Guoping Feng studies the development and function of synapses and their disruption in brain disorders. He uses molecular genetics combined with behavioral and electrophysiological methods to study the molecular components of the synapse and to understand how disruptions in these components can lead to psychiatric disease. Synaptic communication requires neurotransmitter to bind to receptors that are tightly localized to the postsynaptic site. These receptors are anchored in place through a complex of proteins known as the postsynaptic density (PSD). Much more than a passive scaffold, the PSD is a site for neural plasticity that is modulated by experience and learning. Disruption of the PSD is expected to have wide-ranging effects on behavior, a hypothesis that Feng is exploring in his research. Feng has previously shown that mutations in one key component of the PSD known as SAPAP3 causes repetitive grooming behavior in mice that resembles human obsessive-compulsive disorder (OCD). SAPAP3 is specifically expressed in the striatum, a brain region that has been implicated in OCD and many other disease including Parkinson’s and Huntington’s disease. Feng has shown that altered synaptic communication between the cortex and the striatum may account for the repetitive behaviors of the mutant mice. Feng is also studying another synaptic scaffold protein, known as Shank. He has recently found that mutations in this gene lead to repetitive behaviors and abnormalities of social interaction in mice that are reminiscent of autism. Using genetic tools for labeling and manipulating specific cell types in the living brain, Feng is working to dissect the circuit level deficits underlying these abnormal behaviors. He also hopes to create new and more realistic animal models of human psychiatric disorders that can be used to discover new therapies for these conditions. In the course of his work, Feng has developed many genetic tools for probing the function of synapses and circuits in the living brain. These include mice expressing green fluorescent protein in single neurons for long-term imaging; mice expressing light-sensitive ion channels that allow optical manipulation of neural activity; and mice expressing genetically encoded activity sensors to monitor neural activity in vivo.