Fine structure of the fungiform papilla in a ranid frog (rana esculenta).

The freetop of the fungiform papilla shows a sensorial area about 100 micron in diameter, surrounded by a ring of ciliated cells. Externally to the ciliated cells, i.e., in the lateral wall, numerous large goblet cells can be seen devoid of their mucous content. The sensorial area is composed by three types of cells: mucous, supporting, and neuroepithelial cells. Mucous cells form the most superficial layer, while the cell bodies of the other two are deep, and from them basal and apical processes arise. The above mentioned cells are connected by desmosomes preferentially located between the mucous and the supporting cells, rather than between the supporting and the neuroepithelial cells. The lateral wall of the papilla is made up of a multilayered epithelium that comprises two types of cells: the first type contains electron-dense granules and an abundant rough endoplasmic reticulum, the others are ciliated cells. In the connective axis of the papilla, numerous fenestrated capillaries with endothelial vesiculated cells and nerve fibers are found

Paracoronal cavity system and papillary water uptake

In the research it has been carried out a morphological investigation of the paracoronal area of the fungiform papillae. By means of scanning, transmission and light microscopy it has been observed in this area a series of superficial openings around and external to the ciliary crown; and in the epithelium corresponding cavitary system. Each cavity on the other hand appears surrounded by extremely narrow epithelial cells and thus appears able to facilitate the papillary exchange activity. This paracoronal cavitary system is proposed as morphological candidate for the conspicuous water entry in the papillae during osmotic phenomena

Fine structure of the fungiform papilla in a ranid frog (Rana esculenta).

The freetop of the fungiform papilla shows a sensorial area about 100 micron in diameter, surrounded by a ring of ciliated cells. Externally to the ciliated cells, i.e., in the lateral wall, numerous large goblet cells can be seen devoid of their mucous content. The sensorial area is composed by three types of cells: mucous, supporting, and neuroepithelial cells. Mucous cells form the most superficial layer, while the cell bodies of the other two are deep, and from them basal and apical processes arise. The above mentioned cells are connected by desmosomes preferentially located between the mucous and the supporting cells, rather than between the supporting and the neuroepithelial cells. The lateral wall of the papilla is made up of a multilayered epithelium that comprises two types of cells: the first type contains electron-dense granules and an abundant rough endoplasmic reticulum, the others are ciliated cells. In the connective axis of the papilla, numerous fenestrated capillaries with endothelial vesiculated cells and nerve fibers are found

Plasma membrane Ca(2+)-ATPase isoforms in frog crista ampullaris: Identification of PMCA1 and PMCA2 specific splice variants.

Ca2+ ions play a pivotal role in inner ear hair cells as they are involved from the mechano-electrical transduction to the transmitter release. Most of the Ca2+ that enters into hair cells via mechano-transduction and voltage-gated channels is extruded by the plasma membrane Ca-ATPases (PMCAs) that operate in both apical and basal cellular compartments. Here, we determined the identity and distribution of PMCA isoforms in frog crista ampullaris: we showed that PMCA1, PMCA2 and PMCA3 are expressed, while PMCA4 appears to be negligible. We also identify PMCA1bx, PMCA2av and PMCA2bv as the major splice variants produced from PMCA1 and PMCA2 genes. PMCA2av appears to be the major Ca2+-pump operating at the apical pole of the cell, even if PMCA1b is also expressed in the stereocilia. PMCA1bx is, instead, the principal PMCA of hair cells basolateral compartment, where it is expressed together with PMCA2 (probably PMCA2bv) and PMCA3. Frog crista ampullaris hair cells lack a Na/Ca exchanger, therefore PMCAs are the only mechanism of Ca2+ extrusion. The coexpression of specific isozymes in the different cellular compartments responds to the need of a fine regulation of both basal and dynamic Ca2+ levels at the apical and basal pole of the cell

Exposure to reduced gravity impairs junctional transmission at the semicircular canal in the frog labyrinth.

