Differential Increase in Forebrain and Caudal Neurosecretory System Corticotropin-Releasing Factor and Urotensin I Gene Expression Associated with Seawater Transfer in Rainbow Trout

Abstract

Transfer to seawater (SW) in rainbow trout elicits an increase in plasma cortisol and a bout of anorexia. Although the corticotropin-releasing factor (CRF) system has known hypophysiotropic and anorexigenic properties, it is not known whether CRF-related peptides originating from either the forebrain or the caudal neurosecretory system (CNSS) play a role during SW acclimation. Therefore, we examined the effects of SW transfer on food intake, plasma osmolality, hypothalamic-pituitary-interrenal axis activity, and the expression of CRF and urotensin I (UI) in the forebrain and the CNSS. While SW transfer chronically suppressed food intake over a 2-wk period, it transiently increased plasma osmolality, ACTH, and cortisol. Similarly, 24 h after SW transfer, hypothalamic and preoptic area CRF mRNA levels were significantly increased but recovered to pretransfer levels within 7 d. Conversely, SW transfer elicited a delayed increase in hypothalamic UI mRNA levels and had no effect on preoptic area UI expression. In the CNSS, SW exposure was associated with parallel increases in CRF and UI mRNA levels from 24 h post transfer through 7 d. Finally, in situ hybridization demonstrated an extensive and overlapping pattern of CNSS CRF and UI expression. These results differentially implicate specific neuronal populations of the CRF system in the acute and chronic responses to a hyperosmotic stress and suggest that forebrain and CNSS CRF-related peptides have different roles in the coordinated response to fluid balance disturbances.

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

“…We detected CRF mRNA in A. burtoni spinal cord suggesting the existence of the caudal neurosecretory system (CNSS), a unique fish neuroendocrine organ in the most caudal spinal cord which is known to control release of cortisol from the interrenal glands (Lovejoy and Balment, 1999;Winter et al, 2000;Lu et al, 2004;Craig et al, 2005). However, we did not find any difference in spinal cord CRF expressing levels between T and NT males, suggesting that this part of the CRF system may not be involved in regulating stress responses under long term social stress.…”

Effects of freshwater and saltwater adaptation and dietary salt on fluid compartments, blood pressure, and venous capacitance in trout

“…There is accumulating evidence that both FW-to-SW transfer and HS diet are associated with a salt overload. After transfer from FW to SW or dilute SW (ϳ2/3 SW) plasma ions or osmolarity increase dramatically (1,4,7,14,38). After long-term adaptation (days to weeks), they may return to pretransfer levels (4,7,12,20,38) or remain elevated (14,17), whereas the osmoregulatory organs retain features characteristic of salt secretion (21).…”

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

“…All brain tissues and the pituitaries were snap frozen in liquid nitrogen and stored at K80 8C until total RNA extraction. The region of the caudal spinal cord removed consisted of the six most caudal vertebrae and the urostyle after Craig et al (2005). The CNSS was placed in a solution of 4% paraformaldehyde (PFA) in PBS (pH 7 .…”

“…Total RNA from the CNSS was extracted according to Craig et al (2005). Briefly, the urophysis and attached portion of the spinal cord were removed from the PFA-fixed vertebral column, dehydrated in a series of ethanol washes and incubated overnight at 4 8C in 100% ethanol.…”