Dopamine release at the time of a predicted aversive outcome causally controls the trajectory and expression of conditioned behavior

Melanocortin 4 receptor-expressing neurons in the lateral stripe of the striatum regulate affect and motor control

The dopaminergic system is crucial for affect regulation. Melanocortin 4 receptors (MC4R) in the ventral striatum have been shown to be necessary for establishing aversive states. Here, we functionally characterize MC4R-expressing striatal neurons in mice. MC4Rs were enriched in atypical dopamine receptor 1 (D1) neurons in the lateral stripe of the striatum (LSS), an understudied area in the ventrolateral striatum. Fiber photometry recordings showed that MC4R neuron activity and local dopamine release in the LSS increased in response to both rewarding and aversive stimuli. Moreover, MC4R neuronal activity and glutamate release in the LSS correlated with body movement. Optogenetic activation of MC4R-LSS neurons was rewarding in a real-time place preference test and a self-stimulation paradigm, increased locomotor activity, and induced striatal dopamine release. Collectively, our findings suggest that MC4R-LSS neurons are activated by stimuli of both rewarding and aversive character and that they induce positive affect, dopamine release and locomotion.

Altered Neural Activity in the Mesoaccumbens Pathway Underlies Impaired Social Reward Processing in Shank3-Deficient Rats

Social behaviors are crucial for human connection and belonging, often impacted by conditions like Autism Spectrum Disorder (ASD). The mesoaccumbens pathway (ventral tegmental area (VTA) to the nucleus accumbense (NAc)) plays a pivotal role in social behavior and is implicated in ASD. However, the impact of ASD-related mutations on social reward processing remains insufficiently explored. This study focuses on the Shank3 mutation, associated with a rare genetic condition and linked to ASD, examining its influence on the mesoaccumbens pathway during behavior, using the Shank3-deficient rat model. Our findings indicate that Shank3-deficient rats exhibit atypical social interactions, associated with altered neuronal activity of VTA dopaminergic and GABAergic neurons and reduced dopamine release in the NAc. Moreover, they demonstrate that manipulating VTA neuronal activity can normalize this behavior, providing insights into the effects of Shank3 mutations on social reward processing  and identifying a potential neural pathway for intervention.

Effects of KCNQ potassium channel modulation on ventral tegmental area activity and connectivity in individuals with depression and anhedonia

Up to half of individuals with depression do not respond to first-line treatments, possibly due to a lack of treatment interventions informed by neurobiology. A novel therapeutic approach for depression has recently emerged from translational work targeting aberrant activity of ventral tegmental area (VTA) dopamine neurons via modulation of the KCNQ voltage-gated potassium channels. In this study, individuals with major depressive disorder (MDD) with elevated anhedonia were randomized to five weeks of the KCNQ channel opener, ezogabine (up to 900 mg/day) or placebo. Participants completed functional MRI during a monetary anticipation task and resting-state at baseline and at end-of-treatment. The clinical results were reported previously. Here, we examined VTA activity during monetary anticipation and resting-state functional connectivity between the VTA and the ventromedial prefrontal cortex (mesocortical pathway) and ventral striatum (mesolimbic pathway) at baseline and end-of-treatment. Results indicated a significant drug-by-time interaction in VTA activation during anticipation (F(1,34) = 4.36, p = 0.044), where VTA activation was reduced from pre-to-post ezogabine, compared to placebo. Mesocortical functional connectivity was also higher in depressed participants at baseline compared to a healthy control group (t(56) = 2.68, p = 0.01) and associated with VTA hyper-activity during task-based functional MRI at baseline (R = 0.352, p = 0.033). Mesocortical connectivity was also reduced from pre-to-post ezogabine, compared to placebo (significant drug-by-time interaction, F(1,33) = 4.317, p = 0.046). Together this translational work is consistent with preclinical findings highlighting VTA hyper-activity in depression, and suggesting a mechanism of action for KCNQ channel openers in normalizing this hyper-activity in individuals with both depression and anhedonia.

