Orchestrating Opiate-Associated Memories in Thalamic Circuits

Electrophysiological analysis of paraventricular thalamic neurons co-expressing kappa and mu opioid receptors

The paraventricular thalamus (PVT) is a central node in the integration of stress- and reward-related information that may serve as a pivotal site for opioid receptors to exert their effects. Kappa opioid receptors (KOPrs) and mu opioid receptors (MOPrs) have dissociable and opposing roles in circuits of stress and reward. Interestingly, both are highly expressed in the PVT, however it is not known how aversive KOPr and rewarding MOPr signalling converges to dictate PVT activity and, by proxy, whole brain effects. We have investigated the function of KOPrs and MOPrs in single PVT neurons using whole-cell voltage-clamp recordings in brain slices from female and male mice (4-8 weeks). The majority of PVT neurons (69 %) co-expressed KOPr and MOPr. Activation of either receptor produced outward K+ currents, with no age and sex differences. In neurons co-expressing both opioid receptors, the MOPr-induced K+ current reversed around the theoretical equilibrium potential, whilst the KOPr current did not reverse at any holding potential tested. Furthermore, investigation of apparent inward currents produced by MOPr inverse agonists suggested the presence of tonically active MOPrs, predominantly in the anterior PVT. Activation of both KOPrs and MOPrs decreased glutamatergic input to PVT neurons by around 40 %, whereas only KOPr activation decreased GABAergic input, by 46 %. Together these data suggest that the balance of activation of KOPrs and MOPrs in the PVT plays a critical role in integrating stress- and reward-related signals.

Control of Methamphetamine-Induced Place Preference Behavior by the Glutamatergic Neural Projections from IC to BLA in Mice

Drug addiction is closely related to the dysregulation of complex neural circuits. However, the neural pathways underlying methamphetamine (METH)-induced addiction remain unclear. Firstly, we performed ∆FosB (Delta FBJ murine osteosarcoma viral oncogene homolog B) immunofluorescence and fiber-optic recording experiments to assess the neural activity of glutamatergic neurons in the anterior insular cortex (IC) in METH-treated mice. Then, we evaluated the effect of activation or inhibition of glutaminergic neurons in IC on METH-induced conditioned place preference (CPP) behavior through chemogenetic manipulation. Finally, we used adeno-associated virus (AAV)-mediated neural tracing to verify the projections connectivity from IC to the basolateral amygdala (BLA) and investigated their blocking role in METH-mediated CPP behavior using chemogenetic and neural ablation strategies. We found that glutamatergic neurons in the IC were activated by METH. Activation of these neurons enhanced METH-mediated CPP behavior, whereas inhibition of their activity attenuated the CPP expression. Furthermore, we observed robust projections from IC neurons to the BLA. Activation of IC neurons projecting to the BLA enhanced METH-mediated CPP behavior, whereas ablation of BLA neurons receiving projections from IC significantly impaired METH-mediated CPP performance. These results highlight the IC glutaminergic neurons are a major target of METH addiction, with the IC-BLA glutaminergic neural projection playing an important role in regulating METH-mediated CPP behavior. This pathway may provide new insights into the pathophysiology of METH addiction and serve as a potential target for therapeutic strategies.

Altered resting-state functional connectivity in male individuals with methamphetamine use disorder at two different withdrawal periods: spotlight on the paraventricular thalamic nucleus

