title: Local administration of thyroid hormones in silicone chamber increases regeneration of rat transected sciatic nerve.
abstract: Conflicting actions of the exogenous thyroid hormone on regenerating peripheral nerve have been reported. These contradictory results were probably due to daily intraperitoneal injections which induce a high concentration of thyroid hormone after administration. In our present study we adapted a technique which allows a local administration of thyroid hormones in a closed system. The effect of a single and local treatment with triiodothyronine (T3) on axonal growth across a gap between sectioned ends of sciatic nerve within silicone chambers was examined in Wistar rats. After nerve transection and surgical implantation, silicone chambers were filled with either a neutral pH solution of triiodothyronine dissolved in NaOH or with sterile solvent as control. Regeneration of the nerves was examined 2 to 8 weeks following the surgery. Early regeneration (4 weeks) was studied by morphological analysis of nerves which showed a significant difference between T3-treated and control groups. Morphometric analysis revealed: (1) a significant difference in the mean diameter of myelinated axons between T3-treated nerve (phi 3.80 +/- 0.22 microns) and control (phi 3.07 +/- 0.44 microns); (2) that T3 increased significantly (1.4-fold) the number of myelinated axons that grew into the middle and distal ends of regeneration chambers; (3) that ultrastructural analysis showed significantly higher percentage of myelinated axons per total axon population in T3-treated groups (38.8 +/- 5.9%) as compared to control (16.0 +/- 2.3%); and (4) that the myelinated axons had thicker myelin sheaths. The beneficial effects of T3 on regeneration, observed at 4 weeks, were sustained over a prolonged period of time. Thus, at 8 weeks of regeneration, the number, the mean diameter of myelinated axons, and the thickness of myelin sheaths remained significantly greater in T3-treated groups. Therefore, a single and local administration of thyroid hormone at the level of the transected sciatic nerve is sufficient to rapidly set off several mechanisms which, in turn, produce a stimulating and lasting effect on peripheral nerve regeneration. The beneficial effects of T3 upon injured peripheral nerve may have considerable therapeutic potential.
authors.affiliation: Institut de Biologie cellulaire et de morphologie, Faculté de Médecine, Université de Lausanne, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Voinesco
authors.forename: L
authors.initials: L
authors.lastname: Glauser
authors.forename: R
authors.initials: R
authors.lastname: Kraftsik
authors.forename: I
authors.initials: I
authors.lastname: Barakat-Walter
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects; D006133:Growth Substances / Q000008:administration & dosage / Q000494:pharmacology*; D007260:Infusion Pumps; D008854:Microscopy, Electron; D009186:Myelin Sheath / Q000187:drug effects / Q000502:physiology; D009416:Nerve Regeneration / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000187:drug effects / Q000293:injuries / Q000502:physiology*; D012828:Silicones; D013997:Time Factors; D014284:Triiodothyronine / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D006133:Growth Substances; D012828:Silicones; D014284:Triiodothyronine