Tetrodotoxins in Tissues and Cells of Different Body Regions of Ribbon Worms Kulikovia alborostrata and K. manchenkoi from Spokoynaya Bay, Sea of Japan

Nemerteans, or ribbon worms, possess tetrodotoxin and its analogues (TTXs), neurotoxins of bacterial origin, which they presumably use for capturing prey and self-defense. Most TTXs-containing nemertean species have low levels of these toxins and, therefore, have usually been neglected in studies of TTXs functions and accumulation. In the present study, Kulikovia alborostrata and K. manchenkoi, two closely related species, were analyzed for TTXs distribution in the body using the HPLC-MS/MS and fluorescence microscopy methods. The abundance of TTXs-positive cells was determined in the proboscis, integument, and digestive system epithelium. As a result, six TTXs-positive cell types were identified in each species; however, only four were common. Moreover, the proportions of the toxins in different body parts were estimated. According to the HPLC-MS/MS analysis, the TTXs concentrations in K. alborostrata varied from 0.91 ng/g in the proboscis to 5.52 ng/g in the precerebral region; in K. manchenkoi, the concentrations ranged from 7.47 ng/g in the proboscis to 72.32 ng/g in the posterior body region. The differences observed between the two nemerteans in the distribution of the TTXs were consistent with the differences in the localization of TTXs-positive cells. In addition, TTXs-positive glandular cell types were found in the intestine and characterized for the first time. TTXs in the new cell types were assumed to play a unique physiological role for nemerteans.

5, 6, 11-trideoxy tetrodotoxin attracts tiger puffer Takifugu rubripes

Tetrodotoxin (TTX) is a potent neurotoxin that binds to voltage-gated sodium channels and blocks the passage of sodium ions. TTX is widely distributed in both terrestrial and marine organisms, and the toxic puffers are believed to accumulate TTX through the food chain. Although pufferfish was previously thought to be attracted by TTX, recent finding from electroolfactogram (EOG) studies have indicated that the olfactory epithelium of T. alboplumbeus responded to 5, 6, 11-trideoxyTTX (TDT), but not to TTX itself. In this study, we examined behavioral experiments for Takifugu rubripes to distinguish between TTX and TDT under static and flow-through conditions. Our data clearly suggested that T. rubripes juveniles were attracted to TDT, not TTX. Moreover, we determined that the minimum effective dose of TDT to attract the puffer was 1-2 nmol of TDT under static conditions and 50-60 nmol of TDT under flow-through conditions. Following the experiments under static conditions, numerous bite marks by the pufferfish were found solely on the agarose gel infused with TDT. Based on these finding, we hypothesize that the pufferfish are attracted to TDT derived from prey, leading them effectively become toxic.

Wheat germ agglutinin affinity chromatography enrichment and glyco-proteomic characterization of tetrodotoxin-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes)

Efficient enrichment of tetrodotoxin (TTX)-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes) was achieved by ammonium sulfate fractionation and wheat germ agglutinin (WGA) affinity chromatography. The enrichment efficiency was validated by ultrafiltration-LC/MS-based TTX-binding assay and proteomics. Major proteins in the WGA-bound fraction were identified as isoform X1 (125 kDa) and X2 variants (88 and 79 kDa) derived from pufferfish saxitoxin and tetrodotoxin-binding protein (PSTBP) 1-like gene (LOC101075943). The 125-kDa X1 protein was found to be a novel member of the lipocalin family, having three tandemly repeated domains. X2 variants, X2α and X2β, were estimated to have two domains, and X2β is structurally related to Takifugu pardalis PSTBP2 in their domain type and arrangement. Among 11 potential N-glycosylation sites in the X2 precursor, 5 N-glycosylated Asn residues (N55, N89, N244, N308, and N449) were empirically determined. Structural relationships among PSTBP homologs and complexity of their proteoforms are discussed.

Establishment and characterization of the ovary cell line derived from two-spot puffer Takifugu bimaculatus and its application for gene editing and marine toxicology

Takifugu bimaculatus is a marine fish with high nutritional value. Its ovary contains tetrodotoxin (TTX) which is a severe neurotoxin that limits its edible value of it. To understand the mechanism of oogenesis and production of TTX in T. bimaculatus, an ovarian cell line named TBO from an adolescent ovary was established. TBO was composed of fibroblast-like cells that expressed the ovarian follicle cells marker gene Foxl2 and highly expressed TTX binding protein 2 (PSTBP2) but did not express the germ cells marker gene Vasa. Therefore, TBO seems to be mainly composed of follicle cells and possibly a small percentage of oocytes. Electroporation was used to successfully transfect the pEGFP-N1 and pNanog-N1 vectors into the TBO cell line with a high transfection efficiency. The morphological changes and survival rates of the exposed cells proved that this cell line was effective for exposure to conotoxins (CTXs), another group of toxins related to food safety. Furthermore, PSTBP2 was knocked out in TBO using CRISPR/Cas9 technology, showing that sgRNA2 could mutate PSTBP2. The results suggested that TBO will be more convenient, efficient, and rapid for reproduction and toxicology investigation, and gene editing. This study laid the groundwork for future research into the fish gonadal cell culture and food-related marine toxins. In conclusion, a cell line has been generated from T. bimaculatus, which might represent a valuable model for fish studies in the fields of toxicology and gene editing.

Milk Formula Enriched with Sodium Butyrate Influences Small Intestine Contractility in Neonatal Pigs

Butyrate, a by-product of gut bacteria fermentation as well as the digestion of fat in mother’s milk, exerts a wide spectrum of beneficial effects in the gastrointestinal tissues. The present study aimed to determine the effects of sodium butyrate on small intestine contractility in neonatal piglets. Piglets were fed milk formula alone (group C) or milk formula supplemented with sodium butyrate (group B). After a 7-day treatment period, isometric recordings of whole-thickness segments of the duodenum and middle jejunum were obtained by electric field stimulation under the influence of increasing doses of Ach (acetylocholine) in the presence of TTX (tetrodotoxin) and atropine. Moreover, structural properties of the intestinal wall were assessed, together with the expression of cholinergic and muscarinic receptors (M1 and M2). In both intestinal segments (duodenum and middle jejunum), EFS (electric field stimulation) impulses resulted in increased contractility and amplitude of contractions in group B compared to group C. Additionally, exposure to dietary butyrate led to a significant increase in tunica muscularis thickness in the duodenum, while mitotic and apoptotic indices were increased in the middle jejunum. The expression of M1 and M2 receptors in the middle jejunum was significantly higher after butyrate treatment. The results indicate increased cholinergic signaling and small intestinal growth and renewal in response to feeding with milk formula enriched with sodium butyrate in neonatal piglets.

Transcriptomic analysis reveals the genes involved in tetrodotoxin (TTX) accumulation, translocation, and detoxification in the pufferfish Takifugu rubripes

Tetrodotoxin (TTX) is a potent marine neurotoxin that exists in a variety of aquatic and terrestrial organisms. Pufferfish in different habitats show great variation in their TTX contents. Exploring the genes involved in TTX metabolism could contribute to our understanding of the molecular mechanisms underlying TTX accumulation, translocation, and detoxification in pufferfish. In this study, transcriptomic analysis was used to identify the functional genes related to TTX metabolism in the blood, liver, and muscle of the toxic and non-toxic tiger puffer (Takifugu rubripes). A total of 6101 differentially expressed genes (DEGs) were obtained after transcriptomic analysis; of these, 2401 were identified in the blood, 2262 in the liver, and 1438 in the muscle. After enrichment analysis, fourteen genes encoding glutathione S-transferases (GSTs), glutathione peroxidase (GPx), thioredoxins (TXNs), superoxide dismutase (SOD), ATP-binding cassettes (ABCs), apolipoproteins (APOs), inhibitors of apoptosis protein (IAP), and solute carrier (SLC), which are mainly antioxidant enzymes, membrane transporters, or anti-apoptotic factors, were revealed in the blood. Thirty-six genes encoding SLCs, ABCs, long-chain-fatty-acid-CoA ligases (ACSLs), interleukin 6 cytokine family signal transducer (IL6ST), endoplasmic reticulum (ER), and heat shock protein family A (Hsp70) were involved in transmembrane transporter activity and innate immune response. Notably, a large number of slc genes were found to play critical and diverse roles in TTX accumulation and translocation in the liver of T. rubripes. Nine genes from the slc, hsp70, complement C5 (c5), acsl, er, and serpin peptidase inhibitor (serpin) gene families were found to participate in the regulation of protein processing and anti-apoptosis. These results reflect the diverse functions of genes closely related to TTX accumulation, translocation, and detoxification in T. rubripes.

