NUCLEAR TRIIODOTHYRONINE RECEPTOR EXPRESSION IS REGULATED BY AXON-SCHWANN CELL CONTACT

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.