Publications using the RZ5P

Energy homeostasis and motivated behaviours are tightly interconnected processes coordinated by peripheral metabolic signals and central reward circuits. Among these signals, circulating triglycerides (TG) have emerged as neuromodulators of mesolimbic dopamine functions and reward processing. However, whether TG directly regulate the activity of defined neuronal populations within the nucleus accumbens (NAc) during appetitive behaviours remains unknown. Here, we investigated how central TG availability shapes the in vivo activity of NAc dopamine D2 receptor-expressing spiny projection neurons (D2R-SPNs) across distinct nutritional and metabolic states. Using in vivo fiber photometry in Drd2 -Cre mice, we monitored D2R-SPN Ca 2+ dynamics during appetitive Pavlovian conditioning and refeeding. D2R-SPNs progressively developed robust responses to a reward-predictive conditioned stimulus (CS + ) over the course of learning, while their activity during reward consumption remained stable. Acute elevation of central TG levels through carotid infusion did not alter D2R-SPN activity or behavioural performance in lean chow-fed mice, irrespective of whether they were fed or food-restricted. In contrast, in mice exposed to a high-fat diet (HFD), central TG delivery suppressed cue-evoked D2R-SPN activity in food-restricted animals without affecting reward consumption or behavioural outputs. Likewise, TG significantly reduced refeeding-evoked D2R-SPN activation in fasted HFD-mice, while leaving novelty-induced neuronal responses unchanged. Together, these findings demonstrate that obesogenic conditions reveal a metabolic state-dependent sensitivity of accumbal D2R-SPNs to circulating lipids. This work identifies TG as context-dependent modulators of D2R-SPN function and uncovers a mechanism through which dietary history interacts with current metabolic state to reshape the neural encoding of reward-predictive cues and food-directed behaviours.

Everyday decisions depend on associations between sensory stimuli, actions, and outcomes. The striatum supports these sensorimotor associations through dopamine-dependent plasticity. Recent work has characterized a local striatal microcircuit in which cholinergic interneurons (CINs) modulate dopamine release via activation of nicotinic receptors on dopamine axons. Here, we show that visual stimuli evoke dopamine in the dorsomedial striatum partly through this cholinergic mechanism. Using anatomical and functional methods to identify the pathways involved, we found that visual and auditory cortices lack connectivity with CINs and were unable to drive cholinergic-dependent dopamine release. Frontal regions, which were activated by visual stimuli, strongly recruited CINs, producing robust dopamine release both ex vivo and in vivo. These findings reveal a fundamental distinction between sensory and frontal corticostriatal inputs, demonstrating that only the latter can evoke cholinergic-dependent dopamine signals. This work establishes a framework for understanding how cortical circuits shape striatal dopamine to support reinforcement learning.

Hippocampus, a key hub of neural circuits for spatial learning and memory, has attracted tremendous studies. Neuronal information processing in the hippocampus can be regulated by many types of neuropeptides. Cholecystokinin ( Cck ), the most abundant neuropeptide in the central nervous system that is involved in modulating neuronal functions, such as cognition, memory, and neuroplasticity, is widely expressed in the hippocampus. However, whether local excitatory Cck neurons modulate hippocampal function is still unclear. In this study, we showed that CA1 pyramidal neurons receive projections from excitatory Cck neurons in area CA3 (CA3 Cck neurons) in adult mice. Subsequently, activation of the CA1-projecting CA3 Cck neurons triggers the release of Cck . Then, we found that the activity of CA3 Cck -CA1 neurons supports the hippocampal-dependent tasks. Furthermore, inhibition of CA3 Cck -CA1 projections or knockdown of CA3 Cck gene expression markedly impaired the behavioral tasks and neuroplasticity. Taken together, these results may add to a better understanding of how neuromodulators regulate the neural functions in the central nervous system.

Phasic dopamine signalling updates the value of stimuli and actions. Most empirical support for this critical process involves manipulation of extrinsic stimuli (e.g., reward magnitude, reward omission). Yet interoceptive signals clearly influence motivated behaviour. Sodium depletion generates a sodium appetite where the value of sodium increases. How the value of sodium is updated during ingestion and as animals satiate their need remains unknown. Here, we administered sodium chloride solutions via intraoral delivery and measured appetitive behaviour and dopamine release in sodium replete and deplete rats. Two different concentrations of sodium chloride were used to modulate the rate of repletion for sodium deplete rats. Appetitive behaviour was evoked by infusions only when rats were deplete, and this behavioural motif faded away during the session only when high concentration infusions were delivered. Phasic dopamine release in the nucleus accumbens had a similar pattern. We identified transition points for both behaviour and dopamine in the subgroup of rats that reached satiation and found that transitions were sharp, with dopamine decreasing just before behaviour. Moreover, transitions occurred only after enough sodium was infused to replace that typically lost upon depletion. These findings demonstrate that mesolimbic dopamine dynamically updates the value of taste stimuli based on interoceptive signals that relay satiation.

