Regression of the Mammary Branch of the Genitofemoral Nerve May be Necessary for Testicular Descent in Rats

The role of intra-abdominal pressure in human testicular migration

Objectives:

This review aims to study the role of the abdominal wall in testicular migration process during the human fetal period.

Materials and Methods:

We performed a descriptive review of the literature about the role of the abdominal wall in testicular migration during the human fetal period.

Results:

The rise in intra-abdominal pressure is a supporting factor for testicular migration. This process has two phases: the abdominal and the inguinal-scrotal stages. The passage of the testis through the inguinal canal occurs very quickly between 21 and 25 WPC. Bilateral cryptorchidism in Prune Belly syndrome is explained by the impaired contraction of the muscles of the abdominal wall; mechanical obstruction due to bladder distention and structural alteration of the inguinal canal, which hampers the passage of the testis during the inguinoscrotal stage of testicular migration. Abdominal wall defects as gastroschisis and omphaloceles are associated with undescended testes in around 30 to 40% of the cases.

Conclusions:

Abdominal pressure wound is an auxiliary force in testicular migration. Patients with abdominal wall defects are associated with undescendend testis in more than 30% of the cases probably due to mechanical factors; the Prune Belly Syndrome has anatomical changes in the anterior abdominal wall that hinder the increase of intra-abdominal pressure which could be the cause of cryptorchidism in this syndrome.

Regional Variation in Androgen Receptor Expression and Biomechanical Properties May Contribute to Cryptorchidism Susceptibility in the LE/orl Rat

Background: The process of testicular descent requires androgen and insulin-like 3, hormones secreted by fetal Leydig cells. Knowledge concerning distinct and common functions of these hormones in regulating development of the fetal gubernaculum remains limited and/or conflicting. The current studies were designed to better define characteristics of androgen receptor (AR) expression, function and regulation, as well as the biomechanical properties of normal and cryptorchid gubernaculum during fetal development. Methods: We studied fetal gubernacula from Long Evans outbred (LE/wt) rats and an inbred (LE/orl) strain with an inherited form of cryptorchidism associated with an AR signaling defect. Gubernacular cells or whole organs obtained from LE/wt and LE/orl fetal gubernacula underwent AR immunostaining and quantitative image analysis. The effects of dihydrotestosterone (DHT) on AR expression, muscle fiber morphology, hyaluronan (HA) levels and glycosaminoglycan (GAG) content were measured in LE/wt gubernacula. Finally, the spatial mechanics of freshly harvested LE/wt and LE/orl fetal gubernacula were compared using micropipette aspiration. Results: AR is expressed in the nucleus of mesenchymal core, tip and cord cells of the embryonic (E) day 17 and 21 fetal gubernaculum, and is enhanced by DHT in primary cultures of gubernacular mesenchymal cells. Enhanced AR expression at the tip was observed in LE/wt but not LE/orl gubernacula. In in vitro studies of whole mount fetal gubernaculum, DHT did not alter muscle fiber morphology, HA content or GAG production. Progressive swelling with reduced cellular density of the LE/wt gubernaculum at E19-21 was associated with increased central stiffness in LE/wt but not in LE/orl fetuses. Conclusions: These data confirm nuclear AR expression in gubernacular mesenchyme with distal enhancement at the tip/cord region in LE/wt but not LE/orl rat fetuses. DHT enhanced cellular AR expression but had no major effects on muscle morphology or matrix composition in the rat fetal gubernaculum in vitro. Regional increased stiffness and decreased cell density between E19 and E21 were observed in LE/wt but not LE/orl fetal gubernacula. Developmental differences in cell-specific AR expression in LE/orl fetal gubernacula may contribute to the dysmorphism and aberrant function that underlies cryptorchidism susceptibility in this strain.

The importance of the gubernaculum in testicular migration during the human fetal period

OBJECTIVES

The objective of this review is to study the role of the gubernaculum in the testicular migration process during the human fetal period.

MATERIALS AND METHODS

We performed a descriptive review of the literature about the role of the gubernaculum in testicular migration during the human fetal period.

