Dopamine signaling is essential for regulating movement, learning, and reward processing, and its dysregulation has been implicated in neuropsychiatric conditions such as ADHD and substance use disorder. ADGRL3, an adhesion G protein-coupled receptor enriched in the brain, has been genetically linked to these disorders, and Adgrl3 knockout in animals alters expression of dopaminergic markers and impacts dopamine-related behaviors. However, how ADGRL3 influences dopamine dynamics remains poorly understood. Here, we characterized striatal dopamine release in Adgrl3 knockout mice using complementary ex vivo and in vivo approaches. Fast-scan cyclic voltammetry in acute brain slices revealed increased electrically evoked dopamine release in both dorsal and ventral striatum of Adgrl3 knockout mice. In contrast, in vivo fiber photometry using the dopamine sensor dLight1.2 showed reduced cue-induced dopamine signals in the ventral striatum during an operant fixed interval task. This reduction was accompanied by longer latencies to lever press and retrieve rewards, consistent with altered cue-guided behavioral responses reminiscent of task-switching difficulties in individuals with ADHD. Amphetamine challenge experiments indicated that phasic release capacity was similar between genotypes, suggesting that dopamine stores are intact in Adgrl3 KO mice. Together, these findings reveal that ADGRL3 regulates striatal dopamine release and motivate mechanistic studies of how its loss may alter the spatial organization of dopaminergic terminals.

Like dopamine, acetylcholine is modulated in the striatum by reward-predicting cues and outcomes, yet its computational role remains unclear. Here, we manipulated dorsomedial striatal acetylcholine in mice performing a reversal learning task using genetic and physiologically guided optogenetic approaches. Inhibiting phasic acetylcholine modulation impaired reversal learning, while enhancing modulation during non-rewarded trials facilitated reversal learning. Trial-by-trial acetylcholine dynamics were best explained by a reinforcement learning model in which new latent states are created when experience is poorly explained by existing states. A circuit-constrained model further suggested that acetylcholine promotes plasticity when reward- omission is ambiguous leading to a surprising prediction: making reward omission explicit should reduce the need for acetylcholine. We confirmed this in a new experiment in which an auditory omission cue substantially reduced the reversal-learning deficit caused by genetic acetylcholine knockdown. These findings suggest that striatal acetylcholine supports reversal learning by promoting state construction in reinforcement learning.

Importance:In prior work, a transgenic mouse model of the striatal dopamine dysfunction observed in persons with schizophrenia (PSZ) exhibited dopamine-related neuroplasticity in the basal ganglia. This phenotype has never been demonstrated in human PSZ. Objective:To identify a specific dopamine-related alteration of basal ganglia connectivity via task-based and resting-state functional magnetic resonance imaging (fMRI), neuromelanin-sensitive MRI (NM-MRI), and positron emission tomography (PET), in unmedicated PSZ. Design:This case-control study of unmedicated PSZ and healthy controls (HC) occurred between November 2014 and June 2018, with analyses performed between April 2023 and February 2025. Setting:fMRI and NM-MRI were collected at New York State Psychiatric Institute. [11C]-(+)-PHNO PET was collected at Yale University. Participants:Participants were aged 18-55, and demographically matched. PSZ were antipsychotic drug-naïve or drug-free for at least three weeks prior to recruitment. Main Outcomes and Measures:1) task-state and resting-state functional connectivity (FC) between dorsal caudate (DCa) and globus pallidus externus (GPe), 2) NM-MRI contrast ratio in substantia nigra voxels associated with psychotic symptom severity, and 3) baseline and amphetamine-induced change in [11C]-(+)-PHNO binding potential in DCa. Results:37 PSZ (mean±SD age, 32.7±12.7 years, 29.7% female) and 30 HC (32.5±9.7 years, 26.7% female) underwent resting-state fMRI; 29 PSZ (33.4±12.7 years, 31% female) and 29 HC (32.4±9.7 years, 31% female) underwent working memory task-based fMRI. 22 PSZ (35.1±13.9 years, 36.4% female) and 20 HC (29.4±8.5 years, 35% female) underwent NM-MRI. 7 PSZ (23.1±6.3 years, 57.1% female) and 4 HC (31.5±11.9 years, 25% female) underwent [11C]-(+)-PHNO PET with amphetamine challenge. PSZ displayed elevated task-state FC (0.11±0.10 versus 0.05±0.09 in HC; P=0.0252), which was associated with increased NM-MRI contrast ratio (β* [SE] = 0.40 [0.17]; P=0.023), decreased baseline D2 receptor availability (β* [SE] = -0.45 [0.17]; P=0.039), greater amphetamine-induced dopamine release (β* [SE] = -0.82 [0.27]; P=0.021), and worse task performance (β* [SE] = -0.31 [0.13]; P=0.020). Conclusions and Relevance:This study provides in-vivo evidence of a dopamine-associated neural abnormality of DCa and GPe connectivity in unmedicated PSZ. This phenotype suggests a potential neurodevelopmental mechanism of working memory deficits in schizophrenia, representing a critical step towards developing treatments for cognitive deficits.

