Clinical significance of renal biopsies showing concurrent acute rejection and tacrolimus-associated tubular vacuolization

OBJECTIVE: To examine the expression of the c-kit receptor and its ligand, stem cell factor, and their possible relation with apoptosis in infertile men. DESIGN: Prospective laboratory study. SETTING: Urology laboratory in a university hospital. PATIENT(S): Men undergoing testicular biopsy during an investigation of subfertility. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Expression of the c-kit receptor protein, stem cell factor, and apoptosis in the testes. RESULT(S): The c-kit receptor was strongly present in Leydig cells and type A spermatogonia of normal testes, with decreased staining in Leydig cells and type A spermatogonia of testes with maturational arrest, and staining in only Leydig cells of Sertoli cell-only specimens. Stem cell factor was demonstrated in Leydig cells and Sertoli cells in all specimens. Western blotting demonstrated the 150-kd c-kit protein in the normal testes and the testes with maturational arrest, but not in the testes with the Sertoli cell-only pattern. Stem cell factor was expressed in all specimens, with a protein size of 45 kd. Increased apoptosis was demonstrated in type A spermatogonia and spermatocytes of tissue with maturational arrest compared with normal testicular tissue. CONCLUSION(S): C-kit receptor expression is decreased in subfertile testicular tissue compared with normal testicular tissue. Stem cell factor expression is present in Leydig cells and Sertoli cells. Increased apoptosis is seen in tissue with maturational arrest compared with normal tissue.     

Expression of interferons-alpha and -gamma in testicular interstitial tissue and spermatogonia of the rat

The testis is divided into two compartments: the seminiferous tubules and the interstitial tissue. The latter essentially consists of the blood and lymphatic vessels, testosterone-producing Leydig cells, and testicular macrophages. In the exploration of the testicular antiviral defense system, we initially searched for interferon (IFN) production by the seminiferous tubule cells. The site of virus entry into the testis is probably the interstitial compartment; thus, it is important to know whether and how the cells in this compartment are protected against viral infection. In addition, as germ cell precursors (spermatogonia) are only partially protected by the blood-testis barrier, it was important to explore the antiviral capability of these cells. In this study we searched for IFN production by Leydig cells, testicular macrophages, and spermatogonia after exposure to Sendai virus. We also investigated the effect of viral exposure on testosterone production by Leydig cells. Our results show that spermatogonia do not constitutively express IFNs and give a very poor response to the virus. In contrast, testicular macrophages constitutively produced type I IFNs, and this production was markedly stimulated by Sendai virus. Leydig cells produced twice as much type I IFNs as testicular macrophages after viral exposure, and they were the only cells producing both IFNalpha and -gamma, with these IFNs being dramatically induced/ increased in response to exposure to the virus. Furthermore, incubation of Leydig cells with the Sendai virus stimulated testosterone production. In conclusion, this study further establishes the topography of IFN expression within the testis. This allows us to hypothesize that the potential antiviral system represented by Leydig cells and, to a lesser extent, by macrophages plays a key role in protecting both androgen production and spermatogenesis.     

Partial obstruction of the seminal path, a frequent cause of oligozoospermia in men

The objective of this clinical study was to determine the real frequency and clinical importance of partial obstruction of the seminal path in patients with oligozoospermia. We have designed a prospective clinical study including men with oligozoospermia seen at an andrological consultation in both private and institutional hospitals. A testicular biopsy was done on all patients under local anaesthesia. A complete study for sterility was also done [hormonal determinations: follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone, testicular ultrasound, semen analysis, testicular Doppler ultrasound, etc.]. We have made a quantitative and qualitative evaluation of testicular biopsy (percentage of tubules with Sertoli cell only or with hyalinization; mean tubular diameter; number of spermatogonia, primary spermatocytes, young spermatids, mature spermatids and Sertoli cells; and evaluation of testicular interstitium: number of Leydig cell clusters, presence of angiectasis, presence of perivascular inflammation). Sixty one per cent of all oligozoospermia cases were obstructive. The principal cause of obstructive oligozoospermia was the presence of testicular varicocele. In obstructive oligozoospermia, the tubular diameter and number of mature spermatids are statistically significantly higher than in non-obstructive oligozoospermia. Obstructive oligozoospermia is a frequent condition caused by partial obstruction of seminal path. A quantitative analysis of the testicular biopsy is the only method of diagnosis.     

