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BACKGROUNDExcess dopamine release in the dorsal striatum (DS) is linked to psychosis. Antipsychotics are thought to work for positive symptoms by blocking striatal D2 dopamine receptors, but they lack efficacy for the negative and cognitive symptoms. Further, broadly increasing dopamine release improves cognitive function. These observations fueled the dogma that excess dopamine is not involved in negative and cognitive symptoms, but this has never been tested with dopamine pathway specificity.METHODSWe selectively re-expressed excitatory TRPV1 receptors in DS-projecting dopamine neurons of male and female Trpv1 knockout mice. We treated these mice with capsaicin (TRPV1 agonist) to selectively activate these neurons, validated this approach with fiber photometry, and assessed its effects on social and cognitive function. We combined this manipulation with antipsychotic treatment (haloperidol) and compared the pathway-specific manipulation to treatment with the non-selective dopamine releaser amphetamine.RESULTSSelectively activating DS-projecting dopamine neurons increased DS (but not cortical) dopamine release and increased locomotor activity. Surprisingly, this manipulation also impaired behavioral processes linked to negative and cognitive symptoms (social drive and working memory). Haloperidol normalized locomotion, only partially rescued working memory, and had no effect on social interaction. By contrast, amphetamine increased locomotion but did not impair social interaction or working memory.CONCLUSIONSExcess dopamine release, when restricted to the DS, causes behavioral deficits linked to negative and cognitive symptoms. Previous studies using non-selective approaches to release dopamine likely overlooked these contributions of excess dopamine to psychosis. Future therapies should address this disregarded role for excess striatal dopamine in the treatment-resistant symptoms of psychosis.

Overactive dopamine transmission in psychosis is predicted to unbalance striatal output via D1- and D2-dopamine receptor-expressing spiny-projection neurons (SPNs). Antipsychotic drugs are thought to re-balance this output by blocking D2-receptor signaling. Here we imaged D1- and D2-SPN Ca2+dynamics in mice to determine the neural signatures of antipsychotic effect. Initially we compared effective (clozapine and haloperidol) antipsychotics to a candidate drug that failed in clinical trials (MP-10). Clozapine and haloperidol normalized hyperdopaminergic D1-SPN dynamics, while MP-10 only normalized D2-SPN activity. Clozapine, haloperidol or chemogenetic manipulations of D1-SPNs also normalized sensorimotor gating. Given the surprising correlation between clinical efficacy and D1-SPN modulation, we evaluated compounds that selectively target D1-SPNs. D1R partial agonism, antagonism, or positive M4 cholinergic receptor modulation all normalized the levels of D1-SPN activity, locomotion, and sensorimotor gating. Our results suggest that D1-SPN activity is a more relevant therapeutic target than D2-SPN activity for the development of effective antipsychotics.