Acetylcholine as an Excitatory and Inhibitory Transmitter in the Mammalian Central Nervous System

Abstract

Publisher Summary This chapter discusses the muscarinic actions of acetylcholin (ACh) in the hippocampus and thalamus. Using intracellular techniques and in vitro slice preparation of the hippocampus, it was confirmed that the earlier work, which shows the excitatory action of acetylcholine on cortical neurones to be slow in onset. The depolarization, which occurs during the increase in excitability, is a hyperbolic function of the substantial increase in membrane resistance, which always accompanies these changes, as could be predicted if the change were mediated by a decrease in potassium conductance. In the feline thalamus it is shown, by the use of extracellular recording techniques and micro-iontophoresis, that both acetylcholine and electrical stimulation of a putative cholinergic pathway from the midbrain reticular formation have an inhibitory action on almost every cell encountered in the nucleus reticularis. A few millimeters away, in the ventrobasal complex, the opposite effect occurs and every cell is excited. These two opposing actions of acetylcholine seem to be equally important as mediators of the increase in synaptic efficiency, which accompanies arousal.