Testosterone regulation of pigmentation in scrotal epidermis of the rat

Prenatal masculinization of the auditory system in infants: The MIREC-ID study

Sex differences in inner-ear function are detectable in infants, notably through the measurement of otoacoustic emissions (OAEs). Prevailing theories posit that prenatal exposure to high levels of androgens in boys may weaken OAEs, and that this phenomenon may predominantly affect the right ear/left hemisphere (Geschwind-Galaburda (GG) hypothesis). Yet, actual tests of these models have been difficult to implement in humans. Here we examined the relationship between markers of fetal androgen exposure collected at birth (anogenital distances (AGD); penile length/width, areolar/scrotal/vulvar pigmentation) and at 6 months of age (2^nd to 4^th digit ratio (2D:4D)) with two types of OAEs, click-evoked OAEs (CEOAEs) and distortion-product OAEs (DPOAEs) (n = 49; 25 boys; 24 girls). We found that, in boys, scrotal pigmentation was inversely associated with the amplitude and reproducibility of CEOAEs in the right ear at 4 kHz, with trends also present in the same ear for mean CEOAE amplitude and CEOAE amplitude at 2 kHz. Penile length was inversely associated with the mean amplitude of DPOAEs in both the right and left ears, as well as with DPOAE amplitude in the right ear at 2 kHz and the reproducibility of CEOAEs in the left ear at 2.8 kHz. Finally, AGD-scrotum in boys was positively associated in boys with the amplitude of DPOAEs in the left ear at 2.8 kHz. Unexpectedly, there were no sex differences in the amplitude or reproducibility of OAEs, nor, in girls, any associations between androgenic markers and auditory function. Nonetheless, these findings, reported for the first time in a sample of human infants, support both the prenatal-androgen-exposure and GG models as explanations for the masculinization of auditory function in male infants.

Androgenic and estrogenic indices in human newborns and infants: the MIREC-ID study

Prenatal sex steroid exposure plays an important role in determining child development. Yet, measurement of prenatal hormonal exposure has been limited by the paucity of newborn/infant data and the invasiveness of fetal hormonal sampling. Here we provide descriptive data from the MIREC-ID study (n=173 girls; 162 boys) on a range of minimally invasive physical indices thought to reflect prenatal exposure to androgens [anogenital distances (AGDs); penile length/width, scrotal/vulvar pigmentation], to estrogens [vaginal maturation index (VMI) - the degree of maturation of vaginal wall cells] or to both androgens/estrogens [2nd-to-4th digit ratio (2D:4D); areolar pigmentation, triceps/sub-scapular skinfold thickness, arm circumference]. VMI was found to be associated with triceps skinfold thickness (β=0.265, P=0.005), suggesting that this marker may be sensitive to estrogen levels produced by adipose tissue in girls. Both estrogenic and androgenic markers (VMI: β=0.338, P=0.031; 2D:4D - right: β=-0.207, P=0.040; left: β=-0.276, P=0.006; AGD-fourchette - β=0.253, P=0.036) were associated with areolar pigmentation in girls, supporting a role for the latter as an index of both androgen and estrogen exposure. We also found AGD-penis (distance from the anus to the penis) to be associated with scrotal pigmentation (β=0.290, P=0.048), as well as right arm circumference (β=0.462, P<0.0001), supporting the notion that these indices may be used together as markers of androgen exposure in boys. In sum, these findings support the use of several physical indices at birth to convey a more comprehensive picture of prenatal exposure to sex hormones.

A method for gender determination in newborn dark pigmented mice

In many studies using mice, investigators must determine pups' gender at a very early postnatal stage. The gender of mouse pups is typically assessed by measuring the anogenital distance, which is greater in males than in females. This method, however, has proven to be difficult and not completely reliable. The authors describe a quick, easy and reliable method to establish the gender of pigmented mice. In male mice, a pigment spot on the scrotum is visible to the naked eye from the first day of life onwards, whereas female pups lack visible pigmentation in the anogenital region. In lightly pigmented or albino mice, the pigmentation is not obvious or not at all visible. The authors show that identifying this pigment spot is a more accurate and efficient method of determining pup gender compared with measurement of the anogenital distance. This 'spot on' method would therefore be a useful adjunct to conventional methods for determining the gender of pigmented neonatal mice.

Effects of gonadal steroids on melanocytes in developing hamsters

The effects of chronically administered 5 alpha-dihydrotestosterone and estradiol-17 beta on the dorsal costovertebral spots and scrotal skin of intact and hypophysectomized prepubertal male Syrian hamsters were analyzed morphometrically. The 5 alpha-dihydrotestosterone increased pigmentation (optical density) of costovertebral spots and scrotal skin without altering the percentage of pigmented area in intact animals. Spot size and pigment density also increased significantly in hypophysectomized hamsters, but there was no change in the percentage of pigmented area. The 5 alpha-dihydrotestosterone did not alter the percentage of pigmentation in any area of scrotal skin in hypophysectomized animals. In contrast, estradiol produced a dose-related decrease in the number of scrotal skin melanocytes in intact animals. The androgen-induced increase in pigmentation of costovertebral spot hair follicles was reversed by estradiol, which increased pigmentation around the sebaceous glands. These observations suggest that androgenic stimulation of pigmentation in male hamsters is direct, takes place prior to puberty, is probably tissue specific, and is antagonized by estrogens. The differential response to these steroids of melanocytes adjacent to hair follicles and around the perimeter of sebaceous glands may result from changes in the oxidation state of premelanin, an alteration in melanocyte size and shape, or an actual change in the rate of melanin synthesis.

