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, o n long-term potentiation (LTP) of field excitatory postsynaptic potent ial (fEPSP) at Schaffer collateral-CA1 synapse of guinea pig hippocamp al slices using extracellular recording technique. Application of 0.1 mu M CCh to the slices significantly augmented the magnitude of LTP wi thout significant change in the amplitude of pretetanus fEPSP. The enh ancement 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 pirenzepin e, M(1) receptor antagonist. Ten micromolar of carbachol reduced the a mplitude of pretetanus fEPSP, while the magnitude of LTP was significa ntly larger than that in control slices to which tetanus was applied i n a stimulus intensity producing pretetanus fEPSPs with an amplitude c omparable to those during administration of 10 mu M CCh. Neither 0.1 m u M pirenzepine nor 0.1 mu M AF-DX 116 had significant effect on the e nhancement of LTP by 10 mu M CCh. These results suggest that the induc tion of LTP at Schaffer collateral-CA1 synapse was enhanced through th e activation of M(2) receptors by CCh at a lower concentration. (C) 19 97 Elsevier Science Ireland Ltd.