EFFECTS OF CHRONIC NIMODIPINE ON WORKING-MEMORY OF OLD RATS IN RELATION TO DEFECTS IN SYNAPTOSOMAL CALCIUM HOMEOSTASIS

The present study was designed to investigate whether chronic (from 12 to 23 months of age) dietary treatment with the L-type Ca2+ channel b locker nimodipine (30 mg/kg body weight) enhances the cognitive behavi or of aged animals and whether such a treatment would have long-term e ffects on the mechanisms of Ca2+ regulation in synaptic terminals from the aged rat brain. Cognitive behavior was evaluated in an 8-arm radi al maze in 6 test series comprising a total of 105 test sessions, with intervals of no training between series. Nimodipine-treated rats perf ormed better than vehicle-treated, aged matched controls in all the te st series, making more correct choices every time a new series was ini tiated. However, differences between nimodipine- and vehicle-treated r ats were most remarkable in the last three test series, when the rats were 19 to 22 months. In these series 74% of the nimodipine-treated ra ts were able to perform the task in 4 to 9 test sessions whereas only 12%, 14% or none of the control rats learned the task. To study Ca2+ r egulation in synaptosomes derived from cerebral cortex and hippocampus , we analyzed Ca-45(2+) accumulation as well as the levels of the Ca2-binding proteins calbindin-D28K and calreticulin by Western blotting. Nimodipine administration had no effect on hippocampal synaptosomes b ut increased the levels of calbindin-D28K and calreticulin in cerebral cortex preparations. These results indicate that chronic nimodipine t reatment from 12 to 23 months of age prevents age-induced learning def icits without showing any signs of toxicity, and that these effects ar e associated with a small increase in the levels of synaptosomal Ca2+- binding proteins from cerebral cortex. The up-regulation of these prot eins might provide a Link between the long-term effects of nimodipine on gene expression and learning ability in old rats. (C) 1998 Elsevier Science B.V. All rights reserved.