Ultrastructure of normals and castrates and the effects of testosterone and ultraviolet (UVL-B) irradiation on scrotal skin of rats

The ultrastructure of the testosterone dependent epidermal melanocyte system of the scrotal skin of normals and castrates, with and without testosterone replacement therapy, and UVL-B (280-315 nm) radiation in black Long Evans rats is reported. UVL-B increases melanocyte activity, melanosome forming apparatus, (size of Golgi zone and RER, and quantity of cytoplasmic vesicles, dendrites, and stages of melanosomes) in normals and in castrates. Testosterone replacement therapy to castrates is not a prerequisite for stimulation by UVL-B, but it enhances the effects of UVL-B without restoring normalcy as melanosome packaging into complexes predominates. After UVL-B stimulation of normals or castrates, melanocyte dendrites are observed more often. Melanocyte dendrites of skin of castrated rats are observed less often than in normals, but with testosterone replacement therapy, the dendrites become more numerous. Melanosomes donated to keratinocytes are mostly located as singles in normals and as complexes in castrates. After UVL-B, castration, or testosterone replacement therapy, the melanosomes are packaged in keratinocytes in complexes larger than in normals. In the epidermis of long term castrates (9-109 days), non-specific clear cells are observed and Langerhans cells containing melanosomes; we did not observe them in normals. Melanocytes of castrates have a reduced melanosome forming apparatus. The dermis of castrates contains many dermal melanocytes in the superficial dermis with melanosomes in several stages of formation. These cells are not apparent in normals at this location in the dermis. Testosterone replacement therapy and/or UVL-B administered to castrates does not restore the epidermal melanocyte system nor the dermis to precastration ultrastructural appearance; castration has a permanent altering effect as melanosomes are packaged into complexes.

Testosterone and UVL-B stimulation of epidermal melanocytes in rat scrotal skin

The effects of UVL-B and/or testosterone replacemnt therapy are compared in normal and castrated rats in order to determine whether testosterone is required for UVL-B (290-315 nm) stimulation of melanogenesis in the testosterone-dependent epidermal melanocyte system of the scrotal skin of black Long Evans rats. Testosterone is not a prerequisite for UVL-B stimulation of melanocytes as in both castrates and normal animals the melanocytes respond to UVL-B by increases in size, length and number of dendrites (dendriticness), and tyrosinase activity (intensity of Dopa reaction). Addition of testosterone to castrates does enhance the effects of UVL-B. However, UVL-B with or without testosterone cannot maintain normal melanogenesis in rats irradiated immediately after castration nor can it restore normal melanogenesis following long term castration. Bth the amount of UVL nergy/exposure and the number of exposures are important variables in stimulation of the epidermal melanocytes. Administration of a dose of UVL-B to castrates in a single exposure is ineffective, while the same overall dose spread over several exposures increases the size and dendriticness of melanocytes. Testosterone and UVL-B act synergistically in affecting melanogenesis although neither singly nor in combination are they able to fully restore normal melanogenesis.

Organ culture of mammalian skin and the effects of ultraviolet light and testosterone on melanocyte morphology and function

Scrotal skin of black Long-Evans rats and human thigh skin were maintained in vitro as organ cultures for as long as 14 days, and examined histologically using the combined skin splitting and Dopa techniques. Selected rat skin cultures received testosterone in the culture medium and/or were irradiated with ultraviolet light (290-320 nm UVL). With increased time in culture, scrotal melanocytes round up and there is an increase in epidermal pigmentation. Human skin behaves similarly; after eight days in vitro human melanocytes also become rounded, but remain strongly Dopa-positive. Addition of exogenous testosterone to cultured rat skin maintains dendritic morphology of melanocytes, but cell body size is still reduced. UVL irradiation stimulates melanocytes in rat skin cultures, maintaining their dendritic morphology and increasing epidermal and dermal pigmentation. Cultured skin receiving both UVL and testosterone illustrates a synergistic effect. Electron microscopic examination of cultured rat skin shows the presence of large melanosome complexes in keratinocytes, much larger than those found in vivo. Melanocytes appear to be active as they contain an extensive Golgi zone, rough endoplasmic reticulum, and melanosomes in various stages of formation. Dermis contained many dermal melanocytes and macrophages laden with melanosomes, correlating with the increased visible dermal pigmentation in vitro. This UVL stimulation of melanocytes in our skin organ cultures contrasts with the lack of melanogenic stimulation found in melanoma cell cultures. Our findings suggest that the intact epidermal melanin unit may be necessary for UVL stimulation of melanocytes.