Kazuyoshi Arishima

Comparative Functional Morphology of the Masticatory Apparatus in the Long‐snouted Crocodiles

The masticatory muscles and their related structures of the skull were observed in the Indian gavial (Gavialis gangeticus), the false gavial (Tomistoma schlegelii), and the African slender‐snouted crocodile (Mecistops cataphractus) to detail some morphological differences in comparison with the other crocodile species, and to compare and elucidate the functional strategy of themasticatory apparatus in these long‐snouted species. The Musculus pterygoideus posterior was relatively smaller in the three species compared with many short‐snouted crocodiles. It suggests that the masticatory power in fish‐eating long‐snouted species is not so high as in the short‐snouted crocodiles, while the masticatory muscles were morphologically different among the three long‐snouted species as follows. The M. pterygoideus posterior of the false gavial was extended in the lateral side of the lower jaw unlike the Indian gavial. The M. pseudotemporalis and the Fenestra supratemporalis were largely developed in the Indian gavial, however we suggest that the other two species possess the weak bundles in this muscle. The false gavial and the African slender‐snouted crocodile have the pterygoid bone well‐developed extending dorso‐ventrally and it is suggested that the M. adductor mandibulae posterior attached to the pterygoid bone may be much larger than the Indian gavial. These data morphologically clarify the masticatory mechanism in the long‐snouted crocodiles different from the short‐snouted species, and demonstrate that the evolutional strategy to share the functional role in the masticatory muscles have been differently established between the Indian gavial and the other two species. We also obtained the morphological data in the fossil skull of the Machikane crocodile (Toyotamaphymeia machikanense) and concluded from the fossil characters that the considerable developments of the M.pterygoideus posterior and the M.pseudotemporalis in this species had not morphologically been consistent with both the Indian and false gavials.

Histological Changes in the Placenta Induced by Maternal Alcohol Consumption in the Rat

To investigate the placental enlargement which accompanies maternal alcohol consumption during pregnancy, Sprague-Dawley rats were given 20% ethanol for 4 weeks prior to mating and 30% ethanol throughout gestation. Pair-fed controls received an isocaloric amount of corn starch and chow, with water ad libitum, and ad libitum controls received rat chow and water. On days 17, 18, 19 and 20 of gestation, placentas were removed for histological observation. On days 18-20, the placentas of alcohol-fed rats weighted significantly more than did those of controls, although there was no difference in weight on day 17. Giant cells in the basal zone were significantly increased in number and size in alcohol-fed rats compared to controls. Trophoblastic cells in the basal zone were significantly larger in the alcohol group than in the control groups except on day 17. The maternal blood channels in the labyrinth were wider and more filled with blood corpuscles in the alcohol group than in either control group. It is concluded that the increased weight of the placenta may be largely due to stagnated maternal blood cells in the labyrinthine blood channels and also to the increased number and size of giant cells and the enlarged trophoblastic cells in the basal zone.

Vitamin K has the potential to protect neurons from methylmercury-induced cell death in vitro.

Vitamin K (VK) has a protective effect on neural cells. Methylmercury is a neurotoxicant that directly induces neuronal death in vivo and in vitro. Therefore, in the present study, we hypothesized that VK inhibits the neurotoxicity of methylmercury. To prove our hypothesis in vitro, we investigated the protective effects of VKs (phylloquinone, vitamin K1; menaquinone‐4, vitamin K2) on methylmercury‐induced death in primary cultured neurons from the cerebella of rat pups. As expected, VKs inhibited the death of the primary cultured neurons. It has been reported that the mechanisms underlying methylmercury toxicity involve a decrement of intracellular glutathione (GSH). Actually, treatment with GSH and a GSH inducer, N‐acetyl cysteine, inhibited methylmercury‐induced neuronal death in the present study. Thus, we investigated whether VKs also have protective effects against GSH‐depletion‐induced cell death by employing two GSH reducers, L‐buthionine sulfoximine (BSO) and diethyl maleate (DEM), in primary cultured neurons and human neuroblastoma IMR‐32 cells. Treatment with VKs affected BSO‐ and DEM‐induced cell death in both cultures. On the other hand, the intracellular GSH assay showed that VK2, menaquinone‐4, did not restore the reduced GSH amount induced by methylmercury or BSO treatments. These results indicate that VKs have the potential to protect neurons against the cytotoxicity of methylmercury and agents that deplete GSH, without increasing intracellular GSH levels. The protective effect of VKs may lead to the development of treatments for neural diseases involving GSH depletion.

