1.16. Input-output Organization in the Basal Forebrain
(Fig.1.16-1) illustrates schematically the mode of termination of different afferents on corticopetal cholinergic forebrain neurons (red neuron in the center). Only those neurons and connections are included here that have been cross-correlated on the basis of anatomic, fine structural and immunocytochemical identification of the same elements. Note that afferents to cholinergic neurons selectively innervate different portions of the neuron. Amygdala (Zaborszky et al., 1984), noradrenergic (Zaborszky et al., 1993; Zaborszky and Cullinan, 1995) and lateral hypothalamic (Zaborszky and Cullinan, 1989) axons terminate on distal dendrites. Somatostatin, NPY (Zaborszky, 1989 and in preparation), GABAergic (Zaborszky et al., 1986, Ingham et al., 1988; Zaborszky and Cullinan, 1992), medial preoptic (Cullinan and Zaborszky, 1991) and dopaminergic (Gaykema and Zaborszky, 1995) axons innervate predominantly the cell body and proximal dendrites of cholinergic neurons. Corticofugal axons terminate on non-cholinergic neurons in the basal forebrain (Zaborszky et al., 1995), most likely on somatostatin and parvalbumin-containing neurons. GABAergic neurons receive cholinergic (Zaborszky et al., 1986) and dopaminergic terminals (Gaykema and Zaborszky, 1995). The intracortcial circuitry data are from the studies of Freund and Gulyas (1991), Freund and Meskenate (1992) and Beaulieu and Somogyi (1991). At present, no direct data exist that the same dopaminergic neuron terminate on different cell types in the basal forebrain as well as in the prefrontal cortex. Inhibitory neurons and their synapses are drawn with full black, excitatory neurons with open symbols. The synapses of dopaminergic neurons are indicated with a minus sign within an open circle.