THYROID hormones, which play an important role in the development and
regeneration of the nervous system, require the presence of specific n
uclear T3 receptors (NT3R). In this study we provide evidence that NT3
R expression by Schwann cells was up-regulated in response to a loss o
f axonal contact in vitro and in vivo. In dorsal root ganglia explant
cultures, Schwann cells which accompanied axons (nerve fibres) were de
void of NT3R. When Schwann cells were orphaned from axon contact by ax
on transection, all the nuclei of these cells displayed NT3R immunorea
ctivity. Similar results were obtained in situ; in adult rat sciatic n
erve, Schwann cells which ensheathed healthy axons never expressed NT3
R immunoreactivity. After sciatic nerve transection in vivo the nuclei
of Schwann cells deprived of axonal contact displayed a clear NT3R im
munoreaction.