Summary
The left facial nerve was crushed in 50 adult male rats. The animals were allocated to 5 groups: controls received daily subcutaneous injections of slightly alkaline water; experimental animals received triiodothyronine sodium (T3), 1.0 μg per kg for 3, 7 or 28 days or 5.0 μg per kg for 28 days. Functional recovery, due to axonal regeneration, was detected by observing the time required for return of the corneal reflex on the left side. Treatment with T3 did not significantly accelerate this recovery.
The rats were killed on the 28th post-operative day. Axonal diameters and myelin sheath thicknesses were measured in transverse sections of the temporal branches of the facial nerves. Treatment with T3 (5.0 μg per kg, 28 days) did not affect the diameters of axons in the unoperated nerves, but resulted in their myelin sheaths becoming thicker than in the controls. A positive correlation between the two parameters, absent in control animals, appeared after treatment with T3.
In the regenerated nerves, the axonal diameters were smaller in T3-treated than in control animals, but the myelin thicknesses were greater. These changes were more pronounced in rats injected with T3 for 28 days than for shorter times. It is suggested that under the influence of exogenous T3, regenerating neurons synthesize axolemmal components more rapidly than axoplasmic material and that the hormone stimulates myelination of both normal and regenerating axons by an action upon the Schwann cells.
Similar content being viewed by others
References
Balázs, R., Cocks, W. A., Eayrs, J. T., Kovacs, S.: Biochemical effect of thyroid hormones on the developing brain. Ch. 27, pp. 357–379. In: Hormones in Development, ed. M. Hamburgh and E. J. W. Barrington. New York: Appleton-Century-Crofts 1971
Bruesch, S. R.: The distribution of myelinated afferent fibers in the branches of the cat's facial nerve. J. comp. Neurol.81, 169–191 (1944)
Cockett, S. A., Kiernan, J. A.: Acceleration of peripheral nervous regeneration in the rat by exogenous triiodothyronine. Exp. Neurol.39, 389–394 (1973)
Cook, R. A., Kiernan, J. A.: Effects of triiodothyronine on protein synthesis in regenerating peripheral neurons. Exp. Neurol.52, 515–524 (1976)
Fertig, A., Kiernan, J. A., Seyan, S. S. A. S.: Enhancement of axonal regeneration in the brain of the rat by corticotrophin and triiodothyronine. Exp. Neurol.33, 372–385 (1971)
Foley, J. O., DuBois, F. S.: An experimental study of the facial nerve. J. comp. Neurol.79, 79–105 (1943)
Geel, S. E., Valcana, T., Timiras, P. S.: Effect of neonatal hypothyroidism and of thyroxine onl-[14C]-leucine incorporation in protein in vivo and the relationship to ionic levels in the developing brain of the rat. Brain Res.4, 143–150 (1967)
Gelber, S., Campbell, P. L., Deibler, G. E., Sokoloff, L.: Effects ofl-thyroxine on amino acid incorporation into protein in mature and immature rat brain. J. Neurochem.11, 221–229 (1964)
Hamburgh, M.: Evidence for a direct effect of temperature and thyroid hormone on myelinogenesis in vitro. Devel. Biol.13, 15–30 (1966)
Harvey, J. E., Srebnik, H. H.: Locomotor activity and axon regeneration following spinal cord compression in rats treated withl-thyroxine. J. Neuropath. exp. Neurol.26, 661–668 (1967)
Heinicke, E. A.: Influence of exogenous triiodothyronine on axonal regeneration and wound healing in the brain of the rat. J. Neurol. Sci.31, 293–305 (1977)
Isenschmid, R.: Über den Einfluß von Thymus und Schilddrüse auf die Nerven-Regeneration. Schweiz. med. Wochenschr.62, 785–789 (1932)
Kiernan, J. A.: Effects of insulin, triiodothyronine and corticosterone on organ cultures of the adult rat cerebellum. Acta neuropath. (Berl.)30, 25–31 (1974)
Marinesco, G., Minea, J.: Nouvelles recherches sur l'influence qu'exerce l'ablation du corps thyroïde sur la dégénérescence et la régénérescence des nerfs. Compt. rend. Soc. Biol.68, 188–190 (1910)
McIsaac, G., Kiernan, J. A.: Accelarated recovery from peripheral nerve injury in experimental hyperthyroidism. Exp. Neurol.48, 88–94 (1975a)
McIsaac, G., Kiernan, J. A.: Acceleration of neuromuscular reinnervation by triiodothyronine. J. Anat.120, 551–560 (1975b)
McQuarrie, I. G.: Nerve regeneration and thyroid hormone treatment. J. neurol. Sci.26, 499–502 (1975b)
Sanders, F. K.: The thickness of the myelin sheaths of normal and regenerating peripheral nerve fibres. Proc. Roy. Soc. Lond. B135, 323–357 (1948)
Sanders, F. K., Young, J. Z.: The influence of peripheral connexion on the diameter of regenerating nerve fibres. J. exp. Biol.22, 203–212 (1946)
Schröder, J. M.: Altered ratio between axon diameter and myelin sheath thickness in regenerated nerve fibers. Brain Res.45, 49–65 (1972)
Sima, A.: Studies on fibre size in developing sciatic nerve and spinal roots in normal, undernourished and rehabilitated rats. Acta physiol. Scand.92, Suppl.406, 1–55 (1974)
Sokoloff, L.: The action of thyroid hormones. Ch. 17, pp. 525–549. In Handbook of Neurochemistry, Vol. V B, ed. A. Lajtha. New York and London Plenum Press 1971
Stelmack, B. M.: Effects of triiodothyronine on regeneration of the facial and sciatic nerves of the rat. M.Sc. Thesis, University of Western Ontario, London, Canada, 1977
Williams, P. L., Wendell-Smith, C. P.: Some additional parametric variations between peripheral nerve fibre populations. J. Anat.109, 505–526 (1971)
Zar, J. H.: Biostatistical Analysis. Englewood Cliffs, N. J.: Prentice-Hall 1974
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Stelmack, B.M., Kiernan, J.A. Effects of triiodothyronine on the normal and regenerating facial nerve of the rat. Acta Neuropathol 40, 151–155 (1977). https://doi.org/10.1007/BF00688704
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00688704