Striatal dopamine represents valence on dynamic regional scales

Adaptive decision making relies on dynamic updating of learned associations where environmental cues come to predict valenced stimuli, such as food or threat. Cue-guided behavior depends on a network of brain systems, including dopaminergic projections to the striatum. Critically, it remains unclear how dopamine signaling across the striatum encodes multi-valent, dynamic learning contexts, where positive and negative associations must be rapidly disambiguated. To understand this, we employed a Pavlovian discrimination paradigm, where cues predicting food or threat were intermingled during conditioning sessions, and their meaning was serially reversed across training. We found that male and female rats readily distinguished these cues and updated their behavior rapidly upon valence reversal. Using fiber photometry, we recorded dopamine signaling in three major striatal subregions - the dorsolateral striatum (DLS), the nucleus accumbens (NAc) core, and the nucleus accumbens medial shell - finding that valence was represented uniquely across all three regions, indicative of local signals biased for value and salience. Further, ambiguity introduced by cue reversals reshaped striatal dopamine on different timelines: nucleus accumbens signals updated more readily than those in the DLS. Together, these results indicate that striatal dopamine flexibly encodes stimulus valence according to region-specific rules, and these signals are dynamically modulated by changing contingencies in the resolution of ambiguity about the meaning of environmental cues.Significance Statement Adaptive decision making relies on updating learned associations to disambiguate predictions of reward or threat. This cue-guided behavior depends on striatal dopamine, but it remains unclear how dopamine signaling encodes multi-valent, dynamic learning contexts. Here, we employed a paradigm where cues predicting positive and negative outcomes were intermingled, and their meaning was serially reversed across time. We recorded dopamine signaling, finding heterogeneous patterns of valence encoding across striatal subregions, and cue reversal reshaped subregional signals on different timelines. Our results suggest that dopamine flexibly encodes dynamic learning contexts to resolve ambiguity about the meaning of environmental cues.

Fiber photometry analysis of spontaneous dopamine signals: The z-scored data are not the data

Fluorescent sensors have revolutionized the measurement of molecules in the brain, and the dLight dopamine sensor has been used extensively to examine reward- and cue-evoked dopamine release, but only recently has the field turned its attention to spontaneous release events. Analysis of spontaneous events typically requires evaluation of hundreds of events over minutes to hours, and the most common method of analysis, z-scoring, was not designed for this purpose. Here, we compare the accuracy and reliability of three different analysis methods to identify pharmacologically induced changes in dopamine release and uptake in freely moving C57BL/6J mice. The D1-like receptor antagonist SCH23390 was used to prevent dLight sensors from interacting with dopamine in the extracellular space, while cocaine was used to inhibit uptake and raclopride to increase release of dopamine in the nucleus accumbens. We examined peak-to-peak frequency, peak amplitude, and width, the time spent above an established cutoff. The three methods were 1) the widely-used "Z-Score Method", which automatically smooths baseline drift and normalizes recordings using signal-to-noise ratios, 2) a "Manual Method", in which local baselines were adjusted manually and individual cutoffs were determined for each subject, and 3) the "Prominence Method" that combines z-scoring with prominence assessment to tag individual peaks, then returns to the preprocessed data for kinetic analysis. First, SCH23390 drastically reduced the number of signals detected as expected, but only when the Manual Method was used. Z-scoring failed to identify any changes, due to its amplification of noise when signals were diminished. Cocaine increased signal width as expected using the Manual and Prominence Methods, but not the Z-Score Method. Finally, raclopride-induced increases in amplitude were correctly identified by the Manual and Prominence Methods. The Z-Score Method failed to identify any of the changes in dopamine release and uptake kinetics. Thus, analysis of spontaneous dopamine signals requires assessment of the %ΔF/F values, ideally using the Manual Method, and the use of z-scoring is not appropriate.

How Dopamine Enables Learning from Aversion

Dopamine is heavily studied for its role in reward learning, but it is becoming increasingly appreciated that dopamine can also enable learning from aversion. Dopamine neurons modulate their firing and neurotransmitter release patterns in response to aversive outcomes. However, there is considerable heterogeneity in the timing and directionality of the modulation. Open questions remain as to the factors that determine this heterogeneity and how varying patterns of responses to aversion in different dopamine-receptive brain regions contribute to value learning, decision-making, and avoidance. Here, we review recent progress in this area and highlight important future directions.

GABAergic neurons from the ventral tegmental area represent and regulate force vectors

The ventral tegmental area (VTA), a midbrain region associated with motivated behaviors, consists predominantly of dopaminergic (DA) neurons and GABAergic (GABA) neurons. Previous work has suggested that VTA GABA neurons provide a reward prediction, which is used in computing a reward prediction error. In this study, using in vivo electrophysiology and continuous quantification of force exertion in head-fixed mice, we discovered distinct populations of VTA GABA neurons that exhibited precise force tuning independently of learning, reward prediction, and outcome valence. Their activity usually preceded force exertion, and selective optogenetic manipulations of these neurons systematically modulated force exertion without influencing reward prediction. Together, these findings show that VTA GABA neurons continuously regulate force vectors during motivated behavior.

