Energy metabolism of fish brain

Glucosensing and glucose homeostasis: from fish to mammals

This review is focused on two topics related to glucose in vertebrates. In a first section devoted to glucose homeostasis we describe how glucose levels fluctuate and are regulated in different classes of vertebrates. The detection of these fluctuations is essential for homeostasis and for other physiological processes such as regulation of food intake. The capacity of that detection is known as glucosensing, and the different mechanisms through which it occurs are known as glucosensors. Different glucosensor mechanisms have been demonstrated in different tissues and organs of rodents and humans whereas the information obtained for other vertebrates is scarce. In the second section of the review we describe the present knowledge regarding glucosensor mechanisms in different groups of vertebrates, with special emphasis in fish.

Analysis of glucose metabolism in farmed European sea bass (Dicentrarchus labrax L.) using deuterated water

Glucose metabolism in free-swimming fasted and fed seabass was studied using deuterated water ((2)H(2)O). After transfer to seawater enriched with 4.9% (2)H(2)O for 6-h or for 72-h, positional and mole percent enrichment (MPE) of plasma glucose and water were quantified by (2)H NMR and ESI-MS/MS. Plasma water (2)H-enrichment reached that of seawater within 6h. In both fasted and fed fish, plasma glucose MPE increased asymptotically attaining ~55% of plasma water enrichment by 72 h. The distribution of (2)H-enrichment between the different glucose positions was relatively uniform. The gluconeogenic contribution to glucose that was synthesized during (2)H(2)O administration was estimated from the ratio of position 5 and 2 glucose enrichments. For both fed and fasted fish, gluconeogenesis accounted for 98±1% of the glucose that was produced during the 72-h (2)H(2)O administration period. For fasted fish, gluconeogenic contributions measured after 6h were identical to 72-h values (94±3%). For fed fish, the apparent gluconeogenic contribution at 6-h was significantly lower compared to 72-h (79±5% versus 98±1%, p<0.05). This may reflect a brief augmentation of gluconeogenic flux by glycogenolysis after feeding and/or selective enrichment of plasma glucose position 2 via futile glucose-glucose-6-phosphate cycling.

Acute toxicity of carbamazepine to juvenile rainbow trout (Oncorhynchus mykiss): effects on antioxidant responses, hematological parameters and hepatic EROD

Awareness of residual pharmaceutically active compounds (PhACs) in the aquatic environment is growing as investigations into these pollutants are increasing and analytical detection techniques are improving. However, the toxicological effects of PhACs have not been adequately researched. In this study, the toxic effects of carbamazepine (CBZ), an anticonvulsant drug commonly present in surface and groundwater, was studied in juvenile rainbow trout, Oncorhynchus mykiss, by acute semi-static bioassay. Blood parameters, liver xenobiotic-metabolizing response and tissue antioxidant status were evaluated. Compared to the control group, fish exposed to CBZ (96 h LC50) showed significantly higher Er, Hb, MCHC, monocytes, neutrophil granulocytes and plasma enzymes activity, and significantly lower MCV and lymphocytes. CF and HSI were not significantly different among groups such as hepatic EROD. SOD, CAT, GPx and GR activity was significantly higher in liver of experimental groups, but decreased significantly in brain and gill. In general, antioxidant enzyme activity in intestine and muscle was less evident than in liver. Oxidative stress indices (levels of LPO and CP) were significantly higher in gill and brain, despite a trend to increased values were manifested in the remaining tissues. In short, CBZ-induced stress responses in different tissues were reflected in the oxidant stress indices and hematological parameters. However, before those parameters are used as special biomarkers for monitoring residual pharmaceuticals in aquatic environment, more detailed experiments in laboratory need to be performed in the future.

Oxygen limitation and tissue metabolic potential of the African fish Barbus neumayeri: roles of native habitat and acclimatization

Background

Oxygen availability in aquatic habitats is a major environmental factor influencing the ecology, behaviour, and physiology of fishes. This study evaluates the contribution of source population and hypoxic acclimatization of the African fish, Barbus neumayeri, in determining growth and tissue metabolic enzyme activities. Individuals were collected from two sites differing dramatically in concentration of dissolved oxygen (DO), Rwembaita Swamp (annual average DO 1.35 mgO₂ L^-1) and Inlet Stream West (annual average DO 5.58 mgO₂ L^-1) in Kibale National Park, Uganda, and reciprocally transplanted using a cage experiment in the field, allowing us to maintain individuals under natural conditions of oxygen, food availability, and flow. Fish were maintained under these conditions for four weeks and sampled for growth rate and the activities of phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) in four tissues, liver, heart, brain, and skeletal muscle.

Results

Acclimatization to the low DO site resulted in lower growth rates, lower activities of the aerobic enzyme CCO in heart, and higher activities of the glycolytic enzyme PFK in heart and skeletal muscle. The activity of LDH in liver tissue was correlated with site of origin, being higher in fish collected from a hypoxic habitat, regardless of acclimatization treatment.

Conclusions

Our results suggest that the influence of site of origin and hypoxic acclimatization in determining enzyme activity differs among enzymes and tissues, but both factors contribute to higher glycolytic capacity and lower aerobic capacity in B. neumayeri under naturally-occurring conditions of oxygen limitation.

Multimarker approach analysis in common carp Cyprinus carpio sampled from three freshwater sites

The aim of this study is to assess the response of a multimarker approach in common carp Cyprinus carpio sampled from three Tunisian dam lakes selected according to different environmental and ecological characteristics. Glutathione-S-transferase (GST) activity was analyzed in carp liver and used as a phase II detoxification enzyme, hepatic metallothionein content (MTs) was used as a metallic stress indicator, and cholinesterase activities were analyzed in muscle and brain and used as neurotoxicity biomarker. Micronucleus frequency test (MN) as a genotoxicity marker. GST and MT levels showed an increase in fish from the Bir Mcherga site and a decrease in Sidi Saâd site with respect to fish from Nebhana site. Results showed a strong inhibition of cholinesterase activities in fish from Bir Mcherga and Sidi Saâd sites compared to Nebhana site. Relatively high level of MN is reported specially in fish blood from the Bir Mcherga site.

Rapid changes in plasma cortisol, osmolality, and respiration in response to salinity stress in tilapia (Oreochromis mossambicus)

We elucidated a time course for cortisol release in tilapia as it corresponds to changes in plasma osmolytes and respiration. Following exposure of freshwater (FW) tilapia to 25 per thousand seawater (SW), we measured plasma osmolality, [Na(+)], [K(+)], [Cl(-)], hematocrit, cortisol concentration, oxygen-consumption rate (MO2), and ventilation frequency over 5days and compared them to FW control fish. Cortisol increased rapidly by 3h and remained elevated for 3days. Plasma osmolality, [Na(+)], and [Cl(-)] were elevated at 6-8h, peaked 24h following SW exposure, and then decreased to near-FW levels by 3days. MO2 increased at 24h post-SW exposure relative to FW, while ventilation frequency increased by 3h. Overall, we interpret changes in cortisol as resulting from a change in salinity, in contrast to changes in plasma solute concentrations that could be due to adjustments resulting from the fish's cortisol response as it faces osmoregulatory distress. Increases in oxygen-consumption rate at 24h and ventilation frequency at 3h are likely as a result of the cellular stress response occurring during salinity stress. No significant changes in blood hematocrit were observed, which suggests that tilapia are capable of rapidly counteracting dehydration during acute hyperosmotic stress.

Homeostasis of glucose in the rainbow trout (Oncorhynchus mykiss Walbaum): the role of serotonin

In this study, we evaluated, for the first time, the 5-HT (serotonin)-mediated control of glucose homeostasis in the rainbow trout Oncorhynchus mykiss. Intraperitoneal administration of 5-HT increased plasma levels of glucose, adrenaline and noradrenaline. By contrast, intracerebroventricular administration of 5-HT did not cause any significant variation in plasma levels of glucose. The release of endogenous 5-HT following intraperitoneal administration of d-fenfluramine led to a significant increase in plasma levels of glucose and adrenaline. Intraperitoneal administration of (1) MIAN (a 5-HT2 receptor antagonist) did not block either the hyperglycaemic action or the increase in plasma levels of adrenaline induced by 5-HT, but did block the increase in plasma levels of noradrenaline, and (2) 5-CT (a 5-HT1 agonist) increased the plasma levels of glucose and of adrenaline, without altering those of noradrenaline. Administration of TFMPP (a 5-HT1B agonist) did not increase the plasma levels of glucose, and the hyperglycaemic action of 5-HT was not blocked by antagonists of 5-HT1A (WAY 100635), 5-HT1D (BRL 15572), 5-HT2B (SB 204741) or 5-HT7 (pimozide) receptors. It was demonstrated that, in rainbow trout, peripheral 5-HT, but not brain 5-HT intervenes in the modulation of glucose homeostasis with a hyperglycaemic effect. This effect is associated with the release of adrenaline and activation of 5-HT1-like receptors. As far as could be determined in the present study, these 5-HT1-like receptors are unrelated to either the 5-HT1A, 5-HT1B or 5-HT1D receptor subtypes of mammals. The 5-HT2-type receptors may mediate the release of noradrenaline, but not of adrenaline, and furthermore, do not appear to play an important role in the hyperglycaemic effect exerted by 5-HT.

