No description available.

No description available.

Age-related declines in cognitive functioning have been well documented, however, there are vast individual differences in the age of onset and magnitude of these changes. This observation has spurred the investigation of the potential risk factors for cognitive decline. Chronic elevations of the steroid hormone cortisol have been shown to compromise hippocampal- and frontal cortex- dependent cognitive tasks in rodents, non-human primates and Cushing’s disease patients. Several studies have extended these findings to investigate possible associations between cortisol and cognition in aging human populations. However, these previous examinations of the role of cortisol in cognitive aging have been hampered by the predominant use of single time-point measures of cortisol, small sample sizes, limited age ranges and/or constrained cognitive testing batteries. The present cross-sectional study investigated the relationship between basal cortisol levels, indexed by a 24-hr free cortisol to creatinine ratio, and cognitive functioning on twelve cognitive outcomes in a sample of 1,853 non-demented adults aged 18 to 93 years. The results showed that elevated cortisol levels had small but significant negative effects on verbal learning and working memory performance across the lifespan and significant negative effects limited to older age on a measure of speeded processing. Longitudinal investigation is warranted to examine if within-person changes in cortisol level predict cognitive change.

No description available.

No description available.

Seasonal physiology has evolved as an adaptive strategy to changing environments with daylength (photoperiod) used as the predominant environmental cue to suit breeding and other functions to the external season. However, seasonal physiological state is determined not only by the photoperiod that is currently in effect but also by the animal's history, allowing changes in physiology in anticipation to the seasons. Many mammals and birds show internally timed, long-term (circannual) changes in seasonal physiology, synchronised to the seasons by changing photoperiods. The importance of history-dependent photoperiodic programming applies also to puberty attainment in juvenile animals, timed by the photoperiod received by the mother during gestation. In this project I investigated the effects of both types of history-dependent timing on the neuroendocrine pathways for photoperiodic regulation of seasonal physiology. In mammals, photoperiod is transmitted via the pineal hormone melatonin, which acts on the pars tuberalis (PT) to regulate thyrotropin (TSH) expression and in turn controls seasonal physiology via effects on the hypothalamic synthesis of type 2 and 3 thyroid hormone deiodinases (Dio2 and Dio3), and thus the local regulation of thyroid hormone metabolism, and downstream changes in hypothalamic neuropeptidergic signalling. Using two circannual species, the Soay sheep (Ovis aries) –a short-day breeder – and the European hamster (Cricetus cricetus) – a long-day breeder – exposed to constant photoperiodic conditions, my findings reveal that in both models, in the absence of seasonal cues, internal circannual timing is initiated at the PT control of TSH and transmitted to the regulation of hypothalamic T3 regulation and neuropeptides. Siberian hamsters (Phodopus sungorus) were placed under different photoperiods during gestation and transferred to a photoperiod of intermediate duration at weaning. Reproductive activation under these conditions was dependent upon early life exposure and this effect controls history-dependent changes in hypothalamic deiodinases. Interestingly, the gestational experience was reflected in PT TSH expression and Dio2 expression as early as birth time. The same prenatal effects were observed in a strain of seasonal mice, (Mus musculus molossinus). Overall my dissertation has established that: i) both the circannual and the melatonin signals converge on TSH expression to synchronise seasonal biological activity; ii) the photoperiodic pituitary-hypothalamic network is programmed by prenatal experience; and iii) this pathway is already functional before birth. Overall, my results highlight the PT as a conserved central site in mammals for the integration of multiple seasonal cues which via differential control of thyroid hormone levels in the hypothalamus dictates the timing in seasonal physiology.

No description available.

Typescript. / Bibliography: leaves [65]-70. / vii, 70 l illus., tables

Thesis -- Departmental honors in Psychology. / Bibliography: ℓ. 37-40.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. Includes tables. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.