The effects of microgravity on frog semicircular canals have been studied by electrophysiological and morphological approaches. Reduced gravity (microG) was simulated by a random positioning machine (RPM), which continually and randomly modified the orientation in space of the anesthetized animal. As this procedure stimulates the semicircular canals, the effect of altered gravity was isolated by comparing microG-treatment with an identical rotary stimulation in the presence of normal gravity (normoG). Electrophysiological experiments were performed in the isolated labyrinth, extracted from the animals after the treatment, and mounted on a turntable. Junctional activity was measured by recording quantal events (mEPSPs) and spikes from the afferent fibers close to the junction, at rest and during rotational stimulation. MicroG-treated animals displayed a marked decrease in the frequency of resting and evoked mEPSP discharge, vs. both control and normoG (mean decrease approximately 50%). Spike discharge was also depressed: 57% of microG-treated frogs displayed no spikes at rest and during rotation at 0.1 Hz, vs. 23-31% of control or normoG frogs. Among the firing units, during one cycle of sinusoidal rotation at 0.1 Hz microG-treated units emitted an average of 41.8 +/- 8.06 spikes, vs. 77.2 +/- 8.19 in controls. Patch-clamp analysis on dissociated hair cells revealed altered Ca(2+) handling, after microG, consistent with and supportive of the specificity of microG effects. Marked morphological signs of cellular suffering were observed after microG, mainly in the central part of the sensory epithelium. Functional changes due to microgravity were reversible within a few days

Localization of Ca-ATPase in frog crista ampullaris.

The distribution of Ca-ATPase in frog crista ampullaris was mapped ultracytochemically by using a one-step lead citrate reaction. Electron-dense precipitates, as an expression of Ca-ATPase activity, were observed on the surface of stereocilia and on the apical membrane surrounding the cuticular plate of hair cells. Sensory cells of the isthmus region showed more reactivity than those of the peripheral regions of the crista. No reaction products were detectable on the basolateral membranes and in cytoplasmatic organelles. Supporting cells of the crista showed a quite variable Ca-ATPase reaction on microvilli and on basolateral membranes. The presence of an evident reactivity on the stereocilia is consistent with the existence of an apical calcium microdomain involved in the mechano-transduction process and supports the current view that calcium ions enter the stereocilia during natural stimulation. On the other hand, the lack of an observable reactivity on the basolateral membrane of hair cells suggests that in semicircular canals other mechanisms of active transport of calcium ions across the plasma membrane, such as Na-Ca exchange, may be involved in homeostasis of the ion

Morpho-Physiological recovery of frog vestibular hair cells following aminoglycoside toxicity

Aminoglycoside antibiotics, including gentamicin (GM), are known to induce severe degenerative effects in both cochlear and vestibular organs. The discovery that hair cells readily regenerate in fish, amphibians, reptiles and birds after antibiotic treatment has stimulated the study of the mechanisms of repair and regeneration of the hair cells in different inner ear organs. The present investigation was designed to elucidate the morphological and functional recovery of hair cells in frog semicircular canals. GM was administered intraotically close to the perilymphatic cisterna at the concentration of 5 mM (15 μl volume). Frogs were sacrificed at post-injection times ranging from 1 to 20 days. Degenerative changes at hair cell level started 1-2 days after GM treatment and were severe in the intermediate regions of the crista and then involved the central and peripheral regions. Hair cell degeneration in the three crista regions appeared complete after 6-8 days. Damaged hair cells showed stereocilia loss together with a swelling of cell bodies and nuclei. Partially extruded hair cells from the epithelium were also observed together with large epithelial holes. Regenerating hair cells were often seen 6 day after GM treatment. They were identified based on their small cell bodies and nuclei as well as their small immature hair bundles. From this stage, hair cells density increased and the sensory epithelium recovered a normal appearance within 15 days. The functional recovery of hair cells during the regenerative period was studied by using whole cell patch recordings in crista slice preparations up to 20 days from gentamicin treatment. Passive and active electrical properties of hair cells from control animals have been compared with those of regenerating hair cells. Regenerating cells showed patterns of responses qualitatively similar to those of normal hair cells. However, the magnitude of the ionic currents increased during recovery suggesting that new hair cells came from precursors which reacquired progressively their complement of ionic channels. We found that the complement of K+ channels were completely functional in regenerated hair cells at 15 days post-treatment with gentamicin. Moreover, the regenerated cells in each region of the crista neuroepithelium reacquired the same complement of channels of normal preparations