AOP ID and Title:

Short Title: MEK-ERK1/2 activation leading to deficits in learning and cognition

Authors

Of the originating work:

Katherine von Stackelberg (Harvard Center for Risk Analysis, Boston, MA, USA.) (Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA.)

Elizabeth Guzy (Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA.)

Tian Chu (Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA.)

Birgit Claus Henn (Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA.) (Department of Environmental Health, Boston University School of Public Health, Boston, MA, USA.)

Of the content populated in the AOP-Wiki:

Travis Karschnik (General Dynamics Information Technology, Duluth, MN, USA.)

Status

Abstract

Metal mixture activation of ERK1/2 and JNK1/2 in astrocytes leads to increased C^a2+ release (Asit Rai and others 2010).  Alterations to calcium, an essential nutrient which is required in multiple cellular and physiological functions, such as cell adhesion, signal transduction, and neurotransmission can be expected to have downstream effects in those functions (Antonio et al., 2002). Changes in neurotransmission can then lead to changes in learning and cognitition (Neal and Guilarte 2010).

MEK-ERK1/2 is important in understanding uptake of metals into the brain and its relationship to deficits in learning and cognition from exposure to metals commonly detected at Superfund sites including lead, cadmium, manganese, and arsenic.  Current risk assessment guidance dictates a largely chemical-by-chemical evaluation of exposures and risks, which fails to adequately address potential interactions with other chemicals, nonchemical stressors, and genetic factors. Cumulative risk assessment methods and approaches are evolving to meet regulatory needs, (MacDonell et al., 2013; Backhaus and Faust 2012; IPCS Workshop 2009) but significant challenges remain. As our understanding of complex exposures and interactions continues to grow, synthesis and integration across disciplines and studies focused on different aspects of the environmental fate–exposure–toxicology–health outcome continuum are required to assess the likelihood of adverse effects and to support cumulative risk assessment.  Environmental exposures are virtually always to complex mixtures (Katherine von Stackelberg et al., 2015).

Background

An examination of neurodevelopmental disorders and subclinical effects using multi-domain global neurodevelopment assessments is warranted as they can have profound population level implications.  In the context of neurotoxicity, neurodevelopmental pathways in the developing human brain are not fully understood (Schubert et al., 2015; Bal-Price et al., 2015) although there are a number of commonly observed phenomena which may take part in those pathways e.g. changes in intracellular calcium, ROS generation, apoptosis, and neurotransmitter disruption.  This AOP highlights a specific set of response-response relationships using a subset of those commonly observed phenonema related to metals and metal mixture exposures leading to deficits in learning and cognition.

Summary of the AOP

Events

Molecular Initiating Events (MIE), Key Events (KE), Adverse Outcomes (AO)

Key Event Relationships

Stressors

Overall Assessment of the AOP

1. Support for Biological Plausibility of KERs	Defining Question	High (Strong)	Moderate	Low (Weak)
	Is there a mechanistic relationship  between KEup and KEdown consistent with established biological knowledge?	Extensive understanding of the KER based on extensive previous documentation and broad acceptance.	KER is plausible based on analogy to accepted biological relationships, but scientific understanding is incomplete	Empirical support for association between KEs , but the structural or functional relationship between them is not understood.
Relationship 2942: Activation of MEK, ERK1/2 (2146) leads to Increase, intracellular calcium (1339)	Moderate Empirical evidence indicates a complex relationship between MEK, ERK1/2 activation and inhibition and Ca2+ response including Ca2+ feeding back into a ERK1/2 activation.  This relationship appears to vary across species and cell type.
Relationship 2954: Increase, intracellular calcium (1339) leads to Disruption, neurotransmitter release (2151)	Strong Intracellular calcium regulation is broadly known as being an important aspect of a number of processes in a variety of cells and is particularly critical in nerve cell terminals where it mediates transmitter release.
Relationship 2955: Disruption, neurotransmitter release (2151) leads to Impairment, Learning and memory (341)	Strong The role of various neurotransmitters and receptors in cognitive function and memory formation are well studied.

Domain of Applicability

Life Stage Applicability Taxonomic Applicability Sex Applicability

Life Stage

Life stages applicable to this AOP encompass the full life cycle.  Many of the key events are measured in pregnant females with the adverse outcome (impairment, learning and memory) measured at all life stages.

Taxonomic Applicability

Most evidence for this AOP is derived from rodents and humans where rodents were selected with their ability to model human responses.   

Sex Applicability

This AOP is applicable to all sexes.

Essentiality of the Key Events

2. Essentiality of KEs	Defining question	High (Strong)	Moderate	Low (Weak)
	Are downstream KEs and/or the AO prevented if an upstream KE is blocked?	Direct evidence from specifically designed experimental studies illustrating essentiality for at least one of the important KEs	Indirect evidence that sufficient modification of an expected modulating factor attenuates or augments a KE	No or contradictory experimental evidence of the essentiality of any of the KEs.
MIE 2146:Activation of MEK, ERK1/2	Moderate MEK, ERK1/2 activation is fundamental in delivering signals which regulate the cell cycle, proliferation, differentiation, adhesion, and more.  Disruptions in this activation have wide reaching effects however, there is evidence that downstream KEs can also activate this KE.
KE 1339: Increase, intracellular calcium	High Calcium, as a primary intracellular messenger in neurons and regulator of cell responses to stress has been shown to directly affect neurotransmitter release with manipulation.
KE 2151: Disruption, neurotransmitter release	High Neurotransmitter receptor blocking experiments have shown to directly impair learning and memory tasks in rodents.
AO 341: Impairment, Learning and memory	N/A
AOP 499	High/Moderate There is direct evidence contained KER 2955.

