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Relationship: 2954


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

Increase, intracellular calcium leads to Disruption, neurotransmitter release

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
Activation of MEK-ERK1/2 leads to deficits in learning and cognition via disrupted neurotransmitter release adjacent Not Specified Not Specified Travis Karschnik (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 Do not cite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
Rattus norvegicus Rattus norvegicus Moderate NCBI
Homo sapiens Homo sapiens Moderate NCBI
Mus musculus Mus musculus Moderate NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Female Moderate
Mixed Moderate

Life Stage Applicability

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

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

While intracellular Ca regulation is an important aspect of a number of processes in a variety of cells, it is particularly critical in nerve cell terminals where Ca mediates transmitter release (Augustine et al., 1987).  Many synaptic connections during brain development involve calcium signaling, which directs structural as well as functional adaptation in neurons (Lohmann 2009; Michaelson and Lohmann 2010) and astrocytes (Navarette et al., 2013) to establish synaptic selectivity in the developing brain (Katherine von Stackelberg 2015).  While astrocytes have long been known to support neuronal signaling, there is increasing evidence that astrocytes detect synaptic activity and engage in reciprocal signaling with neurons, again based on variations in intracellular Ca2+ (Volterra et al., 2014; Barkera and Ullian 2008).

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

This KER was identified as part of an Environmental Protection Agency effort to represent putative AOPs from peer-reviewed literature which were heretofore unrepresented in the AOP-Wiki. The KER is referenced in publications which were cited in the originating work for the putative AOP "Activation of MEK-ERK1/2 leads to deficits in learning and cognition via disrupted neurotransmitter release", Katherine von Stackelberg & Elizabeth Guzy & Tian Chu & Birgit Claus Henn, 2015. Exposure to Mixtures of Metals and Neurodevelopmental Outcomes: A Multidisciplinary Review Using an Adverse Outcome Pathway Framework, Risk Analysis, John Wiley & Sons, vol. 35(6), pages 971-1016, June.

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

Lead (1-30 uM) was also observed to induce a concentration-dependent release of dopamine from striatal synaptosomes under conditions of spontaneous release (Minnema et al., 1986). Similar lead induced neurotransmitter release has been demonstrated for acetylcholine at the neuromuscular junction, as reflected by increase miniature-end-plate potentials (Cooper and Manalis 1983), and in cortical synaptosomes (Suszkiw et al., 1984). Although the mechanisms by which lead induces transmitter release are unresolved, the increased release may result from an increase in intrasynaptosomal free calcium which has been shown to increase release (Katz 1969).

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

Synaptotagmin I (Syt) is a Ca2+ -sensing protein found in neurotransmitter vesicles and is responsible for promoting vesicular fusion in the presence of Ca2+ signaling (Chicka et al., 2008). Pb2+ bound Syt with 1000-fold higher affinity than Ca2+, which may prevent detection of Ca2+ signaling essential to neurotransmission (Bouton et al., 2001). Although Pb2+ exposure did not affect Syt protein expression in cultured hippocampal neurons (Neal et al., 2010), it is possible that Pb2+ may interfere with the Ca2+-sensing ability of Syt in neurons, thus masking the cellular signal for Ca2+-dependent vesicular release (Neal and Guilarte 2010).

Pb2+ interactions with Syt may be related to the ability of Pb2+ to mimic Ca2+ (Neal and Guilarte 2010). Pb2+ has an ionic radius of 1.2 Å, which is similar to the ionic radius of Ca2+ (0.99 Å) (Chao et al., 1984; Garza et al., 2006). The positive charges and high electronegativity (2.33 on the Pauling scale) of Pb2+ may allow it to interact with the same residues on Ca2+ binding sites that interact with Ca2+ ions (Garza et al., 2006). Pb2+ has been shown to interact with several neuronal intracellular Ca2+-binding proteins in addition to Syt (described above), such as the Ca2+-binding protein calmodulin (CaM) (Chao et al., 1984; Habermann et al., 1983; Kern et al., 2000), the CaM/Ca2+-dependent phosphatase calcineurin (Kern and Audesirk 2000), CaMKII (Toscano et al., 2005), and protein kinase C (Simons 1993; Sun et al., 1999; Toscano and Schanne 2000; Long et al., 1994), suggesting that Ca2+ mimicry may be a common characteristic of Pb2+ toxicity (Bressler et al., 1999; Marchetti 2003; Richardt et al., 1986). Thus, the ability of Pb2+ to mimic Ca2+ may interfere with normal synaptic signaling events (Neal and Guilarte 2010).