Onset of the Constrictive Effect of Indomethacin on the Ductus arteriosus in Fetal Rats

The time of onset of the constrictive effect of indomethacin on the ductus arteriosus (DA) in fetal rats was assessed by measurement of the caliber of the DA after maternal treatment with indomethacin on days 19-21 of gestation. The day following overnight mating was regarded as day 0 of gestation. Observation was performed by direct exposure of the DA by hand shaving of intact frozen fetuses. On days 20 and 21, the DA was significantly constricted 3 h after maternal treatment with 1 mg/kg of indomethacin. When the DA was examined at 19 1/2 and 19 2/3 days of gestation (3 h after indomethacin exposure), it was significantly constricted at 19 2/3 days but not at 19 1/2 days. Higher doses of indomethacin (10 and 100 mg/kg) induced a significant constriction of the DA at day 19 1/2, but not at the beginning of the same day (1.00 a.m.). These results suggest that the onset of the susceptibility of the DA to the constrictive effect of indomethacin occurs in the first half of day 19 of gestation.

Acceleration of methylmercury-induced cell death of rat cerebellar neurons by brain-derived neurotrophic factor in vitro

Brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor (NGF) family and has been shown to promote neuronal survival and contribute to neural development. Although methylmercury, a neurotoxin, induces the cell death of neurons in vitro, there is little information regarding the effects of neurotrophins on the methylmercury-induced cell death of neurons. In the present study, we investigated the effect of BDNF on methylmercury-induced cell death in a primary culture of rat cerebellar granular cells. BDNF increased the viability of the cultured cells when treated alone, but unexpectedly accelerated the cell death induced by administration of methylmercury. Among other growth factors tested, only neurotrophin-4 (NT-4) demonstrated a similar acceleration of methylmercury-induced cell death. The cell death-accelerating effect of BDNF was inhibited by a BDNF-neutralizing antibody or a MAPK inhibitor. To determine whether the effect of BDNF occurs via TrkB, a receptor of BDNF and NT-4, we investigated the effects of BDNF and methylmercury in a TrkB transformant of rat neuroblastoma B35 cells. The methylmercury-induced cell death of the TrkB transformant was accelerated by BDNF, while that of the mock transformant was not. These results indicate that BDNF accelerates methylmercury-induced cell death via TrkB, at least in vitro, and suggest that BDNF and TrkB may also contribute to the sensitivity of neurons to methylmercury toxicity.

Radial sesamoid bone as a part of the manipulation system in the lesser panda (Ailurus fulgens)

The well-developed radial sesamoid bone presented a rod-like shape in the lesser panda. It could be separated into two components: (1) an ulnar cartilaginous, (2) a radial osseous part. The radial sesamoid bone was connected with four elements as follows: (1) the tendon of the M. abductor pollicis longus, (2) M. abductor pollicis brevis and M. opponens pollicis, (3) Aponeurosis palmaris, and (4) Flexor retinaculum. The bone made no articulation with the first metacarpal. The movement of the radial sesamoid bone may be controlled by the connecting muscles and muscle-related structures. It is suggested that the bone acts as a supporting ridge in the gripping action in the lesser panda. However, we suggest that the grasping mechanism is obviously different from that of the giant panda, in which the radial sesamoid bone is connected strongly with the first metacarpal.

Involvement of Independent Mechanism Upon Poly(ADP-ribose) Polymerase (PARP) Activation in Methylmercury Cytotoxicity in Rat Cerebellar Granule Cell Culture

Poly(ADP‐ribose) polymerase (PARP) activation plays a role in repairing injured DNA, while its overactivation is involved in various diseases, including neuronal degradation. In the present study, we investigated the use of a PARP inhibitor, 3,4‐dihydro‐5‐[4‐(1‐piperidinyl)butoxy]‐1(2H)‐isoquinolinone (DPQ), whether methylmercury‐induced cell death in the primary culture of cerebellar granule cells involved PARP activation. DPQ decreased the methylmercury‐induced cell death in a dose‐dependent manner. Unexpectedly, this protective effect was DPQ specific; none of the other PARP inhibitors—1,5‐dihydroxyisoquinoline, 3‐aminobenzamide, or PJ34—affected neuronal cell death. Methylmercury‐induced cell death involves the decrease of glutathione (GSH) and production of reactive oxygen species. Therefore, to understand the mechanism by which DPQ inhibits cytotoxicity, we first studied the effect of DPQ on buthionine sulfoximine– or diethyl maleate–induced death of primary cultured cells and human neuroblastoma IMR‐32 cells, both of which are mediated by GSH depletion. DPQ inhibited the cell death of both cultured cells, but it did not restore the decrease of cellular GSH by buthionine sulfoximine to the control level. Second, we evaluated the antioxidant activity of PARP inhibitors by methods with ABTS (2‐2′‐azinobis(3‐ethylbenzothiazoline 6‐sulfonate) or DPPH (1,1‐diphenyl‐2‐picrylhydrazyl) used as a radical because antioxidants also efficiently suppress methylmercury‐induced cell death. The antioxidant activity of DPQ was the lowest among the tested PARP inhibitors. Taken together, our results indicate that DPQ effectively protects cells against methylmercury‐ and GSH depletion–induced death. Furthermore, they suggest that DPQ exerts its protective effect through a mechanism other than PARP inhibition and direct antioxidation, and that PARP activation is not involved in methylmercury‐induced neuronal cell death.

