Localisation of RA175 (Cadm1), a cell adhesion molecule of the immunoglobulin superfamily, in the mouse testis, and analysis of male infertility in the RA175-deficient mouse

RA175, a member of the immunoglobulin superfamily, plays an important role in cell adhesion, and RA175 gene-deficient mice (RA175(-/-) ) show oligoastheno-teratozoospermia. To understand the function of RA175, location in the testis and the morphological features of its spermatogenic cells in RA175(-/-) mice were investigated. Immunohistochemical studies revealed that RA175 immunoreactivity was observed on the cell surface of the spermatogenic cells at specific stages. A strong reaction was detected from type A spermatogonia to pachytene spermatocytes at stage IV and from step 6 to step 16 spermatids during spermatogenesis. From pachytene spermatocytes at stage VI to step 4 spermatids, the reaction was not detected by the enzyme-labelled antibody method and was faintly detected by the indirect immunofluorescence method. Abnormal vacuoles in the seminiferous epithelium, showing exfoliation of germ cells, and ultrastructural abnormality of the elongate spermatids were revealed in the RA175(-/-) testes. Other members of the immunoglobulin superfamily such as basigin, nectin-2 and nectin-3, which have an important role in spermatogenesis, were immunohistochemically detected in the RA175(-/-) testis. These observations indicate a unique expression pattern of RA175 in the testis and provide clues regarding the mechanism of male infertility in the testis.     

The effect of selective destruction and regeneration of rat Leydig cells on the intratesticular distribution of testosterone and morphology of the seminiferous epithelium

This study was designed to explore the relationship between the intratesticular distribution of testosterone and spermatogenesis by completely destroying the Leydig cells of mature male rats with injection of a single i.p. dose of ethane dimethanesulphonate. After such treatment, testosterone levels in serum, testicular interstitial fluid, seminiferous tubules, and whole testis declined significantly 6 to 24 hours after injection and fell below assay detection limits between 3 and 7 days. At 3 and 7 days, serum LH and FSH levels rose significantly and remained elevated up to 4 and 6 weeks, respectively, in comparison with vehicle-treated controls. Leydig cells disappeared from the interstitium by day 3, but between 2 and 4 weeks postinjection a new generation of fetal-like Leydig cells repopulated the testicular interstitium and, during weeks 6 to 10, were transformed into, or replaced by, Leydig cells with an adult type of morphology. Histologic examination of the seminiferous tubules showed progressive disruption of spermatogenesis between 3 and 14 days post-ethane dimethanesulphonate. The first histologic sign of spermatogenic damage was noted at day 3, with the occurrence of stage-specific degenerating pachytene primary spermatocytes at stages VII to VIII of the spermatogenic cycle. On day 7, these cells and degenerating round, or step 19, spermatids often were observed during stages VII to XI, although qualitatively normal spermatogenesis also was seen in these and all other stages of the cycle. Maximum impairment of spermatogenesis occurred 2 weeks post-ethane dimethane sulphonate, at which time the tubules commonly lacked one or more germ cell generations or, alternatively, showed accumulation of lipid inclusions, extracellular spaces, and variable numbers of degenerating germ cells. Following repopulation of the testis by Leydig cells during weeks 3 and 4, spermatogenesis recovered. By 10 weeks after treatment, qualitatively normal spermatogenesis was seen in the great majority of seminiferous tubules, although a few tubules still remained in which the germ cell complement was severely reduced, and contained only Sertoli cells and spermatogonia.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantitative （stereological） study of incomplete spermatogenic suppression induced by testosterone undecanoate injection in rats

Aim: To evaluate the key lesions in spermatogenesis suppressed partially by testosterone undecanoate(TU) treatment. Methods: Adult male SD rats were treated with vehicle or TU (19 mg/kg) injection (i.m.) every 15 days for 130 days. The numbers of all types of cells (nuclei) in the seminiferous tubules and the interstitial tissue were estimated using a contemporary stereological tool, the optical disector. Results: In response to TU treatment, the numbers of non-type B spermatogonia, type B sperrnatogonia and late elongated spermatids per testis were reduced to 51%, 66% and 14% of the controls, respectively. The conversion ratios from type B spermatogonia to early spermatocytes and pachytene spermatocytes were not significantly affected and the ratios to the later germ cell types fell to 51%-65% of the controls. Less than 1.0 % of immature round spermatids were seen sloughing into the tubule lumen, 4.0% of elongated spermatids retained in the seminiferous epithelium, and about half of the elongated spermatid nuclei appreciably malformed. Leydig cells were atrophied but their number and the peritubular myoid cell number per testis were unchanged. Conclusion: Double inhibition of spermatogenesis (i.e. inhibition at spermiation and spermatogonial conversion to type B spermatogonia), a scenario seen in the monkey and human following gonadotrophin withdrawal, was not sufficiently effective for a complete spermatogenic suppression in the rat after TU treatment, probably due to ineffective inhibition of the Leydig cell population and therefore the intra-testicular test-osterone levels. (Asian J Androl 2004 Dec; 6: 291-297)     

