The Elimination of Polyneuronal Innervation of End-Plates in Developing Rat Muscles with Altered Function

Abstract

Publisher Summary This chapter discusses the elimination of polyneuronal innervation from developing end-plates in rat extensor digitorum longus (EDL) muscles with altered function: (1) during compensatory hypertrophy and (2) after de-afferentation. Results show that the EDL muscles became overloaded, and underwent compensatory hypertrophy after removal of the tibialis anterior muscles in new-born rats. The maturation of end-plates was speeded up. Electrophysiological examination revealed that 74% end-plates already had a monoaxonal supply by day 9, and 94% were monoaxonally supplied by day 14, as compared with 43% and 82% monoaxonal end-plates in corresponding control muscles. After bilateral section of lumbosacral dorsal roots and high transection of the spinal cord in l day old rats, active movements were restricted and the maturation of end-plates in EDL muscles was retarded; only 24% and 37% end plates became monoaxonal by day 9 as determined by electrophysiological and histological method respectively. No difference was found between deafferented and control muscles by day 14, when about 80% of all end-plates investigated already had a monoaxonal supply. The maturation of motor end-plates thus appears to be speeded up by compensatory hypertrophy and slowed down by de-afferentation. The retardation observed after de-afferentation is only temporary; the majority of end-plates become monoaxonally supplied in two weeks time in both experimental and control muscles.