Phylogeny and Toxin Profile of Freshwater Pufferfish (Genus Pao) Collected from 2 Different Regions in Cambodia

The species classification of Cambodian freshwater pufferfish is incomplete and confusing, and scientific information on their toxicity and toxin profile is limited. In the present study, to accumulate information on the phylogeny and toxin profile of freshwater pufferfish, and to contribute to food safety in Cambodia, we conducted simultaneous genetic-based phylogenetic and toxin analyses using freshwater pufferfish individuals collected from Phnom Penh and Kratie (designated PNH and KTI, respectively). Phylogenetic analysis of partial sequences of three mitochondrial genes (cytochrome b, 16S rRNA, and cytochrome c oxidase subunit I) determined for each fish revealed that PNH and KTI are different species in the genus Pao (designated Pao sp. A and Pao sp. B, respectively). A partial sequence of the nuclear tributyltin-binding protein type 2 (TBT-bp2) gene differentiated the species at the amino acid level. Instrumental analysis of the toxin profile revealed that both Pao sp. A and Pao sp. B possess saxitoxins (STXs), comprising STX as the main component. In Pao sp. A, the toxin concentration in each tissue was extremely high, far exceeding the regulatory limit for STXs set by the Codex Committee, whereas in Pao sp. B, only the skin contained high toxin concentrations. The difference in the STX accumulation ability between the two species with different TBT-bp2 sequences suggests that TBT-bp2 is involved in STX accumulation in freshwater pufferfish.

The planocerid flatworm is a main supplier of toxin to tetrodotoxin-bearing fish juveniles

Tetrodotoxin (TTX), a potent neurotoxin, is found in various phylogenetically diverse taxa. In marine environments, the pufferfish is at the top of the food chain among TTX-bearing organisms. The accumulation of TTX in the body of pufferfish appears to be of the food web that begins with bacteria. It is known that toxic pufferfishes possess TTX from the larval/juvenile stage. However, the source of the TTX is unknown because the maternally sourced TTX is extremely small in quantity. Therefore, the TTX has to be obtained from other organisms or directly from the environment. Here, we report evidence that the source of TTX for toxic fish juveniles including the pufferfish (Chelonodon patoca) and the goby (Yongeichthys criniger) is in the food organisms, as seen in their gut contents. Next generation sequencing analysis for the mitochondrial COI gene showed that the majority of the sequence recovered from intestinal contents of these toxic fishes belonged to the flatworm Planocera multitentaculata, a polyclad flatworm containing highly concentrated TTX from the larval stage. PCR specific to P. multitentaculata also showed that DNA encoding the planocerid COI gene was strongly detected in the intestinal contents of the goby and pufferfish juveniles. Additionally, the planocerid specific COI sequence was detected in the environmental seawater collected from the water around the sampling locations for TTX-bearing fish. These results suggest that planocerid larvae are the major TTX supplier for juveniles of TTX-bearing fish species.

Accumulation and Elimination of Tetrodotoxin in the Pufferfish Takifugu obscurus by Dietary Administration of the Wild Toxic Gastropod Nassarius semiplicata

To investigate pufferfish accumulation, elimination, and distribution of tetrodotoxin (TTX), Takifugu obscurus was fed with wild TTX-containing gastropod Nassarius semiplicata to simulate the natural food chain. Three-month-old non-poisonous T. obscurus was fed with wild toxic N. semiplicata at three exposure dose for 28 days, and later, with toxin-free food until day 67. Three fish individuals from each treatment were sampled, and the distribution of TTX in different tissues was measured. The results showed that the accumulation ratio of TTX in the three exposure dose groups ranged from 35.76% to 40.20%. The accumulation ratio in the skin and liver was the highest amongst all tissues, accounting for more than 85% of the total TTX, whereas that in the kidney and gallbladder was the lowest (0.11–0.78%). Studies on the kinetic of TTX accumulation and elimination revealed that the skin was the tissue with the highest accumulation speed constant (8.06), while the liver, kidney, and intestinal tract showed the highest speed of TTX elimination. The time required for TTX reduction to reach the safety limit could be predicted by using standard elimination equations. Qualitative analysis by UPLC-MS/MS revealed the occurrence of seven TTX derivatives in T. obscurus; of these TTX, 5-deoxy TTX, 11-deoxy TTX, 4,9-anhydro TTX were found in all tested tissues.

The Microbial Community of Tetrodotoxin-Bearing and Non-Tetrodotoxin-Bearing Ribbon Worms (Nemertea) from the Sea of Japan

A potent marine toxin, tetrodotoxin (TTX), found in a great variety of marine and some terrestrial species, leaves intriguing questions about its origin and distribution in marine ecosystems. TTX-producing bacteria were found in the cultivable microflora of many TTX-bearing hosts, thereby providing strong support for the hypothesis that the toxin is of bacterial origin in these species. However, metagenomic studies of TTX-bearing animals addressing the whole microbial composition and estimating the contribution of TTX-producing bacteria to the overall toxicity of the host were not conducted. The present study is the first to characterize and compare the 16S rRNA gene data obtained from four TTX-bearing and four non-TTX-bearing species of marine ribbon worms. The statistical analysis showed that different nemertean species harbor distinct bacterial communities, while members of the same species mostly share more similar microbiomes. The bacterial species historically associated with TTX production were found in all studied samples but predominated in TTX-bearing nemertean species. This suggests that deeper knowledge of the microbiome of TTX-bearing animals is a key to understanding the origin of TTX in marine ecosystems.

New tetrodotoxin analogs in Brazilian pufferfishes tissues and microbiome

While tetrodotoxin (TTX) is commonly found in pufferfish tissues, it is unclear if bacterial symbionts isolated from pufferfish tissues can produce TTX. In this investigation, UPLC qTOF-MS/MS analysis of tissue extracts obtained from Sphoeroides spengleri and Canthigaster figuereidoi identified TTX in their composition, indicating their consumption is unsafe. UPLC qTOF-MS/MS analysis coupled with Molecular Networking indicated new TTX analogs (methyl-TTX, TTX-acetate, hydroxypropyl-TTX and glycerol-TTX). Bacterial extracts from sixteen strains revealed a compound with a [M+H]⁺ ion at m/z 320.1088, identical to TTX. However, TTX itself was not detected in these cultures by UPLC-MS/MS. Neurotoxicity of Vibrio A665 purified fraction 2 (with precursor [M+H]⁺ ion at m/z 320.1088) was significant in human neural stem cells (hNSCs), but the Na_v blockage activity was not confirmed by the veratridine/ouabain essays, indicating a possible difference in the mechanism of action between the bacterium A665 purified fraction 2 and TTX. Vibrios symbionts of pufferfish point out involving in the production of TTX precursors.

Prolonged Duration Local Anesthesia by Combined Delivery of Capsaicin- and Tetrodotoxin-Loaded Liposomes

BACKGROUND

Capsaicin, the active component of chili peppers, can produce sensory-selective peripheral nerve blockade. Coadministration of capsaicin and tetrodotoxin, a site-1 sodium channel blocker, can achieve a synergistic effect on duration of nerve blocks. However, capsaicin can be neurotoxic, and tetrodotoxin can cause systemic toxicity. We evaluated whether codelivery of capsaicin and tetrodotoxin liposomes can achieve prolonged local anesthesia without local or systemic toxicity.

