Journal: Fish physiology and biochemistry
In this study, for the first time, both neuropeptides isotocin (IT) and arginine vasotocin (AVT) have been identified and measured in urophysis, the neurohaemal organ of the caudal neurosecretory system of teleost fish. So far, AVT, but not IT, was quantified by radioimmunoassay (RIA) in urophysis of several fish species. We have used high-performance liquid chromatographic assay with fluorescence detection (HPLC-FL) preceded by solid-phase extraction (SPE) and liquid chromatography-electrospray ionization triple-quadrupole tandem mass spectrometry (LC-ESI MS/MS) technique to determine both neuropeptides in urophysis of three fish species. The efficiency of peptide’s SPE extraction was 79-85 %. In HPLC-FL method, the limits of detection (LOD) and quantification (LOQ) were estimated as 1.0 and 3.4 pmol/mL for IT and 0.25 and 2.20 pmol/mL for AVT. In LC-MS/MS method, LOD and LOQ were estimated as 0.4 and 1.2 pmol/mL for IT and 0.06 and 0.2 pmol/mL for AVT. The chromatographic methods are good alternative for RIA, because enable to measure both nonapeptides simultaneously in one sample. In round goby (Neogobius melanostomus), three-spined stickleback (Gasterosteus aculeatus) and sea bream (Sparus aurata), urophysial IT concentrations ranged between 0.056 and 0.678 pmol/mg tissue and AVT concentrations ranged between 0.0008 (or even below detection threshold) and 0.084 pmol/mg tissue.
The pituitary gland is present in all vertebrates, from agnathans (jawless vertebrates) to mammals, but not in invertebrates. Reproduction in gnathostomes (jawed vertebrates) is controlled by two pituitary gonadotropins (GTHs), luteinizing hormone and follicle-stimulating hormone, which are part of the pituitary glycoprotein hormone (GPH) family. Hagfishes, which lack both jaws and vertebrae, are considered the most primitive vertebrate known, living or extinct. Accordingly, they are of particular importance in understanding the evolution of the pituitary GPHs and their functions related to vertebrate reproduction. Nevertheless, key elements of the reproductive endocrine system in hagfish have yet to be elucidated. Our current report has revealed the first identification of a functional GPH composed of two subunits that possess gonadotropic action at the pituitary of brown hagfish. It seems most likely that an ancestral GPH gave rise to only one GTH in hagfish pituitary and that multiplicity of GPHs arose later during the early evolution of gnathostomes. This paper briefly summarizes the latest findings on the hagfish GPH from an evolutionary point of view.
Spontaneous ovarian tunica albuginea contractility was evaluated in gilthead seabream (Sparus aurata L.) at different phases of the reproductive cycle. Fourteen adult females were sampled from February to November 2012 in a commercial fish farm, and ovaries were removed and processed for histological and contractility analyses. Fish reproductive stages were evaluated on haematoxylin-eosin-stained ovary sections or by simple macroscopic observation of hydrated oocytes in spawning individuals. Tunica albuginea spontaneous contractility was recorded by using ovary wall strips mounted in an organ bath containing modified Ringer’s solution. Ovary macro- and microscopic analyses allowed the identification of three different reproductive conditions: vitellogenesis, spawning and regressing. The gilthead seabream tunica albuginea was capable to contract spontaneously, and significant differences were found in mean contraction amplitude among the three reproductive states, with the highest value recorded in individuals in regressing condition and the lowest in individuals at spawning stage. No differences in mean contractility frequency among the three different groups were found. Possible involvement of spontaneous contractility in facilitating developing follicle advancement towards the ovarian lumen within the ovary and in supporting recovery of regressing ovaries may be hypothesized. The low contractility observed during the final oocyte maturation and spawning phases does not seem to support a role of tunica albuginea during ovulation, which could conversely involve theca cell contraction. Alternatively, possible single instantaneous contractions of tunica albuginea muscle fibres, not detected in the present study, could occur during ovulation in response to neuro-hormonal stimulations; a role of abdominal wall musculature in ovary “squeezing” and consequent release of ovulated eggs cannot be excluded.
