Pathology of Domoic Acid Toxicity in California Sea Lions (Zalophus californianus)

Identification of Candidate Protein Biomarkers Associated with Domoic Acid Toxicosis in Cerebrospinal Fluid of California Sea Lions (Zalophus californianus)

Since 1998, California sea lion (Zalophus californianus) stranding events associated with domoic acid toxicosis (DAT) have consistently increased. Outside of direct measurement of domoic acid in bodily fluids at the time of stranding, there are no practical nonlethal clinical tests for the diagnosis of DAT that can be utilized in a rehabilitation facility. Proteomics analysis was conducted to discover candidate protein markers of DAT using cerebrospinal fluid from stranded California sea lions with acute DAT (n = 8), chronic DAT (n = 19), or without DAT (n = 13). A total of 2005 protein families were identified experiment-wide. A total of 83 proteins were significantly different in abundance across the three groups (adj. p < 0.05). MDH1, PLD3, ADAM22, YWHAG, VGF, and CLSTN1 could discriminate California sea lions with or without DAT (AuROC > 0.75). IGKV2D-28, PTRPF, KNG1, F2, and SNCB were able to discriminate acute DAT from chronic DAT (AuROC > 0.75). Proteins involved in alpha synuclein deposition were over-represented as classifiers of DAT, and many of these proteins have been implicated in a variety of neurodegenerative diseases. These proteins should be considered potential markers for DAT in California sea lions and should be prioritized for future validation studies as biomarkers.

The symptomatology and diagnosis of domoic acid toxicosis in stranded California sea lions (Zalophus californianus): a review and evaluation of 20 years of cases to guide prognosis

Introduction

Domoic acid (DA) is a glutaminergic excitatory neurotoxin that causes the morbidity and mortality of California sea lions (Zalophus californianus; CSL) and other marine mammals due to a suite of effects mostly on the nervous and cardiac systems. Between 1998 and 2019, 11,737 live-stranded CSL were admitted to The Marine Mammal Center (TMMC; Sausalito, CA, USA), over 2,000 of which were intoxicated by DA. A plethora of clinical research has been performed over the past 20 years to characterize the range of toxic effects of DA exposure on CSLs, generating the largest dataset on the effects of natural exposure to this toxin in wildlife.

Materials and methods

In this study, we review published methods for diagnosing DA intoxication, clinical presentation, and treatment of DA-intoxicated CSL and present a practical, reproducible scoring system called the neuroscore (NS) to help assess whether a DA-affected CSL is fit for release to the wild following rehabilitation. Logistic regression models were used to assess the relationships between outcome (released vs. euthanized or died) and multiple variables to predict the outcome for a subset of 92 stranded CSLs.

Results

The largest proportion of DA-intoxicated CSLs was adult females (58.6%). The proportions of acute and chronic cases were 63.5 and 36.5% respectively, with 44% of affected CSL released and 56% either dying naturally or euthanized. The average time in rehabilitation was 15.9 days (range 0-169) for all outcomes. The best-performing model (85% accuracy; area under the curve = 0.90) assessing the relationship between outcome and predictor variables consisted of four variables: final NS, change in NS over time, whether the animal began eating in rehabilitation, and the state of nutrition on admission.

Discussion

Our results provide longitudinal information on the symptomatology of CSL intoxicated by domoic acid and suggest that a behavioral scoring system is a useful tool to assess the fitness for the release of DA-intoxicated CSL.

Pinniped electroencephalography: Methodology and findings in California sea lions (Zalophus californianus)

This study was designed to identify abnormalities in the electroencephalograms (EEGs) recorded from stranded California sea lions (Zalophus californianus) with suspected domoic acid (DA) toxicosis. Recordings from animals presenting for non-neurological issues were also obtained to better understand the normal EEG (background activity and transient events) in this species, as, to date, studies have focused on examining natural sleep in pinnipeds. Most animals were sedated for electrode placement and EEG acquisition with some receiving antiepileptic medications or isoflurane during the procedure. A total of 103 recordings were read and scored from 0 (normal) to 3 (severely abnormal). Epileptiform discharges, consisting of spikes, sharp waves, slow waves, and/or spike waves, were present in all EEGs with scores of 1, 2, or 3. The distribution of these events over the scalp varied. While often generalized, others were lateralized over one hemisphere, bifrontal, bioccipital, and/or bitemporal, while some discharges were multifocal. Findings were different between sea lions and occasionally changed within the EEG on a given sea lion. No clinical seizures were observed during the recording but a few sea lions had findings consistent with electroencephalographic seizures. When available, supporting diagnostic results obtained from magnetic resonance imaging (MRI) and/or necropsy/histopathology were described, as well as the status of those sea lions that recovered and were released with satellite tags.

Update on Novel Taxa and Revised Taxonomic Status of Bacteria Isolated from Nondomestic Animals Described in 2018 to 2021

Revisions and new additions to bacterial taxonomy can have a significant widespread impact on clinical practice, infectious disease epidemiology, veterinary microbiology laboratory operations, and wildlife conservation efforts. The expansion of genome sequencing technologies has revolutionized our knowledge of the microbiota of humans, animals, and insects. Here, we address novel taxonomy and nomenclature revisions of veterinary significance that impact bacteria isolated from nondomestic wildlife, with emphasis being placed on bacteria that are associated with disease in their hosts or were isolated from host animal species that are culturally significant, are a target of conservation efforts, or serve as reservoirs for human pathogens.

Prolonged, Low-Level Exposure to the Marine Toxin, Domoic Acid, and Measures of Neurotoxicity in Nonhuman Primates

BACKGROUND

The excitotoxic molecule, domoic acid (DA), is a marine algal toxin known to induce overt hippocampal neurotoxicity. Recent experimental and epidemiological studies suggest adverse neurological effects at exposure levels near the current regulatory limit (20 ppm, ∼0.075-0.1mg/kg). At these levels, cognitive effects occur in the absence of acute symptoms or evidence of neuronal death.

OBJECTIVES

This study aimed to identify adverse effects on the nervous system from prolonged, dietary DA exposure in adult, female Macaca fascicularis monkeys.

METHODS

Monkeys were orally exposed to 0, 0.075, and 0.15mg/kg per day for an average of 14 months. Clinical blood counts, chemistry, and cytokine levels were analyzed in the blood. In-life magnetic resonance (MR) imaging assessed volumetric and tractography differences in and between the hippocampus and thalamus. Histology of neurons and glia in the fornix, fimbria, internal capsule, thalamus, and hippocampus was evaluated. Hippocampal RNA sequencing was used to identify differentially expressed genes. Enrichment of gene networks for neuronal health, excitotoxicity, inflammation/glia, and myelin were assessed with Gene Set Enrichment Analysis.

RESULTS

Clinical blood counts, chemistry, and cytokine levels were not altered with DA exposure in nonhuman primates. Transcriptome analysis of the hippocampus yielded 748 differentially expressed genes (fold change≥1.5; p≤0.05), reflecting differences in a broad molecular profile of intermediate early genes (e.g., FOS, EGR) and genes related to myelin networks in DA animals. Between exposed and control animals, MR imaging showed comparable connectivity of the hippocampus and thalamus and histology showed no evidence of hypomyelination. Histological examination of the thalamus showed a larger microglia soma size and an extension of cell processes, but suggestions of a GFAP+astrocyte response showed no indication of astrocyte hypertrophy.

DISCUSSION

In the absence of overt hippocampal excitotoxicity, chronic exposure of Macaca fascicularis monkeys to environmentally relevant levels of DA suggested a subtle shift in the molecular profile of the hippocampus and the microglia phenotype in the thalamus that was possibly reflective of an adaptive response due to prolonged DA exposure. https://doi.org/10.1289/EHP10923.

