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Relationship: 2005


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

Increased Cholinergic Signaling leads to Cardiovascular dysregulation

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
Acetylcholinesterase inhibition leading to acute mortality adjacent High High Dan Villeneuve (send email) Under Development: Contributions and Comments Welcome Under Development

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

Sex Applicability

An indication of the the relevant sex for this KER. More help

Life Stage Applicability

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

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
  • In the context of cholinergic toxicity induced by AChE inhibition, increased cholinergic signaling leads to impaired cardiovascular function because acetylcholine is an important signalling molecule in the heart. The vagus nerve and cardiomyocytes produce neuronal and non-neuronal acetylcholine, respectively (Saw, 2018, Beckmann, 2013). Cardiac function is controlled by the sympathetic and parasympathetic nervous systems.The heart is innervated by the vagus nerve, a cholinergic nerve that activates muscarinic acetylcholine receptors (M-ChR) on heart smooth muscle tissue.

  • While five different muscarinic receptors classes have been identified (M1-M5), the M2 receptor is most abundant in the heart and it is the most well-studied of the muscarinic receptors (Dhein, 2001, Zang, 2005). The M2 receptor is an inhibitory G-protein-coupled receptor that opens potassium channels in the cell membrane, which alters the heart smooth muscle cell electrophysiology and leads to arrhythmia and decreased heart rate (bradycardia) (Lodish, Zang, 2005). 

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 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
  • The cardiovascular system is responsive to acetylcholine released by the vagus nerve and to non-neuronal acetylcholine released by cardiomyocytes. Acetylcholine acts on muscarinic receptors in the heart and overstimulation of the main muscarinic receptor (M2) leads to bradycardia in mammals and in fish. In addition to being responsive to muscarinic effects, cardiovascular function can also be impaired by neuronal nicotinic signalling, which produces tachycardia or increased heart rate (Costa, Duagsawasdi 1978).
  • The role of acetylcholine in regulating heart rate via its action on M2 receptors is widely accepted dogma in pharmacology, toxicology, and physiology. There is an extensive body of literature on this relationship.
  • Competitive antagonists of muscarinic acetylcholine receptors, like atropine, increase heart rate and are used to treat bradycardia.
  • Carbachol-induced bradycardia was abolished by injection of a M2 mAChR morpholino antisense nucleotide in a dose dependent manner (Hsieh and Liao 2002).
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
  • No known qualitative inconsistencies or uncertainties associated 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
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
  • The presence of cholinergic effects mediated by the vagus nerve innervation of the heart has been extensively studied in many mammals, including humans, dogs, cats, rabbit, and monkeys (comprehensive review in Coote, 2013).

  • In fish, increased transmission of acetylcholine overstimulates the M2 muscarinic receptor regulating heart rate, causing hypoxic bradycardia.


List of the literature that was cited for this KER description. More help
  • Dhein S, van Koppen CJ, Brodde OE. Muscarinic receptors in the mammalian heart. Pharmacol Res. 2001 Sep;44(3):161-82.

  • Zang WJ, Chen LN, Yu XJ. Progress in the study of vagal control of cardiac ventricles. Sheng Li Xue Bao. 2005 Dec 25;57(6):659-72.

  • Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000.

  • Costa.  Toxic effects of pesticides.  In Casarett and Doull's Toxicology: The Basic Science of Poisons. 9th ed. pp 1055-1106.

  • Steele SL, Lo KH, Li VW, Cheng SH, Ekker M, Perry SF. 10.1152/ajpregu.00036.2009. Epub 2009 Jun 10. Loss of M2 muscarinic receptor function inhibits development of hypoxic bradycardia and alters cardiac beta-adrenergic sensitivity in larval zebrafish (Danio rerio). Am J Physiol Regul Integr Comp Physiol. 2009 Aug;297(2)

  • Coote, JH, Myths and realities of the cardiac vagus. J Physiol. 2013 Sep 1; 591(Pt 17): 4073–4085.

  • Olshansky B, Sabbah HN, Hauptman PJ, Colucci WS. Parasympathetic nervous system and heart failure: pathophysiology and potential implications for therapy. Circulation. 2008; 118(8): 863–871

  • Saw, Eng Leng et al. The non-neuronal cholinergic system in the heart: A comprehensive review. Journal of Molecular and Cellular Cardiology, v125, 129 - 139

  • Beckmann, J. Lips, K.S. The Non-Neuronal Cholinergic System in Health and Disease, Pharmacology 2013;92:286–302

  • Duangsawasdi M. 1978. Organophosphate insecticide toxicity in rainbow trout (Salmo gairdneri). Effects of temperature and investigations on the sites of action. PhD thesis. University of Manitoba, Manitoba, Canada.

  • Duangsawasdi M, Klaverkamp JF. 1979. Acephate and fenitrothion toxicity in rainbow trout: Effects of temperature stress and investigations on the sites of action. In Aquatic Toxicology, Vol 2, STP 667. ASTM International, Philadelphia, PA, USA, pp 35–51.