Weight of Evidence Summary

3. Empirical Support for KERs	Defining Questions	High (Strong)	Moderate	Low (Weak)
	Does empirical evidence support that a  change in KEup leads to an appropriate change in KEdown? Does KEup occur at  lower doses and earlier time points than KE  down and is the incidence of KEup > than  that for KEdown? Inconsistencies?	if there is dependent change in both events  following exposure to a wide range of specific stressors (extensive evidence for temporal, dose- response and incidence concordance) and no or  few data gaps or conflicting data	if there is demonstrated dependent change in both events following exposure to a small number of specific stressors and some evidence inconsistent with the expected pattern that can  be explained by factors such as experimental design, technical considerations, differences  among laboratories, etc.	if there are limited or no studies reporting dependent change in both events following  exposure to a specific stressor (i.e., endpoints never measured in the same study  or not at all), and/or lacking evidence  of temporal or dose- response concordance, or identification of significant inconsistencies in empirical support across  taxa and species that don’t align with the expected pattern for the hypothesized AOP
Relationship 2942: Activation of MEK, ERK1/2 (2146) leads to Increase, intracellular calcium (1339)	Moderate The evidence collection strategy for this AOP focused mainly on metal and metal mixture exposures, of which, there were many that showed dependent change in both these events following exposure.
Relationship 2954: Increase, intracellular calcium (1339) leads to Disruption, neurotransmitter release (2151)	Moderate The evidence collection strategy for this AOP focused mainly on metal and metal mixture exposures, of which, there were many that showed dependent change in both these events following exposure.
Relationship 2955: Disruption, neurotransmitter release (2151) leads to Impairment, Learning and memory (341)	Moderate The evidence collection strategy for this AOP focused mainly on metal and metal mixture exposures, of which, there were many that showed dependent change in both these events following exposure.

Considerations for Potential Applications of the AOP (optional)

Developmental neurotoxicity (DNT) is an adverse outcome of concern to multiple regulatory agencies. In vitro screening assays for MEK-ERK1/2 activation would not be recommended as a direct alternative or replacement to established DNT assays like OECD Test No. 426 (OECD 2007). However, detection of MEK-ERK1/2 activation in neuronal cell types may be used to prioritize chemicals with potential to elicit neurotoxicity and flag them for testing in ortogonal assays for evaluating DNT, including proposed alternative test methods (Bal-Price et al. 2018; Crofton et al 2022).  

References

Antonio, M. Teresa, Noelia López, and M. Luisa Leret. "Pb and Cd poisoning during development alters cerebellar and striatal function in rats." Toxicology 176.1-2 (2002): 59-66.

Asit Rai and others, Characterization of Developmental Neurotoxicity of As, Cd, and Pb Mixture: Synergistic Action of Metal Mixture in Glial and Neuronal Functions, Toxicological Sciences, Volume 118, Issue 2, December 2010, Pages 586–601, https://doi.org/10.1093/toxsci/kfq266

Backhaus T, Faust M. Predictive environmental risk assessment of chemical mixtures: A conceptual framework. Environmental Science & Technology, 2012; 46(5):2564–2573.

Bal-Price A, Crofton KM, Sachana M, Shafer TJ, Behl M, Forsby A, Hargreaves A, Landesmann B, Lein PJ, Louisse J, Monnet-Tschudi F, Paini A, Rolaki A, Schrattenholz A, Sunol C, van Thriel C, Whelan M, Fritsche E. Putative adverse outcome pathways relevant to neurotoxicity. Critical Reviews in Toxicology, 2015; 45(1):83–91.

Bal-Price A, Hogberg HT, Crofton KM, Daneshian M, FitzGerald RE, Fritsche E, Heinonen T, Hougaard Bennekou S, Klima S, Piersma AH, Sachana M, Shafer TJ, Terron A, Monnet-Tschudi F, Viviani B, Waldmann T, Westerink RHS, Wilks MF, Witters H, Zurich MG, Leist M. Recommendation on test readiness criteria for new approach methods in toxicology: Exemplified for developmental neurotoxicity. ALTEX. 2018;35(3):306-352. doi: 10.14573/altex.1712081.  Erratum in: ALTEX. 2019;36(3):506. 

Crofton KM, Bassan A, Behl M, Chushak YG, Fritsche E, Gearhart JM, Marty MS, Mumtaz M, Pavan M, Ruiz P, Sachana M, Selvam R, Shafer TJ, Stavitskaya L, Szabo DT, Szabo ST, Tice RR, Wilson D, Woolley D, Myatt GJ. Current status and future directions for a neurotoxicity hazard assessment framework that integrates in silico approaches. Comput Toxicol. 2022 May;22:100223. doi: 10.1016/j.comtox.2022.100223. 

International Programme on Chemical Safety (IPCS),World Health Organization (WHO). Assessment of combined exposures to multiple chemicals. Report of a WHO/IPCS  International Workshop, 2009.

Izquierdo, Ivan. Role of NMDA receptors in memory. Trends in Pharmacological Sciences 12.4 (1991): 128-129

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.

Lupușoru CE, Popa EG, Sandu RB, Buca BR, Mititelu-Tarțău L, Lupușoru RV, The influence of Bidens tripartita extracts on psychomotor abilities and cognitive functions in rats.  Farmacia, 2017; 65(2): 284-288.

MacDonell MM, Haroun LA, Teuschler LK, Rice GE, Hertzberg RC, Butler JP, Chang Y-S, Clark SL, John AP, Perry CS, Garcia SS, Jacob JH, Scofield MA. 2013. Cumulative risk assessment toolbox:Methods and approaches for the practitioner. Journal of Toxicology, 2013; Article ID 310904, doi:10.1155/2013/310904.