Microsurgical epididymal sperm aspiration with motile trophozoite cells but no spermatozoa

This paper reports on a patient in whom the clinical diagnosis of obstructive azoospermia was made according to clinical observations, i.e. azoospermia, normal andrological examination, normal follicle stimulating hormone and a misleading histopathological report of a testicular biopsy. Microsurgical vasoepididymostomy failed to restore fertility, and as a last resort, microsurgical sperm aspiration was performed. Although flagellated cells were observed in the epididymal aspiration, no spermatozoa were observed and wet preparation of multiple testicular biopsies failed to demonstrate any spermatozoon. This patient was diagnosed to have a non-obstructive azoospermia, resulting from maturation arrest associated with trichomonas infection at the level of the epididymis.     

Gonadal damage from chemotherapy and radiotherapy

Treatment with cytotoxic chemotherapy and radiotherapy is associated with significant gonadal damage in men and women. Alkylating agents such as cyclophosphamide and procarbazine are the most common agents implicated. The vast majority of men receiving procarbazine-containing regimens for the treatment of lymphomas become permanently infertile. Cisplatin-based chemotherapy for testicular cancer results in temporary azoospermia in most men, with a recovery of spermatogenesis in about 50% after 2 years and in 80% after 5 years. There is also evidence of Leydig cell impairment in a proportion of these men, although the clinical significance of this is not clear. The germinal epithelium is very sensitive to radiation-induced damage, with changes to spermatogonia occurring following as little as 0.1 Gy and permanent infertility after fractionated doses of 2 Gy and above. Cytotoxic-induced premature ovarian failure is age- and drug-dependent and ensues in approximately half of women treated with procarbazine-containing chemotherapy for lymphomas. High-dose chemotherapy, total body irradiation, and irradiation at an ovarian dose above 6 Gy usually result in permanent ovarian failure. The course of ovarian function after chemotherapy is variable, and late recovery occurs in some patients. Several methods of preserving gonadal function during potentially sterilizing treatment have been considered. Currently, sperm banking remains the only proven method in men, although hormonal manipulation to enhance the recovery of spermatogenesis and cryopreservation of testicular germ cells are possibilities for the future. Transposition of the ovaries to allow better shielding during radiotherapy is of use in some women, and the prospect of cryopreservation and reimplantation of ovarian tissue is promising.     

Atypical spermatogonias as precancerous conditions

Atypical spermatogonia are relatively frequent in the vicinity of testicular teratomas or seminomas. These voluminous cells are seminoma-like, showing broad and clear cytoplasm borders, big nuclei and peculiarly enlarged nucleoli. Atypical spermatogonia usually line the tubules and displace the remaining Sertoli cells towards the middle of the tubules. Recently, such atypical spermatogonia have been described in testicular biopsies performed for fertility disturbances. Two patients showing atypical spermatogonia developed, years later, malignant testicular tumors. Therefore, were checked all of our histological specimens from testicular biopsies over the period 1950-1976 for atypical spermatogonia. They originated from 1935 adult patients in whom biopsy had been performed, in general bilaterally, for fertility disturbances. In fact, atypical spermatogonia were found in the specimens of 9 patients, that is, 0.55%. Five of these patients developed malignant testicular tumours within periods ranging from months to six years, viz. three seminomas, one teratoma and one combined tumor, i.e. a teratoma and seminoma. The remaining four patients with atypical spermatogonia have shown no sign of tumor to date. As the results of our investigation show, atypical spermatogonia in testicular biopsies should not be taken lightly. We therefore strongly advise checks at short intervals on such patients in view of the high risk of their developing malignant testicular tumors.     

Male gonadal function in Hodgkin's disease before and after treatment

Twenty eight histologically confirmed cases of Hodgkin's disease were evaluates with regard to libido, sperm count, FSH, LH and urinary ketosteroid levels, before and during different stages of chemotherapy along with testicular biopsy on 16 cases. Decrease in libido during therapy improved following treatment, 50% cases who were oligospermic before treatment became azospermic, Serum FSH levels increased significantly (p 0.001) during the course of treatment. There was no significant change in LH and urinary ketosteroid levels (p 0.05). Testicular biopsy, normal initially, showed germ cell aplasia and absence of spermatogenesis after therapy. Drug induced testicular change leads to sterility.     

