Aop: 10

Title

A descriptive phrase which references both the Molecular Initiating Event and Adverse Outcome.It should take the form “MIE leading to AO”. For example, “Aromatase inhibition leading to reproductive dysfunction” where Aromatase inhibition is the MIE and reproductive dysfunction the AO. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

Binding to the picrotoxin site of ionotropic GABA receptors leading to epileptic seizures in adult brain

Short name
A name that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
Blocking iGABA receptor ion channel leading to seizures

Graphical Representation

A graphical representation of the AOP.This graphic should list all KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs. More help
Click to download graphical representation template Explore AOP in a Third Party Tool
W1siziisijiwmtyvmtivmdivn3hzbdkymdfnav9jr0fcqvjfqu9qms5qcgcixsxbinailcj0ahvtyiisijuwmhg1mdaixv0?sha=7b8936e9fbed3ad2

Authors

The names and affiliations of the individual(s)/organisation(s) that created/developed the AOP. More help

Ping Gong, Edward J. Perkins, US Army Engineer Research and Development Center

Email: ping.gong@usace.army.mil or edward.j.perkins@usace.army.mil

Point of contact for this AOP entry: Dr. Ping Gong

Point of Contact

The user responsible for managing the AOP entry in the AOP-KB and controlling write access to the page by defining the contributors as described in the next section.   More help
Cataia Ives   (email point of contact)

Contributors

Users with write access to the AOP page.  Entries in this field are controlled by the Point of Contact. More help
  • Ping Gong
  • Edward Perkins
  • Cataia Ives

Status

Provides users with information concerning how actively the AOP page is being developed, what type of use or input the authors feel comfortable with given the current level of development, and whether it is part of the OECD AOP Development Workplan and has been reviewed and/or endorsed. OECD Status - Tracks the level of review/endorsement the AOP has been subjected to. OECD Project Number - Project number is designated and updated by the OECD. SAAOP Status - Status managed and updated by SAAOP curators. More help
Author status OECD status OECD project SAAOP status
Open for citation & comment WPHA/WNT Endorsed 1.15 Included in OECD Work Plan
This AOP was last modified on July 16, 2022 18:37

Revision dates for related pages

Page Revision Date/Time
Reduction, Ionotropic GABA receptor chloride channel conductance February 06, 2018 18:35
Occurrence, A paroxysmal depolarizing shift April 29, 2019 12:32
Occurrence, Epileptic seizure April 29, 2019 12:33
Binding at picrotoxin site, iGABAR chloride channel April 29, 2019 12:27
Reduction, Neuronal synaptic inhibition May 16, 2018 18:42
Generation, Amplified excitatory postsynaptic potential (EPSP) May 18, 2018 19:18
Binding at picrotoxin site, iGABAR chloride channel leads to Reduction, Ionotropic GABA receptor chloride channel conductance April 29, 2019 12:14
Reduction, Ionotropic GABA receptor chloride channel conductance leads to Reduction, Neuronal synaptic inhibition April 29, 2019 12:40
Reduction, Neuronal synaptic inhibition leads to Generation, Amplified excitatory postsynaptic potential (EPSP) May 15, 2018 18:36
Generation, Amplified excitatory postsynaptic potential (EPSP) leads to Occurrence, A paroxysmal depolarizing shift May 15, 2018 18:26
Occurrence, A paroxysmal depolarizing shift leads to Occurrence, Epileptic seizure May 22, 2018 15:38
Picrotoxin November 29, 2016 18:42
Lindane November 29, 2016 18:42
Dieldrin November 29, 2016 18:42
Heptachlor February 11, 2018 00:24
Endosulfan February 11, 2018 00:30
RDX November 29, 2016 18:42
Fipronil November 29, 2016 18:42

Abstract

A concise and informative summation of the AOP under development that can stand-alone from the AOP page. The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance. More help

