Altered Plasticity in Hippocampal CA1, But Not Dentate Gyrus, Following Long-Term Environmental Enrichment

Michael J. Eckert, David K. Bilkey, Wickliffe C. Abraham
2010 Journal of Neurophysiology  
Eckert MJ, Bilkey DK, Abraham WC. Altered plasticity in hippocampal CA1, but not dentate gyrus, following long-term environmental enrichment. Exposure to an enriched environment can improve cognitive functioning in normal animals as well as in animal models of neurological disease and impairment. However, the physiological processes that mediate these changes are poorly understood. Previously we and others have found changes in hippocampal synaptic transmission and plasticity after 2-4 wk of
more » ... after 2-4 wk of enrichment although others have not observed effects. To determine whether long-term enrichment produces more robust changes, we housed rats continuously in an enriched environment for a minimum of 3 mo and then tested for effects on hippocampal physiology in vitro and in vivo. Enriched housing improved spatial learning compared with social and isolated housing, but surprisingly this was not accompanied by changes in basal synaptic transmission in either CA1 or the dentate gyrus as measured either in vitro or in vivo. This lack of change may reflect the operation of homeostatic mechanisms that keep global synaptic weights within a narrow range. In tests of synaptic plasticity, the induction of long-term potentiation was not changed in either CA1 or the dentate gyrus. However, in CA1 of enriched rats, there was less long-term depression in stratum radiatum, less depotentiation in stratum oriens, and altered paired-pulse inhibition of population spikes evoked in stratum oriens. These effects suggest that there are altered synaptic and network dynamics in hippocampal CA1 that contribute to the enrichment-related cognitive improvement. Downloaded from FIG. 6. In vivo measures of synaptic transmission and plasticity. Input-output curves showed no differences in basal synaptic transmission (A) and excitability (B) between enriched and control rats. HFS (4 ϫ 5 trains) induced similar amounts of LTP in each group for both the fEPSP (C) and population spike (D). There was a tendency for the fEPSP of enriched rats to decay faster (C), but this was not statistically significant. EFFECTS OF LONG-TERM ENRICHMENT ON HIPPOCAMPAL FUNCTION
doi:10.1152/jn.01037.2009 pmid:20393057 fatcat:3meowbol4zfyflscwfoy7fco7m