Cannabinoid receptor 1-labeled boutons in the sclerotic dentate gyrus of epileptic sea lions

Pathology in the dentate gyrus, including sclerosis, is a hallmark of temporal lobe epilepsy, and reduced inhibition to dentate granule cells may contribute to epileptogenesis. The perisomatic-targeting axonal boutons of parvalbumin-expressing interneurons decrease in proportion with granule cells in temporal lobe epilepsy. In contrast, dendrite-targeting axonal boutons of somatostatin-expressing interneurons sprout exuberantly in temporal lobe epilepsy. A third major class of GABAergic interneurons expresses cannabinoid receptor type 1 (CB1) on their terminal boutons, but there is conflicting evidence as to whether these boutons are increased or decreased in temporal lobe epilepsy. Naturally occurring temporal lobe epilepsy in California sea lions, with unilateral or bilateral sclerosis, offers the benefit of neuroanatomy and neuropathology akin to humans, but with the advantage that the entirety of both hippocampi from control and epileptic brains can be studied. Stereological quantification in the dentate gyrus revealed that sclerotic hippocampi from epileptic sea lions had fewer CB1-labeled boutons than controls. However, the reduction in the number of granule cells was greater, resulting in increased CB1-labeled boutons per granule cell in sclerotic hippocampi at temporal levels. This suggests that although CB1-expressing boutons are decreased in sclerotic dentate gyri, surviving cells have enhanced innervation from these boutons in epileptic sea lions.

Systematic validation and assessment of immunohistochemical markers for central nervous system pathology in cetaceans, with emphasis on auditory pathways

Cetacean neuropathology is a developing field that aims to assess structural and neurochemical changes involved in neurodegenerative, infectious and traumatic processes, however markers used previously in cetaceans have rarely undergone systematic validation. This is a prerequisite to investigating the potential damage inflicted on the cetacean auditory system by anthropogenic noise. In order to assess apoptotic, neuroinflammatory and structural aberrations on a protein level, the baseline expression of biomarker proteins has to be characterized, implementing a systematic approach to validate the use of anti-human and anti-laboratory animal antibodies in dolphin tissues. This approach was taken to study 12 different antibodies associated with hypoxic-ischemic, inflammatory, plastic and excitatory-inhibitory changes implicated in acoustic trauma within the ventral cochlear nuclei and inferior colliculi of 20 bottlenose dolphins (Tursiops truncatus). Out of the 12 tested antibodies, pro-apoptotic protease factor 1 (Apaf-1), diacylglycerolkinase-ζ (DGK-ζ), B-cell lymphoma related protein 2 (Bcl-2), amyloid-β peptide (Aβ) and neurofilament 200 (NF200) were validated employing Western blot analyses and immunohistochemistry (IHC). The results of the validation process indicate specific patterns of immunoreactivity that are comparable to those reported in other mammals, thus suggesting a key panel of IHC biomarkers of pathological processes in the cetacean brain. As a consequence, the antibodies tested in this study may constitute a valid tool for supporting existing diagnostic methods in neurological diseases. The approach of systematic validation of IHC markers in cetaceans is proposed as a standard practice, in order for results to be transparent, reliable and comparable.

Potential endocrine correlation with exposure to domoic acid in Southern Right Whale (Eubalaena australis) at the Península Valdés breeding ground

In waters off Península Valdés (PV), Argentina, southern right whales (SRW, Eubalaena australis) are occasionally exposed to domoic acid (DA), a neurotoxin produced by diatoms of the genus Pseudo-nitzschia. Domoic acid toxicity in marine mammals can cause gastrointestinal and neurological clinical signs, alterations in hematologic and endocrine variables, and can be fatal in extreme cases. In this study, we validated an enzyme immunoassay to quantify fecal glucocorticoid metabolites (fGCm) in 16 SRW fecal samples from live and dead stranded whales in PV from 2013 to 2018 and assessed fGCm levels associated with DA exposure. Overall, fGCm levels were significantly lower in SRWs with detectable fecal DA (n = 3) as compared to SRWs with undetectable fecal DA levels (n = 13). The highest fecal DA was observed in a live lactating female, which had low fGCm compared to the other lactating females studied. The highest fGCm was observed in a lactating female with undetectable DA; interestingly, at the time of sample collection, this female was sighted with two calves, an extremely unusual occurrence in this species. Though the sample size of these exceptionally rare breeding-season fecal samples was unavoidably small, our study provides evidence of potential adrenal alterations in whales exposed to an environmental neurotoxin such as DA.

Clinical signs, treatment, and outcome for California sea lions (Zalophus californianus) with Sarcocystis-associated polyphasic rhabdomyositis

OBJECTIVE

To describe clinical signs, treatment, and outcome for California sea lions (Zalophus californianus) with Sarcocystis-associated polyphasic rhabdomyositis.

ANIMALS

38 free-ranging juvenile to adult California sea lions examined at a rehabilitation center in California between September 2015 and December 2017.

PROCEDURES

Medical records at The Marine Mammal Center were reviewed to identify sea lions in which sarcocystosis had been diagnosed.

RESULTS

Clinical signs were highly variable and associated with polyphasic rhabdomyositis attributed to Sarcocystis neurona infection. Generalized severe muscle wasting, respiratory compromise, and regurgitation secondary to megaesophagus were the most profound clinical findings. Respiratory compromise and megaesophagus were associated with a poor prognosis. Eight of the 38 sea lions were treated and released to the wild, and 2 subsequently restranded and were euthanized. Two additional animals received no targeted treatment and were released. The remaining 28 animals were either euthanized or died during treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that unlike other marine mammals, which typically develop encephalitis, California sea lions with sarcocystosis often have polyphasic rhabdomyositis with highly variable clinical signs and that extensive diagnostic testing may be required to confirm the diagnosis. Treatment with an antiprotozoal drug in combination with corticosteroids may resolve clinical disease, but the prognosis is guarded.

PHARMACOKINETICS OF SUBCUTANEOUS ALPHA LIPOIC ACID, A PROPOSED THERAPEUTIC AID FOR DOMOIC ACID INTOXICATION IN CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS)

Domoic acid (DA) is a potent neurotoxin produced by certain marine algae that can cause neurologic and cardiac dysfunction by activating glutamate receptors. Glutamate receptor overexcitation results in continuous cellular activation, oxidative damage, and cell death. DA toxicosis causes disorientation and seizures, and antiseizure medications are the primary treatment. Alpha lipoic acid (ALA), a powerful antioxidant and glutathione precursor widely used in humans and dogs, can cross the blood-brain barrier to provide antioxidant availability to brain tissue. Hundreds of stranded California sea lions (CSL; Zalophus californianus) are diagnosed annually with DA toxicosis and thus are an appropriate animal in which to establish ALA dosing recommendations for treatment. The objective of this study was to determine the population pharmacokinetics of a single 10- or 20-mg/kg dose of ALA administered subcutaneously into the interscapular region to healthy rehabilitated CSL. Blood was collected at two time points between 15 min and 24 h after administration. Serum ALA concentrations were measured by liquid chromatography-mass spectrometry, and parameters were evaluated using a nonlinear mixed effects model. ALA was rapidly absorbed for each dose, peaking within 20 to 30 minutes, and t_1/2 of 40 and 32 min (10 and 20 mg/kg, respectively), followed by an initial steep distribution phase and prolonged elimination phase. Peak concentration (C_MAX) was 1,243 ng/ml (10-mg/ml dose) and 5,010 ng/ml (20-mg/ml dose). Serum from 13 CSLd with DA toxicosis treated with 10 mg/kg ALA for 1 to 9 d had measurable levels, and ALA was also measurable in cerebrospinal fluid from two treated CSLs. Therapeutic effects are noted with a C_MAX of 4,000 to 5,000 ng/ml in humans; thus in CSLs, 20 mg/kg administered subcutaneously once daily may be sufficient to achieve a therapeutic level in this species. Determination of efficacy and optimal dosing interval and duration require additional investigation.