This AOP begins with a molecular initiating event (MIE) where a chemical binds to the picrotoxin binding site at or near the central pore of the ionotropic GABA receptor complex causing blockage of the ion channel. As a result, the first key event (KE) is a decrease in inward chloride conductance through the ligand-gated ion channel. This leads to the second KE, a reduction in postsynaptic inhibition, reflected as reduced frequency and amplitude of spontaneous inhibitory postsynaptic current (sIPSC) or abolishment of GABA-induced firing action in GABAergic neuronal membranes. Consequently, the resistance of excitatory neurons to fire is decreased, resulting in the generation of a large excitatory postsynaptic potential (EPSP), i.e., the third KE. The large EPSP is reflected as a spike (rise) of intracellular Ca2+ observed in the affected region, where a large group of excitatory neurons begin firing in an abnormal, excessive, and synchronized manner. Such a giant Ca2+-mediated excitatory firing (depolarization) causes voltage-gated Na+ to open, which results in action potentials. The depolarization is followed by a period of hyper-polarization mediated by Ca2+-dependent K+ channels or GABA-activated Cl influx. During seizure development, the post-depolarization hyperpolarization becomes smaller, gradually disappears, and is replaced by a depolarization. This characteristic depolarization-shrinking hyperpolarization sequence of events represents the fourth KE known as “paroxysmal depolarizing shift” (PDS), which forms a “seizure focus”. A PDS is, essentially, an indication of epilepsy at the cellular level, which serves as the foci to initiate the adverse outcome at the organismal level of epileptic seizure. The severity of symptoms is often dose- and duration- dependent, while the toxicological symptoms are associated with the type and location of affected iGABARs. Mortality can occur if the individual sustains a prolonged or pronounced convulsion or seizure. Neurotoxicity, of which seizures are an end point, is a regulated outcome for chemicals. This AOP allows for screening chemicals for the potential to cause neurotoxicity through the use of in vitro assays that demonstrate binding to the picrotoxin site, electrophysiological assays demonstrating depolarization of neuronal membranes, or electroencephalography that records electrical activity of the adult brain.

AOP Development Strategy

Context

Used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development.The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. More help

Ionotropic GABA receptors (iGABARs) are ligand-gated ion channels which play important functional roles in the nervous system. As the major player in inhibitory neurotransmission, iGABARs are widely distributed in both vertebrates and invertebrates (McGonigle and Lummis 2010; Garcia-Reyero et al. 2011). In vertebrates, the iGABAR includes two subclasses of fast-responding ion channels, GABAA receptor (GABAA-R) and GABAC receptor (GABAC-R). Invertebrate iGABARs do not readily fit the vertebrate GABAA/GABAC receptor categories (Sieghart 1995). The majority of insect iGABARs are distinguished from vertebrate GABAA receptors by their insensitivity to bicuculline and differ from GABAC-Rs in that they are subject to allosteric modulation, albeit weakly, by benzodiazepines and barbiturates (Hosie et al. 1997).

Chemical interactions with iGABARs can cause a variety of pharmacological and neurotoxicological effects depending on the location of the active or allosteric site affected. Three distinct types of interactions at binding sites on iGABARs can antagonize the postsynaptic inhibitory functions of GABA and lead to epileptic seizures and death. These three types of interactions correspond to three AOPs (Gong et al. 2015). One of the three types of interaction is non-competitive channel blocking at the picrotoxin convulsant site located inside of the iGABAR pore that spans neuronal cell membranes, which is the MIE described in the current AOP. The other two types of interactions are negative modulation at allosteric sites and competitive binding at the active orthosteric sites (MIEs to be developed in the future).

It is worth noting that there exist another class of GABA receptors called metabotropic G-protein-coupled receptors (mGABAR) or GABAB receptors. This AOP is not applicable to GABAB receptors because they mediate slow and sustained inhibitory responses to GABA and are involved in absence epilepsy (Han et al. 2012).

