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Hippocampal anatomy, Altered leads to Hippocampal Physiology, Altered
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding||Point of Contact||Author Status||OECD Status|
|Inhibition of Thyroperoxidase and Subsequent Adverse Neurodevelopmental Outcomes in Mammals||adjacent||Moderate||Low||Evgeniia Kazymova (send email)||Open for citation & comment||TFHA/WNT Endorsed|
|Sodium Iodide Symporter (NIS) Inhibition and Subsequent Adverse Neurodevelopmental Outcomes in Mammals||adjacent||Moderate||Low||Evgeniia Kazymova (send email)||Under Development: Contributions and Comments Welcome|
|Thyroid Receptor Antagonism and Subsequent Adverse Neurodevelopmental Outcomes in Mammals||adjacent||Moderate||Low||Evgeniia Kazymova (send email)||Under development: Not open for comment. Do not cite||Under Development|
Life Stage Applicability
|During brain development||High|
Key Event Relationship Description
The hippocampus is a highly integrated and organized communication and information processing network with millions of interconnections among its constitutive neurons (see Andersen et al, 2006). The neuronal spine is the primary site of action for synaptic interface between neurons. Although difficult to measure due to their small size, large number and variable shapes, changes in the frequency and structure of dendritic spines of hippocampal neurons has dramatic effects on synaptic physiology and plasticity (Harris et al., 1992). Anatomical integrity at a more macro-level is also essential for physiological function. The connectivity of axons emanating from one set of cells that synapse on the dendrites of the receiving cells must be intact for effective communication between neurons to be possible. Synaptogenesis is a critical step for neurons to be integrated into neural networks during development. Changes in the placement of cells within the network due to delays or alterations in neuronal migration, the absence of a full proliferation of dendritic arbors and spine upon which synaptic contacts are made, and the lagging of transmission of electrical impulses due to insufficient myelination will independently and cumulatively impair synaptic function.
Evidence Supporting this KER
The weight of evidence supporting the relationship between structural abnormalities in brain induced and altered synaptic function is moderate. There is no doubt that altered structure can lead to altered function. Many examples from knock out models, genetic mutations, prenatal alcohol, nutritional deficits demonstrate a correlative link between altered structure and impaired synaptic function within the hippocampus (Gil-Mohapel et al., 2010; Berman and Hannigan, 2000; Grant et al., 1992; Palop et al., 2010; Ieraci and Herrera, 2007). However, the scientific understanding of the causative and quantitative relationship between the two KEs is incomplete.
The biological plausibility of alterations in hippocampal structure having an impact on synaptic function and plasticity in brain is strong. Because synaptic transmission in the hippocampus relies on the integrity of contacts and the reliability of electrical and chemical transmission between pre- and post-synaptic neurons, it is well accepted that interference on the anatomical levels will very much impact the functional output on the neurophysiological level (Knowles, 1992; Schultz and Engelhardt, 2014).
Uncertainties and Inconsistencies
There are no inconsistencies in this KER, but there are uncertainties. Although several examples are evident to demonstrate direct linkages between alterations in hippocampal anatomy and disruptions in hippocampal physiology, there is not a common cellular mechanism, anatomical insult, or signature pattern of synaptic impairment that defines a common anatomically driven physiological phenotype. In addition, it is also known that there is an interaction between physiological and anatomical development, where anatomy develops first, and can be ‘reshaped’ by the ongoing maturation of physiological function (e.g., Kutsarova et al., 2017)
Information does not exist to develop quantitative relationships between the KEs in this KER. Papers that utilize knock-out and mutant models have not provided ‘dose-response’ information for anatomy-physiology relationships.
Known modulating factors
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
The majority of data in support of this KER is from rodent models. The evolutionary conservation of hippocampal anatomy in mammals, birds, and reptiles (see Hevner, 2016; Streidter, 2015) suggests, with some uncertainty, that this KER is also applicable to multiple species.
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Sofroniew et al., 2006
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