METHODS

Capsaicin- and tetrodotoxin-loaded liposomes were developed. Male Sprague-Dawley rats were injected at the sciatic nerve with free capsaicin, capsaicin liposomes, free tetrodotoxin, tetrodotoxin liposomes, and blank liposomes, singly or in combination. Sensory and motor nerve blocks were assessed by a modified hotplate test and a weight-bearing test, respectively. Local toxicity was assessed by histologic scoring of tissues at the injection sites and transmission electron microscopic examination of the sciatic nerves. Systemic toxicity was assessed by rates of contralateral nerve deficits and/or mortality.

RESULTS

The combination of capsaicin liposomes and tetrodotoxin liposomes achieved a mean duration of sensory block of 18.2 hours (3.8 hours) [mean (SD)], far longer than that from capsaicin liposomes [0.4 hours (0.5 hours)] (P < .001) or tetrodotoxin liposomes [0.4 hours (0.7 hours)] (P < .001) given separately with or without the second drug in free solution. This combination caused minimal myotoxicity and muscle inflammation, and there were no changes in the percentage or diameter of unmyelinated axons. There was no systemic toxicity.

CONCLUSIONS

The combination of encapsulated tetrodotoxin and capsaicin achieved marked prolongation of nerve block. This combination did not cause detectable local or systemic toxicity. Capsaicin may be useful for its synergistic effects on other formulations even when used in very small, safe quantities.

First detection of tetrodotoxin and high levels of paralytic shellfish poisoning toxins in shellfish from Sicily (Italy) by three different analytical methods

Paralytic shellfish toxins (PST) and tetrodotoxin (TTX) are naturally-occurring toxins that may contaminate the food chain, inducing similar neurological symptoms in humans. They are co-extracted under the same conditions and thus their combined detection is desirable. Whilst PST are regulated and officially monitored in Europe, more data on TTX occurrence in bivalves and gastropods are needed before meaningful regulations can be established. In this study, we used three separate analytical methods - pre-column oxidation with liquid chromatography and fluorescence detection, ultrahigh performance hydrophilic interaction liquid chromatography (HILIC) tandem mass spectrometry (MS/MS) and HILIC high resolution (HR) MS/MS - to investigate the presence of PST and TTX in seawater and shellfish (mussels, clams) collected in spring summer 2015 to 2017 in the Mediterranean Sea. Samples were collected at 10 sites in the Syracuse Bay (Sicily, Italy) in concomitance with a mixed bloom of Alexandrium minutum and A. pacificum. A very high PST contamination in mussels emerged, unprecedentedly found in Italy, with maximum total concentration of 10851 μg saxitoxin equivalents per kg of shellfish tissue measured in 2016. In addition, for the first time TTX was detected in Italy in most of the analysed samples in the range 0.8-6.4 μg TTX eq/kg. The recurring blooms of PST-producing species over the 3-year period, the high PST levels and the first finding of TTX in mussels from the Syracuse bay, suggest that monitoring programmes of PST and TTX in seafood should be activated in this geographical area.

The evolution and origin of tetrodotoxin acquisition in the blue-ringed octopus (genus Hapalochlaena)

Tetrodotoxin is a potent non-proteinaceous neurotoxin, which is commonly found in the marine environment. Synthesised by bacteria, tetrodotoxin has been isolated from the tissues of several genera including pufferfish, salamanders and octopus. Believed to provide a defensive function, the independent evolution of tetrodotoxin sequestration is poorly understood in most species. Two mechanisms of tetrodotoxin resistance have been identified to date, tetrodotoxin binding proteins in the circulatory system and mutations to voltage gated sodium channels, the binding target of tetrodotoxin with the former potentially succeeding the latter in evolutionary time. This review focuses on the evolution of tetrodotoxin acquisition, in particular how it may have occurred within the blue-ringed octopus genus (Hapalochlaena) and the subsequent impact on venom evolution.

New Invasive Nemertean Species (Cephalothrix Simula) in England with High Levels of Tetrodotoxin and a Microbiome Linked to Toxin Metabolism

The marine nemertean Cephalothrix simula originates from the Pacific Ocean but in recent years has been discovered in northern Europe. The species has been associated with high levels of the marine neurotoxin Tetrodotoxin, traditionally associated with Pufferfish Poisoning. This study reports the first discovery of two organisms of C. simula in the UK, showing the geographical extent of this species is wider than originally described. Species identification was initially conducted morphologically, with confirmation by Cox 1 DNA sequencing. 16S gene sequencing enabled the taxonomic assignment of the microbiome, showing the prevalence of a large number of bacterial genera previously associated with TTX production including Alteromonas, Vibrio and Pseudomonas. LC-MS/MS analysis of the nemertean tissue revealed the presence of multiple analogues of TTX, dominated by the parent TTX, with a total toxin concentration quantified at 54 µg TTX per g of tissue. Pseudomonas luteola isolated from C. simula, together with Vibrio alginolyticus from the native nemertean Tubulanus annulatus, were cultured at low temperature and both found to contain TTX. Overall, this paper confirms the high toxicity of a newly discovered invasive nemertean species with links to toxin-producing marine bacteria and the potential risk to human safety. Further work is required to assess the geographical extent and toxicity range of C. simula along the UK coast in order to properly gauge the potential impacts on the environment and human safety.

Genome editing of pufferfish saxitoxin- and tetrodotoxin-binding protein type 2 in Takifugu rubripes

The pufferfish saxitoxin- and tetrodotoxin-binding protein 2 (PSTBP2), which is involved in toxin accumulation, was knocked out in Takifugu rubripes embryos by using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 genome-editing technology. Treating the embryos with one of two single-guide RNA (sgRNA) resulted in mutation rates of 57.1% and 62.5%, respectively, as estimated using a heteroduplex mobility assay at 3 days postfertilization. Both sgRNAs might induced frameshift mutations that knocked out the T. rubripes PSTBP2.

Parallel lives of symbionts and hosts: chemical mutualism in marine animals

Covering: up to 2018 Symbiotic microbes interact with animals, often by producing natural products (specialized metabolites; secondary metabolites) that exert a biological role. A major goal is to determine which microbes produce biologically important compounds, a deceptively challenging task that often rests on correlative results, rather than hypothesis testing. Here, we examine the challenges and successes from the perspective of marine animal-bacterial mutualisms. These animals have historically provided a useful model because of their technical accessibility. By comparing biological systems, we suggest a common framework for establishing chemical interactions between animals and microbes.

Difference in Uptake of Tetrodotoxin and Saxitoxins into Liver Tissue Slices among Pufferfish, Boxfish and Porcupinefish

Although pufferfish of the family Tetraodontidae contain high levels of tetrodotoxin (TTX) mainly in the liver, some species of pufferfish, boxfish of the family Ostraciidae, and porcupinefish of the family Diodontidae do not. To clarify the mechanisms, uptake of TTX and saxitoxins (STXs) into liver tissue slices of pufferfish, boxfish and porcupinefish was examined. Liver tissue slices of the pufferfish (toxic species Takifugu rubripes and non-toxic species Lagocephalus spadiceus, L. cheesemanii and Sphoeroides pachygaster) incubated with 50 µM TTX accumulated TTX (0.99-1.55 µg TTX/mg protein) after 8 h, regardless of the toxicity of the species. In contrast, in liver tissue slices of boxfish (Ostracion immaculatus) and porcupinefish (Diodon holocanthus, D. liturosus, D. hystrix and Chilomycterus reticulatus), TTX content did not increase with incubation time, and was about 0.1 µg TTX/mg protein. When liver tissue slices were incubated with 50 µM STXs for 8 h, the STXs content was <0.1 µg STXs/mg protein, irrespective of the fish species. These findings indicate that, like the toxic species of pufferfish T. rubripes, non-toxic species such as L. spadiceus, L. cheesemanii and S. pachygaster, potentially take up TTX into the liver, while non-toxic boxfish and porcupinefish do not take up either TTX or STXs.

