Pinealocyte

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

Monoamines and acetyl-cholinesterase in the pineal gland and habenula of the ferret

Abstract: A histochemical method for demonstrating amines by fluorescence showed that the pinealocytes of the ferret contained a high concentration of a yellow fluorophore (probably 5-HT). Numerous green-fluorescent (noradrenaline-containing) nerve fibres occurred around intrapineal blood vessels, between pinealocytes and in the N. conarii (which entered the gland caudally). A collection of neuron-like cells (the pineal ganglion) lay, surrounded by a meshwork of nerve fibres, in the posterior part of the pineal. Neither the cells nor the fibres of the pineal ganglion contained monoamines, but both showed the presence of acetyl-cholinesterase which otherwise was found in the pineal only in fibres which stretched from the ganglion towards the cranial pole of the gland. The medial habenular nucleus showed a remarkable perivascular green fluorescence not seen in the lateral habenular nucleus nor anywhere else in the adjacent diencephalon and brain stem. The cells and fibres of this nucleus also contained much acetyl-cholinesterase.

Microdialysis of melatonin in the rat pineal-gland - methodology and pharmacological applications

Abstract: The present study describes the development of a new technique to measure melatonin contents in the pineal gland of freely moving rats, by means of on-line microdialysis. The transcerebral cannula was modified, and a sensitive assay of melatonin, using HPLC with fluorimetric detection, was set up. With this system it is possible to monitor the melatonin levels on-line in the pineal gland during day- and nighttime. The nightly increase in melatonin release was recorded. Tetrodotoxin had an inhibitory effect on nighttime levels, whereas even high concentrations did not alter the daytime level. From this we conclude that neuronal activity is necessary to synthesize melatonin and that during daytime no net neuronal activity is present. Melatonin levels could be greatly enhanced by systemic administration of the beta-agonist isoprenaline (ISO). Also, local infusion of ISO or 8-bromoadenosine 3',5'-cyclic monophosphate, an analogue of the second messenger cyclic AMP, resulted in increased melatonin levels, demonstrating the presence of beta-adrenergic receptors, coupled to a cyclic AMP-based second messenger system, on the pineal gland. Injection of phenylephrine had no effect on daytime levels. Only when administered during ISO-induced stimulation of melatonin release did it enhance this stimulated release. This proved the regulatory role of alpha1-receptors on pinealocytes. The method presented is of special interest for investigating the innervation of the pineal gland and the biochemical processes that regulate the biosynthesis of melatonin. Also, for studies on the diurnal rhythms of melatonin release and factors that influence these rhythms in freely moving animals, this model will be of great value.

Role of melatonin and its receptors in the vertebrate retina.

Abstract: Melatonin is a chemical signal of darkness that is produced by retinal photoreceptors and pinealocytes. In the retina, melatonin diffuses from the photoreceptors to bind to specific receptors on a variety of inner retinal neurons to modify their activity. Potential target cells for melatonin in the inner retina are amacrine cells, bipolar cells, horizontal cells, and ganglion cells. Melatonin inhibits the release of dopamine from amacrine cells and increases the light sensitivity of horizontal cells. Melatonin receptor subtypes show differential, cell-specific patterns of expression that are likely to underlie differential functional modulation of specific retinal pathways. Melatonin potentiates rod signals to ON-type bipolar cells, via activation of the melatonin MT2 (Mel1b) receptor, suggesting that melatonin modulates the function of specific retinal circuits based on the differential distribution of its receptors. The selective and differential expression of melatonin receptor subtypes in cone circuits suggest a conserved function for melatonin in enhancing transmission from rods to second-order neurons and thus promote dark adaptation.

Calcified inclusions in the superficial pineal gland of the mongolian gerbil, Meriones unguiculatus.

Abstract: A histological and histochemical study of the pineal gland of neonatal, juvenile and adult gerbils is described. Calcified inclusions appear within pinealocytes in the superficial pineal about the third week of age, and the incidence of inclusions increased with age until, by the eleventh week, they are found in all animals. The inclusions contain an organic matrix composed of a carbohydrate, probably an acid mucopolysaccharide, complexed to protein. Calcification does not occur in the deep pineal. The data are interpreted to indicate that the formation of calcified inclusions is a normal process within the gerbil pineal. The similarity of the process of calcification in the gerbil and in the human pineal suggests that the gerbil may be an animal of choice for the controlled study of the phenomenon of pineal calcification.