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Domoic acid (DA), a neurotoxin, is produced by marine algae and has caused toxications worldwide in animals and humans. However, the toxicokinetics of DA have not been fully evaluated, and information is missing on the disposition of DA following oral exposures at doses that are considered safe for human consumption. In this study, toxicokinetics of DA were investigated in cynomolgus monkeys following single doses of 5 µ g/kg DA intravenously, 0.075 mg/kg DA orally, and 0.15 mg/kg DA orally. After intravenous dosing, DA had a systemic clearance of 124 ± 71 (ml/h)/kg, volume of distribution at steady state of 131 ± 71 ml/kg and elimination half-life of 1.2 ± 1.1 hours. However, following oral dosing, the average terminal half-life of DA was 11.3 ± 2.4 hours, indicating that DA disposition follows flip-flop kinetics with slow, rate-limiting absorption. The absorption of DA was low after oral dosing with absolute bioavailability of 6% ± 4%. The renal clearance of DA was variable [21-152 (ml/h)/kg] with 42% ± 11% of the intravenous DA dose recovered in urine. A physiologically based pharmacokinetic model was developed for DA in monkeys and humans that replicated the flip-flop kinetics observed after oral administration and allowed simulation of urinary excretion and brain and kidney distribution of DA following intravenous and oral dosing. This study is the first to characterize DA disposition at exposure levels close to the current estimated tolerable daily intake and to mechanistically model DA disposition in a model species, providing important information of the toxicokinetics of DA for human safety assessment., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)

The ubiquitous efflux transporter ABCC5 (ATP-binding cassette subfamily C member 5) is present at high levels in the blood-brain barrier, neurons, and glia, but its in vivo substrates and function are not known. Using untargeted metabolomic screens, we show that Abcc5(-/-) mice accumulate endogenous glutamate conjugates in several tissues, but brain in particular. The abundant neurotransmitter N-acetylaspartylglutamate was 2.4-fold higher in Abcc5(-/-) brain. The metabolites that accumulated in Abcc5(-/-) tissues were depleted in cultured cells that overexpressed human ABCC5. In a vesicular membrane transport assay, ABCC5 also transported exogenous glutamate analogs, like the classic excitotoxic neurotoxins kainic acid, domoic acid, and NMDA; the therapeutic glutamate analog ZJ43; and, as previously shown, the anti-cancer drug methotrexate. Glutamate conjugates and analogs are of physiological relevance because they can affect the function of glutamate, the principal excitatory neurotransmitter in the brain. After CO2 asphyxiation, several immediate early genes were expressed at lower levels in Abcc5(-/-) brains than in wild type brains, suggesting altered glutamate signaling. Our results show that ABCC5 is a general glutamate conjugate and analog transporter that affects the disposition of endogenous metabolites, toxins, and drugs., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

Domoic acid (DA), an excitatory amino acid produced by diatoms belonging to the genus Pseudo-nitzschia, is a glutamate analog responsible for the neurologic condition referred to as amnesic shellfish poisoning. To date, the renal effects of DA have been underappreciated, although renal filtration is the primary route of systemic elimination and the kidney expresses ionotropic glutamate receptors. To characterize the renal effects of DA, we administered either a neurotoxic dose of DA or doses below the recognized limit of toxicity to adult Sv128/Black Swiss mice. DA preferentially accumulated in the kidney and elicited marked renal vascular and tubular damage consistent with acute tubular necrosis, apoptosis, and renal tubular cell desquamation, with toxic vacuolization and mitochondrial swelling as hallmarks of the cellular damage. Doses≥0.1 mg/kg DA elevated the renal injury biomarkers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin, and doses≥0.005 mg/kg induced the early response genes c-fos and junb. Coadministration of DA with the broad spectrum excitatory amino acid antagonist kynurenic acid inhibited induction of c-fos, junb, and neutrophil gelatinase-associated lipocalin. These findings suggest that the kidney may be susceptible to excitotoxic agonists, and renal effects should be considered when examining glutamate receptor activation. Additionally, these results indicate that DA is a potent nephrotoxicant, and potential renal toxicity may require consideration when determining safe levels for human exposure., (Copyright © 2014 by the American Society of Nephrology.)

