A cytological study of the effect of reinnervation and cross-innervation on rat striated muscle.

The changes of rat muscle fiber structure and fiber types after the reunification of the nerve and cross-innervation between the nerve to M. soleus (SOL) and M. extensor digitorum longus (EDL) were cytologically studied and the following results were obtained: 1. After the reunification of the nerve, the tendency toward grouping to a single fiber type was observed, although in normal muscle, the red, white and intermediate fibers were distributed in mosaic pattern. 2. After the cross innervation, the changes of fiber types occurred; namely, in SOL, normally composed of red and intermediate fibers, the three types of fibers appeared after the crossinnervation with the nerve to EDL, which originally was composed of the red, white and intermediate muscle fibers, and vice versa. These changes were observed not only in histochemical sections, but also in the ultrastructural level by electron microscope. ∗PMID: 4239565 [PubMed indexed for MEDLINE] Copyright c ©OKAYAMA UNIVERSITY MEDICAL SCHOOL Acta Med. Okayama 22, 219-226 (968) A CYTOLOGICAL STUDY OF THE EFFECT OF REINNERVATION AND CROSS.INNERVATION ON RAT STRIATED MUSCLE Takuro OGATA, Takashi SEITO and Hiro HINO Department of Surgery, Okayama University Medical School, Okayama, Japan (Director: Prof. S. Tanaka) Received for publication, April 1. 1968 Recent histochemical and electron microscope studies (1, 2) reveal that the mammalian striated muscle is composed of the mixture of the different types of fibers. The so-called "white muscle" M. extensor digi. torum longus (EDL), is composed of three types of fibers, i. e. the white, the red and the intermediate fibers, which have different contents of mitochondria, while the so·called "red muscle" M. soleus (SOL) is com· posed of two, the red and the intermediate ones. In this preliminary study, the changes of muscle fiber structure and fiber types after the reunification of the nerve and cross-innervation between the nerve to SOL and to EDL were cytologically clarified. MATERIALS AND METHODS Adults male Wistar rats weighing 150-200 g were used for reinnervation experiments. The animals were anaesthetized with intraperitoneal injection of sodium pentobarbital, the sciatic nerve was exposed and cut at the middle of the thigh and immediately reunified with 8-0 silk or alon-alpha. The animals were killed two weeks, 2, 3, 5, 9 and 15 months after the operation. For cross-union experiments, three week male Wister rats were used. The nerve to SOL was cross.innervated to the nerve to EDL and vice versa. As the control, the same nerve was transected and self-united. The animals were killed three and five months after the operation. Muscles fixed in 10% neutral buffered formalin were washed, embedded in gelatin, and sectioned on a freezing microtome. Sections (5 p.) were stained with Sudan black B and mounted in glycerogel. Control sections were extracted with acetone before staining. For electron microscope study, thin strips of muscle were fixed in 1% osmium tetroxide buffered to pH i. 4 with veronal acetate, and embedded in Epon. Ultrathin sections were stained with uranylacetate and lead hydroxide, and then examined with a Hitachi model HU.llA. electronmicroscope Thicker sections were stained with toluidine blue and examined with the light microscope.