Investigations on learning and memory function in extended one-generation reproductive toxicity studies - when...

Area of Science:

• Toxicology
• Neuroscience
• Endocrinology

Background:

• The European Chemicals Agency (ECHA) requires learning and memory (L&M) tests in extended one-generation reproductive toxicity studies (EOGRTS) based on thyroid hormone signaling disruption.
• This requirement is based on three publications cited by ECHA.

Purpose of the Study:

• This paper challenges the necessity of including L&M tests in EOGRTS.
• It questions the validity of rodent models for assessing thyroid hormone effects on brain development and the reliability of the cited publications.

Main Methods:

• Critically evaluated the methodology, design, and data reporting of three key publications used by ECHA.
• Assessed the causal relationship between thyroid hormone levels and cognitive function in rodent models.

Main Results:

• The cited publications contain significant errors, contradictory findings, and lack crucial information for validation.
• These studies fail to establish a causal link between decreased thyroxine (T4) levels and impaired L&M in rats.
• The reliability of rodent models for assessing thyroid hormone-dependent neurodevelopmental effects is questioned.

Conclusions:

• The three publications used by ECHA are inadequate to justify mandatory L&M testing in EOGRTS.
• Decreases in blood T4 levels alone cannot be concluded to cause impaired L&M in rats based on the available evidence.
• The scientific basis for requiring L&M tests in EOGRTS due to thyroid hormone disruption is unsubstantiated.