Atypical Spindles in Reinnervated Rat Muscles

In young rats, following lesions of a peripheral nerve at birth, immature muscle spindles disintegrate during a short transition period (Zelená, 1957), and even after several months of reinnervation the reinnervated muscles are usually found to contain no spindles (Zelená & HNÍK, 1960). Nevertheless, occasional small spindles of atypical structure are observed in some of these muscles. In the present report, the structure and morphological characteristics of these atypical spindles were studied and compared with normal spindles. Since differences in fast and slow muscles may include differences in muscle receptors (Voss, 1937; Maruseva, 1947; Hagbarth & Wohlfahrt, 1952; Freimann, 1953; Cooper, 1960), the number, size, and distribution of spindles were studied in two muscles representing the two functional groups.