The dorsal cochlear nucleus (DCN) is an auditory brainstem center that integrates auditory signals with multimodal sensory signals thought to aid in orientation to sounds of interest. Our previous studies have identified a number of novel mechanisms of synaptic plasticity in the DCN and have uncovered their influence in the processing of auditory nerve inputs. Here, we propose to investigate the physiological role of an unconventional neurotransmitter that is coreleased with glutamate. DCN parallel fiber terminals contain uniquely high levels of Zn[2+] in their gluatamatergic synaptic vesicles. However, the physiological significance of synaptic Zn[2+] release is completely unknown for the auditory system and remains poorly understood for other brain areas. We hypothesize that synaptically released Zn[2+] is a neurotransmitter in the auditory system that regulates the intrinsic and synaptic properties of DCN neurons. To test this hypothesis we will employ a combination of physiological, anatomical and biochemical techniques that will be applied to brainstem slices prepared from wild type and genetically modified mice. Elucidating the mechanisms and the roles of this novel neurotransmitter system will contribute significantly towards the understanding of synaptic and intrinsic mechanisms that are involved during normal and pathological auditory processing.