domoic-acid and Disease-Models--Animal

In mammals, the period shortly before and shortly after birth is a time of massive brain growth, plasticity and maturation. It is also a time when the developing brain is exquisitely sensitive to insult, often with long-lasting consequences. Many of society's most debilitating neurological diseases arise, at least in part, from trauma around the time of birth but go undetected until later in life. For the past 15 years, we have been studying the consequences of exposure to the AMPA/kainate agonist domoic acid (DOM) on brain development in the rat. Domoic acid is a naturally occurring excitotoxin that enters the food chain and is known to produce severe neurotoxicity in humans and other adult wildlife. Our work, and that of others, however, has demonstrated that DOM is also toxic to the perinatal brain and that toxicity occurs at doses much lower than those required in adults. This raises concern about the current regulatory limit for DOM contamination that is based on data in adult animals, but has also allowed creation of a novel model of neurological disease progression. Herein, we review briefly the toxicity of DOM in adults, including humans, and describe features of the developing nervous system relevant to enhanced risk. We then review the data on DOM as a prenatal neuroteratogen and describe in detail the work of our respective laboratories to characterize the long-term behavioural and neuropathological consequences of exposure to low-dose DOM in the newborn rat.

Topics: Animals; Brain; Disease Models, Animal; Humans; Kainic Acid; Neuromuscular Depolarizing Agents; Rats; Teratogens

Domoic acid of macroalgal origin was used for traditional and medicinal purposes in Japan and largely forgotten until its rediscovery in diatoms that poisoned 107 people after consumption of contaminated mussels. The more severely poisoned victims had seizures and/or amnesia and four died; however, one survivor unexpectedly developed temporal lobe epilepsy (TLE) a year after the event. Nearly a decade later, several thousand sea lions have stranded on California beaches with neurological symptoms. Analysis of the animals stranded over an eight year period indicated five clusters of acute neurological poisoning; however, nearly a quarter have stranded individually outside these events with clinical signs of a chronic neurological syndrome similar to TLE. These poisonings are not limited to sea lions, which serve as readily observed sentinels for other marine animals that strand during domoic acid poisoning events, including several species of dolphin and whales. Acute domoic acid poisoning is five-times more prominent in adult female sea lions as a result of the proximity of their year-round breeding grounds to major domoic acid bloom events. The chronic neurological syndrome, on the other hand, is more prevalent in young animals, with many potentially poisoned in utero. The sea lion rookeries of the Channel Islands are at the crossroads of domoic acid producing harmful algal blooms and a huge industrial discharge site for dichlorodiphenyltrichloroethane (DDTs). Studies in experimental animals suggest that chronic poisoning observed in immature sea lions may result from a spatial and temporal coincidence of DDTs and domoic acid during early life stages. Emergence of an epilepsy syndrome from the ocean brings a human epilepsy model to life and provides unexpected insights into interaction with legacy contaminants and expression of disease at different life stages.

Topics: Animals; DDT; Disease Models, Animal; Epilepsy; Humans; Kainic Acid; Marine Toxins; Neurotoxins; Pesticides; Water Pollutants, Chemical

A novel type of intoxication in Canada in 1987 was traced to consumption of cultivated mussels contaminated with the excitotoxin domoic acid. Studies carried out in rats and monkeys revealed that parenterally administered domoic acid induces in rats neuroexcitatory phenomena culminating in seizures. Monkeys respond with gagging, emesis and less clearly evident seizure activity. CNS damage consisting of dendrotoxic and gliotoxic edema and nerve cell degeneration occurs in structures of the limbic system and the retina in both species. CNS lesion distribution similarities in animals treated with domoic acid or kainic acid suggest that these excitotoxins share a common pathogenesis mediated by glutamic acid, a putative endogenous excitatory neurotransmitter.

Topics: Animals; Central Nervous System; Disease Models, Animal; Kainic Acid; Nervous System Diseases; Nervous System Neoplasms; Neuromuscular Depolarizing Agents; Neurotoxins

The excitatory neurotoxin domoic acid (DA) consistently contaminates food webs in coastal regions around the world. Acute exposure to the toxin causes Amnesic Shellfish Poisoning, a potentially lethal syndrome of gastrointestinal- and seizure-related outcomes. Both advanced age and male sex have been suggested to contribute to interindividual DA susceptibility. To test this, we administered DA doses between 0.5 and 2.5 mg/kg body weight to female and male C57Bl/6 mice at adult (7-9-month-old) and aged (25-28-month-old) life stages and observed seizure-related activity for 90 min, at which point we euthanized the mice and collected serum, cortical, and kidney samples. We observed severe clonic-tonic convulsions in some aged individuals, but not in younger adults. We also saw an association between advanced age and the incidence of a moderately severe seizure-related outcome, hindlimb tremors, and between advanced age and overall symptom severity and persistence. Surprisingly, we additionally report that female mice, particularly aged female mice, demonstrated more severe neurotoxic symptoms following acute exposure to DA than males. Both age and sex patterns were reflected in tissue DA concentrations as well: aged mice and females had generally higher concentrations of DA in their tissues at 90 min post-exposure. This study contributes to the body of work that can inform intelligent, evidence-based public health protections for communities threatened by more frequent and extensive DA-producing algal blooms.

