The anatomy of the cremaster muscle during inguinoscrotal testicular descent in the rat

Morphologic alterations of the genital mesentery implicated in testis non-descent in rats prenatally exposed to flutamide

BACKGROUND

There is an endless debate on whether androgens mediate testis descent through developmental changes in the gubernacular or the cranial suspensory ligament.

OBJECTIVE

To investigate the relation of any possible morphologic changes in the genital mesentery, that is, the system of genital peritoneal folds including the gubernacular and cranial suspensory ligaments, with the event of testis non-descent in rats prenatally exposed to the antiandrogen flutamide.

MATERIALS AND METHODS

Time-pregnant Sprague Dawley rats received flutamide (100 mg/kg/d) or vehicle subcutaneously on gestational days 16-17. Flutamide-treated male offspring (n = 67), and vehicle-treated male (n = 34) and female (n = 28) offspring were surgically explored under microscope on postnatal day 50. Testicular position was examined bilaterally. Dimensions of genital mesentery parts were also assessed bilaterally. Association of flutamide-induced morphologic changes with descended (n = 61) and undescended (n = 50; 33 cryptorchid and 17 ectopic) testes was investigated with logistic regression analysis.

RESULTS

The male genital mesentery comprised a cranial and a caudal fold converging on the vas deferens. Flutamide resulted in enlarged cranial and reduced caudal folds. Of all flutamide-induced alterations, the increased length of the posterior fixation of the cranial fold and the decreased length of the gubernacular ligament of the caudal fold were found to independently increase the odds of testis non-descent. Testicular ectopy, unlike cryptorchidism, was associated with a short gubernacular ligament only. The female genital mesentery consisted of a cranial fold only.

CONCLUSION

Our findings showed a combined contribution of both cranial and caudal folds of the genital mesentery to testis non-descent, through an abnormally long mesentery root and an abnormally short gubernacular ligament, respectively. Inhibition of male-specific development of the genital mesentery with flutamide did not result in a feminized architecture.

Isolation and characterization of myogenic precursor cells from human cremaster muscle

Human myogenic precursor cells have been isolated and expanded from a number of skeletal muscles, but alternative donor biopsy sites must be sought after in diseases where muscle damage is widespread. Biopsy sites must be relatively accessible, and the biopsied muscle dispensable. Here, we aimed to histologically characterize the cremaster muscle with regard number of satellite cells and regenerative fibres, and to isolate and characterize human cremaster muscle-derived stem/precursor cells in adult male donors with the objective of characterizing this muscle as a novel source of myogenic precursor cells. Cremaster muscle biopsies (or adjacent non-muscle tissue for negative controls; N = 19) were taken from male patients undergoing routine surgery for urogenital pathology. Myosphere cultures were derived and tested for their in vitro and in vivo myogenic differentiation and muscle regeneration capacities. Cremaster-derived myogenic precursor cells were maintained by myosphere culture and efficiently differentiated to myotubes in adhesion culture. Upon transplantation to an immunocompromised mouse model of cardiotoxin-induced acute muscle damage, human cremaster-derived myogenic precursor cells survived to the transplants and contributed to muscle regeneration. These precursors are a good candidate for cell therapy approaches of skeletal muscle. Due to their location and developmental origin, we propose that they might be best suited for regeneration of the rhabdosphincter in patients undergoing stress urinary incontinence after radical prostatectomy.

Structural study of the cremaster muscle in patients with retractile testis

OBJECTIVE

To analyze the structure of the cremaster in patients with retractile testis (RT), comparing the distribution of nerves, elastic system and muscles with patients having cryptorchidism and inguinal hernia (IH).

PATIENTS AND METHODS

We studied 31 patients, 17 with RT (mean age=5.17years); 9 with IH (mean age=2.6) and 5 with cryptorchidism (mean age=3). A cremaster biopsy was performed and submitted to routine histological processing and studied using histochemistry and immunohistochemistry. The samples were photographed under an Olympus BX51 microscope. The images were processed with the Image J software and the cremaster muscle structures were quantified. Means were compared statistically using ANOVA and the unpaired t-test (p<0.05).

RESULTS

There were no differences (p=0.08) in diameter of muscle fiber between the groups. The muscle fiber density differed between patients with RT and IH (p=0.02): RT (mean=17.71%, SD=16.67), IH (mean=38.06%, SD=14) and cryptorchidism (mean=21.47%, SD=16.18). There was no difference (p=0.07) in the density of elastic fibers in the three groups. We observed a lower concentration of cremaster nerves of patients with RT compared with IH (p=0.0362): RT (mean=1.72%, SD=0.58), IH (mean=3.28% SD=0.94) and cryptorchidism (mean=2.52%, SD=0.53).

