No description available.

No description available.

No description available.

The circadian rhythm is an internal body cadence, responsible for regulation of sleep in all mammals. In humans, this clock is altered by several factors, including light and secretion of the hormone melatonin. Within the intensive care unit (ICU) population, it is well evidenced that patients suffer from circadian dysregulation, often for long periods of time. Additionally, many parallels have been noted between severely fragmented sleep and delirium, an acute neurological condition frequently observed in ICU patients. A prospective cohort pilot study of five subjects was undertaken to enable a greater understanding of both sleep in the ICU and the relationship between circadian rhythm and delirium. From a total of thirty-six urine samples per subject, excretion of 6-sulphatoxymelatonin (aMT6s), the urinary metabolite of melatonin was analyzed. T-test comparison (p=0.05) of mean aMT6s (ng/mL) revealed significant differences in the nighttime excretion between subjects in this study and healthy individuals. No significant differences were observed with t-test comparison of mean aMT6s of the first 24 hours from the current study to ICU subjects in previous literature. No subjects were identified as delirious in the study and therefore no relationship could be found between circadian rhythmicity, as evidenced by melatonin excretion and delirium in this study population. / February 2017

Melatonin is rhythmically synthesized and released by the pineal gland and, in some species, retina during the night and regulates many physiological and behavioral processes in birds and mammals. Chick diencephalic astrocytes express two melatonin receptor subtypes in vitro, and melatonin plays a role in regulating metabolic activity. We examined the role of glial cells in circadian function and asked if melatonin modulated glial functions within the retina and the brain. Calcium waves were potentiated by physiological concentrations of melatonin. Melatonin increased resting calcium levels and reduced gap junctional coupling among astrocytes at these same concentrations. Both mouse and chick diencephalic and telencephalic astrocytes express melatonin receptor protein. Nanomolar melatonin modulated astrocytic calcium waves of the mouse and chick diencephalon but not waves of the telencephalon. Mammalian intercellular calcium waves spread farther than avian calcium waves, and the nature of the spread of the waves differed between telencephalic and diencephalic mammalian astrocytes. These differences in propagation were abolished by melatonin. Using northern analysis, we identified period2, period3, cryptochrome1, cryptochrome2, clock, melanopsin and peropsin within chick diencephalic astrocytes. The clock genes cry1 and, per2 were expressed rhythmically in a LD cycle, but metabolic activity was not rhythmic. When cells were placed in constant darkness and rhythmically administrated melatonin, a robust rhythm in glucose uptake was induced without a coordinated clock gene rhythm, suggesting rhythmic clock gene expression and metabolic activity are separable processes. Melatonin affected visual function as assessed by electroretinogram. Circadian rhythms of a- and b-wave implicit times and amplitudes were observed. Melatonin (1 mg/kg and 100 ng/kg) decreased a- and b-wave amplitudes greater during the night than during the day and it increased a- and b-wave implicit times while 1 ng/kg melatonin had little to no effect over the saline controls. These data indicate that melatonin modulates glial intercellular communication, affects metabolic activity in astrocytes, and may play a role in regulating a day and night functional shift in the retina, at least partially through Müller glial cells. Thus, melatonin can regulate glia function and thereby, affect outputs of the vertebrate biological clock.

Experiment I studied the effect of dietary gossypol (G) on antler and body growth traits of red deer stags, whereas Experiment II studied the effect of exogenous melatonin on female red deer reproductive traits. Specifically in Experiment I, thirty mature red deer stags were randomly allotted by weight, body condition score, and age to one of three treatment groups (n=10 each): control (C; 5:6 soybean meal:corn), extruded cottonseed pellet (P; 0.04 percent Free G, 0.36 percent Total G) and whole cottonseed-soybean meal (WCS; 5:3 cottonseed:soybean meal, 0.96 percent Free G & Total G). The supplements were mixed to be isocaloric (1661g/d TDN) and isonitrogenous (620-637g CP/d). Stags were fed daily for 155 d from antler casting (2/26/09) until hard antler had been reached (7/31/09). Antlers were measured using the Safari Club International (SCI) scoring method once hard antler was achieved. Hard antlers where removed just above the burr and allowed to dry (60 d) before weighing. Average daily gain did not differ (P > 0.10) among dietary treatment groups. However, average antler weights from C (1.130 plus/minus 0.068 kg) and P (1.297 plus/minus 0.068 kg) were greater (P < 0.04) than WCS (1.041 plus/minus 0.068 kg) weights upon completion of the trial. Although SCI measurements were numerically lowest for WCS, differences were not significant. In Experiment II, 60 mature and 24 yearling red deer hinds were assigned to two treatments on August 3rd; one received melatonin implants (MEL: n=42), while the other served as a control group (CNTRL: n=42). Hinds were evenly distributed to treatment by lactation status, age and body condition score. Antlerless stags were placed with the hinds (1:14) to provide natural service breeding during the trial. Implants were verified to be functional by a serum melatonin assay. Pregnancy status was determined by ultrasonography on d 105 and verified again on d 150. MEL treatment hinds displayed lower ADG (0.003 plus/minus 0.007 kg/d) than CNTRL (0.020 plus/minus 0.007 kg/d) hinds during the trial (P < 0.01). No advancement of estrous cycles was observed in red deer hinds implanted in early August (P > 0.10); however, pregnancy rates for yearling hinds were increased 36.4 percent (P < 0.04).

