Effects of sex and reproductive state on acoustic responsiveness in hamsters

Semi-quantitative [14C]2-deoxyglucose (2DG) autoradiography was used to describe the responses of hamsters to 35 kHz mimics of the "ultrasounds" used for communication during mating. The first study examined the processing of ultrasounds and ambient noise by estrous females, some of which were deafened or hemideafened with plastic ear plugs. These data failed to reveal responses specific to the ultrasounds. However, lateralized responses to the ambient noise were apparent, especially in the hemideafened subjects. For the ventral cochlear nucleus (VCN), 2DG uptake was elevated contralateral to the plug and ipsilateral to the effective stimulus. In contrast, uptake by more rostral structures (dorsal n. of the lateral lemniscus = DNLL; ventral n. of the lateral lemniscus = VNLL; central n. of the inferior colliculus = CIC; medial geniculate n.) was elevated contralateral to the stimulus. A second experiment examined the responses of intact or castrated male and female hamsters to unilaterally presented ultrasounds and ambient noise. As before, relative levels of 2DG uptake differed across hemispheres for structures including the VCN, trapezoid body, VNLL, DNLL, and CIC. More surprisingly, intact females showed more 2DG uptake than males in the DNLL, auditory nerve, and lateral lemniscus. Females also tended to show elevated anterior hypothalamic uptake, but just in the hemisphere contralateral to the stimulus. These results suggest that male and female hamsters differ in acoustic responsiveness, and that this difference is mediated by hormonal effects at several brainstem components of the central auditory system.