Crucian Carp Brain Research Articles

Phosphoproteomic changes in response to anoxia are tissue-specific in the anoxia-tolerant crucian carp (Carassius carassius).

Crucian carp (Carassius carassius), a freshwater fish, can survive chronic anoxia for several months at low temperatures. Consequently, anoxia-related physiological and biochemical adaptations in this species have been studied for more than half a century. Still, despite for the well-known role of protein phosphorylation in regulating cellular processes, no studies have comprehensively characterized the phosphoproteome in crucian carp. In this study, we report the global phosphoproteome in crucian carp brain and liver during anoxia and reoxygenation. By applying a bottom-up proteomic approach on enriched phosphopeptides we found that the brain phosphoproteome shows surprisingly few changes during anoxia-reoxygenation exposure with only 109 out of 4200 phosphopeptides being differentially changed compared to normoxic controls. By contrast, in the liver 395 out of 1287 phosphopeptides changed. Although most changes occurred in the liver phosphoproteome, the pattern of changes indicated metabolic depression and decreased translation in both brain and liver. We also found changes in phosphoproteins involved in apoptotic regulation and reactive oxygen species handling in both tissues. In the brain, some of the most changed phosphopeptides belonged to proteins involved in central nervous system development and neuronal activity at the synaptic cleft. Changed phosphoproteins specific for liver tissue were related to glucose metabolism, such as glycolytic flux and glycogenolysis. In conclusion, protein phosphorylation in response to anoxia and reoxygenation showed both common and tissue-specific changes related to the functional differences between brain and liver.

Expression of prolyl hydroxylase domains, the upstream regulators of HIF, in the brain of the anoxia-tolerant crucian carp during anoxia-reoxygenation.

The hypoxia-inducible factor (HIF) is considered key in the transcriptional response to low oxygen. Yet, the role of HIF in the absence of oxygen (anoxia) and in preparation for reoxygenation remains unclear. Recent studies suggest that mounting a HIF response may be counterproductive for anoxia survival. We here studied one of the champions of anoxia survival, the crucian carp (Carassius carassius), and hypothesized that expression of prolyl hydroxylase domains (PHDs; the upstream regulators of HIF) are upregulated to circumvent an energy-costly activation of HIF in anoxia and to prepare for reoxygenation. We measured whole brain mRNA and protein levels of the three isoforms PHD1, PHD2, and PHD3, coded for by multiple paralogs of the genes egln2, egln1, and egln3, using quantitative PCR and Western blotting in the brain of crucian carps exposed to 5 days normoxia or anoxia, and 5 days anoxia followed by 3 or 24 h of reoxygenation. The mRNA levels of most egln paralogs were increased in anoxia and upon reoxygenation, with egln3 showing the largest increase in mRNA level (up to 17-fold) and highest relative mRNA abundance (up to 75% of expressed egln). The protein level of all PHDs was maintained in anoxia and increased upon reoxygenation. We then explored PHD distribution in different brain regions and found PHD immunoreactivity to be associated with axonal branches and showing region-specific changes during anoxia-reoxygenation. Our results support an overall upregulation of egln under prolonged anoxia and PHDs upon reoxygenation in crucian carp, likely aimed at suppressing HIF responses, although regional differences are apparent in such a complex organ as the brain.NEW & NOTEWORTHY We report a profound upregulation of most egln paralog mRNA levels in anoxia and upon reoxygenation, with egln3ii showing the largest, a 17-fold increase, and highest relative mRNA abundance. The relative abundance of prolyl hydroxylase domain (PHD) proteins was maintained during anoxia and increased at reoxygenation. PHD immunoreactivity was localized to axonal branches with region-specific changes during anoxia-reoxygenation. These dynamic and regional changes in crucian carp, champion of anoxia tolerance, are most likely adaptive and call for further mechanistic studies.

Two decades of research on anoxia tolerance - mitochondria, -omics and physiological diversity.

