Figure 8. Examples of the densest fiber plexus observed in PHR at different ages.
At birth, single unbranching fibers were present in superficial layers of PrS (A), deep layers of PrS (B) and deep layers of MEC (C). At P3, some branching fibers were observed (D, PrS). These fibers typically branched only once or twice. At P11 (E, PrS) the complexity of the fiber plexus increased as fibers have multiple branching points and thin fibers are seen within the plexus. At P12 (F, PrS) the first plexus which was comparable to plexus in adolescent animals (G, PrS) and adults (data not shown) was observed. In the experiment shown in G, the terminal distribution of three differentially labeled projections is illustrated. A plexus resulting from an injection in intermediate-rostral A29 (yellow) terminated throughout layer III of PrS, while the plexus observed after an injection in intermediate-rostral A30 terminated in the center of layer III of PrS (cyan). Fibers originating from a third injections in intermediate-caudal RSC (magenta) are observed, however the densest fiber plexus is located in a section at more ventral levels of PrS. The large, overlapping magenta and yellow structures are endothelium which take up alexa-preconjugated dextran amines. White line depicts the deep and superficial borders of layer III. Scale bars equal 100 μm.