Here, we report that, at CA3-CA1 synapses, a Hebbian form of long-term depression (LTD) induced by muscarinic M1 receptor activation (mLTD) is lost after medial septal lesion.     ///    Sympathetic sprouting drives hippocampal cholinergic reinnervation that prevents loss of a muscarinic receptor-dependent long-term depression at CA3-CA1 synapses.. 