Central projections of C4–C8 dorsal root ganglia in the rat studied by anterograde transport of WGA‐HRP

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Abstract
Injections of WGA‐HRP were made in the rat C4–C8 dorsal root ganglia (DRGs) individually to study the central projections and their relations to each other. The main dorsal horn projections from these DRGs to the dorsal horn lamina II extended for about two segments rostrally and caudally to the injected DRG, whereas the projections to laminae I, III, and IV were less restricted rostrocaudally. Comparisons of the dorsal horn projections from the DRGs investigated indicated a tendency for a somatotopic organization, which was most prominent in lamina II. Labeled central branches from the C4–8 DRGs could be traced in the dorsal column as far caudally as 12‐17 segments caudal to the level of entrance. Most of these fibers appeared to end in the medial dorsal horn base, including the column of Clarke. Labeling of primary afferents in the ventral horn generally extended for at least 3‐4 segments rostral and caudal to the level of the injected DRG. Projections to the central cervical nucleus were most prominent from the C4 DRG and gradually became less prominent from the more caudal DRGs. Heavy projections to the cuneate nucleus (Cun) originated from the C7 and C8 DRG, whereas those from the C4–C6 DRGs were less extensive. The Cun projections from the different DRGs appeared to overlap, and the same was true for the projections to the external cuneate nucleus. Projections to the gracile nucleus, the vestibular nuclear complex, including nucleus X, and to trigeminal sensory nuclei were seen from all DRGs investigated.