A Study of 11-[³H]-Tetrodotoxin Absorption, Distribution, Metabolism and Excretion (ADME) in Adult Sprague-Dawley Rats

Tetrodotoxin (TTX) is a powerful sodium channel blocker that in low doses can safely relieve severe pain. Studying the absorption, distribution, metabolism and excretion (ADME) of TTX is challenging given the extremely low lethal dose. We conducted radiolabeled ADME studies in Sprague-Dawley rats. After a single dose of 6 μg/(16 μCi/kg) 11-[³H]TTX, pharmacokinetics of plasma total radioactivity were similar in male and female rats. Maximum radioactivity (5.56 ng Eq./mL) was reached in 10 min. [³H]TTX was below detection in plasma after 24 h. The area under the curve from 0 to 8 h was 5.89 h·ng Eq./mL; mean residence time was 1.62 h and t_½ was 2.31 h. Bile secretion accounted for 0.43% and approximately 51% of the dose was recovered in the urine, the predominant route of elimination. Approximately 69% was recovered, suggesting that hydrogen tritium exchange in rats produced tritiated water excreted in breath and saliva. Average total radioactivity in the stomach, lungs, kidney and intestines was higher than plasma concentrations. Metabolite analysis of plasma, urine and feces samples demonstrated oxidized TTX, the only identified metabolite. In conclusion, TTX was rapidly absorbed and excreted in rats, a standard preclinical model used to guide the design of clinical trials.

Toxic Takifugu pardalis eggs found in Takifugu niphobles gut: Implications for TTX accumulation in the pufferfish

Pufferfish (Takifugu spp.) possess a potent neurotoxin, tetrodotoxin (TTX). TTX has been detected in various organisms including food animals of pufferfish, and TTX-producing bacteria have been isolated from these animals. TTX in marine pufferfish accumulates in the pufferfish via the food web starting with marine bacteria. However, such accumulation is unlikely to account for the amount of TTX in the pufferfish body because of the minute amounts of TTX produced by marine bacteria. Therefore, the toxification process in pufferfish still remains unclear. In this article we report the presence of numerous Takifugu pardalis eggs in the intestinal contents of another pufferfish, Takifugu niphobles. The identity of T. pardalis being determined by direct sequencing for mitochondrial DNA. LC-MS/MS analysis revealed that the peak detected in the egg samples corresponded to TTX. Toxification experiments in recirculating aquaria demonstrated that cultured Takifugu rubripes quickly became toxic upon being fed toxic (TTX-containing) T. rubripes eggs. These results suggest that T. niphobles ingested the toxic eggs of another pufferfish T. pardalis to toxify themselves more efficiently via a TTX loop consisting of TTX-bearing organisms at a higher trophic level in the food web.

The role of corticosterone and toxicity in the antipredator behavior of the Rough-skinned Newt (Taricha granulosa)

A variety of mechanisms are responsible for enabling an organism to escape a predatory attack, including behavioral changes, alterations in hormone levels, and production and/or secretion of toxins. However, these mechanisms are rarely studied in conjunction with each other. The Rough-skinned Newt (Taricha granulosa) is an ideal organism to examine the relationships between these mechanisms because its behavioral displays and toxin secretion during a predator attack are well documented and readily characterized. While we found no direct relationship between antipredator behavior and endogenous levels of corticosterone (CORT), antipredator behavior was inhibited when exogenous CORT and adrenocorticotropic hormone (ACTH) were administered, resulting in high circulating concentrations of CORT, indicating that CORT may play a role in mediating the behavior. There was no correlation between the animal's toxicity and either CORT or behavior. The results of this study provide evidence that CORT plays an important, yet complex, role in the antipredator response of these amphibians.

[Characterization, identification, and screening for tetrodotoxin production by bacteria associated with the Cephalotrix simula (Ivata, 1952) proboscis worm]

The taxonomic composition of bacteria associated with the Cephalotrix simula proboscis worm was studied and screening of the tetrodotoxin (TTX)-producing bacteria was carried out using confocal laser scanning microscopy and polyclonal antibodies. Bacterial isolates were identified using the 16S rRNA gene sequencing and phenotypic characteristics. A Bacillus species was found to be responsible for tetrodotoxin production in C. simula proboscis worms. Vibrio spp. predominated in the associated microflora (68.18% of the total number of isolates). Analysis of the sensitivity of 16 strains to antibiotics of various classes revealed multiple resistance to three or more antibiotics in all studied isolates. Poor growth of most of the isolates on all laboratory media was an indirect confirmation of the symbiotic relationships between the micro- and macroorganisms.

Microbial diversity associated with tetrodotoxin production in marine organisms

Tetrodotoxin (TTX), is a potent neurotoxin found in genetically diversed organisms. Many TTX producing microorganism have also been isolated from TTX bearing animals. The TTX producing microbes found in four different phylum (Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes), the Proteobacteria are the dominating one. In most of the cases, TTX producing microbes are found in the intestine of the TTX producing vector indicating the origin of TTX through food chain. This paper reviews the TTX and its analogs and the geographic distribution of TTX in symbiotic microorganism and its production.

Removal of toxin (tetrodotoxin) from puffer ovary by traditional fermentation

The amounts of puffer toxin (tetrodotoxin, TTX) extracted from the fresh and the traditional Japanese salted and fermented “Nukazuke” and “Kasuzuke” ovaries of Takifugu stictonotus (T. stictonotus) were quantitatively analyzed in the voltage-dependent sodium current (I_Na) recorded from mechanically dissociated single rat hippocampal CA1 neurons. The amount of TTX contained in “Nukazuke” and “Kasuzuke” ovaries decreased to 1/50–1/90 times of that of fresh ovary during a salted and successive fermented period over a few years. The final toxin concentration after fermentation was almost close to the TTX level extracted from T. Rubripes” fresh muscle that is normally eaten. It was concluded that the fermented “Nukazuke” and “Kasuzuke” ovaries of puffer fish T. Stictonotus are safe and harmless as food.

Inhibitory effect of the recombinant Phoneutria nigriventer Tx1 toxin on voltage-gated sodium channels

Phoneutria nigriventer toxin Tx1 (PnTx1, also referred to in the literature as Tx1) exerts inhibitory effect on neuronal (Na(V)1.2) sodium channels in a way dependent on the holding potential, and competes with μ-conotoxins but not with tetrodotoxin for their binding sites. In the present study we investigated the electrophysiological properties of the recombinant toxin (rPnTx1), which has the complete amino acid sequence of the natural toxin with 3 additional residues: AM on the N-terminal and G on the C-terminal. At the concentration of 1.5 μM, the recombinant toxin inhibits Na(+) currents of dorsal root ganglia neurons (38.4 ± 6.1% inhibition at -80 mV holding potential) and tetrodotoxin-resistant Na(+) currents (26.2 ± 4.9% at the same holding potential). At -50 mV holding potential the inhibition of the total current reached 71.3 ± 2.3% with 1.5 μM rPnTx1. The selectivity of rPnTx1 was investigated on ten different isoforms of voltage-gated sodium channels expressed in Xenopus oocytes. The order of potency for rPnTx1 was: rNa(V)1.2 > rNa(V)1.7 ≈ rNa(V)1.4 ≥ rNa(V)1.3 > mNa(V)1.6 ≥ hNa(V)1.8. No effect was seen on hNa(V)1.5 and on the arthropods isoforms (DmNa(V)1, BGNa(V)1.1a and VdNa(V)1). The IC(50) for Na(V)1.2 was 33.7 ± 2.9 nM with a maximum inhibition of 83.3 ± 1.9%. The toxin did not alter the voltage-dependence of channel gating and was effective on Na(V)1.2 channels devoid of inactivation. It was ineffective on neuronal calcium channels. We conclude that rPnTx1 has a promising selectivity, and that it may be a valuable model to achieve pharmacological activities of interest for the treatment of channelopathies and neuropathic pain.

