Specific sound-induced noradrenergic and serotonergic activation in central auditory structures

We have studied the noradrenergic and serotonergic changes induced by white noise stimulation at 70, 90 or 110 dB SPL for 45 min, in cochlear nuclei, inferior colliculus (IC), primary auditory cortex (PAC) and as a comparison in locus coeruleus (LC) and raphe dorsalis using HPLC. Both noradrenergic and serotonergic pathways were activated in the dorsal+posteroventral cochlear nuclei (DCN+PVCN) without changes in the anteroventral cochlear nucleus (AVCN) and IC. In the DCN+PVCN the noradrenergic activation was restricted to animals exposed to 70 dB SPL whereas the increase of serotonin content was intensity-dependent. In PAC serotonergic activation was observed only after 70 dB SPL exposure. These data suggest that in physiological conditions (70 dB SPL) noradrenergic and serotonergic regulation of the processing of auditory information occurs specifically in the dorsal cochlear nucleus where the control of incoming information to higher auditory structures takes place (i.e. IC and PAC). We suggest that the serotonergic activation in the primary auditory cortex for 70 dB SPL sound stimulation could be related to the fact that low-intensity white noise stimulation could be the most plastic-demanding processing in the auditory cortex.