Topics: Animals; Disease Models, Animal; Female; Kainic Acid; Male; Marine Toxins; Mice; Neurotoxins; Seizures

Domoic acid (DA) is one of the best known marine toxins, causative of important neurotoxic alterations. DA effects are documented both in wildlife and experimental assays, showing that this toxin causes severe injuries principally in the hippocampal area. Accumulating evidence indicates that mitochondrial dysfunction and oxidative stress are involved in DA-induced cognitive functional impairment. Therefore, therapeutics targeted to improve mitochondrial function and increase oxidative stress defence could be beneficial. Quercetin, a bioflavanoid, has been reported to have potent neuroprotective effects and anti-oxidative ability, but its preventive effects on DA-induced mitochondrial dysfunction and cognitive impairment have not been well characterised. In this study, we evaluated the effects of quercetin on DA-induced cognitive deficits in mice and explored its potential mechanism. Our results showed that the oral administration of quercetin to DA-treated mice significantly improved their behavioural performance in a novel objective recognition task and a Morris water maze task. These improvements were mediated, at least in part, by a stimulation of PPARγ coactivator 1α-mediated mitochondrial biogenesis signalling and an amelioration of mitochondrial dysfunction. Moreover, quercetin activated nuclear factorerythroid-2-related factor-2 (Nrf2)-mediated phase II enzymes and decreased reactive oxygen species and protein carbonylation. Furthermore, the AMP-activated protein kinase (AMPK) activity significantly increased in the quercetin-treated group. Taken together, these findings suggest that a reduction in mitochondrial dysfunction through the increase of AMPK activity, coupled with an increase in Nrf2 pathway mediated oxidative defence, may be one of the mechanisms by which quercetin improves cognitive impairment induced by DA in mice.

Topics: Animals; Cognition; Cognitive Dysfunction; Disease Models, Animal; Hippocampus; Kainic Acid; Male; Mice; Mice, Inbred C57BL; Mitochondria; Neuroprotective Agents; Oxidative Stress; Quercetin; Reactive Oxygen Species

Deficits in perceptual, informational, and attentional processing are consistently identified as a core feature in schizophrenia and related neuropsychiatric disorders. Neonatal injections of low doses of the AMPA/kainate agonist domoic acid (DOM) have previously been shown to alter various aspects of perceptual and attentional processing in adult rats. The current study investigated the effects of combined neonatal DOM treatment with isolation rearing on prepulse inhibition behaviour and relevant neurochemical measures, to assess the usefulness of these paradigms in modeling neurodevelopmental disorders. Daily subcutaneous injections of DOM (20 μg/kg) or saline were administered to male and female rat pups from postnatal days (PND) 8-14. After weaning, rats were either housed alone or in groups of 4. Both the magnitude and latency of prepulse inhibition were determined in adulthood (approximately 4.5 months of age) and post-mortem brain tissue was assayed using Western blot. Social isolation alone significantly lowered PPI magnitude in male (but not female) rats while DOM treatment appeared to make animals refractory to this effect. Combining social isolation and DOM treatment caused an additive decrease in PPI startle latency. No statistically significant differences were found in the expression of D1, D2, TH, GAD65 or GAD67 protein in either the prefrontal cortex or hippocampus, although some tendencies toward differences were noted. We conclude that both neonatal low-dose DOM and social isolation affect prepulse inhibition in rats but that each paradigm exerts these effects through different neuronal signalling systems.

Topics: Animals; Animals, Newborn; Blotting, Western; Disease Models, Animal; Female; Hippocampus; Kainic Acid; Male; Prefrontal Cortex; Prepulse Inhibition; Random Allocation; Rats, Sprague-Dawley; Reflex, Startle; Social Isolation

Domoic acid (DA) is an algal neurotoxin that accumulates in marine fish and shellfish. DA can move across the placenta and concentrate in amniotic fluid, which can be swallowed during late gestation. DA also transfers to infants via milk. Preclinical studies to determine effects of developmental DA expose have primarily involved DA exposure during the postnatal period and little is known about late CNS effects following prenatal DA. In the present study, we tested the hypothesis that prenatal exposure of FVB mice to low levels of DA would result in diminished social interaction and sensory motor gating associated with alterations in parvalbumin immunoreactivity in relevant brain regions undergoing development during and following DA exposure. In addition to parvalbumin, we stained with NeuN for a neuronal specific nuclear protein to determine if neuronal loss followed prenatal DA exposure. A single moderate dose of DA administered during gestation produces diminishes social investigation and alters sensorimotor gating, behavioral effects more pronounced in males than females. These behavioral changes were associated with discrete alterations in the parvalbumin-positive subtype of GABAergic neurons in the dentate gyrus and lateral amygdala.

