Seasonal changes in CRF-I and urotensin I transcript levels in masu salmon: Correlation with cortisol secretion during spawning

Abstract

Pacific salmon employ a semelparous reproductive strategy where sexual maturation is followed by rapid senescence and death. Cortisol overproduction has been implicated as the central physiologic event responsible for the post-spawning demise of these fish. Cortisol homeostasis is regulated through the action of hormones of the hypothalamus-pituitary-interrenal (HPI) axis. These include corticotropin-releasing factor (CRF) and urotensin-I (UI). In the present study, masu salmon (Oncorhynchus masou) were assayed for changes in the levels CRF-I and UI mRNA transcripts by quantitative real-time PCR (qRT-PCR). These results were compared to plasma cortisol levels in juvenile, adult, and spawning masu salmon to identify specific regulatory factors that appear to be functionally associated with changes in cortisol levels. Intramuscular implantation of GnRH analog (GnRHa) capsules was also used to determine whether GnRH influences stress hormone levels. In both male and female masu salmon, spawning fish experienced a 5-7 fold increase in plasma cortisol levels relative to juvenile non-spawning salmon. Changes in CRF-I mRNA levels were characterized by 1-2 distinctive short-term surges in adult masu salmon. Conversely, seasonal changes in UI mRNA levels displayed broad and sustained increases during the pre-spawning and spawning periods. The increases in UI mRNA levels were positively correlated (R 2 = 0.21 male and 0.26 female, p<0.0001) with levels of plasma cortisol in the pre-spawning and spawning periods. Despite the importance of GnRH in sexual maturation and reproduction, the administration of GnRHa to test animals failed to produce broad changes in CRF-I, UI or plasma cortisol levels. These findings suggest a more direct role for UI than for CRF-I in the regulation of cortisol levels in spawning Pacific salmon.

Chronic cortisol and the regulation of food intake and the endocrine growth axis in rainbow trout

“…In salmonids, sustained increases in cortisol levels are also associated with social subordination (Gilmour et al 2005) and with specific phases of the life cycle such as smolting (Nilsen et al 2008) and sexual maturation (Fuzzen et al 2011). In fact, plasma cortisol levels can reach several hundred ng/ml and remain elevated for weeks to months in sexually mature and migrating Pacific salmon (Carruth et al 2000, Hinch et al 2006, Westring et al 2008. As such, our findings contribute to our understanding of the mechanisms underlying the dynamic changes in food intake, growth and energy mobilization that characterize various chronic stressors and life history transitions.…”

The in vitro metabolism of cortisol by ovarian follicles of rainbow trout (Oncorhynchus mykiss): comparison with ovulated oocytes and pre-hatch embryos

“…salmonid fishes is to be anticipated in light of the relatively high maternal plasma levels of cortisol in these species (ranging from 140 to 650 ng/ml) during the critical late stages of ovarian maturation (Morrison et al 1985, Kubokawa et al 1999, Carruth et al 2000, Westring et al 2008, McConnachie et al 2012. While the maternal total cortisol concentrations during gonadal maturation are somewhat lower for non-migratory oncorhynchid salmonids, such as rainbow trout (20-70 ng/ml) (Bry 1985, Caldwell et al 1991, Koldjaer et al 2004, w45% of that steroid is in the form of unconjugated hormone (Caldwell et al 1991).…”

Induced reproduction in a migratory teleost species by water level drawdown

“…However, these deleterious effects are associated with prolonged stimuli of aggressive agents resulting in high levels of plasma cortisol (Bayunova et al, 2002;Schreck, 2010). In animals at the final stages of the reproductive cycle, stress appears to have a positive effect on reproduction (Small, 2004;Westring et al, 2008;Milla et al, 2009). Previous studies have found that this effect may be observed especially in females, where treatment with corticosteroids (cortisol, 11-deoxycortisol, 11-deoxycorticosterona) induces ovulation in various fish species (Goetz & Theofan, 1979;Haider & Rao, 1994;Milla et al, 2009).…”