Central terminals of primary afferent fibers detected by anterograde axonal tracing with Neurobiotin. A: Neurobiotin labeling in L3 spinal cord after application of the tracer to L3 dorsal root. There is extensive Neurobiotin labeling of axons in Lissauer's Tract, large and fine-diameter varicose fibers in the dorsal horn (boxed region enlarged in B) and extending into the ventral horn (boxed region enlarged in C). D: Neurobiotin labeling in L2 dorsal horns after application of the tracer to L3 dorsal root on one side of the spinal cord and all six lumbar dorsal roots on the other side. Tracing from multiple roots produces more labeled fibers in the dorsal horn but with a comparable distribution compared with labeling from a single root. E: Neurobiotin labeling in L1 dorsal horn after application of the tracer to the ipsilateral L3 dorsal root. There is strong labeling in the dorsal funiculus, but labeling can still be seen in lamina I. The same section is labeled for IB4-binding (F), CGRP-IR (G), VGluT2-IR (H); overlaid image (I; Neurobiotin; green, IB4; orange, CGRP; red, VGluT2; blue). Representative images from 3 separate experiments; A-C, D, and E-I. Scale bar represents 200 μm in A, D and E, 20 μm in C(also applies to B), and 100 μm in I(also applies to F-H). Lissauer's Tract; LT, dorsal horn; dh, ventral horn; vh, dorsal funiculus; df, central canal; cc, lateral spinal nucleus; lsn, lamina I; I, lamina II; II, lamina III; I.