SYNAPTIC NUMBERS ACROSS CORTICAL LAMINAE AND COGNITIVE PERFORMANCE OFTHE RAT DURING AGING

In this study, we have investigated the changes in the number of indiv idual presynaptic boutons in the neocortex of rats and correlated them with cognitive performance. Brown Norway x Fischer 344 F-1 hybrid rat s, aged from one to 24 months, were used. Using synaptophysin as a mar ker for presynaptic boutons, we found that in the parietal II region o f the neocortex an age-related decrease in the density of immunostaine d punctae representing presynaptic boutons occurred. Regression analys is showed that this decline in the number of presynaptic boutons corre lates with ageing (r=0.495, P<0.05). Interestingly, we found that this age-related depletion of presynaptic boutons was more intense in the deeper cortical lamina, such as laminae V and VI (mean decrease of 18% ), than in the superficial laminae (mean decrease of 8% in laminae I-I V). Using the Morris water maze test, we observed that young rats acqu ired the task at twice the speed of aged animals (48.9 +/- 9.0 s and 9 1.0 +/- 4.9 s for young and aged animals, respectively). Furthermore, at the end of the training period, the aged cohort still showed signif icantly higher escape latencies in the Morris water maze. The present findings support the concept that the decline in cognitive performance s in ageing is related to the loss of synapses in the cerebral cortex. (C) 1998 IBRO. Published by Elsevier Science Ltd.