Muscarinic inhibitory effect in the guinea pig dentate gyrus in vitro.

Various drugs known to affect synaptic transmission were tested for their effects on extracellular field potentials evoked in the dentate granule cell layer of guinea pig hippocampal slices. Presumptive commissural (CF) and perforant path (PP) fibers were stimulated electrically by two separate pairs of stimulating electrodes. CF stimulation elicited a field potential with a current sink and PP stimulation with a current source in the cell layer. Bath-applied carbachol (0.5-10 microM), in an atropine sensitive manner, depressed the CF-evoked field potential, but left the PP-evoked field potential unchanged. Further pharmacological testing revealed that this effect is likely to be mediated by inhibitory neurons in the dentate hilus.