Differential effects of Zn2+ on activation, deactivation, and inactivation kinetics in neuronal voltage-gated Na+ channels

Whole-cell, patch-clamp recordings were carried out in acutely dissociated neurons from entorhinal cortex (EC) layer II to study the effects of Zn(2+) on Na(+) current kinetics and voltage dependence. In the presence of 200 μM extracellular Cd(2+) to abolish voltage-dependent Ca(2+) currents, and 100 mM extracellular Na(+), 1 mM Zn(2+) inhibited the transient Na(+) current, I (NaT), only to a modest degree (~17% on average). A more pronounced inhibition (~36%) was induced by Zn(2+) when extracellular Na(+) was lowered to 40 mM. Zn(2+) also proved to modify I (NaT) voltage-dependent and kinetic properties in multiple ways. Zn(2+) (1 mM) shifted the voltage dependence of I (NaT) activation and that of I (NaT) onset speed in the positive direction by ~5 mV. The voltage dependence of I (NaT) steady-state inactivation and that of I (NaT) inactivation kinetics were markedly less affected by Zn(2+). By contrast, I (NaT) deactivation speed was prominently accelerated, and its voltage dependence was shifted by a significantly greater amount (~8 mV on average) than that of I (NaT) activation. In addition, the kinetics of I (NaT) recovery from inactivation were significantly slowed by Zn(2+). Zn(2+) inhibition of I (NaT) showed no signs of voltage dependence over the explored membrane-voltage window, indicating that the above effects cannot be explained by voltage dependence of Zn(2+)-induced channel-pore block. These findings suggest that the multiple, voltage-dependent state transitions that the Na(+) channel undergoes through its activation path are differentially sensitive to the gating-modifying effects of Zn(2+), thus resulting in differential modifications of the macroscopic current's activation, inactivation, and deactivation. Computer modeling provided support to this hypothesis.

Surface plasmon resonance biosensor for determination of tetrodotoxin: prevalidation study

A label-free surface plasmon resonance biosensor method was applied to determine tetrodotoxin (TTX) in pufferfish matrixes using an antibody inhibition assay format. A prevalidation study was conducted to demonstrate the assay performance characteristics, such as selectivity, LOD, LOQ, repeatability, reproducibility, and accuracy. Three participating laboratories reported standard curves in buffer and pufferfish matrix. A set of blind samples with TTX spiked into buffer as well as in 10% pufferfish extract were analyzed. Additionally, three blind naturally contaminated samples were analyzed, and the results were compared to those obtained using a reference method (HPLC/electrospray ionization-selected reaction monitoring-MS). The developed method was demonstrated to be capable of detecting TTX in pufferfish matrix standard samples in a broad concentration range (2-9000 ng/mL) with an LOD of 1.5 ng/mL. Between-laboratory recovery values were in the range of 51-190% with a mean of 107%, and 64-180% with a mean of 103% for TTX-spiked samples in buffer and pufferfish matrix, respectively. Between-laboratory recoveries were in the satisfactory range of 101-119% for naturally contaminated samples. This robust, rapid, and noninvasive method may serve as an attractive alternative to established methods for detection of TTX in pufferfish extracts.

Genetic architecture of a feeding adaptation: garter snake (Thamnophis) resistance to tetrodotoxin bearing prey

Detailing the genetic basis of adaptive variation in natural populations is a first step towards understanding the process of adaptive evolution, yet few ecologically relevant traits have been characterized at the genetic level in wild populations. Traits that mediate coevolutionary interactions between species are ideal for studying adaptation because of the intensity of selection and the well-characterized ecological context. We have previously described the ecological context, evolutionary history and partial genetic basis of tetrodotoxin (TTX) resistance in garter snakes (Thamnophis). Derived mutations in a voltage-gated sodium channel gene (Na(v)1.4) in three garter snake species are associated with resistance to TTX, the lethal neurotoxin found in their newt prey (Taricha). Here we evaluate the contribution of Na(v)1.4 alleles to TTX resistance in two of those species from central coastal California. We measured the phenotypes (TTX resistance) and genotypes (Na(v)1.4 and microsatellites) in a local sample of Thamnophis atratus and Thamnophis sirtalis. Allelic variation in Na(v)1.4 explains 23 per cent of the variation in TTX resistance in T. atratus while variation in a haphazard sample of the genome (neutral microsatellite markers) shows no association with the phenotype. Similarly, allelic variation in Na(v)1.4 correlates almost perfectly with TTX resistance in T. sirtalis, but neutral variation does not. These strong correlations suggest that Na(v)1.4 is a major effect locus. The simple genetic architecture of TTX resistance in garter snakes may significantly impact the dynamics of phenotypic coevolution. Fixation of a few alleles of major effect in some garter snake populations may have led to the evolution of extreme phenotypes and an 'escape' from the arms race with newts.

The outer vestibule of the Na+ channel-toxin receptor and modulator of permeation as well as gating

The outer vestibule of voltage-gated Na(+) channels is formed by extracellular loops connecting the S5 and S6 segments of all four domains ("P-loops"), which fold back into the membrane. Classically, this structure has been implicated in the control of ion permeation and in toxin blockage. However, conformational changes of the outer vestibule may also result in alterations in gating, as suggested by several P-loop mutations that gave rise to gating changes. Moreover, partial pore block by mutated toxins may reverse gating changes induced by mutations. Therefore, toxins that bind to the outer vestibule can be used to modulate channel gating.

LC/MS analysis of tetrodotoxin and its deoxy analogs in the marine puffer fish Fugu niphobles from the southern coast of Korea, and in the brackishwater puffer fishes Tetraodon nigroviridis and Tetraodon biocellatus from Southeast Asia

Tetrodotoxin (TTX) and its deoxy analogs, 5-deoxyTTX, 11-deoxyTTX, 6,11-dideoxyTTX, and 5,6,11-trideoxyTTX, were quantified in the tissues of three female and three male specimens of the marine puffer fish, Fugu niphobles, from the southern coast of Korea, and in the whole body of the brackishwater puffer fishes, Tetraodon nigroviridis (12 specimens) and Tetrodon biocellatus (three specimens) from Southeast Asia using LC/MS in single ion mode (SIM). Identification of these four deoxy analogs in the ovarian tissue of F. niphobles were further confirmed by LC/MS/MS. TTX and 5,6,11-trideoxyTTX were detected in all three puffer fish species as the major TTX analogs, similar to Japanese Fugu pardalis. While 6,11-dideoxyTTX was also found to be a major analog in almost all tissues of Korean F. niphobles, this analog was minor in the two Tetraodon species and Japanese F. pardalis. Among the tissues of F. niphobles, the concentrations of TTXs were highest in the ovaries (female) and skin (female and male).

Endogenous polyamines regulate cortical neuronal excitability by blocking voltage-gated Na+ channels

Because the excitable properties of neurons in the neocortex depend on the characteristics of voltage-gated Na(+) channels, factors which regulate those characteristics can fundamentally modify the dynamics of cortical circuits. Here, we report on a novel neuromodulatory mechanism that links the availability of Na(+) channels to metabolism of polyamines (PAs) in the cerebral cortex. Using single channel and whole-cell recordings, we found that products of PA metabolism, the ubiquitous aliphatic polycations spermine and spermidine, are endogenous blockers of Na(+) channels in layer 5 pyramidal cells. Because the blockade is activity-dependent, it is particularly effective against Na(+) channels which fail to inactivate rapidly and thus underlie the persistent Na(+) current. At the level of the local cortical circuit, pharmacological depletion of PAs led to increased spontaneous spiking and periods of hypersynchronous discharge. Our data suggest that changes in PA levels, whether associated with normal brain states or pathological conditions, profoundly modify Na(+) channel availability and thereby shape the integrative behavior of single neurons and neocortical circuits.

