DESCRIPTION (provided by applicant): Dynamic assembly and disassembly of the actin cytoskeleton underlies diverse cellular processes, including cell division, developmental polarity and intracellular transport. These changes can be local or global, transforming cell state. Extracellular signals mediate experience-induced changes of actin dynamics within synaptic microdomains of neurons. Recent evidence suggests that actin dynamics of the cell body, distinct from those in the synapse, also may be necessary for neurons to sense and respond to extracellular stimuli. We predict that this process contributes to plasticity of behavior by altering transcription. Our overarching goal is to understand how experience signals long-term state changes in neurons that, in turn, change behavior. We hypothesize that glutamatergic neurotransmission changes actin organization, and this is permissive for transcriptional activation. We will test this hypothesis in the suprachiasmatic nucleus (SCN), a brain site with established molecular substrates necessary for temporal organization of behavior. The SCN is a cell-based, ~24-h clock driven by spatial and temporal oscillations that regulate transcription. Specifically, we hypothesize that signaling cascades initiated by glutamate engage the actin cytoskeleton of SCN cells, changing localization of key transcriptional regulators that alter clock state. We will examine the nature and necessity of such changes in actin and their effects on transcriptional activation of clock genes. We will evaluate these mechanisms in rat and mouse models: cell cultures, brain slices and behaving animals. Specific aims will: 1) characterize and localize stimulus-induced changes in actin; 2) find the role of actin changes in clock function and behavior, and 3) determine the role of actin changes in regulating transcription. We will use cell biological methods, dynamic imaging, biochemistry, neurobiological measures, and behavioral analyses. The breadth of this systems-based analysis will generate insights into how experience is transformed into long-lasting modification in brain state and behavior. This will enhance the understanding of substrates of long-lasting neural state change, with broad relevance for public health and disease prevention. Dysfunctions in the actin system cause severe neurological disorders, including those of cognition, neurodegeneration, movement and autonomic control. Sleep disorders, learning/memory impairments, drug-addiction and aging will be direct beneficiaries.