The western North Atlantic population of right whales (Eubalaena glacialis) is one of the most critically endangered of any whale population in the world. Among the factors considered to have potentially adverse effects on the health and reproduction of E. glacialis are biotoxins produced by certain microalgae responsible for causing harmful algal blooms. The worldwide incidence of these events has continued to increase dramatically over the past several decades and is expected to remain problematic under predicted climate change scenarios. Previous investigations have demonstrated that N. Atlantic right whales are being exposed to at least two classes of algal-produced environmental neurotoxins-paralytic shellfish toxins (PSTs) and domoic acid (DA). Our primary aims during this six-year study (2001-2006) were to assess whether the whales' exposure to these algal biotoxins occurred annually over multiple years, and to what extent individual whales were exposed repeatedly and/or concurrently to one or both toxin classes. Approximately 140 right whale fecal samples obtained across multiple habitats in the western N. Atlantic were analyzed for PSTs and DA. About 40% of these samples were attributed to individual whales in the North Atlantic Right Whale Catalog, permitting analysis of biotoxin exposure according to sex, age class, and reproductive status/history. Our findings demonstrate clearly that right whales are being exposed to both of these algal biotoxins on virtually an annual basis in multiple habitats for periods of up to six months (April through September), with similar exposure rates for females and males (PSTs: ∼70-80%; DA: ∼25-30%). Notably, only one of 14 lactating females sampled did not contain either PSTs or DA, suggesting the potential for maternal toxin transfer and possible effects on neonatal animals. Moreover, 22% of the fecal samples tested for PSTs and DA showed concurrent exposure to both neurotoxins, leading to questions of interactive effects. Targeted studies employing both in vivo and in vitro model systems represent the next logical step in assessing how and to what extent these algal biotoxins might compromise the health and reproduction of this endangered population., (Published by Elsevier Inc.)

The intestinal absorption mechanism of domoic acid (DA) was investigated using Caco-2 cells. DA is a tricarboxylic amino acid that contains a glutamic acid moiety, and causes deficits in short-term memory by binding to glutamate receptors as an agonist of glutamic acid. Caco-2 cell monolayers cultured on permeable membranes were incubated with 100 μM DA on either the apical or basolateral side, and the transcellular transport of DA was measured. The transcellular transport of DA from the apical to basolateral side was about twofold that in the opposite direction. The transcellular transport of DA from the apical side was optimal at a neutral pH, and was temperature- and Cl(-)-dependent, but was Na(+)-independent. Coincubation of DA with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an anion exchange inhibitor, significantly decreased the apical-to-basolateral transport of DA by 48%, and coincubation with probenecid (a non-specific anion transport inhibitor) significantly decreased the transport of DA by 31%. In contrast, coincubation with glutamic acid, succinic acid (a dicarboxylic acid), or citric acid (a tricarboxylic acid) did not decrease the transport of DA. These results suggest that the apical-to-basolateral transport of DA across the Caco-2 cell monolayers is mediated by DIDS-sensitive anion transporters., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

AMPA receptor-mediated responses to the agonist kainate differ from those of glutamate in two important respects. Glutamate is a full agonist that elicits strongly desensitizing responses, whereas kainate is a partial agonist with responses that are often described as weakly desensitizing or non-desensitizing. The efficacy of kainate relative to glutamate has previously been shown to be increased by mutations in the AMPA receptor ligand-binding cleft (Mano et al., 1996) and by coexpression with the auxiliary subunit stargazin (Tomita et al., 2005; Turetsky et al., 2005), but much less is known about factors that affect kainate desensitization. We therefore designed experiments to compare kainate and glutamate desensitization and efficacy in wild-type and mutant AMPA receptors expressed with and without stargazin in HEK293 cells. Desensitization to the two agonists was differentially affected by mutations in the helices participating in bonds between two subunits in the active state of the receptor (Sun et al., 2002), indicating that the protein interactions maintaining the stability of the dimer interface differ depending on which agonist is bound. Kainate efficacy was affected by factors distinct from ligand-binding cleft closure, including mutations in the dimer interface and channel vestibule as well as receptor composition. The increase in kainate responses for AMPA receptors coexpressed with stargazin was the result of both reduced kainate desensitization and increased kainate efficacy. These results provide critical new insights into the agonist dependence of both AMPA receptor activation and desensitization and the mechanism of the effects of stargazin on responses of partial agonists.

