We studied the role of endogenous acetylcholine (Ach) in corticostriatal long-term potentiation (LTP). The muscarinic receptor antagonists scopolamine and pirenzepine fully prevented the induction of LTP suggesting that the activation of Mi-like muscarinic receptors is a crucial event in the conditioning phase of this form of synaptic plasticity. (C) 1999 Elsevier Science Ltd. All rights reserved.