Afferent projections to the rat locus coeruleus demonstrated by retrograde and anterograde tracing with cholera-toxin B subunit and Phaseolus vulgaris leucoagglutinin

Luppi P.H., Aston-Jones G., Akaoka H., Chouvet and Jouvet M.
Neuroscience (1995) Vol:65 Tome:1 pp:119-160


Material and methods


I. Cytoarchitecture of the locus coeruleus area

II. Afferent projections to the locus coeruleus

A) Retrograde tracing experiments

B) Anterograde tracing experiments




I. Cytoarchitecture of the Locus Coeruleus area

The cytoarchitecture of the LC area has been described previously 25, 53, 60, 66. Nevertheless, in the course of our study of LC afferents, we found additional undefined landmarks in this area. To study the organization of the LC area, 20µm frontal LC sections taken every 100µm from control rat brains were stained with neutral red and mounted in rostro-caudal order. At its more caudal tip, the LC is separated medially from the fourth ventricle by a 30µm thick cell poor lamina and the 20 µm thick ependyma. Laterally and ventrally, the nucleus is bordered by the MVe. Dorsally, the LC is bordered by the brachium conjunctivum (Fig. 2F) . Slightly rostrally, the medially located cell poor lamina is thicker (approximately 100µm) and the 5Me appears laterally. At this level, the 5Me is separated from the LC by an area containing few cells in white matter (Fig. A HREF="../figures/fig2b.php">2B) that appears to be a rostral extension of the MVe. Slightly more rostrally, at the level of the maximum extension of the LC, this region becomes thinner and the 5Me is very close to the lateral border of the LC. Medially, the LC is separated from the ventricle by a large undefined area that appears to be part of the pontine periaqueductal gray. At this level and more rostrally, the LC is bordered dorsally by the medial parabrachial nucleus (Fig. 3C). More rostrally, the ventral part of the LC progressively becomes less compact and then disappears and only a dorsal collection of LC cells remains (Fig. 3C). Ventral to them, two groups of cells appear with a morphology distinct from the adjacent periaqueductal gray. One is located just ventral to the few LC cells and medial to the 5Me and is composed of small ovoid cells. The second is located more medially and ventrally and is composed of slightly larger ovoid cells. The first group has not been previously defined. Therefore, because of its localization just medial to the 5Me, we denote this as the Peri-5Me nucleus (Fig. 3C). The second group of cells corresponds to t he previously defined Barrington's nucleus (Bar) 8,59. With regard to the LC noradrenergic neurons, it is noteworthy that a large number of processes (apparently dendrites) were found outside the nuclear core of the LC in select peri-LC regions, particularly in the lamina between the LC and the fourth ventricle and also in the a reas rostromedial and caudodorsal to the LC nucleus proper. Note that LC dendrites did not appear to be extensive lateral to the LC nucleus proper. This topographically specific distribution of presumed LC dendrites is similar to that previously reported in a more extensive analysis 22,61.

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