The neurotoxin domoic acid (DA), produced by diatoms Pseudo-nitzschia spp., is transferred to humans via consumption of contaminated bivalves. This study examines feeding mechanisms, namely reduced filtration, pre-ingestive rejection and poor absorption, that might explain the comparatively low DA levels commonly found in oysters during toxic Pseudo-nitzschia blooms. Clearance rate (CR), absorption efficiency (AE) of organic matter and selective rejection in pseudofeces of oysters (Crassostrea virginica) and mussels (Mytilus edulis) were investigated in relation to the DA levels accumulated during 2-wk, simultaneous exposure to toxic Pseudo-nitzschia multiseries. Effects of temperature and P. multiseries cell size were also tested to identify conditions, if any, under which oysters can accumulate unsafe DA levels. Oysters accumulated 3.0-7.5x less DA than mussels from a short-celled P. multiseries clone (length=24microm) at 12 degrees C. This was related to the 7.4-8.5x lower CRs determined for oysters relative to mussels at this temperature. Exposure to a longer-celled P. multiseries clone (81microm) resulted in up to 70x lower toxin levels in oysters compared to mussels, which was attributed to differential feeding selectivity. Mussels were unable to discriminate between long- and short-celled P. multiseries clones from a mixed suspension, whereas oysters were previously shown to preferentially reject long cells (>70microm) in pseudofeces. Both bivalves selectively rejected P. multiseries cells from mixed suspensions containing a flagellate but not another diatom. AE of organics from P. multiseries cells by oysters and mussels was comparably low (42 and 39%, respectively) and thus unlikely to explain their differential DA accumulation. CR and DA uptake by oysters were negligible at

Background: California sea lions have a large body burden of organochlorine pesticides, and over the last decade they have also been subject to domoic acid poisoning. Domoic acid poisoning, previously recognized in adult animals, is now viewed as a major cause of prenatal mortality. The appearance of a chronic juvenile domoic acid disease in the sea lions, characterized by behavioral abnormalities and epilepsy, is consistent with early life poisoning and may be potentiated by organochlorine burden., Objective: We investigated the interactive effect of DDT (dichlorodiphenyltrichloroethane) on neurodevelopment using a zebrafish (Danio rerio) model for seizure behavior to examine the susceptibility to domoic acid-induced seizures after completion of neurodevelopment., Methods: Embryos were exposed (6-30 hr postfertilization) to either o,p'-DDT or p,p'-DDE (dichlorodiphenyldichloroethylene) during neurodevelopment via a 0.1% dimethyl sulfoxide solution. These larval (7 days postfertilization) fish were then exposed to either the seizure-inducing drug pentylenetetrazol (PTZ) or domoic acid; resulting seizure behavior was monitored and analyzed for changes using cameras and behavioral tracking software., Results: Embryonic exposure to DDTs enhanced PTZ seizures and caused distinct and increased seizure behaviors to domoic acid, most notably a type of head-shaking behavior., Conclusion: These studies demonstrate that embryonic exposure to DDTs leads to asymptomatic animals at completion of neurodevelopment with greater sensitivity to domoic acid-induced seizures. The body burden levels of p,p'-DDE are close to the range recently found in fetal California sea lions and suggest a potential interactive effect of p,p'-DDE embryonic poisoning and domoic acid toxicity.

