MORPHO-FUNCTIONAL ANALYSIS OF THE MALE REPRODUCTIVE TRACT OF THE GREATER CANE RAT (Thryonomys swinderianus)

Abstract

The greater cane rat (Thryonomys swinderianus) is a wild, herbivorous hystricomorphic rodent that is currently undergoing domestication and captive-rearing in parts of Africa. Information on the reproductive biology of this animal is scarce. This study was aimed at investigating the structural and functional anatomy of the testes, excurrent ducts and accessory sex glands of the greater cane rat. This will add to baseline information to enhance its breeding and enrich the knowledge of reproductive anatomy of rodents.

Eighty-five sexually matured cane rats with age range of 7-41months were obtained from two commercial farms in Ogun State, Nigeria. The body mass index (BMI) was obtained using body weight (BW) and the nose-to anus length. Morphological and morphometric investigations of each segment of the reproductive system at gross, histological and ultrastructural levels were carried out. Assay of five reproductive hormones and immunolocalisation of the receptors of progesterone (PR) and estrogen (ERα and ERβ) were carried out using standard methods. Monthly variations of the testis and epididymis to determine reproductive efficiencies at different seasons were evaluated using morphometric tools. Standard mammalian anatomical nomenclatures were used to describe features while numerical data were subjected to correlation analysis at p=0.05.

The average BW of the animals was 2.23 ±0.40 Kg while the BMI ranged from 0.88 – 1.70 g/cm2. The testis was found in varied regions in the animal including abdominal, inguinal and scrotal areas. Also observed was inverted S-shaped epididymis, prostate gland with four lobes on the right and three on the left and Y-shaped cranially branched vesicular gland. Histologically, nine stages of seminiferous epithelium cycle were identified and the epididymis presented six discrete zones in its four typical regions. The prostate showed two distinct zones while the coagulating, vesicular and bulbourethral glands exhibited normal histological features typical of rodents. Distinctive ultrastructural features observed included 12-step spermatids differentiation, large fluid-filled lymphoid sinuses in the testicular interstitium and the presence of intraepithelial macrophages found only in the vas deferens. Also, apocrine secretory pattern in the coagulating gland and the classic electron-dense strands radiating from secretory granules of the bulbourethral gland were observed. The tubular diameter of the cauda epididymis was widest in April (647.9 ±145 µm) and lowest in January (319.3 ±60.7 µm). Significantly positive correlation was observed between the animal’s height and testicular weight and volume. There was double fold increase in serum testosterone level in the rainy season. The epididymis showed selective intense ERβ staining of its narrow, apical and basal cells while PR was immuno-localised in the principal cells of cauda epididymis.

The nine-stage spermatogenic cycle and the 12-step spermatid differentiation coupled with the sequences of acrosomal formation indicate short pattern of spermatogenesis in the male greater cane rat. Also, the distribution pattern of the hormonal receptors as well as seasonal variation in the serum testosterone levels characterise this species as a seasonal breeder with increased reproductive activities during the rainy season.

Keywords: Greater cane rat, Sex hormone receptor, Reproductive anatomy. Word count: 479