Melatonin is rhythmically synthesized and released by the pineal gland and, in some species, retina during the night and regulates many physiological and behavioral processes in birds and mammals. Chick diencephalic astrocytes express two melatonin receptor subtypes in vitro, and melatonin plays a role in regulating metabolic activity. We examined the role of glial cells in circadian function and asked if melatonin modulated glial functions within the retina and the brain. Calcium waves were potentiated by physiological concentrations of melatonin. Melatonin increased resting calcium levels and reduced gap junctional coupling among astrocytes at these same concentrations. Both mouse and chick diencephalic and telencephalic astrocytes express melatonin receptor protein. Nanomolar melatonin modulated astrocytic calcium waves of the mouse and chick diencephalon but not waves of the telencephalon. Mammalian intercellular calcium waves spread farther than avian calcium waves, and the nature of the spread of the waves differed between telencephalic and diencephalic mammalian astrocytes. These differences in propagation were abolished by melatonin. Using northern analysis, we identified period2, period3, cryptochrome1, cryptochrome2, clock, melanopsin and peropsin within chick diencephalic astrocytes. The clock genes cry1 and, per2 were expressed rhythmically in a LD cycle, but metabolic activity was not rhythmic. When cells were placed in constant darkness and rhythmically administrated melatonin, a robust rhythm in glucose uptake was induced without a coordinated clock gene rhythm, suggesting rhythmic clock gene expression and metabolic activity are separable processes. Melatonin affected visual function as assessed by electroretinogram. Circadian rhythms of a- and b-wave implicit times and amplitudes were observed. Melatonin (1 mg/kg and 100 ng/kg) decreased a- and b-wave amplitudes greater during the night than during the day and it increased a- and b-wave implicit times while 1 ng/kg melatonin had little to no effect over the saline controls. These data indicate that melatonin modulates glial intercellular communication, affects metabolic activity in astrocytes, and may play a role in regulating a day and night functional shift in the retina, at least partially through Müller glial cells. Thus, melatonin can regulate glia function and thereby, affect outputs of the vertebrate biological clock.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves.

Thesis (Ph. D.)--University of Hong Kong, 1987.

During embryogenesis, vitamin A metabolism to retinoic acid (RA) is tightly regulated in a precise spatiotemporal pattern. Aberrant retinoid signalling in the wrong place or at the wrong time has devastating consequences for development. Much is understood about the mechanisms by which at the level of specific tissues, RA synthesis from vitamin A is able to occur and activate target genes necessary for the developmental programme at any given stage. However, little is known about how retinoid transport and synthesis at the subcellular level occurs. Chapter 3 of this thesis investigates the subcellular compartments with which the vitamin A metabolising enzyme RALDH2 associates in embryonic neuronal cell lines. It is found that not only is RA synthesis tightly controlled by tissues, but that RA signalling within cells themselves may also be segmented. Aside from the importance of vitamin A during early development, it is now known that this dietary component is also vital in the maintenance of homeostasis during adulthood. This is particularly important for the adult CNS, where it is proposed that RA mediates hippocampal neurogenesis; hypothalamic neurogenesis; and physiological responses to seasonal changes in day length. The nocturnal hormone melatonin is a key signalling molecule relaying the length of the night to the rest of the brain and periphery, and by this means conveying information about the time of year. Vitamin A deficiency is known to severely reduce the amount of melatonin produced by the Quail pineal gland at night. Chapter 4 of this thesis investigates the circadian and circannual rhythms of retinoid genes such as the RALDH enzymes and retinoic acid receptors in both the SCN, and the pineal gland. RA is sufficient to increase the expression of the melatonin synthesising enzyme AANAT, and that this gene expression may be under the control of RALDH1.