No abstract

Most species living in temperate zones adapt their physiology and behavior to seasonal changes in the environment by using the photoperiod as a primary cue. The mechanisms underlying photoperiodic regulation of stress-related functions are not well understood. In this study, we analyzed the effects of photoperiod on the hypothalamic-pituitary-adrenal axis in photoperiod-sensitive Fischer 344 rats. We first examined how photoperiod affects diurnal variations in plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone. ACTH levels did not exhibit diurnal variations under long- and short-day conditions. On the other hand, corticosterone levels exhibited a clear rhythm under short-day condition with a peak during dark phase. This peak was not observed under long-day condition in which a significant rhythm was not detected. To analyze the mechanisms responsible for the photoperiodic regulation of corticosterone rhythms, ACTH was intraperitoneally injected at the onset of the light or dark phase in dexamethasone-treated rats maintained under long- and short-day conditions. ACTH induced higher corticosterone levels in rats examined at dark onset under short-day condition than those maintained under long-day condition. Next, we asked whether melatonin signals are involved in photoperiodic regulation of corticosterone rhythms, and rats were intraperitoneally injected with melatonin at late afternoon under long-day condition for 3 weeks. However, melatonin injections did not affect the corticosterone rhythms. In addition, photoperiodic changes in the amplitude of corticosterone rhythms were also observed in melatonin-deficient C57BL/6J mice, in which expression profiles of several clock genes and steroidgenesis genes in adrenal gland were modified by the photoperiod. Our data suggest that photoperiod regulates corticosterone rhythms by altered adrenal sensitivity through melatonin-independent mechanisms that may involve the adrenal clock.

The effects of photoperiod on dietary preference were examined using young growing Fischer 344 and Wistar rats, which are seasonal and nonseasonal breeders, respectively. Rats were provided a low-fat, high-carbohydrate diet (LFD: 66/10/24% energy as carbohydrate/fat/protein) and high-fat, low-carbohydrate diet (HFD: 21/55/24% energy as carbohydrate/fat/protein) simultaneously under long- (LD: 16 h light/day) and short-day (SD: 8 h light/day) conditions for 3 wk. Fischer 344 rats preferred the LFD to the HFD under the LD condition, whereas preference for both diets was equivalent under the SD condition. Consequently, their body weight and total energy intake exhibited 11-15 and 10-13% increases, respectively, under the LD condition. Calculation of energy intake from macronutrients revealed that rats under the LD condition consumed 20-24 and 9-13% higher energy of carbohydrates and proteins, respectively, than those under the SD condition. In contrast, Wistar rats preferred the LFD to the HFD irrespective of photoperiod and exhibited no photoperiodic changes in any parameters examined. Next, Fischer 344 rats were provided either the LFD or HFD for 3 wk under LD or SD conditions. Calorie intake was 10% higher in the rats fed the LFD than those fed the HFD under SD condition. However, rats under LD condition exhibited 5-10, 14, and 64% increases in body weight, epididymal fat mass, and plasma leptin levels, respectively, compared with those under the SD condition irrespective of dietary composition. In conclusion, photoperiod regulates feeding and energy metabolism in young growing Fischer 344 rats via the interactions with dietary macronutrient composition.

In the present study, the effects of both single (6 mmol L-serine/10 ml/kg orally administrated) and chronic (2% L-serine solution freely given for 28 days) treatments on depression-like behavior were evaluated in Wistar rats, representing the control, and Wistar Kyoto rats, representing an animal model of depression. Both single and chronic L-serine treatments decreased the duration of immobility, which is an index of a depressive-like state, in the forced swimming test in both strains. However, the decreases in the duration of immobility appear to be regulated differently by the different mechanisms involved in single and chronic L-serine treatments. In the prefrontal cortex and hippocampus, single L-serine treatment increased the concentrations of L-serine, but not D-serine, while chronic L-serine treatment increased those of D-serine, but not L-serine. These data suggest that the antidepressant-like effects of single and chronic L-serine treatments may have been induced by the increased L-serine and D-serine concentrations, respectively, in the brain. In addition, chronic L-serine treatment increased cystathionine concentrations in the hippocampus and prefrontal cortex in Wistar rats, but not in Wistar Kyoto rats, suggesting that Wistar Kyoto rats have an abnormality in the serine-cystathionine metabolic pathway. In conclusion, single and chronic L-serine treatments may induce antidepressant-like effects via the different mechanisms related to serine metabolism in the brain.

The statistical variation in observed powder diffraction intensity is often dominated by the limited number of crystallites that satisfy the diffraction condition. This effect has been termed with particle statistics in powder diffraction method [1].We have reported experimental validation of the theory for particle statistics about symmetric reflection mode measurements, and proposed a new method to evaluate the crystallite size and its distribution by statistical analysis based on a generalized theoretical framework [2]. We have also demostrated improvement of structure refinement by application of the maximum likelihood estimation to statistical model explicitly taking the errors caused by the particle statistics into account [3].As the formula suitable for the particle statistics about a continuously spinning flat specimen is still unclear, three kinds of diffraction intensity measurements, (1) in-plane (Φ)-scan, rocking angle (Ω)-scans for (2) stationary and (3) spinning flat specimens, have been conducted for standard powder samples of Si (NIST SRM640c) and lanthanum hexaboride (NIST SRM660a) at a synchrotron powder diffraction beamline BL-4B2 at the Photon Factory, KEK in Tsukuba.The statistical variance observed inΦ-scan and Ω-scan measurements for stationary specimens have shown cosecant dependence of the effective number of diffracting crystallites, just as predicted by the traditional theory. The statistical variance in Ω-scan measurements for spinning specimens has also shown a cosecant behaivior rather than the squared cosecant dependence suggested by de Wolff [1].