FREE RADICAL-INDUCED ELEVATION OF ORNITHINE DECARBOXYLASE ACTIVITY INDEVELOPING RAT-BRAIN SLICES

Objective. In developing brain, we have previously shown both in vivo [L.D. Longo, S. Packianathan, J.A. McQueary, R.B. Stagg, C.V. Byus and C.D. Cain, Acute hypoxia increases ornithine decarboxylase activity a nd polyamine concentrations in fetal rat brain, Proc. Natl. Acad. Sci. USA, Vol. 90 (1993) 692-696] and in vitro [S. Packianathan, C.D. Cain , B.H. Liwnicz and L.D. Longo, Ornithine decarboxylase activity in vit ro in response to acute hypoxia: a novel use of newborn rat brain slic es, Brain Res., Vol. 688 (1995) 61-71] that acute hypoxia is associate d with a significant increase in ornithine decarboxylase (ODC) activit y and polyamine concentrations. We tested the hypothesis that oxygen f ree radicals induce an increase in ODC activity similar to that of hyp oxia and that both this and the hypoxia-induced response are inhibited by free radical scavengers. Materials and methods. Slices of cerebrum , 300-500 mu m thick, were made from P3 newborn Sprague-Dawley rat pup s and equilibrated for 1 h in artificial cerebrospinal fluid continuou sly bubbled with 95% O-2/5% CO2. Free radical-induced ODC activity res ponse was measured beginning after a I-h recovery period. Experiments were performed on slices treated with 5 x 10(-7) M xanthine (X) + 10 m U/ml xanthine oxidase (XO), with or without the free radical scavenger s superoxide dismutase (SOD; 100 U/ml), catalase (CAT; 700 U/ml) or gl utathione peroxidase (GPX; 3 U/ml). We also quantified slice malonalde hyde concentrations in response to hypoxia (21% O-2/5% CO2/74% N-2). R esults. Under control conditions, ODC activity was stable during the 2 -h post-recovery period. In response to X/XO treatment, ODC activity i ncreased 2.3-fold at 1.5 h post-recovery. In examining ODC activity as a function of xanthine dose, we noted that ODC activity increased in response to 2.5 x 10(-7) M xanthine; however, it decreased in response to 7.5 x 10(-7) M or higher concentrations. Free radical-induced ODC activity was significantly decreased by addition of the free radical s cavengers, SOD, CAT or GPX. In addition, the hypoxic-induced increases in ODC activity and malonaldehyde concentration was also eliminated b y the addition of SOD with CAT. Conclusions. (1) Oxygen free radicals, particularly hydroxyl radical (OH), appear to trigger an induction of ODC activity in newborn rat cerebrum slices. (2) Oxygen free radicals also appear to mediate the hypoxic-induced increase in ODC activity. (3) Any consequent increase in polyamine synthesis may have profound e ffects on neurogenesis and neurodifferentiation in the developing brai n. (C) 1997 Elsevier Science B.V.