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Relationship: 364


A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Cell injury/death leads to N/A, Neurodegeneration

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Binding of agonists to ionotropic glutamate receptors in adult brain causes excitotoxicity that mediates neuronal cell death, contributing to learning and memory impairment. adjacent Moderate Allie Always (send email) Open for citation & comment WPHA/WNT Endorsed
Acetylcholinesterase Inhibition Leading to Neurodegeneration adjacent High Low Allie Always (send email) Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER.  More help
Term Scientific Term Evidence Link
rat Rattus norvegicus High NCBI
mouse Mus musculus High NCBI
Macaca fascicularis Macaca fascicularis High NCBI
human Homo sapiens Low NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Unspecific High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help
Term Evidence
Adult High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Cell death of neurons directly causes neurodegeneration characterized by abnormal neuronal loss (Przedborski et al., 2003). While the upstream event is unspecific as to the type of cell affected, neurodegeneration is caused by cell death in neurons specifically.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

As it pertains to AOP 281, evidence was collected in multiple ways: literature searches of external databases, review of related KEs and KERS in the AOPWiki, and consultation with experts.   Extensive literature searches were conducted in Scopus, Pubmed, and Google Scholar using keywords applicable to each KE, with an initial focus on zebrafish data to then focusing on rat data. Related KEs and KERs in the AOPWiki were also reviewed for relevant evidence and their sources.  The “snowball method” was used to find additional articles, i.e., relevant citations within an article were obtained if they provided additional evidence. EndNote reference managing software was used to store results from the literature searches and when possible, a pdf of the manuscript was attached to each record. Papers were reviewed and categorized by whether they contained data to support one or more parts of the AOP. An Excel spreadsheet was used to record reviewed papers and any information worth noting.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help
Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured.   More help

There is well established mechanistic understanding supporting the relationship between these two KEs.

Neurodegeneration in the strict sense of the word, is referring to any pathological condition primarily affecting brain cell populations (Przedborski et al., 2003). At the histopathological level, neurodegenerative conditions are described by neuronal death and reactive gliosis (Przedborski et al., 2003).

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

There are various methods to categorize neurodegeneration from cell death, and there are “different clinical pictures” depending on the area or areas of the brain affected (Przedborski et al., 2003).

Domoic acid considerations:

Zebrafish were exposed for 36-weeks to DomA and showed no excitotoxic neuronal death and no histopathological lesions in glutamate-rich brain areas (Hiolski et al., 2014). 

Administration of DomA (9.0 mg DomA kg(-1) bw, i.p.) to seabream (Sparus aurata) lead to measurement of 0.61, 0.96, and 0.36 mg DomA kg(-1) of brain tissue at 1, 2 and 4 hours. At this dose but also at lower concentrations (0.45 and 0.9 mg DomA kg(-1) bw) no major permanent brain damage was detected (Nogueira et al., 2010). Leopard sharks possess the molecular target for DomA but it has been shown to be resistant to doses of DomA that can cause neurotoxicity to other vertebrates, suggesting the presence of some protective mechanism (Schaffer et al., 2006).

All these reports suggest species specific susceptibility to DomA toxicity.

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help
Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help
Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Neurodegeneration from cell death is widely accepted, neurodegenerative models have used various species including mice and zebrafish for different neurodegenerative diseases (Dawson et al., 2018)

Information Specific to DomA

There is an overall agreement regarding the histopathology of the brain lesions related to acute DomA neurotoxicity across certain species. Data derived from humans, rodents, non-human primates and sea lions suggest that common neurodegeneration features in selected brain areas are found despite the fact that study design, estimated exposure, processing of samples and history of event may differ (Pulido, 2008).

Furthermore, the distribution of brain damage by DomA has also been established by magnetic resonance imaging microscopy (MRM) for both human and rat, demonstrating similar distribution as that described by histopathological studies (Pulido, 2008).

It is important to notice that human sensitivity to DomA exposure is well documented in the published literature and seems to be much higher than in other species (Lefebvre and Robertson 210; Barlow et al., 2004).  In 1987 in Canada, more than 200 people became acutely ill after ingesting mussels contaminated with DomA. The outbreak resulted in 20 hospitalizations and four deaths. Clinical effects observed included gastrointestinal symptoms and neurotoxic effects such as hallucinations, memory loss and coma. For this reason, the condition was termed amnesic shellfish poisoning (Barlow et al., 2004). The neurotoxic properties of DomA result in neuronal degeneration and necrosis in specific regions of the hippocampus (Teitelbaum et al., 1990).


List of the literature that was cited for this KER description. More help

Acon-Chen, C., Koenig, J. A., Smith, G. R., Truitt, A. R., Thomas, T. P. & Shih, T. M. 2016. Evaluation of acetylcholine, seizure activity and neuropathology following high-dose nerve agent exposure and delayed neuroprotective treatment drugs in freely moving rats. Toxicology Mechanisms and Methods, 26, 378-388. DOI: 10.1080/15376516.2016.1197992.Ananth C, Thameem DS, Gopalakrishnakone P, Kaur C., Domoic acid-induced neuronal damage in the rat hippocampus: changes in apoptosis related genes (bcl-2, bax, caspase-3) and microglial response. J Neurosci Res., 2001, 66: 177-190.

