Involvement of M(2) 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 mu M 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 mu M CCh was significantly attenuated by 0.1 mu M AF-DX 116, M(2) receptor antagonist, but not by 0.1 mu M pirenzepine, M(1) 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 mu M CCh. Neither 0.1 mu M pirenzepine nor 0.1 mu M AF-DX 116 had significant effect on the enhancement of LTP by 10 mu M CCh. These results suggest that the induction of LTP at Schaffer collateral-CA1 synapse was enhanced through the activation of M(2) receptors by CCh at a lower concentration. (C) 1997 Elsevier Science Ireland Ltd.