CONCLUSIONS

Retractile testis is not a normal variant, and presented a similar cremaster muscle structure as in patients with cryptorchidism.

LEVEL OF EVIDENCE

II; prospective comparative study.

The syndrome of Spigelian hernia and cryptorchidism: a review of paediatric literature

BACKGROUND/PURPOSE

The purpose of this study is to present a summary of paediatric Spigelian hernia (SH) reported to date, and discuss possible aetiology of SH associated with ipsilateral ectopic testis (SH-ET).

METHODS

Search of PubMed, Medline, Embase, and CINAHL was performed using keywords "Spigelian hernia". The following were extracted from articles describing paediatric SH: demographics, site and contents of SH, comorbidities, proposed aetiology, presence of ipsilateral inguinal canal (IC) and gubernaculum (G).

RESULTS

There were 78 patients with 88 hernias (69 male, 19 female), including 55 male (19 left, 22 right, 7 bilateral) and 16 female (5 left, 5 right, 3 bilateral) nontraumatic SHs. In nontraumatic male SH, 29 hernias contained testis (10 left, 11 right, 4 bilateral), 15 did not, 10 had no data. Of 29 SH-EH, 15 were lacking IC and G, 3 were missing IC (no G data) and 2 had absent G (no IC data). The combination of SH and cryptorchidism is increasingly recognised as a distinct syndrome. However, there is controversy as to the pathogenic mechanism of this association. We hypothesise SH-ET develops because the G, and therefore IC and line of descent, become cranially 'mislocated' along the mammary line, which overlies the Spigelian fascia.

CONCLUSION

SH is rare in children. SH-ET may result by testicular descent to an ectopic site along the embryological mammary line.

The regulation of testicular descent and the effects of cryptorchidism

The first half of this review examines the boundary between endocrinology and embryonic development, with the aim of highlighting the way hormones and signaling systems regulate the complex morphological changes to enable the intra-abdominal fetal testes to reach the scrotum. The genitoinguinal ligament, or gubernaculum, first enlarges to hold the testis near the groin, and then it develops limb-bud-like properties and migrates across the pubic region to reach the scrotum. Recent advances show key roles for insulin-like hormone 3 in the first step, with androgen and the genitofemoral nerve involved in the second step. The mammary line may also be involved in initiating the migration. The key events in early postnatal germ cell development are then reviewed because there is mounting evidence for this to be crucial in preventing infertility and malignancy later in life. We review the recent advances in what is known about the etiology of cryptorchidism and summarize the syndromes where a specific molecular cause has been found. Finally, we cover the recent literature on timing of surgery, the issues around acquired cryptorchidism, and the limited role of hormone therapy. We conclude with some observations about the differences between animal models and baby boys with cryptorchidism.

Expression of estrogen receptors α and β in paratesticular tissues in boys operated on for unilateral cryptorchidism between the 1st and 4th years of life

BACKGROUND

The aim of this study was to assess the expression of estrogen receptors alpha and beta in paratesticular tissues in a group of boys with and without cryptorchidism, and evaluation of karyotypes, localization, morphology and the major length of the undescended testes.

MATERIAL/METHODS

Fifty boys (1-4 years old) with unilateral cryptorchidism were evaluated. Fifty healthy boys within the same age range, with inguinal hernia, served as a control group. Measurements concerning expression of ERalpha ERbeta receptors were preformed using monoclonal mouse antibodies against human receptor alpha and beta.

RESULTS

In the mesothelial layer, the expression of ERalpha was higher in the patients group with undescended testes and it was statistically significant (p=0.04). There was no difference in the expression of ERbeta in this layer between groups. In the stromal cell layer there was statistically significant higher expression of ERbeta (p<0.05) in the group of patients with undescended testes.

CONCLUSIONS

There was no difference between expressions of ERalpha in stromal cell layer. In the endothelial layer there was no difference in expression of ERalpha and ERbeta. In the smooth muscle layer there was no expression of ERalpha in either group. The expression of ERbeta in the smooth muscle layer was nearly identical in both groups. Undescended testes were generally found in the superficial inguinal pouch (n=46). The major lengths of the undescended testes were smaller in comparison to the testes positioned normally. In 9 of the cases the testes had different shape, and turgor deficit, and epididymides were smaller, dysplastic and separated from the testis.

