Mari Kobayashi

Expression and localization of insulin-regulatable glucose transporter (GLUT4) in rat brain

The localization of glucose transporters (GLUTs) was examined in various regions of the rat brain. The mRNA of GLUT1 and GLUT3 were found ubiquitously in every brain region (cortex, hippocampus, midbrain, striatum, hypothalamus, medulla oblongata and cerebellum). The mRNA and protein of GLUT4, an insulin-regulatable glucose transporter in peripheral tissues, were also identified, particularly abundantly in the cerebellum. In situ hybridization analysis revealed that GLUT4 mRNA was present in some discrete cells, such as Purkinje cells in the cerebellum, the vestibular nucleus in the medulla oblongata and also in ependymal cells along the cerebral ventricles. The GLUT4 mRNA level in the cerebellum changed little in fasted or experimentally induced diabetic rats while those in adipose tissues decreased much. The results suggest that insulin-sensitive glucose uptake may occur in some specific cells of the brain but is regulated in a different manner from those in peripheral cells.

Roles of prostaglandins D2 and E2 in interleukin-1-induced activation of norepinephrine turnover in the brain and peripheral organs of rats.

Abstract: Possible roles of prostaglandins (PGs) in interleukin‐1 (IL‐1)‐induced activation of noradrenergic neurons were examined by assessing norepinephrine (NE) turnover in the brain and peripheral organs of rats. An intraperitoneal injection of human recombinant IL‐1β accelerated NE turnover in the hypothalamus, spleen, lung, diaphragm, and pancreas. A similar increase in NE turnover was also observed after intracerebroventricular injection of corticotropin‐releasing hormone (CRH). Pretreatment with indomethacin (cyclooxygenase inhibitor) abolished the IL‐1‐induced, but not the CRH‐induced, increase in hypothalamic and splenic NE turnover. To elucidate which eicosanoid‐cyclooxygenase product(s) is responsible for accelerating NE turnover, PGD2, PGE2, PGF2α, U‐46619 (stable thromboxane A2 analogue), or carbacyclin (stable prostacyclin analogue) was administered intracerebroventricularly. Among them, PGE2 was the only eicosanoid effective in increasing NE turnover in spleen, whereas PGD2 was effective in the hypothalamus. The stimulative effect of PGD2 was abolished by pretreatment with intracerebroventricular injection of a CRH antiserum. These results suggest that the action of IL‐1 is mediated through PGD2 production to activate the noradrenergic neurons in the hypothalamus, and through PGE2 production to increase sympathetic nerve activity in spleen.

Genetic variation in the harbor seal (Phoca vitulina) and spotted seal (Phoca largha) around Hokkaido, Japan, based on mitochondrial cytochrome b sequences

The harbor seal (Phoca vitulina) and spotted seal (Phoca largha) are the main seal species around Hokkaido, Japan. While some investigations have been conducted on the ecology and morphology of these two species, there is a lack of genetic information. We studied variation in mitochondrial cytochrome b sequences in the two species. Fifteen haplotypes were observed in 39 harbor seals from Erimo, Akkeshi, and Nosappu, and 23 were observed in 31 spotted seals from Erimo, Akkeshi, Nosappu, Rausu, Yagishiri Island, and Hamamasu. Phylogenetic trees showed two harbor seal lineages: Group I contained primarily haplotypes from Erimo, and Group II contained haplotypes from Akkeshi and Nosappu. Because the Erimo population had fewer haplotypes and less nucleotide diversity than the Akkeshi and Nosappu populations, we considered it to be Isolated from the others. In contrast, genetic variance within populations of spotted seals (97.3%) was far higher than that among populations (2.7%), determined by analysis of molecular variance. There were no significant difference among the spotted seal populations, indicating the absence of distinct lineages around Hokkaido. The differences in the genetic population structure between the two species could have been generated by their ecological differences. This study provides basic genetic information on these seal species and will contribute to the conservation and management of fisheries and seals throughout Hokkaido.