Immunohistochemical localization of androgen receptor in mouse testicular germ cells during fetal and postnatal development

BACKGROUND: Determination of the cellular distribution of the androgen receptor (AR) in testicular cells is necessary for understanding the mode of AR action in the testis. We here investigated immunohistochemically the localization of AR by use of anti-human AR polyclonal antibody NH27, with special reference to the AR in germ cells in the developing mouse testis. METHODS: ICR mouse testes taken from day 14 post coitum (p.c.) to day 56 post partum (p.p) were used for AR immunohistochemistry by the routine immunoperoxidase method at the light microscopic level and the pre-embedding method at the electron microscopic level. RESULTS: On day 14 p.c., AR immunoreactivity was present in nuclei of prospermatogonia but not in those of Sertoli cells or interstitial cells. On day 14 p.p., the AR was detected in the nuclei of spermatogonia, Sertoli cells, and myoid cells. AR immunoreactivity in nuclei of Leydig cells appeared on day 21 p.p. In the mature mouse testis, the AR was present in the nuclei of spermatogonia, Sertoli cells, myoid cells, and Leydig cells. CONCLUSIONS: AR was present both in germ cells and in somatic cells during fetal and postnatal development of the mouse testis. In the fetal testis, AR was localized exclusively in prospermatogonia and spermatogonia, suggesting that androgen may act directly on germ cells during prespermatogenesis and the early stage of spermatogenesis. Based on the fact that AR is expressed in Sertoli cells, myoid cells, and Leydig cells around the onset of spermatogenesis, the regulation of AR expression in the germ cells seems to be different from that in the somatic cells. Furthermore, our present data suggest the ultrastructural localization in nuclei of mouse testicular cells is similar to that of some other steroid receptors, both in germ cells and somatic cells.     

Hormonal protection from cyclophosphamide-induced inactivation of rat stem spermatogonia

Studies of protection of testicular function from cyclophosphamide with hormonal pretreatment have been limited by the lack of a convenient model for cyclophosphamide-induced inactivation of stem spermatogonia. In the rat, the mortality from cyclophosphamide had prevented the administration of sufficient dosages to produce detectible damage to stem spermatogonia. To overcome this problem, we used bone marrow transplantation and sodium 2-mercaptoethanesulfonate (Mesna) treatment to raise the lethal dose for 50% of the animals (LD50) for cyclophosphamide from 275 to > 400 mg/kg body weight. In addition we used irradiation, 2 weeks prior to injection of cyclophosphamide, to greatly enhance the measured toxicity of cyclophosphamide towards stem spermatogonia. Whereas sperm counts at 9 weeks after a 300 mg/kg cyclophosphamide dose were reduced by only a factor of 1.6 without prior irradiation, they were reduced by a factor of 60 when 2.5 Gy of irradiation had been given. Dramatic protection against this toxicity was produced by hormone treatment with a gonadotropin-releasing hormone (GnRH) antagonist (Nal-Glu) and an antiandrogen (flutamide) following the radiation but prior to cyclophosphamide. This hormone treatment did not modify the stem cell toxicity of the radiation and it therefore must be protecting stem cells against cyclophosphamide-induced damage. Because GnRH antagonist-antiandrogen treatment can protect stem spermatogonial survival and/or function in the rat from cyclophosphamide-induced damage, if the same principles are applicable in human, hormonal pretreatment should be useful for preventing the prolonged azoospermia caused by chemotherapy with cyclophosphamide-containing protocols.     

Effect of short photoperiodic cycles on male genital tract and testicular parameters in male goats (Capra hircus)

This study was performed in adult male goats in which seasonal variations were abolished by rapid alternations of long days and short days. These treatments have been shown previously to prevent seasonal changes in the hypothalamo-pituitary axis and to maintain testis weight and sperm production at a high level. The experimental groups were exposed for 3 years to an alternation of either a 1 month short (16 h dark; 8 h light) and 1 month long (16 L; 8 D) photoperiod (2 month cycle; n = 5) or of a 2 month short and 2 month long photoperiod (4 month cycle; n = 4). The control groups were maintained in natural photoperiodic conditions (45 degrees N) and goats were slaughtered in the non-breeding season (end of April RS; n = 5) at the same period as light-treated bucks, or in the breeding season (end of September BS; n = 6). The total weight of the testes, the length and mean diameter of the seminiferous tubules of light-treated goats were similar to those in the breeding season, and higher than those in the non-breeding season. The total number of A0 spermatogonia was increased by light treatments as compared to control goats in the breeding and non-breeding season. The daily production of A1 spermatogonia, leptonene primary spermatocytes and round spermatids in light-treated goats was maintained at the peak breeding season level. The intra-testicular concentration of testosterone, total volumes of intertubular tissue and of Leydig cells, and the number of Leydig cells per testis did not differ between groups. Although the mean cross-sectional area of Leydig cells in light-treated goats was similar to this area in non-breeding season goats, it was significantly lower than that of breeding season goats. In conclusion, the rapid alternation of short and long days allowed an increase in all the germ cells from the A0 spermatogonia onwards, which was responsible for the maintenance of high spermatogenetic activity of light-treated goats.     

