Spermatogenesis, Serum Testosterone Levels and Immunolocalization of Steroidogenic Enzymes in the Wild Male Japanese Black Bear (Ursus thibetanus japonicus)

Abstract

ABSTRACT. Twenty-one wild male Japanese black bears ( Ursus thibetanus japonicus) were captured in the summer-autumn of 1998-2000 in the vicinity of Neo Village, Gifu Prefecture. Testes were measured, and testicular samples were biopsied and observed histol ogically. Four steroidogenic enzymes, i.e., cholesterol side-chain cleavage cytochrome P450 (P450scc), 3β-hydroxysteroid dehydrogenase (3βHSD), 17-α hydroxylase cytochrome P450 (P450c17), and aromatase cytochrome P450 (P450arom) were immunolocalized. Serum testosterone concentrations were measured by radioimmunoassay. Testis size changed little from 1-3 years of age, increased rapidly at 4 years, and attained its peak at 5 years. Serum testosterone concentrations ranged from 0.05 to 1.78 ng/ml, and the mean ± standard deviation was 0.43 ± 0.48 ng/ml. Age of sexual maturation in wild male Japanese black bears was estimated to be 3-4 years. Seasonal changes in spermatogenesis were obvious; active in June, July and August, degenerated by September. Leydig cells, Sertoli cells and germ cells have the capability of synthesizing androgen, and Leydig cells, Sertoli cells, spermatids and spermatogonia have the capability of synthesizing estrogen in Japanese black bears. KEY WORDS: Japanese black bear, spermatogenesis, steroidogenic enzyme, testosterone, Ursus thibetanus japonicus.J. Vet. Med. Sci. 65(10): 1093-1099, 2003 In order to enhance the conservation and management of wild animals, we have to know the population dynamics of breeding-age animals. For this purpose, age at sexual maturation and seasonal changes in reproductive activity such as gonadal morphology profiles and sexual behavior in the population need to be determined [11]. With this in mind ecological investigations and physiological examinations of the Japanese black bear (Ursus thibetanus japonicus) are being performed in many study areas, and reproductive physiology in the male Japanese black bear has been reported recently from this point of view [11,12,22].The age of sexual maturation (puberty) in male Japanese black bears is estimated to be 2-4 years with some variations among studies based on the histology of testes, their size and weight, and the diameter of seminiferous tubules [11,12,16,22]. It is known that the reproductive physiology of the male Japanese black bear shows notable seasonal changes [25] with mating occurring from June to August [29]. In relation to this, testes indicate physiological and morphological changes, and the period of high spermatogenic activity is limited to several months, including the mating season [13].The aim of this study was to determine the age of sexual maturation and the seasonal changes in spermatogenesis and testicular steroidogenesis in wild male Japanese black bears. MATERIALS AND METHODS Capture and handling:Wild male Japanese black bears that inhabit Neo Village, Gifu Prefecture, were caught by barrel-type traps from 26 June 1998 to 13 November 1998, from 15 May 1999 to 12 November 1999, and from 15 July 2000 to 31 August 2000. Capture of bears was...

Seasonal Changes in Immunolocalization of Inhibin/Activin Subunits and Testicular Activity in Wild Male Raccoon Dogs (Nyctereutes procyonoides)

“…These results suggest that seasonal changes in testicular weight and size are correlated with changes in the numbers of germ cells in the wild male raccoon dog. These findings are similar to those observed in other mammals, such as the roe deer [29], black bear [30,31], and horse [32,33].…”

Localization of Five Steroidogenic Enzyme mRNAs in Japanese Black Bear (Ursus thibetanus japonicus) Testes During the Mating Season by In Situ Hybridization

“…In accordance with the findings in other mammalian species [10,11,21,22], the present study detected the metabolic enzymes from cholesterol to androstenedione (P450scc, 3βHSD and P450c17) in interstitial tissue of the Japanese black bear testis. These results are also in agreement with the immunohistochemical localization of these three enzymes in the Japanese black bear testis [2,9]. This strongly suggests that androstenedione is synthesized in the interstitial tissue, probably in Leydig cells in the bear.…”

“…The Japanese black bear (Ursus thibetanus japonicus), a subspecies of the Asiatic black bear living in Japan, is a typical seasonal breeder that has a mating season in early summer. The changes in the histological appearance of the testicular seminiferous tubules and the concentration of testosterone in peripheral blood have been described for some species of bears, including the Japanese black bear [1][2][3][4][5]. However, the molecular mechanisms that produce reproductive seasonality in the testis have not yet been elucidated in bears.…”

“…Also, there are several reports at the protein level based on the immunohistochemical method in wild animals like brown bears [8], black bears [2,9], raccoon dogs [10] and deer [11]. However, there have been few reports on the gene expression of steroidogenic enzymes in the testes of wild mammals.…”

Electroejaculation and Semen Cryopreservation of Free-Ranging Japanese Black Bears (Ursus thibetanus japonicus)

“…Age of sexual maturation in wild male Japanese black bears was estimated to be 3-4 years [23]. In this study, all the captured bears were considered to be over 4 years old.…”