Changes in Nuclear 3,5,3′‐Triiodothyronine Receptor Expression in Rat Dorsal Root Ganglia and Sciatic Nerve During Development: Comparison with Regeneration

Abstract

Abstract The action of the thyroid hormones on responsive cells in the peripheral nervous system requires the presence of nuclear triiodothyronine receptors (NT 3 R). These nuclear receptors, including both the α and β subtypes of NT 3 R, were visualized by immunocytochemistry with the specific 2B3 monoclonal antibody. In the dorsal root ganglia (DRG) of rat embryos, NT 3 R immunoreactivity was first discretely revealed in a few neurons at embryonic day 14 (E14), then strongly expressed by all neurons at E17 and during the first postnatal week; all DRG neurons continued to possess clear NT 3 R immunostaining, which faded slightly with age. The peripheral glial cells in the DRG displayed a short‐lived NT 3 R immunoreaction, starting at E17 and disappearing from the satellite and Schwann cells by postnatal days 3 and 7 respectively. In the developing sciatic nerve, Schwann cells also exhibited transient NT 3 R immunoreactivity restricted to a short period ranging from E17 to postnatal day 10; the NT 3 R immunostaining of the Schwann cells vanished proximodistally along the sciatic nerve, so that the Schwann cells rapidly became free of detectable NT 3 R immunostaining. However, after the transection or crushing of an adult sciatic nerve, the NT 3 R immunoreactivity reappeared in the Schwann cells adjacent to the lesion by 2 days, then along the distal segment in which the axons were degenerating, and finally disappeared by 45 days, when the regenerating axons were allowed to re‐occupy the distal segment. It is concluded that (1) NT 3 R expression lasts throughout the life of the DRG neurons; (2) NT 3 R expression by peripheral glia is restricted to the perinatal period but may be transiently reactivated in Schwann cells after a nerve injury; and (3) cell‐cell interaction with axons down‐regulates the expression of NT 3 R by Schwann cells in both growing and regenerating nerves.