Transfer profile of intramuscularly administered tetrodotoxin to non-toxic cultured specimens of the pufferfish Takifugu rubripes

Tetrodotoxin (TTX) was intramuscularly administered to non-toxic cultured specimens of the pufferfish Takifugu rubripes to investigate TTX transfer/accumulation profiles in the pufferfish body. In two groups of test fish administered either 50MU/individual of TTX standard (purified TTX; PTTX) or crude extract of toxic pufferfish ovary (crude TTX; CTTX), TTX rapidly transferred from the muscle via the blood to other organs. The toxin transfer profiles differed between groups, however, from 4 to 72h. In the PTTX group, little TTX was retained in the liver, and most (>96%) of the toxin remaining in the body transferred/accumulated in the skin after 12h, whereas in the CTTX group, a considerable amount of toxin (15%-23% of the administered toxin or 28%-58% of the remaining toxin) was transferred/retained in the liver for up to 24h, despite the fact that 89% of the remaining toxin transferred/accumulated in the skin at the end of rearing period (168h). The total amount of toxin remaining in the entire body at 1-4h was approximately 60% of the administered toxin in both groups, which decreased at 8-12h, and then increased again to approximately 60%-80% at 24-168h. Immunohistochemical observation revealed that the toxin accumulated in the skin was localized at the basal cells of the epidermal layer.

Contractile effect of tachykinins on Suncus murinus (house musk shrew) isolated ileum

Recent studies used Suncus murinus to investigate the anti-emetic potential of NK(1) tachykinin receptor antagonists. However, the pharmacology of tachykinin receptors in this species has not been fully characterized. In the present studies, therefore, we examined a range of tachykinin receptor agonists for a capacity to induce contractions of the isolated ileum. The tachykinin NK1 receptor preferring agonists substance P, septide and [Sar9Met(O2)11] substance P, and the tachykinin NK2 preferring agonists neurokinin A and GR 64349 (Lys-Asp-Ser-Phe-Val-Gly-R-gamma-lactam-Leu-Met-NH2) caused concentration dependent contractions with EC50 values in the nanomolar range. However, the tachykinin NK3 preferring agonists neurokinin B and senktide (1nM-1microM) induced only weak contractions. The action of senktide, but not [Sar9Met(O2)11] substance P, septide, or GR 64349, was antagonized significantly by atropine (P<0.05); tetrodotoxin and hexamethonium were inactive. The tachykinin NK1 receptor antagonist CP-99,994 ((+)-[(2S,3S)-3-(2-methoxy-benzyl-amino)-2-phenylpiperidine]) (10-100nM) inhibited substance P- and septide-induced contractions non-competitively. The pA2 value estimated for CP-99,994 against septide was 7.3+/-0.1. It also non-competitively antagonized the contractile responses induced by [Sar9Met(O2)11] substance P with a pA2 of 7.4+/-0.1. CP-99,994 also had a slight inhibitory action on neurokinin A-induced contractions, but did not modify the action of GR 64349. Conversely, the tachykinin NK2 receptor antagonist, saredutant, competitively antagonized GR 64349-induced contractions with a pA2 of 7.34+/-0.02. On the other hand, the presence of both CP-99,994 and saredutant competitively antagonized substance P-induced contraction. The present studies indicate that tachykininNK1 and NK2 receptors exist in the ileum of S. murinus and are involved in mediating contractions directly on smooth muscle, whereas tachykinin NK3 receptors may play a minor role involving a release of acetylcholine.

[Toxicity screening and identification of bacteria isolated from snails Nassarius semiplicatus and their habitat]

OBJECTIVE

Tetrodotoxin and its analogues (TTXs) were responsible for the poisoning incidents associated with snail Nassarius spp. We studied bacteria isolated from toxic snails as well as their habitat to probe into the relationship between bacteria and toxicity of nassariid gastropod.

METHODS

Two snail samples were collected from Sheyang, Jiangsu Province on June 13 and 19, 2006, and the toxicity of the snail samples was tested with mouse bioassay method. Bacteria were isolated from the snail samples and from their habitat. A part of isolated bacteria were then cultured in the lab, and TTX in bacteria were screened with an ELISA method.

RESULTS

The snails collected were identified as Nassarius semiplicatus, and the toxicity of the 2 samples were 247 mouse unit (MU) and 270 MU / 100 g tissue (wet weight), respectively. TTX was detected in 9 strains among the 14 strains of bacteria isolated from the snail samples and their habitat. TTX content in the toxic strains was very low, which ranged from 15 ng/g to 96 ng/g. Partial of the 16S ribosomal DNA (rDNA) of the toxic strains were then sequenced after PCR amplification, and the toxic strains of bacteria were tentatively identified based on the alignment of these sequences with published data. Toxic strains were closely affiliated with Vibrio, Shewanella, Planococcus, Marinomonas, Photobacterium.

CONCLUSION

These findings suggested that TTX-producing bacteria may play an important role in TTX production or accumulation in nassariid gastropod.

Tetrodotoxin--distribution and accumulation in aquatic organisms, and cases of human intoxication

Many pufferfish of the family Tetraodontidae possess a potent neurotoxin, tetrodotoxin (TTX). In marine pufferfish species, toxicity is generally high in the liver and ovary, whereas in brackish water and freshwater species, toxicity is higher in the skin. In 1964, the toxin of the California newt was identified as TTX as well, and since then TTX has been detected in a variety of other organisms. TTX is produced primarily by marine bacteria, and pufferfish accumulate TTX via the food chain that begins with these bacteria. Consequently, pufferfish become non-toxic when they are fed TTX-free diets in an environment in which the invasion of TTX-bearing organisms is completely shut off. Although some researchers claim that the TTX of amphibians is endogenous, we believe that it also has an exogenous origin, i.e., from organisms consumed as food. TTX-bearing animals are equipped with a high tolerance to TTX, and thus retain or accumulate TTX possibly as a biologic defense substance. There have been many cases of human intoxication due to the ingestion of TTX-bearing pufferfish, mainly in Japan, China, and Taiwan, and several victims have died. Several cases of TTX intoxication due to the ingestion of small gastropods, including some lethal cases, were recently reported in China and Taiwan, revealing a serious public health issue.

The scent of danger: arginine as an olfactory cue of reduced predation risk

Animal perception of chemosensory cues is a function of ecological context. Larvae of the California newt (Taricha torosa), for example, exhibit predator-avoidance behavior in response to a chemical from cannibalistic adults. The poison tetrodotoxin (TTX), well known as an adult chemical defense, stimulates larval escape to refuges. Although they are cannibals, adult newts feed preferentially on worms (Eisenia rosea) over conspecific young. Hence, larval avoidance reactions to TTX are suppressed in the presence of odor from these alternative prey. The free amino acid, arginine, is abundant in fluids emitted by injured worms. Here, we demonstrate that arginine is a natural suppressant of TTX-stimulated larval escape behavior. Compared to a tapwater control, larvae initiated vigorous swimming in response to 10(-7) mol l(-1) TTX. This excitatory response was eliminated when larval nasal cavities were blocked with an inert gel, but not when gel was placed on the forehead (control). In additional trials, a binary mixture of arginine and 10(-7) mol l(-1) TTX failed to induce larval swimming. The inhibitory effect of arginine was, however, dose dependent. An arginine concentration as low as 0.3-times that of TTX was significantly suppressant. Further analysis showed that suppression by arginine of TTX-stimulated behavior was eliminated by altering the positively-charged guanidinium moiety, but not by modifying the carbon chain, carboxyl group, or amine group. These results are best explained by a mechanism of competitive inhibition between arginine and TTX for common, olfactory receptor binding sites. Although arginine alone has no impact on larval behavior, it nevertheless signals active adult predation on alternative prey, and hence, reduced cannibalism risk.

6,11-Dideoxytetrodotoxin from the puffer fish, Fugu pardalis

The presence of an unknown dideoxy analog of tetrodotoxin was suggested on the liquid chromatography/electrospray ionization-mass spectrometry mass chromatogram of the ovaries of the puffer fish, Fugu pardalis, in single ion monitoring mode to detect at m/z 288. We succeeded to isolate this analog (approximately 0.4 mg) from 200 g of the ovaries and the structure was determined as 6,11-dideoxytetrodotoxin by spectroscopic methods (high resolution-fast atom bombardment-MS and NMR spectroscopy). The discovery of the new analog is highly significant with respect to the biosynthesis or metabolism of tetrodotoxin. We also roughly determined the value of IC(50) (mice, intraperitoneal) for 6,11-dideoxytetrodotoxin as 420 microg/kg and thus it is 42 times less toxic than tetrodotoxin.

