| dc.description.abstract | In bony fishes such as the rainbow trout, Oncorhynchus mykiss, glucocorticoid (GC) and
estrogenic hormones are associated with a variety of physiological functions. Most notable are
effects of GCs which allow the animal to respond to stressful events (Donaldson, 1981;
Clearwater and Pankhurst, 1997; Stouthart et al., 1998) and the actions of estrogens in the
hormonal control of reproduction (Donaldson, 1973; Arcandhoy and Benson, 1998; Aiukwe and
Goksoyr, 1998). Circulating levels o f GCs and estrogens are regulated largely by activation of the
hypothalamic-pituitary-interrenal (HPI) axis (Donaldson, 1981; Stouthart et ai., 1998), and the
hypothalamic-pituitary-gonadal (HPG) axis (Fostier et al., 1983; Blazquez et al., 1998; Kah et al.,
1997), respectively In the case o f the HPI axis, the initial stimulus for biosynthesis and release of
cortisol, the primary plasnia GC, is corticotropic releasing hormone (CRH). Neurons o f
hypothalamic origin project their axons to pituitary target cells, corticotrophs (Peter et al., 1990).
CRH released onto corticotrophs stimulates release o f adrenocorticotropic hormone (ACTH) into
circulation (Baker et al., 1996; Stouthart et al., 1998). ACTH serves as the final signal in this
pathway by stimulating interrenal tissue to synthesize and release cortisol into circulation
(Chester-Jones et al., 1969). In turn, the level of plasma GCs may provide a feedback signal to the
HPI axis, via activation o f hypothalamic glucorticoid receptors (GRs). | |