Topics: Acoustic Stimulation; Age Factors; Amygdala; Analysis of Variance; Animals; Animals, Newborn; Disease Models, Animal; Female; Interpersonal Relations; Kainic Acid; Male; Mice; Neurons; Neurotoxins; Parvalbumins; Phosphopyruvate Hydratase; Pregnancy; Prenatal Exposure Delayed Effects; Prepulse Inhibition; Psychoacoustics; Sensory Gating; Sex Factors; Vocalization, Animal

Topics: Animals; Disease Models, Animal; Epilepsy, Temporal Lobe; Humans; Kainic Acid; Sea Lions; Temporal Lobe; Water Pollutants, Chemical

Deficits in attention have long been identified as a core feature in schizophrenia and related neuropsychiatric disorders. We have investigated the combined effects of neonatal treatment with domoic acid (DOM) and social isolation rearing (both putative animal models of schizophrenia) on latent inhibition (LI), a measure of attentional processing. Daily subcutaneous injections of 20 μg/kg DOM or saline were administered to rat pups from postnatal days (PND) 8-14. After weaning, rats were housed either alone or in groups of 4 until LI was assessed at PND 110 using a lick-suppression conditional emotional response paradigm. Neonatal treatment with DOM abolished LI behaviour in adult male rats regardless of housing condition when tested 48 h after conditioning, but this effect was not observed in female rats. Social isolation rearing also reduced LI in male rats, but not to the same extent as DOM. When tested again one week later, single-housed males treated with DOM displayed significant LI whereas saline treated or group-housed DOM males did not. No significant differences were found with females 1 week later. We conclude that neonatal DOM and social isolation both impair attentional processing in young adult male, but not female, rats although the mechanisms by which this occurs appear to be different.

Topics: Age Factors; Animals; Animals, Newborn; Attention; Conditioning, Psychological; Disease Models, Animal; Female; Kainic Acid; Male; Rats; Rats, Sprague-Dawley; Schizophrenia; Social Isolation

The harmful alga Pseudo-nitzschia sp. is the cause of human amnesic shellfish poisoning and the stranding of thousands of sea lions with seizures as a hallmark symptom. A human case study and epidemiological report of hundreds of stranded sea lions found individuals presenting months after recovery with a neurological disease similar to temporal lobe epilepsy. A rat model developed to establish and better predict how epileptic disease results from domoic acid poisoning demonstrated that a single episode of status epilepticus (SE), after a latent period, leads to a progressive state of spontaneous recurrent seizure (SRS) and expression of atypical aggressive behaviors. Structural damage associated with domoic acid-induced SE is prominent in olfactory pathways. Here, we examine structural damage in seven rats that progressed to epileptic disease. Diseased animals show progressive neuronal loss in the piriform cortex and degeneration of terminal fields in these layers and the posteromedial cortical amygdaloid nucleus. Animals that display aggressive behavior had additional neuronal damage to the anterior olfactory cortex. This study provides insight into the structural basis for the progression of domoic acid epileptic disease and relates to the California sea lion, where poisoned animals progress to a disease characterized by SRS and aggressive behaviors.

Topics: Aggression; Animals; Brain; Cell Count; Disease Models, Animal; Kainic Acid; Male; Neurons; Rats; Rats, Sprague-Dawley; Recurrence; Seizures; Status Epilepticus

The amnesic shellfish toxin, domoic acid, interferes with glutamatergic pathways leading to neuronal damage, most notably causing memory loss and seizures. In this study, the authors utilized a recently developed rat model for domoic acid-induced epilepsy, an emerging disease appearing in California sea lions weeks to months after poisoning, to identify structural damage that may lead to a permanent epileptic state. Sprague Dawley rats were kindled with several low hourly intraperitoneal doses of domoic acid until a state of status epilepticus (SE) appears. This kindling approach has previously been shown to induce a permanent state of epileptic disease in 96% animals within 6 months. Three animals were selected for neurohistology a week after the initial SE. An amino cupric silver staining method using neutral red counterstain was used on every eighth 40 µm coronal section from each brain to highlight neural degeneration from the olfactory bulb through the brain stem. The most extensive damage was found in the olfactory bulb and related olfactory pathways, including the anterior/medial olfactory cortices, endopiriform nucleus, and entorhinal cortex. These findings indicate that damage to olfactory pathways is prominent in a rat model for domoic acid-induced chronic recurrent spontaneous seizures and aggressive behavior.

Topics: Aggression; Animals; Brain; Copper; Disease Models, Animal; Histocytochemistry; Kainic Acid; Male; Olfactory Pathways; Rats; Rats, Sprague-Dawley; Silver Compounds; Silver Staining; Status Epilepticus

Domoic acid (DA), a naturally occurring environmental toxin, has been observed to induce status epilepticus in humans, sea lions and pelicans. In a recent Sprague Dawley rat model, domoic acid dosing induced a state of status epilepticus which, after a symptom-free latent period without further dosing, progressed to recurrent spontaneous seizures, a hallmark of epilepsy. Certain individuals in this study also developed unusual behavioral changes, in particular an atypical aggression towards conspecifics. In this report we characterized the progression of aggressive behaviors after DA-induced status epilepticus and explored the relationship between aggressive behavior and recurrent spontaneous seizures. Experimental studies in this laboratory rat model are particularly relevant to California sea lions (Zapholus californianus), which show a spectrum of both epileptic and unusual behaviors, including aggression towards conspecifics in rehabilitation facilities, weeks to months after suspected exposure to domoic acid in the wild.

