Stress elevates corticotropin-releasing factor (CRF) and CRF-binding protein mRNA levels in rainbow trout (Oncorhynchus mykiss)

Abstract

The objectives of this study were to characterize rainbow trout (Oncorhynchus mykiss) corticotropin-releasing factor (CRF)-binding protein (CRF-BP) cDNA and to examine the variations in CRF-BP and CRF mRNA levels in response to different intensities of stress. Trout were physically disturbed by a single or three consecutive periods of chasing until exhaustion followed by 2 h of recovery. The pituitary CRF-BP and preoptic area CRF1 mRNA contents were significantly increased only after repeated chasing events. Physical disturbance increased plasma cortisol levels with the largest change occurring in the group of trout that were exposed to repeated chasing events. Trout were also individually isolated in 120 l tanks or confined to 1·5 l boxes for 4, 24 or 72 h. CRF-BP mRNA levels in confined fish were greater than those of isolated fish at 72 h although there were no differences compared with the control group. CRF1 mRNA levels in the preoptic area were greater and remained elevated for a longer period in confined compared with isolated trout. Isolation led to a transient increase in plasma cortisol levels, but the higher cortisol values developed in the confined fish suggest that this treatment was more stressful than isolation. These results demonstrate that the intensity and duration of stress are important factors regulating CRF and CRF-BP mRNA levels in rainbow trout. We hypothesize that pituitary CRF-BP is involved in regulating the activity of the stress axis, possibly by reducing access to CRF1 receptors in the corticotropes.

Heads or tails? Stressor-specific expression of corticotropin-releasing factor and urotensin I in the preoptic area and caudal neurosecretory system of rainbow trout

“…Interestingly, isolation, a stressor with significantly different attributes than either hypoxia or hyperammonemia, was also characterized by parallel increase in POA CRF and UI mRNA levels. In this case, however, as previously observed by Doyon et al (2005) for CRF, the isolation-induced increase in CRF and UI expression were sustained for the duration of the stressor. So while isolation may not pose a chronic threat to homeostasis and HPI axis activity habituation maybe relatively rapid, excitatory pathways involved in relaying the perceived psychological threat of the new environment maybe involved in keeping the CRF and UI mRNA levels elevated through at least 96 h. Similarly, isolation is known to result in a chronic reduction in food intake in rainbow trout (Overli et al 2002), a behavioral response that maybe at least partially mediated by the CRF-related peptides (Bernier 2006).…”

“…Lastly, despite eliciting the most pronounced cortisol response among the challenges tested, subordination was only associated with an increase in CRF expression and not UI. Therefore, our results and those of Doyon et al (2003Doyon et al ( , 2005 suggest that the recruitment of POA CRF neurons is a nearly ubiquitous feature of the stress response in rainbow trout, as previously observed in the PVN of rats (Sawchenko et al 2000, Dayas et al 2001. In contrast, although the response may have been missed due to the limitations of our sampling regime, the recruitment of POA UI neurons appears to be stressor-specific and independent of the stress-induced cortisol response.…”

“…Similarly, the physiological and behavioral responses associated with chronic hypoxia in rainbow trout (Randall 1982, Boutilier et al 1988 may serve to reduce the threat to homeostasis and dampen the HPI axis response. The transient increase in plasma cortisol in the chronically isolated and confined fish corroborates the results of Doyon et al (2005) and suggests that habituation to this social stressor is taking place at the level of the HPI axis. In contrast, while we did not assess the long-term effects of fights for social dominance on plasma cortisol levels, several previous studies have shown that subordination is a chronic stressor in rainbow trout and that plasma cortisol levels remain elevated Table 1 Correlation between corticotropin-releasing factor (CRF) and urotensin I (UI) mRNA levels within a given tissue or between the preoptic area (POA) and the caudal neurosecretory system (CNSS) for a given transcript in rainbow trout exposed to four different stressors: hyperammonemia, hypoxia, isolation, and subordination The relationships between the mRNA levels were analyzed with the Pearson product moment correlation test.…”

Sequences, expression patterns and regulation of the corticotropin-releasing factor system in a teleost

“…CRF also plays a role in suppressing reproduction and is involved in follicle maturation in the mammalian ovary (Nappi and Rivest, 1995;Asakura et al, 1997), which is consistent with our finding that the local CRF and CRF-R2 mRNA is expressed in the ovaries. Taken together, our data show that the molecular conservation of the CRF family is likely reflected in conserved functions based on its distribution in A. burtoni CRF systems are regulated by social stress During short-term physical stress, CRF mRNA and CRF-R1 mRNA levels increase in the mammalian hypothalamus or pituitary (Imaki et al, 1998;Qahwash et al, 2002;Doyon et al, 2005). In the teleost, CRF and CRFBP expression also increase in the hypothalamus, but CRF-R1 expression decreases in the pituitary during acute stress (Huising et al, 2004).…”

Stress in Atlantic salmon: response to unpredictable chronic stress

“…Studies on trout Doyon et al, 2005) reported that CRFBP may play a role in the inhibition of CRF signalling at its receptor in the acute stress response and this mechanism was confirmed by in vitro studies (Manuel et al, 2014). The effect of chronic stress in our study is in line with the findings of another experiment on rainbow trout (Jeffrey et al, 2012) where crfbp mRNA was unaffected by chronic stress caused by social interactions.…”