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Biomedical subjects

C M Peng

Publications and source records attributed to C M Peng.

7 recordsLinked to original sources
PubMed2002

Plasma melatonin, pinealocyte morphology, and surface receptors/antigen expression on macrophages/microglia in the pineal gland following a high-altitude exposure.

The present study examined the effects of high-altitude exposure on the pineal gland, the main source of production of melatonin. It was surmised that hypoxia experienced at high altitude, caused by decreased oxygen tension in the ambient air, might lead to some structural alterations in the pineal gland and, hence, affect its melatonin production. Adult Wistar rats were exposed to an altitude of 8,000 m for 2 hr in an altitude chamber and then sacrificed at various time intervals after the exposure. Normal rats kept at ground level were used as controls. Blood samples were collected at various time intervals for measurement of plasma melatonin level, and the pineal glands from both groups were processed for electron microscopy and immunohistochemistry. The plasma melatonin level showed a steady increase following altitude exposure peaking at 7 days and returned to control levels thereafter. Between 1 and 4 days after altitude exposure, the mitochondrial number and lipid droplets in the pinealocytes appeared to be reduced compared with those in control rats. At 7 days, however, the mitochondrial numbers and lipid droplets were noticeably increased. At the same time interval, the expression of complement type 3 receptors and major histocompatibility class II antigens as detected with the antibodies OX-42 and OX-6, respectively, in macrophages/microglia was up-regulated compared with that in the control rats and those killed at earlier times. This was attributed to the increased serum melatonin after the altitude exposure. By 14 and 21 days, the ultrastructure of pinealocytes and immunoreactivity of macrophages/microglia were comparable with those in the control rats. We conclude from this study that an altitude exposure in rats leads to an increase in melatonin production, which returned to control levels with passage of time.

Altitude Sickness↗
PubMed2002

Upregulation of adrenocorticotrophic hormone in the corticotrophs and downregulation of surface receptors and antigens on the macrophages in the adenohypophysis following an exposure to high altitude.

Altitude exposures lead to the development of hypobaric hypoxia because of low oxygen tension in the ambient air. This study has shown the vigorous upregulation of adrenocorticotrophic hormone (ACTH) expression in corticotrophs of the pars distalis (adenohypophysis) of rats 1-7 days after an altitude exposure. Concomitant to this was the increase in number and hypertrophy of the immunoreactive corticotrophs. It was suggested that this had resulted in an upsurge of ACTH production which may have suppressed the immuno-expression of complement type 3 receptors and major histocompatibility complex class II antigens constitutively expressed by the parenchymal macrophages through paracrine action. Along with ACTH, altered levels of other hormones following such exposures may also contribute to suppression of antigen presenting function and phagocytic activity of macrophages. The effects of altitude (hypobaric hypoxia) exposure, however, were reversible as the above immunohistochemical changes returned to normal 21-28 days after the hypobaric hypoxic insult.

Adrenocorticotropic Hormone↗
PubMed2001

Expression of Fos immunoreactivity in some catecholaminergic brainstem neurons in rats following high-altitude exposure.

This study examined the response of neurons of the cardiorespiratory centers, i.e., the nucleus tractus solitarius and the ventrolateral medulla as well as the area postrema in adult and postnatal rats subjected to high-altitude exposure at 4,000 m and 8,000 m. In adult control rats, sporadic Fos-positive neurons were detected in the above-mentioned areas. On exposure to 4,000 m altitude, the number of Fos-positive neurons was noticeably increased. At 8,000 m, the incidence of labeled cells was markedly increased, with many of them doubly labeled for tyrosine hydroxylase. In postnatal rats, Fos expression was not detected in these areas in either control rats or rats exposed to 4,000 m altitude. Fos-positive cells, however, were observed in the these areas in postnatal rats exposed to 8,000 m. In the latter, tyrosine hydroxylase labeling was observed in some Fos-positive cells in the nucleus tractus solitarius and ventrolateral medulla. In rats killed at 24 hr after exposure to high altitude, Fos expression in both the adult and the postnatal rats was comparable to that in their corresponding control rats. Present results suggest that Fos expression in various brainstem areas was induced by reduced oxygen tension in the ambient air at high altitude. Double labeling of some Fos-positive neurons with tyrosine hydroxylase indicates an increased sympathetic activation, which may be involved in the mediation of cardiorespiratory responses to hypoxia. This, however, was less evident in the postnatal animals. It is possible that the peripheral chemoreceptors or the regulation of autonomic functions is not fully developed in this age group.

Altitude Sickness↗
PubMed1997

Effects of optical correction media on contrast sensitivity.

Contrast sensitivity functions (CSFs) were obtained for 257 emmetropic subjects (514 eyes) and 35 contact lens users (64 eyes) in the Republic of Singapore Air Force using the Vistech Contrast Test System. For the emmetropes, contrast sensitivity tests were carried out with and without plano spectacles (PS). For the myopes, we compared their performances with spectacles, daily-wear soft contact lenses (CLs), and CL plus PS at Snellen visual acuities of 6/6 or better. Paired t-tests showed that there were no significant differences (P > 0.05) when CSFs of the emmetropes were measured with and without PS and when that of the CL users were measured with spectacles, CL and CL plus PS. We therefore conclude that myopic optical correction media do not retard CSF significantly based on the Vistech charts, although they may reduce image size and modify light transmission by being imperfect transparencies. The observed decrease in CSF for myopes even after myopic correction might therefore be related to other factors associated with myopia, such as retinal changes or possibly mild amblyopia.

Contact Lenses↗