Sertoli cell-specific expression of rat androgen-binding protein in transgenic mice: effects on somatic cell lineages

The Sertoli cells of many species produce an androgen binding protein (ABP) which carries testicular androgens to the epididymis and is thought to play a role in sperm maturation. In the present report we analyzed the morphological modifications present in Leydig, Sertoli, and peritubular cells of the testis of young adult male mice transgenic for ABP gene, which overproduce ABP in testis. By in situ hybridization we demonstrated that ABP is specifically produced by Sertoli cells. Using light and electron microscopy, we detected scattered alterations of the seminiferous tubule cells which include cell degeneration and vacuolization. Leydig and Sertoli cells present morphological signs of hyperfunctioning compensatory mechanisms which include increased amounts of lipid droplets probably due to the existence of a stimulated steroid synthesis that in turn could be a consequence of the decreased unbound testosterone and/or a direct paracrine effect of ABP. Peritubular cells also present numerous signs of hyperstimulation.     

Malignant Leydig cell tumor of the testis secreting progesterone

Malignant Leydig cell tumours of the testis occur in only 0.1-0.3% of patients with testicular tumours. Less than 50 cases of malignant Leydig cells tumours have been previously reported. A report of a new case is presented. This tumour was unusual because of high progesterone level. We analyzed malignant pathologic signs of Leydig cell tumours as immunohistochemical proliferation index. Management of this tumour, for which chemotherapy is not yet available, is discussed.     

Ontogeny of estrogen receptor-beta expression in rat testis

The recently discovered estrogen receptor-beta (ERbeta) is expressed in rodent and human testes. To obtain insight in the physiological role of ERbeta we have investigated the cell type-specific expression pattern of ERbeta messenger RNA (mRNA) and protein in the testis of rats of various ages by in situ hybridization and immunohistochemistry. In fetal testes of rats 16 days postcoitum and testes of 4-day-old animals, fetal germ cells (gonocytes) reveal the ERbeta mRNA in their cytoplasm and the ERbeta protein in their nucleus. In testes of 11- and 15-day-old rats, ERbeta mRNA and protein were detected in Sertoli cells and type A spermatogonia. No signal was found in other types of germ cells. In the adult testes, expression of ERbeta mRNA as well as ERbeta protein was found in pachytene spermatocytes from epithelial stages VII-XIV and in round spermatids from stages I-VIII. Low ERbeta expression was observed in all type A spermatogonia, including undifferentiated A spermatogonia, whereas no expression was found in In and type B spermatogonia and early spermatocytes. At all ages, Sertoli cells showed a weak hybridization signal as well as weak immunoreactivity for ERbeta. In adult testes, no ERbeta mRNA or protein was detected in the interstitial tissue, indicating that Leydig cells and peritubular myoid cells do not express ERbeta. The expression of ERbeta in fetal and late male germ cells as well as in Sertoli cells suggests that estrogens directly affect germ cells during testicular development and spermatogenesis.     

What is the relationship between spermatozoa per milliliter at adulthood and the tubular fertility index at surgical age for patients with cryptorchidism?

PURPOSE: The aim of this study was to find out the relationship in the patient with cryptorchidism between the number of spermatogonia at surgical age and spermiogram data at adulthood. METHODS: Between 1971 and 1996 the authors surgically treated 1,550 children for 2,249 undescended testis. In 21 unilateral and 41 bilateral cryptorchidism patients, both testis were biopsied at surgical procedure during childhood. We currently have spermiogram data for a patient at adulthood. RESULTS: By using the best Tubular Fertility Index (TFI) figures of both testis, the Sperman correlation index between the two parameters is r = 0.22, statistically nonsignificant. The TFI test sensitivity is 0.68 and the specificity is 0.60. The likehood ratio for a positive test result is 0.84 and the likehood ratio for a negative test result is 0.37. CONCLUSION: Although the authors have only one spermiogram, and there are few cases, they suspect the TFI is not a good index to predict the potential fertility in cryptorchidism patients.     