Strategy

Provides a description of the approaches to the identification, screening and quality assessment of the data relevant to identification of the key events and key event relationships included in the AOP or AOP network.This information is important as a basis to support the objective/envisaged application of the AOP by the regulatory community and to facilitate the reuse of its components.  Suggested content includes a rationale for and description of the scope and focus of the data search and identification strategy/ies including the nature of preliminary scoping and/or expert input, the overall literature screening strategy and more focused literature surveys to identify additional information (including e.g., key search terms, databases and time period searched, any tools used). More help

Summary of the AOP

This section is for information that describes the overall AOP. The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help

Events:

Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a prototypical stressor and the biological system) of an AOP. More help
Key Events (KE)
A measurable event within a specific biological level of organisation. More help
Adverse Outcomes (AO)
An AO is a specialized KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help
Type Event ID Title Short name
MIE 667 Binding at picrotoxin site, iGABAR chloride channel Binding at picrotoxin site, iGABAR chloride channel
KE 64 Reduction, Ionotropic GABA receptor chloride channel conductance Reduction, Ionotropic GABA receptor chloride channel conductance
KE 669 Reduction, Neuronal synaptic inhibition Reduction, Neuronal synaptic inhibition
KE 682 Generation, Amplified excitatory postsynaptic potential (EPSP) Generation, Amplified excitatory postsynaptic potential (EPSP)
KE 616 Occurrence, A paroxysmal depolarizing shift Occurrence, A paroxysmal depolarizing shift
AO 613 Occurrence, Epileptic seizure Occurrence, Epileptic seizure

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarizes all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP.Each table entry acts as a link to the individual KER description page. More help

Network View

This network graphic is automatically generated based on the information provided in the MIE(s), KEs, AO(s), KERs and Weight of Evidence (WoE) summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Prototypical Stressors

A structured data field that can be used to identify one or more “prototypical” stressors that act through this AOP. Prototypical stressors are stressors for which responses at multiple key events have been well documented. More help

Life Stage Applicability

The life stage for which the AOP is known to be applicable. More help
Life stage Evidence
Adults High

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available. More help
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
mouse Mus musculus High NCBI
rat Rattus norvegicus High NCBI
bobwhite quail Colinus virginianus High NCBI
zebrafish Danio rerio Moderate NCBI

Sex Applicability

The sex for which the AOP is known to be applicable. More help
Sex Evidence
Male High
Female High

Overall Assessment of the AOP

Addressess the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and Weight of Evidence (WoE) for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). More help

Biological plausibility

The biological mechanisms underlying epilepsy (defined as a disorder of the central nervous system characterized by recurrent seizures unprovoked by an acute systemic or neurologic insult) have been investigated for more than six decades and are well understood except for a few intermediate details (Bromfield et al. 2006; Lomen-Hoerth and Messing 2010). As one of the cellular mechanisms of action, blocking postsynaptic GABA-mediated inhibition can lead to epileptic seizure (Dichter and Ayala 1987; Gong et al. 2015). It has been extensively documented that non-competitive ion channel blockers such as picrotoxin, lindane, α-endosulfan and fipronil act through binding to iGABARs (Chen et al. 2006; Casida and Durkin 2015). Despite large structural diversity, it has been postulated that these blockers fit a single binding site in the chloride channel lumen lined by five TM2 (TransMembrane domain 2) segments, which was supported in the β3 homopentamer by mutagenesis, pore structure studies, ligand binding, and molecular modeling (Chen et al. 2006; Casida and Durkin 2015). The downstream cascading key events of this AOP have also been reviewed in multiple publications (e.g., Dichter and Ayala 1987; Bromfield et al. 2006; Lomen-Hoerth and Messing 2010). Based on the extensive evidence supporting the MIE, KEs and the AO, there is a high likelihood and certainty that such GABA antagonists as non-competitive channel blockers produce seizures in both invertebrates and vertebrates that possess GABAergic inhibitory neurotransmission in central nervous systems (Treiman 2001; Raymond-Delpech et al. 2005).

Concordance of dose-response relationships

Numerous pharmacological studies have reported quantitative dose-response relationships between the dose of non-competitive antagonists and the recorded electrophysiological response of epileptic seizures. See examples for picrotoxin (Newland and Cull-Candy 1992; Ikeda 1998; Stilwell et al. 2006), RDX (Williams et al. 2011) and dieldrin (Babot et al. 2007; Ikeda 1998).

