have suggested that the dense-cored vesicles present in pinealocytes may represent morphological evidence of secretory activity. In the present study the ultrastructure of pinealocytes was studied in adult Charles River CD-1 mice blinded by optical enucleation. By one month following optic enucleation the mean number of dense-cored vesicles in the cytoplasm of pinealocytes adjacent to pericapillary spaces had significantly decreased by 55% when compared with intact controls, and remained at this low level at two months and six months. A relative increase in the proportion of large agranular vesicles and an increased number of large, irregular vacuoles was observed also in the pinealocytic polar processes of blinded mice. When compared to control mice the pinealocytic Golgi regions appeared to be hypertrophied in blinded mice. The apparent stimulation of pinealocytic organelles coupled with the observed decrease in dense-cored vesicles suggest an increased synthesis and release of secretory product.

The Mammalian Pineal Gland as an End Organ of the Visual System

Abstract: Visible light is the major environmental factor controlling the circadian production of melatonin in the mammalian pineal gland. Regardless of the activity pattern a species displays, i.e. diurnal, nocturnal or crepuscular, high melatonin production is always associated with the dark phase of the light: dark cycle. Light has two effects on the circadian melatonin rhythm; it precisely entrains the rhythm to 24 hours and light exposure during the night rapidly depresses high nighttime melatonin levels. The intensity of light required to inhibit nocturnal melatonin production varies widely among species with melatonin synthesis in the pineal gland of nocturnal animals having a much greater sensitivity (lower threshold) to light than that of diurnally active animals. While optic enucleation prevents all actions of light on the 24 hour melatonin cycle, destruction of the majority, if not all, the retinal photoreceptors does not alter the ability of light to synchronize the melatonin rhythm and only slightly increases the threshold of the pineal gland to acute light exposure. Beside luminance or intensity, the specific wavelength of light is important in determining its efficacy as an inhibitor of pineal melatonin synthesis. In general, blue-green wavelengths seem to be most inhibitory to the melatonin forming ability of the pineal. Red light (>600 nm) exposure, however, also suppresses pineal and serum melatonin levels. The ability of red light to achieve this effect is retained in rats with total or near total destruction of the retinal photoreceptors. To date there is no adequate explanation as to the retinal mechanisms involved in mediating the inhibitory effect of light on the pineal gland. It is possible, however, that the classical photoreceptors, i.e. the rods and cones, may not be involved in this process.