Involvement of M2 receptor in an enhancement of long-term potentiation by carbachol in Schaffer collateral-CA1 synapses of hippocampal slices.

We examined effects of carbachol (CCh), muscarinic receptor agonist, on long-term potentiation (LTP) of field excitatory postsynaptic potential (fEPSP) at Schaffer collateral-CA1 synapse of guinea pig hippocampal slices using extracellular recording technique. Application of 0.1 microM CCh to the slices significantly augmented the magnitude of LTP without significant change in the amplitude of pretetanus fEPSP. The enhancement of LTP by 0.1 microM CCh was significantly attenuated by 0.1 microM AF-DX 116, M2 receptor antagonist, but not by 0.1 microM pirenzepine, M1 receptor antagonist. Ten micromolar of carbachol reduced the amplitude of pretetanus fEPSP, while the magnitude of LTP was significantly larger than that in control slices to which tetanus was applied in a stimulus intensity producing pretetanus fEPSPs with an amplitude comparable to those during administration of 10 microM CCh. Neither 0.1 microM pirenzepine nor 0.1 microM AF-DX 116 had significant effect on the enhancement of LTP by 10 microM CCh. These results suggest that the induction of LTP at Schaffer collateral-CA1 synapse was enhanced through the activation of M2 receptors by CCh at a lower concentration.