Morphologic changes in skeletal muscle induced by serotonin treatment:: A light- and electron-microscope study

Abstract

Normal, adult mice were injected daily with either one or 10 μg/gm body weight serotonin creatinine sulfate (5-hydroxytryptamine) for periods of three or nine weeks. After three weeks, the most obvious histologic changes were central rowing of nuclei and infrequent fibers with basophilic sarcoplasm. Other fibers, undergoing degenerative changes, had fragmenting sarcoplams with a distinctive loss of striations and staining; leucocytes and phagocytes infiltrated these areas. Electron micrographs showed increased numbers of interfibrillar and subsarcolemmal mitochondria which were enlarged and pleomorphic as compared to control muscle. Although most of the sarcomeres were apparently normal at this time, the Z-lines were indistinct in many fibers from serotonin-treated mice. After nine weeks of treatment with serotonin, these morphologic alterations were exaggerated. Skeletal muscle from the axial musculature and the gracilis and gastrocnemius muscles had numerous regenerating fibers with deeply basophilic sarcoplasm and rows of centrally-arranged, spherical nuclei containing large chromatophilic masses and basophilic nucleoli. Electron micrographs of these muscles showed extensive myofibrillar fragmentation and disorientation with remnants of Z-lines and pleomorphic mitochondria scattered throughout the sarcoplasm.