Dopamine contributes to reward-related decision making, but its contributions to decision contexts that include explicit punishment are less well understood. To elucidate the role of ventral tegmental area (VTA) dopamine neurons in decision making under risk of punishment, we used fiber photometry to record activity in these neurons during a decision-making task in which rats choose between a small, “safe” reward and a large reward associated with varying probabilities of explicit punishment. Dopamine neuron activity exhibited phasic increases during risky “Wins” (reward without punishment) and phasic decreases during risky “Losses” (reward plus punishment), each of which scaled with punishment probability and intensity. Further analyses revealed that this outcome-evoked activity predicted choices on subsequent trials. To determine whether VTA dopamine neuron activity plays a causal role in these risk-based decisions, we used optogenetics to selectively inhibit these neurons during risky Wins and Losses. Inhibition of VTA dopamine neurons during Wins selectively reduced the frequency of risky choices after a Win, whereas inhibition during Losses selectively reduced the frequency of risky choices after a Loss. These data reveal that VTA dopamine neuron activity during outcome receipt is causally related to subsequent decision-making behavior. In addition, the fact that the effects of inhibition on choice behavior were specific to the outcome with which the inhibition was paired suggests that VTA dopamine neuron activity contributes to updating after Wins and Losses independently. Significance Statement Dopamine is implicated in movement, motivation, and learning, and has been strongly linked with substance use and risk-seeking behavior. Despite these associations, it is unclear how the activity of dopamine neurons influences decision making under risk of punishment. To elucidate this, we recorded from ventral tegmental area (VTA) dopamine neurons and found that their activity at the population level integrates reward alongside the probability and intensity of punishment experienced during risky outcomes. Further, inhibition of VTA dopamine neuron activity during risky outcomes decreased risk-seeking behavior in an outcome-specific manner. Our findings align with models suggesting that VTA dopamine neurons signal prediction errors, and provide insight into the role of these neurons in adaptive decision making.

Background/Objectives: Dopamine is well known for its role in reward learning, where phasic activity encodes prediction errors and supports the formation of cue–outcome associations. More recently, dopamine has been implicated in encoding salience, novelty, and aversive events, suggesting a broader function in shaping learning and memory across motivational contexts. However, how accumbal dopamine contributes to the recovery of extinguished fear, a process central to relapse in anxiety and trauma-related disorders, remains unclear. Methods: Here, we examined NAc core dopamine dynamics during shock-induced reinstatement of an extinguished fear memory. Using dLight fiber photometry, we found that a sustained decrease in baseline dopamine marked extinction recall. In contrast, an unexpected reminder footshock prevented this reduction, maintaining dopamine levels near baseline as freezing behavior re-emerged. Results: The reminder shock also evoked a transient dopamine peak, and optogenetic manipulations demonstrated that dopamine signaling during this period bidirectionally modulated reinstatement, with enhancement of dopamine release increasing reinstatement and inhibition of dopamine terminals markedly attenuating it. Together, these results demonstrate that unexpected aversive events reset NAc core dopamine levels and gate the return of extinguished fear. Conclusions: By revealing that accumbal dopamine contributes to fear recovery, this work broadens current models of dopamine function and identifies a neural mechanism through which surprising events may promote relapse of aversive memories in anxiety- and stress-related disorders.

Addicted individuals prefer drug rewards over natural rewards. Dysregulated dopamine (DA) signaling in the nucleus accumbens is thought to trigger this phenomenon, but there is little supporting evidence. Using a genetically encoded sensor, we monitored DA dynamics in mice in an operant associative task with natural (fat solution) or artificial (cocaine or optogenetic DA self-stimulation) rewards. During learning, DA transients emerged at predictive cues for both reward types, vanished at natural reward delivery, but persisted at artificial reward delivery. In choice sessions, animals’ preferences varied from exclusive natural reward to exclusive artificial reward. Individual preferences were predicted by cue-evoked DA response magnitudes. Revaluation of reward contingencies shifted reward-type preference and DA signaling accordingly, but not in mice showing compulsive drug seeking, indicating impaired value updating in these mice. These results support a model in which DA drives adaptive reward seeking, with persistent cue-associated DA signaling underpinning addiction vulnerability.

