The neurobiology of sexual partner preferences in rams

Abstract

The question of what causes a male animal to seek out and choose a female as opposed to another male mating partner is unresolved and remains an issue of considerable debate. The most developed biologic theory is the perinatal organizational hypothesis, which states that perinatal hormone exposure mediates sexual differentiation of the brain. Numerous animal experiments have assessed the contribution of perinatal testosterone and/or estradiol exposure to the development of a male-typical mate preference, but almost all have used hormonally manipulated animals. In contrast, variations in sexual partner preferences occur spontaneously in domestic rams, with as many as 8% of the population exhibiting a preference for same-sex mating partners (male-oriented rams). Thus, the domestic ram is an excellent experimental model to study possible links between fetal neuroendocrine programming of neural mechanisms and adult sexual partner preferences. In this review, we present an overview of sexual differentiation in relation to sexual partner preferences. We then summarize results that test the relevance of the organizational hypothesis to expression of same-sex sexual partner preferences in rams. Finally, we demonstrate that the sexual differentiation of brain and behavior in sheep do not depend critically on aromatization of testosterone to estradiol.

The Palgrave Handbook of the Psychology of Sexuality and Gender

“…Over several decades, research has examined the 'cause' or characteristics of homosexuality. This includes research on the neuroanatomical differences between straight and gay people (Allen & Gorski, 1992;Byne et al, 2001;LeVay, 1991;Swaab et al, 1997), bodily shape and size (Bogaert & Blanchard, 1996;Bogaert & Friesen, 2002;Martin et al, 2008), prenatal androgens in animals (Domínguez-Salazar et al, 2002;Roselli & Stormshak, 2009;Stockman et al, 1985) and humans (Hickey et al, 2010;Hines et al, 2004), and genetic factors (Hamer et al, 1993;Pillard & Bailey, 1998). Most of this research has been controversial and inconclusive.…”

Comportamiento homosexual en rumiantes machos. Revisión

“…Desde hace mucho tiempo se ha intentado determinar si existe una base neural que diferencia a los individuos que despliegan más frecuentemente comportamientos homosexuales (20) . Si bien es difícil atribuir el comportamiento en forma lineal a diferencias neurales, las mismas han sido consideradas una de las posibles causas (2) de un fenómeno que probablemente sea de etiología múltiple.…”

“…For many years researchers searched for a neural basis differing in homosexual and heterosexual individuals (20) . Even if it is difficult to attribute this behavior directly to neural differences, it has been considered as a possible cause (2) of an event which is most probably multietiological.…”

“…La diferencia estaría probablemente dada por la sensibilidad a los estrógenos, dado que la cantidad de receptores de estrógenos en la amígdala es menor en carneros homosexuales que en carneros heterosexuales (34) . En trabajos posteriores, se observó que al aumentar la dosis del inhibidor y el tiempo de tratamiento, tampoco se observó una pérdida de la masculinización cerebral (20) . Aunque no existan trabajos en otros rumiantes, en carneros la aromatización parece no ser necesaria para la masculinización del cerebro.…”

“…Dado que en ratas se ha observado un vínculo entre la cantidad del neurotransmisor cerebral monoamino-oxidasa tipo A (MAO-A) y el comportamiento de dominancia (35) , un estudio (36) comparó la cantidad de MAO-A en la corteza frontal de novillos que aceptan la monta de otros machos y aquéllos que no, encontrando que está disminuida un 75 % en aquellos machos que aceptan ser montados por loss when the dose of the inhibitor or the length of the treatment were increased (20) . Although there are no studies in other ruminants, at least in rams seems that aromatization is not necessary for brain masculinization.…”