Dietary vitamin E: effect on oxidative stress, maze learning performance, and anxiety behaviors in rats.

Abstract

The brain is particularly susceptible to oxidative stress (OS) and damage to membranes is associated with learning and memory decline, impacting animal welfare. Vitamin E is an antioxidant which crosses the blood-brain barrier. Our objectives were to assess the impact of dietary vitamin E concentrations (20, 90, and 400-ppm) on markers of OS, maze learning performance (MLP), and anxious behaviors in 3-wk old Long-Evans rats. Vitamin E concentrations, antioxidant enzymes (superoxide dismutase [SOD] and glutathione peroxidase [GPx]), and oxidative protein damage (protein carbonyls [PC]) were measured in plasma or serum. Lipid damage (thiobarbituric acid reactive substances [TBARS]) was measured in serum and hippocampus. Anxious behaviors, including freezing and grooming, and MLP were assessed in an eight-arm radial maze over 5 weeks. Activity of SOD was lower (P = 0.002), and PC concentrations were higher (P = 0.022) in the 400-ppm group (1.0 U/mL; 0.7 nmol/mg) compared to the 20 (2.9 U/mL; 0.5 nmol/mg) and 90 (1.7 U/mL; 0.5 nmol/mg). Plasma vitamin E increased (P < 0.050) with dietary treatment and SOD decreased as plasma vitamin E increased (R² = 0.46; P = 0.002) but PC (R² = 0.16; P = 0.090) concentrations tended to increase with plasma vitamin E. Dietary treatment did not impact (P > 0.050) maze learning performance. Rats fed 20 ppm vitamin E exhibited greater freezing frequency and duration (P < 0.001) compared to other treatment groups, indicating heightened anxiety. The 400-ppm group exhibited lowest grooming frequency and duration (P < 0.001), possibly indicating less anxiousness. Working memory errors increased with serum TBARS concentrations (R² = 0.26; P = 0.033). In conclusion, higher dietary vitamin E concentrations reduced anxious behaviors, but did not alter MLP and was correlated with increased OS. These results suggest high concentrations of dietary vitamin E are not beneficial for rat welfare.