At the cellular level, cholinergic agonists enhance LTP of glutamatergic association fibers in the piriform cortex and Schaeffer collaterals in the CA1 region of the hippocampus (Huerta and Lisman, 1993). In contrast, M3 mAChRs facilitate long term depression (LTD) of synapses in the monocular area of superficial visual cortex (Kirkwood et al., 1999; McCoy and McMahon, 2007). Surprisingly, the same authors observed enhanced LTP in binocular cortex (McCoy et al., 2008). These regional differences indicate that cell-specific expression of different receptor subtypes is critical for the varied actions of ACh.