Another hypothesis regarding the disruption of neurotransmission is that Pb2+ may interfere with Ca2+ signals by inhibiting Ca2+ channels (Xiao et al., 2006; Braga et al., 1999; 35). Neurotransmission relies on the influx of Ca2+ from P/Q-, N-, and to some extent R-type voltage-gated Ca2+ channels (VGCCs) (Xu et al., 2007).  Pb2+ has been shown to inhibit VGCCs in recombinant systems with high affinity (Peng et al., 2002). Furthermore, removal of extracellular Ca2+ resulted in identical effects on IPSC frequency as Pb2+ exposure, suggesting that the Pb2+-induced inhibition of IPSC frequency is via reduction of Ca2+ influx through VGCCs (Xiao et al., 2006). Inhibition of presynaptic VGCCs may prevent the necessary rise in internal Ca2+ required for fast, Ca2+-dependent vesicular release, thus interfering with neurotransmission (Neal and Guilarte 2010).

Cadmium may block the influx of Ca2+ through membrane channels into the nerve terminal following the action potential, these decrease in calcium influx caused by Cd would be associated with an altered transmitter release (Antonio et al., 1999).

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

Calcium efflux and induced spontaneous transmitter release occur on a seconds to minutes time-scale (Minnema et al., 1988).

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

It has been clear for quite some time that influx of calcium at the synapse mediates synaptic plasticity in adult as well as developing neurons (Malenka et al., 1988). Despite this long-standing appreciation of the importance of calcium signaling for synaptic plasticity, it is virtually unknown what the properties of calcium transients are that determine whether a synapse becomes potentiated or depressed (Malenka and Bear 2004). Some models suggest that moderate increases in calcium may activate primarily phosphatases (e.g., calcineurin and protein phosphatase-1) that in turn facilitate synaptic depression (Mansuy and Shenolikar 2006). In contrast, the activation of kinases (e.g., calcium/calmodulin-dependent protein kinase II, CaMKII) by high-amplitude calcium transients may favor potentiation (Lisman et al., 2002). This is in fact an interesting parallel to the regulation of attractive vs. repulsive axon guidance by calcium: larger calcium transients can activate CaMKII and induce turns toward the side of calcium elevation, whereas smaller calcium increases activate the phosphatases calcineurin and phosphatase-1 and trigger repulsive turns (Wen et al., 2004; Zheng and Poo 2007).

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


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

Augustine, George J., Milton P. Charlton, and Stephen J. Smith. "Calcium action in synaptic transmitter release." Annual review of neuroscience 10.1 (1987): 633-693.

Bardoni, Rita, et al. "Glutamate‐mediated astrocyte‐to‐neuron signalling in the rat dorsal horn." The Journal of physiology 588.5 (2010): 831-846.

Barker AJ, Ullian EM. New roles for astrocytes in developing synaptic circuits. Communicative & Integrative Biology, 2008; 1(2):207–211.

Bouton CMLS, Frelin LP, Forde CE, Godwin HA, Pevsner J (2001) Synaptotagmin i is a molecular target for lead. J Neurochem 76:1724–1735

Braga MFM, Pereira EFR, Albuquerque EX (1999) Nanomolar concentrations of lead inhibit glutamatergic and GABAergic transmission in hippocampal neurons. Brain Res 826:22–34

Bressler J, Kim KA, Chakraborti T, Goldstein G (1999) Molecular mechanisms of lead neurotoxicity. Neurochem Res 24:595–600

Chao SH, Suzuki Y, Zysk JR, Cheung WY (1984) Activation of calmodulin by various metal cations as a function of ionic radius. Mol Pharmacol 26:75–82

Chicka MC, Hui E, Lui H, Chapman ER (2008) Synaptotagmin arrests the snare complex before triggering fast, efficient membrane fusion in response to Ca2+. Nat Struct Mol Biol 15:827–835

Cooper, G., and Manalis, R. (1983). Influence of heavy metals on synaptic transmission: A review. Neurotoxicology 4, 69-84.

