Ovarian function of the algerian wild Libyan jird, Meriones libycus during seasonal reproductive cycle: histological and immunohistochemical expression

Abstract

Meriones libycus (Libyan jird), a nocturnal Saharan rodent, is characterized by a seasonal reproductive cycle with a short active phase (spring and early summer) and a long resting period (late summer, autumn, winter). Histological and immunohistochemical techniques were performed in order to study the seasonal variations in mature ovaries. During the breeding season, the ovary showed a continuous cyclical activity, the various stages of folliculogenesis from primordial to preovulatory follicles were observed; broken follicles and corpora lutea were also observed. During sexual quiescence, the ovarian cycle was interrupted; anovulation was observed without any corpus luteum. Non mature antral follicles entered the atretic process. Steroid and steroidogenic enzyme activities were studied using indirect immunohistochemistry. 17ß-estradiol, progesterone, testosterone hormones and P450 aromatase (P450 arom) were detected in the different components of the ovary and in various stages of healthy and atretic follicles during the seasonal reproductive cycle. Our results indicate that during ovarian folliculogenesis in breeding season steroids hormone and P450 arom present important activities. In comparison with the resting period, steroidogenesis and steroidogenic enzyme activity became less pronounced in the healthy preantral follicle; it seemed that steroid biosynthesis was reduced and could be involved in the stimulation and maintenance of the ovarian structural integrity in early follicle development. In conclusion, the histological and immunohistochemical seasonal variations of ovaries in Meriones libycus support the hypothesis that seasonal fluctuations are indirectly involved in regulating reproduction, inducing significant changes in both ovarian morphology and its hormonal function.