Topics: Aggression; Animals; Disease Models, Animal; Emotions; Kainic Acid; Male; Neurotoxins; Rats; Rats, Sprague-Dawley; Statistics, Nonparametric; Status Epilepticus; Stress, Psychological; Time Factors

Schizophrenia is a complex and severe mental disorder characterized by positive, negative and cognitive symptoms. Characteristic behavioral alterations reflecting these categories of symptoms have been observed in many animal models of this disorder, and are consistent with those manifested in the clinical population. The purpose of this study was to determine whether early alterations in glutamate signaling would result in alterations to prepulse inhibition (PPI) and latent inhibition (LI); two assessments used for evaluating putative novel animal models with relevance to schizophrenia. In the present experiment, daily subcutaneous (s.c.) injections of 20μg/kg of domoic acid (DOM) were administered to rat pups from postnatal days (PND) 8-14. When tested as adults, DOM treated rats displayed deficits in PPI that were dependant on both sex and time of day. No differences in startle amplitude, habituation, or movement were found during any test, indicating that the PPI deficits seen could not be attributed to baseline startle differences. Deficits in LI were also apparent when adult rats were tested using a conditioned taste aversion task, with DOM-treated animals displaying a significantly suppressed LI. These results suggest that early treatment with DOM may serve as a useful tool to model schizophrenia which in turn may lead to a better understanding of the contribution of glutamate, and in particular, kainate receptors, to the development and/or manifestation of schizophrenia or schizophrenia-like symptoms in the clinical population.

Topics: Animals; Animals, Newborn; Behavior, Animal; Disease Models, Animal; Female; Kainic Acid; Male; Rats; Rats, Sprague-Dawley; Schizophrenia

The emergence of an epilepsy syndrome in sea lions poisoned by domoic acid (DA) draws striking parallels to the single case study of temporal lobe epilepsy (TLE) that developed in an 84 yr old man one year after being poisoned by DA. To establish a basis for understanding this disease in sea lions and humans that appears to progress from DA poisoning, we have investigated the potential for a single incident of DA poisoning in rats to progress to spontaneous recurrent seizures (SRS), the hallmark of epilepsy. We have developed a DA administration protocol to induce a nonlethal status epilepticus (SE) and monitored the animals for SRS by 6 h/week of video recording. We demonstrate that a single episode of SE leads to SRS in 94% of rats (n = 23) in 6 months. These findings indicate that DA induced SE can efficiently translate to epileptic disease.

Topics: Animals; Disease Models, Animal; Disease Progression; Epilepsy; Kainic Acid; Male; Marine Toxins; Neurotoxins; Rats; Rats, Sprague-Dawley; Seizures; Videotape Recording

The marine neurotoxin domoic acid (DA) is a rigid analogue of the neurotransmitter glutamate and a potent agonist of kainate subtype glutamate receptors. Persistent activation of these receptor subtypes results in rapid excitotoxicity, calcium-dependent cell death, and neuronal degeneration in regions of the brain where glutamatergic pathways are concentrated. Previous work has shown that DA promotes the expression of inflammatory genes in the brain, such as cyclooxygenase 2 (COX2). To investigate the impact of inflammation on the development of neurodegeneration, and ultimately survival following DA administration, we used selective (L745337, Merck) and non-selective (acetylsalicylic acid (ASA)) COX inhibitors in DA exposed mice. Adult male ICR mice were given a regime of either ASA or L23547 both before and after a single LD50 dose of DA. Mice were observed immediately after toxin introduction and then sacrificed at 2 days post exposure. Our lower dose of L23547 increased survival and was most effective at decreasing neuronal degeneration in the CA1 and CA3 regions of the hippocampus, areas especially sensitive to DA excitotoxicity. This study shows that COX2 plays a role in DA induced neurodegeneration and death, and that inhibitors may be of value for treatment in human and wildlife DA exposure.

Topics: Animals; Aspirin; Cell Survival; Cyclooxygenase Inhibitors; Disease Models, Animal; Drug Administration Schedule; Hippocampus; Indans; Kainic Acid; Lethal Dose 50; Male; Mice; Mice, Inbred ICR; Neurodegenerative Diseases; Neurons; Neurotoxins

Schizophrenia is a debilitating neurological disorder characterized by positive, negative, cognitive and/or emotional symptoms. Decreased social interaction is a common negative symptom. Social interaction can be readily observed in rats and is therefore an ideal target behaviour when evaluating an animal model of schizophrenia. The purpose of this study was to determine whether early alterations in glutamate signaling resulted in social withdrawal; a finding which would be consistent with existing animal models of schizophrenia and is observed within the clinical population. In the present study, male and female SD rat pups received daily injections (s.c.) of very low doses of the glutamate agonist domoic acid (DOM; 20 microg/kg) or saline during a critical period of CNS development (i.e., PND 8-14). As adults, rats were assessed for degree of social interaction. During testing, each test rat was placed in a social interaction arena and scored for social contact with and avoidance of, a same-sex untreated conspecific. No differences were found in overall activity, nor were differences present for time spent engaged in neutral behavior (i.e., not engaged in behaviour, either directed toward or in avoidance of, the stimulus rat). However, domoate-treated male rats demonstrated evidence of social withdrawal, as evidenced by a significantly greater amount of time spent in avoidance behaviour and a significantly less amount of time spent engaged in social contact. These findings are discussed in context of the significance of early alteration to glutamate signaling in the development of human neuropathological disorders.