Just over two decades ago, Bob Boutilier published a much-cited Review in this journal on the mechanisms of cell survival in hypoxia and hypothermia. Here, we celebrate this important Review by describing how our knowledge of the mechanisms behind anoxia tolerance have progressed since 2001, including new key roles of mitochondria, something Boutilier had started exploring. Evidence now suggests that, in anoxia-tolerant brains, mitochondria initiate responses aimed at suppressing electrical activity and energy use. These responses are largely dependent on gamma-aminobutyric acid (GABA) release. Animals that survive anoxia must also tolerate reoxygenation - a major challenge that could cause a massive production of damaging reactive oxygen species (ROS). Here, the handling of succinate, which builds up during anoxia, is critical. Interestingly, there are clear species differences in succinate handling among anoxia-tolerant vertebrates (Trachemys and Chrysemys turtles and crucian carp, Carassius carassius). Trachemys turtles suppress succinate build-up during anoxia, presumably to limit ROS production during reoxygenation. By contrast, in crucian carp, reduction of fumarate to succinate during anoxia appears to be essential for keeping their mitochondria charged and viable. Consequently, during anoxia, crucian carp accumulate much more succinate than Trachemys turtles. Moreover, during anoxia, succinate is apparently transported from crucian carp brain and heart to the liver, which handles succinate upon reoxygenation. This is one example of the striking physiological diversity among vertebrates that survive long-term anoxia. More examples are given, and we argue that -omics approaches are, and will be, helpful in providing new insight and moving the field forward.

Toxicologic effect of short-term enrofloxacin exposure on brain of Carassius auratus var. Pengze

To further explore short-term exposure of enrofloxacin (ENR) induced toxicity in crucian carp brain that has been reported by our previous work, as well as the possible toxicological mechanisms, this study investigated the blood-brain barrier (BBB) permeability to low dosage of ENR through comprehensively assessing expression of BBB constitutive molecules zonula occludens-1 (ZO-1) and permeability glycoprotein (P-gp), as well as ENR residue in brain of crucian carp. Toxicologic effect of ENR on brain tissue was determined through evaluating expression of brain-derived proteins S100B, neuron specific enolase (NSE) and glial fibrillary acidic protein (GFAP) in crucian carp brain tissue, as well as contents of the proteins in serum. The toxicological mechanisms were explored through analyzing transcriptome analysis data. Results showed that ENR possessed excellent permeability to crucian carp BBB, which was closely related to deranged BBB structure and declined ENR efflux that were attributed to downregulated expression of ZO-1 and P-gp by ENR exposure. Meanwhile, S100B, NSE and GFAP were upregulated in brain by ENR, and came out into blood across the damaged BBB. These data revealed that ENR induced disruption of BBB and damage of brain tissue in crucian carp. Transcriptome analysis data indicated that ENR induced toxicologic effect might be related to modification of metabolism, organismal systems, and genetic information processing, etc., and that PI3K/Akt, MAPK, HIF-1, and ubiquitin mediated proteolysis involved the mechanisms, most of the mechanisms were attributed to ENR induced oxidative stress in crucian carp brain.

Integrating Multi-Omics and Biochemical Approaches for Uncovering the Physiological Responses of Crucian Carp Brain to Deltamethrin Exposure at a "Safe" Concentration

Integrating Multi-Omics and Biochemical Approaches for Uncovering the Physiological Responses of Crucian Carp Brain to Deltamethrin Exposure at a "Safe" Concentration

H2S-producing enzymes in anoxia-tolerant vertebrates: Effects of cold acclimation, anoxia exposure and reoxygenation on gene and protein expression.

To lend insight into the potential role of the gasotransmitter hydrogen sulfide (H2S) in facilitating anoxia survival of anoxia-tolerant vertebrates, we quantified the gene expression of the primary H2S-synthesizing enzymes, 3-mercaptopyruvate sulfurtransferase (3MST), cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), in ventricle and brain of normoxic, anoxic and reoxygenated 21°C- and 5°C-acclimated freshwater turtles (Trachemys scripta) and 10°C-acclimated crucian carp (Carassius carassius). Semi-quantitative Western blotting analysis was also conducted to assess 3MST and CBS protein abundance in ventricle and brain of 5°C turtles and 10°C crucian carp subjected to normoxia, anoxia and reoxygenation. We hypothesized that if H2S was advantageous for anoxia survival, expression levels would remain unchanged or be upregulated with anoxia and/or reoxygenation. Indeed, for both species, gene and protein expression were largely maintained with anoxia exposure (24h, 21°C; 5 d, 10°C; 14 d, 5°C). With reoxygenation, 3MST expression was increased in turtle and crucian carp brain at the protein and gene level, respectively. Additionally, the effect of cold acclimation on gene expression was assessed in several tissues of the turtle. Expression levels were maintained in most tissues, but decreased in others. The maintenance of gene and protein expression of the H2S-producing enzymes with anoxia exposure and the up-regulation of 3MST with reoxygenation suggests that H2S may facilitate anoxic survival of the two champions of vertebrate anoxia survival. The differential effects of cold acclimation on H2S enzyme expression may influence blood flow to different tissues during winter anoxia.