Hormonal stimulation of the recovery of spermatogenesis following chemo- or radiotherapy. Review article

Radiation and chemotherapeutic drugs produce prolonged depression of sperm counts in rodents and humans. Previously, three approaches have been developed in experimental animals that have had some success in preventing or reversing this toxicity. These approaches included pretreatment with hormones that suppress spermatogenesis, stimulation of stem cell number, and supplementation with testosterone. A different rationale for the ability of particular hormonal treatments to reverse prolonged azoospermia is presented in this review. In many cases prolonged azoospermia occurs even though the stem spermatogonia survive the toxic insult, but the differentiation of these spermatogonia to produce sperm fails. In the rat, the block appears to be at the differentiation of the A spermatogonia. Hormone treatments with testosterone or with GnRH agonists, which suppress intratesticular testosterone levels, relieve this block and result in the production of differentiating cells. When the hormone treatment is stopped the production of differentiating cells continues, mature sperm are produced, and fertility is restored. If a similar mechanism can be demonstrated to hold in humans, the fertility of men who have been rendered infertile by treatments for testicular and other cancers could be improved.     

Distribution of spermatogenesis in the testicles of azoospermic men: the presence or absence of spermatids in the testes of men with germinal failure

The aim of the study was to determine whether a prior diagnostic testicle biopsy can predict success or failure of testicular sperm extraction (TESE) with intracytoplasmic sperm injection (ICSI) in patients with non-obstructive azoospermia caused by testicular failure, and what is the minimum threshold of sperm production in the testis which must be surpassed for spermatozoa to reach the ejaculate. Forty-five patients with non-obstructive azoospermia caused by testicular failure underwent diagnostic testicle biopsy prior to a planned future TESE-ICSI procedure. The diagnostic testicle biopsy was analysed quantitatively, and correlated with the quantitative findings of spermatogenesis in patients with normal spermatogenesis, as well as with the results of subsequent attempts at TESE-ICSI. Men with non-obstructive azoospermia caused by germinal failure had a mean of 0-6 mature spermatids/seminiferous tubule seen on a diagnostic testicle biopsy, compared to 17-35 mature spermatids/tubule in men with normal spermatogenesis and obstructive azoospermia. These findings were the same for all types of testicular failure whether Sertoli cell only, maturation arrest, cryptorchidism, or post-chemotherapy azoospermia. Twenty-two of 26 men with mature spermatids found in the prior testis biopsy had successful retrieval of spermatozoa for ICSI, 12 of their partners became pregnant, and are either ongoing or delivered. The study suggests that 4-6 mature spermatids/tubule must be present in the testis biopsy for any spermatozoa to reach the ejaculate. More than half of azoospermic patients with germinal failure have minute foci of spermatogenesis which are insufficient to produce spermatozoa in the ejaculate. Prior diagnostic testicle biopsy analysed quantitatively (for the presence of mature spermatids) can predict subsequent success or failure with TESE-ICSI. Incomplete testicular failure may involve a sparse multi-focal distribution of spermatogenesis throughout the entire testicle, rather than a regional distribution. Therefore, it is possible that massive testicular sampling from many different regions of the testes may not be necessary for successful TESE-ICSI.     

Controlled comparison of percutaneous and microsurgical sperm retrieval in men with obstructive azoospermia

A controlled comparison of the efficacy and reliability of sperm retrieval by testicular fine needle aspiration (TFNA), percutaneous testicular needle biopsy (PercBiopsy) and microsurgical epididymal sperm aspiration (MESA) was performed in nine patients with obstructive azoospermia. During a planned MESA procedure, sperm retrieval was attempted on the same testis with TFNA and PercBiopsy. Spermatozoa were obtained from all patients using MESA and PercBiopsy. Spermatozoa were retrieved using TFNA from 6/9 (67%) men. The mean number of epididymal spermatozoa retrieved with MESA (15 x 106) was significantly higher (P = 0.003) than that retrieved percutaneously from the testis. The mean number of spermatozoa obtained by PercBiopsy was 0.116 x 10(6) while TFNA recovered 0.014 x 106 spermatozoa (P = 0.025). MESA is the optimal choice to retrieve the greatest number of spermatozoa with highest motility for assisted reproduction and subsequent cryopreservation. However, percutaneous testicular retrieval does not require microsurgical expertise and is less invasive. Our results suggest that the optimal percutaneous procedure for sperm retrieval from the testis involves percutaneous testicular needle biopsy with an automatic biopsy gun.     