Acetylcholinesterase activity, lipid peroxidation, and bioaccumulation in silver catfish (Rhamdia quelen) exposed to cadmium

Cadmium is a metal with no biological function in superior organisms and it is very toxic even at very low concentrations. Thus the objective of this study was to verify some toxicological parameters in silver catfish (Rhamdia quelen) exposed to cadmium. In this study, silver catfish was exposed to 0 (control), 0.236, and 0.414 mg L(-1) cadmium for 7 and 14 days, followed by the same periods of recovery. The effects of cadmium on acetylcholinesterase (AChE) activity and metal accumulation in brain and muscle were verified. Thiobarbituric acid-reactive substance (TBARS) formation was evaluated in brain. An increase in TBARS levels was verified after exposure and recovery periods and AChE activity in brain was reduced after 14 days of exposure. These parameters did not return to control values after the recovery period. In muscle AChE was altered during both exposure periods. Alterations in AChE activity may be a good indicator of cadmium contamination in R. quelen.

Synchronization of daily rhythms of locomotor activity and plasma glucose, cortisol and thyroid hormones to feeding in Gilthead seabream (Sparus aurata) under a light-dark cycle

Food availability is far from constant but tends to be cyclic, and fish therefore show a variety of circadian rhythms which can be entrained to feeding time. The aim of this study was to investigate the synchronization to mealtimes of behavioral (locomotor activity), metabolic (glucose) and endocrine (cortisol and thyroid hormones) daily rhythms in gilthead seabream. To this end, fish were reared under a 12:12 LD cycle and fed 1% of their body weight once a day either at mid-light (ML) or at mid-dark (MD) of the LD cycle. Fish synchronized their locomotor activity to the phase in which food was delivered, ML and MD fish displaying 86+/-3% and 81+/-1% of their total daily activity during daytime and nighttime, respectively. Daily variations of blood glucose were strongly synchronized to feeding time in both experimental groups, peaking 8h after the meal. A postprandial cortisol peak was observed in both groups. In fish fed at MD the cortisol values were high during the 8h following feeding, whereas in fish fed at ML cortisol levels returned to basal values within 4h. In addition, MD fish showed a higher average daily cortisol value (24.75+/-2.65 ng/ml) than ML fish (10.30+/-2.18 ng/ml). Feeding time affected the magnitude of daily variations in the thyroid hormones. When the time of feeding was delayed by 12h, a shift of the same magnitude could be observed in the glucose daily rhythm and a dramatic change in the cortisol levels of the ML-fed group compared with results mentioned above. In summary, gilthead seabream synchronized their locomotor activity to the phase when food was provided and showed different degrees of synchronization of their behavioral, metabolic and endocrine rhythms to feeding time. Since these parameters are used to evaluate stress responses and welfare in seabream, their daily rhythm and synchronization to light and feeding time should be taken into account.

Cave colonization without fasting capacities: an example with the fish Astyanax fasciatus mexicanus

Subterranean animals have commonly evolved hypoactivity, hypometabolism and/or the sequential use of energetic reserves to tolerate long fasting periods imposed by the low food levels found in subterranean environments. However, some tropical caves are characterized by a potential high level of nutriments. By using the tropical fish Astyanax fasciatus that presents both populations subterranean (Astyanaxfasciatus mexicanus) and epigean (Astyanaxfasciatus fasciatus) populations, we described behavioral, metabolic and biochemical responses during a long-term fasting period followed by a refeeding period. The results demonstrated that fed hypogean fishes exhibited different energy stores together with a hypometabolism. But, despite drastic decreases in locomotory activity and oxygen consumption during fasting, hypogean fishes consumed significantly more glycogen, triglycerides and proteins during the starvation period than epigean fishes. This lower fasting capacity showed by hypogean fishes is confirmed by the higher activation of the compensatory metabolic pathways (ketogenesis and gluconeogenesis). After the refeeding period, cave fishes did not recover from the "food deprivation" stress, and resume fed levels in glycogen, triglyceride reserves and proteins, in contrast to epigean ones. This study thus demonstrates that starvation adaptations are not necessary for cave life, but are rather correlated to the "energetic state" of each ecosystem, and that troglomorphism is not linked to starvation capacities and thus not to the impoverished food availability.

Failure of ATP supply to match ATP demand: the mechanism of toxicity of the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), used to control sea lamprey (Petromyzon marinus) populations in the Great Lakes

Although the pesticide, 3-trifluoromethyl-4-nitrophenol (TFM), has been extensively used to control invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes, it is surprising that its mechanism(s) of toxicity is unresolved. A better knowledge of the mode of toxicity of this pesticide is needed for predicting and improving the effectiveness of TFM treatments on lamprey, and for risk assessments regarding potential adverse effects on invertebrate and vertebrate non-target organisms. We investigated two hypotheses of TFM toxicity in larval sea lamprey. The first was that TFM interferes with oxidative ATP production by mitochondria, causing rapid depletion of energy stores in vital, metabolically active tissues such as the liver and brain. The second was that TFM toxicity resulted from disruption of gill-ion uptake, adversely affecting ion homeostasis. Exposure of larval sea lamprey to 4.6 m gl(-1) TFM (12-h LC50) caused glycogen concentrations in the brain to decrease by 80% after 12h, suggesting that the animals increased their reliance on glycolysis to generate ATP due to a shortfall in ATP supply. This conclusion was reinforced by a 9-fold increase in brain lactate concentration, a 30% decrease in brain ATP concentration, and an 80% decrease in phosphocreatine (PCr) concentration after 9 and 12h. A more pronounced trend was noted in the liver, where glycogen decreased by 85% and ATP was no longer detected after 9 and 12h. TFM led to marginal changes in whole body Na(+), Cl(-), Ca(2+) and K(+), as well as in plasma Na(+) and Cl(-), which were unlikely to have contributed to toxicity. TFM had no adverse effect on Na(+) uptake rates or gill Na(+)/K(+)-ATPase activity. We conclude that TFM toxicity in the sea lamprey is due to a mismatch between ATP consumption and ATP production rates, leading to a depletion of glycogen in the liver and brain, which ultimately leads to neural arrest and death.

Glucose regulates ghrelin, neuropeptide Y, and the GH/IGF-I axis in the tilapia, Oreochromis mossambicus

In general, a fish's ability to clear glucose is sluggish in relation to mammals, which has lead to the idea that fish are glucose intolerant. It has been reported that circulating glucose levels do fluctuate in response to environmental challenges. Recent reports suggest that glucose may function as a metabolic signal regulating 'glucosensors' in the brain in fish, as has been reported in mammals. The current study was designed to investigate the effect of glucose on ghrelin and neuropeptide Y (NPY) signaling in the brain, and on the growth hormone/insulin-like growth factor-I (GH/IGF-I) in the tilapia, Oreochromis mossambicus. Glucose treatment significantly increased plasma and stomach mRNA levels of ghrelin. In the brain, mRNA levels of the ghrelin receptor (GRLN-R) were significantly reduced, whereas NPY mRNA levels were significantly elevated; suggesting that NPY containing neurons may be a "glucosensor" as reported in mammals. Glucose treatment resulted in changes in the GH/IGF-I axis. Liver mRNA levels of both GH receptors (GHR1 and GHR2) were significantly elevated, whereas liver IGF-I mRNA were unaltered by glucose treatment. No change in plasma or pituitary mRNA levels of GH was observed. Glucose significantly reduced plasma IGF-I levels. These data show that glucose regulates endocrine factors involved in appetite, growth, and possibly energy homeostasis, and suggests that glucose may be acting as a signal of metabolic status in fish.