Dopaminergic circuits controlling threat and safety learning

The ability to learn from experience that certain cues and situations are associated with threats or safety is crucial for survival and adaptive behavior. Understanding the neural substrates of threat and safety learning has high clinical significance because deficits in these forms of learning characterize anxiety disorders. Traditionally, dopamine neurons were thought to uniformly support reward learning by signaling reward prediction errors. However, the dopamine system is functionally more diverse than was initially appreciated and is also critical for processing threat and safety. In this review, I highlight recent studies demonstrating that dopamine neurons generate prediction errors for threat and safety, and describe how dopamine projections to the amygdala, medial prefrontal cortex (mPFC), and striatum regulate associative threat and safety learning.

Amplifying School Mental Health Literacy Through Neuroscience Education

Children and adolescents face a wide variety of developmental changes and environmental challenges, and it is estimated that at least one in five children aged 3-17 will experience behavioral or mental health issues. This period of life coincides with major changes in brain structure and function that have profound long-term consequences for learning, decision-making (including risk taking), and emotional processing. For example, continued development of the prefrontal cortex in adolescence is a sensitive period during which individuals are particularly susceptible to risky behaviors, environmental stressors, and substance use. While recent advances in mental health literacy programs have paved the way for increased awareness of the benefits of mental health curricula in schools, these efforts could be greatly bolstered with support in basic neuroscience education in developmentally appropriate and area-specific content. Here, we provide a discussion on the basic structural and functional changes occurring in the brain throughout childhood, how this contributes to changes in cognitive function, and the risk factors posed by early life adversity, stress, and drug use. Finally, we provide a perspective on the benefits of integrating findings from the field of neuroscience and suggestions for tools to better equip students, teachers, administrators, and school mental health staff to provide new directions for addressing the mental health crises faced by millions of children and youth each year.

Synaptogyrin-3 Prevents Cocaine Addiction and Dopamine Deficits

Synaptogyrin-3, a functionally obscure synaptic vesicle protein, interacts with vesicular monoamine and dopamine transporters, bringing together dopamine release and reuptake sites. Synaptogyrin-3 was reduced by chronic cocaine exposure in both humans and rats, and synaptogyrin-3 levels inversely correlated with motivation to take cocaine in rats. Synaptogyrin-3 overexpression in dopamine neurons reduced cocaine self-administration, decreased anxiety-like behavior, and enhanced cognitive flexibility. Overexpression also enhanced nucleus accumbens dopamine signaling and prevented cocaine-induced deficits, suggesting a putative therapeutic role for synaptogyrin-3 in cocaine use disorder.

Salience signaling and stimulus scaling of ventral tegmental area glutamate neuron subtypes

Ventral tegmental area (VTA) glutamatergic neurons participate in reward, aversion, drug-seeking, and stress. Subsets of VTA VGluT2+ neurons are capable of co-transmitting glutamate and GABA (VGluT2+VGaT+ neurons), transmitting glutamate without GABA (VGluT2+VGaT- neurons), or co-transmitting glutamate and dopamine (VGluT2+TH+ neurons), but whether these molecularly distinct subpopulations show behavior-related differences is not wholly understood. We identified that neuronal activity of each VGluT2+ subpopulation is sensitive to reward value but signaled this in different ways. The phasic maximum activity of VGluT2+VGaT+ neurons increased with sucrose concentration, whereas VGluT2+VGaT- neurons increased maximum and sustained activity with sucrose concentration, and VGluT2+TH+ neurons increased sustained but not maximum activity with sucrose concentration. Additionally, VGluT2+ subpopulations signaled consummatory preferences in different ways. VGluT2+VGaT- neurons and VGluT2+TH+ neurons showed a signaling preference for a behaviorally-preferred fat reward over sucrose, but in temporally-distinct ways. In contrast, VGluT2+VGaT+ neurons uniquely signaled a less behaviorally-preferred sucrose reward compared with fat. Further experiments suggested that VGluT2+VGaT+ consummatory reward-related activity was related to sweetness, partially modulated by hunger state, and not dependent on caloric content or behavioral preference. All VGluT2+ subtypes increased neuronal activity following aversive stimuli but VGluT2+VGaT+ neurons uniquely scaled their magnitude and sustained activity with footshock intensity. Optogenetic activation of VGluT2+VGaT+ neurons during low intensity footshock enhanced fear-related behavior without inducing place preference or aversion. We interpret these data such that VTA glutamatergic subpopulations signal different elements of rewarding and aversive experiences and highlight the unique role of VTA VGluT2+VGaT+ neurons in enhancing the salience of behavioral experiences.

