ABSTRACT
Electrophysiological effects of acetylcholine (ACh) on brain neurons have been the subject of a multitude of investigations for more than three decades. Acetylcholine influences neuronal activity via nicotinic or muscarinic receptors and the result can be enhancement of excitability to other transmitters, depolarization and initiation of action potentials, or inhibition. Neurons in the thalamic relay nuclei, reticular nucleus of the thalamus, somatosensory cortex, and visual cortex have received most attention concerning the actions of ACh. Iontophoretic application of acetylcholine to medial and/or lateral geniculate neurons in vivo can result in either increases or decreases in firing rate. Acetylcholine appears to exert excitatory influences on a variety of thalamic relay neurons primarily via muscarinic receptors but also via nicotinic receptors. The perigeniculate nucleus in the cat represents the visual segment of the thalamic reticular nucleus. Application of ACh to hippocampal pyramidal neurons elicits a slow excitation mediated by muscarinic receptors.