Changes in the expression of P-cadherin in the normal, cryptorchid and busulphan-treated rat testis

Adhesion between Sertoli cells and germ cells is important for spermatogenesis. Cadherins are Ca(2+)-dependent transmembrane proteins that mediate cell-cell adhesion. The aim of this study was to compare the expression of P-cadherin in unilaterally cryptorchid and busulphan-treated rat testes using immunohistochemistry. The pattern of expression of P-cadherin in the seminiferous epithelium changed with the stage of the seminiferous epithelium. The membranes of round spermatids and membranes and cytoplasm of spermatocytes were strongly positive. Our experiments revealed that busulphan treatment (2 doses - 10 mg/kg of body weight - 21 days apart) and cryptorchism led to destructive changes in the structure of seminiferous tubules, together with the decrease in P-cadherin expression. The expression of P-cadherin disappeared in the spermatids segregated from the epithelium while segregated spermatocytes remained still positive for P-cadherin during the 3- to 11-day cryptorchid period. In busulphan-treated animals, the expression of P-cadherin was dependent on the presence or absence of the spermatocytes and spermatids in the tubules. Strong positivity for P-cadherin was observed in the spermatocytes that re-appeared in the regenerating seminiferous epithelium. We suggest that P-cadherin participates in the architecture of adherens junctions in testis, plays an important role in maintaining normal spermatogenesis and that cryptorchism and busulphan treatment lead to adherens junction disintegration.     

Stage-specific localization of transforming growth factor β1 and β3 and their receptors during spermatogenesis in men

Aim: To investigate the stage-specific localization of transforming growth factor (TGF) β1 and β3 during spermatogenesis in adult human testis, Methods: The localization of TGFβ1 and β3 was investigated by immunohistochemical staining method employing specific polyclonal antibodies. Results: Both TGFβ1 and β3 and their receptors were preponderant in the Leydig cells. TGFβ1 could not be detected in the seminiferous tubules. TGFβ3 and TGFβ-Receptor (R) Ⅰ were mainly seen in the elongated spermatids, while TGFβ-RⅡ in the pachytene spermatocytes and weak in the spermatogonia, spermatids and Sertoli cells. Only TGFβ-RⅡ was detected in the Sertoli cells.TGFβ3, TGFβ-RⅠ and TGFβ-RⅡ showed a staining pattern dependent upon the stages of the seminiferous epithelium cycle. Conclusion: TGFβ isoforms and their receptors are present in the somatic and germ cells of the adult humantestis, suggesting their involvement in the regulation of spermatogenesis.     

Evaluation of the effect of selective germ cell depletion on subsequent spermatogenesis and fertility in the rat

Rats were treated with a single high dose of methoxy acetic acid (MAA; 650 mg/kg) specifically to deplete seminiferous tubules of pachytene and later spermatocytes. The impact of this selective depletion on subsequent spermatogenesis, sperm output and fertility was then evaluated at intervals ranging from 3 days to 10 weeks. Cauda epididymal sperm number was reduced progressively beyond 2 weeks post-treatment and reached a nadir at 5-6 weeks (28-34% of control values) before recovering progressively back to control levels at 10 weeks. Sperm motility was reduced significantly at 4-7 weeks post-treatment with a nadir at 6 weeks (35% of control values). Thus, at 5-6 weeks after MAA treatment, motile sperm output was reduced by 82-88%. Despite these changes, there was little evidence for infertility in the majority of treated males during a serial mating trial. Evaluation of seminiferous tubule morphology combined with germ cell counts at stage VII of the spermatogenic cycle confirmed that, initially, MAA induced the specific loss of pachytene and later spermatocytes at all stages other than early to mid stage VII. Maturation depletion of germ cells at later intervals was consistent with the initial effects of MAA, although at 21 days post-treatment a number of unpredicted (? secondary) changes in spermatogenesis were observed. These were (a) a reduction in number of pachytene spermatocytes at late stage VII/early stage VIII, (b) retention of sperm at stages IX-XIV, and (c) increased degeneration of pachytene spermatocytes and round spermatids at stage VII and of secondary spermatocytes at stages XIV-I. Whilst none of these changes was severe, together they probably accounted for the unexpectedly prolonged drop in sperm output. It is concluded that whilst deleterious changes in spermatogenesis may occur secondarily following MAA treatment, for the most part spermatogenesis proceeds normally and fertility is largely maintained despite a massive but transient decrease in sperm output.     

