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The Sertoli cell (Sc) has been described as a quiescent cell once the animal has reached sexual maturity. Syrian hamster 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 spontaneous recrudescence groups were established: initial (IR), advanced (AR), and total (TR) recrudescence, which were compared with animal 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 Sc index (PScI) and apoptotic Sc index (AScI), and the total number of Sc were obtained. 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 Sc 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 Sc population during spontaneous recrudescence., (© The Author(s) 2019. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Lectin histochemistry was used to characterise glycoconjugates and cellular apoptosis in the seminiferous epithelium and interstitium of hamster testis during spontaneous recrudescence. An increase in the LTA lectin affinity was observed in spermatids in the Golgi phase. An increase in labelling of PNA and Con-A lectin in acrosome of spermatids (acrosome phase) as well as increased labelling with Con-A in spermatids (cap phase) was observed. Spermatocytes showed decreased affinity with PNA and AAA lectins and an increase in positivity for LTA and GNA lectins. Spermatogonia showed a slight decrease in positivity to WGA and an increase in labelling with Con-A and a decreased affinity for the AAA lectin. At the end of recrudescence, all these germinal cells showed a similar pattern to the control. The Sertoli cells showed a gradual decrease in labelling with the GNA lectin and the Leydig cells an increase in labelling with Con-A and GNA. Particularly unusual was the observation of apoptotic spermatocytes and spermatids positive for PNA, GNA, AAA and Con-A, together with spermatocytes positive to LTA. In conclusion, the normal lectin pattern is recovered during testis recrudescence and germ cell apoptotic activity is low, as is observed by specific lectins for germ cells in apoptosis., (© 2018 Blackwell Verlag GmbH.)

Syrian hamsters are photoperiodic rodents in which reproduction, including testicular function, is stimulated by long photoperiod exposure and curtailed by exposure to a short photoperiod. The objectives of this study were to characterize the testis histomorphometrically and to determine the role of the proliferation and apoptosis phenomena in the recovery of the seminiferous epithelium during spontaneous recrudescence after exposure to short photoperiod. The study was performed using conventional light microscopy, 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 recrudescence groups: initial recrudescence (IR), advanced recrudescence (AR) and total recrudescence (TR). The results morphometrically pointed to the gradual recovery of the testicular and tubular volumes, as well as of the seminiferous epithelium. Among the IR and AR groups, the increase in testicular and tubular volumes was accompanied by an increase in tubular diameter and length, with an increase in interstitial volume. From AR to TR, there was an increase in the tubular and total volumes, but, in this case, with a gradual increase in tubular diameter. Recovery of the seminiferous epithelium was accompanied by changes in apoptosis and proliferation activities. The first decreased halfway through the process, and the second remained higher than the control levels throughout the recrudescence stage. Alterations in the spermatozoa were ultrastructurally observed, which indicated that spermiogenesis was not yet completely normal. In conclusion, spontaneous testicular recrudescence in Syrian hamster comprises two histomorphometrical phases: the first related to an increase in tubular length and diameter and interstitial volume and the second depending principally on the gradual increase in tubular diameter. The restoration of the seminiferous epithelium is due to apoptosis reaching normal values in the AR group accompanied by higher proliferative activity than that observed in the Control group., (© 2018 Blackwell Verlag GmbH.)

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.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]