Aging selectively suppresses vasoactive intestinal peptide messenger RNA expression in the suprachiasmatic nucleus of the Syrian hamster

Senescence, sleep, and circadian rhythms

The goal of this review article is to summarize our knowledge and understanding of the overlapping (interdisciplinary) areas of senescence, sleep, and circadian rhythms. Our overview comprehensively (and visually wherever possible), emphasizes the organizational, dynamic, and plastic nature of both sleep and circadian timing system (CTS) during senescent processes in animals and in humans. In this review, we focus on the studies that deal with sleep and circadian rhythms in aged animals and how these studies have closely correlated to and advanced our understanding of similar processes in ageing humans. Our comprehensive summary of various aspects of the existing research on animal and human ageing, both normal and pathological, presented in this review underscores the invaluable advantage of close collaboration between clinicians and basic research scientists and the future challenges inherent in this collaboration. First, our review addresses the common age-related changes that occur in sleep and temporal organization of both animals and humans. Second, we examine the specific modifications that often accompany sleep and CTS during aging. Third, we discuss the clinical epidemiology of sleep dysfunctions during ageing and their current clinical management, both pharmacological and non-pharmacological. Finally, we predict the possible future promises for complementary and alternative medicine (CAM) that pave the way to the emergence of a "Holistic Sleep Medicine" approach to the treatment of sleep disorders in the ageing population. Further studies will provide additional valuable insights into the understanding of both sleep and circadian rhythms during senescence.

Vasopressin immunoreactivity and release in the suprachiasmatic nucleus of wild-type and tau mutant Syrian hamsters

Despite the prominent role of the Syrian hamster (Mesocricetus auratus) in studies of circadian rhythms, there are no data available on the temporal dynamics of the neuropeptide vasopressin (AVP), a major output system of the suprachiasmatic nucleus (SCN). We studied the hamster SCN-AVP system in vivo across the light period and in vitro using long-term organotypic SCN cultures. Additionally, we compared wild-type and tau mutant hamsters with an endogenous circadian period of approximately 24 h and approximately 20 h, respectively. The in vivo study revealed no differences in the number of SCN-AVP neurons between the two genotypes of hamsters studied at three time points across the light period of the circadian cycle. A significantly higher level of AVP-immunoreactivity, however, was found in the SCN of wild-type compared to tau mutant hamsters at the beginning and in the middle of the light period, but not at the end of the light period. SCN-AVP cell number and immunostaining decreased significantly across the light period in wild-type hamsters, but not in tau mutants. The in vitro study revealed a significantly higher rate of AVP release per 24 h from the tau mutant SCN compared to the wild-type SCN. Robust circadian oscillations in AVP release were not found in either type of hamster. These results may suggest that the SCN-AVP system of hamsters, irrespective of genotype, is relatively weak compared to other species. Moreover, the tau mutation seems to influence the SCN-AVP system by enhancing the rate of AVP release and by reducing AVP content and its daily fluctuation.