Fellin, Tommaso, et al. "Neuronal synchrony mediated by astrocytic glutamate through activation of extrasynaptic NMDA receptors." Neuron 43.5 (2004): 729-743.

Garza A, Vega R, Soto E (2006) Cellular mechanisms of lead neurotoxicity. Med Sci Monit 12:RA57–RA65

Habermann E, Crowell K, Janicki P (1983) Lead and other metals can substitute for Ca2+ in calmodulin. Arch Toxicol 54:61–70

Katherine von Stackelberg & Elizabeth Guzy & Tian Chu & Birgit Claus Henn, 2015. Exposure to Mixtures of Metals and Neurodevelopmental Outcomes: A Multidisciplinary Review Using an Adverse Outcome Pathway Framework, Risk Analysis, John Wiley & Sons, vol. 35(6), pages 971-1016, June.

Katz, B. (1969). The Release of Neural Transmitter Substances. Thomas, Springfield, Ill.

Kern M, Audesirk G (2000) Stimulatory and inhibitory effects of inorganic lead on calcineurin. Toxicology 150:171–178

Kern M, Wisniewski M, Cabell L, Audesirk G (2000) Inorganic lead and calcium interact positively in activation of calmodulin. Neurotoxicology 3:353–363

Kolton, L., and Yarri, Y. (1982). Sites of action of lead on spontaneous transmitter release from motor nerve terminals. Isr. J. Med. Sci. 18, 165-17

Lisman, J., Schulman, H., & Cline, H. (2002). The molecular basis of CaMKII function in synaptic and behavioural memory. Nature Reviews. Neuroscience, 3, 175–190.

Lohmann C. Calcium signaling and the development of specific neuronal connections. Progress in Brain Research, 2009; 175:443–452.

Lohmann, Christian. "Calcium signaling and the development of specific neuronal connections." Progress in brain research 175 (2009): 443-452.

Long GJ, Rosen JF, Schanne FAX (1994) Lead activation of protein kinase C from rat brain. J Biol Chem 269:834–837

M.T. Antonio, I. Corpas, M.L. Leret Neurochemical changes in newborn rat's brain after gestational cadmium and lead exposure Toxicol. Lett., 104 (1999), pp. 1-9

Malenka, R. C., & Bear, M. F. (2004). LTP and LTD: an embarrassment of riches. Neuron, 44, 5–21.

Malenka, R. C., Kauer, J. A., Zucker, R. S., & Nicoll, R. A. (1988). Postsynaptic calcium is sufficient for potentiation of hippocampal synaptic transmission. Science, 242, 81–84.

Mansuy, I. M., & Shenolikar, S. (2006). Protein serine/threonine phosphatases in neuronal plasticity and disorders of learning and memory. Trends in Neurosciences, 29, 679–686.

Marchetti C (2003) Molecular targets of lead in brain neurotoxicity. Neurotox Res 5:221–236

Michaelson K, Lohmann C. Calcium dynamics at developing synapses: Mechanisms and functions. European Journal of Neuroscience, 2010; 32:218–223.

Minnema, Daniel J., I. A. Michaelson, and G. P. Cooper. "Calcium efflux and neurotransmitter release from rat hippocampal synaptosomes exposed to lead." Toxicology and applied pharmacology 92.3 (1988): 351-357.

Minnema, Daniel J., Robert D. Greenland, and I. Arthur Michaelson. "Effect of in vitro inorganic lead on dopamine release from superfused rat striatal synaptosomes." Toxicology and applied pharmacology 84.2 (1986): 400-411.

Navarette M, Perea G, Maglio L, Pastor J, de Sola RG, Araque A. Astrocyte calcium signal and gliotransmission in human brain tissue. Cerebral Cortex, 2013; 23:1240–1246.