AMP-activated protein kinase activity during metabolic rate depression in the hypoxic goldfish, Carassius auratus

Cell survival during hypoxia exposure requires a metabolic reorganization to decrease ATP demands to match the reduced capacity for ATP production. We investigated whether AMP-activated protein kinase (AMPK) activity responds to 12 h exposure to severe hypoxia ( approximately 0.3 mg O2 l(-1)) in the anoxia-tolerant goldfish (Carassius auratus). Hypoxia exposure in goldfish was characterized by a strong activation of creatine phosphate hydrolysis and glycolysis in liver and muscle. AMPK activity increased by approximately 5.5-fold in goldfish liver within 0.5 h hypoxia exposure and this increase in activity was temporally associated with an 11-fold increase in [AMP(free)]/[ATP]. No changes in total AMPK protein amount were observed, suggesting that the changes in AMPK activity are due to post-translational phosphorylation of the protein. Hypoxia exposure had no effect on the expression of two identified AMPK alpha-subunit isoforms and caused an approximately 50% decrease in the mRNA levels of AMPK beta-subunit isoform. Changes in AMPK activity in the liver were associated with an increase in percentage phosphorylation of a well-characterized target of AMPK, eukaryotic elongation factor-2 (eEF2), and decreases in protein synthesis rates measured in liver cell-free extracts. No activation of AMPK was observed in muscle, brain, heart or gill during the 12 h hypoxia exposure suggesting a tissue-specific regulation of AMPK possibly related to a lack of change in cellular [AMP(free)]/[ATP] as observed in muscle.

Altered dietary carbohydrates significantly affect gene expression of the major glucosensing components in Brockmann bodies and hypothalamus of rainbow trout

Carnivorous fish have a limited capacity to utilize dietary carbohydrates even though glucosensing components exist in the hypothalamus and Brockmann bodies. Therefore, we fed trout for 10 days with two experimental diets containing a high level of carbohydrates (20%) or a carbohydrate-free level (<0.3%) to test the capacity of dietary carbohydrates to regulate gene expression of glucosensing components. Fish were fed and killed 1, 6, and 24 h after the meal to analyze plasma glucose levels, glucosensing-related biochemical parameters, and gene expression of the major components of the glucosensing system in the hypothalamus and Brockmann bodies. Glucose facilitative transporter type 2 and glucokinase gene expression were confirmed by real-time PCR data and two new components of the glucosensing mechanism, Kir6.-like and sulfonylurea receptor-like, were detected for the first time in fish in both tissues. In addition, a clear adaptation to dietary carbohydrates was found in trout Brockmann bodies, based on increased gene expression of major components of the system as well as enhanced glucokinase activities and glycogen levels. In contrast, in the hypothalamus, only glucokinase gene expression and activity showed a response to dietary carbohydrates, supporting the key role of that enzyme in glucosensing mechanism. Finally, a differential postprandial profile was found between tissues regarding the glucosensing potential, since the hypothalamus seems to respond to hyperglycemia earlier than the Brockmann bodies, whose response took place later. Altogether, these data describe for the first time in fish a complete response of major glucosensing components to dietary carbohydrates in trout hypothalamus and Brockmann bodies, supporting an efficient adaptation of both tissues to those dietary components.

Tributyltin exposure causes brain damage in Sebastiscus marmoratus

Tributyltin (TBT) is a ubiquitous marine environmental contaminant characterized primarily by its reproductive toxicity. However, the neurotoxic effect of TBT has not been extensively described, especially in fishes which have a high number of species in the marine environment. This study was conducted to investigate the neurotoxic effects of TBT at environmental levels (1, 10, and 100ngl(-1)) on female Sebastiscus marmoratus. The results showed that TBT exposure induced apoptosis in brain cells of three regions including the pallial areas of the telencephalon, the granular layer of the optic tectum, and the cerebellum. In addition, the increase of reactive oxygen species and nitric oxide levels, and the decrease of Na+/K+-ATPase activity were found in the brain. The results strongly indicated neurotoxicity of TBT to fishes. According to the regions in which apoptosis was found in the brain, TBT exposure might influence the schooling, sensory and motorial functions of fishes.

Effect of starvation on transcriptomes of brain and liver in adult female zebrafish (Danio rerio)

We used microarray and quantitative real-time PCR (qRT-PCR) analyses in adult female zebrafish (Danio rerio) to identify metabolic pathways regulated by starvation in the liver and brain. The transcriptome of whole zebrafish brain showed little response to 21 days of starvation. Only agouti-related protein 1 (agrp1) significantly responded, with increased expression in brains of starved fish. In contrast, a 21-day period of starvation significantly downregulated 466 and upregulated 108 transcripts in the liver, indicating an overall decrease in metabolic activity, reduced lipid metabolism, protein biosynthesis, proteolysis, and cellular respiration, and increased gluconeogenesis. Starvation also regulated expression of many components of the unfolded protein response, the first such report in a species other than yeast (Saccharomyces cerevisiae) and mice (Mus musculus). The response of the zebrafish hepatic transcriptome to starvation was strikingly similar to that of rainbow trout (Oncorhynchus mykiss) and less similar to mouse, while the response of common carp (Cyprinus carpio) differed considerably from the other three species.

Dietary carbohydrates induce changes in glucosensing capacity and food intake of rainbow trout

We hypothesize that variations in dietary carbohydrate levels produce changes in glucosensor parameters in previously characterized glucosensing areas (hypothalamus and hindbrain) related with the regulation of food intake of a carnivorous fish species like rainbow trout. Therefore, we fed trout with standard, carbohydrate-free (CF) or high-carbohydrate (HC) diets for 10 days to assess changes in glucosensing system and food intake. Fish fed CF diet displayed hypoglycemia and increased food intake. Fish fed a HC diet displayed hyperglycemia and decreased food intake. Changes in food intake due to dietary carbohydrates were accompanied in hypothalamus and hindbrain of fish fed with HC diet by changes in parameters involved in glucosensing, such as increased glucose, glucose 6-phosphate, and glycogen levels and increased glucokinase (GK), glycogen synthase, and pyruvate kinase activities as well as increased GK and GLUT2 expression. All those results address for the first time in fish, despite the relative intolerance to glucose of carnivorous species, that dietary carbohydrates are important regulators of the glucosensing system in carnivorous fish, suggesting that the information generated by this system can be associated with the changes observed in food intake.

Changes in food intake and glucosensing function of hypothalamus and hindbrain in rainbow trout subjected to hyperglycemic or hypoglycemic conditions

To evaluate the possible role of glucose in the control of food intake (FI) in fish and the involvement of glucosensing system in that role, we have subjected rainbow trout (via intraperitoneal injections) to control, hyperglycemic (500 mg kg(-1) glucose body mass) or hypoglycemic (4 mg kg(-1) bovine insulin) conditions for 10 days. The experimental design was appropriate since hypoglycemia and hyperglycemia were observed the first 5 days after treatment and changes observed in metabolic parameters in liver were similar to those of fish literature. Hyperglycemic conditions elicited small changes in FI accompanied by increased glucose and glycogen levels, glucokinase (GK) activity and glycolytic potential in hypothalamus and hindbrain. In contrast, hypoglycemic conditions elicited a marked increase in FI accompanied by decreased glucose and glycogen levels and GK activity in the same brain regions whereas both regions displayed different responses in glycolytic potential. These results allow us to hypothesize that, despite the relative intolerance to glucose of carnivorous fish, changes in plasma glucose levels in rainbow trout detected by glucosensing areas in brain regions (hypothalamus and hindbrain) are integrated in those or near areas eliciting a response in FI, which was more important under hypoglycemic than under hyperglycemic conditions.

