Comparison of motor endings of the cat's muscle spindle stained for NADH-tetrazolium reductase and cholinesterase

Summary Cat muscle spindles were examined histochemically in serial transverse sections of tenuissimus muscles stained for ATPase, NADH-TR and ChE alternating sequentially. Motor nerve terminals on nuclear bag₁, bag₂ and nuclear chain intrafusal muscle fibers were identified in periodic sections stained for ChE. Intrafusal fiber regions that carried ChE-active areas were then examined in staining for NADH-TR. The motor endings on the three types of intrafusal fiber differed in their apparent histochemical content of both ChE and NADH-TR. The observations suggest that functional differences may exist among motor nerve terminals on the various intrafusal fiber types.