The pineal organ in sockeye salmon and its relation with other epithalamic components has been studied. Histological and histochemlcal methods were used and the influence of experimental photoperiods on the histology and secretion in the juvenile pineals investigated. Photosensory and supporting ependymal cells have been identified. Lipofuchsin and melanin are absent in the pineal epithelium. Besides sensory fibres, efferent end-loops are present on the sensory and supporting cells. The dorsal pineal nerve tract is probably of a mixed type. Although the blood supply is profuse an endocrine or neuroendocrine activity is not indicated. It is proposed that the pineal organ in both juveniles and adults is photosensory and secretory. The apocrine secretory activity of the sensory and some supporting cells is probably associated with either the maintenance of constant chemical composition of the cerebrospinal fluid or supply of certain substances to the nervous tissue. The subcommissural organ is metabolically more active than the pineal. The secretion consists of glycogen, mucopolysaccharides, mucoproteins, glycoproteins and aldehyde-fuchsin positive granules. Chrome-alum positive granules are abundant in the subcommissural organ. Both the pineal organ and the subcommissural organ appear independent of light's influence on secretion and histology. It seems more plausible that apocrine secretory activity is controlled by some internal factors. It is suggested that the pineal organ might be of some advantage in the light dependent behaviour of this species in terms of intensity detection. Future work is necessary in this direction. / Science, Faculty of / Zoology, Department of / Graduate

The role of the fish pineal organ has been studied using the goldfish Carassius auratus and the Pacific salmon Oncorhynchus tshawytscha. To this end, the effects of pinealectomy in goldfish on various behavioural responses, endocrine systems, and the reproductive system were studied. The pineal organs and the retinal tissue from mature and immature salmon were examined by thin-layer chromatography and fluorometry to determine if melatonin, a mammalian hormone, is present in the fishes. Goldfish were injected with melatonin to see if the effect of exogenous melatonin was opposite to that of pinealectomy. Pinealectomized goldfish lost the photo-negative response seen in normal goldfish. Blinding had the same effect on phototaxis as pinealectomy and a combination of the two had the same effect as blinding or pinealectomy alone. It was concluded that the normal phototactic response depended upon both the pineal organ and the eyes. Pinealectomy, blinding, or both was followed by a marked increase in swimming activity. Although this increase was correlated with a decrease in the whole brain serotonin level, a causal relationship was not established between the two. Further, pinealectomy alone produced no significant changes in whole brain serotonin level. Melatonin was localized within the pineal organ of salmon and its concentration in this tissue was analyzed. The pineal melatonin store varied during the reproductive cycle and was found in lower concentrations in the pineal organs of mature salmon. Stored melatonin could not be found in the retinal tissue despite evidence for an active tryptophane metabolism in this tissue. Injection of melatonin into goldfish inhibited the increase in gonad size under long photoperiod; this was accompanied by larger gonadotrophs in the melatonin injected fish. Removal of the pineal organ from goldfish held under short photoperiod caused an increase in gonad size similar to that seen in untreated goldfish exposed to long photoperiod. The effect of pinealectomy on the gonads was limited to that season during which the gonads could be stimulated by increasing day length. At other times of the year, neither photoperiod nor pinealectomy produced any significant effect on the gonad size. From this it was concluded that the pineal gland of the goldfish is related to the reproductive cycle and that its function depends upon photoperiod and the production of melatonin. Pinealectomy had no effect on the interrenal tissue, thyroid tissue, plasma osmotic concentration, or plasma levels of Na⁺, Cl⁻, or Ca⁺⁺, indicating that the effects of this operation are specific for the reproductive system. The data obtained from these studies support the hypothesis that the pineal organ of fishes serves a secretory as well as a sensory function. Further, the functional aspects of the mammalian and fish pineal organs are discussed and it is concluded that the role of the pineal organ is similar in the two groups; that is, the pineal organ of mammals and fish is involved in the timing of reproductive events. / Science, Faculty of / Zoology, Department of / Graduate

published_or_final_version / abstract / Medicine / Master / Doctor of Medicine

No description available.