Ananth C, Gopalakrishnakone P, Kaur C., Induction of inducible nitric oxide synthase expression in activated microglia following domoic acid (DA)-induced neurotoxicity in the rat hippocampus. Neurosci Lett., 2003, 338: 49-52.

Antequera D, Bolos M, Spuch C, Pascual C, Ferrer I, Fernandez-Bachiller MI, Rodríguez-Franco MI, Carro E., Effects of a tacrine-8-hydroxyquinoline hybrid (IQM-622) on Aβ accumulation and cell death: involvement in hippocampal neuronal loss in Alzheimer's disease. Neurobiol Dis., 2012, 46: 682-691.

Appel NM, Rapoport SI, O'Callaghan JP., Sequelae of parenteral domoic acid administration in rats: comparison of effects on different anatomical markers in brain. Synapse, 1997, 25: 350-358.

Barlow Jeffery B, T, Moizer K, Paul S, and Boyle C., Amnesic shellfish poison. Food Chem Toxicol., 42: 545-557.

Cendes F, Andermann F, Carpenter S, Zatorre RJ, Cashman NR., Temporal lobe epilepsy caused by domoic acid intoxication: evidence for glutamate receptor-mediated excitotoxicity in humans. Ann Neurol., 1995, 37: 123-6.

Colman JR, Nowocin KJ, Switzer RC, Trusk TC, Ramsdell JS., Mapping and reconstruction of domoic acid-induced neurodegeneration in the mouse brain. Neurotoxicol Teratol., 2005, 27: 753-767.

Dawson, T. M., Golde, T. E. & Lagier-Tourenne, C. 2018. Animal models of neurodegenerative diseases. Nature Neuroscience, 21, 1370-1379. DOI: 10.1038/s41593-018-0236-8.

Hiolski EM, Kendrick PS, Frame ER, Myers MS, Bammler TK, Beyer RP, Farin FM, Wilkerson HW, Smith DR, Marcinek DJ, Lefebvre KA., Chronic low-level domoic acid exposure alters gene transcription and impairs mitochondrial function in the CNS. Aquat Toxicol., 2014, 155: 151-159.

Jakobsen B, Tasker A, Zimmer J., Domoic acid neurotoxicity in hippocampal slice cultures. Amino Acids, 2002, 23: 37-44.

Lefebvre Kathi A. and Robertson Alison, Domoic acid and human exposure risks: A review, Toxicon, 2010, 56: 218–230.

Lu J, Wu DM, Zheng YL, Hu B, Cheng W, Zhang ZF., Purple sweet potato color attenuates domoic acid-induced cognitive deficits by promoting estrogen receptor-α-mediated mitochondrial biogenesis signaling in mice. Free Radic Biol Med., 2012, 52: 646-659.

Nogueira I, Lobo-da-Cunha A, Afonso A, Rivera S, Azevedo J, Monteiro R, Cervantes R, Gago-Martinez A, Vasconcelos V., Toxic effects of domoic acid in the seabream Sparus aurata. Mar Drugs, 2010, 8: 2721-2732.

Przedborski S, Vila M, Jackson-Lewis V., Neurodegeneration: What is it and where are we? J Clin Invest., 2003, 111: 3-10.

Pulido OM., Domoic acid toxicologic pathology: a review. Mar Drugs, 2008, 6: 180-219.

Qiu S, Currás-Collazo MC., Histopathological and molecular changes produced by hippocampal microinjection of domoic acid. Neurotoxicol Teratol., 2006, 28: 354-362.

Scallet AC, Schmued LC., Johannessen JN. Neurohistochemical biomarkers of the marine neurotoxicant, domoic acid. Neurotoxicol Teratol., 2005, 27: 745-752.

Schaffer P, Reeves C, Casper DR, Davis CR., Absence of neurotoxic effects in leopard sharks, Triakis semifasciata, following domoic acid exposure. Toxicon., 2006, 47: 747-752.

Slikker W Jr, Scallet AC, Gaylor DW., Biologically-based dose-response model for neurotoxicity risk assessment. Toxicol Lett., 1998, 102-103: 429-433.

Teitelbaum JS, Zatorre RJ, Carpenter S, Gendron D, Evans AC, Gjedde A, and Cashman NR., Neurologic sequelae of domoic acid intoxication due to the ingestion of contaminated mussels. N Engl J Med., 1990, 322: 1781-1787.

Tiedeken JA, Muha N, Ramsdell JS., A cupric silver histochemical analysis of domoic acid damage to olfactory pathways following status epilepticus in a rat model for chronic recurrent spontaneous seizures and aggressive behavior. Toxicol Pathol., 2013a, 41: 454-69.

Tiedeken JA, Ramsdell JS., Persistent neurological damage associated with spontaneous recurrent seizures and atypical aggressive behavior of domoic acid epileptic disease. Toxicol Sci., 2013b, 133: 133-43.

Truelove J, Mueller R, Pulido O, Martin L, Fernie S, Iverson F., 30-day oral toxicity study of domoic acid in cynomolgus monkeys: lack of overt toxicity at doses approaching the acute toxic dose. Nat Toxins., 1997, 5: 111-114.

Tryphonas L, Truelove J, Nera E, Iverson F., Acute neurotoxicity of domoic acid in the rat. Toxicol Pathol., 1990, 18: 1-9.