Identification and analysis of a prepro-chicken gonadotropin releasing hormone II (preprocGnRH-II) precursor in the Asian seabass, Lates calcarifer, based on an EST-based assessment of its brain transcriptome

Using a novel library of 5637 expressed sequence tags (ESTs) from the brain tissue of the Asian seabass (Lates calcarifer), we first characterized the brain transcriptome for this economically important species. The ESTs generated from the brain of L. calcarifer yielded 2410 unique transcripts (UTs) which comprise of 982 consensi and 1428 singletons. Based on database similarity, 1005 UTs (41.7%) can be assigned putative functions and were grouped into 12 functional categories related to the brain function. Amongst others, we have identified genes that are putatively involved in energy metabolism, ion pumps and channels, synapse related genes, neurotransmitter and its receptors, stress induced genes and hormone related genes. Subsequently we selected a putative preprocGnRH-II precursor for further characterization. The complete cDNA sequence of the gene obtained was found to code for an 85-amino acid polypeptide that significantly matched preprocGnRH-II precursor sequences from other vertebrates, and possesses structural characteristics that are similar to that of other species, consisting of a signal peptide (23 residues), a GnRH decapeptide (10 residues), an amidation/proteolytic-processing signal (glycine-lysine-argine) and a GnRH associated peptide (GAP) (49 residues). Phylogenetic analysis showed that this putative L. calcarifer preprocGnRH-II sequence is a member of the subcohort Euteleostei and divergent from the sequences of the subcohort Otocephalan. These findings provide compelling evidence that the putative L. calcarifer preprocGnRH-II precursor obtained in this study is orthologous to that of other vertebrates. The functional prediction of this preprocGnRH-II precursor sequence through in silico analyses emphasizes the effectiveness of the EST approach in gene identification in L. calcarifer.

Induction of hepatic enzymes and oxidative stress in Chinese rare minnow (Gobiocypris rarus) exposed to waterborne hexabromocyclododecane (HBCDD)

The objective of this study was to evaluate the sub-lethal toxicity of hexabromocyclododecane (HBCDD) in fish. Adult Chinese rare minnows as in vivo models were exposed to waterborne HBCDD from 1 to 500 microg/l for 14, 28 and 42 days. Hepatic CYP1A1 (ethoxyresorufin-O-deethylase, EROD) and CYP2B1 (pentaoxyresorufin-O-depentylase, PROD) activities were measured. At the same time, molecular biomarkers of oxidative stress were also assayed in the brain, including reactive oxygen species (ROS), lipid peroxidation products (thiobarbituric acid-reactive substances, TBARS), DNA damage and protein carbonyl, as well as superoxide dismutase (SOD) activity and glutathione (GSH) content. DNA damage was evaluated using the Comet assay on erythrocytes. Besides, the content of HBCDD in whole fish was determined after 42 days exposure. The results show that HBCDD could induce EROD and PROD at 500 microg/l after 28 days exposure, and at 100 to 500 microg/l after 42 days exposure (P<0.05), respectively. ROS formation in fish brain was observed to be increased in both time- and dose-dependent manner due to HBCDD exposure. The significant increases in TBARS and protein carbonyl contents occurred in fish brain after 28 and 42 days exposure (P<0.05). Significant DNA damage in erythrocytes by Comet assay was also found in the 100-500 microg/l exposure groups (P<0.05) after 42 days exposure. Moreover, significant depletion in brain GSH content occurred in all treated groups (P<0.05) and apparent inhibition in SOD activity in brain was observed in the groups of 10-500 microg/l concentrations during 42 days exposure. The results demonstrate that increasing duration of HBCDD exposure induced EROD and PROD activities, caused excess ROS formation, finally resulted in oxidative damage to lipids, proteins and DNA and decreased antioxidant capacities in fish. Chemical analysis of HBCDD in whole fish showed accumulation up to 654 microg/g wet weight.

In vitro evidences for glucosensing capacity and mechanisms in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout

We aimed to support in vitro the glucosensing capacity observed in vivo in rainbow trout hypothalamus, hindbrain, and Brockmann bodies (BB) and to obtain preliminary evidence of the mechanisms involved. The response of parameters involved in the glucosensing capacity [hexokinase, hexokinase IV (glucokinase), and pyruvate kinase activities and glucose and glycogen levels] was assessed in these tissues incubated for 1 h with 2, 4, or 8 mM d-glucose alone (control) or with specific agonists/inhibitors of the steps involved in glucosensing capacity in mammals. These agents were a competitor for glucose phosphorylation (15 mM mannose), sulfonylurea receptor-1 effectors (500 μM tolbutamide or diazoxide), glycolytic intermediates (15 mM glycerol, lactate, or pyruvate), and inhibitors of glucose transport (10 μM cytochalasin B), glycolysis [20 mM 2-deoxy-d-glucose (2-DG)], and L-type calcium channel (1 μM nifedipine). Control incubations of the three tissues displayed increased glucose and glycogen levels and glucokinase activities in response to increased medium glucose, thus supporting our previous in vivo studies. Furthermore, critical components of the glucosensing mammalian machinery are apparently functioning in the three tissues. The responses in brain regions to all substances tested (except 2-DG and nifedipine) were similar to those observed in mammals, suggesting a similar glucosensing machinery. In contrast, in BB, only the effects of 2-DG, lactate, pyruvate, diazoxide, and nifedipine were similar to those of mammalian β-cells, suggesting that some of the components of the piscine glucosensing model are different than those of mammals. Such differences may relate to the importance of amino acids rather than glucose signaling in the trout BB.

Toxicity of organophosphates on morphology and locomotor behavior in brine shrimp, Artemia salina

The acute toxicity and hatching success of four organophosphorus insecticides--acephate (ACEP), chlorpyrifos (CPP), monocrotophos (MCP), and profenofos (PF)--was studied in a short-term bioassay using brine shrimp, Artemia salina. Fifty percent hatchability inhibition concentration and median lethal concentration (LC(50)) values were calculated after probit transformation of the resulting data. Among the insecticides tested, CPP is found to be the most toxic and also to inhibit hatching success of A. salina cysts in a concentration-dependent manner. In addition, the effect of these pesticides on locomotor behavior (swimming speed) and morphologic differences were studied in LC(50)-exposed nauplii after 24 hours. The in vivo effect of these insecticides on acetylcholinesterase (Enzyme commission number (EC 3.1.1.7) activity was also determined in LC(50)-exposed nauplii after 24 hours. Maximum percent decrease in their swimming speed and significant morphologic alterations were noticed in CPP-exposed brine shrimps. The order of toxicity was CPP > PF > MCP > ACEP in all the parameters studied.

Evidence for the presence of a glucosensor in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout

The aim of this study was to evaluate the existence of a glucosensor in different regions of the brain and in the Brockmann bodies (BB) of the rainbow trout, Oncorhynchus mykiss. Five groups ( n = 12) of trout were injected intraperitoneally with saline alone (control) or saline-containing bovine glucagon (100 μg/kg), bovine insulin (4 mg/kg), 2-deoxy-d-glucose (100 mg/kg), or d-glucose (500 mg/kg) to promote hyperglycemia (glucagon, d-glucose, 2-deoxy-d-glucose) or hypoglycemia (insulin). Six hours after injection, samples from four brain regions (hypothalamus, telencephalon, hindbrain, and midbrain) and the entire BB were taken. Our results demonstrate within the BB and both the hypothalamus and hindbrain a metabolic response different to that observed in other tissues (midbrain, telencephalon) but similar to that described in tissues known to be glucosensors in mammals. The metabolic responses of these areas to changes in plasma glycemia were characterized by parallel changes in GLUT-2 expression, hexokinase-IV, or glucokinase activity and expression, glycolytic potential, and levels of glycogen and glucose. These changes are similar to those reported in mammalian pancreatic β-cells and glucose-excited (GE) neurons, two cell types containing glucosensors. This study provides evidence for the presence of glucosensors responsive to hyper- and hypoglycemia in rainbow trout BB, hypothalamus, and hindbrain.

