Project Summary Activity patterns in the brain establish the manner in which sensory information is perceived and salience and valence are assigned. Disruptions of these patterns through genetic mutations are likely a major cause of neurodevelopmental disorders and mental illness more broadly defined. The midbrain dopamine system plays an essential role in salience and valence assignment and mutations within several ion channels known to regulate action potential firing patterns by dopamine neurons have been identified in neurodevelopmental disorders, yet virtually nothing is known of the impact of these mutations on dopamine physiology, circuit function, and behavior. We have demonstrated that genetic inactivation of different genes associated with mental illness can have differential effects on dopamine neuron physiology and phenotypic outcomes. Neurodevelopmental disorders such as autism and schizophrenia are represented by a mosaic of phenotypic outcomes that gives rise to the spectral nature of these disorders. Disruption of ion channel function, or channelopathies are a major factor in disorder etiology. Of these, potassium channels are the most diverse group and are among the most broadly implicated in channelopathies. Dopamine neurons express a suite of voltage and non-voltage sensitive potassium channels that regulate the action potential waveform, synaptic integration, and neurotransmitter release. Based on these diverse functions, we propose that elucidating the physiological and phenotypic outcomes associate with a loss of function of these channels in dopamine neurons will provide important insight into how disruption of these channels yields a mosaic of phenotypes. To this end, we have developed a single viral vector-based system for the rapid mutagenesis of potassium channels in dopamine neurons and demonstrated that inactivation of different channels yields both overlapping and non-overlapping phenotypes in mice. The experiments proposed here will further elucidate common and uncommon phenotypic outcomes and the impact of ion channels on the operation of distinct dopamine subsystems.