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.

Neal, A.P., Guilarte, T.R. Molecular Neurobiology of Lead (Pb2+): Effects on Synaptic Function. Mol Neurobiol 42, 151–160 (2010). https://doi.org/10.1007/s12035-010-8146-0

OECD (2007), Test No. 426: Developmental Neurotoxicity Study, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264067394-en.

Schubert D, Martens GJM, Kolk SM. Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders. Molecular Psychiatry, 2013; 2014:1–15.

Appendix 1

List of MIEs in this AOP

Event: 2146: Activation of mitogen-activated protein kinase kinase, extracellular signal-regulated kinase 1/2

Short Name: Activation of MEK, ERK1/2

Key Event Component

AOPs Including This Key Event

Biological Context

Cell term

Organ term

Domain of Applicability

Taxonomic Applicability Life Stage Applicability Sex Applicability

Key Event Description

ERK1 and ERK2 are proteins of 43 and 41 kDa that are nearly 85% identical overall, with much greater identity in the core regions involved in binding substrates (Boulton et al., 1990; 1991). The two phosphoacceptor sites, tyrosine and threonine, which are phosphorylated to activate the kinases, are separated by a glutamate residue in both ERK1 and ERK2 to give the motif TEY in the activation loop (Payne et al., 1991). Both are ubiquitously expressed, although their relative abundance in tissues is variable. For example, in many immune cells ERK2 is the predominant species, while in several cells of neuroendocrine origin they may be equally expressed (Gray Pearson and others 2001). They are stimulated to some extent by a vast number of ligands and cellular perturbations, with some cell type specificity (Lewis et al., 1998). In fibroblasts (the cell type in which the generalizations about their behavior and functions have been developed) they are activated by serum, growth factors, cytokines, certain stresses, ligands for G protein-coupled receptors (GPCRs), and transforming agents, to name a few (Gray Pearson and others 2001). They are highly expressed in postmitotic neurons and other highly differentiated cells (Boulton et al., 1991). In these cells they are often involved in adaptive responses such as long-term potentiation (English and Sweatt 1996; Atkins et al., 1998; Rossi-Arnaud et al., 1997).

How it is Measured or Detected

Western blotting and immunoblotting.

References

Atkins CM, Selcher JC, Petraitis JJ, Trzaskos JM, Sweatt JD 1998 The MAPK cascade is required for mammalian associative learning. Nat Neurosci 1 :602 –609

Boulton TG, Nye SH, Robbins DJ, Ip NY, Radziejewska E, Morgenbesser SD, DePinho RA, Panayotatos N, Cobb MH, Yancopoulos GD 1991 ERKs: a family of protein-serine/threonine kinases that are activated and tyrosine phosphorylated in response to insulin and NGF. Cell 65 :663 –675

Boulton TG, Yancopoulos GD, Gregory JS, Slaughter C, Moomaw C, Hsu J, Cobb MH 1990 An insulin-stimulated protein kinase similar to yeast kinases involved in cell cycle control. Science 249 :64 –67

English JD , Sweatt JD 1996 Activation of p42 mitogen-activated protein kinase in hippocampal long term potentiation. J Biol Chem 271 :24329 –24332

Gray Pearson and others, Mitogen-Activated Protein (MAP) Kinase Pathways: Regulation and Physiological Functions, Endocrine Reviews, Volume 22, Issue 2, 1 April 2001, Pages 153–183, https://doi.org/10.1210/edrv.22.2.0428

Lewis TS, Shapiro PS, Ahn NG 1998 Signal transduction through MAP kinase cascades. Adv Cancer Res 74 :49 –139

Payne DM, Rossomando AJ, Martino P, Erickson AK, Her J-H, Shananowitz J, Hunt DF, Weber MJ, Sturgill TW 1991 Identification of the regulatory phosphorylation sites in pp42/mitogen-activated protein kinase (MAP kinase). EMBO J 10 :885 –892

Rossi-Arnaud C, Grant SG, Chapman PF, Lipp HP, Sturani E, Klein R 1997 A role for the Ras signalling pathway in synaptic transmission and long-term memory. Nature 390 :281 –286

List of Key Events in the AOP

Event: 1339: Increase, intracellular calcium

Short Name: Increase, intracellular calcium

Key Event Component

AOPs Including This Key Event

Biological Context

Cell term

Organ term

Domain of Applicability

Taxonomic Applicability Life Stage Applicability Sex Applicability

Key Event Description

Calcium is arguably the most versatile and important intracellular messenger in neurons (Berridge et al., 2000). Interestingly, although calcium may often promote neuronal death, it can also activate pathways that promote survival. For example, calcium can promote survival through a pathway involving activation of protein kinase B (PKB/Akt) by calcium/calmodulin-dependent protein kinase (Yano et al., 1998). Calcium is a prominent regulator of cellular responses to stress, activating transcription through the cyclic-AMP response element-binding protein (CREB), which can promote neuron survival in experimental models of developmental cell death (Hu et al., 1999). Calcium can also activate a rapid neuroprotective signalling pathway in which the calcium-activated actin-severing protein gelsolin induces actin depolymerization, resulting in suppression of calcium influx through membrane NMDA (N-methyl-d-aspartate) receptors and voltage-dependent calcium channels (Furukawa et al., 1997). This may occur through intermediary actin-binding proteins that interact with NMDA receptor and calcium channel proteins. Finally, signals such as calcium and secreted amyloid precursor protein-α (sAPP-α), which increase cyclic GMP production, can induce activation of potassium channels and the transcription factor NF-κB, and thereby increase resistance of neurons to excitotoxic apoptosis (Furukawa et al., 1996).

