Cochlear and middle ear effects on metabolism in the central auditory pathway during silence: A 2-deoxyglucose study

Abstract

The [ 14C]2-deoxy- d-glucose (2-DG) autoradiographic technique was used to investigate metabolic activity in the central auditory pathways during silence. Relative 2-DG uptake was assessed in silence for three groups of Mongolian gerbils: control animals; those with unilateral cochlear ablations, and those with unilateral conductive hearing losses. Control subjects showed no differences between the two sides of their central auditory pathways. Subjects with unilateral cochlear ablations showed markedly lower 2-DG uptake in the major afferent projection pathway from the ablated cochlea compared with 2-DG uptake in contralateral structures. That is, relative 2-DG uptake was significantly lower ipsilateral to the ablation in the anteroventral and dorsal cochlear nuclei, and contralateral to the ablation in the ventral nucleus of the lateral lemniscus, the dorsal nucleus of the lateral lemniscus, and the inferior colliculus. No effect of ablation was seen in the superior olivary complex, the medial geniculate nucleus or the auditory cortex. Subjects with a unilateral conductive hearing loss, unexpectedly, showed significantly higher 2-DG incorporation in the major afferent projection from the impaired side. That is, relative 2-DG uptake was higher in the anteroventral cochlear nucleus, the dorsal cochlear nucleus and the lateral superior olivary nucleus ipsilateral to the hearing loss, and in the dorsal nucleus of the lateral lemniscus contralateral to the hearing loss. These increases in 2-DG uptake following conductive hearing loss represent a mechanism which may account for clinical hearing disorders such as tinnitus. It is concluded that, even under conditions of silence, the intact cochlea and middle ear conductive apparatus significantly influence metabolic activity in the central auditory pathway up through the level of the inferior colliculus.