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OECD Series on Adverse Outcome Pathways

An Adverse Outcome Pathway (AOP) describes a logical sequence of causally linked events at different levels of biological organisation, which follows exposure to a chemical and leads to an adverse health effect in humans or wildlife. AOPs are the central element of a toxicological knowledge framework, promoted by member countries through OECD, built to support chemical risk assessment based on mechanistic reasoning. These AOPs are available in the AOP Wiki, an interactive and virtual encyclopaedia for AOP development. Following their development and review, the endorsed AOPs are published the OECD Series on Adverse Outcome Pathways. As scientific knowledge progresses, the publication of an AOP in this series does not preclude the regular update or new contributions to a given AOP in the AOP Wiki. While the AOP Wiki is a dynamic tool, only impactful changes to the AOP will be reflected in subsequent updates of the published AOP. The number 1 in the OECD Series on Adverse Outcome Pathways is the Users’ Handbook, which is a supplement to the Guidance Document for developing and assessing AOPs. This handbook contains an updated template for AOP development and provides focused and practical instructions for both AOP developers and reviewers.

English

Adverse Outcome Pathway on inhibition of Na+/I- symporter (NIS) leads to learning and memory impairment

The thyroid hormones (TH) are essential for brain development, maturation, and function as they regulate the early key developmental processes. Normal human brain development and cognitive function relays on sufficient production of TH during the perinatal period. The function of Na+/I- symporter (NIS) is critical for the physiological production of TH levels in the serum. The present AOP describes causative links between inhibition of NIS function leading to the decreased levels of TH in the blood and consequently in the brain, causing learning and memory deficit in children. Learning and memory depend upon the coordinated action of different brain regions and neurotransmitter systems creating functionally integrated neural networks. Hippocampus and cortex are the most critical brain structures involved in the process of cognitive functions. The function of NIS and its essentiality for TH synthesis is well known across species, however, quantitative information of KERs is limited.

English

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