Chapter 26 Human brain cholinergic pathways

This chapter describes the human brain cholinergic pathways. Acetylcholine is one of the most ubiquitous neurotransmitters in the mammalian central nervous system. Neuroanatomical experiments described in the chapter indicate that the cholinergic innervation of a given brain structure can be intrinsic or extrinsic. The innervation of the striatum is almost exclusively intrinsic and arises from cholinergic interneurons. In contrast, the cholinergic innervations of limbic structures, neocortex, thalamus, and superior colliculus are predominantly extrinsic. In the rodent, as much as a third of presynaptic cholinergic markers in the cerebral cortex originates from choline acetyltransferase (ChAT)-positive interneurons. Such putatively cholinergic interneurons may also exist in the fetal primate brain. The major cholinergic innervation for limbic structures and neocortex arises from four groups of cholinergic neurons in the basal forebrain: for the thalamus from two cholinergic cell groups in the pontomesencephalic brainstem, for the interpeduncular nucleus from the medial habenula, and for the superior colliculus from the parabigeminal nucleus. In addition to these major pathways, there are also lesser cholinergic projections from the basal forebrain to the striatum, thalamus, and the interpeduncular nucleus; from the pontomesencephalic cell groups to the cerebral cortex and the superior colliculus; and from the parabigeminal nucleus to the thalamus.