Showing papers on "Pinealocyte published in 1973"

Synaptic ribbons of a mammalian pineal gland circadian changes

Abstract: Synaptic ribbons (SR) of the mammalian pineal gland are functionally enigmatic. In the present study it is shown that in male guinea-pigs kept under a lighting regimen of 12 hrs illumination (7.00–19.00) and 12 hrs darkness (19.00–7.00) the SR of pinealocytes vary about 25-fold in number over a period of 24 hrs. An increase is found between 15.00 and 6.00 and a decrease between 6.00 and 15.00. Analysis of the intracellular localization and the topographical relationships indicate that SR lie near the cell membrane of pinealocytes throughout the 24 hr period and that they are related to adjacent pinealocytes. A working hypothesis put forward implies that SR represent cell organelles involved in intercellular communication and that it is their function to either enhance the secretory activity of the pineal gland or to establish circuits within the gland between adjacent pinealocytes, similar to neuronal circuits.

Structure and innervation of the pineal gland of the rabbit, Oryctolagus cuniculus (L.). II. An electron microscopic investigation of the pinealocytes.

Abstract: In the rabbit pineal gland two types of postganglionic nerve endings were found which are characterized by the presence of small dense-core vesicles or small clear vesicles. Pharmacological and cytochemical experiments showed then to be noradrenergic and cholinergic, respectively. Both types were often present in the same nerve bundle, occasionally in close opposition. Intrapineal neurons were only rarely observed. They showed cholinergic synapses on their perikaryon and dendrites as well as noradrenergic axo-dendritic close contacts. Bilateral extirpation of the superior cervical ganglia revealed the postganglionic sympathetic origin of the pineal noradrenergic nerve fibres. Moreover, it appeared that these ganglia are hardly, if at all, involved in the pathway of pineal cholinergic innervation. The results obtained from lesions of both facial nerves, taken together with the results reported in the literature, led to the conclusion that the postganglionic cholinergic nerve fibers in the pineal are of parasympathetic origin. A model for the sympathetic and parasympathetic pineal innervation is proposed.

Growth hormone regulation by melatonin and serotonin.

Abstract: THERE is evidence to suggest the existence of a pineal gland substance which moderates growth both in man and the rat. In man, non-parenchymal tumours, such as gliomas or teratomas which result in destructive lesions of the pineal gland, are associated with precocious puberty1,2 and it has been hypothesized that such lesions prevent the pineal from secreting gonadal2 and growth3,4 inhibitory factors. It was recently reported5 that the ability of the pineal gland to influence both growth and gonadal development may be due to two distinct physiological mechanisms. Rats which are blinded or kept in constant darkness show reduced body weight4,5, reduced tibeal length4, and reduced accessory organ weights4 as well as retarded puberty2,5,6. Blinded rats were also found4 to have significantly reduced pituitary gland stores of growth hormone. The effects of blinding or constant darkness on growth and growth hormone stores were abolished by pinealectomy4,7—a procedure also found8 to increase the gain of body weight in otherwise normal rats. Pinealectomy has also been reported to result in increased growth of experimental tumours in rats9. The observation10 of a diurnal fluctuation in the secretion of growth hormone in the rat further suggests that the lighting regime can modify this release. When lighting is reduced, concentrations of the pineal hormone melatonin (N-acetyl-o-methylserotonin) are increased because it is synthesized within the pineal gland from serotonin (5-hydroxytryptamine) by the action of the enzymes serotonin-N-acetyltransferase and hydroxyindole-o-methyltransferase, both of which exhibit their highest activities in the absence of light11,12. The fact that the conditions favouring high melatonin production correlate with those which cause reduced growth (and the other way round) suggests that melatonin has an inhibitory role in growth hormone secretory mechanisms. Collu et al.13 demonstrated that intraventricular injections of serotonin stimulate secretion of growth hormone in the rat, and they proposed that in this animal secretion of growth hormone is controlled through serotoninergic pathways. Serotonin has also been implicated as the stimulus for secretion of growth hormone after the onset of slow-wave (non-rapid eye movement, NREM) sleep in normal humans14. It thus seems that serotonin and its pineal derivative, melatonin, may have opposing effects on the secretion of growth hormone. We describe here experiments which support this contention.

The synaptic ribbons of the guinea-pig pineal gland under normal and experimental conditions.

