Ultrastructural Characterization of Stem Cell‐Derived Replacement Vestibular Hair Cells Within Ototoxin‐Damaged Rat Utricle Explants

Ultrastructural characteristics of Azolla leaf cavities were examined using transmission electron microscopy. An extracellular inner envelope, which forms a boundary between the central cavity region and the peripheral region containing cyanobacteria and (or) bacteria, was found in all closed leaf cavities of symbiotic and Anabaena-free Azolla species. In the youngest leaf, which is in the process of developing a cavity, a continuous inner envelope was never observed. However, in young leaves that contained closed cavities, and in older leaves, continuous inner envelopes were always observed. The inner envelope may serve to restrict the symbionts to the cavity periphery. The inner envelope was similar in appearance to the outer envelope, which encloses the symbionts and hair cells within leaf cavities. Examination of the inner envelope using three different fixation procedures revealed that it was most distinct in fronds fixed in potassium permanganate, suggesting that it is membranelike in structure. The envelope was occasionally seen folded back upon itself or curled, which is also characteristic of a membranelike structure. Nevertheless, the envelope did not exhibit typical tripartite membrane ultrastructure. The occurrence of the inner envelope in Anabaena-free Azolla indicates that this envelope is of eubacterial or plant origin.

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Ultrastructural identification of three types of sensory setae on copepod antennae

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100141159 ◽

1995 ◽

Vol 53 ◽

pp. 956-957

Author(s):

T. M. Weatherby ◽

P.H. Lenz

Keyword(s):

Phase Locking ◽

Membrane Surface ◽

Reaction Times ◽

High Sensitivity ◽

Structural Features ◽

Calanoid Copepods ◽

Marine Food Webs ◽

Dendritic Membrane ◽

Ultrastructural Characterization

Crustaceans, as well as other arthropods, are covered with sensory setae and hairs, including mechanoand chemosensory sensillae with a ciliary origin. Calanoid copepods are small planktonic crustaceans forming a major link in marine food webs. In conjunction with behavioral and physiological studies of the antennae of calanoids, we undertook the ultrastructural characterization of sensory setae on the antennae of Pleuromamma xiphias.Distal mechanoreceptive setae exhibit exceptional behavioral and physiological performance characteristics: high sensitivity (<10 nm displacements), fast reaction times (<1 msec latency) and phase locking to high frequencies (1-2 kHz). Unusual structural features of the mechanoreceptors are likely to be related to their physiological sensitivity. These features include a large number (up to 3000) of microtubules in each sensory cell dendrite, arising from or anchored to electron dense rods associated with the ciliary basal body microtubule doublets. The microtubules are arranged in a regular array, with bridges between and within rows. These bundles of microtubules extend far into each mechanoreceptive seta and terminate in a staggered fashion along the dendritic membrane, contacting a large membrane surface area and providing a large potential site of mechanotransduction.

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