Auditory hallucinations are linked to elevated striatal dopamine, but their underlying computational mechanisms have been obscured by regional heterogeneity in striatal dopamine signaling. To address this, we developed a normative circuit model in which corticostriatal plasticity in the ventral striatum is modulated by reward prediction errors to drive reinforcement learning while that in the sensory-dorsal striatum is modulated by sensory prediction errors derived from internal belief to drive self-supervised learning. We then validate the key predictions of this model using dopamine recordings across striatal regions in mice, as well as human behavior in a hybrid learning task. Finally, we find that changes in learning resulting from optogenetic stimulation of the sensory striatum in mice and individual variability in hallucination proneness in humans are best explained by selectively enhancing dopamine levels in the model sensory striatum. These findings identify plasticity mechanisms underlying biased learning of sensory expectations as a biologically plausible link between excess dopamine and hallucinations.

The ability to adapt previously learned behaviors is crucial for survival in dynamically changing environments. The hippocampus has been implicated in associative learning, but how hippocampus activity along its septotemporal axis contributes to flexible adaptation is unknown. Using in vivo Ca2+ recordings and functional inhibition of dorsal CA1 (dCA1) and ventral CA1 (vCA1) neurons in mice during complementary cognitive flexibility tasks, we find that dCA1 is engaged and functionally required during consolidation of a learned contingency both before and after a rule change, whereas vCA1 is uniquely recruited during, and necessary for, early adaptation to a new contingency. This vCA1-dependent adaptation relies on a perseverative error signal, which is encoded in vCA1 and required for behavior updating. These results highlight a previously unknown division of labor within the hippocampus, in which vCA1 enables flexible adaptation when mismatches in expected and actual outcomes are detected, whereas dCA1 stabilizes newly learned information.

Dopaminergic signaling is essential for regulating movement, learning, and reward. Disruptions in this system are linked to neuropsychiatric disorders such as ADHD. ADGRL3, an adhesion G protein-coupled receptor highly expressed in the brain, is genetically associated with increased ADHD risk. ADGRL3 knockout in animals alters expression of dopaminergic markers and induces dopamine-related behavioral changes. However, its precise role in modulating dopamine signaling remains unclear. We investigated how ADGRL3 knockout affects striatal dopamine release in mice using ex vivo fast-scan cyclic voltammetry and in vivo fiber photometry with a dopamine sensor. Ex vivo measurements showed increased electrically-evoked dopamine release across the striatum. Conversely, in vivo recordings revealed reduced task-induced dopamine signals in the nucleus accumbens during an operant fixed interval task. This reduction was not due to impaired dopamine availability, as amphetamine-evoked release was unchanged. These findings suggest ADGRL3 modulates dopamine release in complex ways via different pre- and postsynaptic mechanisms.

In applying model organisms to study the neurobiology of mental disorders, rodents offer unique potential for probing, with high spatiotemporal resolution, the neural and molecular mechanisms underlying behavior in a mammalian system. Furthermore, investigators can wield exceptional power to manipulate genes, molecules, and circuits in mice to pin down causal relationships. While these advantages have allowed us to understand much more deeply than ever before the brain mechanisms regulating complex behaviors, the impact of rodent models on developing therapeutic strategies for psychiatric disorders has remained thus far limited. Herein, we will discuss the opportunities and limits of using mouse models in the context of schizophrenia, a complex psychiatric disorder with strong genetic basis that poses various unmet clinical needs calling out for basic science research. We review approaches for employing behavioral, genetic, and circuit-based methods in rodents to inform schizophrenia symptomatology, pathophysiology, and, ultimately, treatment.

