The organization of knee articular cartilage of the bullfrog (Lithobates catesbeianus) differs in relation to morphofunctional adaptation in many aspects from similar structures in mammals. Thus, we investigated the structural organization and distribution of the extracellular matrix components in three articular cartilage regions in the distal epiphysis of the femur and proximal epiphysis of the tibia in male bullfrogs at 7, 540 and 1,080 days after metamorphosis. Cartilage thickness and cell density decreased in all regions with age. The basophilia differed among cartilage sites during aging. Calcium deposits were detected in growth cartilage of the femur and tibia in older animals. Immunohistochemical staining for chondroitin-6-sulfate was positive in the pericellular and territorial matrix in all samples. Positive immunostaining for type I collagen was observed in the superficial layer at all ages and in ossification centers of older animals. Reactivity to type II collagen was intense and was found throughout the stroma at all ages. Ultrastructural analysis of the epiphyseal region, in young animals, showed that the cytoplasm of chondrocytes was rich in rough endoplasmic reticulum, Golgi complex and mitochondria. In old animals, were observed a reduction in the size and number of mitochondria, disintegration of rough endoplasmic reticulum, and vacuolization of the Golgi complex. The bullfrog articular cartilage presented structural and organizational changes during aging which may contribute to the functional cartilage deterioration in old animals. © 2014 Springer-Verlag Berlin Heidelberg.1332245256Archer, C.W., Morrison, E.H., Bayliss, M.T., Ferguson, M.W., The development of articular cartilage: II. The spatial and temporal patterns of glycosaminoglycans and small leucine-rich proteoglycans (1996) J Anat, 189, pp. 23-35Bland, Y.S., Ashhurst, D.E., Development and ageing of the articular cartilage of the rabbit knee joint: distribution of the fibrillar collagens (1996) Anat Embr, 194, pp. 607-619Bland, Y.S., Ashhurst, D.E., Fetal and postnatal development of the patella, patellar tendon and suprapatella in the rabbitchanges in the distribution of the fibrillar collagens (1997) J Anat, 190, pp. 327-342Bobacz, K., Erlacher, L., Smolen, J., Soleiman, A., Graninger, W.B., Chondrocyte number and proteoglycan synthesis in the aging and osteoarthritic human articular cartilage (2004) Ann Rheum Dis, 63, pp. 1618-1622Corvol, M.T., The chondrocyte: from cell aging to osteoarthritis (2000) Joint Bone Spine, 67, pp. 557-560de Bont, L.G., Liem, R.S., Boering, G., Ultrastructure of the articular cartilage of the mandibular condyle: aging and degeneration (1985) Oral Surg Med Pathol, 60, pp. 631-641Dell'Orbo, C., Gioglio, L., Quacci, D., Morphology of epiphyseal apparatus of a ranid frog (Rana esculenta) (1992) Histol Histopath, 7, pp. 267-273Dickson, G.R., Ultrastructure of growth cartilage in the proximal femur of the frog, Rana temporaria (1982) J Anat, 135, pp. 549-564Erismis, U.C., Chinsamy, A., Ontogenetic changes in the epiphyseal cartilage of Rana (Pelophylax) caralitana (Anura: Ranidae) (2010) Anat Rec, 293, pp. 1825-1837Eyre, D.R., Collagens and cartilage matrix homeostasis (2004) Clin Orthop Rel Res, 427 S, pp. S118-S122Felisbino, S.L., Carvalho, H.F., The epiphyseal cartilage and growth of long bones in Rana catesbeiana (1999) Tissue Cell, 31, pp. 301-307Felisbino, S.L., Carvalho, H.F., Growth cartilage calcification and formation of bone trabeculae are late and dissociated events in the endochondral ossification of Ranacatesbeiana (2001) Cell Tissue Res, 306, pp. 319-323Felisbino, S.L., Carvalho, H.F., Ectopic mineralization of articular cartilage in the bullfrog Rana catesbeiana and its possible involvement in bone closure (2002) Cell Tissue Res, 307, pp. 357-365Gilmore, R.S.C., Palfrey, A.J., Chondrocyte distribution in the articular cartilage of human femoral condyles (1988) J Anat, 157, pp. 23-31Gyarmati, J., Földes, I., Kern, M., Morphological studies on the articular cartilage of old rats (1985) Acta Morph Hung, 35, pp. 111-124Hall, A.C., Horwitz, E.R., Wilkins, R.J., The cellular physiology of articular cartilage (1996) Exp Phys, 81, pp. 535-545Heise, N., Toledo, O.M., Age-related changes in glycosaminoglycan distribution in different