Enriched Environmental Housing Conditions and Hippocampal Structures of Aged Rats

Ageing comprises a number of physiological modifications, including structural changes. Hippocampal information processing can deteriorate during normal ageing in the absence of significant neuronal loss. These findings imply that a circuit-specific pattern of variability in the connectional organization of the hippocampus is coupled to individual differences in the cognitive outcome of normal ageing. We addressed the question how enriched environment influences hippocampal structures in aged rats. We used 19 hybrid Fischer 344* Brown Norway rats (FBNF1 rats) of following ages: 3 months (3 animals as controls), 36 months (16 animals divided into 8 animals housed in standard environment and 8 animals housed under enriched living conditions during the last three months of their life) to investigate alterations of glial fibrillary acidic protein (GFAP), extracellular matrix protein as revealed by Wisteria floribunda agglutinin (WFA), neurofilaments (SMI-32 and MAP2), the presynaptic vesicle protein synaptophysin and the calcium-binding protein calretinin. GFAP showed a complementary distribution pattern to WFA binding sites. With progressing age (12–36 months), a strong increase of gliosis occurred, whereas a concomitant, area-specific loss of WFA binding sites was found especially in the CA1 region. The loss of extracellular matrix protein and the reduction of SMI-32 were in part reduced or prevented by housing the animals under enriched environmental conditions between 33–36 months of age. Synaptophysin was nearly lost in CA3 in the control rats. Calretinin which labeled the CA2 region exclusively displayed a small reduction only. Taken together we found area-specific both age-related and environment-dependent alterations in the hippocampus of aged rats.