Background and Objectives: Prenatal exposure to asymptomatic doses of domoic acid (DA) causes learning and memory deficits later in life; therefore, we sought to measure distribution of DA in maternal plasma and brain, prenatal brain, and amniotic fluid 1 hr after exposure, a time frame that normally encompasses acute seizure behavior., Methods: Pregnant rats were given a single intravenous dose of DA (0.6 or 1.6 mg/kg body weight) at either gestational day (GD) 13 or GD20, which correspond to the beginning of rat embryo neurogenesis and the last day of gestation, respectively. Using a direct ELISA, dose-dependent levels of DA were detected in each sample matrix tested., Results: An average of 6.6 and 14 ng DA/g brain tissue was found in GD13 and GD20 prenatal rats, respectively. Brain concentrations of DA in the GD13 prenates were identical to amniotic fluid levels, consistent with no restriction for DA to enter the GD13 prenatal brain. At GD20 the prenatal brain contained half the concentration of DA in the amniotic fluid, and was approximately half that found in the brain of the dams. After 1 hr, fetal brain and amniotic fluid contained between 1 and 5% of DA found in the maternal circulation. The amniotic fluid levels of DA in this study were also within the same range measured in stranded California sea lions that showed reproductive failure., Conclusions: DA crosses the placenta, enters brain tissue of prenates, and accumulates in the amniotic fluid. Amniotic fluid appears to be a useful fluid to monitor DA exposure.

Domoic acid (DA) is a potent neurotoxin naturally produced by some pennate diatom species of the genus Pseudo-nitzschia. It is well known that during harmful algal blooms fish can accumulate DA in the gastrointestinal (GI) tract and act as vectors of the toxin to higher trophic level piscivores, often with severe neurotoxic consequences to the predators. Although neurotoxicity and mass mortality have been observed in vertebrates (i.e. marine mammals and sea birds) feeding on contaminated fish, to date there has been no evidence of neurobehavioral toxicity in the fish vectors themselves. It has been hypothesized that fish may not absorb DA from the digestive tract, thus making them insensitive to dietary consumption of DA. To test this hypothesis, we performed oral gavage exposures followed by a time series of tissue dissections to characterize uptake, depuration, and tissue distribution of DA in fish. Intracoelomic (IC) injection exposures (which bypass the GI tract) were also performed to determine if coho neurons are neurologically susceptible to DA. Excitotoxic symptoms were observed in fish via IC injection at similar toxin levels that have been reported to induce excitotoxic symptoms in intraperitoneal (IP) exposures with mammalian models such as mice, suggesting that fish neurons have a similar sensitivity to DA as other vertebrates. Surprisingly, after oral gavage with ecologically relevant doses of DA, the toxin was detected in plasma collected from the dorsal aorta via a permanent intraarterial catheter within 15 min, yet excitotoxic symptoms were not observed. Additionally, DA was detected in liver, heart, spleen, kidney, muscle, brain and bile. These data indicate that although DA is absorbed from the gut, fish do not exhibit neuroexcitatory effects at maximum ecologically relevant oral doses of DA. Tissue distribution and DA uptake and depuration patterns suggest that a majority of the absorbed toxin is excreted via the kidneys and bile, thereby preventing toxic levels of DA from reaching sensitive nervous tissue. Additionally, greater than 20% of total IC administered DA doses were sequestered in bile within 1h of injection in five symptomatic fish, providing evidence for biliary sequestration of the toxin from blood. Here, we comprehensively describe the uptake, depuration, and tissue distribution patterns of DA and propose that renal and biliary processes may serve as primary routes of toxin clearance in fish.

