Activity patterns in the brain establish the manner in which sensory information is perceived and salience is assigned. Disruptions of these patterns through genetic mutations are likely a major cause of mental illness. The midbrain dopamine system plays an essential role in salience assignment and mutations within several ion channels known to regulate action potential firing patterns by dopamine neurons have been identified, yet virtually nothing is known of the impact of these mutations on dopamine physiology, circuit function, and behavior. We have demonstrated that a mutation in the calcium activated, small conductance potassium channel, SK3, identified in a patient with schizophrenia alters dopamine neuron activity pattern regulation. Selective, expression of this dominant-negative human SK3 mutant in dopamine neurons of mice shifts balance between tonic and phasic activity of dopamine neurons towards a more phasic state. The resulting dysregulation of activity patterns in dopamine neurons leads to impairments in sensory and attention gating processes. The major challenge that lies ahead is discovering how alterations in tonic-to-phasic dopamine ratios impact cortical and striatal circuits important for gating sensory information and to further defin behavioral domains impacted by such disruptions. Here, I outline several innovate approaches that we will utilize to determine how imbalances in dopamine activity patterns impact corticostriatal connectivity and function. Utilizing combinatorial viral vector gene delivery, we wll optogentically isolate inputs from the prefrontal cortex to the nucleus accumbens region of the striatum and define how expression of the human SK3 mutation in dopamine neurons impacts the connectivity of these two structures using in vivo fiber-optic confocal microscopy and imaging of a genetically encoded calcium indicator. We will monitor activity- dependent process in the nucleus accumbens using fiber-optic confocal microscopy and define how alterations in tonic-to-phasic dopamine activity influences activity in direct and indirect pathway neurons of the striatum in freely behaving mice during an attention gating task. Finally, we will use viral-mediated circuit dissection to define the minimal network elements in the brain required for dopamine-dependent modulation of sensory and attention gating.
Discrete neuronal activity patterns define how information is processed in the brain. The manner in which disruption of these patterns by disease-associated mutations impacts behavioral regulation is poorly understood, but likely contributes to the etiology of many symptom domains of mental illness. We will use advanced genetic techniques coupled to fiber-optic imaging of deep brain tissue in mice to precisely define how a disease-related mutation in an ion channel critical for dopamine neuron activity pattern regulation alters corticostriatal network function and impacts behavior.
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