Effect of chronic low dose of methotrexate on cellular proliferation during spermatogenesis in rats

This study was conducted to evaluate cellular proliferation of germinal and non-germinal elements of seminiferous tubules following continuous Day 1 to Day 17 exposure of methotrexate (12.5 microgram) in male rats. There was significant decrease in the diameter of seminiferous tubules (P < 0.10) followed by increase of interstitial space (P < 0.01). The size of various stages of primary, secondary spermatocytes, and spermatids was altered significantly compared to controls. Vacuolization/decondensation of "chromatin-mass" in spermatocytes changed from rounded to oval. The size of the Sertoli and Leydig cells were reduced significantly. Basement membrane at some places seems to be disrupted and thin in experimental testis. Methotrexate induced cytotoxicity on the proliferation of cellular contents of seminiferous tubules elucidating the mechanism of dose-dependent drug induced testicular damage during spermatogenesis.     

Is testosterone involved in the initiation of spermatogenesis in humans? A clinicopathological presentation and physiological considerations in four patients with Leydig cell tumours of the testis or secondary Leydig cell hyperplasia

The purpose of this study was to evaluate the role of testosterone on the puberal development of spermatogenesis and to present additional clinicopathological data which bring about new information to this controversial subject. Four pre-pubertal patients are presented, 2 of them bearing Leydig cell tumours of the testis in the form of nodular masses. In both cases seminiferous tubules in the immediate vecinity to the tumours showed complete development of spermatogenesis, while those located away from the tumours were infantile in nature. Gonadotrophic levels were within the normal pre-pubertal range in these 2 cases. In one of the patients, testosterone concentration in the testis showed higher values than normal, and a concentration gradient was detected between the tumoral nodule and non-tumoral parenchyma. The 3rd patient had a pineal choriocarcinoma producing high amounts of hCG and consequently a diffuse hyperplasia of Leydig cells with high levels of plasma testosterone. Seminiferous tubules showed development up to pachytene spermatocytes. The last case was a precocious puberty in a boy with a tumour of the 3rd ventricle area. He had elevated levels of testosterone in the testis and plasma. In the testicular biopsy, stimulation of Leydig cells was detected. The seminiferous tubules showed mature Sertoli cells and pachytene spermatocytes. FSH levels were abnormally low. These 4 cases present in common different situations in which abnormally high amounts of testos-happens in the immature rat, the interaction between testosterone and gonadotrophins is essential for the normal initiation of spermatogenesis in normal puberty. Considerations are discussed on the possible synergistic role of gonadotrophins or other factors in relation with stimulation of seminiferous tubules by testosterone.     

Effect of nitrofurazone on the reproductive organs in adult male mice

Aim: To study the effect of 5-nitro-2-furaldehyde semicarbazone (nitrofurazone), a derivative of nitrofuran, on male reproductive organs of Parkes (P) strain mice. Methods: Mice were given nitrofurazone orally at a dose of 64mg/kg body weight per day, for 10 and 20 days, and were killed 24 h and/or 56 days after the last treatment. Histological appearance of testis, motility and number of spermatozoa in cauda epididymidis, and biochemical indices in epididymis and seminal vesicle were evaluated. Results: Histologically, testis showed marked regressive changes in the seminiferous tubules in mice treated with nitrofurazone. Ten days after treatment, there was much depletion of germ cells in the seminiferous tubules, and the germinal epithelium was lined mainly with Sertoli cells, spermatogonia, spermatocytes, and a few round spermatids; intraepithelial vacuoles and multinucleated giant cells were also observed in tubules. By 20 days, regressive changes in the seminiferous tubules were further pronounced, and pachytene spennatocytes were the most advanced germ cells noticed in the tubules. In severe cases, the tubules were lined with a thin layer of Sertoli cells and spermatogonia. The treatment also caused marked reductions in the motility and number of spermatozoa in the cauda epididymidis, in weight and the level of fructose in the seminal vesicle, and in sialic acid level in the epididymis. Fifty six days after drug withdrawal, the alterations induced in the reproductive organs returned to control levels. Conclusion: Our results suggest that nitrofurazone treatment in P mice induces marked alterations in the male reproductive organs, and that the alterations are reversible following cessation of treatment.     