Harmful algal blooms and their eco-environmental indication

Harmful algal blooms (HABs) in freshwater lakes and oceans date back to as early as the 19th century, which can cause the death of aquatic and terrestrial organisms. However, it was not until the end of the 20th century that researchers had started to pay attention to the hazards and causes of HABs. In this study, we analyzed 5720 published literatures on HABs studies in the past 30 years. Our review presents the emerging trends in the past 30 years on HABs studies, the environmental and human health risks, prevention and control strategies and future developments. Therefore, this review provides a global perspective of HABs and calls for immediate responses.

Exploration of serum cardiac troponin I as a biomarker of cardiomyopathy in southern sea otters (Enhydra lutris nereis)

OBJECTIVE

To compare serum cardiac troponin I (cTnI) concentrations between sea otters with and without cardiomyopathy and describe 2 cases of cardiomyopathy with different etiologies.

ANIMALS

25 free-ranging southern sea otters (Enhydra lutris nereis) with (n = 14; cases) and without (11; controls) cardiomyopathy and 17 healthy managed southern sea otters from aquariums or rehabilitation centers (controls).

PROCEDURES

Serum cTnI concentration was measured in live sea otters. Histopathologic and gross necropsy findings were used to classify cardiomyopathy status in free-ranging otters; physical examination and echocardiography were used to assess health status of managed otters. Two otters received extensive medical evaluations under managed care, including diagnostic imaging, serial cTnI concentration measurement, and necropsy.

RESULTS

A significant difference in cTnI concentrations was observed between cases and both control groups, with median values of 0.279 ng/mL for cases and < 0.006 ng/mL for free-ranging and managed controls. A cutoff value of ≥ 0.037 ng/mL yielded respective sensitivity and specificity estimates for detection of cardiomyopathy of 64.3% and 90.9% for free-ranging cases versus free-ranging controls and 64.3% and 94.1% for free-ranging cases versus managed controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Cardiomyopathy is a common cause of sea otter death that has been associated with domoic acid exposure and protozoal infection. Antemortem diagnostic tests are needed to identify cardiac damage. Results suggested that serum cTnI concentration has promise as a biomarker for detection of cardiomyopathy in sea otters. Serial cTnI concentration measurements and diagnostic imaging are recommended to improve heart disease diagnosis in managed care settings.

Public health risks associated with chronic, low-level domoic acid exposure: A review of the evidence

Domoic acid (DA), the causative agent for the human syndrome Amnesic Shellfish Poisoning (ASP), is a potent, naturally occurring neurotoxin produced by common marine algae. DA accumulates in seafood, and humans and wildlife alike can subsequently be exposed when consuming DA-contaminated shellfish or finfish. While strong regulatory limits protect people from the acute effects associated with ASP, DA is an increasingly significant public health concern, particularly for coastal dwelling populations, and there is a growing body of evidence suggesting that there are significant health consequences following repeated exposures to levels of the toxin below current safety guidelines. However, gaps in scientific knowledge make it difficult to precisely determine the risks of contemporary low-level exposure scenarios. The present review characterizes the toxicokinetics and neurotoxicology of DA, discussing results from clinical and preclinical studies after both adult and developmental DA exposure. The review also highlights crucial areas for future DA research and makes the case that DA safety limits need to be reassessed to best protect public health from deleterious effects of this widespread marine toxin.

Domoic acid and saxitoxin in seabirds in the United States between 2007 and 2018

As harmful algal blooms (HABs) increase in magnitude and duration worldwide, they are becoming an expanding threat to marine wildlife. Over the past decade, blooms of algae that produce the neurotoxins domoic acid (DA) and saxitoxin (STX) and documented concurrent seabird mortality events have increased bicoastally in the United States. We conducted a retrospective analysis of HAB related mortality events in California, Washington, and Rhode Island between 2007 and 2018 involving 12 species of seabirds, to document the levels, ranges, and patterns of DA and STX in eight sample types (kidney, liver, stomach, intestinal, cloacal, cecal contents, bile, blood) collected from birds during these events. Samples (n = 182) from 83 birds were examined for DA (n = 135) or STX (n = 17) or both toxins simultaneously (n = 30), using ELISA or LCMS at the National Oceanographic and Atmospheric Administration, National Marine Fisheries Service (NOAA-NMFS) Wildlife Algal-toxin Research and Response Network (WARRN-West) or the University of California, Santa Cruz (UCSC). DA or STX was detected in seven of the sample types with STX below the minimum detection limit in blood for the three samples tested. DA was found in 70% and STX was found in 23% of all tested samples. The ranges of detectable levels of DA and STX in all samples were 0.65-681,190.00 ng g^-1 and 2.00-20.95 ng g^-1, respectively. Cloacal contents from a Pacific loon (Gavia pacifica) collected in 2017 from Ventura County, California, had the highest maximum level of DA for all samples and species tested in this study. The highest level of STX for all samples and species was detected in the bile of a northern fulmar (Fulmarus glacialis) collected in 2018 from San Luis Obispo County, California. DA detections were consistently found in gastrointestinal samples, liver, bile, and kidney, whereas STX detections were most frequently seen in liver and bile samples. Co-occurring HAB toxins (DA and STX) were detected in white-winged scoters (Melanitta deglandi) in 2009, a Brandt's cormorant (Phalacrocorax penicillatus) in 2015, and a northern fulmar and common murre (Uria aalge) in 2018. This article provides DA and STX tissue concentrations and patterns in avian samples and shows the utility of various sample types for the detection of HAB toxins. Future research to understand the pharmacodynamics of these toxins in avian species and to establish lethal doses in various bird species would be beneficial.

An MRI protocol for anatomical and functional evaluation of the California sea lion brain

BACKGROUND

Domoic acid (DOM) is a neurotoxin produced by some harmful algae blooms in coastal waters. California sea lions (Zalophus californianus) exposed to DOM often strand on beaches where they exhibit a variety of symptoms, including seizures. These animals typically show hippocampal atrophy on MRI scans.

NEW METHOD

We describe an MRI protocol for comprehensive evaluation of DOM toxicosis in the sea lion brain. We intend to study brain development in pups exposed in utero. The protocol depicts the hippocampal formation as the primary region of interest. We include scans for quantitative morphometry, functional and structural connectivity, and a cerebral blood flow map.

RESULTS

High-resolution 3D anatomical scans facilitate post hoc slicing in arbitrary planes and accurate morphometry. We demonstrate the first cerebral blood flow map using MRI, and the first structural tractography from a live sea lion brain.

COMPARISON WITH EXISTING METHODS

Scans were compared to prior anatomical and functional studies in live sea lions, and structural connectivity in post mortem specimens. Hippocampal volumes were broadly in line with prior studies, with differences likely attributable to the 3D approach used here. Functional connectivity of the dorsal left hippocampus matched that found in a prior study conducted at a lower magnetic field, while structural connectivity in the live brain agreed with findings observed in post mortem studies.

CONCLUSIONS

Our protocol provides a comprehensive, longitudinal view of the functional and anatomical changes expected to result from DOM toxicosis. It can also screen for other common neurological pathologies and is suitable for any pinniped that can fit inside an MRI scanner.