The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Nav1.6 voltage-dependent sodium channel

The blocking efficacy of 4,9-anhydro-TTX (4,9-ah-TTX) and TTX on several isoforms of voltage-dependent sodium channels, expressed in Xenopus laevis oocytes, was tested (Nav1.2, Nav1.3, Nav1.4, Nav1.5, Nav1.6, Nav1.7, and Nav1.8). Generally, TTX was 40–231 times more effective, when compared with 4,9-ah-TTX, on a given isoform. An exception was Nav1.6, where 4,9-ah-TTX in nanomole per liter concentrations sufficed to result in substantial block, indicating that 4,9-ah-TTX acts specifically at this peculiar isoform. The IC50 values for TTX/4,9-ah-TTX were as follows (in nmol/l): 7.8 ± 1.3/1,260 ± 121 (Nav1.2), 2.8 ± 2.3/341 ± 36 (Nav1.3), 4.5 ± 1.0/988 ± 62 (Nav1.4), 1,970 ± 565/78,500 ± 11,600 (Nav1.5), 3.8 ± 1.5/7.8 ± 2.3 (Nav1.6), 5.5 ± 1.4/1,270 ± 251 (Nav1.7), and 1,330 ± 459/>30,000 (Nav1.8). Analysis of approximal half-maximal doses of both compounds revealed minor effects on voltage-dependent activation only, whereas steady-state inactivation was shifted to more negative potentials by both TTX and 4,9-ah-TTX in the case of the Nav1.6 subunit, but not in the case of other TTX-sensitive ones. TTX shifted steady-state inactivation also to more negative potentials in case of the TTX-insensitive Nav1.5 subunit, where it also exerted profound effects on the time course of recovery from inactivation. Isoform-specific interaction of toxins with ion channels is frequently observed in the case of proteinaceous toxins. Although the sensitivity of Nav1.1 to 4,9-ah-TTX is not known, here we report evidence on a highly isoform-specific TTX analog that may well turn out to be an invaluable tool in research for the identification of Nav1.6-mediated function, but also for therapeutic intervention.

Neonatal functional blockade of the entorhinal cortex results in disruption of accumbal dopaminergic responses observed in latent inhibition paradigm in adult rats

Latent inhibition (LI) has been found to be disrupted in non-treated patients with schizophrenia. Dopaminergic (DAergic) dysfunctioning is generally acknowledged to occur in schizophrenia. Various abnormalities in the entorhinal cortex (ENT) have been described in patients with schizophrenia. Numerous data also suggest that schizophrenia has a neurodevelopmental origin. The present study was designed to test the hypothesis that reversible inactivation of the ENT during neonatal development results in disrupted DA responses characteristic of LI in adult rats. Tetrodotoxin (TTX) was microinjected locally in the left ENT at postnatal day 8 (PND8). DA variations were recorded in the dorsomedial shell and core parts of the nucleus accumbens (Nacc) using in vivo voltammetry in freely-moving grown-up rats in a LI paradigm. In the first session the animals were pre-exposed (PE) to the conditional stimulus (banana odour) alone. In the second they were aversively conditioned to banana odour. In the third (test) session the following results were obtained in PE animals subjected to temporary inactivation of the ENT at PND8: (1) aversive behaviour was observed in TTX-PE conditioned animals; (2) DA variations in the dorsomedial shell and core parts of the Nacc were similar in TTX-PE and non-pre-exposed conditioned rats. These findings strongly suggest that neonatal disconnection of the ENT disrupts LI in adult animals. They may further our understanding of the pathophysiology of schizophrenia.

Isolation and characterization of bacteria from the copepod Pseudocaligus fugu ectoparasitic on the panther puffer Takifugu pardalis with the emphasis on TTX

A total of 50 bacterial isolates was obtained from the copepod Pseudocaligus fugu, which is a common parasite, collected from the body surface of the panther puffer Takifugu pardalis. On the basis of colony characteristics, these bacterial isolates were grouped into six types, of which only two (Types-I and -II) showed a high affinity for adhesion to the carapace of the banana shrimp Penaeus merguiensis. These two types of adhesive bacteria were identified through 16S rRNA sequence analysis as Shewanella woodyi (Type-I) and Roseobacter sp. (Type-II). Representative isolates of these two adhesive bacteria were examined for tetrodotoxin (TTX) production by high-performance liquid chromatography (HPLC)-fluorometric system, gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). It was rather unexpectedly revealed that TTX and anhydroTTX were present in the supernatant of culture of the Type-II isolate Roseobacter sp.

Heterogeneous population of dopaminergic neurons derived from mouse embryonic stem cells: preliminary phenotyping based on receptor expression and function

The possibility exists that directed differentiation of mouse embryonic stem (mES) cells is capable of yielding enriched populations of dopaminergic neurons, but at present there is little understanding of the pharmacological properties of these cells; or whether such cells represent a pharmacologically, phenotypically similar population. In this study we used a simple culture protocol to generate dopaminergic neurons and offer a preliminary pharmacological investigation of these cells using Ca2+ imaging and [3H]-dopamine release studies. In fluo-4 AM loaded cells, 13-17 days postplating, and after the addition of tetrodotoxin some of the population of mouse embryonic stem cell-derived neurons responded to adenosine triphosphate (ATP), noradrenaline (NA), acetylcholine (ACh) and L-glutamate (L-glut) with elevations of Ca2+ influx. Within the microtubule-associated protein and tyrosine hydroxylase (TH)-positive cell population adenosine triphosphate, noradrenaline, acetylcholine and L-glutamate elicited positive elevations of Ca2+ in 74, 66, 58 and 67% of the population; cells could be further subdivided into three major pharmacologically distinct populations based on the combinations of agonist they responded to. Acetylcholine (30 microM) and noradrenaline (30 microM) were the only agonists to elicit significant tritium overflow from [3H]-dopamine loaded cells. The acetylcholine effect was blocked by atropine (1 microM) and tetrodotoxin (1 microM) and elevated by haloperidol (100 nM). The noradrenaline effects were reduced by cocaine (10 microM), but not by tetrodotoxin (100 nM). These data indicate that the dopaminergic neurons derived from mouse embryonic stem cells represent a heterogeneous population possessing combinations of purinergic, adrenergic, cholinergic and glutamatergic receptors located on the cell soma.

Identification of novel genes related to tetrodotoxin intoxication in pufferfish

To investigate the genes related to the biosynthesis or accumulation of tetrodotoxin (TTX) in pufferfish, mRNA expression patterns in the liver from pufferfish, akamefugu Takifugu chrysops and kusafugu Takifugu niphobles, were compared by mRNA arbitrarily primed reverse transcription-polymerase chain reaction (RAP RT-PCR) with fish bearing different concentrations of TTX and its derivatives. RAP RT-PCR provided a 383 bp cDNA fragment and its transcripts were higher in toxic than non-toxic pufferfish liver. Its deduced amino acid sequence was similar to those of fibrinogen-like proteins reported for other vertebrates. Northern blot analysis and rapid amplification of cDNA ends (RACE) revealed that the cDNA fragment of 383 bp was composed of at least three fibrinogen-like protein (flp) genes, flp-1, flp-2 and flp-3. Relative mRNA levels of flp-1, flp-2 and flp-3 showed a linear correlation with toxicity of the liver for two pufferfish species.