Adolescent inhibition of thalamo-cortical projections from postnatal day P20-50 leads to long lasting deficits in prefrontal cortex function and cognition in the adult mouse. While this suggests a role of thalamic activity in prefrontal cortex maturation, it is unclear how inhibition of these projections affects prefrontal circuit connectivity during adolescence. Here, we used chemogenetic tools to inhibit thalamo-prefrontal projections in the mouse from P20-35 and measured synaptic inputs to prefrontal pyramidal neurons by layer (either II/III or V/VI) and projection target twenty-four hours later using slice physiology. We found a decrease in the frequency of excitatory and inhibitory currents in layer II/III nucleus accumbens (NAc) and layer V/VI medio-dorsal thalamus projecting neurons while layer V/VI NAc-projecting neurons showed an increase in the amplitude of excitatory and inhibitory currents. Regarding cortical projections, the frequency of inhibitory but not excitatory currents was enhanced in contralateral mPFC-projecting neurons. Notably, despite these complex changes in individual levels of excitation and inhibition, the overall balance between excitation and inhibition in each cell was only changed in the contralateral mPFC projections. This finding suggests homeostatic regulation occurs within subcortically but not intracortical callosally-projecting neurons. Increased inhibition of intra-prefrontal connectivity may therefore be particularly important for prefrontal cortex circuit maturation. Finally, we observed cognitive deficits in the adult mouse using this narrowed window of thalamocortical inhibition (P20-P35).

Working memory is the cognitive capacity for temporarily holding information in mind for processing or use. It has been theorized to depend upon executive and mnemonic subcomponents, although the contextual mapping of these subcomponents is not complete. Perturbations of prefrontal cortex (PFC) delay activity disrupt spatial working memory performance in rodent tasks. However, recordings of unperturbed PFC delay activity do not consistently contain mnemonic representations of spatial information in these tasks, calling into question the role that mnemonic PFC representations play in freely-moving spatial working memory. We hypothesized that increasing task complexity might increase the likelihood of mnemonic PFC representation emergence. We therefore used an automated eight-arm radial maze to implement a novel match-to-sample rodent spatial working memory task with seven options on each trial, and recorded calcium activity in PFC neurons during task performance. We found that the delay-phase activity of PFC neurons indeed contained mnemonic representations of spatial information at the population level. These representations were retrospective rather than prospective, and surprisingly were more evident on error trials. Together with previous results, these observations suggest that in freely-moving spatial working memory tasks, PFC mnemonic representations emerge to empower deviation from a routine behavioral strategy. ### Competing Interest Statement The authors have declared no competing interest.

Adolescent inhibition of thalamocortical projections from postnatal days P20 to 50 leads to longlasting deficits in prefrontal cortex function and cognition in the adult mouse. While this suggests a role of thalamic activity in prefrontal cortex maturation, it is unclear how inhibition of these projections affects prefrontal circuitry during adolescence. Here, we used chemogenetic tools to inhibit thalamoprefrontal projections in male/female mice from P20 to P35 and measured synaptic inputs to prefrontal pyramidal neurons by layer (either II/III or V/VI) and projection target (mediodorsal thalamus (MD), nucleus accumbens (NAc), or callosal prefrontal projections) 24 h later using slice physiology. We found a decrease in the frequency of excitatory and inhibitory currents in layer II/III NAc and layer V/VI MD-projecting neurons while layer V/VI NAc-projecting neurons showed an increase in the amplitude of excitatory and inhibitory currents. Regarding cortical projections, the frequency of inhibitory but not excitatory currents was enhanced in contralateral mPFC-projecting neurons. Notably, despite these complex changes in individual levels of excitation and inhibition, the overall balance between excitation and inhibition in each cell was only altered in the contralateral mPFC projections. This finding suggests homeostatic regulation occurs within subcortically but not intracortical callosal-projecting neurons. Increased inhibition of intraprefrontal connectivity may therefore be particularly important for prefrontal cortex circuit maturation. Finally, we observed cognitive deficits in the adult mouse using this narrowed window of thalamocortical inhibition.

Schizophrenia is a neuropsychiatric disorder with postulated neurodevelopmental etiology. Genetic and imaging studies have shown enhanced dopamine and D2 receptor occupancy in the striatum of patients with schizophrenia. However, whether alterations in postnatal striatal dopamine can lead to long-lasting changes in brain function and behavior is still unclear. Here, we approximated striatal D2R hyperfunction in mice via designer receptor-mediated activation of inhibitory Gi-protein signaling during a defined postnatal time window. We found that Gi-mediated inhibition of the indirect pathway (IP) during postnatal days 8-15 led to long-lasting decreases in locomotor activity and motivated behavior measured in the adult animal. In vivo photometry further showed that the motivational deficit was associated with an attenuated adaptation of outcome-evoked dopamine levels to changes in effort requirements. These data establish a sensitive time window of D2R-regulated striatal development with long-lasting impacts on neuronal function and behavior.