Domoic acid (DA) is a highly toxic phycotoxin produced by bloom forming marine diatoms Pseudo-nitzschia spp. Bivalves can accumulate this toxin to a high level through their feeding activities, and thus illness or death in can occur in consumers of bivalves. In this study, king scallop, Pecten maximus, larvae were exposed to dissolved domoic acid (DA) for 25d, and the toxin accumulation and effects of harbouring this toxin were investigated. Scallop larvae incorporated DA continuously during the larval culture period and accumulated a maximum DA level of 5.21pgind(-1) when exposed to a solution of 50ngml(-1) dissolved DA. As a result of the DA treatment, larval growth, measured in terms of shell length and the appearance of the eye-spot, and larval survival were significantly compromised. This is the first study on DA incorporation dynamics in P. maximus larvae, signifying the potential of using shellfish larvae for the study on mechanisms of phycotoxin accumulation. The negative effect of DA exposure suggests that this toxin could possibly influence natural recruitment in P. maximus, and it may be necessary to protect hatchery-cultured scallop larvae from DA during toxic Pseudo-nitzschia blooms.

Domoic acid (DA) is a phycotoxin produced by some diatoms, mainly from the Pseudo-nitzschia genus, and has been detected throughout the marine food web. Although DA has been frequently found in cephalopod prey such as crustaceans and fish, little is known about DA accumulation in these molluscs. This study presents the first data showing relevant concentrations of DA detected in the common cuttlefish, Sepia officinalis, which is one of the most studied cephalopod species in the world. Domoic acid was consistently found throughout 2003 and 2004 in the digestive gland of cuttlefish reaching concentrations of 241.7 microg DA g(-1). The highest DA values were detected during spring and summer months, periods when Pseudo-nitzschia occur in the plankton. In fact, Pseudo-nitzschia blooms preceded the highest DA concentrations in cuttlefish. Evaluation of DA tissue distribution showed elevated DA concentrations in the digestive gland and branchial hearts. Further, DA isomers comprised a relevant percentage of the toxin profile, indicating degradation and biotransformation of the toxin in the branchial hearts. The common cuttlefish, like other cephalopod species, plays a central position in the food web and might be a new DA vector to top predators like marine mammals. Human intoxications are not expected since DA was only seldom detected in the mantle and even then in very low levels (max 0.7 microg DA g(-1)). However, in some countries whole juvenile animals are consumed (i.e. without evisceration) and in this case they might represent a risk to human health. This study contributes to understanding the occurrence of phycotoxins in cephalopods and reveals a new member of the marine food web able to accumulate DA.

Post-mortem studies have yet to produce consistent findings on cortical glutamatergic markers in schizophrenia; therefore, it is not possible to fully understand the role of abnormal glutamatergic function in the pathology of the disorder. To better understand the changes in cortical glutamatergic markers in schizophrenia, we measured the binding of radioligands to the ionotropic glutamate receptors (N-methyl D-aspartate, [3H]CGP39653, [3H]MK-801), amino-3-hydroxy-5-methyl-4-isoxazole ([3H]AMPA), kainate ([3H]kainate), and the high-affinity glutamate uptake site ([3H]aspartate) using in situ radioligand binding with autoradiography and levels of mRNA for kainate receptors using in situ hybridization in the dorsolateral prefrontal cortex from 20 subjects with schizophrenia and 20 controls matched for age and sex. Levels of [3H]kainate binding were significantly decreased in cortical laminae I-II (p = 0.01), III-IV (p < 0.05), and V-VI (p < 0.01) from subjects with schizophrenia. By contrast, levels of [3H]MK-801, [3H]AMPA, [3H]aspartate, or [3H]CGP39653 binding did not differ between the diagnostic cohorts. Levels of mRNA for the GluR5 subunit were decreased overall (p < 0.05), with no changes in levels of mRNA for GluR6, GluR7, KA1, or KA2 in tissue from subjects with schizophrenia. These data indicate that the decreased number of kainate receptors in the dorsolateral prefrontal cortex in schizophrenia may result, in part, from reduced expression of the GluR5 receptor subunits.

