Scientific perspectives on in vivo developmental neurotoxicity testing: study design, regulatory context, and future directions

Abstract

Developmental neurotoxicity (DNT) potential of (agro)chemicals is assessed in rodents according to OECD Test Guidelines (TG) 426 (DNT) or 443 (Extended One-Generation Reproductive Toxicity; EOGRTS) incorporating a DNT cohort. While the EOGRTS evaluates reproductive and neurotoxicity endpoints across multiple life stages, key differences in study design, dose selection, and exposure duration between OECD 426 and OECD 443 can complicate data interpretation and impact hazard identification and risk assessment. This manuscript evaluates current DNT testing strategies and examines the feasibility of a combined DNT-EOGRTS approach aimed at generating data for regulatory decision making. This combined approach requires substantial modifications to the EOGRTS design, and its implementation should be approached with caution. Given the increased complexity and logistical challenges, additional cognitive assessments such as learning and memory (L&M) should only be included when scientifically justified on a substance specific basis. Retrospective analyses indicate that L&M is among the least sensitive DNT endpoints, and its inclusion in an EOGRTS does not yield a functional equivalent of a standalone DNT. The review also examines regulatory triggers and recent regulatory decisions relevant to inclusion of cognitive assessments. Finally, the status and limitations of alternative approaches, including the in vitro DNT battery and zebrafish embryo models, are discussed. Overall, OECD 426 remains the scientifically preferred approach for DNT assessment. While a combined design may be feasible, it is inherently suboptimal for DNT evaluation. Collectively, this comprehensive review provides recommendations for generating robust DNT data while supporting animal welfare-conscious, future-oriented regulatory testing strategies.