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

Oct 6, 2026

Study of wild male Japanese black bears (Ursus thibetanus japonicus) evaluates how puberty age and reproductive seasonality relate to testicular spermatogenesis and steroidogenic activity. Twenty-one bears captured during 1998–2000 had testes measured, biopsied for histology, and four steroidogenic enzymes immunolocalized. Serum testosterone was quantified by radioimmunoassay. Testis size peaked around 5 years, maturation was estimated at 3–4 years, testosterone ranged 0.05–1.78 ng/ml, and spermatogenesis was highest in June–August. Immunolocalization links Leydig and Sertoli-related cells to androgen and estrogen synthesis through steroidogenic enzymes.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages7

Reading Time18 min

AccessFree to download

Materials and Methods

Capture and handling

Microscopic observations

Radioimmunoassay

Immunohistochemistry

# Spermatogenesis,Serum Testosterone Levels and Immunolocalization ofSteroidogenic Enzymes in the Wild Male Japanese Black Bear(Ursus thibetanusjaponicus) Tsukasa OKANO¹),Tetsuma MURASE¹,2)and Toshio TSUBOTA1.2)* United Graduate School ofVeterinary Medicine and²)Divsion of Veterinary Medicine,Faculty of Agriculture,Gifu University,I-1 Yanagido,Gifu 501-1193,Japan (Received 8 January 2003/Accepted 14 July 2003) KEY WORDS:Japanese black bear,spermatogenesis,steroidogenic enzyme,testosterone,Ursus thibetanus japonicus. In order to enhance the conservation and management ofwild animals,we have to know the population dynamics ofbreeding-age animals.For this purpose,age at sexual matu-ration and seasonal changes in reproductive activity such asgonadal morphology profiles and sexual behavior in thepopulation need to be determined [11].With this in mindecological investigations and physiological examinations ofthe Japanese black bear(Ursus thibetanus japonicus)arebeing performed in many study areas,and reproductivephysiology in the male Japanese black bear has beenreported recently from this point of view [11,12,22]. The age of sexual maturation (puberty)in male Japaneseblack bears is estimated to be 2-4 years with some varia-tions among studies based on the histology of testes,theirsize and weight,and the diameter of seminiferous tubules[11,12,16,22]It is known that the reproductive physiol-ogy of the male Japanese black bear shows notable seasonalchanges [25]with mating occurring from June to August[29].In relation to this,testes indicate physiological andmorphological changes,and the period of high spermatoge-nic activity is limited to several months,including the mat-ing season [13]. The aim of this study was to determine the age of sexualmaturation and the seasonal changes in spermatogenesis andtesticular steroidogenesis in wild male Japanese black bears. ABSTRACT.Twenty-one wild male Japanese black bears(Ursus thibetanus japonicus)were captured in the summer-autumn of 1998-2000in the vicinity of Neo Village,Gifu Prefecture.Testes were measured,and testicular samples were biopsied and observed histologically.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.Serumtestosterone concentrations were measured by radioimmunoassay.Testis size changed itle from 1-3 years of age,increased rapldly at4 years,and attained its peak at 5 years.Serum testosterone concentrations ranged from 0.05 to 1.78 ng/ml,and the mean ±standarddeviation was 0.43±0.48 ng/ml.Age of sexual maturation in wild male Japanese black bears was estimated to be 3-4 years.Seasonalchanges in spermatogenesis were obvious;active in June,July and August,degenerated by September.Leydig cells,Sertoli cells andgerm cells have the capability of synthesizing androgen,and Leydig cells,Sertoli cels,spermatids and spermatogona have the capabilityof synthesizing estrogen in Japanese black bears. J.Vet.Med.Sci.65(10):1093-1099,2003 ## MATERIALS AND METHODS Capture and handling:Wild male Japanese black bearsthat inhabit Neo Village,Gifu Prefecture,were caught bybarrel-type traps from 26 June 1998 to 13 November 1998,from 15 May 1999 to 12 November 1999,and from 15 July2000 to 31 August 2000.Capture of bears was performedwith the permission of the former Environment Agency,Japan.Allthetraps were checked twice a week for capturedbears.After capture,bears were handled on the next day. Trapped bears were immobilized by an intramuscularadministration of ketamine HCI(Veterinary Ketalar 50(10mg/kg)and medetomidine HCI(Domitor:0.04 mg/kg),orZolazepam HCl and Tiletamine HCI(Zoletil:9 mg/kg).After immobilization,bears were weighed and their physi-cal condition was monitored for body temperature,pulseand respiration.Then blood samples were obtained from thejugular vein with vacuum blood drawing t

FAQs

What is the main goal of the study on wild male Japanese black bears?

To determine the age of sexual maturation and seasonal changes in spermatogenesis and testicular steroidogenesis in wild male Japanese black bears.

How were serum testosterone levels measured?

Serum testosterone concentrations were measured by radioimmunoassay using testosterone antiserum, a standard testosterone preparation, and tritiated testosterone as the tracer.

Which period showed the most active spermatogenesis, and how did it change over the year?

Spermatogenesis was active in June, July, and August, then degenerated by September.

Oct 6, 2026

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