How it is Measured or Detected

An increase in [Ca^2+]i was measured using Fluo3 AM as an indicator dye after the addition of metals (single or in mixture) to the culture wells following an optimized protocol (Arey et al., 2022). The fluorescent signals were read by fluorescence imaging plate reader Synergy HT (BioTek, Winooski, VT) (Rai and others 2010).

Briefly, Ca2+ levels in human astrocytes were monitored by fluorescence microscopy using the Ca2+ indicator fluo-4. Slices were incubated with fluo-4-AM (2–5 µL of 2 mM dye were dropped over the tissue, attaining a final concentration of 2–10 µM and 0.01% of pluronic) and Sulforhodamine 101 (100 µM) for 30–60 min at room temperature (Navarrete and others 2013). In these conditions, most of the Fluo-4-loaded cells were astrocytes as indicated by their SR101 staining (Nimmerjahn et al., 2004; Dombeck et al., 2007; Kafitz et al., 2008; Takata and Hirase 2008), and confirmed in some cases by their electrophysiological properties. Astrocytes were imaged with an Olympus FV300 laser-scanning confocal microscope or a CCD camera (Retiga EX) attached to the Olympus BX50WI microscope (Navarrete and others 2013).

Diversity of endogenous Ca2+ activity in a mature hippocampal astrocyte in situ: Ca2+ signals in cell body and processes are different. (A) Cumulative Ca2+ activity recorded in an astrocyte over a 165 s period revealed by the calcium indicator Fluo4-AM. The visible boundaries of the astrocyte are shown in white. Note the different intensities of spatially-
confined local activity in the astrocyte cell body (s), primary process (p1) stemming from the soma and secondary processes (p2) branching from a primary process. Intensity of the
normalized cumulative activity is expressed in arbitrary units (a.u.) and shown in pseudocolour, from dark (lowest) to white (highest). (B) Frequency map of the Ca2+ activity in the astrocyte during the 165 s period as in A. Activity is measured in individual pixels, expressed in mHz and color-coded from black (never active) to dark red (frequently active). Most of the activity is within the white boundaries and the most frequently active pixels are in defined small regions (arrowheads) of the primary and secondary processes (30 mHz), whereas pixels of the soma are less active (~10 mHz) (Volterra et al., 2014). 

Free intracellular calcium ions were measured using the fluorescent calcium indicator FLUO-3/AM (Molecular probes, Eugene, OR, USA). Cells (4 × 10⁴ cells/cm²) were seeded in 24-well plates for 24 h to reach 60%–70%, and then treated for 24 h with As(III) (0.5 and 1 mg/l), or coexposed to As(III) (1 mg/l) and F (2.5, 5, and 10 mg/l). After treatment, supernatant was collected and combined with trypsinized cells. Pelleted samples were resuspended in 500 μl of FLUO-3/AM (4 μmol/l) and incubated at 37 °C for 30 min. After centrifugation, cells were washed with HBSS (Hank's Buffered Salt Solution, Sigma), made up to 400 μl with HBSS and analyzed by flow cytometry. The signal from FLUO-3/AM bound to Ca²⁺ was recorded using the Fl-1 channel (Rocha et al., 2011).

Fluo-4/AM was used as an intracellular free Ca²⁺ fluorescent probe to analyze [Ca²⁺]_i in Cd-exposed cerebral cortical neurons. In short, the harvested cells were incubated with Fluo-4/AM (5 µmol/L final concentration) for 30 min at 37°C in the dark, washed with PBS, and analyzed on a BD-FACS Aria flow cytometry. Intracellular [Ca²⁺]_i levels were represented by fluorescent intensity. Fluorescent intensity was recorded by excitation at 494 nm and emission at 516 nm. The data were analyzed by Cell Quest program (Becton Dickinson), and the mean fluorescence intensity was obtained by histogram statistics (Yuan et al., 2013).

References

Arey BJ Seethala R Ma Z Fura A Morin J Swartz J Vyas V Yang W Dickson JK JrFeyen JH A novel calcium-sensing receptor antagonist transiently stimulates parathyroid hormone secretion in vivo Endocrinology 2005 146 2015 2022

Asit Rai and others, Characterization of Developmental Neurotoxicity of As, Cd, and Pb Mixture: Synergistic Action of Metal Mixture in Glial and Neuronal Functions, Toxicological Sciences, Volume 118, Issue 2, December 2010, Pages 586–601, https://doi.org/10.1093/toxsci/kfq266

Berridge, M. J., Lipp, P. & Bootman, M. D. The versatility and universality of calcium signaling. Nature Rev. Mol. Cell Biol. 1, 11– 21 (2000).

Dombeck DA, Khabbaz AN, Collman F, Adelman TL, Tank DW. Imaging large-scale neural activity with cellular resolution in awake, mobile mice, Neuron, 2007, vol. 56 (pg. 43-57)

Furukawa, K. et al. The actin-severing protein gelsolin modulates calcium channel and NMDA receptor activities and vulnerability to excitotoxicity in hippocampal neurons. J. Neurosci. 17, 8178– 8186 (1997).

Furukawa, K., Barger, S. W., Blalock, E. M. & Mattson, M. P. Activation of K+ channels and suppression of neuronal activity by secreted β-amyloid-precursor protein. Nature 379, 74–78 (1996).