RESULTS

In the first phase of testicular migration, the gubernaculum enlarges to hold the testis near the groin and in the second phase the gubernaculum migrates across the pubic region to reach the scrotum. The proximal portion of the gubernaculum is attached to the testis and epididymis and the presence of multiple insertions in the distal gubernaculum is extremely rare. The presence of muscle and nerves in the human gubernaculum is very poor. The gubernaculum of patients with cryptorchidism has more fibrous tissue and less collagen and when the patients are submitted to hormonal treatment, the gubernaculum components alter significantly.

CONCLUSIONS

The gubernaculum presents significant structural modifications during testicular migration in human fetuses.

Regulation of testicular descent

Testicular descent occurs in two morphologically distinct phases, each under different hormonal control from the testis itself. The first phase occurs between 8 and 15 weeks when insulin-like hormone 3 (Insl3) from the Leydig cells stimulates the gubernaculum to swell, thereby anchoring the testis near the future inguinal canal as the foetus grows. Testosterone causes regression of the cranial suspensory ligament to augment the transabdominal phase. The second, or inguinoscrotal phase, occurs between 25 and 35 weeks, when the gubernaculum bulges out of the external ring and migrates to the scrotum, all under control of testosterone. However, androgen acts mostly indirectly via the genitofemoral nerve (GFN), which produces calcitonin gene-related peptide (CGRP) to control the direction of migration. In animal models the androgen receptors are in the inguinoscrotal fat pad, which probably produces a neurotrophin to masculinise the GFN sensory fibres that regulate gubernacular migration. There is little direct evidence that this same process occurs in humans, but CGRP can regulate closure of the processus vaginalis in inguinal hernia, confirming that the GFN probably mediates human testicular descent by a similar mechanism as seen in rodent models. Despite increased understanding about normal testicular descent, the common causes of cryptorchidism remain elusive.

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.

Mathematical modelling of gubernaculum during inguino-scrotal migration shows limb bud characteristics

PURPOSE

The gubernaculum is postulated to grow like an embryonic limb bud during inguinoscrotal descent in rodents. Recently, modelling of limb bud growth suggests the undifferentiated, distal "progress zone" provides molecular morphogenic signals, rather than cell division, as previously thought. We aimed to develop a mathematical gubernacular growth model, hypothesising that it would mimic limb buds through evolutionary conservation.

METHODS

Histology was done on Sprague-Dawley rats (day 2, 8; n=7/group) to determine gubernacular length, width, cell density in distal growth centre, middle and proximal cremaster muscle. Analysis of measurements enabled gubernacular growth modelling under variable growth centre sizes/densities, assuming no apoptosis.

RESULTS

Modelling found that gubernacular growth occurred mostly within cremaster muscle, rather than primarily in the undifferentiated mesenchymal tip, despite its higher mitotic rate. The growth centre accounted for ≤ 10% of total gubernacular enlargement/elongation.

CONCLUSIONS

These results suggest the gubernaculum elongates by proliferation throughout cremaster muscle like a limb bud. The distal undifferentiated tip may provide signalling molecules for growth, which could be a fruitful source for causes of failed migration/elongation in cryptorchidism.

Journal of Pediatric Surgery-Sponsored Fred McLoed Lecture. Undescended testis: the underlying mechanisms and the effects on germ cells that cause infertility and cancer

Testicular descent is a complex morphological process that occurs in at least 2 stages, with different hormonal control. Insl3 controls the first step of gubernacular enlargement, although the abnormality long gubernacular cord in persistent Műllerian duct syndrome remains unexplained. Androgens control inguinoscrotal migration, which may be triggered by local signalling from the mammary line, and which requires the genitofemoral nerve. However, there is still much to learn about this phase, which when abnormal frequently leads to cryptorchidism. Orchidopexy is being recommended in the first year of age, because increasing research suggests that the stem cells for spermatogenesis form between 3 and 9 months, with surgery aiming to permit this normally, although this is not yet proven. Acquired cryptorchidism is now becoming accepted and is likely to be caused by inadequate elongation of the postnatal spermatic cord. It is not yet known whether orchidopexy is always needed, as this remains controversial.