Abstract: “Synaptic” ribbons (SR), functionally enigmatic structures of mammalian pinealocytes, were studied electron microscopically with regard to number, intracellular localization and topographical relationships, both under normal and experimental conditions. Pineal glands of guinea-pigs serving as controls contained 1.75 ribbon fields/unit area in the males and 2.58 in the females. In animals subjected to continuous illumination for 64 days the number of ribbon fields increased 20-fold in the males and 9-fold in the females. Continuous darkness (26 to 70 days) had varying effects; in some animals SR increased either strongly or moderately, in others they appeared unchanged. Under continuous illumination a higher percentage of ribbon fields bordered the cell membrane than in the controls. Moreover, paired ribbon fields occurred. The topographical analysis revealed that 98 % of the ribbon fields bordering the cell membrane lay opposite another pinealocyte and the remainder opposite nerve fibres, blood vessels and collagenous fibres. It is suggested that SR of mammalian pinealocytes do not represent non-functioning phylogenetic relics but true organelles possibly involved in coupling adjacent pinealocytes functionally.

Cytological aspects of pineal development in rats and hamsters.

Abstract: Evidence has been accumulating which supports the hypothesis that through phylogenetic evolution, the mammalian pinealocyte has evolved from the pineal photoreceptor-cell which is characteristic of certain lower vertebrates. In the present study, developing pineal glands in fetal rats and hamsters were studied at light and electron microscopic levels to determine whether or not the ontogenetic development of pineal cells affords clues to their phylogenetic origin. Pineal development in fetal rats occurs during the last eight days of gestation (14–22) and in fetal hamsters, during the last five days of gestation (11–16). The pineal gland exhibits many similarities in the two species as it develops from a tubular evagination of the diencephalic roof into a compact cellular mass. Different cellular types could not be readily distinguished in fetal material from either species. In both animals, as long as lumina persist, cells bordering on these lumina exhibit surface modifications reminiscent of developing photoreceptor-cells, i.e., an “ellipsoid-like” apical cytoplasmic bulge which often contains one or two centrioles and bears a ciliary derivative exhibiting a 9 + 0 tubular configuration. As pineal tissue proliferates, the lumina and cilium-like structures disappear. The findings, when considered with phylogenetic studies, strengthen the hypothesis that the mammalian pineal gland contains cells derived from the photoreceptor-cell line.

CSF contacting axons and synapses in the lumen of the pineal organ.

Abstract: Free-running, naked axons (diameter 2000 to 7000 A) can be found in the lumen of the pineal organ. Their axoplasm contains microtubules, mitochondria as well as synaptic (diameter 350 to 450 A) and granulated vesicles (diameter 500 to 1500 A). In Pleurodeles waltlii, the axons in the pineal lumen form synapses on the free, apical surface of the pineal ependyma which is supplied with microvilli. In addition to usual cytoplasmic elements the innervated ependymal cells contain myeloid bodies and accumulations of glycogen granules. Without forming synapses these axons pass by and occasionally contact the inner and/or outer segments of the pinealocytes. The synapses found on the pineal ependymal cells furnish evidence of a neuronal control of these glial elements. The nerve fibers of the pineal lumen are being compared with known CSF contacting axons; they resemble one another in their ultrastructure and synaptic connections. Therefore and since in amphibians the pineal lumen communicates with the 3rd ventricle, the axons of the pineal lumen are considered to represent CSF contacting axons and to belong to the so-called CSF contacting axon system of the brain. In addition, the pineal CSF contacting axons are being compared with the following nerve fibers and terminals found in the pineal tissue: 1) axons containing large, granulated vesicles (diameter 1300 to 1500 A) and terminating on the dendrites of nerve cells situated among the basal processes of the pinealocytes; 2) the synaptic ribbons-containing pinealocyte processes forming likewise synapses on the nerve cells; 3) the neurohormonal, synaptic semidesmosomes of pinealocytic processes on the lamina basalis separating the connective tissue spaces of the pia mater from the proper nervous tissue of the pineal organ; 4) the perivasal, autonomic nerve fibers of the pial septa. Though granulated vesicles of various diameters are present in all these terminals the greatest morphological similarity is found between the pineal CSF contacting axons and those nerve fibers containing large, granulated vesicles and forming axo-dendritic synapses on the pineal nerve cells. A similar nature and origin of both axons are suggested.