Activity of the mesolimbic dopamine system has long been implicated in encoding primary rewards and contributing to the addictive properties of drugs of abuse. Dopamine neurons in the ventral tegmental area (VTA DA ) of the midbrain typically show patterns of spontaneous burst activity that align with the onset of salient events or rewarding stimuli, resulting in phasic dopamine release in the nucleus accumbens (NAc). Fiber photometry is increasingly being used as an accessible technique to quantify neural activity with high temporal resolution at sensors offering signal specificity in stable recordings over extended periods of time. It has been well established by multiple techniques that opioids increase mesolimbic dopamine activity, likely through disinhibition of VTA DA neurons. Here we used fiber photometry to compare sub-second transient events from VTA DA neurons with GCaMP6f and dopamine release in the lateral shell of the NAc with dLight1.3b and GRABDA2h in response to morphine treatment. In weekly sessions, one dose of morphine was administered in escalating order (2.5, 5,7.5, and 10 mg/kg, intraperitoneal). Consistent with prior literature, both GCaMP6f in VTA DA neurons and dLight1.3b in NAc showed patterns of increased signal following morphine treatment. In contrast, morphine suppressed transient activity at GRABDA2h sensors. Further analyses of whole signal streams from each sensor showed a generalized increase, but reduction in variability of the GRABDA2h signal, consistent with the interpretation of sensor saturation. Such results emphasize the importance of the inclusion of appropriate controls to contextualize the interpretation of biosensor responses, particularly in response to pharmacological treatment. HIGHLIGHTS Morphine elicited increased signaling in VTA DA GCaMP6f and NAc dLight1.3b, consistent with prior literature Morphine suppressed NAc GRABDA2h signaling of transient events, suggesting saturation of GRABDA2h sensor Sensor validation with pharmacological challenges is critical for interpretation of data

The basolateral amygdala (BLA) is important for assigning emotional weight to environmental stimuli to guide learning, discrimination, and adaptive vigilance. The contribution of neuromodulator inputs such as dopamine to this process is unclear. Here, we recorded in vivo BLA dopamine signals across emotional learning paradigms. We show that BLA dopamine scales with a stimulus's emotional intensity, but not value or associative strength, and reward-predictive cues evoke BLA dopamine signals that diminish, rather than grow, with training. In a complex learning context, where rats discriminated between multiple valenced associations, the magnitude of cue-evoked BLA dopamine re-scaled to report the level of relative emotional saliency. Threat and safety cues prompted larger, sustained dopamine signals compared to reward and neutral cues. Together, our data reveal a pattern of dopamine encoding with a unique contribution to learning, for dynamic disambiguation of affective states.

Adaptive behavior requires that behaviorally relevant signals gain access to neural circuits guiding action. The thalamus has long been proposed to regulate information flow to cortical and subcortical systems, yet whether it also tracks internally generated goal signals remains unclear. Here, we show that neurons in the paraventricular thalamus (PVT) projecting to the nucleus accumbens (NAc) encode the motivational value of safety during active avoidance. As mice learn to avoid threat, PVT→NAc neurons develop a signal that emerges selectively at successful avoidance, is experience-dependent, and diminishes following outcome devaluation. Selective silencing of the PVT→NAc pathway at safety onset reduces the motivational value assigned to safety without impairing action–outcome learning. Mechanistically, PVT input engages cholinergic interneurons (CIN) in the NAc to regulate dopamine release via synaptic potentiation mediated by GluA2-lacking AMPA receptors at PVT–CIN synapses. Disrupting this plasticity reduces the motivational impact of safety. These findings identify a thalamostriatal mechanism through which learned goals gain stable access to motivational circuitry.

Sensory experience refines neural circuits during critical periods of postnatal development 1–3 . Although neuronal activity is known to orchestrate the circuit wiring that underlies this process 4,5 , the environmental cues that restrain developmental plasticity as animals mature are less clear. Here we examine the experience-dependent maturation of the mouse primary visual cortex across postnatal development using paired single-cell transcriptomic and chromatin accessibility sequencing. In addition to identifying the activity-dependent gene programs that emerge within each cortical cell type, we find that light exposure drives astrocyte maturation through cell-type-specific recruitment of the glucocorticoid receptor (encoded by Nr3c1 ) to chromatin. Astrocyte glucocorticoid receptor signalling activates an extensive gene regulatory program that is partially conserved in human brain development and promotes maturation processes that may regulate critical period closure. Collectively, these findings reveal that astrocyte glucocorticoid receptor signalling restricts neuronal plasticity. Glucocorticoid regulation of astrocyte maturation may also contribute to the effects of early-life stress across the brain, and the disruption of this process may increase susceptibility to neuropsychiatric disease.