Development of two brain cell lines from goldfish and silver crucian carp and viral susceptibility to Cyprinid herpesivirus-2.

Two cell lines were established from silver crucian carp and goldfish brain tissue and used as the biological tool for monitoring viral diseases. Characterization including optimal growth kinetics study, karyotyping, and mitochondrial ribosomal RNA (rRNA) genotyping were performed. The primary cultures of these cells were generated by the explant technique using the medium 199 supplemented with 20% fetal bovine serum and epidermal/fibroblast growth factors. The cells grew over the range of 15 to 30°C, while the optimal temperature for culture was 30°C. The cell lines were maintained in vitro and could be subcultured over 40 times. Following cryopreservation in liquid nitrogen, thawed cells exhibit viability of > 90% after a 13-mo period of storage. The chromosome count of two cell lines were determined to be 154 and 110, respectively, which agreed well with triploid crucian carp brain cells and diploid goldfish brain cells. Polymerase chain reaction amplification and sequence analysis indicated 100% and 94% match with known crucian carp mitochondrial DNA sequences. Cytopathic effect was continuously observed in both cell lines over 10 passages after inoculation with tissue homogenates of sick or died goldfish from cyprinid herpesvirus 2 (CyHV-2) outbreaks. These newly established cell lines could be a diagnostic tool for viral diseases in fish species.

1H-NMR study of the metabolome of an exceptionally anoxia tolerant vertebrate, the crucian carp (Carassius carassius)

The crucian carp (Carassius carassius) can tolerate anoxia for days to months, depending on the temperature. In this study, we applied 1H-NMR-based metabolomics to polar extracts of crucian carp brain, heart, muscle and liver samples obtained from fish exposed to either control normoxic conditions, acute anoxia (24 h), chronic anoxia (1 week) or reoxygenation (for 1 week following chronic anoxia) at 5 °C. Spectra of the examined tissues revealed changes in several energy-related compounds. In particular, anoxic stress resulted in decreased concentrations of phosphocreatine (muscle, liver) and glycogen (liver) and ATP/ADP (liver, heart and muscle) and increased concentrations of lactate (brain, heart, muscle) and beta-hydroxybutyric acid (all tissues). Likewise, increased concentrations of inhibitory compounds (glycine, gamma-amino butyric acid or GABA) and decreased concentrations of excitatory metabolites (glutamate, glutamine) were confirmed in the anoxic brain extracts. Additionally, a decrease of N-acetylaspartate (NAA), an important neuronal marker, was also observed in anoxic brains. The branched-chain amino acids (BCAA) valine/isoleucine/leucine increased in all anoxic tissues. Possibly, this general tissue increase can be due to an inhibited mitochondrial function or due to protein degradation/protein synthesis inhibition. In this study, the potential and strength of the 1H-NMR is highlighted by the detection of previously unrecognized changes in metabolites. Specifically, myo-inositol substantially decreased in the heart of anoxic crucian carp and anoxic muscle tissue displayed a decreased concentration of taurine, providing novel insights into the anoxia responses of the crucian carp.

Proteomic changes in the crucian carp brain during exposure to anoxia

During exposure to anoxia, the crucian carp brain is able to maintain normal overall protein synthesis rates. However, it is not known if there are alterations in the synthesis or expression of specific proteins. This investigation addresses this issue by comparing the normoxic and anoxic brain proteome. Nine proteins were found to be reduced by anoxia. Reductions in the glycolytic pathway proteins creatine kinase, fructose biphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, triosephosphate isomerase and lactate dehydrogenase reflect the reduced production and requirement for adenosine tri-phosphate during anoxia. In terms of neural protection, voltage-dependent anion channel, a protein associated with neuronal apoptosis, was reduced, along with gefiltin, a protein associated with the subsequent need for neuronal repair. Additionally the expression of proteins associated with neural degeneration and impaired cognitive function also declined; dihydropyrimidinase-like protein-3 and vesicle amine transport protein-1. One protein was found to be increased by anoxia; pre-proependymin, the precursor to ependymin. Ependymin fulfils multiple roles in neural plasticity, memory formation and learning, neuron growth and regeneration, and is able to reverse the possibility of apoptosis, thus further protecting the anoxic brain.