Ultrastructural features of the pineal gland from cold-exposed golden hamsters.

Abstract: Golden hamsters exposed to various temperatures (5 and 25 °C) and photoperiods (8∶16 L∶D and 12∶10 L∶D), were killed at the end of 4, 8 and 12 weeks of exposure. The pineal glands were examined electron microscopically. Ultrastructural differences in the pineal gland were observed between the cold-exposed animals and the corresponding controls. The most striking difference was the occurrence of membranous whorls in pinealocytes of cold-exposed hamsters. These membranous whorls were of varying sizes and degree of complexity suggesting possible developmental stages of the membranous whorls. An apparent increase in ribosomal density and nuclear polymorphism were observed in the pinealocytes of cold-exposed hamsters. Short photoperiod appeared to augment the formation of membranous whorls in animals exposed to cold. It is suggested that the membranous whorls are focal sites of membrane reorganization that may be requisite for cellular activity under these environmental conditions. It is also suggested that gonadal involution owing to cold exposure may be mediated by the pineal gland.

Effects of melatonin on the synthesis of proteins by the rat hypothalamus, hypophysis and pineal organ.

Abstract: After decades of contradictory results it has become apparent that the mammalian pineal exerts an inhibitory influence on several neuroendocrine functions, namely the hypophysial-gonadal system, the adrenal cortex and the thyroid gland (Wurtman, Axelrod & Kelly, 1968). Among pineal secretory products the best characterized is melatonin (5-methoxy-N-acetyltryptamine), which reverses many of the endocrine changes that follow pinealectomy and mimics the effect of injecting pineal extracts into experimental animals. In the last 15 years considerable information has been accumulated on the mechanisms involved in the regulation of pineal melatonin synthesis; very little is known, however, about the biochemical processes evoked by melatonin in its target organs. Exogenous melatonin has been shown to become concentrated within the hypothalamus (Ant\l=o' -Tay& Wurtman, 1969; Cardinali, Hyypp\l=a"\& Wurtman, 1973). Implants of melatonin in the hypothalamus decrease pituitary gonadotrophin levels (Fraschini, 1969); moreover, melatonin perfusions of the third ventricle decrease plasma levels of follicle-stimulating and luteinizing hormones and raise plasma prolactin (Kamberi, Mical & Porter, 1970, 1971). In addition, hypothalamic serotonin (Antón-Tay, Chou, Antón & Wurtman, 1968) and y-aminobutyric acid content (Antón-Tay, 1971) increase rapidly after melatonin administration. The present experiments were designed to determine whether mela¬ tonin modifies the synthesis of proteins in the hypothalamus, the hypophysis and the pineal organ. Adult, male, Wistar rats (200-230 g) were kept under light between 07.00 h and 21.00 h daily, and given access to food and water ad libitum. In a first experiment 48 rats were divided into two groups: (a) melatonin, dissolved in ethanol : saline (5:95, v/v) just before use, was injected s.c. at 14.00 h daily for 5 days, at a dose of 10 fig/day ; (b) s.c. injections of vehicle were given. Four hours after the last injection the rats were killed and the hypothalamus, hypophysis and pineal organ were rapidly excised and frozen on dry ice. Individual hypothalami and hypophyses and pools of three pineals were incubated for 1 h at 37 °C in Krebs-Ringer bicarbonate buffer, containing 2 /tCi L-[4,5-3H]leucine (sp. act. 5 Ci/mmol) under a 95 % oxygen : 5 % carbon dioxide atmosphere. The incubations were stopped by freezing on dry ice and, after washing in saline solution, tissues were homogenized in 10 % trichloroacetic I.L.A.F.I.R., Universidad del Salvador, CC. 10, San Miguel (P.B.A.), Argentina

Ultrastructural characteristics and innervation of the pineal organ of the antarctic seal Leptonychotes weddelli

Abstract: The electron microscopy of the epiphysis cerebri of the antarctic seal Leptonychotes weddelli revealed a highly organized organ. The general cytological characteristics of the pinealocytes and the glial cells are described. The capillary blood vessels are the nonfenestrated type. The organ is richly innervated by mainly unmyelinated nerve fibers. Most of the axons end in the inner part of the organ, around vessels, some of them in relation with pinealocytes. The significance of the findings is discussed.