Valence ambiguity dynamically shapes striatal dopamine heterogeneity

Adaptive decision making relies on dynamic updating of learned associations where environmental cues come to predict positive and negatively valenced stimuli, such as food or threat. Flexible cue-guided behaviors depend on a network of brain systems, including dopamine signaling in the striatum, which is critical for learning and maintenance of conditioned behaviors. Critically, it remains unclear how dopamine signaling encodes multi-valent, dynamic learning contexts, where positive and negative associations must be rapidly disambiguated. To understand this, we employed a Pavlovian discrimination paradigm, where cues predicting positive and negative outcomes were intermingled during conditioning sessions, and their meaning was serially reversed across training. We found that rats readily distinguished these cues, and updated their behavior rapidly upon valence reversal. Using fiber photometry, we recorded dopamine signaling in three major striatal subregions -,the dorsolateral striatum (DLS), the nucleus accumbens core, and the nucleus accumbens medial shell - and found heterogeneous responses to positive and negative conditioned cues and their predicted outcomes. Valence ambiguity introduced by cue reversal reshaped striatal dopamine on different timelines: nucleus accumbens core and shell signals updated more readily than those in the DLS. Together, these results suggest that striatal dopamine flexibly encodes multi-valent learning contexts, and these signals are dynamically modulated by changing contingencies to resolve ambiguity about the meaning of environmental cues.

Combinatory Actions of Co-transmitters in Dopaminergic Systems Modulate Drosophila Olfactory Memories

Dopamine neurons (DANs) are extensively studied in the context of associative learning, in both vertebrates and invertebrates. In the acquisition of male and female Drosophila olfactory memory, the PAM cluster of DANs provides the reward signal, and the PPL1 cluster of DANs sends the punishment signal to the Kenyon cells (KCs) of mushroom bodies, the center for memory formation. However, thermo-genetical activation of the PPL1 DANs after memory acquisition impaired aversive memory, and that of the PAM DANs impaired appetitive memory. We demonstrate that the knockdown of glutamate decarboxylase, which catalyzes glutamate conversion to GABA in PAM DANs, potentiated the appetitive memory. In addition, the knockdown of glutamate transporter in PPL1 DANs potentiated aversive memory, suggesting that GABA and glutamate co-transmitters act in an inhibitory manner in olfactory memory formation. We also found that, in γKCs, the Rdl receptor for GABA and the mGluR DmGluRA mediate the inhibition. Although multiple-spaced training is required to form long-term aversive memory, a single cycle of training was sufficient to develop long-term memory when the glutamate transporter was knocked down, in even a single subset of PPL1 DANs. Our results suggest that the mGluR signaling pathway may set a threshold for memory acquisition to allow the organisms' behaviors to adapt to changing physiological conditions and environments.SIGNIFICANCE STATEMENT In the acquisition of olfactory memory in Drosophila, the PAM cluster of dopamine neurons (DANs) mediates the reward signal, while the PPL1 cluster of DANs conveys the punishment signal to the Kenyon cells of the mushroom bodies, which serve as the center for memory formation. We found that GABA co-transmitters in the PAM DANs and glutamate co-transmitters in the PPL1 DANs inhibit olfactory memory formation. Our findings demonstrate that long-term memory acquisition, which typically necessitates multiple-spaced training sessions to establish aversive memory, can be triggered with a single training cycle in cases where the glutamate co-transmission is inhibited, even within a single subset of PPL1 DANs, suggesting that the glutamate co-transmission may modulate the threshold for memory acquisition.

Altered neural activity in the mesoaccumbens pathway underlies impaired social reward processing in Shank3-deficient rats

Social behaviors are crucial for human connection and belonging, often impacted in conditions like Autism Spectrum Disorder (ASD). The mesoaccumbens pathway (VTA and NAc) plays a pivotal role in social behavior and is implicated in ASD. However, the impact of ASD-related mutations on social reward processing remains insufficiently explored. This study focuses on the Shank3 mutation, associated with a rare genetic condition and linked to ASD, examining its influence on the mesoaccumbens pathway during behavior, using the Shank3-deficient rat model. Our findings indicate that Shank3-deficient rats exhibit atypical social interactions and have difficulty adjusting behavior based on reward values, associated with modified neuronal activity of VTA dopaminergic and GABAergic neurons and reduced dopamine release in the NAc. Moreover, we demonstrate that manipulating VTA neuronal activity can normalize this behavior, providing insights into the effects of Shank3 mutations on social reward and behavior, and identify a potential neural pathway for intervention.