The caudal sublenticular region/anterior amygdaloid area is the only part of the rat forebrain and mesopontine tegmentum occupied by magnocellular cholinergic neurons that receives outputs from the central division of extended amygdala

Ascending cholinergic projections and the central nucleus of the amygdala (CeA) have both been implicated in attentional and orienting mechanisms leading to adaptive behavioral responses. In view of this, the present study was carried out to identify relevant neuroanatomical relationships in the form of projections from the CeA and a related structure, the dorsolateral divison of the bed nucleus of the stria terminalis (dlBST), to parts of the basal forebrain and mesopontine tegmentum that contain magnocellular cholinergic neurons. The CeA and dlBST are components of the 'central division of extended amygdala'. Following injections of the anterogradely transported compounds, Phaseolus vulgaris-leucoagglutinin or biotinylated dextran amine, into the CeA or dlBST, sections were processed with immumohistochemical reagents to localize the anterograde tracer and choline acetyltransferase (ChAT). The trajectories of efferent projections from CeA and dlBST were qualitatively similar. Few ChAT-immunoreactive (ir) neurons were present within the extended amygdala or regions containing the dense terminations of its efferent projections, with the striking exception of the caudal sublenticular/anterior amygdaloid region. The ChAT-ir neurons there, however, were significantly smaller and weakly ChAT-ir as compared to those located outside of the dense extended amygdaloid terminations. In the mesopontine tegmentum, the robust downstream projection from the extended amygdala was centered medial to ChAT-ir neurons of the pedunculopontine tegmental nucleus. The differentiated character of the relationships between extended amygdala and forebrain and mesopontine districts containing ChAT-ir neurons that give rise to ascending projections may have significant implications for the control of cortical and diencephalic acetylcholine release and accompanying effects on attention, vigilance and locomotor activation. (C) 2002 Elsevier Science B.V. All rights reserved.