EFFECT OF VITAMIN-B-6 DEFICIENCY ON GLUTAMIC-ACID DECARBOXYLASE ACTIVITY IN RAT OLFACTORY-BULB AND BRAIN

The effect of dietary vitamin B-6 deficiency on L-glutamic acid decarboxylase (GAD) activity in the olfactory bulb and whole brain of young growing rats was measured. Male Charles River CD albino rats of similar age (23 days) and weight (40 to 50 g) were divided into three dietary groups: one was fed a purified control diet (2 mg pyridoxine Δ HCl/100 g diet) ad libitum (C); the second group (D) was fed an identical diet deficient in vitamin B-6 (15.3 μg pyridoxine Δ HCl/100 diet); the third group (R) was fed the control diet in restricted amounts, paired to the average amount consumed by D. After 102 days of feeding the respective diets, some of the D rats were repleted by injecting (ip) 10 mg pyridoxine α. HCl and subsequently feeding the control diet ad libitum for varying lengths of time. By measuring GAD activity with and without added pyridoxal phosphate (PLP) in the assay medium, it was shown that the reduced GAD activity in the olfactory bulb and whole brain tissues of D (approximately 50% of the control values) was due to cofactor depletion and not to a decreased synthesis of GAD protein. Although body weight was decreased by feeding restricted amounts of the control diet, none of the other parameters (olfactory bulb and whole brain GAD activity, serum glutamic oxalacetic transaminase (GOT) activity, urinary xanthurenic acid excretion) for R were significantly different from C. GAD activity measured without added PLP in the olfactory bulb and whole brain of D, as well as serum GOT activity and urinary xanthurenic acid excretion were affected after 5 days of feeding. The mean body weight of D was significantly lower than R after 2 weeks of feeding. Repletion quickly returned GAD activity in olfactory bulb and whole brain, serum GOT activity, and urinary xanthurenic acid excretion to control values. Body weights of the repleted rats increased dramatically and reached the mean weight of R. It was concluded that the GAD activity of the olfactory bulb and of the whole brain respond similarly to dietary vitamin B-6 deficiency.