Motor nerve terminals of cat nuclear chain fibers studied by the cholinesterase technique

Abstract

Muscle spindles were traced in serial transverse sections of freshly frozen cat tenuissimus muscles. Adenosine triphosphatase histochemical staining was used to identify nuclear bag 1, nuclear bag 2 and nuclear chain intrafusal muscle fibers. Unlike typical nuclear chain fibers, the long nuclear chain fibers extended for more than 1000 μm beyond the termination of the spindle capsule. Both simple ‘rim’ and more elaborate ‘plate’ type motor nerve terminals were demonstrated along the poles of the typical nuclear chain fibers by staining for cholinesterases. Most of the long nuclear chain fibers and the majority of nuclear bag fibers had motor innervation limited to ‘plate’-type endings as identified by staining for cholinesterases. These histochemical observations are discussed with regard to the current concepts of the functional organization of motor innervation of the mammalian muscle spindle.