Hu, S. C., Chrivia, J. & Ghosh, A. Regulation of CBP-mediated transcription by neuronal calcium signaling. Neuron 22, 799– 808 (1999).

Kafitz KW, Meier SD, Stephan J, Rose CR. Developmental profile and properties of sulforhodamine 101-labeled glial cells in acute brain slices of rat hippocampus, J Neurosci Methods, 2008, vol. 169 (pg. 84-92)

Marta Navarrete and others, Astrocyte Calcium Signal and Gliotransmission in Human Brain Tissue, Cerebral Cortex, Volume 23, Issue 5, May 2013, Pages 1240–1246, https://doi.org/10.1093/cercor/bhs122

Nimmerjahn A, Kirchhoff F, Kerr JN, Helmchen F. Sulforhodamine 101 as a specific marker of astroglia in the neocortex in vivo, Nat Methods, 2004, vol. 1 (pg. 31-37)

R.A. Rocha, J.V. Gimeno-Alcañiz, R. Martín-Ibañez, J.M. Canals, D. Vélez, V. Devesa, Arsenic and fluoride induce neural progenitor cell apoptosis, Toxicology Letters, Volume 203, Issue 3, 2011, Pages 237-244, ISSN 0378-4274, https://doi.org/10.1016/j.toxlet.2011.03.023.

Takata N, Hirase H. Cortical layer 1 and layer 2/3 astrocytes exhibit distinct calcium dynamics in vivo., PLoS ONE, 2008, vol. 3 pg. e2525

Volterra, Andrea, Nicolas Liaudet, and Iaroslav Savtchouk. "Astrocyte Ca2+ signalling: an unexpected complexity." Nature Reviews Neuroscience 15.5 (2014): 327-335.

Yano, S., Tokumitsu, H. & Soderling, T. R. Calcium promotes cell survival through CaM-K kinase activation of the protein-kinase-B pathway. Nature 396, 584–587 (1998).

Yuan Y, Jiang C-y, Xu H, Sun Y, Hu F-f, Bian J-c, et al. (2013) Cadmium-Induced Apoptosis in Primary Rat Cerebral Cortical Neurons Culture Is Mediated by a Calcium Signaling Pathway. PLoS ONE 8(5): e64330. https://doi.org/10.1371/journal.pone.0064330

Event: 2151: Disruption, neurotransmitter release

Short Name: Disruption, neurotransmitter release

Key Event Component

AOPs Including This Key Event

Biological Context

Cell term

Organ term

Domain of Applicability

Taxonomic Applicability Life Stage Applicability Sex Applicability

Key Event Description

How it is Measured or Detected

References

List of Adverse Outcomes in this AOP

Event: 341: Impairment, Learning and memory

Short Name: Impairment, Learning and memory

Key Event Component

AOPs Including This Key Event

Biological Context

Domain of Applicability

Taxonomic Applicability Life Stage Applicability Sex Applicability

Basic forms of learning behavior such as habituation have been found in many taxa from worms to humans (Alexander, 1990). More complex cognitive processes such as executive function likely reside only in higher mammalian species such as non-human primates and humans. Recently, larval zebrafish has also been suggested as a model for the study of learning and memory (Roberts et al., 2013).

Life stage applicability: This key event is applicable to various life stages such as during brain development and maturity (Hladik & Tapio, 2016). 

Sex applicability: This key event is not sex specific (Cekanaviciute et al., 2018), although sex-dependent cognitive outcomes have been recently ; Parihar et al., 2020). 

Evidence for perturbation by a prototypic stressor: Current literature provides ample evidence of impaired learning and memory being induced by ionizing radiation (Cekanaviciute et al., 2018; Hladik & Tapio, 2016). 

Key Event Description

 

Learning can be defined as the process by which new information is acquired to establish knowledge by systematic study or by trial and error (Ono, 2009). Two types of learning are considered in neurobehavioral studies: a) associative learning and b) non-associative learning. Associative learning is based on making associations between different events. In associative learning, a subject learns the relationship among two different stimuli or between the stimulus and the subject’s behaviour. On the other hand, non-associative learning can be defined as an alteration in the behavioural response that occurs over time in response to a single type of stimulus. Habituation and sensitization are some examples of non-associative learning.

The memory formation requires acquisition, retention and retrieval of information in the brain, which is characterised by the non-conscious recall of information (Ono, 2009). There are three main categories of memory, including sensory memory, short-term or working memory (up to a few hours) and long-term memory (up to several days or even much longer).

Learning and memory depend upon the coordinated action of different brain regions and neurotransmitter systems constituting functionally integrated neural networks (D’Hooge and DeDeyn, 2001). Among the many brain areas engaged in the acquisition of, or retrieval of, a learned event, the hippocampal-based memory systems have received the most study. For example, the hippocampus has been shown to be critical for spatial-temporal memory, visio-spatial memory, verbal and narrative memory, and episodic and autobiographical memory (Burgess et al., 2000; Vorhees and Williams, 2014). However, there is substantial evidence that fundamental learning and memory functions are not mediated by the hippocampus alone but require a network that includes, in addition to the hippocampus, anterior thalamic nuclei, mammillary bodies cortex, cerebellum and basal ganglia (Aggleton and Brown, 1999; Doya, 2000; Mitchell et al., 2002, Toscano and Guilarte, 2005; Gilbert et al., 2006, 2016). Thus, damage to variety of brain structures can potentially lead to impairment of learning and memory. The main learning areas and pathways are similar in rodents and primates, including man (Eichenbaum, 2000; Stanton and Spear, 1990).While the prefrontal cortex and frontostriatal neuronal circuits have been identified as the primary sites of higher-order cognition in vertebrates, invertebrates utilize paired mushroom bodies, shown to contain ~300,000 neurons in honey bees (Menzel, 2012; Puig et al., 2014).

