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

Abstract

Distortion-product otoacoustic emissions (DPOAEs) were weak or absent in about one-third of sheep (Ovis aries) of both sexes tested for otoacoustic emissions (OAEs) even though their click-evoked OAEs (CEOAEs) seemingly were typical of other sheep of the same sex. Various pieces of evidence suggest that the absence of measurable DPOAEs was unlikely to be attributable to anesthetic effects, a poorly located probe tip, a pressure differential between middle and outer ears, season of the year, body position during testing, temperature effects, or previous medical history. Sheep apparently can exhibit a marked dissociation between DPOAEs and CEOAEs. In those sheep having measurable DPOAEs, the DPOAEs were stronger in males than in females, which is the opposite direction of effect from the CEOAEs measured in these same sheep and in humans. In female sheep exposed to higher-than-normal levels of androgens during gestation, the measurable DPOAEs were stronger than in untreated females. Although this also was the opposite direction of effect from expected, it still was a shift in the male direction, in accord with past findings about the masculinizing effects of androgens on OAEs. In sheep, androgen exposure appears to have different effects on the mechanisms underlying DPOAEs from those underlying CEOAEs.

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

“…As noted, we observed an unusual partial dissociation between CEOAEs and DPOAEs in these sheep that will be discussed further elsewhere (McFadden et al, 2008b). This colony of sheep does not contain any of the “gay rams” that are reported to prefer to engage in sex behavior with other males rather than with females (e.g., Roselli et al, 2004).…”

“…As noted above and detailed elsewhere (McFadden et al, 2008b), some sheep had unmeasurable, or quite weak, DPOAEs, but normal-appearing CEOAEs. Initially, all CEOAE comparisons and analyses reported here were done with the 16 sheep having no DPOAEs excluded.…”

“…Thus, the weak CEOAEs in sheep compared to other species might be attributable to the halothane anesthetic none of the other species received (but compare Guven et al, 2006). However, any explanation of that sort also needs to explain why the DPOAEs of sheep (McFadden et al, 2008b) were comparably strong as the DPOAEs of these same rhesus monkeys and spotted hyenas. Might DPOAEs also be dissociated from other forms of OAE in the way they respond to anesthetics?…”

“…Here, the presence of strong CEOAEs makes cochlear injury an unlikely explanation. Elsewhere (McFadden et al, 2008b) we discuss this dissociation between and DPOAEs and CEOAEs in sheep and describe some of the tests we made to document its existence. Here we describe only the CEOAE data, which appear to be unaffected by the dissociation from the DPOAE data.…”

Sex differences in distortion-product and transient-evoked otoacoustic emissions compared

“…Rhesus monkeys (McFadden et al, 2006) and sheep (McFadden et al, 2008a, b) show stronger TEOAEs in females than in males, and, just as for humans, the sex difference in rhesus monkeys and sheep was smaller for DPOAEs than for TEOAEs. Lonsbury-Martin and Martin (1988) observed human-like sex and ear differences in the SOAEs of a colony of pigtail macaques, although the number of males tested and the number of SOAEs recorded both were small.…”