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Relationship: 213


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

Inhibition, NMDARs leads to Decreased, Calcium influx

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
Chronic binding of antagonist to N-methyl-D-aspartate receptors (NMDARs) during brain development induces impairment of learning and memory abilities adjacent Moderate Agnes Aggy (send email) Open for citation & comment WPHA/WNT Endorsed
Chronic binding of antagonist to N-methyl-D-aspartate receptors (NMDARs) during brain development leads to neurodegeneration with impairment in learning and memory in aging adjacent Moderate Arthur Author (send email) Open for citation & comment WPHA/WNT Endorsed

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

The NMDA receptor is distinct in two ways: firstly, it is both ligand-gated and voltage-dependent and secondly, it requires co-activation by two ligands: glutamate and either D-serine or glycine.

NMDA receptor activation allows the influx of Ca2+ only when the receptor is occupied by L-glutamate or other agonists (and removal of Mg++ block) resulting in the postsynaptic membrane depolarization. In contrast, binding of antagonist to NMDA receptor decreases or eliminates Ca2+ influx and consequently dramatically decreases intracellular influx of Ca2+ levels (reviewed in Higley and Sabatini, 2012).

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 relationship between KE (NMDARs, Inhibition) and KE (Calcium influx, Decreased) is plausible as the function evaluation of NMDA receptors is commonly carried out by measurement of intracellular influx of Ca2+ upon NMDA receptor stimulation by agonist. Calcium imaging techniques have been extensively utilized to investigate the relationship between these two KEs. Almost 15% of the current through NMDA receptors is mediated by Ca2+ under physiological conditions (Higley and Sabatini, 2012).

It has been shown that less than five and, occasionally only a single NMDA receptor opens under physiological conditions, causing a total Ca2+ influx of about 6000 ions into a dendritic spine head reaching a concentration of ∼10 µM (Higley and Sabatini, 2012). However, the majority of the ions are rapidly eliminated by binding Ca2+ proteins, reaching ∼1 µM of free Ca2+ concentration (Higley and Sabatini, 2012).

In rat primary forebrain cultures, the intracellular Ca2+ increases after activation of the NMDA receptor and this increase is blocked when the cells are cultured under Ca2+ free conditions, demonstrating that the NMDA-evoked increase in intracellular Ca2+ derives from extracellular and not intracellular sources (Liu et al., 2013).

Neurons in brain slices from wild-type (GluRε2+/+) mice showed increase of intracellular Ca2+ in the presence of 100 μM NMDA that was completely inhibited after exposure to 100 mM APV. In contrast, the NMDA-mediated increase in Ca2+ was absent in brain slices from GluRε2−/− mice that do not possess any functional NMDA receptors in the developing neocortex (Okada et al., 2003).

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

The structural diversity of NMDA subunits can influence the functionality of the receptors and their permeability to Ca2+. For example, NR2B subunits show higher affinity for glutamate binding and higher Ca2+ permeability (reviewed in Higley and Sabatini, 2012). But NMDA receptor subunit composition is not the only parameter that influences Ca2+ entrance in the cytosol. Membrane potential due to pore blockade by extracellular Mg2+ and receptor phosphorylation are two additional regulator of Ca2+ influx through NMDA receptors (reviewed in Higley and Sabatini, 2012).

Entrance of Ca2+ into neuronal cell can also happen through KA and AMPA receptors but to a smaller extent compared to NMDA receptors (reviewed in Higley and Sabatini, 2012). However, recent findings suggest that AMPA receptors may also contribute to Ca2+ signalling during CNS development (reviewed in Cohen and Greenberg, 2008). Early in development cortical pyramidal neurons express calcium-permeable, GluR2 subunit–lacking AMPA receptors. During postnatal development these neurons undergo a switch in the subunit composition of AMPA receptors, expressing instead GluR2-containing, calcium-impermeable AMPA receptor suggesting that the main point entrance of Ca2+ at this developmental stage are NMDA receptors.

Furthermore, Ca2+ entry occurs through L- and H-type voltage-dependent Ca2+channels (L-VDCCs) (Perez-Reyes and Schneider, 1994; Berridge, 1998; Felix, 2005) that are encountered in neurons, suggesting that there are more possible entrance sites for Ca2+ to get into the cytosol rather than only through NMDA receptors.

Interestingly, Pb2+ has the ability to mimic or even compete with Ca2+ in the CNS (Flora et al., 2006). Indeed, Pb2+ is accumulated in the same mitochondrial compartment as Ca2+ and it has been linked to disruptions in intracellular calcium metabolism (Bressler and Goldstein, 1991). So, it can be that the reduced levels of Ca2+ after Pb2+ exposure may not be attributed to NMDA receptor inhibition but also to the ability of this heavy metal to compete with Ca2+. To make things more complicated, recent findings suggest that BDNF can also acutely elicit an increase in intracellular Ca2+ concentration, which is attributed not only to the influx of extracellular Ca2+ but also to Ca2+ mobilization from intracellular calcium stores (Numakawa et al., 2002; He et al., 2005). These findings derive from primary cultures of cortical neurons (E18 or 2-3 PND), where BDNF-evoked Ca2+ signals have not been altered neither by tetrodotoxin nor by a cocktail of glutamate receptor blockers (CNQX and APV), pointing out the importance of BDNF in Ca2+ homeostasis (Numakawa et al., 2002; He et al., 2005).