The major contribution of brain GABAergic function to anoxic survival

the paper by ellefsen et al. ([3][1]) is a fascinating large-scale analysis of genes associated with GABA neurotransmission in an extremely important model of anoxia tolerance, the crucian carp, Carassius carassius . Under conditions of anoxia the crucian carp brain increases its extracellular GABA

Expression of genes involved in GABAergic neurotransmission in anoxic crucian carp brain (Carassius carassius)

The crucian carp, Carassius carassius, survives days to months without oxygen, depending on temperature. In the anoxic crucian carp brain, increased GABAergic inhibition, mediated by increased extracellular levels of GABA, has been shown to suppress electric activity and ATP consumption. To investigate an involvement of gene expression in this response, we utilized real-time RT-PCR to test the effect of 1 and 7 days anoxia (8 degrees C) on the expression of 22 genes, including nine GABA(A) receptor subunits (alpha(1-6), beta(2), delta, and gamma(2)), three GABA(B) receptor subunits (G(B)1a-1b and G(B)2), three enzymes involved in GABA metabolism (GAD65 and GAD67, GABAT), four GABA transporters (GAT1, 2a-b and 3), two GABA(A) receptor-associated proteins (GABARAP 1 and 2), and the K(+)/Cl(-) cotransporter KCC2. While the expression of GABA(A) receptor subunits was dominated by alpha(4)-, alpha(6)-, and delta-subunits, all of which are located to extrasynaptic sites in mammalian brains and respond to elevations in extracellular levels of GABA by showing tonic activity patterns, the expression of GABA transporters was dominated by GAT2 (a and b) and GAT3, which also show extrasynaptic location in mammals. These expression patterns differ from those observed in mammals and may be a prerequisite for GABAergic inhibition of anoxic metabolic rate in crucian carp. Furthermore, while the expression of the majority of the genes was largely unaltered by anoxia, the expression of GAT2 and GAT3 decreased to 20%. This suggests impairment of GABA transport, which could be a mechanism behind the accumulation of extracellular GABA and the increased GABAergic inhibition.

Expression of genes involved in excitatory neurotransmission in anoxic crucian carp (Carassius carassius) brain

The crucian carp, Carassius carassius, survives months without oxygen. During anoxia it needs to keep energy expenditure low, particularly in the brain, with its high rate of ATP use related to neuronal activity. This could be accomplished by reducing neuronal excitability through altered expression of genes involved in excitatory neurotransmission. Through cloning and the use of a recently developed real-time RT-PCR approach, with an external RNA control for normalization, we investigated the effect of 1 and 7 days of anoxia (12 degrees C) on the expression of 29 genes, including 8 3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits, 6 N-methyl-d-aspartate (NMDA) receptor subunits, 7 voltage-gated sodium and calcium channels, 4 glutamate transporters, and 4 genes involved in NMDA receptor-mediated neuroplasticity. The subunits of the majority of the gene families had expression profiles similar to those observed in the mammalian brain and showed remarkably stable expression during anoxia. This suggests that the genes may have similar functions in crucian carp and mammals, and that the excitatory abilities of the crucian carp brain are retained during anoxia. Although the data generally argue against profound neural depression ("channel arrest"), NMDA receptor subunit (NR) expression showed features that could mediate reduced neural excitability. Primarily, the NR2 subunit expression, which was dominated by NR2B and NR2D, resembled that seen in hypoxia-tolerant neonatal rats, and decreased anoxic expression of NR1, NR2C, and NR3A indicated reduced numbers of functional NMDA receptors. We also report the full-length sequence of crucian carp NR1 mRNA and a novel NR1 splice cassette introducing an N-glycosylation site into the extracellular S1S2 domain.

Extracellular levels of amino acid neurotransmitters during anoxia and forced energy deficiency in crucian carp brain

The crucian carp is one of the few vertebrates that has the ability to survive long periods of anoxia. A devastating event in the anoxic mammalian brain is a massive release of excitatory neurotransmitters, particularly glutamate. Using microdialysis to measure extracellular levels of several amino acid neurotransmitters and related compounds in the telencephalon of crucian carp in vivo, we show here that this species avoids a release of glutamate during anoxia, which is probably related to its ability to maintain energy charge. Instead, 6 h of anoxia produced a doubling of the extracellular level of GABA, the major inhibitory neurotransmitter in brain. The release of GABA may be a mechanism for lowering neuronal activity and energy use, thereby facilitating the maintenance of energy charge. Perfusing the microdialysis probe with a high-K + Ringer showed that the telencephalon had the ability to release both glutamate and GABA. Moreover, if energy deficiency was produced during anoxia, by inhibiting glycolysis with iodoacetate (IAA), the resulting release of GABA was more rapid and profound than that of glutamate, possibly reflecting a second line of anoxia defence aimed at minimising the effect of a temporary energy failure.