Marine harmful algal blooms (HABs) in the United States: History, current status and future trends

Harmful algal blooms (HABs) are diverse phenomena involving multiple. species and classes of algae that occupy a broad range of habitats from lakes to oceans and produce a multiplicity of toxins or bioactive compounds that impact many different resources. Here, a review of the status of this complex array of marine HAB problems in the U.S. is presented, providing historical information and trends as well as future perspectives. The study relies on thirty years (1990-2019) of data in HAEDAT - the IOC-ICES-PICES Harmful Algal Event database, but also includes many other reports. At a qualitative level, the U.S. national HAB problem is far more extensive than was the case decades ago, with more toxic species and toxins to monitor, as well as a larger range of impacted resources and areas affected. Quantitatively, no significant trend is seen for paralytic shellfish toxin (PST) events over the study interval, though there is clear evidence of the expansion of the problem into new regions and the emergence of a species that produces PSTs in Florida - Pyrodinium bahamense. Amnesic shellfish toxin (AST) events have significantly increased in the U.S., with an overall pattern of frequent outbreaks on the West Coast, emerging, recurring outbreaks on the East Coast, and sporadic incidents in the Gulf of Mexico. Despite the long historical record of neurotoxic shellfish toxin (NST) events, no significant trend is observed over the past 30 years. The recent emergence of diarrhetic shellfish toxins (DSTs) in the U.S. began along the Gulf Coast in 2008 and expanded to the West and East Coasts, though no significant trend through time is seen since then. Ciguatoxin (CTX) events caused by Gambierdiscus dinoflagellates have long impacted tropical and subtropical locations in the U.S., but due to a lack of monitoring programs as well as under-reporting of illnesses, data on these events are not available for time series analysis. Geographic expansion of Gambierdiscus into temperate and non-endemic areas (e.g., northern Gulf of Mexico) is apparent, and fostered by ocean warming. HAB-related marine wildlife morbidity and mortality events appear to be increasing, with statistically significant increasing trends observed in marine mammal poisonings caused by ASTs along the coast of California and NSTs in Florida. Since their first occurrence in 1985 in New York, brown tides resulting from high-density blooms of Aureococcus have spread south to Delaware, Maryland, and Virginia, while those caused by Aureoumbra have spread from the Gulf Coast to the east coast of Florida. Blooms of Margalefidinium polykrikoides occurred in four locations in the U.S. from 1921-2001 but have appeared in more than 15  U.S. estuaries since then, with ocean warming implicated as a causative factor. Numerous blooms of toxic cyanobacteria have been documented in all 50  U.S. states and the transport of cyanotoxins from freshwater systems into marine coastal waters is a recently identified and potentially significant threat to public and ecosystem health. Taken together, there is a significant increasing trend in all HAB events in HAEDAT over the 30-year study interval. Part of this observed HAB expansion simply reflects a better realization of the true or historic scale of the problem, long obscured by inadequate monitoring. Other contributing factors include the dispersion of species to new areas, the discovery of new HAB poisoning syndromes or impacts, and the stimulatory effects of human activities like nutrient pollution, aquaculture expansion, and ocean warming, among others. One result of this multifaceted expansion is that many regions of the U.S. now face a daunting diversity of species and toxins, representing a significant and growing challenge to resource managers and public health officials in terms of toxins, regions, and time intervals to monitor, and necessitating new approaches to monitoring and management. Mobilization of funding and resources for research, monitoring and management of HABs requires accurate information on the scale and nature of the national problem. HAEDAT and other databases can be of great value in this regard but efforts are needed to expand and sustain the collection of data regionally and nationally.

Exposure to domoic acid is an ecological driver of cardiac disease in southern sea otters✰

Harmful algal blooms produce toxins that bioaccumulate in the food web and adversely affect humans, animals, and entire marine ecosystems. Blooms of the diatom Pseudo-nitzschia can produce domoic acid (DA), a toxin that most commonly causes neurological disease in endothermic animals, with cardiovascular effects that were first recognized in southern sea otters. Over the last 20 years, DA toxicosis has caused significant morbidity and mortality in marine mammals and seabirds along the west coast of the USA. Identifying DA exposure has been limited to toxin detection in biological fluids using biochemical assays, yet measurement of systemic toxin levels is an unreliable indicator of exposure dose or timing. Furthermore, there is little information regarding repeated DA exposure in marine wildlife. Here, the association between long-term environmental DA exposure and fatal cardiac disease was investigated in a longitudinal study of 186 free-ranging sea otters in California from 2001 - 2017, highlighting the chronic health effects of a marine toxin. A novel Bayesian spatiotemporal approach was used to characterize environmental DA exposure by combining several DA surveillance datasets and integrating this with life history data from radio-tagged otters in a time-dependent survival model. In this study, a sea otter with high DA exposure had a 1.7-fold increased hazard of fatal cardiomyopathy compared to an otter with low exposure. Otters that consumed a high proportion of crab and clam had a 2.5- and 1.2-times greater hazard of death due to cardiomyopathy than otters that consumed low proportions. Increasing age is a well-established predictor of cardiac disease, but this study is the first to identify that DA exposure affects the risk of cardiomyopathy more substantially in prime-age adults than aged adults. A 4-year-old otter with high DA exposure had 2.3 times greater risk of fatal cardiomyopathy than an otter with low exposure, while a 10-year old otter with high DA exposure had just 1.2 times greater risk. High Toxoplasma gondii titers also increased the hazard of death due to heart disease 2.4-fold. Domoic acid exposure was most detrimental for prime-age adults, whose survival and reproduction are vital for population growth, suggesting that persistent DA exposure will likely impact long-term viability of this threatened species. These results offer insight into the pervasiveness of DA in the food web and raise awareness of under-recognized chronic health effects of DA for wildlife at a time when toxic blooms are on the rise.

Amyloid-beta peptide and phosphorylated tau in the frontopolar cerebral cortex and in the cerebellum of toothed whales: aging versus hypoxia

Hypoxia could be a possible risk factor for neurodegenerative alterations in cetaceans' brain. Among toothed whales, the beaked whales are particularly cryptic and routinely dive deeper than 1000 m for about 1 h in order to hunt squids and fishes. Samples of frontal cerebral and cerebellar cortex were collected from nine animals, representing six different species of the suborder Odontoceti. Immunohistochemical analysis employed anti-β-amyloid (Aβ) and anti-neurofibrillary tangle (NFT) antibodies. Six of nine (67%) animals showed positive immunolabeling for Aβ and/or NFT. The most striking findings were intranuclear Aβ immunopositivity in cerebral cortical neurons and NFT immunopositivity in cerebellar Purkinje neurons with granulovacuolar degeneration. Aβ plaques were also observed in one elderly animal. Herein, we present immunohistopathological findings classic of Alzheimer's and other neurodegenerative diseases in humans. Our findings could be linked to hypoxic phenomena, as they were more extensive in beaked whales. Despite their adaptations, cetaceans could be vulnerable to sustained and repetitive brain hypoxia.

Marine toxin domoic acid induces in vitro genomic alterations in human peripheral blood cells

Domoic acid (DA) is an excitatory marine neurotoxin produced by diatoms Pseudo-nitzschia spp. as a defence compound that accumulates in the food web and is associated with amnesic shellfish poisoning in humans. Although its toxicity has been well established in marine species, there is limited data on DA cytogenotoxicity in human non-target cells. Therefore, we aimed to investigate the cytogenotoxic potential of DA (0.01-10 μg/mL) in human peripheral blood cells (HPBCs) using a battery of bioassays in vitro. In addition, the influence of DA on oxidative stress parameters as a possible mechanism of action was assessed. Results revealed that DA induced dose- and time-dependent cytotoxic effects. DA significantly affected genomic instability by increasing the frequency of micronuclei and nuclear buds. Furthermore, a slight induction of primary DNA strand breaks was detected after 24 h of exposure accompanied by a significant increase in the number of abnormal size tailed nuclei. No induction of hOGG1 (human 8-oxoguanine DNA glycosylase) sensitive sites was determined upon exposure to DA. Additionally, DA induced oxidative stress by increased production of reactive oxygen species accompanied by changes in glutathione, superoxide dismutase, malondialdehyde and protein carbonyl levels. Overall, the obtained results showed adverse genotoxic effects of DA in non-target HPBCs.