Spatiotemporal expression patterns of natriuretic peptides in rat testis and epididymis during postnatal development

Natriuretic peptide (NP) family is composed of atrial, brain and C‐type NP (NPPA, NPPB and NPPC). Here, we aimed to investigate NP expression in testis and epididymis during postnatal development. NPPA expression was observed in gonocytes at prepubertal period but in only spermatocytes in pachytene and leptotene/zygotene stage at pubertal period. In prepubertal and pubertal periods, we detected NPPB expression in only Leydig cells. However, NPPC expression was detected in all of the gonocytes and Sertoli cells, spermatocytes and some interstitial cells in prepubertal and pubertal periods. In postpubertal and mature periods, NPPA and NPPB staining were detected in Leydig cells, elongated and round spermatids but not in spermatogonia and spermatocytes. However, we observed NPPC expression in all cells of the seminiferous tubules and Leydig cells in the postpubertal and mature periods. Epididymal epithelium showed intense NPPC expression during postnatal period but weak NPPA and NPPB expression in prepubertal and pubertal periods. The expression of three NPs in the testis significantly increased after puberty. In conclusion, puberty had a significant effect on NP expression in testis. Unlike NPPA and NPPB, expression of NPPC in all cells of the seminiferous tubule suggests that NPPC is effective in each step of spermatogenesis.     

The length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts

Xenografting of immature mammalian testis tissue into mice can accelerate sperm production. To determine whether this shortened time to sperm production is because of reduced length of the spermatogenic cycle, we applied bromodeoxyuridine (BrdU) incorporation to analyze the spermatogenic cycle in porcine and ovine testis xenografts. Small testis fragments from newborn pigs and sheep were ectopically grafted into mice. Once complete spermatogenesis was present in grafted tissue, mice were injected with BrdU and grafts were recovered at different time points thereafter. In porcine grafts, the most advanced germ cells labeled 1 hour, 9 days, 12.3 days, and 18 days after BrdU injection were stage 1 preleptotene/leptotene primary spermatocytes, stage 1 pachytene primary spermatocytes, stage 5 newly-formed round spermatids, and late stage 2 elongating spermatids, respectively. In ovine grafts, the most advanced labeled germ cells at 1 hour, 11 days, and 22 days post-BrdU injection were stage 2 preleptotene/leptotene primary spermatocytes, late stage 1 pachytene primary spermatocytes, and stage 2 elongating spermatids, respectively. These results indicate that each spermatogenic cycle in porcine and ovine xenografts lasts approximately 9 and 11 days, respectively, which is similar to their durations in situ. Therefore, the length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts. This is consistent with earlier reports showing that the cycle length is inherent to the germ cell genotype. The shortened time to sperm production in xenografts therefore appears attributable to accelerated maturation of the testicular somatic compartments. Our results suggest that testis xenografts provide a useful model to study the timing of testicular maturation and spermatogenesis in different mammalian species.     

Regulatory influence of germ cells on sertoli cell function in the pre-pubertal rat after acute irradiation of the testis

While germ cell regulation of Sertoli cells has been extensively explored in adult rats in vivo, in contrast, very little is known about germ cell influence on Sertoli cell function at the time when spermatogenesis begins and develops. In the present study various Sertoli cell parameters (number, testicular androgen binding protein (ABP) and testin, serum inhibin-B and, indirectly, follicle-stimulating hormone (FSH)) were investigated after the exposure of 19-day-old rats to a low dose of 3 Grays of gamma-rays. Differentiated spermatogonia were the primary testicular targets of the gamma-rays, which resulted in progressive maturation depletion, sequentially and reversibly affecting all germ cell classes. Testicular weight declined to a nadir when pachytene spermatocytes and spermatids were depleted from the seminiferous epithelium and complete or near complete recovery of spermatogenesis and testicular weight was observed at the end of the experiment. Blood levels of FSH and ABP were normal during the first 11 days after irradiation, when spermatogonia and early spermatocytes were depleted. While the number of Sertoli cells was not significantly affected by the irradiation, from days 11-66 after gamma-irradiation, ABP production declined and FSH levels increased when pachytene spermatocytes and spermatids were depleted and the recovery of these parameters was only observed when spermatogenesis was fully restored. Comparison of the pattern of change in serum levels of inhibin-B and testicular levels of testin and of germ cell numbers strongly suggest a relationship between the disappearance of spermatocytes and spermatids from the seminiferous epithelium and the decrease in levels of inhibin-B and increase in levels of testin from 7 to 36 days post-irradiation. Levels of testin and inhibin-B were restored before spermatogenesis had totally returned to normal. In conclusion, this in vivo study shows that pre-pubertal Sertoli cell function is under the complex control of various germ cell classes. This control presents clear differences when compared with that previously observed in adult animals and depends on the Sertoli cell parameter of interest, as well as on the germ cell type.     

