Dehydroepiandrosterone and exercise in golden hamsters

Effects of Aromatase Inhibition on the Physical Activity Levels of Male Mice

Increasing activity levels in an inactive population can lead to associative increases in health and well-being. Both biologic and genetic factors have been identified that alter physical activity levels in humans and rodents with an extensive early literature regarding sex steroid effects on physical activity. Currently, it is suggested that the androgens require conversion to estrogens prior to eliciting any effects on activity patterns. Recent data contradicts this assertion; thus, the purpose of this study was to evaluate the necessity of the aromatase complex in activity regulation. Wheel running was assessed in male C57BL/6J mice under various sex steroid-disrupted and aromatase-inhibited conditions. Inhibition of the aromatase complex was achieved through administration of two different aromatase inhibiting substances-letrozole and exemestane. Wheel running was unaffected by aromatase inhibition in reproductively intact and sex steroid supplemented mice. Orchidectomy significantly reduced wheel running activity. Steroid replacement recovered wheel running to pre-surgical levels; however, aromatase inhibition did not further affect wheel running levels. The recovery of wheel running in mice with androgen supplementation and the further persistence of wheel running in mice with compromised aromatase function suggests that the androgens-testosterone in particular-may directly affect wheel running patterns in male mice.

Effects of Supraphysiological Doses of Sex Steroids on Wheel Running Activity in Mice

The regulatory mechanisms of physical activity are postulated to include environmental and biological/genetic factors. In particular, the sex steroids appear to have profound effects on wheel running in rodents. The purpose of this project was to investigate the effects of 17β-estradiol and testosterone on wheel running distance, duration, and speed in male and female C57BL/6J mice. The mice (N=46) were provided free access to running wheels interfaced with computers to track daily running distance, duration, and speed. Activity was assessed at baseline in intact mice, after surgical gonadectomy, and after replacement with either 17β-estradiol or testosterone. Upon removal of the gonads, physical activity levels were significantly reduced in both males and females. Distance (10–30% of baseline) and duration (20–47% of baseline) measures were most affected by the loss of endogenous steroids, while running speed (60–77% of baseline) though significantly reduced-decreased by a much lower magnitude. Testosterone replacement fully recovered running distance, duration, and speed to pre-surgical levels in both sexes (100% of baseline). Distance (30–42% of baseline) and duration (43–47% of baseline) were partially recovered by 17β-estradiol, but not to baseline levels. Speed (100% of baseline) was fully recovered by 17β-estradiol replacement in males and females. This study suggests that physical activity in mice is affected by endogenous steroids and can be altered by exogenous steroid replacement. The differences in the recovery abilities of 17β-estradiol and testosterone suggest that both estrogenic and androgenic pathways may be involved to variable degrees in activity regulation.

Physical activity and cancer prevention : pathways and targets for intervention

The prevalence of obesity, an established epidemiological risk factor for many cancers, has risen steadily for the past several decades in the US and many other countries. Particularly alarming are the increasing rates of obesity among children, portending continuing increases in the rates of obesity and obesity-related cancers for many years to come. Modulation of energy balance, via increased physical activity, has been shown in numerous comprehensive epidemiological reviews to reduce cancer risk. Unfortunately, the effects and mechanistic targets of physical activity interventions on the carcinogenesis process have not been thoroughly characterized. Studies to date suggest that exercise can exert its cancer-preventive effects at many stages during the process of carcinogenesis, including both tumour initiation and progression. As discussed in this review, exercise may be altering tumour initiation events by modifying carcinogen activation, specifically by enhancing the cytochrome P450 system and by enhancing selective enzymes in the carcinogen detoxification pathway, including, but not limited to, glutathione-S-transferases. Furthermore, exercise may reduce oxidative damage by increasing a variety of anti-oxidant enzymes, enhancing DNA repair systems and improving intracellular protein repair systems. In addition to altering processes related to tumour initiation, exercise may also exert a cancer-preventive effect by dampening the processes involved in the promotion and progression stages of carcinogenesis, including scavenging reactive oxygen species (ROS); altering cell proliferation, apoptosis and differentiation; decreasing inflammation; enhancing immune function; and suppressing angiogenesis. A paucity of data exists as to whether exercise may be working as an anti-promotion strategy via altering ROS in initiated or preneoplastic models; therefore, no conclusions can be made about this possible mechanism. The studies directly examining cell proliferation and apoptosis have shown that exercise can enhance both processes, which is difficult to interpret in the context of carcinogenesis. Studies examining the relationship between exercise and chronic inflammation suggest that exercise may reduce pro-inflammatory mediators and reduce the state of low-grade, chronic inflammation. Additionally, exercise has been shown to enhance components of the innate immune response (i.e. macrophage and natural killer cell function). Finally, only a limited number of studies have explored the relationship between exercise and angiogenesis; therefore, no conclusions can be made currently about the role of exercise in the angiogenesis process as it relates to tumour progression. In summary, exercise can alter biological processes that contribute to both anti-initiation and anti-progression events in the carcinogenesis process. However, more sophisticated, detailed studies are needed to examine each of the potential mechanisms contributing to an exercise-induced decrease in carcinogenesis in order to determine the minimum dose, duration and frequency of exercise needed to yield significant cancer-preventive effects, and whether exercise can be used prescriptively to reverse the obesity-induced physiological changes that increase cancer risk.

Concepts of CNS Plasticity in the Context of Brain Damage and Repair

BACKGROUND

How effectively the brain can respond to injury and undergo structural repair has become one of the most exciting areas of contemporary basic and translational neuroscience research. Although there are no clinical treatments yet available to enhance repair of the damaged brain, there are a number of potential therapies being investigated. New drugs are designed to provide some degree of neuroprotection by preventing injured or vulnerable nerve cells from dying, or they are given in the hope of stimulating regenerative processes that could lead to the restoration or the formation of new connections that were lost because of the injury.

MAIN OUTCOME MEASURES

The developments in pharmacology are based primarily upon understanding the molecular mechanisms of drug actions at the level of the genome or with respect to cellular metabolism. Although there is a substantial interest in the pharmacology of brain repair, there seems to be less concern with the various theories of central nervous system plasticity, organization, and reorganization after an injury.

CONCLUSIONS

This review discusses some of the older and current ideas and theories that have been presented over the years to explain recovery of function. We then provide an overview of what is being done in the laboratory to develop new and safe drugs for the treatment of traumatic brain injuries.