Clinical signs and mortality of non-released stranded California sea lions housed in display facilities: the suspected role of prior exposure to algal toxins

Stranded California sea lions considered unable to survive in the wild are often placed in public display facilities. Exposure to the biotoxin domoic acid (DA) is a common cause of stranding, and chronic effects are observed long after initial exposure. Medical records for 171 sea lions placed in US institutions between 2000 and 2016 were reviewed, including results from clinical examinations, histopathology, behavioural testing and advanced imaging. There was a statistically significant increase in neurological disease detected in neonates (24%) compared with other age classes (11%). Sixty per cent of all neurological cases died during the study period. In the 11 neurological neonate cases, six died (55%) and five are still alive with three of five developing epilepsy during placement. Of the six neurological neonate cases that died, one was attributed to DA toxicosis, one to seizures and four to acute unexplained neurological disease. This survey suggests delayed neurological disease can develop in sea lions after stranding as neonates. These data coupled with stranding records and epidemiological data on DA-producing algal blooms suggest further research into effects of neonatal exposure to DA on risk of neurological disease in later life is warranted. California sea lions offer a natural model of DA exposure to study such effects.

Growth dynamics and domoic acid production of Pseudo-nitzschia sp. in response to oil and dispersant exposure

The diatom genus Pseudo-nitzschia is a common component of phytoplankton communities in the Gulf of Mexico and is potentially toxic as some species produce the potent neurotoxin domoic acid. The impact of oil and chemical dispersants on Pseudo-nitzschia spp. and domoic acid production have not yet been studied; preliminary findings from a mesocosm experiment suggest this genus may be particularly resilient. A toxicological study was conducted using a colony of Pseudo-nitzschia sp. isolated from a station off the coast of Louisiana in the Gulf of Mexico. The cultures were exposed to a water accommodated fraction (WAF) of oil and a diluted chemically enhanced WAF (DCEWAF) which was a mix of oil and dispersant (20:1). Exposure to WAF induced a lag phase but did not inhibit growth rates once in exponential growth. Cultures grown in DCEWAF did not experience a lag phase but had significantly lower growth rates than the Control and WAF cultures. The cellular quota of domoic acid was higher in cultures treated with DCEWAF and WAF relative to their control values, and half of the domoic acid had leaked out of the cells into the surrounding seawater in the DCEWAF cultures while all the domoic acid remained inside the cells in WAF-treated cultures. These results suggest that the presence of oil could lead to toxic blooms, but that the application of dispersant could decrease bioaccumulation of domoic acid through the food web.

Discovery of a Potential Human Serum Biomarker for Chronic Seafood Toxin Exposure Using an SPR Biosensor

Domoic acid (DA)-producing harmful algal blooms (HABs) have been present at unprecedented geographic extent and duration in recent years causing an increase in contamination of seafood by this common environmental neurotoxin. The toxin is responsible for the neurotoxic illness, amnesic shellfish poisoning (ASP), that is characterized by gastro-intestinal distress, seizures, memory loss, and death. Established seafood safety regulatory limits of 20 μg DA/g shellfish have been relatively successful at protecting human seafood consumers from short-term high-level exposures and episodes of acute ASP. Significant concerns, however, remain regarding the potential impact of repetitive low-level or chronic DA exposure for which there are no protections. Here, we report the novel discovery of a DA-specific antibody in the serum of chronically-exposed tribal shellfish harvesters from a region where DA is commonly detected at low levels in razor clams year-round. The toxin was also detected in tribal shellfish consumers’ urine samples confirming systemic DA exposure via consumption of legally-harvested razor clams. The presence of a DA-specific antibody in the serum of human shellfish consumers confirms long-term chronic DA exposure and may be useful as a diagnostic biomarker in a clinical setting. Adverse effects of chronic low-level DA exposure have been previously documented in laboratory animal studies and tribal razor clam consumers, underscoring the potential clinical impact of such a diagnostic biomarker for protecting human health. The discovery of this type of antibody response to chronic DA exposure has broader implications for other environmental neurotoxins of concern.

Proportional loss of parvalbumin-immunoreactive synaptic boutons and granule cells from the hippocampus of sea lions with temporal lobe epilepsy

One in 26 people develop epilepsy and in these temporal lobe epilepsy (TLE) is common. Many patients display a pattern of neuron loss called hippocampal sclerosis. Seizures usually start in the hippocampus but underlying mechanisms remain unclear. One possibility is insufficient inhibition of dentate granule cells. Normally parvalbumin-immunoreactive (PV) interneurons strongly inhibit granule cells. Humans with TLE display loss of PV interneurons in the dentate gyrus but questions persist. To address this, we evaluated PV interneuron and bouton numbers in California sea lions (Zalophus californianus) that naturally develop TLE after exposure to domoic acid, a neurotoxin that enters the marine food chain during harmful algal blooms. Sclerotic hippocampi were identified by the loss of Nissl-stained hilar neurons. Stereological methods were used to estimate the number of granule cells and PV interneurons per dentate gyrus. Sclerotic hippocampi contained fewer granule cells, fewer PV interneurons, and fewer PV synaptic boutons, and the ratio of granule cells to PV interneurons was higher than in controls. To test whether fewer boutons was attributable to loss versus reduced immunoreactivity, expression of synaptotagmin-2 (syt2) was evaluated. Syt2 is also expressed in boutons of PV interneurons. Sclerotic hippocampi displayed proportional losses of syt2-immunoreactive boutons, PV boutons, and granule cells. There was no significant difference in the average numbers of PV- or syt2-positive boutons per granule cell between control and sclerotic hippocampi. These findings do not address functionality of surviving synapses but suggest reduced granule cell inhibition in TLE is not attributable to anatomical loss of PV boutons.

Chronic, low-level oral exposure to marine toxin, domoic acid, alters whole brain morphometry in nonhuman primates

Domoic acid (DA) is an excitatory neurotoxin produced by marine algae and responsible for Amnesiac Shellfish Poisoning in humans. Current regulatory limits (˜0.075-0.1 mg/kg/day) protect against acute toxicity, but recent studies suggest that the chronic consumption of DA below the regulatory limit may produce subtle neurotoxicity in adults, including decrements in memory. As DA-algal blooms are increasing in both severity and frequency, we sought to better understand the effects of chronic DA exposure on reproductive and neurobehavioral endpoints in a preclinical nonhuman primate model. To this end, we initiated a long-term study using adult, female Macaca fascicularis monkeys exposed to daily, oral doses of 0.075 or 0.15 mg/kg of DA for a range of 321-381, and 346-554 days, respectively. This time period included a pre-pregnancy, pregnancy, and postpartum period. Throughout these times, trained data collectors observed intentional tremors in some exposed animals during biweekly clinical examinations. The present study explores the basis of this neurobehavioral finding with in vivo imaging techniques, including diffusion tensor magnetic resonance imaging and spectroscopy. Diffusion tensor analyses revealed that, while DA exposed macaques did not significantly differ from controls, increases in DA-related tremors were negatively correlated with fractional anisotropy, a measure of structural integrity, in the internal capsule, fornix, pons, and corpus callosum. Brain concentrations of lactate, a neurochemical closely linked with astrocytes, were also weakly, but positively associated with tremors. These findings are the first documented results suggesting that chronic oral exposure to DA at concentrations near the current human regulatory limit are related to structural and chemical changes in the adult primate brain.