Serum AMH concentration as a marker evaluating gonadal function in boys operated on for unilateral cryptorchidism between 1st and 4th year of life

The aim of this study was to measure the serum AMH (anti-Mullerian hormone) concentrations in a group of boys with or without cryptorchidism, evaluation of karyotypes, testicular position, morphology, and major length of the undescended testes. Fifty boys who were 1-4 years old (median = 2.4 years) with unilateral cryptorchidism were evaluated. All of them underwent orchidopexy in 2010. Prior to the procedure, all of the subjects had undergone karyotyping to exclude chromosomal abnormalities. Fifty healthy boys within the same age range (median = 2.1 years) admitted for planned inguinal hernia repair in 2010, served as controls. Blood samples were collected, while obtaining blood for standard laboratory tests routinely performed before the surgeries. Medians of AMH in boys with cryptorchidism were lower than in boys with inguinal hernia and differed significantly between two groups. Undescended testes were generally found in superficial inguinal pouch (n = 46), in two cases were noted to be in the external ring of the inguinal canal, and in another two instances, in the abdominal cavity. The major lengths of the undescended testes were smaller in comparison to the testes positioned normally (mean of 1 cm vs. a mean of 1.5 cm, respectively). In nine of the cases, the testes had turgor deficit, a drop shape, with epididymides that were small, dysplastic, and separated from the testis. The authors found that AMH was lower in boys with unilateral cryptorchidism (also found to have smaller testis) when compared with the control group.

The role of cremaster muscle in testicular descent in humans and animal models

Testicular descent is a complex developmental process involving anatomical and hormonal regulation. The gubernaculum undergoes a "swelling reaction" during the transabdominal phase and is mainly under the control of Insulin-Like Peptide 3 (INSL-3) and Mullerian Inhibitory Substance/Anti-Mullerian Hormone (MIS/AMH). The second phase of testicular descent is regulated by androgens and calcitonin gene-related peptide (CGRP) release from the sensory nucleus of the genitofemoral nerve (GFN). In rodents, the active proliferation of the gubernacular tip and cremaster muscle, its rhythmic contraction, as well as the chemotactic gradient provided by the CGRP result in eventual migration of the testis into the scrotum. This review illustrates the structural aspects and hormonal control of cremaster muscle development to better understand the mechanism of testicular descent in normal rodents and humans, compared to diseased rodent models. The analysis showed the cremaster muscle is formed from mesenchymal differentiation of the gubernacular tip and is not a direct passive extension of internal oblique muscle. Cremaster muscle matures slower than other body muscles, and the persistence of immature myogenic proteins seen in cardiac muscle allows rhythmic contraction to guide the testis into the scrotum. Finally, remodelling of the cremaster muscle enables gubernacular eversion. Further understanding of the molecular regulators governing the structural and hormonal changes in the cremaster muscle may lead to new advances in the treatment of undescended testes.

The role of the gubernaculum in the descent and undescent of the testis

Testicular descent to the scrotum involves complex anatomical rearrangements and hormonal regulation. The gubernaculum remains the key structure, undergoing the 'swelling reaction' in the transabdominal phase, and actively migrating out of the abdominal wall to the scrotum in the inguinoscrotal phase. Insulin-like hormone 3 (Insl3) is the primary regulator of the first phase, possibly augmented by Müllerian inhibiting substance/anitmüllerian hormone (MIS/AMH), and regression of the cranial suspensory ligament by testosterone. The inguinoscrotal phase is controlled by androgens acting both directly on the gubernaculum and indirectly via the genitofemoral nerve, and release of calcitonin gene-related peptide from its sensory fibres. Outgrowth of the gubernaculum and elongation to the scrotum has many similarities to an embryonic limb bud.Cryptorchidism occurs because of both failure of migration congenitally, and failure of elongation of the spermatic cord postnatally. Germ cell development postnatally is disturbed in congenital cryptorchidism, but our current understanding of germ cell biology suggests that early orchidopexy, around 6 months of age, should provide a significant improvement in prognosis compared with a previous generation. Hormone treatment is not currently recommended. Acquired cryptorchid testes may need orchidopexy once they no longer reach the scrotum, although this remains controversial.