Purpose: Glutamate receptor 6 is strongly implicated in human refractory epilepsy and in kainic acid (KA)-induced status epilepticus (SE). In vitro pharmacologic studies with newer antiepileptic drugs (AEDs) are increasingly indicating the role of glutamate receptor 5 (GluR5) in epilepsy. Glutamate receptor 7 (GluR7) has been the least investigated in the context of epilepsy. We studied the messenger ribonucleic acid (mRNA) and protein expression of GluR5, GluR6, and GluR7 in rat hippocampus 72 h, 90 days, and 180 days after KA-induced SE., Methods: SE was induced by injecting KA intraperitoneally (i.p.) into adult rats. The hippocampi were isolated 72 h, 90 days, and 180 days after SE. Reverse transcription-polymerase chain reaction (RT-PCR) was performed for mRNA expression. Western blots determined the protein expression., Results: A significant increase was noted in GluR5 expression in KA-treated animals compared with controls at 72 h and 180 days, with no significant difference at the intervening 90-day point. Protein levels for GluR5 increased at 72 h and remained elevated until 180 days. GluR7 mRNA showed a significant decrease at 90 days after seizures. Neither the mRNA expression nor the protein levels of GluR6 differed from controls at any of the times after SE., Conclusions: KA-induced SE leads to an upregulation of GluR5 mRNA and protein and a downregulation of GluR7 mRNA in rat hippocampus, with no change in GluR6 mRNA or protein expression.

Domoic acid (DA), produced by the diatom genus Pseudo-nitzschia, is a glutamate analog and a neurotoxin in humans. During diatom blooms, DA can contaminate filter-feeding organisms, such as shellfish, and can be transferred by ingestion to higher trophic levels. Several intoxication events involving both humans and various marine mammals have been attributed to DA. Affected organisms show neurological symptoms such as seizures, ataxia, headweaving, and stereotypic scratching, as well as prolonged deficits in memory and learning. Neonatal animals have been shown to be substantially more sensitive to DA than adults. However, it has not been demonstrated whether DA can be transferred to nursing young from DA-exposed mothers. This study demonstrates transfer of DA from spiked milk (0.3 and 1.0 mg/kg) to the plasma of nursing neonatal rats and an overall longer DA retention in milk than in plasma after 8 hr in exposed dams. DA was detectable in milk up to 24 hr after exposure (1.0 mg/kg) of the mothers, although the amount of DA transferred to milk after exposure was not sufficient to cause acute symptoms in neonates.

The glutamate receptor (GluR) agonist-binding site consists of amino acid residues in the extracellular S1 and S2 domains in the N-terminal and M3-M4 loop regions, respectively. In the present study, we sought to confirm that the conserved ligand-binding residues identified in the AMPA receptor S1S2 domains also participate in ligand binding of GluR6 kainate receptors. Amino acid substitutions were made in the GluR6 parent at R523, T690, and E738 to alter their potential interactions with ligand. Mutant receptors were expressed in human embryonic kidney 293 cells, confirmed by Western blot analysis, and tested by [3H]kainate binding and patch-clamp recording. Each of the binding site mutations was sufficient to reduce [3H]kainate binding to undetectable levels and eliminate functional responses to glutamate or kainate. As with our studies of other nonfunctional mutants (Fleck et al., 2003), immunocytochemical staining and cell-surface biotinylation studies showed that the mutant receptors were retained intracellularly and did not traffic to the cell surface. Endoglycosidase-H digests and colocalization with endoplasmic reticulum (ER) markers demonstrated that the mutant receptors are immaturely glycosylated and retained in the ER. Immunoprecipitation, native PAGE, and functional studies confirmed that the GluR6-binding site mutants are capable of multimeric assembly, indicating their retention in the ER does not result from a gross protein folding error. Together, these results confirm the role of R523, T690, and E738 directly in ligand binding to GluR6 and further support our previous report that nonfunctional GluRs are retained intracellularly by a functional checkpoint in ER quality control.

