Differential regulation of 3-beta-hydroxysteroid dehydrogenase and vanilloid receptor TRPV1 mRNA in sensory neurons by capsaicin and NGF.

It was the aim of the present study to investigate by RT-PCR the regulation of the mRNA of the neurosteroid-synthesizing enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and of the vanilloid receptor TRPV1 in dorsal root ganglia (DRGs) of rats during the process of capsaicin denervation of primary sensory neurons and the following regeneration. The expression of 3beta-HSD in DRG was increased 3 days after the capsaicin treatment, and it remained at that level during a 22 day observation period. The expression of TRPV1, a specific marker of capsaicin-sensitive small sensory neurons connected to C- and Adelta-fibers, was markedly reduced 3 days after the capsaicin treatment. It slowly recovered during the 22 days observation period reaching almost control levels on day 22. When the capsaicin-treated rats received 5 intraplantar injections of nerve growth factor (NGF), the prototypical neurotrophin for capsaicin-sensitive neurons, on day 1, 2, 3, 5 and 6, both the 3beta-HSD and the TRPV1 mRNA had returned to control levels at the time point 8 days after capsaicin. The present results demonstrate that both 3beta-HSD and TRPV1 are markers for neurodegeneration and neuroregeneration in capsaicin-sensitive primary afferent neurons, and that NGF is an effective tool to induce recovery after peripheral nerve injury.