Hidetoshi Toh

Factors influencing otolith strontium/calcium ratios in Anguilla japonica elvers

The effects of temperature and salinity on the concentration ratios of strontium (Sr) to calcium (Ca) within the sagittal otoliths of elvers of the Japanese eel, Anguilla japonica, were studied by spot analysis using a wavelength dispersive X-ray electron microprobe. A total of 340 elvers were used: 100 elvers were reared for 15 days under various salinity conditions (freshwater, one-third seawater, two-thirds seawater and pure seawater at 22 °C; 240 elvers were reared for 58 days under various water temperature conditions (12, 17, 22, 27 °C) in either freshwater or pure seawater. Otolith Sr/Ca ratios were found to be positively correlated with water salinity. On the other hand, the Sr/Ca ratios were not found to be significantly different among the various temperature groups. The above results strongly suggest that the physiological mechanism of incorporation of Sr and Ca within the otolith of an eurythermal fish, Japanese eel, does not change within this range of temperatures (12–27 °C).

Effect of Denervation on Morphogenesis of the Rat Fungiform Papilla

In an attempt to elucidate the effects of denervation on development and maintenance of the structure of the fungiform papilla, unilateral neurectomy of the chorda tympani-lingual nerve of rats was performed at day 1 and at weeks 1, 2, 3, 4, 7, and 10 after birth. Specimens were obtained at days 3, 7 and 10, weeks 2, 3, 4, 6, and 8, and months 3 and 4 after neurectomy for examination by light and scanning electron microscopy. At first, the fungiform papillae were atrophic, then progressed to forms resembling filiform papillae. When an immature fungiform papilla was denervated, it eventually changed to papilla identical to normal filiform papillae. The elicited changes differed according to the time of neurectomy; it was found that early neurectomy resulted in a more rapid and marked morphological change of the fungiform papillae. The filiform-like papillae derived from the fungiform ones showed various shapes, sizes, and orientations and were rarely present on the unoperated control side of the lingual dorsum. Sections of the filiform-like papillae revealed that they had no taste buds. These findings suggest: (1) Morphogenesis and structural maintenance of the fungiform papillae require the presence of the chorda tympani and/or lingual nerve. (2) Completion of differentiation and maturation differ in time among fungiform papillae. (3) Fungiform papillae may be transformed filiform papillae induced and maintained by a neurotrophic factor of factors coming from the chorda tympani and/or lingual nerve. (4) Fungiform papillae are rarely innervated contralaterally.

Determination of the freshwater mark in otoliths of Japanese eel elvers using microstructure and Sr/Ca ratios

The microstructure, in particular checks within the otolith edge, of Anguilla japonica glass-eels and elvers and changes in otolith Sr/Ca ratios were examined to ascertain the environmental history of the eels, especially with regard to the time when glass-eels entered the river, and as a benchmark for count daily increments. The percentage of glass eels and elvers with checks and the mean number of checks within the otoliths of glass-eels caught at four localities, Tosa Bay off Tosa City, the mouth of the Gokase River, the mouth of the Saigo River and the dam of the Tsuri River were 0% (0), 15.0% (0.2), 51.6% (1.0) and 100.0% (4.2), respectively. The Sr/Ca ratios and Sr content peaked in the region where checks were formed and the values decreased rapidly towards the edge of the checks; on the other hand, these decreased gradually in the otolith when checks were not formed. These checks were estimated to be formed by stress when the glass-eels were affected by ambient fresh water within the river. The innermost check was called the ‘freshwater mark’ in the present study and this mark may be useful as a benchmark in studying the growth history of the eel before and after entering freshwater.

Ultrastructure of Weber's salivary glands of the root of the tongue in the rat

The mammalian tongue encompasses several sizeable agglomerations of minor salivary glands. The ultrastructure of the various glands in the body of that organ has already been determined. In contrast, almost nothing is known of the structure of Webers glands, a collection of salivary glands in the root of the tongue.

Fine structure of the horny teeth of the lamprey, Entosphenus japonicus

SummaryThe fine structure of the horny teeth of the lamprey, Entosphenus japonicus, was examined by light- and electron-microscopy. Most of the horny teeth consisted of two horny and two nonhorny layers. The primary horny layer was well keratinized, and the cells were closely packed and intensely interdigitated, being joined together by many modified desmosomes. The plasma membrane of the horny cell, unlike the membranes of other vertebrates, was not thickened. The intercellular spaces were filled with electron-dense material. Microridges were seen on the free surface. Structures resembling microridges were found on the underside of the primary horny layer. The secondary horny layer displayed various stages of keratinization. The keratinization started at the apex and developed toward the base. In the early stage of keratinization, the superficial cells became cylindrical and were arranged in a row forming a dome-shaped line. Their nuclei were situated in the basal part of the cells. The appearance of the nonhorny layers varied according to the degree of keratinization of the horny layers beneath them. The nonhorny cells were joined together by many desmosomes and possessed many tonofilament bundles. The replacement and keratinization of the horny teeth are discussed in the light of these results.