Browsing by Author "SAITUA, F"

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    AXONAL MICROTUBULES - COMPARATIVE ANATOMY IN VERTEBRATES, INCLUDING MAN
    (1991) VERGARA, J; SERRA, M; SAITUA, F; ITURRIAGA, R; ALVAREZ, J
    The microtubular density was assessed with the electron microscope in 3-mu-m myelinated fibers, myelin excluded, of 11 species from the following classes: Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia. The average for all species was 20.6 microtubules/mu-m2. Dispersion of values was restricted as shown by a coefficient of variation of 15.8. The microtubular content of nonmedullated axons was assessed in trout, lizard, finch, and man. In the four species, the number of microtubules increased with the cross sectional area of the axon. In trout, lizard and finch, the microtubular density decreased from over 100 microtubules/mu-m2 in fibers smaller than 0.1-mu-m2 to about 30 in 1-mu-m2 fibers; in axons of equal size, the packing of microtubules of nonmedullated was similar between them, and with reported values for peripheral axons of cat and rat. In man, the microtubular density of nonmedullated fibers exhibited only a mild decrease with the axonal size. In the finch, myelinated and nonmedullated axons overlapped in the range 0.23-0.60-mu-m2 and both groups exhibited similar microtubular densities. We conclude that the packing of microtubules of the vertebrate peripheral axon is a feature largely conserved during evolution.
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    DO AXONS GROW DURING ADULTHOOD - A STUDY OF CALIBER AND MICROTUBULES OF SURAL NERVE AXONS IN YOUNG, MATURE, AND AGING RATS
    (1988) SAITUA, F; ALVAREZ, J
    Calibers and microtubules of sural nerve axons were studied in young (6-week-old), mature (14-week-old), and aging (2-year-old) rats.The mean cross-sectional area of nonmedullated fibers was about 0.50 .mu.m2 (range: 0.47-0.52) in the three age groups. Their caliber spectra were also similar. In contrast, myelinated axons grew from 6.6 to 16.7 .mu.m2between the sixth and 14th week of age. The increase of cross-sectinal area was greater, the greater the initial caliber of axon (range 44-154%). No further change of caliber was observed in the aging rat. The cross-sectional area of nerve allotted per myelinated fiber was 42, 66, and 97 .mu.m2 in young, mature, and aging rats, respectively. The fraction of nerve tissue occupied by the axoplasm, though, did not change substantially; it was 20, 28, and 21%, respectively.The microtubular density of 3-.mu.m myelinated axons had a general average of 21 microtubules/.mu.m2. Differences between groups were not significant. In nonmedullated fibers, the microtubular density decreased as the size of the axon increased. No differences were observed between age groups. We conclude that nonmedullated fibers of the sural nerve stop growing before the sixth week whereas myelinated fibers keep growing until the 14th week of age. The correlation between microtubular content and axonal caliber is a lifelong feature of axons.
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    MICROTUBULAR PACKING VARIES ALONG THE COURSE OF MOTOR AND SENSORY AXONS - POSSIBLE REGULATION OF MICROTUBULES BY ENVIRONMENTAL CUES
    (1989) SAITUA, F; ALVAREZ, J
    In the toad Xenopus laevis, the microtubular density of 3-.mu.m myelinated fibres was assessed in peripheral nerves, dorsal and ventral roots, and dorsal and ventral funiculi of the spinal cord. In the roots, the axonal microtubular density was 6 microtubules/.mu.m2 and twice as much at the other sampling sites. This indicates that the pattern of the microtubular packing may vary along the course of the axon. We propose that axonal microtubules are regulated by local cues.