Navarrete, Marta, and Alfonso Araque. "Endocannabinoids mediate neuron-astrocyte communication." Neuron 57.6 (2008): 883-893.

Neal AP, Stansfield KH, Worley PF, Thompson RE, Guilarte TR (2010) Lead exposure during synaptogenesis alters vesicular proteins and impairs vesicular release: potential role of NMDA receptor-dependent BDNF signaling. Toxicol Sci 116:249–263

Neal, A.P., Guilarte, T.R. Molecular Neurobiology of Lead (Pb2+): Effects on Synaptic Function. Mol Neurobiol 42, 151–160 (2010).

Parri, H. Rheinallt, Timothy M. Gould, and Vincenzo Crunelli. "Spontaneous astrocytic Ca2+ oscillations in situ drive NMDAR-mediated neuronal excitation." Nature neuroscience 4.8 (2001): 803-812.

Peng S, Hajela RK, Atchison WD (2002) Characteristics of block by Pb2+ of function of human neuronal L-, N-, and R-type Ca2+ channels transiently expressed in human embryonic kidney 293 cells. Mol Pharmacol 62:1418–1430

Perea, Gertrudis, and Alfonso Araque. "Properties of synaptically evoked astrocyte calcium signal reveal synaptic information processing by astrocytes." Journal of Neuroscience 25.9 (2005): 2192-2203.

Richardt G, Federolf G, Habermann E (1986) Affinity of heavy metal ions to intracellular Ca2+-binding proteins. Biochem Pharmacol 35:1331–1335

Sasaki, Takuya, et al. "Locally synchronized astrocytes." Cerebral cortex 21.8 (2011): 1889-1900.

Shigetomi, Eiji, et al. "Two forms of astrocyte calcium excitability have distinct effects on NMDA receptor-mediated slow inward currents in pyramidal neurons." Journal of Neuroscience 28.26 (2008): 6659-6663.

Simons TJB (1993) Lead-calcium interactions in cellular lead toxicity. Neurotoxicology 14:77–86

Snelling, R., and Nicholls, D. (1985). Calcium efflux and cycling across the synaptosomal plasma membrane. Biochem. J. 226,225-23 1

Sun X, Tian X, Tomsig JL, Suszkiw JB (1999) Analysis of differential effects of Pb2+ on protein kinase C isozymes. Toxicol Appl Pharmacol 156:40–45

Suszkiw et al., (1984) Effects of Pb2+ and Cd2+ on acetylcholine release and Ca2+ movements in synaptosomes subcellular fractions from rat brain and torpedo electric organ. Brain Res. 323, 3 1-46.

Thompson, J., and Nechay, B. (1981). Inhibition by metals of canine renal calcium, magnesium-activated adenosinetriphosphatase. J. Toxicol. Environ. Health 7, 901-908

Toscano CD, O’Callaghan JP, Guilarte TR (2005) Calcium/calmodulin-dependent protein kinase II activity and expression are altered in the hippocampus of Pb2+-exposed rats. Brain Res 1044:51–58

Toscano CD, Schanne FAX (2000) Lead-induced activation of protein kinase C in rat brain cortical synaptosomes. Ann NY Acad Sci 919:307–311

Volterra A, Liaudet N, Savtchouk I. Astrocyte Ca2+ signalling: An unexpected complexity. Nature Reviews Neuroscience,  2014; 15:327–335,

Wen, Z., Guirland, C., Ming, G. L., & Zheng, J. Q. (2004). A CaMKII/calcineurin switch controls the direction of Ca(2+)-dependent growth cone guidance. Neuron, 43, 835–846.

Xiao C, Gu Y, Zhou CY, Wang L, Zhang MM, Ruan DY (2006) Pb2+ impairs GABAergic synaptic transmission in rat hippocampal slices: a possible involvement of presynaptic calcium channels. Brain Res 1088:93–100

Xu J, He L, Wu LG (2007) Role of Ca2+ channels in short-term synaptic plasticity. Curr Opin Neurobiol 17:352–35

Zheng, J. Q., & Poo, M. M. (2007). Calcium signaling in neuronal motility. Annual Review of Cell and Developmental Biology, 23, 375–404.