Topics: Analysis of Variance; Animals; Animals, Newborn; Behavior, Animal; Critical Period, Psychological; Disease Models, Animal; Excitatory Amino Acid Agonists; Female; Glutamic Acid; Kainic Acid; Male; Rats; Rats, Sprague-Dawley; Schizophrenia; Social Behavior

Exposure to the excitotoxin domoic acid (DOM) has been shown to produce cardiac lesions in both clinical and animal studies. We have previously shown that DOM failed to directly affect cardiomyocyte viability and energetics, but the development of this cardiomyopathy has remained unexplained. The present study compared effects of high-level seizure induction obtained by intraperitoneal (2 mg/kg) or intrahippocampal (100 pmol) bolus administration of DOM on development of cardiac pathologies in a rat model. Assessment of cardiac pressure derivatives and coronary flow rates revealed a significant time-dependent decrease in combined left ventricular (LV) systolic and diastolic function at 1, 3, 7, and 14 days after intraperitoneal administration and at 7 and 14 days after intrahippocampal DOM administration. LV dysfunction was matched by a similar time-dependent decrease in mitochondrial respiratory control, associated with increased proton leakage, and in mitochondrial enzyme activities. Microscopic examination of the LV midplane revealed evidence of progressive multifocal ischemic damage within the subendocardial, septal, and papillary regions. Lesions ranged from reversible early damage (vacuolization) to hypercontracture and inflammatory necrosis progressing to fibrotic scarring. Plasma proinflammatory IL-1α, IL-1β, and TNF-α cytokine levels were also increased from 3 days after seizure induction. The observed cardiomyopathies did not differ between intraperitoneal and intrahippocampal groups, providing strong evidence that cardiac damage after DOM exposure is a consequence of a seizure-evoked autonomic response.

Topics: Animals; Behavior, Animal; Cardiomyopathies; Cytokines; Disease Models, Animal; Kainic Acid; Male; Mitochondria; Myocardial Ischemia; Neuromuscular Depolarizing Agents; Rats; Rats, Sprague-Dawley; Respiration; Seizures; Ventricular Dysfunction, Left

Previously we have shown that low-dose domoic acid (DA) preconditioning produces tolerance to the behavioral effects of high-dose DA. In this study, we used electrocorticography (ECoG) to monitor subtle CNS changes during and after preconditioning. Young adult male Sprague-Dawley rats were implanted with a left cortical electrode, and acute recordings were obtained during preconditioning by contralateral intrahippocampal administration of either low-dose DA (15 pmoles) or saline, followed by a high-dose DA (100 pmoles) challenge. ECoG data were analyzed by fast Fourier transformation to obtain the percentage of baseline power spectral density (PSD) for delta to gamma frequencies (range: 1.25-100 Hz). Consistent with previous results, behavioral analysis confirmed that low-dose DA preconditioning 60 min before a high-dose DA challenge produced significant reductions in cumulative seizure scores and high level seizure behaviors. ECoG analysis revealed significant reductions in power spectral density across all frequency bands, and high-frequency/high-amplitude spiking in DA preconditioned animals, relative to saline controls. Significant correlations between seizure scores and ECoG power confirmed that behavioral analysis is a reliable marker for seizure analysis. The reduction of power in delta to gamma frequency bands in contralateral cortex does not allow a clear distinction between seizure initiation and seizure propagation, but does provide objective confirmation that pharmacological preconditioning by DA reduces network seizure activity.

Topics: Analysis of Variance; Animals; Disease Models, Animal; Dopamine; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Electroencephalography; Hippocampus; Kainic Acid; Linear Models; Male; Rats; Rats, Sprague-Dawley; Seizures; Spectrum Analysis; Statistics, Nonparametric

In the rat, early postnatal development is a critical period for neuronal migration, differentiation and network formation, requiring appropriate and timely glutamate and gamma-aminobutyric acid (GABA) signaling. Insults that affect either of these systems may result in increased excitatory activity, potentially leading to changes in neuronal proliferation and/or connectivity. We have previously shown that postnatal administration of low doses of domoic acid (DOM) can produce many of the behavioral and morphological changes found in current animal models of temporal lobe epilepsy (TLE), as well as the human condition. Using immunohistochemical techniques, we sought to characterize alterations in specific hippocampal GABAergic subpopulations at various locations along the septo-temporal axis in the DOM model. Results show decreased levels of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) in the ventral hilus and region- and sex-specific reductions in parvalbumin (PV)-containing immunoreactivity, but no alterations in somatostatin (SST) expression. These regional and sex-dependent changes in specific subpopulations of GABAergic interneurons may contribute to seizure development in this slowly progressing developmental model of TLE, and highlight how even subtle intervention may alter the interplay between glutamate and GABA systems during critical developmental stages.

Topics: Animals; Brain; Disease Models, Animal; Epilepsy; Female; gamma-Aminobutyric Acid; Glutamate Decarboxylase; Image Processing, Computer-Assisted; Immunohistochemistry; Kainic Acid; Male; Neuromuscular Depolarizing Agents; Neurons; Rats; Rats, Sprague-Dawley; Sex Characteristics; Somatostatin