We report the crystal structure of the glycosylated ligand-binding (S1S2) domain of the kainate receptor subunit GluR6, in complex with the agonist domoate. The structure shows the expected overall homology with AMPA and NMDA receptor subunit structures but reveals an unexpected binding mode for the side chain of domoate, in which contact is made to the larger lobe only (lobe I). In common with the AMPA receptor subunit GluR2, the GluR6 S1S2 domain associates as a dimer, with many of the interdimer contacts being conserved. Subtle differences in these contacts provide a structural explanation for why GluR2 L483Y and GluR3 L507Y are nondesensitizing, but GluR6, which has a tyrosine at that site, is not. The structure incorporates native glycosylation, which has not previously been described for ionotropic glutamate receptors. The position of the sugars near the subunit interface rules out their direct involvement in subunit association but leaves open the possibility of indirect modulation. Finally, we observed several tetrameric assemblies that satisfy topological constraints with respect to connection to the receptor pore, and which are therefore candidates for the native quaternary structure.

Loreclezole (5 mg/kg) exerted a significant protective action in amygdala-kindled rats, reducing both seizure and afterdischarge durations. The combinations of loreclezole (2.5 mg/kg) with valproate, clonazepam, or carbamazepine (applied at their subprotective doses) also exhibited antiseizure effect in this test. However, only two first combinations occurred to be of pharmacodynamic nature. Among several chemoconvulsants, bicuculline, N-methyl-D-aspartic acid and BAY k-8644 (the opener of L-type calcium channels) reversed the protective activity of loreclezole alone and its combination with valproate. On the other hand, bicuculline, aminophylline and BAY k-8644 inhibited the anticonvulsive action of loreclezole combined with clonazepam. The results support the hypothesis that the protective activity of loreclezole and its combinations with other antiepileptics may involve potentiation of GABAergic neurotransmission and blockade of L-type of calcium channels.

The depuration kinetics of the domoic acid of four body fractions (digestive gland, adductor muscle, gonad+kidney and gills+mantle) of the scallop Pecten maximus was studied over 295 days. The scallops, which had acquired the toxins during a Pseudo-nitzschia australis episode that took place the week before the beginning of the experiment, were maintained in tanks with running seawater. All the body fractions, except the adductor muscle, decreased their domoic acid burden throughout the experiment. The amount of toxin in the muscle dropped sharply at the start of the experiment but increased again at the end, to levels that were higher than the initial ones. Several dynamic models of depuration kinetics, which included the depuration of each fraction (excluding the adductor muscle) and the transfers between them, were constructed, implemented and fitted to the data to obtain their parameters. The estimated depuration rates were very low, both considering and not considering the transfer of toxin between organs or the effect of weight loss. There were strong differences in the domoic acid burden of the body fractions studied but not between their depuration rates. No net transfer from the digestive gland, the tissue with highest domoic acid concentration, to the other fractions was found, as the inclusion of these processes in the models produced only a marginally better fit to the data. The depuration of domoic acid was slightly, but significantly, affected by biomass. Weight loss induced domoic acid loss, suggesting that part of the depuration may be produced by the direct loss of bivalve cells. The concentration or dilution effect, due to decreases or increases in biomass, documented for other species and toxins, has little importance in Pecten maximus.

Abnormalities of molecules associated with the glutamate synapse have been implicated in the pathophysiology of schizophrenia. Of the many glutamate receptors, those most commonly suggested to be involved in schizophrenia are the ionotropic subtypes, the NMDA, AMPA, and kainate receptors. Both the NMDA and AMPA subtypes have been extensively studied in postmortem brains of individuals with schizophrenia, but relatively little is known about the expression of the kainate subtype of glutamate receptor. In this study, we have determined cortical and striatal kainate receptor expression in brains from persons with schizophrenia and a comparison group, using both in situ hybridization and receptor autoradiography. At the level of subunit mRNA expression, a shift in subunit stoichiometry was evident in multiple regions of the prefrontal cortex, with increased expression of gluR7 mRNA and decreased expression of KA2 mRNA. Decreased kainate receptor binding was also observed in the subjects with schizophrenia, but was restricted to infragranular laminae of the prefrontal cortex. No differences in kainate receptor binding or subunit mRNA levels were found in striatum or occipital cortex, suggesting that these findings may be restricted to association cortex. These data add to the growing literature implicating ionotropic glutamate receptor disturbances in schizophrenia, and indicate that in addition to AMPA and NMDA receptors, the kainate receptors are also abnormally expressed in this illness.

