BRIEF COMMUNICATION Ultrastructural Demonstration of Cilia in the Adult Human Ependyma ' SUBIMAL ROY, ASAO HIRANO AND HARRY M. ZIMMERMAN Division of Neuropathology, Department of Pathology, Montefiore Hospital a n d Medical Center, a n d Albert Einstein College of Medicine, Bronx, N e w York, N e w York 10467 Ependyma from random sites of lateral, third and fourth ventricles including the aqueduct in five adult human brains was examined by transmission electron microscopy. In all the specimens studied, cilia were present in variable numbers in the ependymal cells. Our study thus establishes that there is widespread presence of cilia in the ependymal cells of the ventricular system in the adult human brain. ABSTRACT It has been stated in many standard textbooks that human ependymal cells are ciliated only in embryonic life and that in the adult, cilia are either absent or occur only in patchy areas (Strong and Elwyn, '53; Ranson and Clark, '59; Bloom and Fawcett, '62; Truex and Carpenter, '70). These observations are apparently based on light microscopic study which does not appear to provide unequivocal evidence of the presence or absence of cilia. Worthington and Cathcart ('63) showed evidence of ciliary movement in the adult human ependymal cells examined by water immersion lenses. Scanning electron microscopic examination by Bruni, Montemurro, Clattenburg and Singh ('72) has also suggested the presence of cilia in the adult human ependyma in the third ventricle. However, since there is a possibility that the cilia may be confused with elongated microvilli under the scanning electron microscope (Bruni et al., '72), transmission electron microscopic demonstration of cilia is considered to be definitive evidence of their presence. Malinsky ('68) examined human adult ependyma only from the lateral ventricle in one case and demonstrated the presence of both cilia and microvilli in the ependymal cells. The purpose of the present investigation was to examine the adult human ependyma from the lateral, third and fourth ventricles, including the aqueduct, for the presence of absence of cilia. MATERIALS AND METHODS Small pieces of ventricular wall with ANAT. REC., 180: 547-550. ependymal lining were collected from random sites of the lateral, third and fourth ventricles and the aqueduct of five adult human brains.a The brains were fixed in formalin for 10 to 14 days before the tissues for electron microscopy were obtained. The pieces were post-fixed in 4% glutaraldehyde and then in 1% osmium tetroxide and processed for electron microscopy. The tissue was flat-embedded to maintain the proper orientation of the ependymal surface. Thin sections were cut with the ultramicrotome, stained with uranyl acetate and lead citrate and examined under the electron microscope. OBSERVATIONS In all five brains, cilia were found in many ependymal cells of all the ventricles and the aqueduct. In some cells, only occasional cilia were present (fig. 1 ) while in others, many cilia were observed (fig. 2). The cilia in the human ependymal cells were found to have structural similarity to those present in many other cells (Fawcett, '66). Thus, they appeared as tubular structures containing ten pairs of filaments within them with characteristic (9 4-2) pattern, i.e. nine pairs of peripherallyarranged filaments and a pair in the center. Their association with the basal body could be found in sections cut at appropriate planes. Received April 1, '74. Accepted June 20, '74. 1 This investigation received financial support from the World Health Organizatlon. zThe specimens were obtained at autopsy with the consent and signature of the next of kin. 547 548 SUBIMAL ROY, ASAO HIRANO AND HARRY M. ZIMMERMAN Fig. 1 Ependymal cell with a small number of cilia ( C ) . Many microvilli ( M ) are also present. Formalin-fixed postmortem material from the fourth ventricle. X 12,000. In many cells, well preserved microvilli were also found (fig. 3 ) . They, too, were variable in number and were particularly numerous in a small number of cells. They appeared smaller and thinner than the cilia, had a different internal structure and occasionally showed branching. In many cells, both microvilli and cilia could be observed (fig. 1 ) . DISCUSSION Cilia have been demonstrated by electron microscopy in ventricular ependymal cells of many adult animals like cat (Klinkerfuss, '64) ; rat (Brightman and Palay, '63; Rinne, '66; Hirano, Zimmerman and Levine, '66; Hirano and Zimmerman, '67; Westergaard, '70); rabbit (Tennyson and Pappas, '62); and monkey (Knowles and Anand Kumar, '69 ) . In man only, embryonic ependymal cells are generally believed to be ciliated. The presence of cilia in the adult human ependymal cells has not been adequately demonstrated. Although the scanning electron microscopic study of Bruni et al. ('72) suggested the presence of cilia in the adult human ependymal cells of the third ventricle, they pointed out that similar structures (cilia) may be interpreted by others as microvilli. Transmission electron microscopic study of Malinsky ('68) based on the examination of ependyma only from the lateral ventricle in one human adult brain did show the presence of cilia in the ependymal cells. The present ultrastructural study also showed unequivocal presence of cilia in the adult human ependyma1 cells. Further, it appears from our observations that the presence of cilia in adult ependyma is quite widespread, being present in all the ventricles of the brain and the aqueduct. The ultrastructure of cilia in the adult human ependyma appears to be similar to those present in ependyma of various adult animals ADULT HUMAN EPENDYMA 549 Fig. 2 Ependymal cell with many cilia cut in longitudinal, transverse and oblique planes. Note ( 9 2 ) arrangement of filaments i n transversely cut cilia (C). Basal bodies ( B ) are also present. Formalin-fixed postmortem material from the third ventricle. x 23,500. + (Tennyson and Pappas, '62; Brightman and Paley, '63; Klinkerfuss, '64; Fleischhauer, ' 7 2 ) , including their association with the basal body. ACKNOWLEDGMENT The authors acknowledge the technical help of Ms Ernestine Middleton. LITERATURE CITED Bloom, W., and D. W. 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