Temporal concordance among the key events and the adverse outcome

Given that the basic mechanism of neuronal excitability is the action potential, a hyperexcitable state can result from many causes including decreased inhibitory neurotransmission (KE2). Moreover, action potentials occur due to depolarization of the neuronal membrane, with membrane depolarization propagating down the axon to induce neurotransmitter release at the axon terminal. The action potential occurs in an all-or-none fashion as a result of local changes in membrane potential brought about by net positive inward ion fluxes. Membrane potential thus varies with the activation of ligand-gated channels, whose conductance is affected by binding to neurotransmitters. For instance, the conductance is decreased (KE1) due to the binding at allosteric sites in the chloride channel of iGABAR by non-competitive blockers (MIE).

Seizure initiation: The hypersynchronous discharges that occur during a seizure may begin in a very discrete region of the cortex and then spread to neighboring regions. Seizure initiation is characterized by two concurrent events: 1) high-frequency bursts of action potentials, and 2) hypersynchronization of a neuronal population. The synchronized bursts from a sufficient number of neurons result in a so-called spike discharge on the EEG (electroencephalogram), i.e., amplified excitatory postsynaptic potential (KE3). At the level of single neurons, epileptiform activity consists of sustained neuronal depolarization resulting in a burst of action potentials, a plateau-like depolarization associated with completion of the action potential burst, and then a rapid repolarization followed by hyperpolarization. This sequence is called the paroxysmal depolarizing shift (KE4).

Seizure propagation (AO), the process by which a partial seizure spreads within the brain, occurs when there is sufficient activation to recruit surrounding neurons. This leads to a loss of surround inhibition and spread of seizure activity into contiguous areas via local cortical connections, and to more distant areas via long association pathways such as the corpus callosum. The propagation of bursting activity is normally prevented by intact hyperpolarization and a region of surrounding inhibition created by inhibitory neurons. With sufficient activation there is a recruitment of surrounding neurons via a number of mechanisms. The above description is excerpted and summarized from Bromfield et al. (2006).

Strength, consistency, and specificity of association of adverse effect and initiating event

Drug- or chemical-induced focal or generalized seizures are not limited to any specific group of chemical structures, neuroreceptors or taxonomy. This AOP addresses a specific group of chemicals that are capable of binding to the picrotoxin convulsant site of iGABARs, leading to epileptic seizures. Literature evidence strongly and consistently supports such a forward association, i.e., binding to the picrotoxin site leads to epileptic seizures (see reviews Gong et al. 2015; Bromfield et al. 2006; Raymond-Delpech et al. 2005; Treiman 2001; Dichter and Ayala 1987). For instance, dose- and time-dependent correlations between picrotoxin site binding by chlorinated pesticides and convulsions were observed in mice (Cole and Casida 1986), whereas poisoning with the organochlorine insecticide endosulfan caused seizure, status epilepticus, or refractory status epilepticus in humans (Durukan et al. 2009; Moon et al. 2017; Moses and Peter 2010; Parbhu et al. 2009; Roberts et al. 2004), and eventually led to the death of a farmer (Roberts et al. 2004) and a toddler (Parbhu et al. 2009).

Uncertainties, inconsistencies, and data gaps

No inconsistencies have been reported so far, though some uncertainties and data gaps do exist. For instance, the process by which seizures typically end, usually after seconds or minutes, and what underlies the failure of this spontaneous seizure termination in the life-threatening condition known as status epilepticus are less well understood (Bromfield et al. 2006). The spread of epileptic activity throughout the brain, the development of primary generalized epilepsy, the existence of “gating", mechanisms in specific anatomic locations, and the extrapolation of hypotheses derived from simple models of focal epilepsy to explain more complex forms of epilepsies observed in human and other animals, all are also not yet fully understood (Dichter and Ayala 1987). The remarkable plasticity of GABAergic neurons and iGABARs (e.g., iGABAR regulation by phosphorylation, and expression of potassium chloride cotransporters (KCCs) or sodium dependent anion exchangers (NDAE)) in response to insults and injury constitutes additional complexity and creates another layer of uncertainties in the emergence of epileptic seizures (Ben-Ari 2006; Galanopoulou 2008; Scharfman and Brooks-Kayal 2014).

