MYXOID TISSUE - ITS MORPHOLOGY, HISTOCHEMISTRY, AND RELATIONSHIP WITHOTHER SUPPORTING TISSUES

Myxoid tissue was studied in the supporting organ of the cat epiglotti s (''epiglottic cartilage''). Under the light microscope, myxoid tissu e was characterized by stellate cells placed into an avascular acidic extracellular matrix. This extracellular matrix was alcianophilic at p H = 2.5, reacting with the colloidal iron stain, and staining metachro matically with toluidine blue O at pH = 5.0. Treatment of sections wit h testicular hyaluronidase abolished these reactions. In addition, sta ining persisted after methylation/saponification pretreatment, indicat ing hyaluronic acid as the main acidic component of myxoid extracellul ar matrix. Under the electron microscope, myxoid extracellular matrix formed flocculent electron dense precipitates. Stellate myxoid cells w ere characterized by bundles of intermediate (8 nm) cytoplasmic filame nts, Myxoid cells were devoid of a basal lamina, contained a few small lipid droplets, and stored some glycogen. Bundles of collagen fibrils , 80-120 nm in diameter, were seen in myxoid areas. Myxoid cells react ed to S-100 protein, glial fibrillary acidic protein, and neuron speci fic enolase. Moreover, in adult animals, myxoid cells stained for neur ofilament protein 200. All these markers were also present in chondroc ytes of elastic and fibrous cartilage, indicating a close relationship between myxoid cells and chondrocytes. This was supported by the obse rvation of continuous transitional forms of myxoid tissue into elastic or fibrous cartilage. In 8-week-old kittens, the supporting organ of the epiglottis was found mainly to consist of myxoid tissue with only a few interspersed islets of chondrocytes. It is therefore concluded t hat myxoid tissue can serve as a precursor of cartilage.