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Relationship: 1857

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

ACh Synaptic Accumulation leads to Activation, Muscarinic Acetylcholine Receptors

Upstream event

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

ACh Synaptic Accumulation

Downstream event

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

Activation, Muscarinic Acetylcholine Receptors

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	High	Karen Watanabe (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 Do not cite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
human	Homo sapiens	High	NCBI
zebrafish	Danio rerio	High	NCBI
rat	Rattus norvegicus	High	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

Acetylcholine (ACh) is a neurotransmitter within the central nervous system and peripheral nervous system that activates both muscarinic and nicotinic receptors (Haga, 2013). Muscarinic receptors are metabotropic and act using slower transmission signaling compared to the more direct ionotropic receptors (Miller and Yeh, 2016).

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 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

Binding of Ach to muscarinic receptors has been well documented to activate the receptor (Miller and Yeh, 2016). Using radiolabeled ACh ([3H]-ACh), experimenters have determined the binding kinetics between ACh and muscarinic receptors (Kellar et al., 1985, Uchida et al., 1978). Additionally, a computational model was recently developed modeling a CA1 pyramidal neuron’s response to activation of M1 receptors in the presence of ACh (Mergenthal et al., 2020)

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

It is well known that muscarinic receptors bind ACh. Muscarinic receptors are found in the target organs of parasympathetic neurons and in various parts of the central nervous system (Haga, 2013). Muscarinic receptors expressed in the brain are the M1, M2, and M4 subtypes more than the M3 or M5 subtypes (Lebois et al., 2018).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Symptoms from increasing ACh levels are partially reduced when pretreated with muscarinic antagonists like atropine (Faria et al., 2015, King and Aaron, 2015).
Rats and rabbits pretreated with a combination of Neostigmine or Physostigmine (reversible AChE inhibitor), Mecamylamine (nicotinic receptor antagonist), or Atropine (mAChR antagonist) and later exposed to Soman, a strong irreversible AChE inhibitor, showed a significantly increased survival rate and overall reduced brain ACh levels compared to the control group (Harris et al., 1980).

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 no known uncertainties or inconsistencies with this relationship.

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

Table 1. Summary of available quantitative data describing responses of mAChR activation by ACh. k₁ and k_-1 are the forward and reverse rate binding constants, respectively. K_d is the dissociation constant, IC₅₀ is the half maximal inhibitory concentration, and B_max is the maximal binding capacity.

Upstream Synaptic ACh Accumulation	Downstream Muscarinic Receptor Activation	Brief Summary	Species / Model	Reference
Upstream Synaptic ACh Accumulation	Downstream Muscarinic Receptor Activation	Brief Summary	Species / Model	Reference
[3H]-Acetylcholine	Non-specific mAChR (cerebral cortex tissue): k₁ = 0.034 nM^-1 min^-1 k_-1 = 1.04 min^-1 K_d = 35.2 ± 3.2 nM IC₅₀ = (many) B_max = 18.2 ± 1.0 fmol/mg tissue \| 318 ± 17 fmol/mg protein	Provides binding constants to various tissues in the rat brain and rat heart atrium, providing association and dissociation rate constants, K_d values, IC₅₀ values against various competing compounds, and B_max for radiolabeled acetylcholine.	Male Sprague-Dawley rats (250-350g)	Kellar et al. (1985)
Acetylcholine	M1 Receptor kinetic parameters fitted to Falkenburger et al. (2010) data: k₁ (k_f^L1) = 2.78 mM^-1 ms^-1 k_-1 (k_b^L1) = 2.15x10^-3 ms^-1	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)
[3H]-Acetylcholine	Non-specific mAChR: K_d = 20 nM B_max (maximum binding): 0.8-1.2 pmoles/mg protein	Using radiolabeled acetylcholine ([3H]acetylcholine), Sprague-Dawley rats, provides K_d and maximum binding values for acetylcholine to 'synaptic membrane' from brain tissue.	Sprague-Dawley rats (200-300g)	Uchida et al. (1978)

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

Muscarinic receptors are found in a wide variety of species, both vertebrates and invertebrates, and cholinergic transmissions occur at all stages in (Burke et al., 2017, Garcia et al., 2016, Miller and Yeh, 2016).