Gubernacular development in the mouse is similar to the rat and suggests that the processus vaginalis is derived from the urogenital ridge and is different from the parietal peritoneum

BACKGROUND

Gubernacular development and testicular descent have been studied most extensively in rat models, but new transgenic mouse models require a deep understanding of normal mouse development so that results can be extrapolated to the human. We aimed to compare gubernacular anatomy during development in the mouse with that of the rat.

METHODS

Time-mated mice (C57BL/6) and Sprague-Dawley rats were used to collect male fetuses at embryonic (E) days E13, E14, E15, E17, E18, and E19 and neonates at postnatal (P) days P0 and P2. Fetuses and newborn were processed for serial sections (sagittal, transverse, and coronal) and stained with hematoxylin and eosin, muscle markers (embryonic myosin, desmin), a neuronal marker (Tuj1), a mitotic marker (Ki67), and keratin marker to label epithelium.

RESULTS

Early development of cremaster in the mouse was related to transversus abdominis muscle, but not internal oblique muscle (as in rats), and forms a monolaminar cremaster layer. There is close association between the regressing inguinal mammary bud and the gubernaculum in the mouse at E13. The peritoneal surface of the processus vaginalis (PV) covering the gubernaculum and epididymis was morphologically distinct from the remaining parietal peritoneum throughout development.

CONCLUSIONS

Gubernacular development in mouse is similar to that in the rat except for certain structures, such as cremaster muscle. The PV seems to be derived from the surface of the urogenital ridge, separate from the remaining parietal peritoneum. This study suggests that the PV has evolved to aid testicular descent in this species, rather than a nondescript diverticulum of parietal peritoneum.

The common fetal development of the mammary fat pad and gubernaculum

BACKGROUND/AIMS

Recent work both from our laboratory and in marsupial models of testicular descent suggests a strong connection between the mammary line and gubernacular migration. This study investigated the relationship between the mammary fat pad (MFP) that underlies the mammary line and the developing gubernaculum by fluorescent immunohistochemistry.

METHODS

Rats at E17 and E19 were fixed and processed for immunohistochemistry. Sagittal sections of male fetuses were stained with antibodies against androgen receptor (AR), prolyl-4 hydroxylase β, Desmin, activated Notch-1, Jagged-1, and Ki-67. These were analyzed by fluorescent confocal microscopy.

RESULTS

At E17 and E19, the MFP anlage forms a continuous distribution of fibroblasts passing immediately adjacent the gubernaculum to the future scrotum. Within this exists a distinct subpopulation of fibroblasts expressing AR distributed over the path of inguinoscrotal descent of the gubernaculum. Proliferation and Notch-1 signaling were similar throughout the MFP with differential Notch-1 signaling in the E19 gubernaculum.

CONCLUSION

This investigation has identified the presence of a distinct AR-expressing subpopulation of MFP fibroblasts over the path of inguinoscrotal descent during the key androgenic programming window of this phase. This unique developmental pattern is consistent with a prime role for the MFP in testicular descent.

What is new in cryptorchidism and hypospadias--a critical review on the testicular dysgenesis hypothesis

It has been hypothesized that poor semen quality, testis cancer, undescended testis, and hypospadias are symptoms of one underlying entity--the testicular dysgenesis syndrome--leading to increasing male fertility impairment. Though testicular cancer has increased in many Western countries during the past 40 years, hypospadias rates have not changed with certainty over the same period. Also, recent studies demonstrate that sperm output may have declined in certain areas of Europe but is probably not declining across the globe as indicated by American studies. However, at the same time, there is increasing recognition of male infertility related to obesity and smoking. There is no certain evidence that the rates of undescended testes have been increasing with time during the last 50 years. In more than 95% of the cases, hypospadias is not associated with cryptorchidism, suggesting major differences in pathogenesis. Placental abnormality may occasionally cause both cryptorchidism and hypospadias, as it is also the case in many other congenital malformations. The findings of early orchidopexy lowering the risk of both infertility and testicular cancer suggest that the abnormal location exposes the cryptorchid testis to infertility and malignant transformation, rather than there being a primary abnormality. Statistically, 5% of testicular cancers only are caused by cryptorchidism. These data point to the complexity of pathogenic and epidemiologic features of each component and the difficulties in ascribing them to a single unifying process, such as testicular dysgenesis syndrome, particularly when so little is known of the actual mechanisms of disease.