Possible role of elongated spermatids in control of stage-dependent changes in the diameter of the lumen of the rat seminiferous tubule

Adult male rats were treated with a single dose of 650 mg/kg methoxy acetic acid to deplete the seminiferous tubules specifically of pachytene and later spermatocytes. The effect of this treatment and the subsequent maturation-depletion of later germ cell types on the diameter of the seminiferous tubule and its lumen and the area of the seminiferous epithelium were studied in relation to the stages of the spermatogenic cycle. At 21 days after methoxy acetic acid treatment, the diameter of the tubule and the area of the epithelium were reduced below control values at all stages, consistent with the reduced number of early (stage VIII) or late (all other stages) spermatids. Unexpectedly, diameter of the lumen was also reduced at all stages other than VIII, and especially at stage VII. In controls, lumen diameter at stages VII and VIII was increased by approximately 50% compared with earlier and later stages. In rats treated 21 days previously with methoxy acetic acid no change occurred at stage VII (lacking elongated spermatids) while a normal increase did occur at stage VIII (lacking round but not elongated spermatids). At earlier times after methoxy acetic acid treatment when stage VII tubules were depleted of pachytene spermatocytes alone (3 days) or together with early spermatids (7 days), the diameter of the lumen was not significantly different from the control value. These data suggest that lumen diameter may be regulated by elongated spermatids, especially at stages VII and VIII.     

The selective removal of pachytene spermatocytes using methoxy acetic acid as an approach to the study in vivo of paracrine interactions in the testis

Testicular weight and morphology, serum gonadotropins, intratesticular levels of testosterone and ABP levels in testicular interstitial fluid were studied in adult rats at intervals of 1 to 70 days after a single oral dose of 650 mg/kg methoxy acetic acid. At 3 days, this treatment resulted in the selective loss or depletion of pachytene and later spermatocytes from seminiferous tubules at all stages other than VIII to XI of the spermatogenic cycle. At later times this lesion was expressed as an absence mainly of round (14 days) or elongated (21 days) spermatids from the majority of seminiferous tubules. Other than these changes, spermatogenesis did not appear to be affected by treatment and was qualitatively normal in all tubules at 70 days after treatment. As deduced from cell counts at 3 days posttreatment, the initial action of methoxy acetic acid was restricted to late zygotene spermatocytes (stage XII) and pachytene spermatocytes at all stages other than early- to mid-stage VII. Levels of FSH in serum and those of ABP in testicular interstitial fluid indicated that Sertoli cell function was altered in rats treated with methoxy acetic acid. Both were increased at 1 to 3 days posttreatment, returned to normal at 7 to 14 days but were increased again at 21 days before finally returning to control levels at 28 days. In contrast, the levels of testosterone in serum, isolated seminiferous tubules and testicular interstitial fluid were unaffected by treatment, as also were the serum levels of LH. The two periods of increase in FSH and ABP levels coincided with the times of greatest decrease (approximately 20%) in testicular weight, and may be related either to the type of germ cell missing from the affected tubules and/or to the stage of the cycle of the affected (or unaffected) tubules. These data suggest that chemicals such as methoxy acetic acid may prove useful in the study of paracrine interactions in vivo.     

Status of spermatogenesis and sperm parameters in langur monkeys following long-term vas occlusion with styrene maleic anhydride