Acetaminophen (APAP)-induced liver damage is one of the most common problems among the population. Therefore, the study was aimed to investigate the hepatoprotective effect of celery leaves on APAP-induced toxicity in a freshwater fish, Pangasius sutchi. Fish were divided into four experimental groups of 6 fish each. Group 1 served as control. Group 2 fish were exposed to APAP (500 mg/kg) for 24 h. Groups 3 and 4 fish were exposed to APAP + celery leaf powder (CE) (500 mg/kg) and CE for 24 h, respectively. The severity of liver damage, hepatic lipid, glycogen, ions status and histological alterations was examined. The characterization of CE extract was also performed. APAP-exposed fish showed elevated levels of both circulating and tissue hepatotoxic markers (AST, ALT and ALP), reduced hepatic glycogen and lipid contents (TG and cholesterol), increased tissue lipid peroxidation markers (TBARS, LHP and PCO), altered tissue levels of enzymatic (SOD, CAT, GPx and GST) and non-enzymatic (GSH) antioxidants and cellular thiol levels (T-SH, P-SH and NP-SH), and reduced hepatic ions (Na(+), K(+) and Ca(2+)) and abnormal liver histology. The abnormalities associated with APAP exposure were reversed on treatment with CE. The TLC separation and HPLC quantification of petroleum ether/acetone extract of CE showed the peaks for highly efficient flavonoids such as rutein, quercetin and luteolin. The observed hepatoprotective effect of CE might be due to its rich flavonoids.
Fish gills are the vital multifunctional organ in direct contact with external environment. Therefore, activation of the cytoprotective mechanisms to maintain branchial cell viability is important for fish upon stresses. Salinity is one of the major factors strongly affecting cellular and organismal functions. Reduction of ambient salinity may occur in coral reef and leads to osmotic stress for reef-associated stenohaline fish. However, the physiological responses to salinity stress in reef-associated fish were not examined substantially. With this regard, the physiological parameters and the responses of protein quality control (PQC) and osmoregulatory mechanisms in gills of seawater (SW; 33-35 ‰)- and brackish water (BW; 20 ‰)-acclimated blue-green damselfish (Chromis viridis) were explored. The results showed that the examined physiological parameters were maintained within certain physiological ranges in C. viridis acclimated to different salinities. In PQC mechanism, expression of heat-shock protein (HSP) 90, 70, and 60 elevated in response to BW acclimation while the levels of ubiquitin-conjugated proteins were similar between the two groups. Thus, it was presumed that upregulation of HSPs was sufficient to prevent the accumulation of aggregated proteins for maintaining the protein quality and viability of gill cells when C. viridis were acclimated to BW. Moreover, gill Na(+)/K(+)-ATPase expression and protein amounts of basolaterally located Na(+)/K(+)/2Cl(-) cotransporter were higher in SW fish than in BW fish. Taken together, this study showed that the cytoprotective and osmoregulatory mechanisms of blue-green damselfish were functionally activated and modulated to withstand the challenge of reduction in salinity for maintaining physiological homeostasis.
Testicular germ cells of channel catfish, Ictalurus punctatus, and blue catfish, I. furcatus were separated into four layers with Percoll density gradient centrifugation, containing different cell types (40 % in the first layer were spermatogonial stem cells, SSCs). Expression of seventeen genes was analyzed for cells from different layers by real-time quantitative PCR. Pfkfb4, Urod, Plzf, Integrin6, IntegrinV, Thy1 and Cdh1 genes showed the same expression change pattern in both channel and blue catfish as these genes were down-regulated in the spermatocytes and even more so in spermatids. Plzf and Integrin6 had especially high expression in SSCs and can be used as SSCs specific markers. Sox2 gene was up-regulated in spermatocytes and even more highly up-regulated in spermatids, which indicated it could be a spermatid marker. In contrast to channel catfish, Id4, Smad5 and Prdm14 gene expressions were strongly down-regulated in spermatocyte cells, but up-regulated in spermatid cells in blue catfish. Smad5 gene was down-regulated in spermatocytes, but up-regulated in both spermatogonia and spermatids, allowing identification as a marker for spermatocytes in blue catfish. Oct4, Id4, Gfrα2, Pum2 and Prdm14 genes showed different expression patterns in the testicular germ cells of channel and blue catfish. This may be a partial explanation to the differing responses of channel catfish and blue catfish to induced spawning technologies. The SSCs specific markers can be used for further SSCs labeling, which can increase the SSCs sorting efficiency and be applied in various studies involving SSCs and other germ cells.
