Abstract
The local gill production of corticotropin releasing hormone (crh) and crh-receptor (crhr) is hypothesized to play important roles during seawater (SW) and freshwater (FW) acclimation in euryhaline black porgy (Acanthopagrus schlegelii). The mRNA expression of crh, crhr, and Na+/K+-ATPase (a-nka) was examined in SW and FW diencephalon (Dien) and in the gills at different exposure time by Q-PCR analysis. The in situ hybridization results indicate that crh mRNA hybridization signals were more abundant in FW fish in the gigantocellular (PMgc) and parvocellular (PMpc) part of the magnocellular preoptic nucleus versus SW fish. The crh and crhr-expressing cells were located in basal cells of gill filament. Furthermore, in vitro dexamethasone (DEX) treatment could increase the crh-system in the gill. Increased transcripts of the crh-system in the gill via in vitro and in vivo CRH treatments suggest that CRH may regulate the system in a local manner. The a-Nka cells were localized in the filament and secondary lamellae mitochondria rich cells (MRCs) of FW fish at 8 h and 1 day. a-Nka cells were seen in both filament and lamellae in the FW but much less in SW fish indicating that gills play key roles in black porgy osmoregulation. Gill crh and crhr play important roles in the response to salinity stress.
Highlights
Stress stimulates the corticotrophin releasing hormone and crh-receptor from the hypothalamus and pituitary by activation of the hypothalamic pituitary interrenal (HPI/fish) and/or hypothalamic pituitary adrenal (HPA/mammals)-axis (Dautzenberg and Hauger, 2002)
A strong band of crh and crhr was found in the Dien and gill
The expression of a-nka was strong, but no expression was observed in Dien (Figure 1A). crh, crhr, and a-nka mRNA levels were determined by RT-PCR in Dien and gill of SW and FW black porgy. gapdh was used as an internal control (Figure 1A)
Summary
Stress stimulates the corticotrophin releasing hormone (crh) and crh-receptor (crhr) from the hypothalamus and pituitary by activation of the hypothalamic pituitary interrenal (HPI/fish) and/or hypothalamic pituitary adrenal (HPA/mammals)-axis (Dautzenberg and Hauger, 2002). Stress acts in the nervous system and converges at the hypothalamus, and the final products are corticosteroid hormones, cortisol, which is believed to regulate homeostasis This same corticosteroid terminates the stress crh/chr in Brain/Gill response by interacting directly with the hypothalamus or anterior pituitary to attenuate crh and crhr production (Slominski et al, 2000). The body surfaces of teleosts are continuously exposed to an aquatic environment and are in intimately physiological contact with fish via the body fluid compartments and the epithelium of the gill, kidney, and intestine (Flik et al, 2006) Physiological processes, such as gas exchange, osmoregulation, excretion of nitrogenous waste products and acid-base balance, take place in the osmoregulatory organs (Evans et al, 2005). Damage to these organs could result in the compromise of fish survival
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