Direct electrospray-ionization mass spectrometric analysis of the major ganglioside from crucian carp liver after thin layer chromatography

Ganglioside patterns from crucian carp brain, muscle, and liver as well as liver gangliosides of roach, carp, the cichlid Oreochromis mossambicus, pigeon, dwarf hamster, and calf were comparatively analyzed by high performance thin layer chromatography (HPTLC). To achieve a rapid estimation on potentially interesting ganglioside compounds, electrospray-ionization mass spectrometry (MS) was directly applied to a chloroform/methanol extract of the major TLC band of crucian carp liver. The spectrum, obtained from a few micrograms of this crude biological sample, revealed a series of peaks corresponding to GM4-like monosialoganglioside species. GC-MS analysis revealed hydroxylated fatty acids ranging from 2 h 20 min:0 to 2 h 26 min:0 for the [M'H] − ions of m/ z 1061–1145. Collision induced dissociation tandem MS/MS of the major peak with a [M'H] − ion of m/ z 1117 demonstrated the presence of N-acetylneuraminic acid as sialic acid compound. The sugar composition was confirmed by GLC as galactose and sialic acid in a 1:1 molar ratio. Thus, the structure of the ion at m/ z 1117 is N-acetylneuraminylgalactosylceramide (NeuAc-Gal-Cer) with the long chain base d18:1 and the hydroxylated fatty acid 2 h 24 min:0. The results demonstrate for the first time unambiguously that NeuAc-Gal-Cer is the main ganglioside fraction in fish liver and that electrospray ionization-mass spectrometry (ESI-MS) can be used to elucidate the chemical composition of a ganglioside fraction obtained by convenient extraction of a HPTLC band.

Brain Na +/K +-ATPase activity in two anoxia tolerant vertebrates: crucian carp and freshwater turtle

The crucian carp ( Carassius carassius) and freshwater turtles ( Trachemys scripta) are among the very few vertebrates that can survive extended periods of anoxia. The major problem for an anoxic brain is energy deficiency. In the brain, the Na +/K +-ATPase is the single most ATP consuming enzyme, being responsible for maintaining ion gradients. We here show that the Na +/K +-ATPase activity in the turtle brain is reduced by 31% in telencephalon and by 34% in cerebellum after 24 h of anoxia. Both changes were reversed upon reoxygenation. By contrast, the Na +/K +-ATPase activities were maintained in the anoxic crucian carp brain. These results support the notion that crucian carp and turtles use divergent strategies for anoxic survival. The fall in Na +/K +-ATPase activities displayed by the turtle is likely to be related to the strong depression of brain electric and metabolic activity utilized as an anoxic survival strategy by this species.

Roles of energy status, KATP channels and channel arrest in fish brain K+ gradient dissipation during anoxia

The crucian carp (Carassius carassius L.) is one of the most anoxia-tolerant vertebrates known, being able to maintain ion homeostasis in its brain for many hours of anoxia. This study aims to clarify the importance of glycolysis during anoxia and also to investigate whether the extreme tolerance to anoxia could be due to down-regulation of K+ permeability ('channel arrest') and/or activation of ATP-sensitive K+ (KATP) channels. The latter was also tested in rainbow trout (Oncorhynchus mykiss). The results suggest that, during anoxia, the crucian carp brain is completely dependent on glycolysis, since blocking glycolysis with iodoacetic acid (IAA) rapidly caused an increase in [K+]o that coincided with a drastic drop in ATP level and energy charge. Testing the channel arrest hypothesis by measuring the K+ efflux rate after Na+/K+-ATPase had been blocked by ouabain revealed no change in K+ permeability in crucian carp brain in response to anoxia. Furthermore, superfusing the brain of anoxic crucian carp with the KATP channel blocker glibenclamide did not alter the efflux rate of K+ after glycolysis had been inhibited with IAA. Glibenclamide had no effect on K+ efflux rate in rainbow trout brain during anoxia.