Repeated low level domoic acid exposure increases CA1 VGluT1 levels, but not bouton density, VGluT2 or VGAT levels in the hippocampus of adult mice

Domoic acid (DA) is a neurotoxin produced during harmful algal blooms that accumulates in marine organisms that serve as food resources for humans. While acute DA neurotoxicity can cause seizures and hippocampal lesions, less is known regarding how chronic, subacute DA exposure in adulthood impacts the hippocampus. With more frequent occurrences of harmful algal blooms, it is important to understand the potential impact of repeated, low-level DA exposure on human health. To model repeated, low-dose DA exposure, adult mice received a single low-dose (0.75 ± 0.05 μg/g) of DA or vehicle weekly for 22 consecutive weeks. Quantitative immunohistochemistry was performed to assess the effects of repeated, low-level DA exposure on hippocampal cells and synapses. Vesicular glutamate transporter 1 (VGluT1) immunoreactivity within excitatory boutons in CA1 of DA-exposed mice was increased. Levels of other vesicular transporter proteins (i.e., VGluT2 and the vesicular GABA transporter (VGAT)) within boutons, and corresponding bouton densities, were not significantly altered in CA1, CA3, or dentate gyrus. There were no significant changes in neuron density or glial fibrillary acidic protein (GFAP) immunoreactivity following chronic, low-dose exposure. This suggests that repeated low doses of DA, unlike high doses of DA, do not cause neuronal loss or astrocyte activation in hippocampus in adult mice. Instead, these findings demonstrate that repeated exposure to low levels of DA leads to subtle changes in VGluT1 expression within CA1 excitatory boutons, which may alter glutamatergic transmission in CA1 and disrupt behaviors dependent on spatial memory.

A decade and a half of Pseudo-nitzschia spp. and domoic acid along the coast of southern California

Blooms of the marine diatom genus Pseudo-nitzschia that produce the neurotoxin domoic acid have been documented with regularity along the coast of southern California since 2003, with the occurrence of the toxin in shellfish tissue predating information on domoic acid in the particulate fraction in this region. Domoic acid concentrations in the phytoplankton inhabiting waters off southern California during 2003, 2006, 2007, 2011 and 2017 were comparable to some of the highest values that have been recorded in the literature. Blooms of Pseudo-nitzschia have exhibited strong seasonality, with toxin appearing predominantly in the spring. Year-to-year variability of particulate toxin has been considerable, and observations during 2003, 2006, 2007, 2011 and again in 2017 linked domoic acid in the diets of marine mammals and seabirds to mass mortality events among these animals. This work reviews information collected during the past 15 years documenting the phenology and magnitude of Pseudo-nitzschia abundances and domoic acid within the Southern California Bight. The general oceanographic factors leading to blooms of Pseudo-nitzschia and outbreaks of domoic acid in this region are clear, but subtle factors controlling spatial and interannual variability in bloom magnitude and toxin production remain elusive.

Multifocal Necrotizing Myopathy in Northern Elephant Seal ( Mirounga angustirostris) Pups, San Miguel Island, California

A field study addressing causes of mortality in freshly dead northern elephant seals ( Mirounga angustirostris, Gill, 1866) was conducted on San Miguel Island, California, in February 2015. Necropsies were performed on 18 pups ranging in age from stillbirths to approximately 7 to 8 weeks. The primary gross diagnoses in these pups included trauma, myopathy, starvation/emaciation, infections, congenital anomalies, and perinatal mortality. However, 6 (33%) had a previously unrecognized myopathy characterized by multiple white streaks that were most obvious within the inner layer of the abdominal wall and the small innermost ventral intercostal muscles. Following histological examination, 2 more pups from San Miguel Island and 6 pups from The Marine Mammal Center (Sausalito, California) were found to have similar lesions. Histologically, the lesions within the skeletal muscles were characterized by a multifocal polyphasic, mild to severe, acute to subacute necrotizing myopathy with mineralization. Acute necrosis and degeneration characterized by pyknotic nuclei, eosinophilic cytoplasm and cytoplasmic vacuolization were found in smooth muscle myocytes within the urinary bladder and digestive system. Degeneration of myocytes was present in the tunica media of a few small- to medium-sized vessels and was characterized by a vacuolar degeneration and occasionally necrosis. This condition has been termed multifocal necrotizing myopathy. A cause of this myopathy was not identified.

Presence and persistence of the amnesic shellfish poisoning toxin, domoic acid, in octopus and cuttlefish brains

Domoic acid (DA) is a neurotoxin that causes degenerative damage to brain cells and induces permanent short-term memory loss in mammals. In cephalopod mollusks, although DA is known to accumulate primarily in the digestive gland, there is no knowledge whether DA reaches their central nervous system. Here we report, for the first time, the presence of DA in brain tissue of the common octopus (Octopus vulgaris) and the European cuttlefish (Sepia officinalis), and its absence in the brains of several squid species (Loligo vulgaris, L. forbesi and Todarodes sagittatus). We argue that such species-specific differences are related to their different life strategies (benthic/nektobenthic vs pelagic) and feeding ecologies, as squids mainly feed on pelagic fish, which are less prone to accumulate phycotoxins. Additionally, the temporal persistence of DA in octopus' brain reinforces the notion that these invertebrates can selectively retain this phycotoxin. This study shows that two highly-developed invertebrate species, with a complex central nervous system, where glutamatergic transmission is involved in vertebrate-like long-term potentiation (LTP), have the ability of retaining and possibly tolerating chronic exposure to DA, a potent neurotoxin usually acting at AMPA/kainate-like receptors. Here, we filled a gap of information on whether cephalopods accumulated this neurotoxin in brain tissue, however, further studies are needed to determine if these organisms are neurally or behaviourally impaired by DA.

Pinnipediae

This chapter reviews common diseases of pinnipeds, including species in the Otariidae (fur seals and sea lions), Phocidae (true seals), and Odobenidae (walrus) families. Much of the knowledge on pathologic conditions of pinnipeds comes from necropsies of stranded animals and those housed in captivity. As such, disease knowledge is biased toward species frequently housed in zoos and aquaria, those that strand more commonly, or those in which free-ranging populations are more easily accessible. Though historically systematic evaluations of wild populations have rarely been accomplished, in the past 10 years, with advances in marine mammal medicine and anesthesia, biologists and veterinarians more frequently completed live animal health field investigations to evaluate health and disease in free-ranging pinniped populations.

What California sea lions exposed to domoic acid might teach us about autism: lessons for predictive and preventive medicine

Autism spectrum disorder (ASD) shares many biological and behavioral similarities with the deleterious effects of domoic acid (DA) exposure. DA is produced by marine algae and most commonly by species of Pseudo-nitzschia. Humans and marine mammals can be exposed to DA when they consume whole fish or shellfish. The mammalian fetus is highly sensitive to the deleterious effects of DA exposure. Both ASD and exposures to toxic levels of DA feature repetitive behaviors, challenges with social interaction, and seizures. They can also share a commonality in brain anatomy and function, particularly the balance between excitatory and inhibitory mechanisms. The current article is relevant to predictive, preventive, and personalized medicine for three reasons. First, shellfish consumption may be a risk factor for ASD and the regulatory limit for DA should be adjusted to prevent this possibility. Human contributions to increased algal production of DA in coastal waters should be identified and reduced. Second, evaluations of sentinel species wild and free-roaming in the environment, though typically outside the purview of biomedical research, should be much more fully employed to gain insights to risk factors for human disease. To better identify and prevent disease, biomedical researchers should study wild populations. Third, studies of DA exposure highlight the possibility that glutamate additives to processed foods may also have deleterious impacts on human brain development and behavior.

