Jan G.D. Lambert

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After ovulation, female African catfish are strongly attracted by the odor of male conspecifics. This attraction depends on the presence of the seminal vesicle, a part of the male reproductive organs. Removal of the seminal vesicle illustrates this fact. A low dose of seminal vesicle fluid, added to the water, appears to be highly attractive for catfish(More)
Aromatase activity was determined in small discrete areas of the brain of the African catfish, Clarias gariepinus, by a radiometric assay. The fore- and midbrain were divided into eighteen 500-microns transverse sections. From these sections several punches (0.3 mg of tissue) were taken and incubated with [19-3H]-androstenedione. The aromatase activity,(More)
In the brain of the African catfish aromatase activity was demonstrated with two different methods using [7-3H]androstenedione and [19-3H]androstenedione as substrates. Kinetic analysis of estrogen formation following incubations of a cell-free fraction of brain homogenates showed that the apparent Km is the same for both substrates (0.03 micro M), but the(More)
Non-breeding stickleback males were gonadectomized or sham-operated in winter. Treatment with long photoperiod at high temperature stimulated sexual maturation in control fish. Brains were freeze-sectioned and punches were taken with hollow needles from different diencephalic regions and the punches incubated with [19-3H]-androstenedione. After extraction(More)
The onset and regulation of puberty is determined by functional development of the brain-pituitary-gonad (BPG) axis. Stress has been shown to interfere with reproduction and the functioning of the BPG axis. The response to chronic and severe stress may require much energy and force the organism to make adaptive choices. Energy that is normally available for(More)
Previous work showed that prolonged elevated cortisol levels, implicated in the stress adaptation, inhibits testicular pubertal development in male common carp, as well as an impairment of the synthesis of the 11-oxygenated androgens. This may be a direct effect of cortisol on the testis or via the gonadotropin secretion by the pituitary. The aim of the(More)
This is the first study to show that apoptosis as an immune regulatory mechanism is conserved in fish, demonstrating its importance in maintaining immunological homeostasis. The data further show that this mechanism is subject to control by glucocorticosteroids. Carp plasma cortisol concentrations increase from 20 to 434 ng/ml and cortisone from 5 to 50(More)
Gonadal homogenates of rainbow trout from D(ay) 60, D100 and D200 after fertilization have been incubated in vitro in the presence of dehydroepiandrosterone-3H to demonstrate 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and delta 5,4-isomerase activity, of pregnenolone-3H to assess the synthesis of "progestins" and of androstenedione-3H to determine(More)