Chie Fujitsuka

Acceleration by MS-818 of early muscle regeneration and enhanced muscle recovery after surgical transection.

The synthesized pyrimidine compound MS‐818 has neurotrophic effects in several kinds of neuronal cells, but its effect with respect to muscle cells remains unknown. We therefore examined the effects of MS‐818 on regeneration for 12 weeks in a wounded area (damaged and gap areas) of cut muscle in adult rats. The right semitendinosus muscles of reated and control groups were severed and sutured at the belly and the left semitendinosus muscles were left intact. MS‐818 was administered intraperitoneally to the treated group at a dose of 5 mg/kg once daily. Control rats received an equal volume of physiological saline. A reference group underwent no surgical procedure. MS‐818 significantly increased the maximal isometric twitch tension (Tmax) compared to control and reference rats after week 4 (approximately 1.4‐fold control value; 0.6‐fold reference value). Northern blotting showed that MS‐818 enhanced myogenin mRNA expression to about 1.5‐fold above the control level at 2, 4, and 7 days after surgery. Immunohistochemical and histochemical studies showed significant enhancement in the treated group since myogenic cells expressed desmin and were positive for neonatal myosin, and the fiber diameters and numbers of premature myofibers and end plates were increased when compared with those in the control group. These results show that MS‐818 accelerated the proliferation and differentiation of activated satellite cells and the fusion of myotubes to form immature myofibers. At week 12, Tmax, fiber diameter, and number of end plates in the treatment group recovered 60, 85, and more than 100%, respectively, compared to the reference group. The mechanism of MS‐818 effects on the accelerated regeneration of cut muscle is discussed.

Intramembrane structure of the sensory axon terminals in bullfrog muscle spindles

Much physiologic and morphologic research has been done into the sensory mechanism of the frog muscle spindle. However, no freeze‐fracture study has described in detail the shape and intramembrane structure of the nonmyelinated sensory axon terminals of the frog muscle spindle. In this study, muscle spindles were isolated from the red part of bullfrog semitendinous muscles. Chemically fixed spindles were subjected to freeze fracturing. The sensory axon endings were reconstructed, and the size and density of intramembrane particles (IMPs) were measured along the sensory nerve endings. The axon terminals had four distinctive parts: parent trunks (>0.5 μm in diameter), primary branches (0.15–0.5 μm), terminal branches (<0.1 μm), and varicosities (0.02–0.5 μm). IMPs ranged from 5 nm to 21 nm in diameter and were present in the intramembrane space of the plasma membrane all throughout the nonmyelinated sensory nerve endings. Mean IMP sizes in the protoplasmic face (PF) and the external face (EF), respectively, were 8.1 nm and 8.4 nm in the parent trunks, 8.8 nm and 8.8 nm in the primary branches, 9.4 nm and 9.0 nm in the varicosities, and 8.7 nm and 8.7 nm in the terminal branches. Mean IMP size in the PF was smallest in the parent trunk and largest in the varicosity. Mean IMP densities (numbers of IMPs per μm2) in the PF and the EF, respectively, were 2,500 and 700 in the parent trunks, 2,200 and 500 in the primary branches, 1,700 and 400 in the varicosities, and 1,000 and 300 in the terminal branches. Density decreased with the tapering of the axon terminal, with IMPs distributed evenly in the PF and the EF. The characteristic intramembrane structure of sensory nerve endings is discussed. Anat. Rec. 252:340–354, 1998.

Recruitment Patterns of Intrafusal and Extrafusal Fibres in Mice During Prolonged Swimming

Though recruitment patterns of fast and slow extrafusal fibres in exercise are well established (Armstrong, Saubert, Sembrovich, Shepherd & Gollnick, 1974), there have been no reports to date regarding the recruitment of different intrafusal fibres of mammalian muscle spindles during voluntary movement. We have used glycogen depletion during prolonged swimming to investigate recruitment patterns of the three intrafusal fibre types in mice. The degree of glycogen depletion was estimated by two methods, visual inspection (VI) and our newly developed optical scanning (OS) of periodic acid Schiff (PAS)-stained sections. Fibre typing was done by combining morphological, histochemical, and immunohistochemical characteristics, and we compared the results for intrafusal and extrafusal fibres.