Dysregulation of metabotropic glutamate receptor 5 (mGluR5) and cholecystokinin (CCK) signaling has been implicated in major depressive disorder (MDD), but the underlying circuit mechanisms remain unclear. Here, we define how mGluR5 regulates depressive‐like behaviors through CCK signaling in the entorhinal cortex (EC) to basolateral amygdala (BLA) pathway. Anatomical tracing and optogenetics show that CCK‐expressing neurons in the EC project to the BLA and that their activation increases glutamatergic activity in this region. Bidirectional circuit manipulation establishes causality: optogenetic stimulation induces, whereas inhibition alleviates, depressive‐like phenotypes. Expansion microscopy reveals postsynaptic mGluR5 enrichment along this pathway. Chronic social defeat stress (CSDS) downregulates mGluR5 in the BLA. Pharmacologically, mGluR5 antagonism phenocopies CCK‐driven pro‐depressive effects, whereas CCK knockout mice resist behavioral consequences of mGluR5 inhibition. Mechanistically, mGluR5 agonism suppresses CCK release, disrupts BLA long‐term potentiation, and mitigates CSDS‐induced behaviors. Circuit‐specific mGluR5 knockdown in the EC CCK →BLA pathway increases stress susceptibility. These findings identify an mGluR5‐CCK axis within an EC CCK →BLA circuit that governs stress‐induced affective states.

Internal states including stress and satiety, affect cue-induced feeding behaviors, yet the underlying neural mechanisms remain poorly understood. The nucleus of the solitary tract (NTS), a key hindbrain hub that integrates interoceptive and viscerosensory signals and projects to reward processing nuclei, is anatomically well-positioned to modulate cue-induced feeding behaviors in response to internal state changes. Using behavioral paradigms combined with chemogenetics and fibre photometry, this study investigated the hypothesis that NTS mediates the effects of stress and satiety on cue-induced feeding behaviors via A2 neurons and modulation of ventral tegmental area (VTA) dopamine signaling. We first showed that both foot shock stress and outcome specific satiety (i.e., sucrose prefeed) reduced cue-induced appetitive behavior. Inhibition of NTS neurons only attenuated the suppressive effect of foot shock stress, but not that of outcome specific satiety, indicating that NTS is required for stress-induced suppression of cue-induced appetitive behavior. Further investigation into the contributing neural phenotype revealed that stimulation of NTS A2 neurons reduced conditioned approach and suppressed cue-evoked VTA dopamine neural activity, without any effects on lateral hypothalamus (LH) neuron activity. Together, these findings suggest that NTS neurons mediate the effects of foot shock stress, but not outcome specific satiety, on cue-induced appetitive behavior, in part through activation of NTS A2 neurons and modulation of cue-evoked VTA dopamine neural activity. These results provide an NTS-mediated mechanism through which stress suppresses cue-induced feeding behavior.

Glucose-dependent insulinotropic polypeptide (GIP) is a gut-derived incretin hormone, and pharmacologic modulation of central GIP receptors (GIPRs) improves energy homeostasis and prevents conditioned taste avoidance (CTA). However, the mechanisms by which GIPR signaling impact food intake and aversion are incompletely understood. Here, we show that GIPR agonism abrogates the aversive and enhances the anorexigenic effects of the pro-inflammatory cytokine interleukin-1β (IL-1β). Aversion-encoding parabrachial calcitonin gene-related peptide (CGRP) neurons were required for IL-1β-induced CTA but not anorexia. Moreover, systemic IL-1β increased CGRP neural activity in vivo, and this was significantly attenuated by co-administration of a GIPR agonist. By contrast, GIPR in the dorsal vagal complex was required for the acute anorectic effect of GIPR agonism but not its anti-aversive effect. Taken together, our data suggest that GIPR agonism reduces food intake and prevents aversion via distinct circuits and that GIPR agonism may represent an effective approach to alleviate inflammation-induced aversion.

