A comparative study of muscle spindles in slow and fast neonatal muscles of normal and dystrophic mice

Abstract

Muscle spindles from the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles of genetically dystrophic mice of the dy2J/dy2J strain were compared with age-matched normal animals at neonatal ages of 1-3 weeks according to histochemical, quantitative, and ultrastructural parameters. Intrafusal fibers in both the soleus and EDL exhibited similar regional differences in myosin ATPase activity, and conformed to those noted previously in various adult species. In distal polar regions, all nuclear bag fibers resembled extrafusal fibers of the type 1 variety, whereas in capsular zones they could be divided into two subtypes. Nuclear chain fibers possessed a staining pattern similar to type 2 extrafusal fibers, and in contrast to the bag fibers they exhibited no regional variations. These features were consistently observed in both the normal and dystrophic muscles at all ages. Spindles varied only slightly in their number and distribution in the two types of muscle, and their location followed the neurovascular branching pattern in each. Irrespective of age or genotype, spindles in the soleus were more homogeneously dispersed, but those in the EDL were concentrated along the dorsal aspect of the muscle. No significant differences were noted in the total number of spindles between normal and dystrophic muscles. In addition, no dramatic differences were observed in the muscle spindle index for soleus and EDL. The first obvious disease-related changes were noted in extrafusal fibers of the soleus of 3-week-old mice, and spindles were often located close to these areas of fiber degeneration. Despite alterations in the surrounding tissue, however, spindles appeared morphologically unaltered in dystrophy. These observations indicate that intrafusal fibers of spindles in neonatal mice appear enzymatically and histologically unaffected in incipient stages of progressive muscular dystrophy.

Analysis of Proprioceptive Sensory Innervation of the Mouse Soleus: A Whole-Mount Muscle Approach

“…Our reported average of 11.3 ± 0.4 MS occupies the middle of the range of numbers from 10 to 12 MS reported elsewhere [17,33–38]. GTO numbers in mouse soleus have been less frequently quantified, but again numbers reported here (5.2 ± 0.2) agree with published reports [36,39].…”

Somatic and intramuscular distribution of muscle spindles and their relation to muscular angiotypes

“…Such an intramuscular disposition could account for the immediate apposition of the spindle capsule to various parallel intramuscular blood vessels and lymphatics found often in the literature (e.g. Merrillees, 1962;Cooper and Daniel, 1963;Dow et al, 1980;Diwan and Milburn, 1986;Johnson and Ovalle, 1986;Maier and Mayne, 1987;Sanes, 1994;Nahirney et al, 1997). A sample of such histological findings supporting an apposition of the capsular region of mouse spindles to small vessels is shown in Fig.…”

“…Other investigators note that spindles distribute within the muscle ''according to the branching pattern of the neurovascular bundle'', introducing thus the vascular tree as an additional parameter influencing intramuscular spindle distribution (Dow et al, 1980;Johnson and Ovalle, 1986;Maier, 1999). Related to this is the fact that there is an early congruence of peripheral nerves and vessels during development (from Bates et al, 2002).…”

“…2). According to Johnson and Ovalle (1986), spindles appear morphologically unaltered in dystrophy, despite alterations in the surrounding tissue. (d) Representative camera Lucida drawing from an 8-week-old chicken leg muscle.…”

Histochemical heterogeneity of intrafusal muscle fibres in slow and fast skeletal muscles of the rat

“…Although Barker et al (1976) also showed low regular ATPase activity in the bag2 fibres of the rabbit tenuissimus muscle, this is the first report that documents the presence of chain fibres with low regular ATPase activity in some muscle spindles. It would be valuable to ascertain whether or not there is a true heterogeneity between the different chain fibres, or whether this reflects only a regional variability in ATPase reaction within a single chain fibre, as is recognized for the bag1 fibres (Yellin, 1974;Soukup, 1976;Johnson & Ovalle, 1986).…”