Project Summary / Abstract An estimated 3% of the population will experience psychosis at some point in their lifetime, yet we know little about the altered neural circuitry underlying psychosis. To address this gap in knowledge, our lab created a mouse model in which region-specific functional knockout (FKO) of the 14-3-3 protein family is achieved through the viral delivery of a small peptide inhibitor called difopein. These 14-3-3 FKO mice display several phenotypes that are thought to correlate to symptoms of psychosis, including novelty-induced locomotor hyperactivity. This phenotype was further shown to be mediated by both hippocampal hyperactivity and overactive dopamine signaling, leading to our recent discovery of a dorsal hippocampus CA1 (dCA1) – lateral septum (LS) - ventral tegmental area (VTA) pathway. The goal of this project is to further characterize the synaptic and functional connectivity of this neural circuitry: which cell types are connected, and how neuronal excitability at each level of the circuit influences the observed phenotypes. Based on our findings and the known organization of these brain regions, we hypothesize that the dCA1- LS-VTA pathway is composed of a dCA1glutamate– LSGABA – VTAGABA – VTAdopamine circuit by which 14-3-3 inhibition induced CA1 hyperactivity ultimately leads to the dis-inhibition of VTA dopamine neurons. Our first aim is to identify the synaptic connectivity within the dCA1-LS-VTA pathway, and determine whether GABA or dopamine neurons in the VTA receive direct synaptic input from LS GABA neurons. To do this we will use the viral-genetic tracing methods known as TRIO and cTRIO in wildtype and transgenic mice. Our second aim is understand how signaling at each level of this circuit functionally modulates downstream neural activity and psychosis-related phenotypes. We will virally deliver inhibitory or excitatory chemogenetic channels that allow for the manipulation of the neuronal activity of specific sets of neurons within the dCA1-LS-VTA circuit. We will then measure the effect of these manipulations on novelty-induced locomotor behavior and mesolimbic dopamine signaling. The proposed studies will allow for the deeper understanding of a novel neural circuit that correlates to key symptoms of psychosis, contributing valuable knowledge to the field that may be used in the development of more targeted treatments.