For the purposes of this KE (AO), impaired learning and memory is defined as an organism’s inability to establish new associative or non-associative relationships, or sensory, short-term or long-term memories which can be measured using different behavioural tests described below.

How it is Measured or Detected

In laboratory animals: in rodents, a variety of tests of learning and memory have been used to probe the integrity of hippocampal function. These include tests of spatial learning like the radial arm maze (RAM), the Barnes maze, Hebb-Williams maze, passive avoidance and Spontaneous alternation and most commonly, the Morris water maze (MWM). Test of novelty such as novel object recognition, and fear based context learning are also sensitive to hippocampal disruption. Finally, trace fear conditioning which incorporates a temporal component upon traditional amygdala-based fear learning engages the hippocampus. A brief description of these tasks follows.

1) RAM, Barnes, MWM, Hebb-Williams maze are examples of spatial tasks, animals are required to learn the location of a food reward (RAM); an escape hole to enter a preferred dark tunnel from a brightly lit open field area (Barnes maze), or a hidden platform submerged below the surface of the water in a large tank of water (MWM) (Vorhees and Williams, 2014). The Hebb-Williams maze measures an animal’s problem solving abilities by providing no spatial cues to find the target (Pritchett & Mulder, 2004).

2) Novel Object recognition. This is a simpler task that can be used to probe recognition memory. Two objects are presented to animal in an open field on trial 1, and these are explored. On trial 2, one object is replaced with a novel object and time spent interacting with the novel object is taken evidence of memory retention – I have seen one of these objects before, but not this one (Cohen and Stackman, 2015).

3) Contextual Fear conditioning is a hippocampal based learning task in which animals are placed in a novel environment and allowed to explore for several minutes before delivery of an aversive stimulus, typically a mild foot shock. Upon reintroduction to this same environment in the future (typically 24-48 hours after original training), animals will limit their exploration, the context of this chamber being associated with an aversive event. The degree of suppression of activity after training is taken as evidence of retention, i.e., memory (Curzon et al., 2009).

4) Trace fear conditioning. Standard fear conditioning paradigms require animals to make an association between a neutral conditioning stimulus (CS, a light or a tone) and an aversive stimulus (US, a footshock). The unconditioned response (CR) that is elicited upon delivery of the footshock US is freezing behavior. With repetition of CS/US delivery, the previously neutral stimulus comes to elicit the freezing response. This type of learning is dependent on the amygdala, a brain region associated with, but distinct from the hippocampus. Introducing a brief delay between presentation of the neutral CS and the aversive US, a trace period, requires the engagement of the amygdala and the hippocampus (Shors et al., 2001).

5) Operant Responding. Performance on operant responding reflects the cortex’ ability to organize processes (Rabin et al., 2002). 

In humans:  A variety of standardized learning and memory tests have been developed for human neuropsychological testing, including children (Rohlman et al., 2008). These include episodic autobiographical memory, perceptual motor tests, short and  long term memory tests, working memory tasks, word pair recognition memory; object location recognition memory. Some have been incorporated in general tests of intelligence (IQ) such as the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler. Modifications have been made and norms developed for incorporating of tests of learning and memory in children. Examples of some of these tests include:

1) Rey Osterieth Complex Figure test (RCFT) which probes a variety of functions including as visuospatial abilities, memory, attention, planning, and working memory (Shin et al., 2006).

2) Children’s Auditory Verbal Learning Test (CAVLT) is a free recall of presented word lists that yields measures of Immediate Memory Span, Level of Learning, Immediate Recall, Delayed Recall, Recognition Accuracy, and Total Intrusions. (Lezak 1994; Talley, 1986).

3) Continuous Visual Memory Test (CVMT) measures visual learning and memory. It is a free recall of presented pictures/objects rather than words but that yields similar measures of Immediate Memory Span, Level of Learning, Immediate Recall, Delayed Recall, Recognition Accuracy, and Total Intrusions. (Lezak, 1984; 1994).

4) Story Recall from Wechsler Memory Scale (WMS) Logical Memory Test Battery, a standardized neurospychological test designed to measure memory functions (Lezak, 1994; Talley, 1986).

5) Autobiographical memory (AM) is the recollection of specific personal events in a multifaceted higher order cognitive process. It includes episodic memory- remembering of past events specific in time and place, in contrast to semantic autobiographical memory is the recollection of personal facts, traits, and general knowledge. Episodic AM is associated with greater activation of the hippocampus and a later and more gradual developmental trajectory. Absence of episodic memory in early life (infantile amnesia) is thought to reflect immature hippocampal function (Herold et al., 2015; Fivush, 2011).

6) Staged Autobiographical Memory Task. In this version of the AM test, children participate in a staged event involving a tour of the hospital, perform a series of tasks (counting footprints in the hall, identifying objects in wall display, buy lunch, watched a video). It is designed to contain unique event happenings, place, time, visual/sensory/perceptual details. Four to five months later, interviews are conducted using Children’s Autobiographical Interview and scored according to standardized scheme (Willoughby et al., 2014).

7) Attentional set-shifting (ATSET) task. Measures the ability to relearn cues over various schedules of reinforcement (Heisler et al., 2015).

8. Comprehensive developmental inventory for infants and toddlers (CDIIT).  The CDIIT was designed and standardized in 1996, and it measures the global, cognitive, language, motor, gross motor, fine motor, social, self-help and behavioral developmental status of children from 3 to 71 months old (Wang et al., 1998).

