Abstract

mTOR complex 1 (mTORC1) is a central coordinator of cell growth and metabolism. Mutations in regulators of mTORC1 cause syndromic disorders with a high prevalence of cognitive and psychiatric conditions. To elucidate the cellular origins of these manifestations, we conditionally deleted the gene encoding the mTORC1 negative regulator Tsc1 from mouse midbrain dopamine neurons, which modulate motor, affective, and cognitive behaviors that are frequently affected in psychiatric disorders. Loss of Tsc1 and constitutive activation of mTORC1 strongly impacted the properties of dopamine neurons, causing somatodendritic hypertrophy, reduced intrinsic excitability, altered axon terminal ultrastructure, and severely impaired dopamine release. These perturbations were associated with selective deficits in cognitive flexibility, which could be prevented by genetic reduction of the obligatory mTORC1 protein Raptor. Our results establish a critical role for mTORC1 in setting the functional properties of midbrain dopamine neurons, and indicate that dopaminergic dysfunction may underlie cognitive inflexibility in mTOR-related syndromes.