Organization of central cholinergic systems

This chapter provides an update and overview of the anatomy of central cholinergic systems, and discusses some areas about which controversy and uncertainty still exist. Cholinergic neurons in the basal forebrain are distributed across several classically defined nuclei, including the medial septa1 nucleus, the nucleus of the diagonal band of Broca (vertical and horizontal limbs), the magnocellular preoptic area, the substantia innominata, and the globus pallidus. Many laboratories have studied the anatomy of these magnocellular neurons and there appears to be widespread agreement about their distribution in the basal forebrain. On the basis of connectivity patterns, the cholinergic neurons in the basal forebrain can be subdivided into four groups. Chl and Ch2 represent cholinergic neurons within the medial septal nucleus and the vertical limb of the diagonal band and provide the major source of cholinergic afferents to the hippocampus. Ch3 is contained primarily within the lateral part of the horizontal limb of the diagonal band, including the magnocellular preoptic area, and is the major source of cholinergic activity in the olfactory bulb. Ch4 consists of cholinergic neurons that are defined by the fact that they project to the neocortical mantle.