Effect of prenatal androgens on click-evoked otoacoustic emissions in male and female sheep (Ovis aries)

Abstract

Otoacoustic emissions (OAEs) were measured in male and female Suffolk sheep (Ovis aries). Some sheep had been administered androgens or estrogens during prenatal development, some were gonadectomized after birth, and some were allowed to develop normally. As previously reported for spotted hyenas, gonadectomy did not alter the OAEs for either sex; accordingly, the untreated/intact and the untreated/gonadectomized animals were pooled to form the control groups. The click-evoked otoacoustic emissions (CEOAEs) exhibited by the female control group (N = 12) were slightly stronger (effect size = 0.42) than those in the male control group (N = 15), which is the same direction of effect reported for humans and rhesus monkeys. Females administered testosterone prenatally (N = 16) had substantially weaker (masculinized) CEOAEs than control females (effect size = 1.15). Both of these outcomes are in accord with the idea that prenatal exposure to androgens weakens the cochlear mechanisms that underlie the production of OAEs. The CEOAEs of males administered testosterone prenatally (N = 5) were not different from those of control males, an outcome also seen in similarly treated rhesus monkeys. Males administered dihydrotestosterone (DHT) prenatally (N = 3) had slightly stronger (hypo-masculinized) CEOAEs than control males. No spontaneous otoacoustic emissions (SOAEs) were found in any ears, a common finding in non-human species. To our knowledge, this is the first ruminant species measured for OAEs.

Click-Evoked Otoacoustic Emissions in Children and Adolescents with Gender Identity Disorder

“…Consistent with several earlier studies McFadden, 1998;McFadden et al, 2009;Moulin et al, 1993;Strickland et al, 1985), sex differences in emission strengths were observed in the control group, with girls having significantly stronger emission amplitudes than boys. Our finding that boys with GID showed stronger, more female-typical emissions compared to control boys suggests that boys with GID might have been exposed to relatively lower amounts of androgens during early development.…”

“…Results from several animal studies support the idea that higher concentrations of androgens, naturally present in males, exert inhibitory effects on CEOAEs.Forinstance,maleandfemalerhesusmonkeys(Macaca mulatta), treated with testosterone prenatally, showed weaker (i.e., masculinized) CEOAEs when 5-6 years old, whereas male monkeys that had received androgen receptor blockers during early development had stronger CEOAEs compared to untreated males (McFadden, Pasanen, Raper, Lange, & Wallen, 2006a). Similar hormonal manipulation studies have been conducted in other animal species such as the spotted hyena and sheep (McFadden, Pasanen, Valero, Roberts, & Lee, 2009;McFadden, Pasanen, Weldele, Glickman, & Place, 2006b). In both sexes of both species, prenatal treatment with testosterone had diminishing effects whereas treatment with androgen receptor blockers enhanced CEOAE amplitudes.…”

Estrogenic modulation of auditory processing: A vertebrate comparison

“…In both cases, they found that testosterone treatment masculinized the CEOAEs of female offspring. Intriguingly, there was a trend for prenatal E 2 treatment to similarly masculinize sheep CEOAEs (McFadden et al, 2009b), but the sample size of only 2 animals was too small to allow for any firm conclusions. Nevertheless, these findings collectively raise the interesting possibility that prenatal masculinization of the auditory periphery and brainstem may be mediated by testosterone and/or its estrogenic metabolites, leading to fundamental differences in auditory detection and localization.…”

“…Similarly, it has been proposed that prenatal hormone exposure may contribute both to the development of a non-heterosexual orientation, and masculinized CEOAEs (McFadden and Pasanen, 1998), SOAEs (McFadden and Pasanen, 1999), and wave-V ABR latencies (McFadden and Champlin, 2000) in homosexual and bisexual women. In a direct test of this hypothesis, McFadden and colleagues measured OAEs in rhesus monkeys ( Macaca mulatta ; McFadden et al, 2006), and Suffolk sheep ( Ovis aries , McFadden et al, 2009b) that had been administered testosterone during prenatal development. In both cases, they found that testosterone treatment masculinized the CEOAEs of female offspring.…”

Dissociation between distortion-product and click-evoked otoacoustic emissions in sheep (Ovis aries)

“…Accordingly, we believe that these are true instances of CEOAEs existing in ears lacking DPOAEs, which is logically possible if the mechanisms underlying the two types of OAE are different (Shera and Guinan, 1999). The CEOAE data from sheep already have been reported (McFadden et al, 2008b); the DPOAE data are reported separately here because of their significance for research on underlying mechanisms. The implication is that the processes primarily responsible for producing DPOAEs can be weak without preventing that ear from producing CEOAEs.…”