The characteristics of ACh release from different brain regions as described in this review strongly confirm th hypothesis that ACh is a neurotransmitter in the CNS as other experimental approaches, such as microiontophoretic investigations and biochemical experiments, have also suggested. The central cholinergic pathways are a diffuse system ascending to the cortex, which can be stimulated through the mesencephalic reticular formation and is associated with but not identical to that subserving EEG and behavioural arousal; a diffuse system ascending to the cortex and originating from or passing through the septum, as shown by the effect of septal stimulation and of septal lesions; a diffuse intracortical system as shown by the release from chronic and acute cortical slabs. Other cholinergic systems can be found in cholinergic synapses in the caudate nucleus which can be activated by a number of stimulatory conditions. Their role should be considered in the light of the large amount of physiological and pharmacological information concerning the caudate nucleus. The demonstration of ACh release from thalamic nuclei from the hypothalamus and from the medulla illustrates the involvement of ACh in many nervous pathways, but these are only starting points for further investigation. Studies on ACh release in the spinal cord give final confirmation of the already known cholinergic nature of the synapses between the motor axon collaterals and the Renshaw cells.
Pepeu, G. (1973). The release of acetylcholine from the brain: An approach to the study of the central cholinergic mechanisms. Progress in Neurobiology, 2(PART 3), 259–288. https://doi.org/10.1016/0301-0082(73)90009-9