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Relationship: 1889

Title

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

Activation, Muscarinic Acetylcholine Receptors leads to Occurrence, Focal Seizure

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Activation, Muscarinic Acetylcholine Receptors

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Occurrence, Focal Seizure

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
Acetylcholinesterase Inhibition Leading to Neurodegeneration	adjacent	Moderate	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 Do not cite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
mouse	Mus musculus	High	NCBI
rat	Rattus norvegicus	High	NCBI
guinea pig	Cavia porcellus	Moderate	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
All life stages	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

Muscarinic receptors are metabotropic, affecting a target enzyme which typically sends secondary messenger signals (Kandel et al., 2013). Pharmacological evidence indicates the mAChR M1 subtype modulates the M current in sympathetic ganglion neurons. In mice, M1 agonists suppress the M current and results in membrane depolarization that leads to focal seizures (Hamilton et al., 1997). Seizures occurring through the M1 muscarinic receptor have been observed to start at 5-15 minutes after exposure in rats and guinea pigs (Miller, 2015, Sparenborg et al., 1992).

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

Evidence Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Title	First Author	Biological Plausibility	Dose Concordance	Temporal Concordance	Incidence Concordance

Biological Plausibility

Dose Concordance Evidence

Temporal Concordance Evidence

Incidence Concordance Evidence

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

Experiments blocking the M2 subtype have not led to a decrease in seizures from acetylcholinesterase inhibitors, only the antagonist for M1 subtype decreased seizure activity (Cruickshank et al., 1994). This demonstrates that the M1 subtype is vital for muscarinic receptor caused seizures. Many studies have noted that delaying administration of M1 antagonist, even for just a short amount of time after exposure, does not halt status epilepticus development (Miller, 2015). This indicates that M1 receptors are not responsible for maintaining seizure activity, they are only responsible for the initial phase (Hamilton et al., 1997). The secondary generalization of the focal seizure is continued by some other mechanism.

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

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

The papers in the table below present EEG data from timepoint 0 onwards through injection of seizure-inducing compounds. Focal seizures can be seen to occur in EEG where there is activity localized between a set or sets of electrodes while normal activity continues in the remaining electrodes (Britton et al., 2016). Additionally, the full spectrum of the EEG is not published, and one would need to contact the author.

Table 1. Summary of available quantitative data describing responses of focal seizure to mAChR activation. CHO = Chinese hamster ovary, DFP = diisopropylfluorophosphate, EEG = electroencephalogram; GABA = gamma-aminobutyric acid; Glu = glutamate.

Upstream Muscarinic Receptor Activation	Downstream Focal Seizure	Brief Summary	Species / Model	Reference
Upstream Muscarinic Receptor Activation	Downstream Focal Seizure	Brief Summary	Species / Model	Reference
Pilocarpine (10 mM) through microdialysis cannula in the hippocampus	EEG activity (ECoG). Seizure severity score over time.	Induced seizure activity through intrahippocampal administration of pilocarpine and monitored EEG activity. Additionally measured various neurotransmitter concentrations including Glu and GABA.	Male albino Wistar rats (270-320g)	Meurs et al. (2008)
Pilocarpine (240 mg/kg; 280mg/kg; 320 mg/kg) IP	EEG activity (surface electrodes on skull)	Induced seizure activity through pilocarpine (ip) and measured EEG activity. An additional experiment performed involving injection of methylscopolamine (1 mg/kg) before injection of 320 mg/kg pilocarpine.	Adult male Sprague-Dawley rats (225-250g)	Tetz et al. (2006)
Pilocarpine (2 doses of 20 mg/kg, i.p., per 30 min)	EEG (intracranial). Seizure stages over time.	Induced seizure activity through pilocarpine injection. Monitored EEG activity for 24 hrs from injection time and onwards. Additionally compared activity to DFP and soman injection models.	Young adult male Sprague-Dawley rats (250-300g)	Reddy et al. (2021)
Pilocarpine (for M3 mAchR) (k_on = 4.47 ± 0.53 × 10^5 M^-1 min^-1 k_off = 15.3 ± 2.3 min^-1 t_1/2 = 3.0 ± 0.4 s)	NA	Activity and binding data for pilocarpine through a competitive binding assay with l-[N-methyl]-[3H]scopolamine methyl chloride, for M3 mAChRs.	CHO cells transfected with human M3 mAChR	Sykes et al. (2009)
Acetylcholine	Electrophysiological response of CA1 neuron to mAChR activation	Computational model of a CA1 pyramidal neuron that incorporates mAChR activation through acetylcholine application, intracellular calcium dynamics, and its electrophysiological response. They provide the kinetics in response to acetylcholine application and provide the associated kinetic rate constants.	Computational model	Mergenthal et al. (2020)

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

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

M1 activation leading to focal seizure activity appears in many different species, both genders, and at various life stages. Specific experiments are listed under the empirical evidence above.