Effect of aging on cortical spreading depression

RESUMO

The effects of aging on spreading depression (SD) were investigated in the Mongolian gerbil (G; age range 1.5 to 58 months; N = 35) and in the albino rat (R; 2.5 to 24 months; N = 100). Two strains of rats were studied: Wistar (W; N = 35) and Sprague-Dawley (SDAW; N = 65). SDAW rats were divided into two groups: one group was fed a commercial lab chow diet (CD) containing 22 per cent protein (N = 47), and the other was fed a 22 per cent casein diet (CAS; N = 18). SD was elicited on the frontal cortical surface by 1-min application of 2 per cent KCl and its appearance was recorded (ECoG and DC potential) at two points in the parieto-occipital area of the same hemisphere. SD propagation velocity was measured on the basis of the time spent for an SD "wave" to cross the distance between the two recording points. Within the age range studied, older animals displayed significantly lower SD velocities than the younger ones, independent of the species, strain or diet (velocity ranges, in mm/min: G, 2.22-5.99; W, 2.47-4.12; SDAW-CD, 2.32-4.42 and SDAW-CAS, 2.65-4.14). The correlation coefficients between age and SD velocity were: G, -0.78; W, -0.45; SDAW-CD, -0.68 and SDAW-CAS, -0.72 (P<0.05 in all cases). As a rule, at each time point the gerbils presented higher SD velocities than the rats of the same age. In another set of experiments, in order to test the role of free radicals in SD, 7 gerbils (14-51 months old) and 13 W rats (3-24 months old) were fed a 22 per cent casein diet free of the antioxidant vitamins C and E for 4-6 weeks before the experiments. No correlation was found between age and SD propagation in these animals fed a diet free of vitamins C and E, although gerbils displayed higher SD velocities than age-matched rats (velocities: G, 3.70-5.34; R, 3.25-4.44 mm/min; correlation coefficients: G, -0.39; W, -0.29; P>0.05). These data indicate that gerbils have higher SD susceptibility than rats of the same age, and that this susceptibility decreases with aging in both species. The lack of correlation between age and SD velocity in the animals fed a diet free of antioxidant vitamins suggests a possible role of free radicals in cortical SD, in accordance with evidence from other laboratories obtained in the isolated retina.