Changes in LH secretion in response to an estradiol challenge in male- and female-oriented rams and in ewes

Abstract

Two experiments were conducted to determine whether an estradiol challenge could cause a female-type LH surge in castrated male-and female-oriented rams (MORs and FORs). Administration of 17b-estradiol to castrated MORs and FORs and ovariectomized ewes caused an initial reduction in LH secretion followed for 12-20 h by a surge release of LH in the ewes. No surge release of LH occurred in the MORs and FORs. The pattern of changes in LH secretion within rams and ewes did not differ between the breeding and nonbreeding seasons. Treatment failed to elicit female-typical receptive sexual behaviors in the rams but did stimulate increased sexual receptivity in the ewes as determined by the measures of responsiveness to the teaser ram. Overall, no differences were found in hypothalamichypophyseal function in response to exogenous estradiol between MORs and FORs. These data are interpreted to suggest that in contrast to sexual attraction, the neural mechanisms controlling the LH surge and female receptivity are defeminized in MORs. Reproduction (2008) 135 733-738

The neurobiology of sexual partner preferences in rams

“…Male-oriented rams actively court other rams using male-typical sexual behaviors, while completely ignoring estrous ewes. Yet, with respect to their responses to gonadal hormones and capacity to exhibit sex-typical consummatory behaviors, male-oriented rams show male-typical mounting, not estrogen-induced receptivity and LH surge secretion (Stormshak et al, 2008). These observations can be interpreted to suggest that male-oriented rams, like female-oriented rams, are masculinized and defeminized with respect to mounting, receptivity, and gonadotropin secretion, but not for sexual partner preferences.…”

“…This is because prenatal exposure to testosterone either from the fetal testis or exogenously administered, defeminizes the brain mechanisms controlling these responses (Foster et al, 2002). Tests show that the LH surge response is nonfunctional (defeminized) in male-oriented rams like it is in female-oriented rams (Perkins et al, 1995; Stormshak et al, 2008). Moreover, neither male- nor female-oriented rams express female-typical receptive behaviors in response to estradiol (Stormshak et al, 2008).…”

“…Tests show that the LH surge response is nonfunctional (defeminized) in male-oriented rams like it is in female-oriented rams (Perkins et al, 1995; Stormshak et al, 2008). Moreover, neither male- nor female-oriented rams express female-typical receptive behaviors in response to estradiol (Stormshak et al, 2008). Taken together, these data suggest that the neural mechanisms controlling the LH surge and female receptivity are defeminized regardless of their sexual partner preference.…”

Comportamiento homosexual en rumiantes machos. Revisión

“…Therefore, this response could be an indicator of an incomplete brain masculinization. However, no rams secreted LH in response to estrogen treatments, regardless of their sexual preference (34,41) . Therefore in these studies it is suggested that brain masculinization in ruminants takes place in the prenatal period irrespective of sexual orientation, thus rendering impossible a LH response to estradiol treatments (2) .…”

“…Por tanto, esta respuesta sería un indicador de una masculinización incompleta del cerebro. Sin embargo, ningún carnero secretó LH como respuesta a la administración de estrógenos, independientemente de que fueran homo o heterosexuales (34,41) . Por tanto, en estos trabajos se sugiere que el cerebro de los rumiantes, se masculiniza durante el periodo prenatal independientemente de la orientación sexual, imposibilitando la respuesta de LH al tratamiento con estradiol (2) .…”