In Honey Bees: For over 50 years an assay for evaluating olfactory conditioning of the proboscis extension reflex (PER) has been used as a reliable method for evaluating appetitive learning and memory in honey bees (Guirfa and Sandoz, 2012; LaLone et al., 2017). These experiments pair a conditioned stimulus (e.g., an odor) with an unconditioned stimulus (e.g., sucrose) provided immediately afterward, which elicits the proboscis extension (Menzel, 2012). After conditioning, the odor alone will lead to the conditioned PER. This methodology has aided in the elucidation of five types of olfactory memory phases in honey bee, which include early short-term memory, late short-term memory, mid-term memory, early long-term memory, and late long-term memory (Guirfa and Sandoz, 2012). These phases are dependent on the type of conditioned stimulus, the intensity of the unconditioned stimulus, the number of conditioning trials, and the time between trials. Where formation of short-term memory occurs minutes after conditioning and decays within minutes, memory consolidation or stabilization of a memory trace after initial acquisition leads to mid-term memory, which lasts 1 d and is characterized by activity of the cAMP-dependent PKA (Guirfa and Sandoz, 2012). Multiple conditioning trials increase the duration of the memory after learning and coincide with increased Ca2+-calmodulin-dependent PKC activity (Guirfa and Sandoz, 2012). Early long-term memory, where a conditioned response can be evoked days to weeks after conditioning requires translation of existing mRNA, whereas late long-term memory requires de novo gene transcription and can last for weeks (Guirfa andSandoz, 2012)."

Regulatory Significance of the AO

A prime example of impairments in learning and memory as the adverse outcome for regulatory action is developmental lead exposure and IQ function in children (Bellinger, 2012). Most methods are well established in the published literature and many have been engaged to evaluate the effects of developmental thyroid disruption. The US EPA and OECD Developmental Neurotoxicity (DNT) Guidelines (OCSPP 870.6300 or OECD TG 426) as well as OECD TG 443 (OECD, 2018) both require testing of learning and memory (USEPA, 1998; OECD, 2007) advising to use the following tests passive avoidance, delayed-matching-to-position for the adult rat and for the infant rat, olfactory conditioning, Morris water maze, Biel or Cincinnati maze, radial arm maze, T-maze, and acquisition and retention of schedule-controlled behaviour.  These DNT Guidelines have been deemed valid to identify developmental neurotoxicity and adverse neurodevelopmental outcomes (Makris et al., 2009).

Also, in the frame of the OECD GD 43 (2008) on reproductive toxicity, learning and memory testing may have potential to be applied in the context of developmental neurotoxicity studies. However, many of the learning and memory tasks used in guideline studies may not readily detect subtle impairments in cognitive function associated with modest degrees of developmental thyroid disruption (Gilbert et al., 2012).

References

Aggleton JP, Brown MW. (1999) Episodic memory, amnesia, and the hippocampal-anterior thalamic axis. Behav Brain Sci. 22: 425-489.

Alexander RD (1990) Epigenetic rules and Darwinian algorithms: The adaptive study of learning and development. Ethology and Sociobiology 11:241-303.

Bellinger DC (2012) A strategy for comparing the contributions of environmental chemicals and other risk factors to neurodevelopment of children. Environ Health Perspect 120:501-507.

Burgess N (2002) The hippocampus, space, and viewpoints in episodic memory. Q J Exp Psychol A 55:1057-1080. Cohen, SJ and Stackman, RW. (2015). Assessing rodent hippocampal involvement in the novel object recognition task. A review. Behav. Brain Res. 285: 105-1176.

Cekanaviciute, E., S. Rosi and S. Costes. (2018), "Central Nervous System Responses to Simulated Galactic Cosmic Rays", International Journal of Molecular Sciences, Vol. 19/11, Multidisciplinary Digital Publishing Institute (MDPI) AG, Basel,  https://doi.org/10.3390/ijms19113669. 

Cohen, SJ and Stackman, RW. (2015). Assessing rodent hippocampal involvement in the novel object recognition task. A review. Behav. Brain Res. 285: 105-1176.

Curzon P, Rustay NR, Browman KE. Cued and Contextual Fear Conditioning for Rodents. In: Buccafusco JJ, editor. Methods of Behavior Analysis in Neuroscience. 2nd edition. Boca Raton (FL): CRC Press/Taylor & Francis; 2009.

D'Hooge R, De Deyn PP (2001) Applications of the Morris water maze in the study of learning and memory. Brain Res Brain Res Rev 36:60-90.

Doya K. (2000) Complementary roles of basal ganglia and cerebellum in learning and motor control. Curr Opin Neurobiol. 10: 732-739.

Eichenbaum H (2000) A cortical-hippocampal system for declarative memory. Nat Rev Neurosci 1:41-50.

Fivush R. The development of autobiographical memory. Annu Rev Psychol. 2011;62:559-82.

Gilbert ME, Sanchez-Huerta K, Wood C (2016) Mild Thyroid Hormone Insufficiency During Development Compromises Activity-Dependent Neuroplasticity in the Hippocampus of Adult Male Rats. Endocrinology 157:774-787.

Gilbert ME, Rovet J, Chen Z, Koibuchi N. (2012) Developmental thyroid hormone disruption: prevalence, environmental contaminants and neurodevelopmental consequences. Neurotoxicology 33: 842-52.

Gilbert ME, Sui L (2006) Dose-dependent reductions in spatial learning and synaptic function in the dentate gyrus of adult rats following developmental thyroid hormone insufficiency. Brain Res 1069:10-22.

