Development of the noradrenergic innervation of the rat hippocampus by the nucleus locus coeruleus was examined immunohistochemically in the roller tube organotypic cultured slice preparation. Slices of rat hippocampus and locus coeruleus were co-cultured on glass coverslips for 2-6 weeks and evaluated for the presence of dopamine-beta-hydroxylase (DBH) and tyrosine hydroxylase (TH) immunoreactive cells and fibers. Large, multipolar DBH- and TH-positive cells were visible within the locus coeruleus; an occasional cell appeared near or just within co-cultured hippocampal tissue and in connecting fiber tracts. DBH-positive cells tended to concentrate near the edges of locus coeruleus tissue. Locus coeruleus slices cultured alone showed little indication of fiber outgrowth in any direction. In co- cultures, however, beaded DBH- and TH-positive fibers were directed toward the hippocampus. The majority of these fibers entered the hippocampus in the hilar/CA3 region and formed extensive collateral branches. Light microscopy suggests that DBH-positive fiber growth was densest at or near the pyramidal cell layer in CA3b and CA3c and in the infragranular region of the dentate hilus. This pattern of noradrenergic innervation of hippocampus by co- cultured locus coeruleus in vitro appears very similar to the pattern established in vivo (see Moudy et al., companion article, this issue).
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