Correlation of cloacal gland histomorphology, ultrastructure and androgen receptor expression with testosterone levels during sexual maturation in the Japanese quail (Coturnix coturnix japonica)

Abstract

The cloacal gland of the Japanese quail is an enlarged glandular protuberance, found on the dorsal wall of the cloaca. The gland is unique to the genus Coturnix and is present in both male and female quails, but only sexually active males demonstrate functional development. There is a positive correlation between the size of the gland and circulating testosterone levels. Furthermore, it is known that testicular activity and cloacal gland size are influenced by photoperiod. However, it is unknown whether sexual maturation during a period of decreasing daylength affects the morphology of the cloacal gland. Thus, the aim of the current study was to investigate the correlation of cloacal gland histomorphology and ultrastructure with testosterone levels in the Japanese quail during sexual maturation through a period of decreasing daylength. A total of 7 pre-pubertal, 7 pubertal and 7 adult male Japanese quails were used in this study. The cloacal glands of the birds were investigated using: haematoxylin and eosin staining; periodic acid Schiff and alcian blue histochemistry; terminal deoxynucleotidyl transferase-mediated deoxyuridine 5’-triphosphate nick-end labelling (TUNEL); androgen receptor immunohistochemistry and transmission electron microscopy. In addition, testosterone levels were measured in blood samples collected during euthanasia. Histological examinations revealed that the glandular units of the cloacal glands in pre-pubertal, pubertal and adult birds were lined by columnar secretory cells. The secretory cells showed positive staining for periodic acid Schiff and alcian blue, indicating the presence of both acidic and neutral mucopolysaccharides. The cloacal gland cells in pre-pubertal birds were TUNEL negative, while positive TUNEL staining was observed in nuclei of the secretory cells in pubertal and adult birds. These results suggest that decreasing daylengths caused a decrease in testicular activity which led to a reduction in circulating testosterone levels in the pubertal and adult birds. Due to the fact that the cloacal gland is an androgen-dependent organ, the reduction in testosterone resulted in glandular regression. At an ultrastructural level apoptotic cells were observed in the glandular units of pubertal and adult birds. These ultrastructural findings corroborate the TUNEL results. This study has shown that changes in plasma testosterone concentrations, during sexual maturation, are positively correlated with histomorphological and ultrastructural alterations in the cloacal glands of Japanese quails.