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

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.