[Influence of combined vitamin deficiency on unconditioned reflexes and learning in growing rats]

The aim of this study was to investigate the effect of combined deficiency of all vitamins on the manifestation of unconditioned reflex and learning (in response to an electric current) in growing Wistar rats with initial body weight 53.4 ± 1.2 g (45.5-62.0 g). 20 of 46 tested male rats (latent period of transition from the illuminated chamber to the dark compartment did not exceed 60 s) were included in the experiment. Rats were randomly divided into 2 groups (control and experimental) for the duration of the latent period and body mass. Within 23 days the rats of the control group received a complete semisynthetic diet. Combined vitamin deficiency in tested rats was caused by 5-fold diet decrease of the amount of vitamin mixture without vitamin E. On the 12th day the second phase of testing was performed, during which the rat received electrocutaneous irritation on paws (current 0.4 mA, 8 seconds) after transition to the dark compartment of the chamber. Preservation of the conducted reflex was performed 24 h and 9 days after training. On the 23rd day pre-anesthetized with ether rats were taken out from the experiment by decapitation. The content of vitamin A (retinol and retinol palmitate) and E (tocopherols) in plasma and liver and in the sunflower oil was analyzed by HPLC, the level of vitamins B1 and B2 in liver and casein by fluorimetric method, blood serum malondialdehyde content--by spectrophotometric method. Reducing of vitamin mixture amount of the diet lead to significant reduction in liver vitamin A, E, B1, and B2 level and in blood plasma vitamin A and E concentration by the end of the experiment, but had no effect on blood plasma MDA concentration. On the 12th day of vitamin deficiency in rats manifestation of unconditioned reflex (photophobia) has been deteriorated, as evidenced by the significant 3,2-fold increase of latent period of transition to the dark compartment compared with animals fed a complete diet (47.8 ± 15.8 vs 14.8 ± 3.6 sec), but their ability to learn hadn't been effected. Based on the data that vitamin deficiency, especially of vitamin-antioxidants, causes oxidative stress, and that increase of corticosterone level in hippocampus during aging significantly inhibits the function of the brain, we can assume that increasing of corticosterone level may be one of the cause of the detected cognitive impairment, as isolated vitamin A deficiency in rats increases tissue corticosterone levels.