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Male deer mice (Peromyscus maniculatus) respond to short photoperiod with a range of spermatogenic responses. About one-third of all short day exposed mice exhibit a complete cessation of spermatogenesis (reproductive responsive), while about an equal number remain reproductively competent (reproductive nonresponsive). These differential spermatogenic(More)
The capacity of the pituitary to suppress hormone secretion in response to somatostatin (SRIF) is markedly age dependent. Immature pituitaries are relatively resistant to SRIF effects, and increasing sensitivity to SRIF with advancing age is believed to cause characteristic developmental changes in pituitary hormone secretion in mammals. However, the(More)
We investigated the role of declining daylength and gonadal steroids on body weight and food intake in male deer mice (Peromyscus maniculatus). This species was chosen for study because individual males display different reproductive responses to inhibitory daylength. About one-third of all mice exposed to short days undergo testicular regression and(More)
We investigated pineal function as well as reproductive and energetic characteristics in male deer mice (Peromyscus maniculatus) that differentially respond to short photoperiod with full, partial or no gonadal regression. In mice at both high (23 °C) and low temperature (1 °C), these phenotypic differences in reproductive responses to short days were not(More)
The mechanisms governing age-dependent patterns of GH secretion are not well understood. Studies have shown that pituitaries of fetal and neonatal mammals are highly responsive to the stimulatory effect of GH-releasing hormone (GHRH) compared to those of mature mammals. Differential pituitary responsiveness to GHRH may, therefore, contribute to the elevated(More)
The GH-releasing hormone receptor (GHRH-R) is a critical link between hypothalamic GH-releasing hormone (GHRH) and pituitary GH secretion. However, the factors that regulate GHRH-R are not well understood. Despite the importance of thyroid hormone and glucocorticoids in influencing the GH axis in vivo, it is not known whether these hormones act directly at(More)
While significant attention has been devoted to the identification of hormonal factors that control body mass, little attention has been paid to the role of mechanical loading on animal mass. Here, we provide evidence that intraperitoneal implantation of metabolically inert mass results in a compensatory reduction in tissue mass. Deer mice (Peromyscus(More)
The GHRH receptor is expressed in the somatotroph cell of the anterior pituitary, where it functions to mediate GHRH-stimulated GH release. To study pituitary and somatotroph cell-specific expression of this gene, a transgenic mouse model and complementary cell culture experiments were developed. The activity of the 1.6-kb proximal rat GHRH receptor(More)
The neural mechanisms by which short photoperiod induces gonadal regression among seasonally breeding mammals are not well understood. One hypothesis suggests that the proximate cause of seasonal gonadal regression is a photoperiod-induced modification in GnRH secretion. This hypothesis is indirectly supported by our recent findings using(More)
The purpose of this study was twofold: 1) to examine photoperiod-dependent and steroid-dependent adjustments in hypothalamic GnRH and catecholamine content in male deer mice, Peromyscus maniculatus, and 2) to evaluate whether the commonly used measure of GnRH accumulation serves as an accurate indicator of altered reproductive function in short-day-housed(More)