Helen I'anson

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In the present study, we determined the involvement of brainstem catecholaminergic inputs to the paraventricular nucleus (PVN) on estrogen receptor alpha (ERalpha) expression in this nucleus during conditions of 48-h fasting, 2-deoxy-d-glucose (2DG)-induced acute glucoprivation and 1-h immobilization, in ovariectomized rats. Our approach was to examine the(More)
The present study determined whether exposure to gonadal steroids in utero dictates the postnatal control of gonadotropin secretion in the lamb. There is a marked sex difference in the timing of neuroendocrine sexual maturation in sheep; while male lambs undergo a reduction in sensitivity to inhibitory gonadal steroid feedback by 10 weeks of age, females(More)
We tested the hypothesis that hindbrain catecholamine (norepinephrine or epinephrine) neurons, in addition to their essential role in glucoprivic feeding, are responsible for suppressing estrous cycles during chronic glucoprivation. Normally cycling female rats were given bilateral injections of the retrogradely transported ribosomal toxin, saporin,(More)
In female sheep, photoperiod regulates the timing of the transition to adulthood. We tested the hypothesis that photoperiod very early in development influences the timing of the pubertal LH rise that initiates sexual maturation. The first experiment was designed to determine the influence of day length information perceived before birth by varying prenatal(More)
The objective of this study was to determine whether the previously observed effects of photoperiod on body weight in Siberian hamsters were due to changes in the daily patterns of locomotor activity, energy expenditure, and/or feeding behavior. Adult males were monitored through a seasonal cycle using an automated comprehensive laboratory animal monitoring(More)
In spring-born female lambs, the long days of summer, followed by their gradual decrease, provide the seasonal cue necessary to time puberty to early autumn (approximately 30 wk of age). Male lambs begin spermatogenesis during mid-summer, some 20 wk before puberty occurs in females. Unlike young female lambs, male lambs attain puberty at the same age under(More)
To test the hypothesis that the anestrous increase in estradiol negative feedback prevents estrous cycles by suppressing hypothalamic gonadotropin-releasing hormone (GnRH) pulse frequency, a variety of regimens of increasing GnRH pulse frequency were administered to anestrous ewes for 3 days. A luteinizing hormone (LH) surge was induced in 45 of 46 ewes(More)
Growth retardation induced by dietary restriction in the lamb results in a low GnRH pulse frequency, and thus, puberty is delayed. In our experimental model, in which ovariectomized lambs are maintained at weaning weight (approximately 20 kg BW), hypothalamic GnRH is present and releasable, suggesting that central mechanisms limit the release of GnRH during(More)
Growth retardation induced by dietary restriction results in hypogonadotropism, and thus, puberty is delayed. The present studies determined 1) whether reduced LH secretion in the growth-retarded condition is due to a reduction in the frequency and/or in the amplitude of GnRH secretion, and 2) whether the mechanism regulating LH secretion is being actively(More)