A topographical study of the electroplax sodium channel with site-directed antibodies

Three peptides corresponding to residues (13-23C), (Y1419-1431), and (1809-1820) of the electric eel sodium channel have been synthesized and used to raise antisera in rabbits. All the antibodies produced specifically recognized the corresponding peptides in an ELISA assay. However, their avidities to the channel protein were different. Two antibodies, against the sequence (1809-1820) and (13-23C) which are directed to the C-terminus region and to the adjacent portion of N-terminus, respectively, recognized the 250 kDa channel protein in the immunoblot and an ELISA assay. Binding of the two antibodies to the sodium channel in oriented electroplax membrane vesicles was increased 4-5-fold after permeabilizing the vesicles with 0.01% saponin, implying cytoplasmic orientation for the two peptides. The cytoplasmic orientation of the N- and C-terminal regions were further confirmed by immunogold electron microscopy. By contrast, antibody raised against the sequence (Y1419-1431) which has been proposed to be the transmembrane segment S4 of internal repeat IV, did not react with the channel protein not only after the saponin treatment but also even under the immunoblot conditions following SDS-PAGE. The antibody could recognize fragments of the channel protein after digestion with lysyl endoproteinase, suggesting that the region may apparently form a strictly well-ordered conformation in the transmembrane part of the channel molecule.

Stable isotope ratios of carbon, nitrogen and oxygen in killer whales (Orcinus orca) stranded on the coast of Hokkaido, Japan.

We analyzed δ(13)C, δ(15)N and δ(18)O in the muscle and liver from killer whales stranded on the coast of Japan. The δ(15)N values in the muscle samples from calves were apparently higher than those in their lactating mothers, suggesting that nursing may result in the higher δ(15)N values in the muscle samples of calves. The δ(15)N value in the muscle samples of male and female whales, except for the calves, were positively correlated with the δ(13)C values and body length, suggesting that the increases in δ(15)N were due to the growth of the whales and increase in their trophic level. In contrast, the δ(18)O values in the muscle samples of female whales except for the calves were negatively correlated with the δ(13)C and δ(15)N values. The δ(18)O may be lower in whales occupying higher trophic positions (δ(15)N), although it might also be affected by geographic and climatic conditions.

Mitochondrial DNA reveals secondary contact in Japanese harbour seals, the southernmost population in the western Pacific

In this study, we used relatively large number of samples (n = 178) and control region of mtDNA (454bp) to clearify the divergence history of Japanese harbour seals (Phoca vitulina stejnegeri) and phylogenetic relationship between the seals in Japan and other countries. Our results suggested that Japanese harbour seals possibly consisted of more than two lineages and secondary contact of populations after a long isolation. Furthermore, one of the lineage was made only by Japanese harbour seals (Group P1). The proportion of Group P1 was the highest at the South West and gradually decreased towards the North East of Hokkaido, Japan. On the other hand, the haplotypes do not belonged to Group P1 showed close relationship to the seals in the North Pacific. Based on the fossil record of harbour seal in Japan and the range of sea ice during the Last Glacial Maximum (LGM), Group P1 might have entered Japan before the LGM and became isolated due to the geographical boundary, and gradually extended its range from the South West towards the North East of Hokkaido after the disappearance of the sea ice, while the seals which are not in Group P1 immigrated into Japan from the North Pacific.

Use of Haul-Out Sites by Spotted Seals (Phoca largha) on Rebun and Todojima Islands in the Japan Sea from 2008 to 2009

