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Enriched Environment Overcomes Genetic Deficits

If genetic damage is targeted at the hippocampus, which is an important locus for nonspatial memory, can anything mitigate memory deficits? Using recombinant DNA technology, these researchers created mice that were unable to express an N-methyl-D-aspartate receptor (NMDAR1), which is a subunit of the glutamate receptor, in the CA1 region of the hippocampal formation. This glutamate receptor subtype, which mediates long-term potentiation throughout the brain, plays an essential role in learning and memory.

The CA1-knockout mice exhibited profound impairments in object recognition, olfactory discrimination, and contextual fear memory. However, when the knockout mice were exposed for 3 hours daily for 2 months to an enriched environment containing frequently changed toys, running wheels, and small houses (compared with the standard plastic cage), the mice showed significant improvement in their nonspatial memory and performed as well as control mice on certain tasks. Electron microscopic analysis revealed that the environmental enrichment increased the density of synapses in the CA1 region of the hippocampus in the knockout mice.

Comment: This study provides additional evidence for the important role of experience in optimizing cognitive functions. It is particularly striking that the enriched environment could overcome a genetically targeted disruption of a synaptic process thought to be essential for memory. Thus, the results suggest that an enriched environment causes the brain to exploit other synaptic mechanisms that circumvent the genetic defect. The findings are reminiscent of reported increases in IQ that have been observed in patients with Down's syndrome after de-institutionalization and early intervention.

— J Coyle

Published in Journal Watch Psychiatry April 1, 2000

Citation(s):

Rampon C. Enrichment induces structural changes and recovery from nonspatial memory deficits in CA1 NMDAR1-knockout mice. Nat Neurosci 2000 Mar 3 238-244.

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