Spermatogenic timing, dose, and route of administration as determinants of paternal transmission of developmental neurotoxicity.

Growing evidence challenges the long-standing assumption that the paternal germline is insulated from environmental perturbation and identifies preconception paternal exposure as an underrecognized pathway of developmental neurotoxicity. Across mammalian models, paternal exposure to substances of abuse, including cocaine, nicotine, ethanol, morphine, and cannabinoids, induces reproducible, often sex-specific alterations in offspring brain function and behavior, including changes in cognition, stress responsivity, reward processing, and affective behaviors, accompanied by transcriptional and epigenetic modifications. A critical but underappreciated determinant of these outcomes is exposure design, particularly exposure duration relative to the spermatogenic cycle, which emerges as a primary toxicodynamic relevant variable. Exposures spanning a full spermatogenic cycle frequently produce persistent neurobehavioral and molecular alterations, whereas shorter exposures targeting late spermatids or mature sperm can also generate robust offspring phenotypes, highlighting stage-specific germ cell vulnerability. Importantly, delaying mating beyond a complete spermatogenic cycle often attenuates offspring effects, suggesting that temporal separation between exposure and conception may mitigate neurodevelopmental risk. Mechanistically, paternal exposures disrupt sperm epigenetic regulation, including altered DNA methylation, histone modifications, and small RNA profiles, often linked to germline oxidative stress as a potential upstream mediator. Exposure dose and route further modulate transmission through pharmacokinetic effects on systemic and germline exposure. We propose a stage-specific framework in which paternal transmission magnitude and persistence are primarily determined by exposure duration relative to spermatogenesis, with dose and route acting as key modifiers. This framework integrates behavioral and molecular findings and provides a biologically grounded basis for developmental neurotoxicity risk assessment and male preconception health.