Reaction of spinal cord central canal cells to cord transection and their contribution to cord regeneration

After transection, the spinal cord of the eel Anguilla quickly regrows and reconnects, and function recovers. We describe here the changes in the central canal region that accompany this regeneration by using serial semithin plastic sections and immunohistochemistry. The progress of axonal regrowth was followed in material labeled with DiI. The canal of the uninjured cord is surrounded by four cell types: S-100-immunopositive ependymocytes, S-100- and glial fibrillary acidic protein (GFAP)-immunopositive tanycytes, vimentin-immunopositive dorsally located cells, and lateral and ventral liquor-contacting neurons, which label for either gamma-aminobutyric acid (GABA) or tyrosine hydroxylase (TH). After cord transection, a new central canal forms rapidly as small groups of cells at the leading edges of the transection create flat "plates" that serve as templates for subsequent formation of the lateral and dorsal walls. Profile counts and 5-bromo-2'-deoxyuridine immunohistochemistry indicate that these cells are dividing rapidly during the first 20 days of the repair process. The newly formed canal, which bridges the transection by day 10 but is not complete until about day 20, is greatly enlarged (less than or equal to100 times) and is dominated by ependymocytes that are vimentin immunopositive, but cells expressing GABA, TH, and GFAP do not appear until days 11, 13, and 16, respectively. The proliferating ependyma do not provide a supportive scaffold for the regrowing axons, inasmuch as some have crossed the bridge before the canal has formed. However, their modified phenotype suggests a role, possibly trophic, for the central canal region following injury. (C) 2003 Wiley-Liss, Inc.