Fetal poisoning of California sea lions (CSLs; Zalophus californianus) has been associated with exposure to the algal toxin domoic acid. These same sea lions accumulate a mixture of persistent environmental contaminants including pesticides and industrial products such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). Developmental exposure to the pesticide dichlorodiphenyltrichloroethane (DDT) and its stable metabolite 1,1-bis-(4-chlorophenyl)-2,2-dichloroethene (p,p -DDE) has been shown to enhance domoic acid-induced seizures in zebrafish; however, the contribution of other co-occurring contaminants is unknown.. We formulated a mixture of contaminants to include PCBs, PBDEs, hexachlorocyclohexane (HCH), and chlordane at levels matching those reported for fetal CSL blubber to determine the impact of co-occurring persistent contaminants with p,p -DDE on chemically induced seizures in zebrafish as a model for the CSLs.. Embryos were exposed (6-30 hr postfertilization) to p,p -DDE in the presence or absence of a defined contaminant mixture prior to neurodevelopment via either bath exposure or embryo yolk sac microinjection. After brain maturation (7 days postfertilization), fish were exposed to a chemical convulsant, either pentylenetetrazole or domoic acid; resulting seizure behavior was then monitored and analyzed for changes, using cameras and behavioral tracking software.. Induced seizure behavior did not differ significantly between subjects with embryonic exposure to a contaminant mixture and those exposed to p,p -DDE only.. These studies demonstrate that p,p -DDE--in the absence of PCBs, HCH, chlordane, and PBDEs that co-occur in fetal sea lions--accounts for the synergistic activity that leads to greater sensitivity to domoic acid seizures.

Topics: Animals; Dichlorodiphenyl Dichloroethylene; Disease Models, Animal; Environmental Pollutants; Fetus; Halogenated Diphenyl Ethers; Hexachlorocyclohexane; Kainic Acid; Polychlorinated Biphenyls; Seizures; Zebrafish

Domoic acid and its isomers are produced via algal blooms and are found in high concentrations in shellfish. Here, we assessed the acute seizurogenic potencies of isomers-D, -E and -F and their binding affinities at heterogeneous populations of KA receptors from rat cerebrum. In addition, binding affinities of all six isomers (Iso-A through -F) were assessed at AMPA receptors. Radioligand displacement studies indicated that the seizurogenic potency of Iso-F (E-configuration) closely correlates with its affinities at both KA and AMPA receptors, whereas isomers-D (Z) and -E (E), which exhibit distinctly lower seizurogenic potencies, are quite weak displacers. Previously observed functional potencies for isomers-A, -B and -C (Sawant et al., 2008) correlated with AMPA receptor affinities observed here. Taken together, these findings call into question previous structure-activity rules. Significantly, in our hands, Iso-D was ten-fold less potent than Iso-F. To further explain observed links between structural conformation and functional potency, molecular modeling was employed. Modeling results closely matched the rank order of potency and binding data observed. We further assessed the efficacy of isomers-D, -E and -F as pharmacological preconditioning agents. Acute preconditioning with low-dose Iso-D, -E or -F, before high-dose DA failed to impart behavioural tolerance. This study has shed new light on structural conformations affecting non-NMDA ionotropic glutamate receptor binding and functional potency, and provides a foundation for future work in areas of AMPA and KA receptor modeling.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Analysis of Variance; Animals; Binding, Competitive; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; GluK2 Kainate Receptor; Hippocampus; Isomerism; Kainic Acid; Male; Models, Molecular; Molecular Conformation; Neuromuscular Depolarizing Agents; Protein Binding; Rats; Rats, Sprague-Dawley; Receptors, Kainic Acid; Seizures; Synaptosomes; Tritium

Exposing Sprague-Dawley rat pups to very low, sub-convulsant doses of domoic acid (DOM) during perinatal development has been previously shown to result in seizure-like activity in adulthood similar to partial complex epilepsy in humans, and to produce cellular and molecular changes in the dentate gyrus and area CA-3 of the hippocampus. To further these investigations we recorded electroencephalographical and behavioural activity in DOM and control rats following a normally sub-convulsant dose (25 mg/kg) of pentylenetetrazol. During this exposure, 50% of DOM-treated rats experienced a Stage V (tonic-clonic) seizure (X(2)((1))=5.33, P=0.021), indicating a lowering of generalized seizure threshold in these animals. In a separate experiment we explored focal seizure (afterdischarge) threshold as well as seizure propagation rates in treated rats, using a 25 consecutive day standard amygdala kindling paradigm. We report that the afterdischarge threshold for DOM-treated rats was significantly lower than controls (F((1,27))=7.117, P=0.013). No difference between groups was found in seizure progression as measured by afterdischarge duration, latency to first Stage V seizure, or latency to reach a fully kindled state (defined as five consecutive Stage V seizures). Timm staining to assess mossy fibre sprouting (MFS) in the hippocampus revealed a significant MFS increase relative to sham at the ventral level in both left and right inner molecular layer of the dentate gyrus for all DOM-treated animals, as well as in the dorsal stratum oriens of CA3 contralateral to electrode placement, and these increases were further enhanced by the kindling procedure. We conclude that perinatal exposure to subconvulsive doses of DOM results in permanent changes in neuronal excitability in the adult rat, as demonstrated by a lowering of both generalized seizure and focal afterdischarge threshold, and produces increased MFS following kindling.