Zebrafish Slc5a12 Encodes an Electroneutral Sodium Monocarboxylate Transporter (SMCTn)

We have identified and characterized two different sodium-coupled monocarboxylate cotransporters (SMCT) from zebrafish (Danio rerio), electrogenic (zSMCTe) and electroneutral (zSMCTn). zSMCTn is the 12th member of the zebrafish Slc5 gene family (zSlc5a12). Both zSMCT sequences have approximately 50% homology to human SLC5A8 (hSMCT). Transport function and kinetics were measured in Xenopus oocytes injected with zSMCT cRNAs by measurement of intracellular Na(+) concentration ([Na(+)](i)) and membrane potential. Both zSMCTs oocytes increased [Na(+)](i) with addition of monocarboxylates (MC) such as lactate, pyruvate, nicotinate, and butyrate. By using two electrode voltage clamp experiments, we measured currents elicited from zSMCTe after MC addition. MC-elicited currents from zSMCTe were similar to hSMCT currents. In contrast, we found no significant MC-elicited current in either zSMCTn or control oocytes. Kinetic data show that zSMCTe has a higher affinity for lactate, nicotinate, and pyruvate (K(m)(L-lactate) = 0.17 +/- 0.02 mM, K(m)(nicotinate) = 0.54 +/- 0.12 mM at -150 mV) than zSMCTn (K(m)(L-lactate) = 1.81 +/- 0.19 mM, K(m)(nicotinate) = 23.68 +/- 4.88 mM). In situ hybridization showed that 1-, 3-, and 5-day-old zebrafish embryos abundantly express both zSMCTs in the brain, eyes, intestine, and kidney. Within the kidney, zSMCTn mRNA is expressed in pronephric tubules, whereas zSMCTe mRNA is more distal in pronephric ducts. zSMCTn is expressed in exocrine pancreas, but zSMCTe is not. Roles for Na(+)-coupled monocarboxylate cotransporters have not been described for the brain or eye. In summary, zSMCTe is the zebrafish SLC5A8 ortholog, and zSMCTn is a novel, electroneutral SMCT (zSlc5a12). Slc5a12 in higher vertebrates is likely responsible for the electroneutral Na(+)/lactate cotransport reported in mammalian and amphibian kidneys.

Daily changes in parameters of energy metabolism in brain of rainbow trout: Dependence on feeding

We assessed the daily patterns of parameters involved in energy metabolism in plasma and brain of rainbow trout. Where daily rhythms were found, we analyzed the potential influence of feeding. Immature rainbow trout were randomly distributed in 3 groups: fish fed for 7 days, fish fasted for 7 days, and fish fasted for 7 days and refed for 4 days. On sampling day, fish of fed and refed groups were fed at 11.00 h, and all fish were sampled from each treatment group using the following time schedule: 14.00, 18.00, 21.00, 00.00, 04.00, 07.00, 10.00 and 14.00 h. The results obtained from metabolic parameters assessed in plasma and brain can be grouped into three different categories, such as (i) those displaying no 24 h changes in fed fish such as plasma lactate, protein or acetoacetate levels, as well as brain amino acid and protein levels, and lowKm(glucose) hexokinase, and aspartate aminotransferase activities, (ii) those displaying 24 h changes that were apparently dependent on feeding since they disappeared in fasted fish such as the case of plasma cortisol, glucose and triglyceride levels, as well as brain glycogen, glucose, and lactate levels, and pyruvate kinase and hexokinase IV activities, and (iii) those parameters displaying 24 h changes apparently not dependent on feeding such as plasma amino acids, brain acetoacetate levels as well as several enzyme activities measured in brain such as glucose 6-phosphate dehydrogenase, alpha-glycerophosphate dehydrogenase, glutamate dehydrogenase, and lactate dehydrogenase-oxidase. In general, 24 h changes dependent on feeding indicate an increased use of glucose in brain several hours post-feeding whereas those changes not dependent on feeding were characterized by reduced levels/activity at the night period suggesting a metabolic depression in brain during darkness.

The impact of hypoxia on in vivo glucose uptake in a hypoglycemic fish,Myoxocephalus scorpius

The mechanisms controlling carbohydrate utilization in teleost fish are poorly understood, particularly in the heart. Tissue glucose uptake and cardiovascular characteristics were measured in the short-horned sculpin, Myoxocephalus scorpius, a species exhibiting low blood glucose levels, during normoxia and hypoxia to assess the role of adenosine receptors in the control of glucose uptake and anaerobic metabolism. As expected, hypoxia exposure (300 min at 2 mg/l dissolved oxygen) resulted in a bradycardia and plasma lactate accumulation, but glucose uptake rates did not change in heart, brain, gill, spleen, and white muscle. Plasma glucose-to-intracellular glucose ratios indicated that glucose uptake was the rate-limiting step in glucose utilization. The majority of intracellular glucose was unphosphorylated, however, suggesting that hexokinase is also important in controlling the tissue glucose gradient. During hypoxia, the cholinergic blocker atropine resulted in tachycardia but did not significantly change tissue glucose uptake rates or heart and brain adenosine levels. In contrast, the combined treatment of atropine and an adenosine receptor blocker [8-( p-sulfophenyl)theophylline] during hypoxia increased heart glucose uptake to levels fivefold higher than normoxic fish, with no additive effects on cardiovascular parameters. Significant tissue lactate accumulation was observed in this group of fish, signifying that adenosine receptors may depress anaerobic metabolism, even though tissue adenosine accumulation was absent during hypoxia. White muscle accumulated glucose during normoxia, suggesting the presence of gluconeogenic pathways or active uptake mechanisms not previously described in this tissue.

Insulin expression in the brain and pituitary cells of tilapia (Oreochromis niloticus)

While the presence of immunoreactive insulin in the central nervous system of many vertebrate species is well known, the origin of brain insulin is still debated. In this study, we applied RT-PCR, quantitative RT-PCR (qRT-PCR), and Northern hybridization to examine expression of the insulin gene in different tissues of an adult teleost fish, the Nile Tilapia (Oreochromis niloticus). We found that the insulin gene is transcribed at a high level in Brockmann bodies (pancreatic islet organs) and at a low level in the brain and pituitary gland. In the brain, insulin transcripts were detected in all areas by qRT-PCR and in situ hybridization. The highest level of insulin mRNA was found in the hypothalamus. The level of insulin transcription in the pituitary gland was 6-fold higher than that in the brain and 4.6-fold higher than that in the hypothalamus. Furthermore, insulin mRNA and immunoreactive insulin-like protein was detected in the pituitary gland using in situ hybridization, immunohistochemistry, and Western blot analysis. Our results indicate that in adult tilapia insulin expression is not restricted to the endocrine pancreatic cells, but also occurs in endocrine cells of the pituitary gland and in the neuronal cells of the brain, suggesting that the brain/pituitary gland might represent extrapancreatic origin of insulin production.

Effects of long-term hypoxia on enzymes of carbohydrate metabolism in the Gulf killifish, Fundulus grandis

The goal of the current study was to generate a comprehensive, multi-tissue perspective of the effects of chronic hypoxic exposure on carbohydrate metabolism in the Gulf killifish Fundulus grandis. Fish were held at approximately 1.3 mg l(-1) dissolved oxygen (approximately 3.6 kPa) for 4 weeks, after which maximal activities were measured for all glycolytic enzymes in four tissues (white skeletal muscle, liver, heart and brain), as well as for enzymes of glycogen metabolism (in muscle and liver) and gluconeogenesis (in liver). The specific activities of enzymes of glycolysis and glycogen metabolism were strongly suppressed by hypoxia in white skeletal muscle, which may reflect decreased energy demand in this tissue during chronic hypoxia. In contrast, several enzyme specific activities were higher in liver tissue after hypoxic exposure, suggesting increased capacity for carbohydrate metabolism. Hypoxic exposure affected fewer enzymes in heart and brain than in skeletal muscle and liver, and the changes were smaller in magnitude, perhaps due to preferential perfusion of heart and brain during hypoxia. The specific activities of some gluconeogenic enzymes increased in liver during long-term hypoxic exposure, which may be coupled to increased protein catabolism in skeletal muscle. These results demonstrate that when intact fish are subjected to prolonged hypoxia, enzyme activities respond in a tissue-specific fashion reflecting the balance of energetic demands, metabolic role and oxygen supply of particular tissues. Furthermore, within glycolysis, the effects of hypoxia varied among enzymes, rather than being uniformly distributed among pathway enzymes.

Biochemical alterations in euryhaline fish, Oreochromis mossambicus exposed to sub-lethal concentrations of an organophosphorus insecticide, monocrotophos

The euryhaline fish, Oreochromis mossambicus was exposed to sub-lethal concentration (1.15 mg l(-1)) of a organophosphorus insecticide, monocrotophos (MCP) for 30 days and allowed to recover for seven days. Alanine aminotransferase (ALAT), aspartate aminotransferase (AAT), acid phosphatase (AcP), alkaline phosphatase (ALP), glycogen, lactate dehydrogenase (LDH), Reduced glutathione (GSH), gluthathione-S-transferase (GST) and acetylcholinesterase (AChE), were assayed in plasma and different tissues at regular intervals of day -3, -7, -15, -30 and after recovery period of seven days. The ALAT and AAT activities were increased in plasma and kidney, where as liver and gill showed decrease. Increase in AcP and ALP activities were observed in plasma, gill and kidney, and reduction of 42% and 50% was observed in liver. Glycogen was depleted in plasma, liver and gill indicates of typical stress related response of the fish with pesticide. LDH activity was decreased in liver and muscle, indicating tissue damage and muscular harm, but a significant increase in LDH activity in gill and brain was observed. Depletion in GSH activity was observed in all the tissues, there by enhancing the lipid peroxidation resulting in cell damage. The induction in hepatic GST levels indicates the protection against the toxicity of xenobiotic-induced lipid peroxidation. There was a significant recovery in all the above biochemical parameters studied in plasma and different tissues, after seven days recovery period. These results revealed that MCP affects the intermediary metabolism of O. mossambicus and that the assayed enzymes can work as good biomarkers of organophosphorus contamination.

