Enriched environment exposure alters the input-output dynamics of synaptic transmission in area CA1 of freely moving rats

We examined in freely moving animals whether EE exposure directly alters synaptic transmission in CA1 of the hippocampus. Adult male Sprague-Dawley rats were chronically implanted with recording and stimulating electrodes in CA1 and housed singly in standard cages. After stable recordings were established for field excitatory postsynaptic potentials (fEPSPs), the effects of three levels of environmental enrichment for 19 days were assessed. A change in fEPSPs was observed only after repeated overnight enriched environment exposure, such that response potentiation occurred at high stimulus intensities but a reduced response was evident at low stimulus intensities. Behavioural tests confirmed that EE exposure was sufficient to facilitate performance on spatial working memory tasks. These results suggest that overnight EE exposure refines the dynamics of CA1 synaptic transmission in a way that may contribute to augmented information processing and thus performance on hippocampus-dependent tasks.