anatomical sites on the surface of knee-joint articular cartilage in young rabbits (1993) Ann Anat, 175, pp. 35-40Huldelmaier, M., Glaser, C., Englmeier, K.H., Age-related changes in the morphology on deformational behaviour of knee joint cartilage (2001) Arthritis Rheum, 44, pp. 2556-2561Hunziker, E.B., Quinn, T.M., Häuselmann, H.J., Quantitative structural organization ofnormal adult human articular cartilage (2002) Osteoarthritis Cartilage, 10, pp. 564-572Jeffery, A.K., Blunn, G.W., Archer, C.W., Three-dimensional collagen architecture in bovine articular cartilage (1991) J Bone Joint Surg Br, 73, pp. 795-801Karvonen, R.L., Negendank, W.G., Teitge, R.A., Factors affecting articular cartilage thickness in osteoarthritis and aging (1994) J Rheum, 21, pp. 1310-1318Király, K., Hyttinen, M.M., Lapveteläinen, T., Specimen preparation and quantification of collagen birefringence in unstained sections of articular cartilage using image analysis and polarizing light microscopy (1997) Histoch J, 29, pp. 317-327Leng, C.G., Yu, Y., Ueda, H., The ultrastructure of anionic sites in rat articular cartilage as revealed by different preparation methods and polyethyleneimine staining (1998) Histoch J, 30, pp. 253-261Leutert, G., Morphological aging changes in human articular cartilage (1980) Mech Ageing Dev, 14, pp. 469-475Li, S., Duan, H., Nagata, T., Age-related alterations of proteoglycan in mouse tracheal cartilage matrix: an electron histochemical analysis with the cationic dye of polyethyleneimine (1994) Cell Mol Biol, 40, pp. 129-135Martin, J.A., Buckwalter, J.A., Roles of articular cartilage aging and chondrocyte senescence in the pathogenesis of osteoarthritis (2001) Iowa Orthop J, 21, pp. 1-7Martin, J.A., Buckwalter, J.A., Aging, articular cartilage chondrocyte senescence and osteoarthritis (2002) Biogerontology, 3, pp. 257-264Martin, J.A., Buckwalter, J.A., The role of chondrocyte senescence in the pathogenesis of osteoarthritis and in limiting cartilage repair (2003) J Bone Joint Surg Am, 85 A, pp. 06-110Minns, R.J., Steven, F.S., The collagen fibril organization in human articular cartilage (1977) J Anat, 123, pp. 437-457Mobasheri, A., Role of chondrocytes death and hypocellularity in aging human articular cartilage and the pathogenesis of osteoarthritis (2002) Med Hypothese, 58, pp. 193-197Modis, L., (1990) Organization of the Extracellular Matrix: A Polarization Microscopic Approach, , New York: CRC PressMorrison, E.H., Ferguson, M.W., Bayliss, M.T., Archer, C.W., The development of articular cartilage: I. The spatial and temporal patterns of collagen types (1996) J Anat, 189, pp. 9-22Poole, A.R., Kojima, T., Yasuda, T., Composition and structure of articular cartilage: a template for tissue repair (2001) Clin Orthop Rel Res, 391 S, pp. S26-S33Roughley, P.J., The structure and function of cartilage proteoglycans (2006) Eur Cell Mater, 30, pp. 92-101Roy, S., Meachim, G., Chondrocyte ultrastructure in adult human articular cartilage (1968) Ann Rheum Dis, 27, pp. 544-558Rozenblut, B., Ogielska, M., Development and growth of long bones in European water frogs (Amphibia: Anura: Ranidae), with remarks on age determination (2005) J Morph, 265, pp. 304-317Sauren, Y.M., Mieremet, R.H., Lafeber, F.P., Changes in proteoglycans of ageing and osteoarthritic human articular cartilage: an electron microscopic study with polyethyleneimine (1994) Anat Rec, 240, pp. 208-216Schroeppel, J.P., Crist, J.D., Anderson, H.C., Molecular regulation of articular chondrocyte function and its significance in osteoarthritis (2011) Histol Histopath, 26, pp. 377-394Takahashi, I., Mizoguchi, I., Sasano, Y., Age-related changes in the localization of glycosaminoglycans in condylar cartilage of the mandible in rats (1996) Anat Embryol, 194, pp. 489-500Verbruggen, G., Cornelissen, M., Almqvist, K.F., Influence of aging on the synthesis and morphology of the aggrecans synthesized by differentiated human articular chondrocytes (2000) Osteoarthr Cartil, 8, pp. 170-179Vignon, E., Arlot, M., Patricot, L.M., Vignon, G., The cell density of human femoral head cartilage (1976) Clin Orthop, 121, pp. 303-308Yamamoto, K., Shishido, T., Masaoka, T., Imakiire, A., Morphological studies on the ageing and osteoarthritis of the articular cartilage in C57 black mice (2005) J Orthop Surg, 13, pp. 8-18