Project Summary/Abstract Impaired inhibitory signaling underlies the development of various neuropsychiatric disorders including anxiety, epilepsy, autism, and schizophrenia. Inhibition is mediated by interneurons (INs), a small but diverse population of cells that coordinates network activity of principal neuron underlying cognition. Glutamatergic excitation of INs determines subsequent firing and control of downstream circuits, and glutamatergic synapses received by INs have unique basal transmission properties and exhibit distinct synaptic plasticity compared to excitatory neurons. These differences in functionality are likely due to cell-type specific differences in postsynaptic density (PSD) composition and maintenance mechanisms. For example, recently identified postsynaptic proteins such as Btbd11 which are expressed exclusively in glutamatergic IN-PSD could underly the unique synaptic properties seen in INs. Growing evidence supports the idea that the PSD is organized through liquid-liquid phase separation (LLPS), the process of maintaining protein-dense, membrane-less organelles. Btbd11 has been shown to i) regulate synaptic function in INs and ii) undergo LLPS with key glutamatergic scaffolding proteins. However, whether Btbd11’s regulation of glutamatergic synapses requires LLPS is not yet known, and the extent to which Btbd11 mediates synaptic composition has not been explored. To investigate how the protein composition of glutamatergic IN-PSD contributes to the unique function of INs and subsequent role in pathophysiology, this application will utilize molecular biology, proteomic analysis, live cellular imaging and electrophysiology to address the novel hypothesis that Btbd11 promotes glutamatergic IN-PSD function through stabilizing interactions with Psd-95 and associated protein complexes via LLPS. In Aim 1, we will examine how Btbd11 ablation alters the IN-PSD proteome and levels of glutamatergic signaling molecules to determine a role in synaptic