Developmental toxicity of indium: embryotoxicity and teratogenicity in experimental animals.

ABSTRACT  Indium, a precious metal classified in group 13 (IIIB) in the periodic table, has been used increasingly in the semiconductor industry. Because indium is a rare metal, technology for indium recycling from transparent conducting films for liquid crystal displays is desired, and its safety evaluation is becoming increasingly necessary. The developmental toxicity of indium in experimental animals was summarized. The intravenous or oral administration of indium to pregnant animals causes growth inhibition and the death of embryos in hamsters, rats, and mice. The intravenous administration of indium to pregnant animals causes embryonic or fetal malformation, mainly involving digit and tail deformities, in hamsters and rats. The oral administration of indium also induces fetal malformation in rats and rabbits, but requires higher doses. No teratogenicity has been observed in mice. Caudal hypoplasia, probably due to excessive cell loss by increased apoptosis in the tailbud, in the early postimplantation stage was considered to account for indium‐induced tail malformation as a possible pathogenetic mechanism. Findings from in vitro experiments indicated that the embryotoxicity of indium could have direct effects on the conceptuses. Toxicokinetic studies showed that the embryonic exposure concentration was more critical than the exposure time regarding the embryotoxicity of indium. It is considered from these findings that the risk of the developmental toxicity of indium in humans is low, unless an accidentally high level of exposure or unknown toxic interaction occurs because of possible human exposure routes and levels (i.e. oral, very low‐level exposure).

The sensitivity of the fetal rat adrenal gland to adrenocorticotropic hormone in vivo and in vitro.

Rat fetuses were treated with 1 IU ACTH on day 16 or 17 of gestation and autopsied on the next day. Other fetuses of the same litter were treated with saline alone. The adrenal glands of ACTH-treated fetuses were significantly heavier than those of saline-treated fetuses and of intact controls in every experimental period. These changes in the weight of fetal adrenal glands reflect histologically on changes in the size of adrenocortical cells which were enlarged in response to injected ACTH. Adrenal glands from rat fetuses of different ages were explanted to organ cultures for 2 days, in medium with or without ACTH added. The 13-day adrenal glands were not able to respond to ACTH, but the response appeared abruptly in the 14-day adrenal glands, judging from the increased cell size in histological sections. The overall results suggest that the fetal adrenal gland begins to respond to ACTH from day 14 of gestation.

The structure of the masseter muscle in the giraffe (Giraffa camelopardalis).

In the giraffe (Giraffa camelopardalis), the masseter muscle was divided into several layers. The superficial and more medial (second) tendinous sheets of the masseter muscle fused with each other at the dorso‐caudal part and a fleshy portion was located between these tendinous sheets. In the rostral part, the most superficial tendinous sheet turned around as a compact tendon and attached to the facial crest (Crista facialis). The turned tendinous sheet, however, never fused with the second tendinous sheet and this layer of the masseter muscle, that originated from the facial crest with the turned sheet, was inserted into the mandible with its fleshy portion. In the cattle, goat, sheep and Sika deer, the rostral layer of the masseter muscle arises from the facial crest with its fleshy portion and is inserted into the tubercle on the mandible through the strong tendinous sheet. In this study, the takin also showed the same structure of the masseter muscle. In the giraffe, however, the rostral layer inserted into the mandible through the strong tendinous sheet could not be distinguished, thus, there was no conspicuous tubercle on the mandible. Moreover in the masseteric region of the skull, the giraffe was similar to the Sika deer in several ways. However, it is suggested that the giraffe exerts smaller forces on the cheek teeth than does the Sika deer because of its longer Margo interalveolaris.