The timing of fasting leads to different levels of food consumption and PYY3-36 in nocturnal mice.

PURPOSE: The daily circadian cycle is known to modulate both feeding behavior and metabolism. As such, the timing of food consumption can play a role in regulating overall health. The purpose of this study is to determine whether fasting at different times of the day alters subsequent food consumption and levels of PYY3-36, a hormone secreted after a meal which inhibits appetite. METHODS: Separate groups of mice were fasted at different times of the day: (1) start of the day, (2) middle of the day, (3) start of the night, and (4) middle of the night, and either injected with vehicle or PYY3-36 to assess their subsequent food consumption patterns, PYY3-36 levels, and glucose and insulin levels. We also investigated whether light exposure during the night would alter food consumption and PYY3-36 levels after fasting. RESULTS: Mice fasted during the start of the daytime exhibited increased food consumption post-fast compared to mice fasted during the night. Injections of PYY3-36 during the night were more effective in reducing food consumption compared to PYY3-36 administration during the day. Constant light exposure suppressed food consumption after fasting and increased fasting PYY3-36 levels. CONCLUSIONS: These results indicate that mice exhibit distinct food consumption patterns after being presented with a fast at different times of the day. Light exposure also modulates both food consumption after a fast and levels of PYY3-36.

Substrain specific behavioral responses in male C57BL/6N and C57BL/6J mice to a shortened 21-hour day and high-fat diet.

Altered circadian rhythms have negative consequences on health and behavior. Emerging evidence suggests genetics influences the physiological and behavioral responses to circadian disruption. We investigated the effects of a 21 h day (T = 21 cycle), with high-fat diet consumption, on locomotor activity, explorative behaviors, and health in male C57BL/6J and C57BL/6N mice. Mice were exposed to either a T = 24 or T = 21 cycle and given standard rodent chow (RC) or a 60% high-fat diet (HFD) followed by behavioral assays and physiological measures. We uncovered numerous strain differences within the behavioral and physiological assays, mainly that C57BL/6J mice exhibit reduced susceptibility to the obesogenic effects of (HFD) and anxiety-like behavior as well as increased circadian and novelty-induced locomotor activity compared to C57BL/6N mice. There were also substrain-specific differences in behavioral responses to the T = 21 cycle, including exploratory behaviors and circadian locomotor activity. Under the 21-h day, mice consuming RC displayed entrainment, while mice exposed to HFD exhibited a lengthening of activity rhythms. In the open-field and light-dark box, mice exposed to the T = 21 cycle had increased novelty-induced locomotor activity with no further effects of diet, suggesting daylength may affect mood-related behaviors. These results indicate that different circadian cycles impact metabolic and behavioral responses depending on genetic background, and despite circadian entrainment.

Constant light alters serum hormone levels related to thyroid function in male CD-1 mice.

Disruptions to the circadian rhythm can lead to altered metabolism. Modification of thyroid function may be a reason why circadian misalignment may contribute to future metabolic disorders. We investigated whether circadian disruption through constant light (LL) can lead to variations in hormone levels associated with thyroid function. Mice were exposed to LL or a 12:12 Light:Dark (LD) cycle for 6 weeks; then glucose tolerance and thyroid hormone levels were measured at ZT 6 and ZT 18. There was day/night variation in glucose tolerance, but LL had no effect. LL reduced TSH, increased fT4, and abolished day/night variation in fT3 and leptin. These findings illustrate that LL alters thyroid-related hormones, providing evidence of a link between circadian disruption and thyroid function.

Confirmation of tick bite by detection of antibody to Ixodes calreticulin salivary protein.

Ticks introduce a variety of pharmacologically active molecules into their host during attachment and feeding in order to obtain a blood meal. People who are repeatedly exposed to ticks may develop an immune response to tick salivary proteins. Despite this response, people usually are unaware of having been bitten, especially if they are not repeatedly exposed to ticks. In order to develop a laboratory marker of tick exposure that would be useful in understanding the epidemiology of tick-borne infection and the immune response to tick bite, we developed an enzyme-linked immunosorbent assay (ELISA) to detect antibody to a recombinant form of calreticulin protein found in the salivary glands of Ixodes scapularis, a member of a complex of Ixodes ticks that serve as the vectors for Lyme disease, human babesiosis, and human granulocytic anaplasmosis. Using this assay, we tested sera obtained from C3H/HeN and BALB/c mice before and after experimental deer tick infestation. These mice developed antibody to Ixodes calreticulin antigen after infestation. We then used the same assay to test sera obtained from people before and after they experienced deer tick bite(s). People experiencing deer tick bite(s) developed Ixodes calreticulin-specific antibody responses that persisted for up to 17 months. This Ixodes recombinant calreticulin ELISA provides objective evidence of deer tick exposure in people.