Target‐determined expression of α 3 isoform of the Na + ,K + ‐ATPase in the somatic nervous system of rat

Factors that determine the differential expression of isoforms of Na + ,K + ‐ATPase in the nervous system of vertebrates are not understood. To address this question we studied the expression of α 3 Na + ,K + ‐ATPase in the L5 dorsal root ganglia (DRG) of developing rat, the normal adult rat, and the adult rat after peripheral axotomy. During development, the first α 3 Na + ,K + ‐ATPase‐positive DRG neurons appear by embryonic day 21. At birth, the L5 DRG have a full complement (14 ± 2%) of these neurons. By 15 days after sciatic nerve transection in adult rat, the number of α 3 Na + ,K + ‐ATPase‐positive DRG neurons and small myelinated L5 ventral root axons decreases to about 35% of control counts. These results combined with data from the literature suggest that the expression of α 3 Na + ,K + ‐ATPase by rat somatic neurons is determined by target‐muscle spindle‐derived factors. J. Comp. Neurol. 483:114–123, 2005. © 2005 Wiley‐Liss, Inc.