1,721,000 research outputs found
The brain-pituitary-gonadal axis in the rainbow trout, Salmo gairdneri : III. Absence of an inhibiting action of testosterone on gonadotrophin release in juveniles
No full textIn juvenile rainbow trout the effects of exogenous testosterone and of a synthetic gonadotrophin-releasing hormone (GnRH) on the secretion of gonadotrophin (GTH) were investigated. Treatment with implanted testosterone resulted in an accumulation of GTH in the pituitary, but did not affect the concentration of GTH in the plasma. After the testosterone implants were removed, the levels of testosterone in the circulation dropped to undetectable or control values, but the concentration of GTH in the plasma did not increase. These results indicate that testosterone stimulated the synthesis and storage of GTH, and did not prevent the release of this hormone. The synthetic GnRH, des-Gly10[-Ala6]LH-RH ethylamide (LH-RHa) stimulated the release of GTH when injected into testosterone-pretreated fish, indicating that accumulated GTH is present in a releasable pool
Role of the leptin signaling system in energy homeostasis
No full textA regulated factor that contributes to maintenance of energy homeostasis is body weight and especially the size of its fat mass. Leptin as well as insulin are synthesized and secreted in proportion to body fat and each form a unique link between energy availability and CNS mechanisms that subserve the regulation of energy homeostasis. Both insulin and leptin affect signaling systems in the hypothalamus that involve a number of neuropeptides that serve a role in the regulation of food intake and energy expenditure. This chapter pays attention to to the interactions of leptin and insulin with hypopthalamic neuronal circuitry that contains neuropeptide Y (NPY), agouti-related peptide (AgRP) and proopiomelanocortin (POMC), and how these interactions affect appropriate changes in food intake and energy expenditure.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The African catfish, Clarias gariepinus, a model for the study of reproductive endocrinology in teleosts
No full textIn their natural habitat African catfish, Clarias gariepinus, show a discontinuous reproductive cycle. This cycle follows changes in the gonadotropic activity of the pituitary. Gonadotropin release has been shown to be under dual hypothalamic control, i.e. a gonadotropin-releasing hormone (GnRH) and a gonadotropin release-inhibiting factro (GRIF), which turned out to be dopamine.
Gonadal sex hormones influence gonadotropin release by a negative feedback, and a model has been developed to explain their mode of action.
Steroid formation has been studied in testes, seminal vesicles and ovaries and correlated with the annual reproductive cycle. Steroid glucuronides, originating from the seminal vesicle, act as male sex pheromones; ovulation seems to be synchronized by female pheromones.
Techniques for the induction of ovulation were developed. Only broodfish, reared from eggs to maturity under favourable conditions, show a continuous reproductive cycle and can be induced to produce viable eggs throughout the year
- …
