Our previous studies demonstrate that exposure to a novel environment during induction of the medial perforant path-dentate gyrus (DG) synapse in freely-moving rats increases the probability, magnitude and longevity of LTP (Davis-Hart, SFN, 1997).Our studies also indicate this facilitation effect is independent from general arousal, ongoing theta rhythm, ambulation, or increases in brain temperature (Davis-Hart, SFN, 1998,1999). However, prior exposure to novel stimuli reduces the facilitation (Davis-Hart, SFN, 1999), suggesting that facilitation was dependent on novel stimuli within the environment. Exploration increases several neuromodulators in the hippocampus, including norepinephrine and acetylcholine, which are known to produce physiological states conducive to LTP induction. We therefore examined whether noradrenergic or cholinergic systems are involved in novelty-induced facilitation of LTP. Perforant path-DG responses were collected daily for 1 week in the home cage. Following collection of stabl...