Brain-Derived neurotrophic factor Val66met is associated with sex-specific impairment of cognitive flexibility under stress: A reversal learning search strategy analysis in a rat model

• BDNF val66met may modulate cognitive flexibility but role of sex and stress unclear. • Reversal learning tested in BDNF val66met rats under stressful water maze conditions. • All groups rapidly learned new location of the platform and showed stress response. • Mediation analysis showed differential use of spatial strategies. • Sequential analysis showed lower flexibility in met/met males and val/met females. Cognitive flexibility is a core executive function vital for adaptation and adjustment to new information. The brain-derived neurotrophic factor (BDNF) single nucleotide polymorphism, val66met, has been suggested to modulate cognitive flexibility but it remains unclear how confounding variables such as stress and sex influence this relationship. Environmental enrichment (EE) may protect against stress-induced effects. The aim of this study was to test whether BDNF val66met alters reversal learning, a key component of cognitive flexibility, when tested under stressful water maze conditions. We used a Sprague Dawley val66met rat model where pregnant val/met dams were moved to either low or high EE environments. Dams and offspring stayed in these environments until weaning, after which the offspring was moved to standard, moderate enrichment housing. Adult male and female val/val, val/met and met/met offspring then underwent a water maze reversal learning protocol. All groups rapidly learned the new location of the platform. Mediation analysis showed the relationship between val66met and cognitive flexibility was mediated by differential use of spatial strategies. Sequential clustering analysis demonstrated that val66met interacted with sex to predict cognitive flexibility performance with lower flexibility in met/met males and val/met females compared to other genotypes. EE was not a strong promotor of cognitive flexibility. Water maze testing increased corticosterone levels, confirming the stressful nature of the test. This study demonstrates the importance of considering stress and sex when investigating the role of BDNF val66met in cognitive flexibility.