DECREASE IN HIGHLY POLYSIALYLATED NEURONAL CELL-ADHESION MOLECULES AND IN SPATIAL-LEARNING DURING AGING ARE NOT CORRELATED

Age-dependent spatial memory impairments have been related to a declin e in hippocampal plasticity. Highly polysialylated neuronal cell adhes ion molecules (PSA-NCAM) show a strong expression during adulthood wit hin regions associated with neuroplastic events. Furthermore, NCAM mol ecules have been proposed to mediate neuronal plasticity during learni ng and memory. The aim of the present study was to examine the effect of ageing on the expression of PSA-NCAM within the hippocampus. To inv estigate whether age-dependent changes in expression of PSA-NCAM were accentuated in aged rats with learning impairment, animals were in a f irst step assessed for their cognitive abilities using a Morris water maze. Seven-month-old and 24-month-old rats were tested for their perf ormance in the Morris water maze. The animals were sacrificed and brai n sections were processed for PSA-NCAM immunohistochemistry. Ageing wa s accompanied by an overall decrease in PSA-NCAM-immunoreactivity (-IR ) within the forebrain, presenting a important decrease of the number of PSA-NCAM-IR perikarya within the hippocampus. These results were co nfirmed by Western blot analysis. No difference in PSA-NCAM immunoreac tivity was observed in aged rats with or without spatial learning impa irment. It is concluded that although changes in PSA-NCAM accompanied the decrease in cognitive abilities, our data did not evidence a causa l relationship between these two parameters.