ENVIRONMENTAL ENRICHMENT RESULTS IN HIGHER LEVELS OF NERVE GROWTH-FACTOR MESSENGER-RNA IN THE RAT VISUAL-CORTEX AND HIPPOCAMPUS

Evidence for structural modifications in the brain following environme ntal changes have been provided during the last decades. The most pron ounced alterations following environmental manipulations have been fou nd in the visual cortex. These plastic changes are supposed to reflect reorganization of neuronal connections involved in postnatal developm ent and adult adjustments of connections involved in sensori-perceptua l processing and learning. Potential candidates to mediate these chang es are neurotrophins. Nerve growth factor (NGF) has been associated wi th cognitive functions and shown to improve the performance of aged ra ts in spatial learning and memory tasks. In the central nervous system , NGF is of importance for development and maintenance of cholinergic neurons and atrophy of cholinergic neurons is strongly correlated with learning and memory impairments. Exposure to enriched environmental c onditions improves learning and problem-solving ability and results in plastic changes in the brain. This study examined the effect of envir onmental enrichment on expression of NGF mRNA in the rat visual cortex and hippocampus. Rats housed in groups in a stimulus-rich environment for 30 days had significantly higher levels of NGF mRNA than rats hou sed individually in single cages without stimulus-enrichment. We have recently presented results showing higher levels of neurotrophin-3 (NT -3) mRNA and improved spatial learning following environmental enrichm ent, and suggest that an interplay involving the neurotrophins NGF and NT-3 may be mediating experience-induced structural changes. (C) 1998 Elsevier Science B.V. All rights reserved.