Male parenting behavior is highly conserved and activated only after offspring are born. Here we show that the behavioral switch from infanticide in virgin male mice to caregiving in wild-type sires is associated with enhanced expression and activation of Transient receptor potential channel 5 (Trpc5) in estrogen receptor α (Esr1)-expressing neurons in the hypothalamic medial preoptic area (MPOA). While selective deletion of Trpc5 from Esr1 MPOA neurons diminishes paternal behavior in sires, overexpression of Trpc5 in these neurons converts the otherwise infanticidal virgin males to exhibit care to pups. Mechanistically, Trpc5-dependent changes in neuronal excitability underlie fatherhood-associated Esr1 MPOA neuron plasticity. Notably, Trpc5 overexpression also enhances escape behavior and elicits exploratory diving behavior, suggesting that these neurons control a broader adaptive parenting response in males. These findings establish a Trpc5-dependent MPOA neural signal as a critical regulator of paternal behavior.

Salivation supports oral health, taste sensation, swallowing, and digestion, but the brain mechanisms that regulate this process remain largely unknown. Here, we identify a salivatory center in the mouse brain stem that integrates sensory and learned anticipatory signals to control salivation. We show that activating choline acetyltransferase-expressing neurons in the inferior salivatory nucleus (IS) is sufficient to trigger saliva secretion. Using fiber photometry, we monitor real-time IS neural responses to mechanosensory and gustatory stimulation and find tight correlation with salivatory output. We further demonstrate that IS neurons receive input from local brain stem circuits, mediating rapid hardwired responses to taste, as well as direct cortical projections. Notably, gustatory cortex input is required for salivatory responses to predictive sensory cues in a Pavlovian conditioning paradigm. Together, our findings define the circuit underlying taste-evoked and anticipatory salivation and provide a foundation for dissecting this autonomic response in health and disease.

Avoiding actions with negative consequences is fundamental to adaptive behavior. Traditional theories suggest GABAergic inhibition of midbrain dopamine neurons, including those within ventral tegmental area (VTA DA ), mediate suppression of actions that lead to aversive outcomes. However, the role of dopamine inhibition in punishment learning remains unclear. To examine this, we conducted fiber photometry, pharmacological, and chemogenetic experiments in rats to measure VTA DA activity and GABA input across punishment learning, and test their causal contribution to behavior. VTA DA activity and GABA input phasically increased to response-elicited outcomes, with VTA DA activity being more strongly activated by rewards, while GABA input being more strongly activated by shock punishers during initial punishment. Pharmacologically blocking GABA A receptors in VTA or chemogenetically activating VTA DA neurons during initial, but not later, punishment sessions produced enduring deficits in punishment avoidance. These findings suggest long-term avoidance depends upon a critical window of GABA-mediated VTA DA inhibition during punishment learning.

Serotonin (5-hydroxytryptamine; 5HT) has long been considered anti-aggressive, but the mechanisms by which 5HT regulates downstream circuits to control aggression remain unclear. Combining fiber photometry, optogenetics, and miniaturized microscope recordings in double-transgenic male mice, we find that 5HT levels ramp up in the nucleus accumbens during aggression, inhibiting a subset of D1 medium spiny neurons to suppress attacks. Our results reveal a novel 5HT-mediated neuromodulatory mechanism for limiting aggressive behavior.

Animals must constantly scan their environment for imminent threats to their safety. However, they must also integrate their past experiences across long timescales to assess the potential recurrence of new threats. Though visual inputs are critical for the detection of environmental danger, whether and how visual information shapes an animal's assessment of whether a new threat is likely to reappear in a given context is unknown. In this work, we developed a behavioral assessment of long-term threat avoidance behavior where animals will avoid a familiar location where they previously experienced a single threat exposure. This avoidance behavior is highly sensitive and lasts for multiple days. Intriguingly, we find that the melanopsin-expressing, intrinsically photosensitive retinal ganglion cells tune this behavior via a perihabenula-nucleus accumbens circuit distinct from canonical visual threat detection circuits in male mice. These findings define a long-term threat avoidance behavior that is shaped by a defined retinal cell type based on prior experience.

Brain systems mediating responses to previously encountered threats provide critical survival functions. Fear memory and extinction are underpinned by neural representations in the basolateral amygdala (BLA) 1–7 , but the contribution of non-neuronal cells, including astrocytes, to these processes remains unresolved. Here, using in vivo calcium (Ca 2+ ) imaging and causal astrocyte manipulations, we find that BLA astrocytes dynamically track fear state and support fear memory retrieval and extinction. By combining astrocyte manipulations with in vivo BLA neuronal Ca 2+ imaging and electrophysiological recordings, we show that astrocyte Ca 2+ signalling enables neuronal encoding of fear memory retrieval and extinction, and readout through a BLA–prefrontal circuit. Our findings reveal a key role for astrocytes in the generation and adaptation of fear-state-related neural representations, revising neurocentric models of critical amygdala-mediated adaptive functions.