Effects of hexachlorobenzene on antioxidant status of liver and brain of common carp (Cyprinus carpio)

Hexachlorobenzene (HCB)-induced oxidative damages have been published in rats while the effects have not yet been reported in fishes. Juvenile common carps (Cyprinus carpio) were exposed to waterborne HCB from 2 to 200 microg l-1 for 5, 10 or 20 days. Liver and brain were analyzed for various parameters of oxidative stress. There were no significant changes of glutathione (GSH) content and superoxide dismutase (SOD) activity in liver after 5 or 10 days exposure, whereas obvious drops were observed at higher concentrations after 20 days exposure. Significant decreases of GSH content and SOD activity in brain were found during all the exposure days. In brain, HCB also significantly elevated the contents of reactive oxygen species (ROS), thiobarbituric acid- reactive substances (TBARS, as an indicator of lipid peroxidation products), glutathione disulfide (GSSG), and activities of nitric oxide synthase (NOS), glutathione peroxidase (GPx), and glutathione reductase (GR), and inhibited activities of acetylcholinesterase (AchE) and glutathione S-transferase (GST). The results clearly demonstrated that environmentally possible level of HCB could result in oxidative stress in fish and brain was a sensitive target organ of HCB toxicity.

Osmoregulatory and metabolic changes in the gilthead sea bream Sparus auratus after arginine vasotocin (AVT) treatment

The influence of arginine vasotocin (AVT) on osmoregulation and metabolism in gilthead sea bream Sparus auratus was evaluated by two experimental approaches. In the first, seawater (SW, 36 ppt)-acclimatized fish were injected intraperitoneally with vehicle (vegetable oil) or two doses of AVT (0.5 and 1 microg/g body weight). Twenty-four hours later, eight fish from each group were sampled; the remaining fish were transferred to low saline water (LSW, 6 ppt, hypoosmotic test), SW (transfer control), and hypersaline water (HSW, 55 ppt, hyperosmotic test). After another 24h (48-h post-injection), fish were sampled. The only significant effect observed was the increase of sodium levels in AVT-treated fish transferred to HSW. In the second experiment, fish were injected intraperitoneally with slow-release vegetable oil implants (mixture 1:1 of coconut oil and seeds oil) alone or containing AVT (1 microg/g body weight). After 3 days, eight fish from each group were sampled; the remaining fish were transferred to LSW, SW, and HSW as above, and sampled 3 days later (i.e. 6 days post-injection). In the AVT-treated group transferred from SW to SW, a significant increase vs. control was observed in gill Na(+),K(+)-ATPase activity. Kidney Na(+),K(+)-ATPase activity decreased in the AVT-treated group transferred to LSW and no changes were observed in the other groups. These osmoregulatory changes suggest a role for AVT during hyperosmotic acclimation based on changes displayed by gill Na(+),K(+)-ATPase activity. AVT treatment increased plasma cortisol levels in fish transferred to LSW and HSW. In addition, AVT treatment affected parameters of carbohydrate, lipid, amino acid, and lactate metabolism in plasma and tissues (gills, kidney, liver, and brain). The most relevant effects were the increased potential of liver for glycogen mobilization and glucose release resulting in increased plasma levels of glucose in AVT-treated fish transferred to LSW and HSW. These changes may be related to the energy repartitioning process occurring during osmotic adaptation of S. auratus to extreme environmental salinities and could be mediated by increased levels of cortisol in plasma.

Time course of osmoregulatory and metabolic changes during osmotic acclimation in Sparus auratus

Changes in different osmoregulatory and metabolic parameters over time were assessed in gills, kidney, liver and brain of gilthead sea bream Sparus auratus transferred either from seawater (SW, 38 p.p.t.) to hypersaline water (HSW, 55 p.p.t.) or from SW to low salinity water (LSW, 6 p.p.t.) for 14 days. Changes displayed by osmoregulatory parameters revealed two stages during hyperosmotic and hypo-osmotic acclimation: (i) an adaptive period during the first days of acclimation (1-3 days), with important changes in these parameters, and (ii) a chronic regulatory period (after 3 days of transfer) where osmotic parameters reached homeostasis. From a metabolic point of view, two clear phases can also be distinguished during acclimation to hyperosmotic or hypo-osmotic conditions. The first one coincides with the adaptive period and is characterized by enhanced levels of plasma metabolites (glucose, lactate, triglycerides and protein), and use of these metabolites by different tissues in processes directly or indirectly involved in osmoregulatory work. The second stage coincides with the chronic regulatory period observed for the osmoregulatory parameters and is metabolically characterized in HSW-transferred fish by lower energy expenditure and a readjustment of metabolic parameters to levels returning to normality, indicative of reduced osmoregulatory work in this stage. In LSW-transferred fish, major changes in the second stage include: (i) decreased glycolytic potential, capacity for exporting glucose and potential for amino acid catabolism in liver; (ii) enhanced use of exogenous glucose through glycolysis, pentose phosphate and glycogenesis in gills; (iii) increased glycolytic potential in kidney; and (iv) increased glycogenolytic potential and capacity for use of exogenous glucose in brain.

Growth hormone and prolactin actions on osmoregulation and energy metabolism of gilthead sea bream (Sparus auratus)

The gilthead sea bream (Sparus auratus) is an euryhaline fish where prolactin (PRL) and growth hormone (GH) play a role in the adaptation to different environmental salinities. To find out the role of these pituitary hormones in osmoregulation and energy metabolism, fish were implanted with slow release implants of ovine GH (oGH, 5 microg g(-1) body mass) or ovine prolactin (oPRL, 5 microg g(-1) body mass), and sampled 7 days after the start of the treatment. GH increased branchial Na(+),K(+)-ATPase activity and decreased sodium levels in line with its predicted hypoosmoregulatory action. GH had metabolic effects as indicated by lowered plasma protein and lactate levels, while glucose, triglycerides and plasma cortisol levels were not affected. Also, GH changed liver glucose and lipid metabolism, stimulated branchial and renal glucose metabolism and glycolytic activity, and enhanced glycogenolysis in brain. PRL induced hypernatremia. Furthermore, this hormone decreased liver lipid oxidation potential, and increased glucose availability in kidney and brain. Both hormones have opposite osmoregulatory effects and different metabolic effects. These metabolic changes may support a role for both hormones in the control of energy metabolism in fish that could be related to the metabolic changes occurring during osmotic acclimation.

Glucokinase and hexokinase expression and activities in rainbow trout tissues: changes with food deprivation and refeeding

The expression and activities of glucokinase (GK) and hexokinase (HK) were assessed in different tissues of rainbow trout (Oncorhynchus mykiss) under different feeding conditions (fed, fasted for 14 days, and refed for 7 days). Two different HK-I cDNAs were identified with different tissue distributions. One transcript named heart or H-HK-I was observed in the four brain regions assessed, white muscle, kidney, and gills but not in liver or erythrocytes. A second transcript named liver or L-HK-I was found in all tissues surveyed. GK mRNA was identified only in liver and the four brain regions. GK expression was altered by feeding conditions, especially in liver and hypothalamus where food deprivation decreased and re-feeding increased expression; changes in expression reflected activity changes and changes in tissue glycogen levels. In contrast, feeding conditions did not alter expression of either HK-I transcript but did alter tissue HK activities. The reduced phosphorylating capacity noted with food deprivation correlates primarily with changes in tissue HK, whereas increased capacity, as with refeeding, was associated with changes in GK; these changes fit with the different K(m) values of the GK and HK enzymes. These results provide evidence for the hypothalamus acting as a glucosensor in trout, as hyperglycemia produced increased GK expression and activity, as well as increased glycogen levels. Thus, even though trout use glucose poorly, none of the parameters tested here relate to this inability to use glucose and suggest that, at least, rainbow trout, if given an appropriate carbohydrate diet, could metabolically adjust to such a diet.