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

Besides the above studies described in rodents, intracellular Ca2+ regulation has been studied at the neuromuscular junction of larval Drosophila exposed to 0, 100 μM or 250 μM Pb2+ (He et al., 2009).


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

Berridge MJ. (1998) Neuronal calcium signaling. Neuron 21: 13-26.

Bressler JP, Goldstein GW. (1991) Mechanisms of lead neurotoxicity. Biochem Pharmacol. 41: 479-484.

Carpenter DO, Hussain RJ, Berger DF, Lombardo JP, Park HY. (2002) Electrophysiologic and behavioral effects of perinatal and acute exposure of rats to lead and polychlorinated biphenyls. Environ Health Perspect. 110: 377-386.

Cohen S, Greenberg ME. (2008) Communication between the synapse and the nucleus in neuronal development, plasticity and disease. Annu Rev Cell Dev Biol. 24: 183-209.

Cordova FM, Rodrigues LS, Giocomelli MBO, Oliveira CS, Posser T, Dunkley PR, Leal RB. (2004) Lead stimulates ERK1/2 and p38MAPK phosphorylation in the hippocampus of immature rats. Brain Res. 998: 65-72.

Felix R. (2005) Molecular regulation of voltage-gated Ca2+ channels. J Recept Signal Transduct Res. 25: 57-71.

Ferguson C, Kern M, Audesirk G. (2000) Nanomolar concentrations of inorganic lead increase Ca2+ efflux and decrease intracellular free Ca2+ ion concentrations in cultured rat hippocampal neurons by a calmodulin-dependent mechanism. Neurotoxicology 21: 365-378.

Flora SJS, Flora G, Saxena G. (2006) Environmental occurrence, health effects and management of lead poisoning, in Lead: Chemistry, Analytical Aspects, Environmental Impacts and Health Effects (Cascas SB and Sordo J eds) Elsevier, Amsterdam, The Netherlands, pp 158-228.

He J, Gong H, Luo Q. (2005) BDNF acutely modulates synaptic transmission and calcium signalling in developing cortical neurons. Cell Physiol Biochem. 16: 69-76.

He T, Hirsch HV, Ruden DM, Lnenicka GA. (2009) Chronic lead exposure alters presynaptic calcium regulation and synaptic facilitation in Drosophila larvae. Neurotoxicology 30: 777-784.

Higley MJ, Sabatini BL. (2012) Calcium signalling in dendritic spines. Cold Spring Harb Perspect Biol 4: a005686.

Hussain RJ, Parsons PJ, Carpenter DO. (2000) Effects of lead on long-term potentiation in hippocampal CA3 vary with age. Brain Res Dev Brain Res. 121: 243-252.

Kirberger, M. (2011) Defining a Molecular Mechanism for Lead toxicity via Calcium-Binding Proteins. Chemistry Dissertation. Georgia State University. ScholarWorks@Georgia State University.

Li XM, Gu Y, She JQ, Zhu DM, Niu ZD, Wang M, Chen JT, Sun LG, Ruan DY. (2006) Lead inhibited N-methyl-D-aspartate receptor-independent long-term potentiation involved ryanodine-sensitive calcium stores in rat hippocampal area CA1. Neuroscience. 139: 463-473.

Liu F, Patterson TA, Sadovova N, Zhang X, Liu S, Zou X, Hanig JP, Paule MG, Slikker W Jr, Wang C. (2013) Ketamine-induced neuronal damage and altered N-methyl-D-aspartate receptor function in rat primary forebrain culture. Toxicol Sci. 131: 548-557.

Numakawa T, Yamagishi S, Adachi N, Matsumoto T, Yokomaku D, Yamada M, Hatanaka H (2002) Brain-derived neurotrophic factor-induced potentiation of Ca2+ oscillations in developing cortical neurons. J Biol Chem. 277: 6520-6529.

Okada H, Miyakawa N, Mori H, Mishina M, Miyamoto Y, Hisatsune T. (2003) NMDA receptors in cortical development are essential for the generation of coordinated increases in [Ca2+](i) in "neuronal domains". Cereb Cortex. 13 :749-757.

Perez-Reyes E, Schneider T. (1994) Calcium channels: Structure, function, and classification. Drug Dev Res. 33: 295–318.

Sandhir R, Gill KD. (1994) Alterations in calcium homeostasis on lead exposure in rat synaptosomes. Mol Cell Biochem. 131: 25-33.

Schneider JS, Mettil W, Anderson DW. (2012) Differential Effect of Postnatal Lead Exposure on Gene Expression in the Hippocampus and Frontal Cortex. J Mol Neurosci. 47: 76-88.

Sinner B, Friedrich O, Zink W, Martin E, Fink RH, et al. (2005) Ketamine stereoselectively inhibits spontaneous Ca2+-oscillations in cultured hippocampal neurons. Anesthesia and analgesia 100: 1660-1666.

Toscano CD, Guilarte TR. (2005) Lead neurotoxicity: From exposure to molecular effects. Brain Res Rev. 49: 529-555.

Toscano CD, Hashemzadeh-Gargari H, McGlothan JL, Guilarte TR. (2002) Developmental Pb2+ exposure alters NMDAR subtypes and reduces CREB phosphorylation in the rat brain. Dev Brain Res. 139: 217-226.

Toscano CD, McGlothan JL, Guilarte TR. (2003) Lead exposure alters cyclic-AMP response element binding protein phosphorylation and binding activity in the developing rat brain. Dev Brain Res. 145: 219-228.