Cryptorchidism

Cryptorchidism is a very common anomaly of the male genitalia, affecting 2%-4% of male infants and is more common in premature infants. There are two separate stages of testicular descent. The first stage occurs at 8-15 weeks' gestation in the human fetus and is characterized by enlargement of the genito-inguinal ligament, or gubernaculum, and regression of the cranial suspensory ligament. The testis remains close to the future inguinal region as the fetal abdomen grows. Leydig cells in the testis produce insulin-like hormone 3, which stimulates the caudal gubernaculum to grow and become thicker. Mullerian inhibiting substance may have a role in the first phase of descent by stimulating the swelling reaction in the gubernaculum. The second phase of testicular descent requires migration of the gubernaculum and testis from the inguinal region to the scrotum, between 25 and 35 weeks' gestation. The genitofemoral nerve releases calcitonin gene-related peptide, a neurotransmitter that provides a chemotactic gradient to guide migration. The exact cause of cyrptorchidism remains elusive. Information is mainly derived from animal studies (especially in rodents), which may not extrapolate to the human setting. These findings, however, do have some similarities among mammalian species. The current recommended timing for orchidopexy is between 6 and 12 months of life in an effort to preserve the spermatogonia--the stem cells for subsequent spermatogenesis. Despite surgical treatment by orchidopexy, the long-term outcome still remains problematic and controversial. Impaired fertility (33% in unilateral cases and 66% in bilateral undescended testes) and a cancer risk 5-10 times greater than normal is observed over time. Further research into the cause and management of undescended testes is necessary.

The antiandrogen flutamide perturbs inguinoscrotal testicular descent in the rat and suggests a link with mammary development

AIM

Inadequate androgen activity is a likely cause of cryptorchidism in humans, affecting inguinoscrotal testicular descent. Flutamide, a nonsteroidal antiandrogen, produces cryptorchidism in rats. We aimed to determine the anatomical and histologic effects of flutamide.

METHODS

Time-mated Sprague-Dawley female rats were injected subcutaneously with flutamide (75 mg/kg in sunflower oil) on days 16 to 19 of pregnancy. Embryonic (E) and postnatal (P) male offspring were collected (E16, E19, P0, P2, P4, P8) in control and flutamide-treated groups (n = 5-10). Samples were fixed in 4% paraformaldehyde. Five-micrometer-thick sections were prepared for hematoxylin and eosin, trichrome and immunohistochemical stains (Desmin, TuJ1, Ki67). This identified muscle and neural cells and areas of cell proliferation.

RESULTS

Postnatally, the gubernaculum in flutamide-treated rats had more mesenchyme and muscle than controls. Gubernacular eversion failed, and mammary tissue persisted around the gubernaculum in flutamide-treated rats. Flutamide had no effect on embryonic gubernacular anatomy and histology.

CONCLUSIONS

Prenatal androgens altered postnatal gubernacular anatomy and histology in the postnatal period. Our findings indicate that the failure of gubernacular differentiation and migration may be because of the ongoing presence of mammary tissue in the region of the external inguinal ring.

Growth of the rat gubernaculum in vitro and localisation of its growth centre

PURPOSE

Recent studies suggest that testicular descent is accomplished by outgrowth of the gubernaculum from the abdominal wall. The tip of the gubernaculum has been proposed as the primary site of growth, similar to an embryonic limb bud. We aimed to determine the maximum site of growth in organ culture.

METHODS

Gubernacula from 1-day-old Sprague-Dawley rats (n = 40) were collected and divided into 4 groups as follows: whole gubernaculum (control), truncated gubernaculum (tip excised), gubernacular tip alone, and grafted gubernaculum with an extra tip on its side. Tissues were cultured with or without calcitonin gene-related peptide (CGRP) (714nmol/L) in medium for 24 hours. The area of each gubernaculum was determined by "Image J" analysis of digital photos collected via a Leica Wild M28 microscope (Leica Microsystems, Wetzler GmbH Germany) taken before and after culture.

RESULTS

In organ culture, the neonatal rat gubernaculum normally shrank 10% to 15%, but this was prevented by the presence of exogenous CGRP (0.8% vs 11.8%; P < .003). By contrast, gubernacula with their tips excised were not affected by CGRP (3.4% vs 4.7%; not significant). Gubernacular tips alone did respond to CGRP (2.7% vs 13.5%; P < .03). Transplantation of the tip to another gubernaculum caused it to develop 2 tips.

CONCLUSIONS

These results suggest that the rat gubernaculum contains a growth centre in its distal tip that can respond to CGRP. This is consistent with a limb bud model of gubernacular growth during the inguinoscrotal descent of the testis.