Domain of Applicability

Addressess the relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context. More help

This AOP is applicable to all vertebrates and invertebrates possessing iGABARs, without restrictions pertaining to sex and taxonomy. This AOP may not be applicable to young animals during their embryonic and early developmental stages when GABA acts as an excitatory neurotransmitter due to increased intracellular Clˉ concentration in immature or developing neurons (Taketo and Yoshioka 2000; Galanopoulou 2008; Ben-Ari 2006). A key feature of the immature type function of GABAA receptors is the depolarizing signaling, attributed to the inability of young neurons to maintain low intracellular chloride. The regulation of GABAergic switch is different in neurons with depolarizing vs hyperpolarizing GABAergic signaling. In mature neurons, recurrent and prolonged seizures may trigger a pathological reemergence of immature features of GABAA receptors, which compromises the efficacy of GABA-mediated inhibition. In immature neurons with depolarizing GABAergic signaling, the physiological and pathological regulation of this system is completely different, possibly contributing to the different outcomes of early life seizures (Galanopoulou 2008).

Essentiality of the Key Events

The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently, evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence. The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs. More help

The MIE, four key events and resulted adverse outcome listed for this AOP are all essential based on current knowledge and understanding of the structure, pharmacology, localization, classification of ionotropic GABA receptors (e.g., GABAA receptors) (Olsen 2015; Olsen and Sieghart 2009), the basic neurophysiology, neurochemistry and cellular mechanisms underlying epilepsies (Dichter and Ayala 1987; Bromfield et al. 2006), and the pathophysiology of seizures (Lomen-Hoerth and Messing 2010).

Evidence Assessment

Addressess the biological plausibility, empirical support, and quantitative understanding from each KER in an AOP. More help

A novel subject matter expertise driven approach was developed for weight of evidence (WoE) assessment (Collier et al. 2016). This approach, tailored toward the needs of AOPs and in compliance with the AOP Users' Handbook (OECD 2017), was based on criteria and metrics related to data quality and causality (i.e., the strength of causal linkage between key events). The methodology consists of three main steps: (1) assembling evidence (preparing the AOP), (2) weighting evidence (criteria weighting and scoring), and (3) weighting the body of evidence (aggregating lines of evidence). We adopted the General Assessment Factors (GAF) established by the US EPA as the criteria for data quality evaluation, and a set of five criteria known as Bradford Hill criteria to measure the strength of causal linkages (see Table below). The numerical scoring scale corresponds to the descriptive scoring scale recommended in the Users' Handbook as follows: 4 or 5 is equivalent to High, 3 is equivalent to Moderate, and 1 or 2 is equivalent to Low. Detailed description on, supporting evidence for and quantitative understanding of each KE/KER can be found by clicking the link on each KE/KER above. 

The authors of Collier et al. (2016), who served as the developers for several AOPs (including this one), represented subject matter experts, and they applied their expertise and best professional judgment to assign weights to the criteria and scores to each line of evidence. Final criteria scoring represented the consensus scores agreed upon after debates among the authors. For example, the MIE has been intensively reviewed where numerous documented studies provided supporting evidence. Hence, the MIE received high scores for all five GAF criteria. However, the Bradford Hill criteria connecting KE2-->KE3 and KE3-->KE4 received relatively lower scores because there still exist knowledge gaps in the spread of epileptic activity throughout the normal CNS and the mechanism underlying the generalized epilepsies. The following table shows the results of our WoE assessment (note that scores may be inexact due to rounding).

ScoreTable.jpg

Known Modulating Factors

Modulating factors (MFs) may alter the shape of the response-response function that describes the quantitative relationship between two KES, thus having an impact on the progression of the pathway or the severity of the AO.The evidence supporting the influence of various modulating factors is assembled within the individual KERs. More help

Quantitative Understanding

Optional field to provide quantitative weight of evidence descriptors.  More help

Many studies have reported quantitative relationships between chemicals such as drugs and pesticides and electrophysiological response. For instance, long-term exposure of primary cerebellar granule cell cultures to 3 µM dieldrin reduced the GABAA receptor function to 55% of control, as measured by the GABA-induced 36Cl- uptake (Babot et al. 2007). Juarez et al. (2013) observed that picrotoxin exerted concentration-dependent and reversible inhibition of GABA-induced membrane currents in primary cultured neurons obtained from the guinea-pig small intestine. The stepwise qualitative relationships between consecutive events (MIE, KEs and AO) are well established but quantitative ones are rarely documented.