Vas occlusion by styrene maleic anhydride (SMA), trade name RISUG (one of the promising male contraceptive procedures currently in phase III clinical trials), at 60 mg/vas deferens dissolved in 120 micro L dimethyl sulphoxide (DMSO) at up to a 540-day study period caused severe oligospermia in the first 2 to 3 ejaculations and uniform azoospermia in the subsequent ejaculations without toxicity in langur monkeys. The ejaculated spermatozoa were necroasthenoteratozoospermic, suggesting instant sterility. Routine hematology and clinical chemistry parameters and the serum testosterone and sperm antibody titers remained unchanged from their pretreatment values until 540 days vas occlusion. Histology of testes revealed continued spermatogenesis throughout the study period. The stages of spermatogenesis appeared normal until 300 days of vas occlusion. At 360 days of vas occlusion, germ cells appeared in the lumen. Degeneration of seminiferous epithelium was evident in some of the tubules. Following 420 days of vas occlusion, the central portion of the testis showed regressed seminiferous tubules depicting various shapes and devoid of germ cells, which continued until 540 days of vas occlusion. Ultrastructure of the testes after 540 days of vas occlusion revealed vacuolization in the cytoplasm of Sertoli cells and degenerative features in the membranes of the spermatocytes and spermatids in the affected seminiferous tubules. The sub-cellular features of the normal tubules were similar to those of controls. The results suggest focal degeneration of seminiferous epithelium in the central portion of the testis following long-term vas occlusion with SMA.     

The effects of ethylene glycol monomethyl ether on testicular histology in F344 rats

Ethylene glycol monomethyl ether (EGME) has been found to produce testicular atrophy in experimental rodents. The studies that follow were designed to determine the testicular cell type(s) most susceptible to EGME administration. For histologic studies, F344 rats were gavaged with 150 mg/kg/day of EGME 5 days per week, and serially sacrificed. In sections from perfusion-fixed tissue, necrotic changes were observed in some meiotic and premeiotic spermatocytes 24 hours after a single dose. Also, nuclear condensation was seen in occasional early pachytene spermatocytes. These effects were magnified after two doses; there were more necrotic pachytene and meiotic spermatocytes than necrotic stage I pachytene spermatocytes. By day 4, testes from all treated animals were affected; there was a pronounced maturation-depletion effect, seen as the absence of round spermatids from tubules in stages I to III. These effects continued to develop at days 7 and 10, leaving only Sertoli cells, spermatogonia, and late stage spermatids populating the epithelium. Other animals were treated similarly, but subject to efferent duct ligation 16 hours prior to sacrifice. Fluid production, as judged by weight gain in the testes after efferent duct ligation, was unaffected by EGME treatment. Analysis of the fluid collected at the rete testis indicated that there was no treatment-related change in the relative amounts of androgen binding protein. The data indicate that the spermatocyte is the primary target cell for the histologic effects of EGME in the testis of F344 rats.     

FSH immunoneutralization acutely impairs spermatogonial development in normal adult rats

Follicle-stimulating hormone (FSH) plays an important part in testicular development. Its role in the regulation of spermatogenesis in the adult, however, remains controversial. This study aimed to explore the role of FSH in the maintenance of adult rat spermatogenesis by using immunoneutralization to selectively withdraw FSH action for periods of up to 8.5 days and then assessing the outcome by quantification of germ cell number. Adult rats received either an ovine polyclonal rat FSH antibody (FSHAb, 2 mg/kg subcutaneous daily-a dosage known to neutralize >90% of FSH in serum) for 2, 4, 7, or 8.5 days or a control sheep immunoglobulin (ConAb, 2 mg/kg) for 8.5 days. Testes were perfusion fixed, and germ cell numbers per testis were quantified using the optical disector (sic) stereological method. The percentage of seminiferous tubules displaying apoptotic cells was determined by the in situ end labeling method (TUNEL). FSHAb treatment for 4, 7, or 8.5 days significantly reduced the number of type A/intermediate spermatogonia (approximately 74% of control values) associated with stages I-IV. Similar reductions were seen in type B spermatogonial and preleptotene spermatocyte numbers after 8.5 days of FSHAb treatment (approximately 69% of control values; P < 0.05). Decreases (P < 0.05) in the numbers of pachytene spermatocytes in stages I-III and VIII, round spermatids in stages I-III, VII, and VIII (approximately 70% of control values), and step 19 elongated spermatids in stage VII (51% of control values) were achieved after 8.5 days of FSHAb treatment. Compared with control, FSHAb treatment increased the percentage of stage XIV-III tubules containing TUNEL-positive cells by about twofold after 7 days of FSHAb treatment (P < 0.05). This study supports a role for FSH in the maintenance of quantitatively normal adult rat spermatogenesis, specifically by regulating A3 and A4 spermatogonial subtypes. FSH may act on these spermatogonia by enhancing the stage-dependent survival of type A spermatogonia. Effects at other sites in spermatogenesis are suggested by the changes in spermatocyte and spermatid populations. However, to clarify these effects, selective FSH withdrawal would need to be prolonged until steady state had been achieved.