Biomedical subjects
Publications and source records attributed to L Dickenson.
Although hepatitis can be a significant problem for dialysis patients and staff, the risk of contracting hepatitis can be reduced. Next month, part two will address preventive strategies that may be utilized to reduce the risk of transmission of hepatitis between patients and staff.
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In nocturnal rodents, exposure to light results in an increase in Fos expression in two regions that receive direct retinal input: the suprachiasmatic nuclei (SCN) of the hypothalamus and the intergeniculate leaflet (IGL) of the thalamus. The induction of Fos within the SCN of nocturnal rodents is phase dependent, with light presented during the subjective night increasing Fos expression and light presented during the subjective day having little effect. By contrast, Fos expression increases in the IGL when light is presented during the subjective day or night. It is unclear whether Fos is part of the pathway mediating light-induced phase shifts in diurnal rodents. In the present study, the ability of light to induce immunostaining for Fos in the SCN and IGL was compared in diurnal rodents, Octodon degus (degus), and nocturnal rats. Degus and rats were either maintained in constant darkness or exposed to a 1-h light pulse at circadian time (CT) 4 or 16. Degus exhibit robust phase shifts at each of those circadian hours, whereas rats demonstrate phase shifts only at CT 16. In degus, exposure to a 1-h light pulse at CT 16 resulted in an increase in the number of Fos-immunopositive (Fos+) cells in the ventrolateral SCN. By contrast, a 1-h light pulse at CT 4 resulted in a decrease in the number of Fos+ cells in the dorsomedial portion of the SCN. In rats, a light pulse presented at CT 16 resulted in an increase in Fos+ cells throughout the SCN, and a pulse at CT 4 had no effect on Fos staining. Both degus and rats showed increases in Fos expression in the IGL after light exposure at CTs 4 and 16. The authors conclude that light pulses presented at times that produce phase shifts in activity rhythms also alter Fos expression in the SCN and IGL of degus. Although these effects of light exposure on Fos expression are not identical in diurnal and nocturnal rodents, it is likely that Fos and other immediate early genes are part of the pathway mediating the effects of light in both diurnal and nocturnal rodents.
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One substance abuse hypothesis proposes that rewarding effects of drugs are causally related to their psychostimulant effects. We examined this hypothesis by comparing operant self-administration of ethanol in mice selectively bred for either high (Fast) or low (Slow) locomotor stimulation response to ethanol. Mice were trained to lever press for ethanol using postprandial induction and were then tested over a range of conditions to determine the degree of self-administration. There were no significant differences between Fast and Slow mice in either the amount of work produced to obtain ethanol or the amount of ethanol consumed. In general, none of the groups of mice showed robust ethanol-reinforced behavior. This is in contrast with C57BL/6J mice tested concurrently, which showed substantial ethanol-reinforced behavior. Further analysis revealed individual differences in responding within each of the selected lines. However, there was no systematic pattern within or between groups for these individual differences, suggesting that the genes mediating ethanol-reinforced behavior are segregating in a manner independent from genes mediating the locomotor stimulant response to ethanol, and thus, the mechanistic processes mediating reinforcement from ethanol are distinct from those that influence the psychomotor stimulant response to this drug.