Modulatory effects of Terminalia arjuna against domoic acid induced toxicity in Caco-2 cell line

Domoic acid is a potent marine algal toxin produced by diatomic genus of Pseudo-nitzschia causing amnesic shell fish poisoning. Domoic acid toxicosis mainly involves excitotoxic effects coupled with oxidative stress. The present study was aimed to evaluate the protective effects of hydro-alcoholic extract of Terminalia arjuna (TA) against domoic acid induced toxic effects in Caco-2 cell line. It was observed that the toxicity induced by domoic acid in Caco-2 cells was mediated by oxidative insult leading to morphological changes, DNA damage and apoptosis. In our study pre-treatment of the cells with TA (10, 20 and 30 μg/ml) showed significant protection against domoic acid induced morphological, oxidative and apoptotic damages in a dose dependent manner. The effect of phytocompounds present in TA viz., kaempferol and arjungenin showed significant protection against domoic acid induced toxicity in Caco-2 cell line. Hence, it could be inferred that the protective effect of TA extract against domoic acid induced toxicity could be due to the individual or synergistic effects of kaempferol and argungenin. However, further clinical studies are warranted to consider TA as a natural remedy to prevent amnesic shell fish poisoning.

Human Heart Glutamate Receptors—Implications for Toxicology, Food Safety, and Drug Discovery

Excitatory amino acids (EAAs) mediate their effects through the glutamate receptors (GluRs) in the brain. GluRs play an important role in the treatment of a variety of neuropsychiatric conditions and are central to the neurotoxicity of EAAs such as domoic and kainic acid. Unstained histological preparations of human heart tissues were used for the histopathological assessment, the anatomical identification of specific cardiac structures and the presence of the GluRs. Immunohistochemical stains with the biomarkers protein gene product (PGP 9.5) and the neurofilaments (NF 160 and NF 200) were used to identify neural structures and the components of the conducting system. Several subtypes of GluRs were differentially expressed and each had a specific distribution. In contrast to nonhuman primates, GluRs are more widely expressed in humans, where the working myocardium and the wall of blood vessels stained for GluRs. The immunolabelling was observed within the specialized structures of the conducting system, intramural nerves, and ganglia cells. These receptors may be involved in important cardiac functions such as contraction, rhythm, coronary circulation, and thus may be implicated in the pathobiology of some cardiac disease. The GluRs in the heart could be targets for the effects of excitatory compounds and is therefore an important consideration for the safety evaluation of foods and therapeutic products.

Post-mortem findings in southern right whales Eubalaena australis at Península Valdés, Argentina, 2003-2012

Between 2003 and 2012, 605 southern right whales (SRW; Eubalaena australis) were found dead along the shores of Península Valdés (PV), Argentina. These deaths included alarmingly high annual losses between 2007 and 2012, a peak number of deaths (116) in 2012, and a significant number of deaths across years in calves-of-the-year (544 of 605 [89.9%]; average = 60.4 yr(-1)). Post-mortem examination and pathogen testing were performed on 212 whales; 208 (98.1%) were calves-of-the-year and 48.0% of these were newborns or neonates. A known or probable cause of death was established in only a small number (6.6%) of cases. These included ship strike in a juvenile and blunt trauma or lacerations (n = 5), pneumonia (n = 4), myocarditis (n = 2), meningitis (n = 1), or myocarditis and meningitis (n = 1) in calves. Ante-mortem gull parasitism was the most common gross finding. It was associated with systemic disease in a single 1-2 mo old calf. Immunohistochemical labeling for canine distemper virus, Toxoplasma gondii and Brucella spp., and PCR for cetacean morbillivirus (CeMV), influenza A, and apicomplexan protozoa were negative on formalin-fixed, paraffin-embedded lung and brain samples from a subset of whales; PCR for Brucella spp. was positive in a newborn/neonate with pneumonia. Skin samples from whales with gull parasitism were PCR negative for CeMV, poxvirus, and papillomavirus. This is the first long-term study to investigate and summarize notable post-mortem findings in the PV SRW population. Consistent, significant findings within or between years to explain the majority of deaths and those in high-mortality years remain to be identified.

Fetal domoic acid exposure affects lateral amygdala neurons, diminishes social investigation and alters sensory-motor gating

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.

Algal toxin impairs sea lion memory and hippocampal connectivity, with implications for strandings

Domoic acid (DA) is a naturally occurring neurotoxin known to harm marine animals. DA-producing algal blooms are increasing in size and frequency. Although chronic exposure is known to produce brain lesions, the influence of DA toxicosis on behavior in wild animals is unknown. We showed, in a large sample of wild sea lions, that spatial memory deficits are predicted by the extent of right dorsal hippocampal lesions related to natural exposure to DA and that exposure also disrupts hippocampal-thalamic brain networks. Because sea lions are dynamic foragers that rely on flexible navigation, impaired spatial memory may affect survival in the wild.

Feline hippocampal and piriform lobe necrosis as a consequence of severe cluster seizures in two cats in Finland

Feline hippocampal and piriform lobe necrosis (FHN) has been reported from several countries worldwide and is considered an important aetiology for feline epileptic seizures. The aetiology of FHN remains unclear, however it is suspected that FHN might occur secondary to intense epileptic activity as described in humans and dogs although this has not yet been documented in cats. The purpose of our report is to describe the first cases of FHN in Finland diagnosed by magnetic resonance imaging (MRI) and histopathology. The two cases we describe had a well documented history of pre-existing seizures with normal brain MRI at the onset of cluster seizures but MRI done when the cats exhibited clinical deterioration secondary to severe seizure activity, revealed lesions in the hippocampus and piriform lobes typical of FHN. Our report confirms that feline hippocampus and piriform lobe necrosis does occur in the Finnish cat population and should therefore be considered as a differential diagnosis in cats with seizures. In addition, the presentation, clinical findings, results of MRI and/or histopathology shows that cats may develop FHN secondary to severe seizure activity.

Brain Pathology in Adult Rats Treated With Domoic Acid

Domoic acid (DA) is a neurotoxin reported to produce damage to the hippocampus, which plays an important role in memory. The authors inoculated rats intraperitoneally with an effective toxic dose of DA to study the distribution of the toxin in major internal organs by using immunohistochemistry, as well as to evaluate the induced pathology by means of histopathologic and immunohistochemical methods at different time points after toxin administration (6, 10, and 24 hours; 5 and 54 days). DA was detected by immunohistochemistry exclusively in pyramidal neurons of the hippocampus at 6 and 10 hours after dosing. Lesions induced by DA were prominent at 5 days following treatment in selected regions of the brain: hippocampus, amygdala, piriform and perirhinal cortices, olfactory tubercle, septal nuclei, and thalamus. The authors found 2 types of lesions: delayed death of selective neurons and large areas of necrosis, both accompanied by astrocytosis and microgliosis. At 54 days after DA exposure, the pathology was characterized by still-distinguishable dying neurons, calcified lesions in the thalamus, persistent astrocytosis, and pronounced microgliosis. The expression of nitric oxide synthases suggests a role for nitric oxide in the pathogenesis of neuronal degeneration and chronic inflammation induced by DA in the brain.

Proteomic Analysis of Plasma from California Sea Lions (Zalophus californianus) Reveals Apolipoprotein E as a Candidate Biomarker of Chronic Domoic Acid Toxicosis

Domoic acid toxicosis (DAT) in California sea lions (Zalophus californianus) is caused by exposure to the marine biotoxin domoic acid and has been linked to massive stranding events and mortality. Diagnosis is based on clinical signs in addition to the presence of domoic acid in body fluids. Chronic DAT further is characterized by reoccurring seizures progressing to status epilepticus. Diagnosis of chronic DAT is often slow and problematic, and minimally invasive tests for DAT have been the focus of numerous recent biomarker studies. The goal of this study was to retrospectively profile plasma proteins in a population of sea lions with chronic DAT and those without DAT using two dimensional gel electrophoresis to discover whether individual, multiple, or combinations of protein and clinical data could be utilized to identify sea lions with DAT. Using a training set of 32 sea lion sera, 20 proteins and their isoforms were identified that were significantly different between the two groups (p<0.05). Interestingly, 11 apolipoprotein E (ApoE) charge forms were decreased in DAT samples, indicating that ApoE charge form distributions may be important in the progression of DAT. In order to develop a classifier of chronic DAT, an independent blinded test set of 20 sea lions, seven with chronic DAT, was used to validate models utilizing ApoE charge forms and eosinophil counts. The resulting support vector machine had high sensitivity (85.7% with 92.3% negative predictive value) and high specificity (92.3% with 85.7% positive predictive value). These results suggest that ApoE and eosinophil counts along with machine learning can perform as a robust and accurate tool to diagnose chronic DAT. Although this analysis is specifically focused on blood biomarkers and routine clinical data, the results demonstrate promise for future studies combining additional variables in multidimensional space to create robust classifiers.