Considerations for Potential Applications of the AOP (optional)

Addressess potential applications of an AOP to support regulatory decision-making.This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. More help

This AOP can be used to establish the mode of neurotoxicological actions for chemicals capable of binding to the picrotoxin convulsant site of iGABARs. It can also be applied to risk assessment where AOP can assist in predictive modeling of chemical toxicity. Chemicals acting through this AOP can be distinguished from neurotoxicants acting on other types of iGABAR sites (e.g., orthosteric or allosteric binding sites) or other types of neuroreceptors (e.g., ardrenergic, dopaminergic, glutaminergic, cholinergic and serotonergic receptors). More information relevant to this topic can be found in Gong et al. (2015).

References

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

Babot Z, Vilaro M T, Sunol C. (2007) Long-term exposure to dieldrin reduces gamma-aminobutyric acid type A and N-methyl-D-aspartate receptor function in primary cultures of mouse cerebellar granule cells. J Neurosci Res, 85(16):3687-3695.

Ben-Ari Y. (2006) Seizures beget seizures: the quest for GABA as a key player. Crit Rev Neurobiol. 18(1-2):135-44.

Bromfield EB, Cavazos JE, Sirven JI. (2006) Chapter 1, Basic Mechanisms Underlying Seizures and Epilepsy. In: An Introduction to Epilepsy [Internet]. West Hartford (CT): American Epilepsy Society; Available from: http://www.ncbi.nlm.nih.gov/books/NBK2510/.

Casida JE, Durkin KA. (2015) Novel GABA receptor pesticide targets. Pesticide Biochem Physiol. 121:22-30.

Chen L, Durkin KA, Casida J. (2006) Structural model for gamma-aminobutyric acid receptor noncompetitive antagonist binding: widely diverse structures fit the same site. Proc Natl Acad Sci USA. 103(13):5185-5190.

Cole LM, Casida JE. (1986) Polychlorocycloalkane insecticide-induced convulsions in mice in relation to disruption of the GABA-regulated chloride ionophore. Life Sci. 39 (20):1855-62.

Collier ZA, Gust KA, Gonzalez-Morales B, Gong P, Wilbanks MS, Linkov I, Perkins EJ. (2016) A weight of evidence assessment approach for adverse outcome pathways. Regul Toxicol Pharmacol. 75:46-57.

Dichter MA, Ayala GF. (1987) Cellular mechanisms of epilepsy: A status report. Science 237: 157-164.

Durukan P, Ozdemir C, Coskun R, Ikizceli I, Esmaoglu A, Kurtoglu S, Guven M. (2009) Experiences with endosulfan mass poisoning in rural areas. Eur J Emerg Med. 16(1):53-6.

Galanopoulou AS. (2008) GABAA Receptors in Normal Development and Seizures: Friends or Foes? Curr Neuropharmacol. 6(1): 1–20.

Garcia-Reyero N, Habib T, Pirooznia M, Gust KA, Gong P, Warner C, Wilbanks M, Perkins E. (2011) Conserved toxic responses across divergent phylogenetic lineages: a meta-analysis of the neurotoxic effects of RDX among multiple species using toxicogenomics. Ecotoxicology. 20(3):580-94.

Gong P, Hong H, Perkins EJ. (2015) Ionotropic GABA receptor antagonism-induced adverse outcome pathways for potential neurotoxicity biomarkers. Biomarkers in Medicine 9(11):1225-39.

Han HA, Cortez MA, Snead OC III. 2012. GABAB Receptor and Absence Epilepsy. In: Noebels JL, Avoli M, Rogawski MA, et al., editors. Jasper's Basic Mechanisms of the Epilepsies [Internet]. 4th edition. Bethesda (MD): National Center for Biotechnology Information (US); 2012. Available from: https://www.ncbi.nlm.nih.gov/books/NBK98192/.

Hosie AM, Aronstein K, Sattelle DB, ffrench-Constant RH. (1997) Molecular biology of insect neuronal GABA receptors. Trends Neurosci. 20(12): 578-583.