Evidence that acetylcholine mediates increased cerebral blood flow velocity in crucian carp through a nitric oxide-dependent mechanism.

Nitric oxide (NO)-dependent regulation of brain blood flow has not been proved to exist in fish or other ectothermic vertebrates. Using epi-illumination microscopy on the brain surface (optic lobes) of crucian carp (Carassius carassius), we show that superfusing the brain with acetylcholine (ACh) induces an increase in cerebral blood flow velocity that can be completely blocked by the NO synthase inhibitors NG-nitro-L-arginine methylester (L-NAME) and NG-nitro-L-arginine. Also, sodium nitroprusside, which decomposes to liberate NO, causes an increase in cerebral blood flow velocity. By contrast, L-NAME does not block the increase in blood flow velocity caused by anoxia. The results suggest that NO is an endogenous vasodilator in crucian carp brain that mediates the effects of ACh. Because teleost fish deviated from other vertebrates 400 million years ago, these results suggest that NO-dependent brain blood flow regulation was an early event in vertebrate evolution.

Effects of Anoxia on Energy Metabolism in Crucian Carp Brain Slices Studied With Microcalorimetry

Crucian carp (Carassius carassius L.) is an exceptionally anoxia-tolerant vertebrate. To determine whether isolated crucian carp brain tissue survives anoxia and whether it displays anoxic metabolic depression, heat production (using microcalorimetry), lactate production, ethanol production and the maintenance of ATP, ADP and AMP levels and energy charge were measured in telencephalic brain slices during anoxia. In response to anoxia, heat output decreased by 37 %, corresponding to a 31 % fall in ATP turnover rate. Adenylate phosphates and energy charge were well maintained and no ethanol was produced during anoxia. It is concluded that crucian carp brain tissue has an intrinsic capacity to tolerate anoxia and that it responds to anoxia by depressing metabolic rate and elevating the glycolytic rate, thereby maintaining ATP levels.

Turnover of serotonin in brain of an anoxia-tolerant vertebrate, the crucian carp

Serotonin (5-HT) is a neurotransmitter in the vertebrate brain. Estimates of 5-HT turnover times range between 1 h (mammals) and 10 h (goldfish). Synthesis and catabolism of 5-HT are dependent on molecular oxygen, hence, 5-HT turnover comes to a halt during anoxia. Nevertheless, a few vertebrates, such as the crucian carp (Carassius carassius L.), tolerate anoxia for several weeks. To assess the ability of the crucian carp brain to tolerate a stop in 5-HT turnover during anoxia, it is essential to know its normoxic rate of 5-HT turnover. The turnover of 5-HT was estimated in different brain regions of winter-acclimatized crucian carp held in normoxia at 8 degrees C using two different methods, i.e., 1) by measuring the increase seen in 5-HT after monoamine oxidase inhibition (by pargyline), and 2) by measuring the rate of 5-hydroxytryptophan (5-HTP) accumulation, after the conversion of 5-HTP to 5-HT had been inhibited (by N-m-hydroxybenzylhydrazine). Both methods suggested similar turnover rates (approximately 10-20 pmol/g h) and turnover times (1-3 days). This is probably the slowest 5-HT turnover ever measured in a vertebrate (less than 1/100 of that of mammals). The slow 5-HT turnover could be explained by a high degree of recycling of the same 5-HT molecules, in combination with a decreased turnover at low temperatures. Moreover, the slow 5-HT turnover might be a prerequisite for preserving the functional integrity of the 5-HT system during anoxia.

Effects of Anoxia on Serotonin Metabolism in Crucian Carp Brain

ABSTRACT In the brain, oxygen is required for both the synthesis and the degradation of monoamine transmitters, so monoaminergic systems can be expected to be strongly affected by anoxia. However, crucian carp (Carassius carassius L.) may survive anoxia for many days or even weeks. In the present study, crucian carp were exposed to anoxia for 22, 76, and 160 h at 8°C. All survived and were found to excrete ethanol at a constant rate. The brain concentrations of serotonin and its two main metabolites, 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophol, were analysed after each experiment. In a preliminary experiment, it was found that the brain of the crucian carp contained about the same amount of serotonin and 5-HIAA as two species less tolerant to anoxia - the common carp and the rainbow trout. The levels of the serotonin metabolites decreased drastically (by 80–90%) during anoxia, whereas serotonin levels were only slightly reduced (by 15 % or less). These results suggest a complete or nearly complete stop in serotonin metabolism during anoxia.