Qualitative Study of Young, Adult, and Aged Wistar Rats Temporomandibular Synovial Membrane Employing Light, Scanning, and Transmission Electron Microscopy CHRISTIANO CONY DURO, 1 ADRIANO POLICAN CIENA, 2,3 SONIA REGINA YOKOMIZO DE ALMEIDA, 2 MARTA MARIA DA SILVA RIGHETTI, 2 DE ´ BORA DE FREITAS GRISOLIA, 2 JOA ˜ O PAULO MARDEGAN ISSA, 4 MARCELO CAVENAGHIPEREIRA DA SILVA, 1 AND II-SEI WATANABE 1,2,3 * 1 Department of Morphology and Genetics, Federal University of Sa ˜ o Paulo, Sa ˜ o Paulo, Brazil 2 Department of Anatomy, Institute of Biomedical Sciences, University of Sa ˜ o Paulo, Sa ˜ o Paulo, Brazil 3 Department of Surgery, Faculty of Veterinary Medicine and Animal Science, University of Sa ˜ o Paulo, Sa ˜ o Paulo, Brazil 4 Department of Morphology, Stomathology and Physiology, Faculty of Dentistry of Ribeira ˜ o Preto, University of Sa ˜ o Paulo, Ribeira ˜ o Preto, Brazil KEY WORDS temporomandibular joint; synovial membrane; aging; microscopy, electron ABSTRACT The aim of this study was to analyze the rat temporomandibular joint (TMJ) syno- vial membrane at different ages using light, scanning, and transmission electron microscopy. Under light microscopic analysis, the TMJ structures were observed such as condyle, capsule, disk, the synovial membrane collagen type, and cells distribution. In the scanning electron microscopy, the synovial membrane surface exhibited a smooth aspect in young animals and there was an increase with ageing in the number of folds. The transmission electron microscopic analysis showed more synoviocytes in the synovial layer in the young group and still a great number of vesicles and cis- terns dilation of rough endoplasmic reticulum in the aged group. In the three groups, a dense layer of collagen fibers in the synovial layer and cytoplasmic extensions were clearly seen. It was possible to conclude that synovial membrane structures in aged group showed alterations contributing to the decrease in joint lubrication and in the sliding between disk and joint surfaces. These character- istic will reflect in biomechanics of chewing, and may cause the TMJ disorders, currently observed in clinical processes. Microsc. Res. Tech. 75:1522–1527, 2012. V V C 2012 Wiley Periodicals, Inc. INTRODUCTION Temporomandibular joint (TMJ) disorders in humans have controversial treatment among health- care professionals and hence the normal structural and ultrastructural morphology in different stages of life is necessary to propose more effective treatments. Studies in humans are usually carried out from autopsy samples but the clinical conditions and the artic- ular pre-existing illnesses cannot be accurately eval- uated through the familiar and clinical histories (Lekkas et al., 1988). Considering these facts and other difficul- ties such as standardized operational protocols of age, gender, race, and period of treatment or illness, animal specimens are being used for the TMJ study and the ex- istence of anatomical and functional differences between animal species must be considered (Ogi et al., 1997). Several structural and ultrastructural articular aspects were studied using methods of light, transmis- sion, and scanning electron microscopy, such as ultra- structure of articular cartilage of the mouse TMJ (Yoshida et al., 2004), calcification of articular cartilage in monkeys (Luder and Schroeder, 1992), the normal morphology and steroids use in rat knee synovial mem- brane (Murashige et al., 1999), the ultrastructure of articular cartilage of the chicken knee (Graf et al., 1993), and synovial membrane vascular architecture of the rat knee joint (Funk et al., 1995). Ageing is a natural process, which causes several morphological and physiological changes in different tissues and organs. These changes predispose tissues to various diseases, and the temporomandibular disor- ders have shown a drastic increase in dentistry offices in the last years (Nozawa-Inoue et al., 2003). Although it is widely known the structures and func- tions of synovial membrane, little is known about their structural and ultrastructural aspects during the age- ing process. The aim of this study was to analyze the rat TMJ synovial membrane at different ages, using the methods of light, scanning, and transmission elec- tron microscopy. MATERIALS AND METHODS In this descriptive study, 27 male Wistar rats used were divided into three groups: Young (1 month of age), Adult (4 months of age), and Aged (24 months of age). In each group, three animals were used for light microscopy, three for scanning electron microscopy, and three for transmission electron microscopy. The procedures were approved by the Ethics Com- mittee on Animal Experiments of the Federal Univer- sity of Sa ˜ o Paulo (Protocol 0233/08). The animals were kept in cages with light/dark cycle of 12 h, room tem- perature (25 6 28C), chow, and water ad libitum. *Correspondence to: Ii-Sei Watanabe, Department of Anatomy, Institute of Biomedical Sciences (ICB)—University of Sa ˜o Paulo (USP), Av. Prof. Lineu Pre- stes, 2415-Butanta ˜ 05508-900, Sa ˜o Paulo, SP, Brazil. E-mail: watanabe@icb.usp.br Received 8 December 2011; accepted in revised form 11 June 2012 DOI 10.1002/jemt.22095 Published online 13 July 2012 in Wiley Online Library (wileyonlinelibrary.com). V V C 2012 WILEY PERIODICALS, INC. MICROSCOPY RESEARCH AND TECHNIQUE 75:1522–1527 (2012)