Learning action sequences is necessary for normal daily activities. Medium spiny neurons (MSNs) in the dorsal striatum (dStr) encode action sequences through changes in firing at the start and/or stop of action sequences or sustained changes in firing throughout the sequence. Acetylcholine (ACh), released from cholinergic interneurons (ChIs), regulates striatal function by modulating MSN and interneuron excitability, dopamine and glutamate release, and synaptic plasticity. Cholinergic neurons in dStr pause their tonic firing during the performance of learned action sequences. Activation of dopamine type-2 receptors (D2Rs) on ChIs is one mechanism of ChI pausing. In this study we show that deleting D2Rs from ChIs by crossing D2-floxed with ChAT-Cre mice (D2Flox-ChATCre), which inhibits dopamine-mediated ChI pausing and leads to deficits in an operant action sequence task and lower breakpoints in a progressive ratio task. These data suggest that D2Flox-ChATCre mice have reduced motivation to work for sucrose reward, but show no generalized motor skill deficits. D2Flox-ChATCre mice perform similarly to controls in a simple reversal learning task, indicating normal behavioral flexibility, a cognitive function associated with ChIs. In vivo electrophysiological recordings show that D2Flox-ChatCre mice have deficits in sequence encoding, with fewer dStr MSNs encoding entire action sequences compared to controls. Thus, ChI D2R deletion appears to impair a neural substrate of action chunking. Virally replacing D2Rs in dStr ChIs in adult mice improves action sequence learning, but not the lower breakpoints, further suggesting that D2Rs on ChIs in the dStr are critical for sequence learning, but not for driving the motivational aspects of the task. Significance statement The role of striatal projection neurons in encoding action sequences has been extensively studied, and cholinergic interneurons play a central role in striatal physiology, but we do not yet understand how cholinergic interneurons contribute to action sequencing. Using a combination of mouse genetics, behavior, and in vivo electrophysiology this work shows that genetic deletion of D2 receptors from striatal cholinergic interneurons disrupts the learning, performance, and encoding of action sequences, without changing general locomotion or motor skill learning. Virally replacing D2 receptors specifically in dorsal striatal cholinergic interneurons is sufficient to rescue the sequence behavior. Our observations may be useful in understanding and treating movement disorders in which dopamine and acetylcholine are imbalanced.

In the classical model of the basal ganglia, direct pathway striatal projection neurons (dSPNs) send projections to the substantia nigra (SNr) and entopeduncular nucleus to regulate motor function. Recent studies have re-established that dSPNs also possess "bridging" collaterals within the globus pallidus (GPe), yet the significance of these collaterals for behavior is unknown. Here we use in vivo optical and chemogenetic tools combined with deep learning approaches to dissect the roles of bridging collaterals in motor function. We find that dSPNs projecting to the SNr send synchronous motor-related information to the GPe via axon collaterals. Inhibition of native activity in dSPN GPe terminals impairs motor activity and function via regulation of pallidostriatal Npas1 neurons. We propose a model by which dSPN GPe collaterals ("striatopallidal Go pathway") act in concert with the canonical terminals in the SNr to support motor control by inhibiting Npas1 signals going back to the striatum.

After repeatedly failing to get out of a stressful, uncontrollable environment, mice switch from escape behavior to inactivity. In this issue of Neuron, Li et al. identify a circuit involving noradrenergic projections from the locus coeruleus to GABAergic projection neurons in the orbitofrontal cortex that participate in this adaptive behavior.

Adolescence is a period of increased vulnerability for the development of psychiatric disorders, including schizophrenia. The prefrontal cortex (PFC) undergoes substantial maturation during this period, and PFC dysfunction is central to cognitive impairments in schizophrenia. As a result, impaired adolescent maturation of the PFC has been proposed as a mechanism in the etiology of the disorder and its cognitive symptoms. In adulthood, PFC function is tightly linked to its reciprocal connections with the thalamus, and acutely inhibiting thalamic inputs to the PFC produces impairments in PFC function and cognitive deficits. Here, we propose that thalamic activity is equally important during adolescence because it is required for proper PFC circuit development. Because thalamic abnormalities have been observed early in the progression of schizophrenia, we further postulate that adolescent thalamic dysfunction can have long-lasting consequences for PFC function and cognition in patients with schizophrenia.