The developmental pattern of the neuromuscular junction (NMJ) in masseter muscles of the Japanese field vole, Microtus montebelli, was investigated using acetylcholinesterase (AChE) staining and electron microscopy. At birth, intense AChE activity limited to the site of the NMJ where many axon terminals with the cholinergic nature were converging was observed, indicating that cholinergic neuronal activity in the vole masseter muscle begins at this stage. The major morphogenesis of the NMJ such as : AChE staining reaction, concentration of myonuclei at the subneural site, elimination of the axon terminals, formation of the myeline sheath in the intramuscular axons, and the appearance of numerous junctional folds in the postsynaptic membrane was accelerated after postnatal day five, and amended dramatically at day ten with the maturation time of these NMJ components at around day fifteen. From the combination of the present and previous studies, it is clear that both AChE reaction and neuronal structures alter considerably at a time when structural and functional improvements give rise dramatically to muscle fibers. This must be considered in relation to the critical role of the neuronal influence on the differentiation and maturation of the vole masseter muscles that are required for the accomplishment of its own characteristic herbivorous food habits.

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To study genetic diversity of populations of the sika deer, Cervus nippon, in Hokkaido, polymorphism of three microsatellite loci (OarFCB193, BOVIRBP and INRA040) were examined and compared with that of the population of Chiba Prefecture in the Japanese main island (Honshu). The microsatellite genotype frequency significantly well agreed with the Hardy-Weinberg expectation at each locus of each population except for INRA040 of the Chiba population. Average observed heterozygosity (Ho=0.21±0.11) of the Hokkaido population was relatively smaller than that of the Chiba population (Ho=0.23±0.09). Moreover, observed heterozygosities of OarFCB193 and BOVIRBP of the Hokkaido population were lower than that of the Chiba population, and the number of alleles observed at each locus was smaller in the Hokkaido population than in the Chiba population. These results indicate a lower genetic diversity in the Hokkaido population, resulting from their historical bottleneck(s) previously reported. The present study provides information of useful microsatellite markers and gives an insight for better understanding population genetics of the Japanese sika deer.

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Knowing demographic parameters is important in order tounderstand the life history of mammals. As an example, the twinning rate of sika deer, Cervus nippon, on Mt. Goyo was determined based on 2,064 samples collected from 1981 to 1997. The sex ratio of single fetuses (n=1,946) was even (49.8% males and 50.2% females). Six pairs (0.29%) of twins were found. One pair was composed of male and female embryos, suggesting that at least some conceptions are dizygotic. It was concluded that twinning is rare in sika deer. This rate was similar to, or lower than, that found in red deer, C. elaphus.

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A new telemetric system known as the “Trace Recorder” was developed in order to reduce labor costs and to avoid radio-tracking location errors. It was first tested during studies of habitat utilization by raccoon dog, Nyctereutes procyonoides viverrinus, in Japan. The Trace Recorder (TR) consists of four separate units : beacons, recording units (RU), an automatic collar release system (ACRS) and a personal computer for processing data. The beacons emit 8 kHz magnetic signals periodically. A total of 600 different magnetic codes can be used in order to identify locations. The collar-based RU intercepts and records signals when the study animal is within 3 m of a beacon. The ACRS installed on the collar alongside the RU allows the collar to be released by a special code and recovered so as to facilitate the retrieval of stored data. In order of evaluate the capabilities of the trace recorder system, we used the TR in the analysis of the habitat use of a raccoon dog for 25 days between 16 November and 10 December 1996 in Hinode Town, suburb of Tokyo. Twenty-four beacons were set at along paths, at a garbage site, and at badger setts and animal latrines. The RU recorded 91 time units and durations of visits to trails and to some cores sites were collected. The TR system is capable of recording census data 24 hours every day for three months. The new TR system proved to be more accurate than current radio-telemetry equipment for recording frequency, duration and times of visits to target sites by the study animal.

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