Involvement of carrier-mediated transport system in uptake of tetrodotoxin into liver tissue slices of puffer fish Takifugu rubripes

Although puffer fish contain tetrodotoxin (TTX) at a high concentration mainly in liver, the underlying mechanism remains to be elucidated. In the present study, uptake of TTX into the liver tissue slices of puffer fish Takifugu rubripes was investigated by in vitro incubation experiment. When T. rubripes liver slices were incubated with 0-2000microM TTX at 20 degrees C for 60min, the uptake rates exhibited non-linearity, suggesting that the TTX uptake into T. rubripes liver is carrier-mediated. The TTX uptake was composed of a saturable component (V(max) 47.7+/-5.9pmol/min/mg protein and K(m) 249+/-47microM) and a non-saturable component (P(dif) 0.0335+/-0.0041microL/min/mg protein). The uptake of TTX was significantly decreased to 0.4 and 0.6 fold by the incubation at 5 degrees C and the replacement of sodium-ion by choline in the buffer, respectively, while it was not affected by the presence of 1mM l-carnitine, p-aminohippurate, taurocholate or tetraethylammonium. The TTX uptake by black scraper Thamnaconus modestus liver slices was much lower than that of T. rubripes and independent of the incubation temperature, unlike T. rubripes. These results reveal the involvement of carrier-mediated transport system in the TTX uptake by puffer fish T. rubripes liver slices.

Synaptic inputs to retinal ganglion cells that set the circadian clock

Melanopsin-containing retinal ganglion cells (RGCs) project to the suprachiasmatic nuclei (SCN) and mediate photoentrainment of the circadian system. Melanopsin is a novel retinal-based photopigment that renders these cells intrinsically photosensitive (ip). Although genetic ablation of melanopsin abolishes the intrinsic light response, it has a surprisingly minor effect on circadian photoentrainment. This and other non-visual responses to light are lost only when the melanopsin deficiency is coupled with mutations that disable classical rod and cone photoreceptors, suggesting that melanopsin-containing RGCs also receive rod- and cone-driven synaptic inputs. Using whole-cell patch-clamp recording, we demonstrate that light triggers synaptic currents in ipRGCs via activation of ionotropic glutamate and gamma-aminobutyric acid (GABA) receptors. Miniature postsynaptic currents (mPSCs) were clearly observed in ipRGCs, although they were less robust and were seen less frequently than those seen in non-ip cells. Pharmacological treatments revealed that the majority of ipRGCs receive excitatory glutamatergic inputs that were blocked by DNQX and/or kynurenic acid, as well as inhibitory GABAergic inputs that were blocked by bicuculline. Other ipRGCs received either glutamatergic or GABAergic inputs nearly exclusively. Although strychnine (Strych)-sensitive mPSCs were evident on many non-ipRGCs, indicating the presence of glycinergic inputs, we saw no evidence of Strych-sensitive events in ipRGCs. Based on these results, it is clear that SCN-projecting RGCs can respond to light both via an intrinsic melanopsin-based signaling cascade and via a synaptic pathway driven by classical rod and/or cone photoreceptors. It remains to be determined how the ipRGCs integrate these temporally distinct inputs to generate the signals that mediate circadian photoentrainment and other non-visual responses to light.

Distribution of tetrodotoxin in the body of the blue-ringed octopus (Hapalochlaena maculosa)

Tetrodotoxin (TTX) was quantitatively assayed in six specimens of semi-adult blue-ringed octopus, Hapalochlaena maculosa, by a post-column fluorescent-HPLC system. TTX was found to be present in all body parts, e.g. in high concentrations in the arms followed by the abdomen and cephalothorax. The toxin is not associated exclusively with the posterior salivary gland.

Ion channels and their neural functions: contribution to general problems from studies of brains in non-mammalian species

Ion channels and their neural functions have often been studied in the brains of mammals. However, the brains of some teleost fish species have special features that, at first glance, appear to be atypical and peculiar to that species alone. These teleost fish will contribute considerably to the understanding of general features of the ion channels and their neural functions. We have been interested in the neural mechanisms underlying the adaptive and flexible response of animals to changing environments and have been studying gonadotropin-releasing hormone (GnRH) peptidergic neuron systems, which we think are central for controlling such biologically adaptive responses. We have also been interested in a pretectal nucleus, corpus glomerulosum, which is tentatively regarded to play important roles in the organization of visually-guided feeding behaviors. In both systems, we found that certain types of apparently 'non-typical' Na(+) channels play important roles in neurobiological functions. Here we discuss how the study of functions of these apparently non-typical ion channels might contribute to our understanding of neural functions of vertebrate brains in general.

Distribution of tetrodotoxin, saxitoxin, and their analogs among tissues of the puffer fish Fugu pardalis

The anatomical distribution of tetrodotoxin (TTX), saxitoxin (STX) and their analogs (TTXs, STXs) in three female and three male specimens of the marine puffer fish Fugu pardalis from Miyagi Prefecture, 2005, Japan, were studied. 5-DeoxyTTX, 11-deoxyTTX, and 5,6,11-trideoxyTTX were quantified by liquid chromatography/mass spectrometry (LC/MS) for the first time, and other TTXs and STXs were determined by liquid chromatography-fluorescent detection (LC-FLD). As a result, 5,6,11-trideoxyTTX was found to be the major TTX analog in all tissues tested, whereas 5-deoxyTTX and 11-deoxyTTX were minor components. Especially, in female (n=3), the ratios of 5,6,11-trideoxyTTX to total of all TTX analogs (mole/mole) in ovaries (mean+/-SD, 0.42+/-0.055) were significantly larger than those in livers (0.17+/-0.025) (P<0.05). In contrary, the ratios of 4,9-anhydroTTX to total of all TTX analogs in livers (0.27+/-0.047) were significantly larger than those in ovaries (0.073+/-0.040) (P<0.01). The ratios of TTX to total of all TTX analogs were not significantly different between ovaries (0.47+/-0.078) and livers (0.55+/-0.067). In male (n=3), all these ratios were not significantly different between livers and testis. 4-S-CysteinylTTX was detected in liver, spleen, gall, and intestine in 1-6mole% of total of all TTX analogs, supporting our previous hypothesis that 4-S-cysteinylTTX is a metabolite of TTX.

Adaptive evolution of tetrodotoxin resistance in animals

Tetrodotoxin (TTX), first isolated from pufferfish (tetraodontids), is a highly potent neurotoxin that selectively binds to voltage-gated sodium channels (Na(v)) in muscle and nerve tissues causing paralysis and death. Saxitoxin (STX) is a TTX-related neurotoxin produced by dinoflagellates. Recent investigations have implicated diverse substitutions in the P-loop regions of skeletal muscle and neuronal Na(v) channels in the convergent evolution of neurotoxin resistance in pufferfish, garter snakes and softshell clams, which has enabled them to feed on TTX- and STX-bearing organisms.

Carbamazepine interacts with a slow inactivation state of NaV1.8-like sodium channels

Carbamazepine was tested on high-threshold TTX-resistant Na+ currents (TTX-R-currents), evoked from acutely isolated rat dorsal root ganglion (DRG) cells. Under control conditions, the TTX-R-currents recorded from different DRG cells varied greatly regarding use-dependent inactivation (TTX-R-current UDI), measured as the percent decrease in current amplitude induced by changing the current activation rate from 0.1 Hz to 1.0 Hz. Also, when TTX-R-currents were evoked at 0.1 Hz from a holding potential (hp) of -60 mV, a larger fraction of TTX-R-channels resided tonically in a slow inactivation state in DRG cells with more TTX-R-current UDI versus those with less TTX-R-current UDI. The block of TTX-R-currents evoked from hp -60 mV by 100-microM carbamazepine and the EC50 for carbamazepine block was positively correlated with TTX-R-current UDI. The slope factors estimated for the concentration-response curves averaged 0.68, suggesting the presence of low and high affinity sites. Fitting the data with a two-site binding isotherm gave estimates of 30 microM and 760 microM for the EC50s of the high and low affinity sites, respectively. The fraction of the total fit attributed to the high affinity site was positively correlated with TTX-R-current UDI. Carbamazepine increased the fast and slow time constants for recovery from inactivation and the fraction of the fit attributed to the slow time constant. These data suggest that carbamazepine interacts with a slow inactivation state of TTX-R-channels. This particular mechanism might be exploited in future research aimed at developing pain medications that selectively block Na(V)1.8 channels or Na+ channels in general.