Topics: Action Potentials; Animals; Animals, Newborn; Convulsants; Disease Models, Animal; Epilepsy; Kainic Acid; Kindling, Neurologic; Male; Neuromuscular Depolarizing Agents; Pentylenetetrazole; Rats; Rats, Sprague-Dawley

Domoic acid (DA) is an excitatory amino acids (EAAs) analog which induced excitotoxicity lesion to central nervous system, but whether induced adult animal spinal cord is not known, furthermore, previous studies have shown that EAAs play an important role in spinal cord lesion, however, the molecular pathways in spinal cord lesion are not fully known. Therefore, a motor neuron-like cell culture system and a DA-induced spinal cord lesioned mice model were used to study the effect of DA on spinal cord in adult mice and the possible molecular pathways of EAAs in spinal cord lesions. Exposure of motor neuron-like cells NSC34 to DA dramatically increased reactive oxygen species (ROS) production by the DCF fluorescent oxidation assay, reduced mitochondrial function by MTT assay, cell viability by trypan blue exclusion assay, and was accompanied by an increase of cell apoptosis by histone protein release assay. In DA-induced spinal cord lesioned mice model, we showed that the decrease of proteasome activity, increase of UCP4 expression by immunohistochemistry and neural cell apoptosis by TUNEL staining, and was accompanied by an decrease of motor disturbance grade during the different stages of DA treatment. Taken together, the in vitro and in vivo data presented in the current report demonstrated that DA induces spinal cord lesions in adult mice, and the multiple molecular pathways promoted by EAAs in spinal cord lesions, at least partially was associated with ROS generation increase, mitochondrial dysfunction, proteasome activity decrease and UCP4 expression increase.

Topics: Animals; Cell Death; Cell Line, Transformed; Disease Models, Animal; DNA Fragmentation; Dose-Response Relationship, Drug; Female; In Situ Nick-End Labeling; Kainic Acid; Mice; Mice, Inbred C57BL; Movement Disorders; Proteasome Endopeptidase Complex; Reactive Oxygen Species; Severity of Illness Index; Signal Transduction; Spinal Cord Injuries; Tetrazolium Salts; Thiazoles

To date, nothing is known of the pharmacological properties of isomers of domoic acid (DA) in vivo in mammals. Here we assessed the acute seizurogenic and toxic properties of DA, isodomoic acids A, B and C (Iso-A, -B, -C), and the therapeutic potential of these compounds as pharmacological preconditioning agents. DA, Iso-A, Iso-B, and Iso-C all produced significant dose-dependent increases in seizure activity following intrahippocampal administration; doses producing half maximal cumulative seizure scores (ED50) were 137 pmol, 171 pmol, 13,000 pmol, and 3150 pmol, respectively. Pharmacological preconditioning with low-dose DA or Iso-A, 60 min before a high test dose of DA produced a significant reduction in seizure scores. In contrast, Iso-B and Iso-C each failed to induce any detectable tolerance to high-dose DA. Radioligand binding indicated a significant correlation between seizurogenic potency and kainate receptor affinity with KIs of 2.4 nM, 4.4 nM, 4990 nM and 170 nM for DA, Iso-A, Iso-B and Iso-C, respectively. Our in vivo results indicate that DA and Iso-A are functionally equipotent in acute seizure induction by direct intrahippocampal administration, while Iso-B and Iso-C are distinctly less potent.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Heptanoic Acids; Hippocampus; Isomerism; Kainic Acid; Male; Marine Toxins; Protein Binding; Rats; Rats, Sprague-Dawley; Receptors, Kainic Acid; Seizures

Altered functioning of the glutamate system during critical periods of development is believed to play a role in various neurodevelopmental disorders, such as schizophrenia. Prepulse inhibition (PPI) of the acoustic startle response is deficient in people with schizophrenia. This study investigated the theory that neonatal treatment with domoic acid (DOM), a glutamate agonist, leads to deficient PPI. Results indicate that neonatal treatment with DOM leads to lowered PPI in adult males and an increased startle response in adult females.

Topics: Animals; Animals, Newborn; Disease Models, Animal; Female; Glutamic Acid; Humans; Kainic Acid; Male; Neuromuscular Depolarizing Agents; Rats; Reflex, Acoustic; Reflex, Startle; Schizophrenia; Sex Factors; Time Factors

Epilepsy research relies heavily on animal models that mimic some, or all, of the clinical symptoms observed. We have previously described a new developmental rat model of epilepsy that demonstrates both behavioural seizures and changes in hippocampal morphology. In the current study we investigated whether these rats also show changes in cognitive performance as measured using the Morris water maze task, and emotionality as measured using the Elevated plus maze task. In the water maze, significant differences between male and female rats were found in several performance variables regardless of treatment. In addition, female but not male rats, treated neonatally with domoic acid had significant impairments in learning new platform locations in the water maze. In the elevated plus maze, a significant proportion of female rats spent more time in the open arm of the maze following prior exposure to the maze whereas this effect was not seen in male rats. We conclude that perinatal treatment with low doses of domoic acid results in significant gender-based changes in cognition and emotionality in adult rats.

Topics: Animals; Disease Models, Animal; Emotions; Epilepsy; Female; Hippocampus; Kainic Acid; Male; Maze Learning; Neuromuscular Depolarizing Agents; Rats; Rats, Sprague-Dawley; Sex Characteristics