The spotted seal (Phoca largha) is known to breed (give birth and nurse) on sea ice. The species is known to migrate over a large area, moving to northern feeding grounds to catch a prey in summer and breeding on the edge of sea ice in winter (Kobayashi 2008). There are seven known breeding areas of spotted seals on sea ice, including the southern Bering Sea, east Kamchatka, the northern Okhotsk Sea (above 55°N), the southern Okhotsk Sea from north Sakhalin to Hokkaido, the Tatar Strait, Peter the Great Bay, and the Bohai Gulf in China (Shaughnessy and Fay 1977; Lowry 1985). During non-breeding periods, the spotted seal is distributed on the continental shelf of the Beaufort Sea, the Chukchi Sea, the southeastern East Siberian Sea, the Bering Sea, the Okhotsk Sea, southward throughout the Japan Sea near Hokkaido, and in the northern Yellow Sea (Burns and Fay 1972; Naito and Nishiwaki 1972; Shaughnessy and Fay 1977; Naito and Konno 1979; Lowry 1985). In Japan, the distribution of spotted seals is limited to around Hokkaido in winter (Naito 1977; Naito and Konno 1979; Uno and Yamanaka 1988). Breeding areas close to Japan have been reported in the Okhotsk Sea and in the Nemuro Channel (Naito and Nishiwaki 1972; Naito and Konno 1979). In the late 1970s, many seals concentrated along the drift ice on the Kitami-Yamato Bank and in the Nemuro Channel. Haul-out sites included Lake Saroma, Cape Notoro, the entire coastline of the Shiretoko Peninsula, Odaito, and Lake Furen (Naito 1977). Generally, the population migrating to the Okhotsk Sea was considered to travel south from Russian waters; in early spring, the population moved north to its summer habitats on the coast of Sakhalin and elsewhere (Bigg 1981). However, some seals do not follow the northward summer migration and remain in the area near Hokkaido. Kobayashi (2008) observed that during the summer, seals inhabited Odaito, Lake Furen, Habomai islands, and Shikotan, Kunashiri, and Etorofu Islands. On the other hand, Naito (1977) reported that seals rarely appeared and no haul-out sites were recorded in the Japan Sea. Until the 1980s, spotted seals were commercially hunted for meat, pelage, and fat in the sea around Hokkaido. Since the 1980s, seals have seldom been hunted (Yoshida 1977; Uni 2000; Kobayashi 2008). As a result, seals have increased in the Okhotsk Sea (Fedoseev 2000; Mizuno et al. 2002). From aerial surveys, Fedoseev (2000) estimated a 4-fold increase (from 67,000 to 268,000) in the abundance of spotted seals in the Okhotsk Sea between 1968 and 1990. In the late 1990s, the distribution of spotted seals expanded to the Japan Sea and many haul-out sites were

Host characteristics and infection level of an intestinal parasite Corynosoma strumosum (Acanthocephala) in the Kuril harbor seal of Erimo Cape, Hokkaido, Japan

The Kuril harbor seal around Hokkaido is presently recovering from a resource crisis while conflicts with local fisheries have become a concern. However, its feeding habits, which are fundamental information for taking proper preventive measures, are still poorly understood. We thus examined the infection status of a trophically-transmitted parasite, Corynosoma strumosum in the seals of Erimo Cape, to assess the hosts feeding habits with a practical view of the parasite as a biological indicator. A total of 2802 worms were found from 20 male and 20 female by-caught animals in salmon set nets within local fisheries during August to November 2014. The parasite abundance was explained mainly by the hosts developmental stage and intestinal length while weakly affected by gender and body size, through an estimation of generalized linear models combined with hierarchical partitioning. Considering the past records that demersal fishes are the probable main sources of infection, the infection level may owe to individual host differences regarding these sources and/or feeding grounds with relating the host characteristics. This supports that the resource management of Kuril harbor seals requires careful consideration of the individual differences in feeding behavior.

Seasonal and Spatial Occurrence of Northern Fur Seals Callorhinus ursinus Around Northern Japan

Abstract. Northern fur seals (Callorhinus ursinus) disperse to broad areas and overwinter in the North Pacific Ocean during the non-breeding season. Fur seals breeding on islands off Russia mainly overwinter in the Sea of Japan and the off Pacific side of Japan in this season. Although the distribution of fur seals seems to vary with sexes and growth stages in this season, there is little information around Japan. We analysed data on stranding and collecting records of fur seals in the non-breeding season around northern Japan during 2005–2014 for investigating their intra-seasonal and spatial occurrence. The sex and growth stage composition differed between sampling areas. Adult males were dominant in the Sea of Japan, while juveniles and adult females were dominant in the Pacific coast of northern Japan. Compared with previous researches, our results can provide important information for elucidating migration pattern and habitat selection of each sex and growth stage around northern Japan.

Occurrence of the Kuril Harbour Seal (Phoca vitulina) at a small fixed fishing net in Akkeshi Bay, Hokkaido, Japan

1Graduate School of Fisheries Sciences, Hokkaido University, 3–1–1 Minato–cho, Hakodate, Hokkaido, 041–8611, Japan. 2Current Address: Laboratory of Animal Ecology, Research Faculty of Agriculture, Hokkaido University, Kita-9, Nishi-9, Kita-ku, Sapporo, Hokkaido, 060-8589, Japan. 3Department of Aqua Bioscience and Industry, Tokyo University of Agriculture, Abashiri, Hokkaido, 099-2493, Japan 4Akkeshi town Fisherman, Akkeshi, 088–0875, Japan.