Vitamin A is an essential dietary component which primarily acts through its active metabolite, retinoic acid (RA), a potent transcriptional regulator that also has non-genomic activities. There is increasing evidence for a role for vitamin A in the regulation of circadian rhythms, and previous studies suggest that it serves important roles in the pineal gland, an integral component of the circadian system due to its function of melatonin production. However very little is currently known about how these effects are mediated, or about RA signalling in the pineal gland. This study aimed to establish whether RA is synthesised in the rat pineal gland and determine its role here. This included investigating whether RA is subject to diurnal changes in synthesis and signalling, and examining its involvement in the key rhythms in this gland: melatonin synthesis, kinase activation and clock gene expression. Organotypic culture of rat pineal glands, qPCR and western blotting were among the techniques employed to do this, as well as RA quantification using a reporter cell line. The rat pineal gland was found to produce RA and robust diurnal changes in synthesis were detected. Furthermore, diurnal changes in expression of RA signalling genes suggested there are corresponding changes in RA activity. RA was not found to rapidly regulate Aanat transcription, melatonin synthesis or clock gene expression in vitro, however it was found to rapidly down-regulate extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. Furthermore, strong cytoplasmic expression of RA receptor α was detected in pinealocytes. These results suggest RA has a non-genomic role in the pineal gland and may be involved in driving the diurnal rhythm in kinase activation.

Thesis (Ph. D.)--University of Hong Kong, 1989.

Thesis (Ph. D.)--University of Adelaide, Dept. of Obstetrics and Gynaecology, 1987. / Includes bibliographical references (leaves 89-118).

No description available.

The influence of the gonadal sex steroids namely, estradiol, progesterone and testosterone on the two major enzymes responsible for the synthesis of melatonin in the pineal gland was investigated. These enzymes are Serotonin-N-acetyltransferase (SNAT) and Hydroxyindole-O-methyltransferase (Hl0MT). Testosterone was found to be the only sex steroid capable of influencing SNAT activity whereas all three of the sex steroids were found to influence Hl0MT activity in a biphasic dose-dependent manner. The influence of these sex steroids on radiolabeled serotonin metabolism by pineals in organ culture was also investigated. Ovariectomy, castration and the sex steroids were all found to alter the pattern of the radiolabeled serotonin metabolism by these pineal glands in organ culture. / KMBT_363 / Adobe Acrobat 9.53 Paper Capture Plug-in

Dopamine mechanisms in the central nervous system are important in the control of both normal and abnormal motor function. The recent observations in both animal and human studies, that melatonin, the principal hormone of the pineal gland, may have a role in the control of movement and the pathophysiology of movement disorders, have given rise to the concept that melatonin may have a modulatory influence on central dopaminergic neurotransmission. This study makes use of three animal behavioural models as well as a biochemical model of central dopaminergic function to further investigate the concept. Results from studies using the biochemical model, which investigated the effect of melatonin on dopamine and apomorphine stimulation of dopamine-sensitive adenylate cylase, suggest that melatonin is neither a competitive antagonist nor agonist at the D₁ receptor level, although the possibility of physiological stimulation or antagonism is not excluded. In behavioural studies, prior melatonin mg/kg administration (1 and 10 (8M) ip) inhibited apomorphine induced stereotypy and locomotor activity in normal rats, and apomorphine-induced rotational behaviour in 6-hydroxydopamine and quinolinic acid lesioned rats. The possibility that these results may have physiological significance is borne out by the observation that, under enviromental lighting conditions that are associated with raised endogeous melatonin levels, apomorphine- induced stereotypy and locomotor activity is attenuated. The general conclusion is that melatonin has an inhibitory influence on central nervous system dopaminergic function, suggesting therefore, that the pineal gland and melatonin may have a role in the pathophysiology and treatment of movement and behavioural disorders associated with dopaminergic dysfunction