Ikeda T, Nagata K, Shono T, Narahashi T. (1998) Dieldrin and picrotoxinin modulation of GABA(A) receptor single channels. Neuroreport 9(14):3189-3195.

Juarez EH, Ochoa-Cortes F, Miranda-Morales M, Espinosa-Luna R, Montano L M, Barajas-Lopez C. (2013) Selectivity of antagonists for the Cys-loop native receptors for ACh, 5-HT and GABA in guinea-pig myenteric neurons. Auton Autacoid Pharmacol, 34(1-2):1-8.

Lomen-Hoerth C, Messing RO. (2010) Chapter 7: Nervous system disorders. In: Stephen J. McPhee, and Gary D. Hammer (Eds), Pathophysiology of disease: an introduction to clinical medicine (6th Edition). New York: McGraw-Hill Medical. ISBN 9780071621670.

McGonigle I, Lummis SC. (2010) Molecular characterization of agonists that bind to an insect GABA receptor. Biochemistry. 49(13):2897-902.

Moon JM, Chun BJ, Lee SD. (2017) In-hospital outcomes and delayed neurologic sequelae of seizure-related endosulfan poisoning. Seizure. 51:43-49.

Moses V, Peter JV. (2010) Acute intentional toxicity: endosulfan and other organochlorines. Clin Toxicol (Phila). 48(6):539-44.

Newland CF, Cull-Candy SG. (1992) On the mechanism of action of picrotoxin on GABA receptor channels in dissociated sympathetic neurones of the rat. J Physiol, 447: 191–213.

OECD. (2017) Users' Handbook Supplement to the Guidance Document for Developing and Assessing AOPs. OECD Environment Directorate, Environment, Health and Safety Division, Series on Testing & Assessment No. 233, Series on Adverse Outcome Pathways No. 1, ENV/JM/MONO(2016)12, Paris, France.

Olsen RW. (2015) Allosteric ligands and their binding sites define γ-aminobutyric acid (GABA) type A receptor subtypes. Adv Pharmacol. 73:167-202.

Olsen RW, Sieghart W. (2009) GABA A receptors: subtypes provide diversity of function and pharmacology. Neuropharmacology. 56(1):141-8.

Parbhu B, Rodgers G, Sullivan JE. (2009) Death in a toddler following endosulfan ingestion. Clin Toxicol (Phila). 47(9):899-901.

Raymond-Delpech V, Matsuda K, Sattelle BM, Rauh JJ, Sattelle DB. (2005) Ion channels: molecular targets of neuroactive insecticides. Invert Neurosci, 5(3-4):119-133.

Roberts DM, Dissanayake W, Sheriff MHR, Eddleston M. (2004) Refractory status epilepticus following self-poisoning with the organochlorine pesticide endosulfan. J Clinical Neurosci. 11(7): 760-2.

Scharfman HE, Brooks-Kayal AR. (2014) Is Plasticity of GABAergic Mechanisms Relevant to Epileptogenesis? In: Scharfman HE and Buckmaster PS (eds.), Issues in Clinical Epileptology: A View from the Bench, Advances in Experimental Medicine and Biology 813, pp.133-150.

Sieghart W.(1995) Structure and pharmacology of gamma-aminobutyric acid A receptor subtypes. Pharmacol.Rev. 47(2):181-234

Stilwell GE, Saraswati S, Littleton JT, Chouinard SW. (2006) Development of a Drosophila seizure model for in vivo high-throughput drug screening. Eur J Neurosci, 24(8):2211-22.

Taketo M, Yoshioka T (2000) Developmental change of GABA(A) receptor-mediated current in rat hippocampus. Neuroscience 96(3):507-514.

Treiman DM. (2001) GABAergic mechanisms in epilepsy. Epilepsia, 42(Suppl. 3):8–12.

Williams LR, Aroniadou-Anderjaska V, Qashu F, Finne H, Pidoplichko V, Bannon D I et al. (2011) RDX binds to the GABA(A) receptor-convulsant site and blocks GABA(A) receptor-mediated currents in the amygdala: a mechanism for RDX-induced seizures. Environ Health Perspect, 119(3):357-363.