Guirfa, M., Sandoz, J.C., 2012. Invertebrate learning and memory: fifty years of olfactory conditioning of the proboscis extension response in honeybees. Learn. Mem. 19 (2),
54–66.

Herold, C, Lässer, MM, Schmid, LA, Seidl, U, Kong, L, Fellhauer, I, Thomann,PA, Essig, M and Schröder, J. (2015). Neuropsychology, Autobiographical Memory, and Hippocampal Volume in “Younger” and “Older” Patients with Chronic Schizophrenia. Front. Psychiatry, 6: 53.

Hladik, D. and S. Tapio. (2016), "Effects of ionizing radiation on the mammalian brain", Mutation Research/Reviews in Mutation Research, Vol. 770, Elsevier B. b., Amsterdam, https://doi.org/10.1016/j.mrrev.2016.08.003. 

Heisler, J. M. et al. (2015), "The Attentional Set Shifting Task: A Measure of Cognitive Flexibility in Mice", Journal of Visualized Experiments, 96, JoVe, Cambridge, https://doi.org/10.3791/51944. Heisler, J. M. et al. (2015), "The Attentional Set Shifting Task: A Measure of Cognitive Flexibility in Mice", Journal of Visualized Experiments, 96, JoVe, Cambridge, https://doi.org/10.3791/51944. 

LaLone, C.A., Villeneuve, D.L., Wu-Smart, J., Milsk, R.Y., Sappington, K., Garber, K.V., Housenger, J. and Ankley, G.T., 2017. Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death. STOTEN. 584-585, 751-775.

Lezak MD (1984) Neuropsychological assessment in behavioral toxicology--developing techniques and interpretative issues. Scand J Work Environ Health 10 Suppl 1:25-29.

Lezak MD (1994) Domains of behavior from a neuropsychological perspective: the whole story. Nebr Symp Motiv 41:23-55.

Makris SL, Raffaele K, Allen S, Bowers WJ, Hass U, Alleva E, Calamandrei G, Sheets L, Amcoff P, Delrue N, Crofton KM.(2009) A retrospective performance assessment of the developmental neurotoxicity study in support of OECD test guideline 426. Environ Health Perspect.  Jan;117(1):17-25.

Menzel, R., 2012. The honeybee as a model for understanding the basis of cognition. Nat. Rev. Neurosci. 13 (11), 758–768.

Mitchell AS, Dalrymple-Alford JC, Christie MA. (2002) Spatial working memory and the brainstem cholinergic innervation to the anterior thalamus. J Neurosci. 22: 1922-1928.

OECD. 2007. OECD guidelines for the testing of chemicals/ section 4: Health effects. Test no. 426: Developmental neurotoxicity study. www.Oecd.Org/dataoecd/20/52/37622194.Pdf [accessed may 21, 2012].

OECD (2008) Nr 43 GUIDANCE DOCUMENT ON MAMMALIAN REPRODUCTIVE TOXICITY TESTING AND ASSESSMENT. ENV/JM/MONO(2008)16

Ono T. (2009) Learning and Memory. Encyclopedia of neuroscience. M D. Binder, N. Hirokawa and U. Windhorst (Eds). Springer-Verlag GmbH Berlin Heidelberg. pp 2129-2137.

Parihar, V. K. et al. (2020), "Sex-Specific Cognitive Deficits Following Space Radiation Exposure", Frontiers in Behavioral Neuroscience, Vol. 14, https://doi.org/10.3389/fnbeh.2020.535885. 

Pritchett, K. and G. Mulder. (2004), "Hebb-Williams mazes.", Contemporary topics in laboratory animal science, Vol. 43/5, http://www.ncbi.nlm.nih.gov/pubmed/15461441. 

Puig, M.V., Antzoulatos, E.G., Miller, E.K., 2014. Prefrontal dopamine in associative learning and memory. Neuroscience 282, 217–229.

Rabin, B. M. et al. (2002), "Effects of Exposure to 56Fe Particles or Protons on Fixed-ratio Operant Responding in Rats", Journal of Radiation Research, Vol. 43/S, https://doi.org/10.1269/jrr.43.S225. 

Roberts AC, Bill BR, Glanzman DL. (2013) Learning and memory in zebrafish larvae. Front Neural Circuits 7: 126.

Rohlman DS, Lucchini R, Anger WK, Bellinger DC, van Thriel C. (2008) Neurobehavioral testing in human risk assessment. Neurotoxicology. 29: 556-567.

Shin, MS, Park, SY, Park, SR, Oeol, SH and Kwon, JS. (2006). Clinical and empirical applications of the Rey-Osterieth complex figure test. Nature Protocols, 1: 892-899.

Shors TJ, Miesegaes G, Beylin A, Zhao M, Rydel T, Gould E (2001) Neurogenesis in the adult is involved in the formation of trace memories. Nature 410:372-376.

Stanton ME, Spear LP (1990) Workshop on the qualitative and quantitative comparability of human and animal developmental neurotoxicity, Work Group I report: comparability of measures of developmental neurotoxicity in humans and laboratory animals. Neurotoxicol Teratol 12:261-267.

Talley, JL. (1986). Memory in learning disabled children: Digit span and eh Rey Auditory verbal learning test. Archives of Clinical Neuropsychology, Elseiver.

U.S.EPA. 1998. Health effects guidelines OPPTS 870.6300 developmental neurotoxicity study. EPA Document 712-C-98-239.Office of Prevention Pesticides and Toxic Substances.

Vorhees CV, Williams MT (2014) Assessing spatial learning and memory in rodents. ILAR J 55:310-332.

 

Appendix 2

List of Key Event Relationships in the AOP