Insulins, leptin and feeding in a population of Peromyscus leucopus (white-footed mouse) with variable fertility.

This article is part of a Special Issue "Energy Balance". Natural populations display a variety of reproductive responses to environmental cues, but the underlying physiology that causes these responses is largely unknown. This study tested the hypothesis that heritable variation in reproductive traits can be described by heritable variation in concentrations of hormones critical to both energy balance and reproduction. To test this hypothesis, we used mouse lines derived from a wild population and selectively bred for response to short day photoperiod. Reproductive and metabolic traits of Peromyscus leucopus display heritable variation when held in short photoperiods typical of winter. Our two lines of mice have phenotypes spanning the full range of variation observed in nature in winter. We tested male and female mice for heritable variation in fasted serum concentrations of three hormones involved in energetic regulation: leptin, insulin-like growth factor 1 (IGF-1) and insulin, as well as the effects of exogenous leptin and a high energy diet on reproductive maturation. Exogenous leptin decreased food intake, but protected males from the reduction in testis mass caused by equivalent food restriction in pair-fed, saline-infused controls. A high energy diet resulted in calorie adjustment by the mice, and failed to alter reproductive phenotype. Concentrations of the three hormones did not differ significantly between selection lines but had correlations with measures of food intake, fertility, blood glucose, and/or body mass. There was evidence of interactions between reproductive traits and hormones related to energy balance and reproduction, but this study did not find evidence that variation in these hormones caused variation in reproductive phenotype.

Atypical fatigue.

CASE STUDY: Mrs. S is a 63-year-old retired teacher who returns to the office for breast cancer follow-up. She was diagnosed with intraductal carcinoma, and her treatment included a modified radial mastectomy followed by four cycles of doxorubicin and cyclophosphamide. Her tumor was estrogen receptor-positive, progesterone receptor-positive, and human epidermal growth factor receptor 2-negative by fluorescence in-situ hybridization. Chemotherapy was completed nine months ago, and she is taking adjuvant tamoxifen. She has recovered quite well; her only complaint is fatigue. She states, "I expected to be tired during and immediately after chemotherapy, but I thought I would have all my energy back by now. I still feel the need to take a nap in the afternoon. In fact, I feel sleepy all the time!" Mrs. S's medical history is significant for moderate obesity and hypertension for 10 years, which is controlled with the angiotensin converting enzyme inhibitor lisinopril. She has not exercised since her breast cancer diagnosis but has been trying to lose weight with dietary changes. She believes that tamoxifen is hampering her weight-loss efforts. She takes no other medications.

Atypical Femoral Fractures: Implications for the Advanced Practitioner in Oncology.

Bone-health issues may arise for oncology patients as a side effect of their treatments. One of these may be the development of an atypical femoral fracture. Advanced practitioners should be aware of the risk factors for atypical femoral fractures, and be able to promptly recognize signs, provide patient education, and manage them competently.

Genetic variation in male sexual behaviour in a population of white-footed mice in relation to photoperiod.

In natural populations, genetic variation in seasonal male sexual behaviour could affect behavioural ecology and evolution. In a wild-source population of white-footed mice, Peromyscus leucopus, from Virginia, U.S.A., males experiencing short photoperiod show high levels of genetic variation in reproductive organ mass and neuroendocrine traits related to fertility. We tested whether males from two divergent selection lines, one that strongly suppresses fertility under short photoperiod (responder) and one that weakly suppresses fertility under short photoperiod (nonresponder), also differ in photoperiod-dependent sexual behaviour and responses to female olfactory cues. Under short, but not long, photoperiod, there were significant differences between responder and nonresponder males in sexual behaviour and likelihood of inseminating a female. Males that were severely oligospermic or azoospermic under short photoperiod failed to display sexual behaviour in response to an ovariectomized and hormonally primed receptive female. However, on the day following testing, females were positive for spermatozoa only when paired with a male having a sperm count in the normal range for males under long photoperiod. Males from the nonresponder line showed accelerated reproductive development under short photoperiod in response to urine-soiled bedding from females, but males from the responder line did not. The results indicate genetic variation in sexual behaviour that is expressed under short, but not long, photoperiod, and indicate a potential link between heritable neuroendocrine variation and male sexual behaviour. In winter in a natural population, this heritable behavioural variation could affect fitness, seasonal life history trade-offs and population growth.