To induce status epilepticus (SE) followed by the subsequent onset of spontaneous recurrent seizures, thus characterizing a new model of temporal lobe epilepsy in a nonhuman primate.. Male and female marmosets (Callithrix jacchus) (n = 18), ages between 2 and 8 years, were injected with domoic acid (0.5-4 mg/kg, i.p.) or saline, and behaviorally assessed with regard to the presence of acutely induced seizures and for < or = 6 months for spontaneous seizures. Injection of doses ranging from 3.5 to 4 mg/kg either did not induce SE or resulted in fatal SE. Even a 5-min SE duration (SE blockade resulting from diazepam injection) proved lethal to marmosets within 1 h of domoate administration, regardless of intensive care and monitoring of the animals. Animals injected with doses ranging from 0.5 to 3 mg/kg that developed only a few minor convulsive signs were allowed a 6-month survival period for the assessment of spontaneous epileptic events. At the end of the experiment, 6-month period, or acute intoxication associated with SE induction, animals were deeply anesthetized and had their brains subjected to histologic processing for Nissl and delta-FosB.. For the animals injected with domoate that did not develop SE (i.e., those that survived), we could not detect any behavioral signs of spontaneous epileptic seizures in the 6-month observation period, and only minor indications of neuropathologic changes (i.e., neuronal death) over Nissl-stained sections, as well as some small changes in the staining for delta-FosB in a few of the animals.. Systemic administration of domoic acid to marmosets is not effective for the generation of a model of chronic temporal lobe epilepsy. Administration of domoic acid at doses that do not lead to SE also did not lead to the development of temporal lobe epilepsy or clear-cut behavioral changes over a 6-month period.

Topics: Animals; Behavior, Animal; Brain; Callithrix; Disease Models, Animal; Dose-Response Relationship, Drug; Epilepsy, Temporal Lobe; Female; Follow-Up Studies; Injections, Intraperitoneal; Kainic Acid; Male; Motor Activity; Neurotoxicity Syndromes; Status Epilepticus

Physical exercise ameliorates age-related neuronal loss and is currently recommended as a therapeutical aid in several neurodegenerative diseases. However, evidence is still lacking to firmly establish whether exercise constitutes a practical neuroprotective strategy. We now show that exercise provides a remarkable protection against brain insults of different etiology and anatomy. Laboratory rodents were submitted to treadmill running (1 km/d) either before or after neurotoxin insult of the hippocampus (domoic acid) or the brainstem (3-acetylpyridine) or along progression of inherited neurodegeneration affecting the cerebellum (Purkinje cell degeneration). In all cases, animals show recovery of behavioral performance compared with sedentary ones, i.e., intact spatial memory in hippocampal-injured mice, and normal or near to normal motor coordination in brainstem- and cerebellum-damaged animals. Furthermore, exercise blocked neuronal impairment or loss in all types of injuries. Because circulating insulin-like growth factor I (IGF-I), a potent neurotrophic hormone, mediates many of the effects of exercise on the brain, we determined whether neuroprotection by exercise is mediated by IGF-I. Indeed, subcutaneous administration of a blocking anti-IGF-I antibody to exercising animals to inhibit exercise-induced brain uptake of IGF-I abrogates the protective effects of exercise in all types of lesions; antibody-treated animals showed sedentary-like brain damage. These results indicate that exercise prevents and protects from brain damage through increased uptake of circulating IGF-I by the brain. The practice of physical exercise is thus strongly recommended as a preventive measure against neuronal demise. These findings also support the use of IGF-I as a therapeutical aid in brain diseases coursing with either acute or progressive neuronal death.

Topics: Animals; Behavior, Animal; Cell Count; Cerebellar Diseases; Disease Models, Animal; Disease Progression; Glucose; Hippocampus; Immunohistochemistry; Injections, Subcutaneous; Insulin-Like Growth Factor I; Kainic Acid; Male; Mice; Mice, Inbred C57BL; Motor Activity; Neurodegenerative Diseases; Neurons; Neuroprotective Agents; Olivary Nucleus; Physical Conditioning, Animal; Purkinje Cells; Pyridines; Rats; Rats, Wistar; Treatment Outcome

The recent outbreak of "amnesic" mussel poisoning syndrome, attributed to domoic acid contamination of edible mussels claimed several lives and left many victims impaired with a peculiar loss of memory. We administered the whole mussel extract (WMX) and the mussel hepatopancreas extract (MHX, hepatopancreas being the major site for sequestration of domoic acid in mussels) in Swiss-Webster mice. A characteristic syndrome featuring sluggishness, scratching stereotypy, convulsions and death was noticed. Infant mice were some 3- to 4-fold more sensitive to the WMX toxicity. Kynurenic acid (KYN), an endogenous nonselective excitotoxin antagonist offered significant protection against the toxicosis after its onset had been provoked by the mussel extract. This observation emphasizes the feasibility of using KYN or related compounds in the therapy of poisoning from excitotoxins. As a logical extension of this possibility we examined the possibility that endogenous KYN could be exploited for similar protection against domoate toxicosis in our murine model. The time frame during which KYN was protective was increased by probenecid, a blocker of organic acid transport and by tryptophan, a precursor of endogenous KYN. We examined also the classical anticonvulsants phenytoin and ethosuximide, as well as dextromethorphan at its excitotoxin antagonistic dose. The infant mouse model of domoate-toxicity holds promise for being developed into a rapid, sensitive, reliable and inexpensive biological assay for screening commercial batches of mussel for excitotoxin contamination. Kynurenic acid and dextromethorphan should be further examined as antidotes for possible therapeutic use in existing victims and in the treatment of future domoate toxicosis occurring here or elsewhere.

Topics: Age Factors; Animals; Antidotes; Behavior, Animal; Bivalvia; Disease Models, Animal; Kainic Acid; Male; Marine Toxins; Mice; Nervous System Diseases; Neurotoxins