Presynaptic action of acetylcholine in thin sections from the guinea pig dentate gyrus in vitro.

Effects of acetylcholine (Ach) upon electrical activities of the dentate gyrus were studied in vitro in thin sections prepared from the guinea pig brain. In the presence of physostigmine, Ach suppressed the potential evoked by direct stimulation in the slice including the intact granule cell layer, but it was without effect upon the potential elicited in the slice consisting of the molecular layer alone. The threshold concentration to cause such suppression was about 1 × 10−7m. Atropine blocked the action of Ach. The effects of atropine could not be removed by repeated washing of the slice. The suppressing effects of Ach were observed in the Cl-deficient medium. The single neuron discharge elicited in the granule cell by direct stimulation was suppressed during perfusion with the medium containing Ach, but the spontaneous neuron discharge was induced by Ach. From these findings, it was concluded that Ach affected the presynaptic terminals making synapses with the granule cell soma and proximal dendrites, while the synaptic terminals making synapses with the distal portion of the dendrites were free from the action of Ach.