Effects of malathion and cadmium on acetylcholinesterase activity and metallothionein levels in the fish Seriola dumerilli

The potential use of acetylcholinesterase (AChE) and metallothionein (MT) responses as biomarker of organophosphorous (OPs) and trace metal were assessed in fish Seriola dumerilli exposed to 0, 4, 6 mg/kg of malathion for 2, 7 and 13 days, and to 0, 50, 100, 250 mug/kg of Cd for 2 days. Brain AChE was significantly inhibited after 2 and 7 days of malathion exposure, in a dose-response manner, but no inhibition was observed after 13 days of exposure. When exposed to Cd for 2 days, S. dumerelli presented an increase in AChE activity at a concentration of 50 mug/kg, but a strong and dose-dependent AChE inhibition at 100 and 250 mug/kg. Cd treatment also caused a rapid increase in MTs concentration in liver, even at the lower concentration. Our experiments indicate that the measurement of hepatic MT concentration and brain AChE activity in S. dumerilli would be useful biomarkers of OP and Cd exposure and/or effects.

Expression and function of alpha-adrenoceptors in zebrafish: drug effects, mRNA and receptor distributions

The alpha2-adrenoceptors are G-protein-coupled receptors that mediate many of the physiological effects of norepinephrine and epinephrine. Mammals have three subtypes of alpha2-adrenoceptors, alpha2A, alpha2B and alpha2C. Zebrafish, a teleost fish used widely as a model organism, has five distinct alpha2-adrenoceptor genes. The zebrafish has emerged as a powerful tool to study development and genetics, with many mutations causing diseases reminiscent of human diseases. Three of the zebrafish adra2 genes code for orthologues of the mammalian alpha2-adrenoceptors, while two genes code for alpha2Da- and alpha2Db- adrenoceptors, representing a duplicated, fourth alpha2-adrenoceptor subtype. The three different mammalian alpha2-adrenoceptor subtypes have distinct expression patterns in different organs and tissues, and mediate different physiological functions. The zebrafish alpha2-adrenergic system, with five different alpha2-adrenoceptors, appears more complicated. In order to deduce the physiological functions of the zebrafish alpha2-adrenoceptors, we localized the expression of the five different alpha2-adrenoceptor subtypes using RT-PCR, mRNA in situ hybridization, and receptor autoradiography using the radiolabelled alpha2-adrenoceptor antagonist [ethyl-3H]RS-79948-197. Localization of the alpha2A-, alpha2B- and alpha2C-adrenoceptors in zebrafish shows marked conservation when compared with mammals. The zebrafish alpha2A, alpha2Da, and alpha2Db each partially follow the distribution pattern of the mammalian alpha2A: a possible indication of subfunction partitioning between these subtypes. The alpha2-adrenergic system is functional in zebrafish also in vivo, as demonstrated by marked locomotor inhibition, similarly to mammals, and lightening of skin colour induced by the specific alpha2-adrenoceptor agonist, dexmedetomidine. Both effects were antagonized by the specific alpha2-adrenoceptor antagonist atipamezole.

Actions of growth hormone on carbohydrate metabolism and osmoregulation of rainbow trout (Oncorhynchus mykiss)

Rainbow trout Oncorhynchus mykiss were injected intraperitoneally with slow-release implants of vegetable oil alone or containing ovine growth hormone (oGH) (2 and 5 microgg(-1) body weight), and sampled after 5 days to assess the simultaneous effects of GH on both osmoregulation and carbohydrate metabolism. An enhanced hypoosmoregulatory capacity of oGH-implanted fish is suggested by the increase observed in gill Na+,K+-ATPase activity, and the decrease observed in plasma ion concentration (Na+ and Cl-) and osmolality. GH treatment also elicited increased plasma glucose levels and metabolic changes in liver, gills, kidney, and brain. Major metabolic changes elicited by GH treatment included (1) decreased glycolytic potential and capacity for exporting glucose in liver, (2) enhanced glycogenolytic potential and capacity for use of exogenous glucose in gills and kidney, as well as increased glycolytic capacity in the later tissue, and (3) enhanced glycogenolytic and glycolytic capacities in brain. These metabolic changes elicited by GH treatment support a role for GH in the control of carbohydrate metabolism in salmonids that could be related either to the metabolic changes occurring during osmotic acclimation in nature (a process in which changes in GH levels and carbohydrate metabolism have both been reported) or to metabolic changes associated with growth.

Interactive effects of high stocking density and food deprivation on carbohydrate metabolism in several tissues of gilthead sea breamSparus auratus

The influence of high stocking density (HSD) and food deprivation was assessed on carbohydrate metabolism of several tissues of gilthead sea bream Sparus auratus for 14 days. Fish were randomly assigned to one of four treatments: (1) fed fish under normal stocking density (NSD) (4 kg m(-3)); (2) fed fish under HSD (70 kg m(-3)); (3) food-deprived fish under NSD; and (4) food-deprived fish under HSD. After 14 days, samples were taken from the plasma, liver, gills, kidney and brain for the assessment of plasma cortisol, levels of metabolites and the activity of several enzymes involved in carbohydrate metabolism. HSD conditions alone elicited important changes in energy metabolism of several tissues that in some cases were confirmatory (5-fold increase in plama cortisol, 20% increase in plasma glucose, 60% decrease in liver glycogen and 20% increase in gluconeogenic potential in the liver) whereas in others provided new information regarding metabolic adjustments to cope with HSD in the liver (100% increase in glucose phosphorylating capacity), gills (30% decrease in capacity for phosphorylating glucose), kidney (80% increase in the capacity of phosphorylating glucose) and brain (2.5-fold increase in ATP levels). On the other hand, food deprivation alone resulted in increased plasma cortisol, and metabolic changes in the liver (enhanced gluconeogenic and glycogenolytic potential of 13% and 18%, respectively) and brain (10% increase in glycolytic capacity), confirmatory of previous studies, whereas new information regarding metabolic adjustments during food deprivation was obtained in the gills and kidney (decreased lactate levels in both tissues of 45% and 55%, respectively). Furthermore, the results obtained provided, for the first time in fish, information indicating that food deprivation increased the sensitivity of gilthead sea bream to the stress induced by HSD compared with the fed controls, as demonstrated by increased plasma cortisol levels (50% increase vs. fed fish) and a further increase in the capacity to export glucose mobilized from liver glycogen stores (70% decrease vs. fed fish). These results lend support for a cumulative effect of both stressors on plasma cortisol and parameters assessed on carbohydrate metabolism in the present experiments, and provide information regarding reallocation of metabolic energy to cope with simultaneous stressors in fish.

D-Glucose uptake in fish hepatocytes: mediated by transporter in rainbow trout (Oncorhynchus mykiss), but only by diffusion in prespawning lamprey (Lampetra fluviatilis) and in RTH-149 cell line

The transport of D-glucose into rainbow trout (Oncorhynchus mykiss) and river lamprey (Lampetra fluviatilis) hepatocytes, as well as into rainbow trout hepatoblastoma cell line RTH-149 was studied using tracer methods. The half-time for D-glucose equilibration was 15 s for rainbow trout. The half-times for the non-metabolizable D-glucose analog, 3-O-methyl-D-glucose equilibration were 8 s, 37 s and 38 s for rainbow trout, lamprey and RTH-149 cells, respectively. The 3-O-methyl-D-glucose was taken up by rainbow trout hepatocytes by facilitated diffusion in addition to simple diffusion. The uptake showed saturation kinetics with the K(m) of 37 mM and V(max) of 62 mmol kg(-1) cells min(-1). The uptake was sensitive to phloretin and cytochalasin B, but not affected by ouabain. The 3-O-methyl-D-glucose uptake by lamprey hepatocytes and RTH-149 cells showed no indication of saturation up to 160 mM, and was not affected by phloretin, cytochalasin B or ouabain, which suggests the mode of transport to be by passive diffusion. However, immunocytochemical stainings revealed the existence of mammalian type GLUT1 and GLUT2 transporters in all cells studied. The lack of a functioning carrier-mediated glucose uptake in lamprey hepatocytes might be due to its physiological state (prespawning starvation). The minor 3-O-methyl-D-glucose uptake into RTH-149 cells compared to freshly isolated rainbow trout hepatocytes might reflect low metabolic activity of the cell lines. Under the conditions applied the RTH-149 cell line is no suitable in vitro model for glucose transport in fish cells.