Applications and implications of neurochemical biomarkers in environmental toxicology

Thousands of environmental contaminants have neurotoxic properties, but their ecological risk is poorly characterized. Contaminant-associated disruptions to animal behavior and reproduction, both of which are regulated by the nervous system, provide decision makers with compelling evidence of harm, but such apical endpoints are of limited predictive or harm-preventative value. Neurochemical biomarkers, which may be used to indicate subtle changes at the subcellular level, may help overcome these limitations. Neurochemical biomarkers have been used for decades in the human health sciences and are now gaining increased attention in the environmental realm. In the present review, the applications and implications of neurochemical biomarkers to the field of ecotoxicology are discussed. The review provides a brief introduction to neurochemistry, covers neurochemical-based adverse outcome pathways, discusses pertinent strengths and limitations of neurochemical biomarkers, and provides selected examples across invertebrate and vertebrate taxa (worms, bivalves, fish, terrestrial and marine mammals, and birds) to document contaminant-associated neurochemical disruption. With continued research and development, neurochemical biomarkers may increase understanding of the mechanisms that underlie injury to ecological organisms, complement other measures of neurological health, and be integrated into risk assessment practices.

Hippocampal neuropathology of domoic acid-induced epilepsy in California sea lions (Zalophus californianus)

California sea lions (Zalophus californianus) are abundant human-sized carnivores with large gyrencephalic brains. They develop epilepsy after experiencing status epilepticus when naturally exposed to domoic acid. We tested whether sea lions previously exposed to DA (chronic DA sea lions) display hippocampal neuropathology similar to that of human patients with temporal lobe epilepsy. Hippocampi were obtained from control and chronic DA sea lions. Stereology was used to estimate numbers of Nissl-stained neurons per hippocampus in the granule cell layer, hilus, and pyramidal cell layer of CA3, CA2, and CA1 subfields. Adjacent sections were processed for somatostatin immunoreactivity or Timm-stained, and the extent of mossy fiber sprouting was measured stereologically. Chronic DA sea lions displayed hippocampal neuron loss in patterns and extents similar but not identical to those reported previously for human patients with temporal lobe epilepsy. Similar to human patients, hippocampal sclerosis in sea lions was unilateral in 79% of cases, mossy fiber sprouting was a common neuropathological abnormality, and somatostatin-immunoreactive axons were exuberant in the dentate gyrus despite loss of immunopositive hilar neurons. Thus, hippocampal neuropathology of chronic DA sea lions is similar to that of human patients with temporal lobe epilepsy.

Domoic acid-induced seizures in California sea lions (Zalophus californianus) are associated with neuroinflammatory brain injury

California sea lions (CSLs) exposed to the marine biotoxin domoic acid (DA) develop an acute or chronic toxicosis marked by seizures and act as sentinels of the disease. Experimental evidence suggests that oxidative stress and neuroinflammation are important mechanisms underlying the seizurogenic potential of environmental toxicants but these pathways are relatively unstudied in CSLs. In the current study, we investigated the role of glutamate-glutamine changes and gliosis in DA-exposed CSLs to better understand the neurotoxic mechanisms occurring during DA toxicity. Sections from archived hippocampi from control and CSLs diagnosed with DA toxicosis were immunofluorescently stained for markers of gliosis, oxidative/nitrative stress and changes in glutamine synthetase (GS). Quantitative assessment revealed increasing loss of microtubule associated protein-2 positive neurons with elevations in 4-hydroxynonenal correlating with chronicity of exposure, whereas the pattern of activated glia expressing nitric oxide synthase 2 and tumor necrosis factor followed pathological severity. There was no significant change in the amount of GS positive cells but there was increased 3-nitrotyrosine in GS expressing cells and in neurons, particularly in animals with chronic DA toxicosis. These changes were consistently seen in the dentate gyrus and in the cornu ammonis (CA) sectors CA3, CA4, and CA1. The results of this study indicate that gliosis and resultant changes in GS are likely important mechanisms in DA-induced seizure that need to be further explored as potential therapies in treating exposed wildlife.

Domoic acid epileptic disease

Domoic acid epileptic disease is characterized by spontaneous recurrent seizures weeks to months after domoic acid exposure. The potential for this disease was first recognized in a human case study of temporal lobe epilepsy after the 1987 amnesic shellfish-poisoning event in Quebec, and was characterized as a chronic epileptic syndrome in California sea lions through investigation of a series of domoic acid poisoning cases between 1998 and 2006. The sea lion study provided a breadth of insight into clinical presentations, unusual behaviors, brain pathology, and epidemiology. A rat model that replicates key observations of the chronic epileptic syndrome in sea lions has been applied to identify the progression of the epileptic disease state, its relationship to behavioral manifestations, and to define the neural systems involved in these behavioral disorders. Here, we present the concept of domoic acid epileptic disease as a delayed manifestation of domoic acid poisoning and review the state of knowledge for this disease state in affected humans and sea lions. We discuss causative mechanisms and neural underpinnings of disease maturation revealed by the rat model to present the concept for olfactory origin of an epileptic disease; triggered in dendodendritic synapases of the olfactory bulb and maturing in the olfactory cortex. We conclude with updated information on populations at risk, medical diagnosis, treatment, and prognosis.

Electrocardiograms of bottlenose dolphins (Tursiops truncatus) out of water: habituated collection versus wild postcapture animals

Electrocardiography (ECG) was performed on captured free-ranging bottlenose dolphins (Tursiops truncatus) during a health assessment exercise and compared with that of a Navy collection of dolphins habituated to handling out of water in order to assess possible cardiovascular impacts of capture and handling. Six-lead recordings (I, II, III, aVr, aVl, and aVf) in the frontal plane and direct thorax leads were collected from both groups, with a modified base-apex lead additionally employed with the Navy collection dolphins. Measured and calculated parameters included amplitudes of P, R, S, and T waves and total QRS complex; T:S and T:QRS ratios; heart rate; durations of P wave; QRS complex, PR, QT, and RR intervals; maximum minus minimum RR interval; ST segment elevation-depression; and mean electrical axis (MEA). Physiologically minor but statistically significant differences were detected in S wave amplitude, PR interval, QRS duration, and MEA. The PR interval, QRS duration, and S wave amplitude were slightly greater and the MEA oriented slightly rightward in wild postcapture dolphins compared to Navy collection dolphins. There were no differences in heart rate or maximum minus minimum RR interval, which serves as a proxy for the expected sinus arrhythmia of dolphins. The base-apex lead resulted in greater QRS amplitude than lead II, as expected for the category B ventricular activation of dolphins. The left-side direct thorax lead was more consistent than that of the right side. Clinically, ECG was a useful adjunct to auscultation and thoracic palpation for monitoring heart rate and rhythm and generated a record for archiving. Safe capture and handling protocols in place, under which dolphins are immediately returned to the water at progressive signs of distress, may make cardiovascular decompensation less likely to be detected by ECG. It appears that the dolphin cardiovascular system compensates suitably well to capture, as measured by ECG under the conditions of this study.