Testicular sperm retrieval by percutaneous fine needle sperm aspiration compared with testicular sperm extraction by open biopsy in men with non-obstructive azoospermia

The efficiency of testicular sperm retrieval by testicular fine needle aspiration (TEFNA) was compared with open biopsy and testicular sperm extraction (TESE), in 37 rigorously selected patients with non-obstructive azoospermia. All patients underwent TEFNA and TESE consecutively. Thus, each patient served as his own control. The case was regarded as successful if at least one testicular spermatozoon was found allowing intracytoplasmic sperm injection (ICSI) of at least one oocyte. The mean age of the male patients was 32.7 years (range 24-47). Whereas by TEFNA spermatozoa enabling performance of ICSI were found in only four patients out of 37 (11%), open biopsy and TESE yielded spermatozoa in 16 cases (43%). The negative predictive value of high serum follicle stimulating hormone (FSH) concentrations (> or =10 IU/l) (predicting failure to find spermatozoa for ICSI) was low (38.4%). The positive predictive value (predicting the chance to find spermatozoa for ICSI) of normal-sized testicle was not different from that of small-sized (<15 ml) testicle (50%). Complications included one case of testicular bleeding following fine needle aspiration, treated locally, and two cases of extratunical haematomata following TESE requiring no intervention. In patients with non-obstructive azoospermia, TEFNA has a significantly lower yield compared to TESE. Performance of ICSI with testicular sperm in these cases resulted in satisfactory fertilization and high embryo transfer rates. The implantation and pregnancy rates per embryo transfer were 13 and 29% respectively. Neither serum FSH values nor testicular size were predictive of the chances to find spermatozoa for ICSI. Some complications may occur even following TEFNA.     

Expression of oestrogen receptor beta (ER beta) occurs in multiple cell types, including some germ cells, in the rat testis

The identification of a second oestrogen receptor (beta) has prompted a re-evaluation of the potential sites of action of oestrogens. The aim of the present study was to characterize immunoexpression of ER beta expression in the testis to complement earlier data which had demonstrated that expression of ER alpha is confined to testicular interstitial Leydig cells. In all testes studied, including those from both fetal (day 20.5 p.c.) and adult rats, ER beta was found to be expressed in multiple cell types. Sertoli cell nuclei were immunopositive at all ages. In adult testes expression in Sertoli cells was not stage dependent and was unaffected by ablation of Leydig cells. In fetal testes ER beta was also expressed in peritubular cells, fetal Leydig cells and gonocytes. In the pubertal and adult testis ER beta was detected in the nuclei of spermatogonia and most pachytene spermatocytes. Weak immunopositive staining was present in the cytoplasm of spermatocytes undergoing the second meiotic division. In conclusion the widespread expression of ER beta in the testis is consistent with a role for oestrogens in modulating spermatogenesis, and hence fertility, in the male.     

Differential localization of fibroblast growth factor receptor-1, -2, -3, and -4 in fetal, immature, and adult rat testes

Fibroblast growth factors (FGFs) are essential for embryonic development and have been implicated in testis development and function. The effects of FGFs are mediated through four high-affinity receptors (FGFRs), which have different binding affinities for each of the ligands. We have used indirect avidin-biotin-horseradish peroxidase-enhanced immunohistochemistry to localize FGFR-1, -2, -3, and -4 in fetal, immature, and adult rat testes. In the fetal testis, immunoreactivity for FGFR-1 was seen in gonocytes, Sertoli cells, Leydig cells, and mesenchyme, and FGFR-3 was localized in gonocytes. In the immature testis, FGFR-1 was localized to spermatogonia, and all four FGFRs were localized in pachytene spermatocytes, immature adultlike Leydig cells, and peritubular cells. In the adult testis epithelium, Sertoli cells were immunoreactive for FGFR-4, and germ cells were immunoreactive for all four FGFRs, with specific receptors localized to specific stages of germ cell development. In the adult testis interstitium, FGFR-1, -2, and -4 were localized in Leydig cells, and FGFR-1 and -4 were also localized in peritubular cells. The discrete cell- and stage-specific localization of FGFRs in the fetal, immature, and adult rat testis suggests that FGFs exert specific roles through these receptors in spermatogenesis, Leydig cell function, and testicular development.