Brain glucose and insulin: effects on food intake and brain biogenic amines of rainbow trout

The effects of central (intracerebroventricular, 9 microg fish(-1)) and peripheral (intraperitoneal, 4 mg kg(-1)) administration of bovine insulin, as well as the effect of hyperglycemia (oral administration of 1 g glucose fish(-1)) and brain glucodeprivation (intracerebroventricular administration of 2-deoxy-D-glucose) on food intake and levels of brain (telencephalon, preoptic area, and hypothalamus) biogenic amines (serotonin, dopamine, noradrenaline and their metabolites 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid) were assessed on rainbow trout ( Oncorhynchus mykiss). Treatment with insulin inhibited food intake after 26 or 52 h of administration, central or peripheral, respectively. This effect was still apparent after 74 h of central treatment. When assessing changes in the levels of biogenic amines after 26 h of central insulin administration, there was a significant increase in the levels of 5-hydroxyindoleacetic acid, and in the ratio of dihydroxyphenylacetic acid/dopamine of insulin-treated fish, in telencephalon and hypothalamus, respectively. These results suggest that peripherally administered insulin is involved in a feedback regulatory loop with food intake and body weight. Moreover, at least part of the effects of insulin could be mediated by hypothalamic dopaminergic activity. The strong hyperglycemia induced by oral administration of glucose did not induce significant changes either on food intake (control versus treated), or in brain levels of biogenic amines. The intracerebroventricular administration of 2-deoxy-D-glucose induced an increase in food intake without altering plasma glucose levels, suggesting that fish brain possesses a control system for detecting hypoglycemia in plasma and therefore keep brain glucose levels high enough for brain function.

Chronic dietary mercury exposure causes oxidative stress, brain lesions, and altered behaviour in Atlantic salmon (Salmo salar) parr

Atlantic salmon (Salmo salar L.) parr were fed for 4 months on fish meal based diets supplemented with mercuric chloride (0, 10, or 100 mg Hg kg(-1) DW) or methylmercury chloride (0, 5, or 10 mg Hg kg(-1) DW) to assess the effects of inorganic (Hg) and organic dietary mercury on brain lipid peroxidation and neurotoxicity. Lipid peroxidative products, endogenous anti oxidant enzymes, brain histopathology, and overall behaviour were measured. Methylmercury accumulated significantly in the brain of fish fed 5 or 10 mg kg(-1) by the end of the experiment, and inorganic mercury accumulated significantly in the brain only at 100 mg kg(-1) exposure levels. No mortality or growth reduction was observed in any of the exposure groups. Fish fed 5 mg kg(-1) methylmercury had a significant increase (2-fold) in the antioxidant enzyme super oxide dismutase (SOD) in the brain. At dietary levels of 10 mg kg(-1) methylmercury, a significant increase (7-fold) was observed in lipid peroxidative products (thiobarbituric acid reactive substances, TBARS) and a subsequently decrease (1.5-fold) in anti oxidant enzyme activity (SOD and glutathione peroxidase, GSH-Px). Fish fed 10 mg kg(-1) methylmercury also had pathological damage (vacoulation and necrosis), significantly reduced neural enzyme activity (5-fold reduced monoamine oxidase, MAO, activity), and reduced overall post-feeding activity behaviour. Pathological injury started in the brain stem and became more widespread in other areas of the brain at higher exposure levels. Fish fed 100 mg Hg kg(-1) inorganic mercury had significant reduced neural MAO activity and pathological changes (astrocyte proliferation) in the brain, however, neural SOD and GSH-Px enzyme activity, lipid peroxidative products (TBARS), and post feeding behaviour did not differ from controls. Compared with other organs, the brain is particular susceptible for dietary methylmercury induced lipid peroxidative stress at relative low exposure concentrations. Doses of dietary methylmercury in the range of 5 mg kg(-1) induces protective redox defences in the brain as seen from the induction of anti-oxidant enzyme SOD activity. However, above a threshold of 10 mg kg(-1) methylmercury these defences are overcome and lipid peroxidative injury (TBARS) as well as severe pathological damage and adverse behaviour become apparent.

Acclimation of S aurata to various salinities alters energy metabolism of osmoregulatory and nonosmoregulatory organs

The impact of different environmental salinities on the energy metabolism of gills, kidney, liver, and brain was assessed in gilthead sea bream (Sparus aurata) acclimated to brackish water [BW, 12 parts/thousand (ppt)], seawater (SW, 38 ppt) and hyper saline water (HSW, 55 ppt) for 14 days. Plasma osmolality and levels of sodium and chloride presented a clear direct relationship with environmental salinities. A general activation of energy metabolism was observed under different osmotic conditions. In liver, an enhancement of glycogenolytic and glycolytic potential was observed in fish acclimated to BW and HSW compared with those in SW. In plasma, an increased availability of glucose, lactate, and protein was observed in parallel with the increase in salinity. In gills, an increased Na+-K+-ATPase activity, a clear decrease in the capacity for use of exogenous glucose and the pentose phosphate pathway, as well as an increased glycolytic potential were observed in parallel with the increased salinity. In kidney, Na+-K+-ATPase activity and lactate levels increased in HSW, whereas the capacity for the use of exogenous glucose decreased in BW- and HSW- acclimated fish compared with SW-acclimated fish. In brain, fish acclimated to BW or HSW displayed an enhancement in their potential for glycogenolysis, use of exogenous glucose, and glycolysis compared with SW-acclimated fish. Also in brain, lactate and ATP levels decreased in parallel with the increase in salinity. The data are discussed in the context of energy expenditure associated with osmotic acclimation to different environmental salinities in fish euryhaline species.

Intracerebroventricular Injections of Noradrenaline Affect Brain Energy Metabolism of Rainbow Trout

To assess the role of noradrenaline (NA) as a possible regulator of brain energy metabolism in teleost fish, the impact of increased noradrenaline levels within the brain on several parameters of energy metabolism was assessed in rainbow trout brain. Accordingly, two different doses of noradrenaline, producing increases in brain NA levels comparable to those occurring in several physiological processes in nature, were selected. In a subsequent set of three different experiments, fish were intracerebroventricularly injected with 1 microL 100 g(-1) body weight of Cortland saline alone (control) or containing NA (5 nmol NA and 10 nmol NA); after 30 min, brain and plasma samples were taken to assess changes in parameters of energy metabolism due to NA treatment. The results obtained clearly show dose-dependent changes in NA-treated fish in several parameters, including decreased glycogen and ATP levels, increased lactate and pyruvate levels, decreased fructose 1,6-bisphosphatase activity, and increased pyruvate kinase and lactate dehydrogenase activities. Altogether, the present experiments show for the first time in a teleost fish evidence supporting that increased noradrenaline levels in the brain elicit metabolic changes in the brain (enhanced glycogenolysis and glycolysis), resulting in an increased energy demand. These metabolic changes may be related to those occurring under several physiological conditions in nature such as hypoxia, in which increased energy demand and increased noradrenaline levels occur in the brain simultaneously.

Influence of cortisol on osmoregulation and energy metabolism in gilthead seabream Sparus aurata

Gilthead seabream Sparus aurata were injected intraperitoneally with slow-release implants of coconut oil alone or containing cortisol (50 and 100 microg x g(-1) body weight), and sampled after two, five, and seven days to assess the simultaneous effects of cortisol on both osmoregulation and energy metabolism. Plasma cortisol levels increased in treated fish to 50-70 ng x ml(-1). An enhanced hypoosmoregulatory capacity of cortisol-implanted fish is suggested by the increase observed in gill Na+, K+-ATPase activity, and the decrease observed in plasma ion concentration (Na+ and Cl-) and osmolality. Cortisol also elicited metabolic changes in liver (increased gluconeogenic potential suggested by elevated FBPase activity, and decreased potential of glycolysis and pentose-phosphate shunt, suggested by the decreased activities of both PK and G6PDH) supporting changes in levels of plasma metabolites suitable for use in other tissues. Thus in this study, we demonstrate for the first time in fish that cortisol treatments elicit changes in the use of exogenous glucose in gills (decreased HK activity) and an increased glycolytic and glycogenic potential in brain (increased GPase, PK and PFK activities).