As both a photoreceptor and pacemaker in the avian circadian clock system, the pineal gland is crucial for maintaining and synchronizing overt circadian rhythms in processes such as locomotor activity and body temperature through its circadian secretion of the pineal hormone melatonin. In addition to receptor presence in circadian and visual system structures, high-affinity melatonin binding and receptor mRNA are present in the song control system of male oscine passeriform birds. The present study explores the role of pineal melatonin in circadian organization of singing and calling behavior in comparison to locomotor activity under different lighting conditions. Similar to locomotor activity, both singing and calling behavior were regulated on a circadian basis by the central clock system through pineal melatonin, since these behaviors free-ran with a circadian period and since pinealectomy abolished them in constant environmental conditions. Further, rhythmic melatonin administration restored their rhythmicity. However, the rates by which these behaviors became arrhythmic and the rates of their entrainment to rhythmic melatonin administration differed among locomotor activity, singing and calling under constant dim light and constant bright light. Overall, the study demonstrates a role for pineal melatonin in regulating circadian oscillations of avian vocalizations in addition to locomotor activity. It is suggested that these behaviors might be controlled by separable circadian clockworks and that pineal melatonin entrains them all through a circadian clock.

BACKGROUND-Several epidemiological studies have reported an inverse association between physical activity and the risk of prostate cancer. To date, there are few animal studies looking at physical activity and cancer incidence, although the results are consistent with the epidemiological evidence. In general, as exercise intensity increased in the rats/mice, the likelihood that physical activity inhibited carcinogenesis increased.

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Several epidemiological studies have reported an inverse association between physical activity and the risk of prostate cancer. In general, as exercise intensity increased in the rats/mice, the likelihood that physical activity inhibited carcinogenesis increased. In order to establish an animal model to investigate the effects of physical activity on prostate cancer development, the present study used C3(1)Tag mice that are predisposed to prostate cancer due to the directed expression of SV40 oncogenes combined with voluntary wheel running exercise. The results presented indicate that prostatic cancer progression is likely delayed or diminished by wheel running in a dose dependent manner. Mice that ran > 5Km/group exhibited 83% of the dorsolateral prostates as within normal levels for pathology vs. 43% for the < 5 km/day group (p=0.16). In addition, the pathologic progression to high‐grade PIN and local invasion, considered to be an early event in the formation of prostate adenocarcinoma, was significantly reduced with increased running. Forty three percent of dorsolateral prostates from mice that ran less than 5 km/day were classified with advanced pathology as compared to none in mice that ran more than 5.0 km/day (p=0.05). These findings provide further evidence that exercise acts to decrease the progression of prostate cancer and they establish a transgenic animal model for future mechanistic studies.