BACKGROUND: This study was conducted on human cervical mucus using light microscopy (LM) and scanning electron microscopy (SEM). The objective was the morphological characterization of the different mucus types, with samples taken from the lumen of the cervix and from the different secretory zones of the cervical mucosa. METHODS: A total of 230 samples from 195 women were spread out on slides and air dried. The phenomenon of ‘ferning’ was observed and assessed in these samples using both LM and SEM. Further samples from the lumen of the cervix and the different secretory crypts were spread out on cover slips and fixed with glutaraldehyde (2.5%) to be studied by SEM. RESULTS: The results show the presence of four different morphological mucus types, namely L, S, P and G, in both types of sample using dried and fixed techniques. CONCLUSIONS: Mucus from the lumen of the cervix appears to be a morphologically heterogeneous entity. It contains different types of secretions, the proportions of which vary throughout the menstrual cycle. The different mucosal types show different types of crystallization, different patterns of ultrastructure (probably related to the arrangement of the glycoprotein network) and are produced in different secretory zones of the crypts in the cervix.

Summary: In the hamster, male reproductive quiescence is accomplished via testicular atrophy and the germinal epithelium is regressed to spermatogonia and spermatocytes after 8–14 weeks of short photoperiods. However, the cellular mechanisms involved in this process have not been elucidated. As it is suggested that the regulation of seasonal testicular activity is characterized by coordinated shifts in the relationships between mitosis, meiosis and apoptosis, the changes in the proliferative and apoptotic activity in the seminiferous epithelium of photoinhibited Syrian hamster were examined and compared with those maintained in natural photoperiod. The proliferative activity was studied using BrdU immunostaining, and germ cell apoptosis was assessed by in situ TUNEL labelling and transmission electron microscopy. A significant increase in the rate of apoptosis (percentage of TUNEL‐positive spermatogonia + spermatocytes) was observed in photoinhibited animals (2.84 ± 0.16) compared with those exposed to natural photoperiod (0.77 ± 0.03, p < 0.05). The majority of apoptotic germ cells were spermatocytes and in some occasions spermatogonia. Germ cell apoptosis was confirmed by morphological characteristics: condensation of the chromatin and nuclear fragmentation. The rate of proliferation (percentage of BrdU‐positive spermatogonia + preleptotene spermatocytes) was significantly higher in photoinhibited hamsters (42.7 ± 2.6) compared with animals exposed to natural photoperiod (31.1 ± 1.6, p < 0.05). After the exposure to a short photoperiod the apoptotic index positively correlated with the proliferative index (r = 0.8150, p < 0.05). In conclusion, the seminiferous epithelium of photoinhibited Syrian hamsters is characterized by an increased rate of apoptosis associated to an enhanced rate of proliferation.

During the non‐breeding season some animals exhibit testicular atrophy, decreased testicular weight and reduced seminiferous tubule diameter accompanied by depletion of the seminiferous epithelium. Some cellular factors involved in this depletion are changes in germ cell proliferation and apoptosis. In the Syrian hamster this depletion has been studied histologically and in terms of the involvement of proliferation and apoptosis in the seminiferous epithelium of fully regressed testes. The objectives of this study included the histomorphometrical characterization of the testis and the determination of the proliferative and apoptotic activity of germ cells in the seminiferous epithelium during testicular regression owing to short photoperiod. The study was performed using conventional light microscopy (hematoxylin and eosin), proliferating cell nuclear antigen and terminal deoxynucleotidyl transferase (TdT)‐mediated dUTP in situ nick end labelling staining, image analysis software, and transmission electron microscopy in three established regression groups: mild regression (MR), strong regression (SR), and total regression (TR). Morphometrically a gradual decrease in total tubular area and in the testicular, tubular, and epithelial volumes was observed during testicular regression. Interstitial and luminal volumes decreased from the MR group onwards. The tubular length decreased from MR to SR. As regards spermatogonial proliferation, only an initial decrease in proliferative activity was observed, whereas apoptotic germ cell activity increased throughout regression. The number of germ cells studied decreased throughout the process of testicular regression. In conclusion, testicular regression in Syrian hamster comprises two histomorphometrical phases, the first involving a decrease in seminiferous tubular diameter and volume and the second involving shortening of the seminiferous tubule and a decrease in interstitial volume. At the cellular level, there is an initial decrease in proliferation and increase in apoptosis involving all germ cells. At the end of regression, the proliferative and apoptotic activities of the spermatogonia recover the values observed prior to regression in preparation for recrudescence.

Aging and short photoperiod exposure induce germ cell apoptosis in the Syrian hamster; however, the specific germ cells affected and the molecular pathways triggered have not been elucidated. We analyzed germ cell apoptosis and the expression of the Fas/Fas‐L system, Bcl‐2 family, and p53 in aged and photoinhibited hamsters and compared with those young maintained in natural photoperiod. Aging increased apoptosis in spermatogonia and spermatocytes, but in photoinhibited hamster testes only an increase in apoptotic spermatocytes was observed. Apoptosis was higher in aged hamsters in stages I—IV, V—VI and VII—VIII. Aging increased apoptosis of spermatogonia in stages I—IV and V—VI. Apoptotic pachytene spermatocytes were significantly higher in stages I—IV, V—VI, and VII—VIII in aging. Apoptotic preleptotene and pachytene spermatocytes were higher in aging, but no differences were observed in leptotene‐zygotene. Fas‐L was expressed by Sertoli cells, of young, aged, and photoinhibited hamsters. Bcl‐x_L was strongly expressed in germ cells on young hamsters and slightly in aging and after short photoperiod exposure. Spermatocytes of photoinhibited hamsters were intensively stained with Fas, Bax, Bcl‐xs/L, and p53. In conclusion, aging increases apoptosis in spermatogonia and spermatocytes, depending on the stage of the seminiferous epithelium cycle, whereas after a short photoperiod exposure only an increase in apoptotic spermatocytes is observed. The results suggest that Fas, Bcl‐x_L, Bax, and p53 participate in germ cell apoptosis induction after short photoperiod exposure, whereas only Bcl‐x_L is involved in aging.

Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

The Sertoli cell (Sc) has been described as a quiescent cell once the animal has reached sexual maturity. Syrian hamster (Mesocricetus auratus), is an animal that displays testicular regression due to short photoperiod, during which process germ cells and Sc are removed through apoptosis. The aim of this work was to investigate histochemically whether the spontaneous testicular recrudescence processes after exposure to a short photoperiod lead to an increase in Sc proliferative activity in order to restore the normal population. Three spontaneus recrudescence groups were established: Initial (IR), Advanced (AR) and Total (TR) recrudescence, which were compared with animal groups undergoing the regression process (mild: MRg, strong: SRg and total: TRg) and animals in long photoperiod (Controls). Histological sections were submitted to histochemical techniques for detecting apoptotic and proliferative Sc with bright-field and fluorescence microscopy. For each group, the proliferative Sertoli cell index (PScI) and apoptotic Sertoli cell index (AScI) were obtained, and the total number of Sc was studied by a stereological point method. The results revealed the existence of Vimentin+/TUNEL+ as well as Vimentin+/PCNA+ cells. The PScI was significantly higher in TRg and IR than in the other groups. The AScI was only significantly higher in MRg and SRg with respect to the other groups. The total number of Sc increased among TRg, IR and AR, reaching values similar to those of the controls. In conclusion, the increase in Sertoli cell proliferation from final regression and recrudescence, accompanied by a similar rate of apoptosis to the control group is the cause of the restoration of the Sertoli cell population during spontaneous recrudescence.