Dopamine neurons of the ventral tegmental area (VTA) regulate reward association and motivation. It remains unclear whether there are distinct dopamine populations to mediate these functions. Using mouse genetics, we isolated two populations of dopamine-producing VTA neurons with divergent projections to the nucleus accumbens (NAc) core and shell. Inhibition of VTA-core-projecting neurons disrupted Pavlovian reward learning, and activation of these cells promoted the acquisition of an instrumental response. VTA-shell-projecting neurons did not regulate Pavlovian reward learning and could not facilitate acquisition of an instrumental response, but their activation could drive robust responding in a previously learned instrumental task. Both populations are activated simultaneously by cues, actions, and rewards, and this co-activation is required for robust reinforcement of behavior. Thus, there are functionally distinct dopamine populations in the VTA for promoting motivation and reward association, which operate on the same timescale to optimize behavioral reinforcement.

Generalized fear is a maladaptive behavior in which non-threatening stimuli elicit a fearful response. Here, we demonstrate that discrimination between predictive and non-predictive threat stimuli is highly sensitive to probabilistic discounting and increasing threat intensity in mice. We find that dopamine neurons of the ventral tegmental area (VTA) encode both the negative valence of threat-predictive cues and the certainty of threat prediction. As fear generalization emerges, the dopamine neurons that are activated by a threat predictive cue (CS+) decrease the amplitude of activation and an equivalent signal emerges to a non-predictive cue (CS-). Temporally precise enhancement of dopamine neurons during threat conditioning to high threat levels or uncertain threats can prevent generalization. Moreover, phasic enhancement of genetically captured dopamine neurons activated by threat cues can reverse fear generalization. These findings demonstrate the dopamine neurons reflect the certainty of threat prediction that can be used to inform and update the fear engram.

Mice engineered for conditional, cell type-specific gene inactivation have dominated the field of mouse genetics because of the high efficiency of Cre-loxP-mediated recombination. Recent advances in CRISPR/Cas9 technologies have provided alternatives for rapid gene mutagenesis for loss-of-function (LOF) analysis. Whether these strategies can be streamlined for rapid genetic analysis with the efficiencies comparable with those of conventional genetic approaches has yet to be established. We show that a single adeno-associated viral (AAV) vector containing a recombinase-dependent Staphylococcus aureus Cas9 (SaCas9) and a single guide RNA (sgRNA) are as efficient as conventional conditional gene knockout and can be adapted for use in either Cre- or Flp-driver mouse lines. The efficacy of this approach is demonstrated for the analysis of GABAergic, glutamatergic, and monoaminergic neurotransmission. Using this strategy, we reveal insight into the role of GABAergic regulation of midbrain GABA-producing neurons in psychomotor activation.

Although de novo missense mutations have been predicted to account for more cases of autism than gene-truncating mutations, most research has focused on the latter. We identified the properties of de novo missense mutations in patients with neurodevelopmental disorders (NDDs) and highlight 35 genes with excess missense mutations. Additionally, 40 amino acid sites were recurrently mutated in 36 genes, and targeted sequencing of 20 sites in 17,688 patients with NDD identified 21 new patients with identical missense mutations. One recurrent site substitution (p.A636T) occurs in a glutamate receptor subunit, GRIA1. This same amino acid substitution in the homologous but distinct mouse glutamate receptor subunit Grid2 is associated with Lurcher ataxia. Phenotypic follow-up in five individuals with GRIA1 mutations shows evidence of specific learning disabilities and autism. Overall, we find significant clustering of de novo mutations in 200 genes, highlighting specific functional domains and synaptic candidate genes important in NDD pathology.