Mature male and female mice from six inbred stains were tested for susceptibility to behavioral seizures induced by a single injection of cocaine. Cocaine was injected ip over a range of doses (50-100 mg/kg) and behavior was monitored for 20 minutes. Seizure end points included latency to forelimb or hindlimb clonus, latency to clonic running seizure and latency to jumping bouncing seizure. A range of strain specific sensitivities was documented with A/J and SJL mice being most sensitive and C57BL/6J most resistant. DBA/2J, BALB/cByJ and NZW/LacJ strains exhibited intermediate sensitivity. EEG recordings were made in SJL, A/J and C57BL/6J mice revealing a close correspondence between electrical activity and behavior. Additionally, levels of cocaine determined in hippocampus and cortex were not different between sensitive and resistant strains. Additional studies of these murine strains may be useful for investigating genetic influences on cocaine-induced seizures.

Domoic acid (DA) is an environmental neurotoxin to humans. This work examines whether repeated exposure to subsymptomatic or symptomatic nonlethal doses of domoic acid leads to enhanced symptomatic toxicity in ICR outbred and DBA inbred strains of laboratory mice. A multiple independent exposure paradigm was designed in which doses were administered intraperitoneally every other day for 7 days to achieve four separate exposures to domoic acid. We first examined the effect of repeated exposure on serum clearance of domoic acid. Serum domoic acid levels did not differ following a single or repeated exposure. We next examined the effect of repeated exposure on symptomatic toxicity. The mean toxicity scores did not show a significant difference between single and repeated exposures of either subsymptomatic (0.5 mg/kg) or symptomatic sublethal (2.0 mg/kg) doses of domoic acid. We then examined the effects of repeated domoic acid exposure on a second strain of mouse. DBA mice were chosen based upon their sensitivity to kainic acid-induced seizures; however, the ICR mice were more sensitive to low-dose domoic acid toxicity, particularly in terms of onset and duration of stereotypic scratching behavior. Our results indicate that both strains of mice have comparable concentration-dependent toxic responses to domoic acid; however, differences exist in the magnitude of the response and in specific symptoms. The mean toxicity scores did not show a significant difference when a single exposure (1.0 and 2.0 mg/kg domoic acid) and repeated exposure of the same dose were compared in the DBA mice. This study provides no evidence that short-term repeated exposure to domoic acid in laboratory mice alters domoic acid clearance from the serum, or leads to a more sensitive or a greater neurotoxic response.

The renal clearance (Clr) of the seafood toxin domoic acid (DA) was investigated in the rat. Following cannulation of the right femoral artery, the left femoral vein and the bladder of anaesthetized rats, a single bolus injection of either [3H]DA, [14C]p-aminohippuric acid (PAH) or [3H]inulin was administered through the venous cannula. Blood samples were taken from the arterial cannula at 1, 2, 10, 30, 50, 70, 90, 110 and 130 min following injection, and urine samples were collected at 20-min intervals starting from the time of bolus injection. Based on plasma concentration-time profiles, the total clearances (Clt) for DA, PAH and inulin were 9.12, 33.17 and 7.50 ml/min/kg body weight, respectively. The Clr calculated from urinary excretion rates were not significantly different from the Clt. Probenecid significantly reduced the Clr of PAH but did not affect that of DA. When DA was given at doses of 0.5 ng, 0.5 mg and 2.0 mg/kg body weight, the pharmacokinetic parameters Clt, Clr, elimination-rate constant and apparent volume of distribution at steady state were not statistically different between doses. The entire dose of 3H was recovered in the urine by 160 min after dosing, and analysis of urine samples by HPLC confirmed that the radiolabel (3H) was associated predominantly with the parent form of DA. The results of the present study demonstrate that DA is cleared from plasma primarily through the kidneys. DA clearance occurs primarily by renal glomerular filtration since its Clt is comparable with that of inulin, is less than that of PAH and is not affected by probenecid.