Understanding Circuits

Project Summary Developing new methodological and analytical tools to address currently insurmountable experimental questions is crucial to the future of neuroscience. While recent advances in two-photon microscopy and activity sensors have revolutionized our understanding of the cellular and circuit basis of behavior, many barriers still exist that preclude fully exploring the molecular basis of these processes in vivo.

SUMMARY/ABSTRACT A major goal of neuroscience is to understand how neuromodulatory systems regulate core processes of brain and behavior, from motor function and learning to reward, aversion, attention, and sleep. These systems go awry in schizophrenia and disorders of mood, motor control and cognition. Treatment for these conditions often turns to pharmacological manipulation of neuromodulators and their receptors. Understanding of neuromodulatory circuits has advanced considerably thanks to optogenetics and chemogenetics. But neuromodulation is difficult to crack.

Abstract While current efforts in the analysis of neural circuits focus on interneuronal connectivity mediated by chemical synapses, less is known about the contribution of electrical synapses. Electrical transmission is mediated by neuronal gap junctions, which are widely distributed throughout the vertebrate brain.

Project Summary New tools are urgently needed to selectively target constructs that monitor and manipulate the activity of individual cell types without having to rely on genetic manipulation.

The goal of this research is to establish new robust methods for manipulation of specific circuits and genetically defined neuron types in brains of model organisms with small molecules. While several chemical-genetic techniques are already available, these techniques have drawbacks that limit their utility.

PROJECT SUMMARY A goal of the BRAIN initiative is to develop and validate novel tools to map and manipulate neural circuits. The definition and control of behaviorally relevant circuits requires both retrograde and anterograde trans-synaptic technologies that perform well in vivo.

PROJECT SUMMARY Tools for exclusively targeting neuronal and glial subtypes are needed to advance our understanding of the brain. “Intersectional” systems improve targeting by restricting “reporter/effector” transgenes to a subdomain defined by the expression overlap between two activating factors. “Split-driver” systems have enhanced targeting precision in flies and are operable in fish, but have yet to be systematically deployed in vertebrate systems.

Abstract The brain is remarkably complex, and our understanding of this organ is still in its infancy. Many fundamental questions about brain development and function remain. Single cell genomics promises new ways to answer these questions, but nearly all single-cell methods share shortcoming – cells are destroyed when their molecular states are measured.

PROJECT SUMMARY Methods for regulating cellular processes within distinct populations of neurons are needed to elucidate relationships between molecular mechanisms, circuits, and behavior; and to develop cell type- or circuit- selective treatments for neurological disorders. We propose a novel, non-genetic, small molecule method— transcription factor-chemically induced proximity (TF-CiP)—that harnesses the cell type- and circuit-specificity of endogenous transcription factors to regulate gene expression in subsets of neurons.

From Electron Microscopy to Neural Circuit Hypotheses: Bridging the gap Recent advances in experimental technology promise rapid progress in developing a mechanistic understanding of how neural circuit structure, at the synaptic scale, leads to complex sensory, cognitive, and motor behaviors. Volume EM techniques have advanced to the point that neural tissue can be imaged at synaptic resolution in volumes large enough (~ 100 µm) to contain a entire small neuron .