EFFECT OF AGING ON CORTICAL SPREADING DEPRESSION

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 t he 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 r ats were divided into two groups: one group was fed a commercial lab c how diet (CD) containing 22% protein (N = 47), and the other was fed a 22% casein diet (GAS; N = 18). SD was elicited on the frontal cortica l surface by 1-min application of 2% KCl and its appearance was record ed (ECoG and DC potential) at two points in the parieto-occipital area of the same hemisphere. SD propagation velocity was measured on the b asis of the time spent for an SD ''wave'' to cross the distance betwee n the two recording points. Within the age range studied, older animal s displayed significantly lower SD velocities than the younger ones, i ndependent 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 case s). As a rule, at each time point the gerbils presented higher SD velo cities than the rats of the same age. In another set of experiments, i n order to test the role of free radicals in SD, 7 gerbils (14-51 mont hs old) and 13 W rats (3-24 months old) were fed a 22% casein diet fre e of the antioxidant vitamins C and E for 4-6 weeks before the experim ents. No correlation was found between age and SD propagation in these animals fed a diet free of vitamins C and E, although gerbils display ed higher SD velocities than age-matched rats (velocities: G, 3.70-5.3 4; 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 vel ocity in the animals fed a diet free of antioxidant vitamins suggests a possible role of free radicals in cortical SD, in accordance with ev idence from other laboratories obtained in the isolated retina.