Bidirectional modulation of long-term potentiation by novelty-exploration in rat dentate gyrus.

Previous studies have shown that exploration of a novel environment reverses hippocampal long-term potentiation (LTP). Here we demonstrate a bidirectional modulation of LTP measured in the dentate gyrus of freely moving rats by means of novelty exploration. A transient form of LTP lasting about 6 h was induced in perforant path-granular cell-synapses by a weak tetanization protocol (three bursts of 15 pulses at f=200 Hz). LTP was reversed when non-restricted exploration of a novel environment started 2 min after LTP induction. In contrast, using the same interval and limiting the exploration duration to 1 min led to LTP-prolongation. Furthermore, LTP-reinforcement was also obtained when a not-restricted exploration started within 2 min before tetanization. The observed interplay of LTP-impairing and -enhancing factors may be relevant for the modulation of memory formation by novelty.