Alterations of diaphragm neuromuscular junctions with
hypothyroidism.
Prakash, Y. S., L. E. Gosselin, W. Z. Zhan, and G. C. Sieck.
Departments of Anesthesiology and Physiology & Biophysics, Mayo
Clinic and Foundation, Rochester, MN 55905
APStracts 3:0192A, 1996.
Hypothyroidism (HYPO) often manifests as neuromuscular symptoms;
however, little is known about its effects on the neuromuscular
junction (NMJ). The present study examined changes in NMJ morphology
and neuromuscular transmission failure (NTF) in the rat diaphragm
muscle (DIAm) following 3 weeks of HYPO. Three-color fluorescence
immunocytochemistry and confocal microscopy were used to
simultaneously visualize nerve terminals and axons, motor endplates,
and myosin heavy chain (MHC) isoform expression in DIAm fibers. NTF
was assessed in vitro by comparing muscle fatigue induced by nerve
versus direct muscle stimulation. Compared to control (CTL),
diameters of axons innervating type I fibers were 30% smaller in the
HYPO DIAm. Planar areas of nerve terminals and endplates on type I
and IIa fibers were 15-35% smaller in HYPO than CTL. The extent of
overlap between nerve terminals and endplates of type I fibers was
10% less in HYPO. Susceptibility to NTF during repetitive nerve
stimulation was 20% greater in the CTL DIAm, compared to HYPO;
however, changes in NMJ morphology could not fully account for the
effect of HYPO on NTF.
Received 13 December 1995; accepted in final form 27 March 1996.
APS Manuscript Number A1304-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96