An autoradiographic, semistereotaxic mapping of major projections from locus coeruleus and adjacent nuclei in Macaca mulatta

The autoradiographic method was used to trace projections from the monkey locus coeruleus (LC) and adjacent nuclei (nn. parabrachiales, n. tractus mesencephalicus nervus trigemini, substantia grisea centralis). Pathways attributed to LC are presented diagrammatically in a set of 26 coronal sections. They include a descending pathway along the tractus tegmentalis centralis, a caudal pathway entering the corpus medullaris cerebellaris via the lateral wall and roof of ventriculus quartus, and an ascending pathway along the tractus tegmentalis centralis giving off branches to the commissura posterior, tractus habenulo-interpeduncularis, centrum medianum and n. ventralis posteromedialis thalami, fasciculus lenticularis, lamina medullaris thalami lateralis, capsula interna, commissura supraoptica dorsalis, tractus supraoptico-hypophyseus, stria terminalis, laminae medullaris interna and medialis and pars interna of globus pallidus, corpus subfornicale, capsula externa, stria longitudinalis, cingulum, and gyrus rectus. A contribution to the branches entering n. ventralis posteromedialis thalami and the commissura supraoptica dorsalis was attributed to the nn. parabrachiales. Axons entering trigeminal structures via the tractus mesencephalicus nervus trigemini were attributed to labeling of cells in the nucleus of that tract. Terminal areas attributed to labeling of LC axons were evident in decreasing order of density in the bed nucleus of stria terminalis, substantia innominata, nn. amygdalae anterior, centralis and basalis (dorsal portion), nn. paraventricularis, supraopticus and dorsomedialis hypothalami, and n. antero-ventralis thalami.