FS STRESS INDUCES LONG-LASTING MEMORY FACILITATION - INVOLVEMENT OF CHOLINERGIC PATHWAYS

We tested in vivo the hypothesis that foot-shock (FS) stress-induced p rolongation of latencies in the one-trial step-through passive avoidan ce learning task in mice occurred through a long-term facilitation pro cess. Whereas behavioral responses in control mice lasted for 24 h, de creasing progressively in the subsequent days, FS-stress exposure for 15 min before training (pretraining), immediately after training (post training), or 15 min before the test (pretest) resulted in a profound and sustained enhancement of test latencies that lasted for at least 9 6 h. These facilitating effects disappeared when FS exposure was deliv ered with a 2- or 3-h difference with respect to the training trial. S copolamine (Scop) (1 mg/kg, intraperitoneally) 30 min before the train ing session caused impairment of test latencies in control and pretest stressed animals, but failed to affect both pre- and posttraining FS stress-induced enhancement. Our working hypothesis is that FS stress m ay increase the levels of acetylcholine in the presynaptic terminal or the firing rate of cholinergic input. Animals pretreated with FS stre ss daily for 1 or 4 days followed by the acute schedule described abov e showed no enhancements of test latencies. Pretraining Scop impaired test latencies in pre- and posttraining and pretest stressed animals, suggesting that unpredictability is a critical factor in activating be havioral long-term facilitation.