References

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

Burke, R. D., Todd, S. W., Lumsden, E., Mullins, R. J., Mamczarz, J., Fawcett, W. P., Gullapalli, R. P., Randall, W. R., Pereira, E. F. R. & Albuquerque, E. X. 2017. Developmental neurotoxicity of the organophosphorus insecticide chlorpyrifos: from clinical findings to preclinical models and potential mechanisms. Journal of Neurochemistry, 142, 162-177. DOI: 10.1111/jnc.14077.

Falkenburger, B. H., Jensen, J. B. & Hille, B. 2010. Kinetics of M1 muscarinic receptor and G protein signaling to phospholipase C in living cells. The Journal of general physiology, 135, 81-97. DOI: 10.1085/jgp.200910344.

Faria, M., Garcia-Reyero, N., Padrós, F., Babin, P. J., Sebastián, D., Cachot, J., Prats, E., Arick Ii, M., Rial, E., Knoll-Gellida, A., Mathieu, G., Le Bihanic, F., Escalon, B. L., Zorzano, A., Soares, A. M. & Raldúa, D. 2015. Zebrafish Models for Human Acute Organophosphorus Poisoning. Sci Rep, 5, 15591. DOI: 10.1038/srep15591.

Garcia, G. R., Noyes, P. D. & Tanguay, R. L. 2016. Advancements in zebrafish applications for 21st century toxicology. Pharmacology and Therapeutics, 161, 11-21. DOI: 10.1016/j.pharmthera.2016.03.009.

Haga, T. 2013. Molecular properties of muscarinic acetylcholine receptors. Proceedings of the Japan Academy Series B: Physical and Biological Sciences, 89, 226-256. DOI: 10.2183/pjab.89.226.

Harris, L. W., Stitcher, D. L. & Heyl, W. C. 1980. The effects of pretreatments with carbamates, atropine and mecamylamine on survival and on soman-induced alterations in rat and rabbit brain acetylcholine. Life Sci, 26, 1885-91. DOI: 10.1016/0024-3205(80)90617-7.

Kellar, K. J., Martino, A. M., Hall, D. P., Jr., Schwartz, R. D. & Taylor, R. L. 1985. High-affinity binding of [3H]acetylcholine to muscarinic cholinergic receptors. J Neurosci, 5, 1577-82. DOI: 10.1523/jneurosci.05-06-01577.1985.

King, A. M. & Aaron, C. K. 2015. Organophosphate and Carbamate Poisoning. Emergency Medicine Clinics of North America, 33, 133-151. DOI: 10.1016/j.emc.2014.09.010.

Lebois, E. P., Thorn, C., Edgerton, J. R., Popiolek, M. & Xi, S. 2018. Muscarinic receptor subtype distribution in the central nervous system and relevance to aging and Alzheimer's disease. Neuropharmacology, 136, 362-373. DOI: 10.1016/j.neuropharm.2017.11.018.

Mergenthal, A., Bouteiller, J.-M. C., Yu, G. J. & Berger, T. W. 2020. A Computational Model of the Cholinergic Modulation of CA1 Pyramidal Cell Activity. Frontiers in Computational Neuroscience, 14. DOI: 10.3389/fncom.2020.00075.

Miller, S. L. & Yeh, H. H. 2016. Neurotransmitters and Neurotransmission in the Developing and Adult Nervous System. Conn's Translational Neuroscience.

Uchida, S., Takeyasu, K., Ichida, S. & Yoshida, H. 1978. Muscarinic cholinergic receptors in mammalian brain: differences between bindings of acetylcholine and atropine. Jpn J Pharmacol, 28, 853-62. DOI: 10.1254/jjp.28.853.