The aim of the present study was to evaluate the effect of β-glucan on acute hypoxia-induced oxidative stress and the changes in energy metabolism by determining ROS production, activities and mRNA levels of energy metabolism enzyme (PK, F-ATPase, SDH and MDH), and in gene expression of HIF-1α in the liver of large yellow croaker. Fish were injected with β-glucan at a dose of 0 or 5 mg kg(-1) body weight on 6, 4 and 2 days before exposed to 1.5 and 7.0 mg DO L(-1) for 48 h. The results showed that β-glucan enhanced survival rate and reduced ROS during the lethal hypoxic stress, indicating that β-glucan could ameliorate hypoxia-induced oxidative stress. Obtained results also showed that β-glucan could up-regulate activities and mRNA levels of PK, demonstrating that β-glucan increased anaerobic glycolysis capacity. Furthermore, a coordinated transcriptional regulation of energy metabolism enzyme genes was observed, suggesting that HIF-1α is required for regulating these genes. In conclusion, β-glucan could alleviate cute hypoxia-induced oxidative stress in large yellow croker by enhancing anaerobic glycolysis capacity, emphasizing a central role of transcription factor HIF-1α in the process.
The effect of different farming systems (cage, pond) upon digestive enzyme activities of Nile tilapia was evaluated. Juvenile Nile tilapia (87.61 ± 1.52 g) were simultaneously cultured in pond and cage systems during 90 days. Cages used nutritional biphasic plan (35 and 32 % crude protein-CP feeds) and ponds used nutritional triphasic plan (35, 32 and 28 % CP feeds). Biometric measurements were monthly performed for adjustments in feeding regimes and removal of intestine tissues to evaluate the performance of enzyme activities. Total proteolytic, amylase and lipase activities were not statistically different between the treatments throughout the periods analyzed (31, 63 and 94 days of culture). However, trypsin and chymotrypsin activities were higher with 31 and 63 days of culture in fish from pond system, suggesting that natural food may have influenced these activities. A positive correlation was observed between the recommended concentration of essential amino acids for Nile tilapia and specific aminopeptidases activity in fish cage system. Substrate-SDS-PAGE revealed 12 active proteolytic bands in both systems. However, integrated density (ID) values were higher in the bands of ponds. Specimens of either cage or pond exhibited five bands of amylolytic activity. Fish from cage and pond systems showed the highest values of ID within 31 days of cultivation. In this study, the complexity of digestive functions could be verified for animals maintained under commercial conditions. Some of the assessed enzymes may show adaptations of their activities and/or expression that allow the fish to achieve a more efficient nutrient assimilation.
Aspects of peripheral and central nociception have previously been studied through recording of somatosensory evoked potentials (SEPs) to putative noxious stimuli in specific brain regions in a few freshwater fish species. In the present study, we describe a novel, minimally invasive method for recording SEPs from the central nervous system of the Atlantic cod (Gadus morhua). Cutaneous electric stimulation of the tail in 15 fish elicited SEPs at all stimulus intensities (2, 5, 10 and 20 mA) with quantitative properties corresponding to stimulus intensity. In contrast to previous fish studies, the methodological approach used in Atlantic cod in the current study uncovered a number of additional responses that could originate from multiple brain regions. Several of these responses were specific to stimulation at the highest stimulus intensities, possibly representing qualitative differences in central processing between somatosensory and nociceptive stimuli.
Long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis is an important metabolic pathway in vertebrates, especially fish, considering they are the major source of n-3 LC-PUFA in the human diet. However, most fish have only limited capability for biosynthesis of LC-PUFA. The rabbitfish (Siganus canaliculatus) is able to synthesize LC-PUFA as it has all the key enzyme activities required including Δ6Δ5 Fads2, Δ4 Fads2, Elovl5, and Elovl4. We previously reported a direct interaction between the transcription factor Hnf4α and the promoter regions of Δ4 and Δ6Δ5 Fads2, which suggested that Hnf4α was involved in the transcriptional regulation of fads2 in rabbitfish. For functionally investigating it further, a full-length cDNA of 1736-bp-encoding rabbitfish Hnf4α with 454 amino acids was cloned, which was highly expressed in intestine, followed by liver and eyes. Similar to the expression characteristics of its target genes Δ4 and Δ6Δ5 fads2, levels of hnf4α mRNA in liver and eyes were higher in fish reared at low salinity than those reared in high salinity. After the rabbitfish primary hepatocytes were, respectively, incubated with alverine, benfluorex or BI6015, which were anticipated agonists or antagonist for Hnf4α, the mRNA level of Δ6Δ5 and Δ4 fads2 displayed a similar change tendency with that of hnf4α mRNA. Furthermore, when the mRNA level of hhf4α was knocked down using siRNA, the expression of Δ6Δ5 and Δ4 fads2 also decreased. Together, these data suggest that Hnf4α is involved in the transcriptional regulation of LC-PUFA biosynthesis, specifically, by targeting Δ4 and Δ6Δ5 fads2 in rabbitfish.