Project Summary/Abstract Synapses are the fundamental unit of information transfer in the central nervous system (CNS) and are composed a highly complex molecular machinery that tightly regulates synaptic transmission and neuronal circuit output. A multitude of combinations of synaptic proteins and their isoforms creates synapses with distinct functional properties to enable the broad diversity of information encoding by neuronal circuits. Human mutations in synaptic proteins result in synaptic dysfunction which causes neurological disorders such as schizophrenia, epilepsy, ataxia, autism, and intellectual disability. Currently, 1.5 billion people worldwide suffer from a CNS disorder, however there are limited therapeutic options. Therefore, elucidating the molecular mechanisms that control synaptic function are fundamental to developing novel therapeutics for CNS disorders. The α2δ proteins (α2δ 1-4) are extracellular proteins initially identified as auxiliary subunits of voltage-gated Ca2+ (CaV) channel complexes and they are drug targets. However, multiple roles have been described for the α2δ isoforms in independently regulating synaptic function and CaV channel complexes. Human mutations specific to each α2δ isoform are correlated to distinct brain disorders. Despite being highly expressed throughout the CNS and the clear linkage between human mutations in α2δ2 and α2δ3 and CNS disorders, very little is known about the roles of α2δ2 and α2δ3 in regulating synaptic function. In mammals, the globular bushy cells (GBCs) in the auditory brainstem highly express both α2δ2 and α2δ3. The GBC axon gives rise to the calyx of Held, a glutamatergic presynaptic terminal which is the sole input to drive action-potential (AP) spiking and utilizes rapid, temporally precise AP signaling to encode auditory information. The calyx is an exceptional model for gaining mechanistic insights into the presynaptic regulation of synaptic function and neuronal circuit output Therefore our goal is to establish how presynaptic α2δ2 and α2δ3 regulate synaptic function and neuronal circuit output. We will use novel transgenic mouse models and viral vectors to manipulate the α2δ2 and α2δ3 at the calyx during different developmental stages and analyze how their loss impact synaptic transmission and neuronal circuit output.. Ultimately, our findings will provide fundamental insights into how information is encoded by the CNS and will facilitate the development of treatments for a wide range of neurological disorders due to α2δ2 and α2δ3 mutations. Finally, our novel animal models will be valuable reagents to the Illuminating the Druggable Genome (IDG) program