How individual muscle fibers become specialized to perform different functions is a major subject of developmental neuroscience. The muscle spindle, a receptor found throughout skeletal muscle to detect the degree of muscle contraction, is a unique structure because it receives both sensory and motor innervation. Dr. Kucera will conduct the first formal inquiry into the developmental sequence whereby the spindle acquires its sensory and motor nerve connections. Neural and muscular features of spindles in the soleus muscle will be compared by light and electron microscopy between developing and adult rats. In a complementary study, these features of developing spindles will be compared between normal controls and experimentally deafferented animals. These comparisons will be used to: (a) determine the temporal sequence of the development of sensory and motor innervation to spindles, (b) establish whether transient, immature patterns of innervation proceed the emergence of the adult pattern of neural connections of spindles, (c) determine whether the motor innervation can direct the differentiation of spindles in the absence of sensory innervation, and (d) explore whether coated organelles could mediate the ontogenetic effects of sensory axons of spindle structure. Dr. Kucera is a recognized expert in the morphological study of muuscle spindles. These studies are the first rigorous attempt to address the basic questions of developmental neurobiology of the muscle spindle organ. The results of these experiments will provide new and important information about the process of muscle fiber specialization.