Preclinical research highlights the paraventricular thalamic nucleus as important in various stages of substance use disorder. However, there is limited research on it in relation to methamphetamine, especially regarding its functional changes after long-term abstinence. This study aims to understand the alterations in functional connectivity of the paraventricular thalamic nucleus in methamphetamine abstainers and its correlation with drug craving at two different withdrawal periods. A total of 49 subjects were allocated to the short-term withdrawal group, 44 to the long-term withdrawal group, and 42 to the healthy control group, all of whom are male and adult. Craving scores were assessed using a visual analogue scale. Functional connectivity was evaluated through resting-state functional MRI, which reflects the correlation between connectivity in different brain regions. Significant differences in functional connectivity between the paraventricular thalamic nucleus and the left caudate nucleus were observed across the three groups. The healthy control group exhibited the strongest connectivity, followed by the long-term withdrawal group, while the short-term withdrawal group demonstrated the weakest connectivity. Within the short-term withdrawal group, functional connectivity of the paraventricular thalamic nucleus with both the left parahippocampal gyrus (r = -0.45, p = 0.001) and the left inferior temporal gyrus (r = -0.43, p = 0.002) was significantly correlated with craving scores. This study confirms abnormalities in the paraventricular thalamic nucleus among male methamphetamine abstainers, emphasizes its potential role in regulating methamphetamine use disorder and craving mechanisms, and offers insights into long-term changes in brain function after abstinence.

Regulation of PVT-CeA Circuit in Deoxynivalenol-Induced Anorexia and Aversive-Like Emotions

Neuronal plasticity in the central amygdala (CeA) is essential for modulating feeding behaviors and emotional responses, potentially influencing reactions to Deoxynivalenol (DON). Acute oral administration of DON elicits a dose-responsive reduction in food intake, accompanied by pronounced alterations in locomotor activity and feeding frequency. This study investigates circuitry adaptations that mediate DON's effects on feeding, by targeting of GABA neurons in the CeA. Following exposure to DON, an increase in connectivity between the paraventricular nucleus of the thalamus (PVT) and CeAGABA neurons is observed, suggesting the involvement of this pathway in DON's adverse effects on feeding and emotional states. Chemogenetic and optogenetic manipulations of CeAGABA neurons resulted in substantial alterations in mice's feeding and overall activity. These findings suggest that CeAGABA neurons are involved in DON-induced anorexia and aversive-like emotional responses. Additionally, the administration of the SCN10A antagonist (A-803467) effectively mitigated DON-induced anorexia and aversive-like emotions, highlighting the pivotal role of the PVT-CeA circuit and CeAGABA neurons in regulating the physiological and emotional impacts of DON. These findings have significant implications for public health and clinical interventions, offering potential therapeutic strategies to mitigate DON's adverse effects on human health.

Prefrontal FGF1 Signaling is Required for Accumbal Deep Brain Stimulation Treatment of Addiction

Deep brain stimulation (DBS) has emerged as a prospective treatment for psychiatric disorders; for example, DBS targeting the nucleus accumbens (NAc) abolishes addictive behaviors. However, neither the core pathway nor the cellular mechanisms underlying these therapeutic effects are known. Here, morphine-induced conditioned place preference (CPP) in mice as an addiction model and NAc-DBS combined with adeno-associated virus gene delivery for activity-dependent tagging, transgenic and chemogenetic manipulation of recruited neuronal networks are used. It is reported that a cortical-accumbal pathway and local fibroblast growth factor 1 (FGF1) signaling in the medial prefrontal cortex (mPFC) are critical for NAc-DBS to be effective in altering morphine CPP. It is shown that NAc-DBS retrogradely activates mPFC neurons projecting to the NAc, and chemogenetic activation/inhibition of these DBS-activated neuron ensembles in the mPFC reproduces the NAc-DBS effects on CPP. Sustained therapeutic effects accompany reductions in local FGF1 binding to fibroblast growth factor receptor 1 (FGFR1) in these neurons. Additionally, overexpressing FGF1 in the mPFC-NAc pathway abolishes the therapeutic effects of NAc-DBS. These results demonstrate that the mPFC-NAc pathway forms a top-down motif to regulate the therapeutic effects of subcortical DBS on addiction. These results support the potential for addiction treatments involving FGF1 signaling and highlight the mPFC as a target for noninvasive brain stimulation.

Protocol to study the role of medial entorhinal cortex-basolateral amygdala circuit in context-induced retrieval of morphine withdrawal memory in mice

The medial entorhinal cortex (MEC) is crucial for context memory, yet its role in context-induced retrieval of morphine withdrawal memory remains to be investigated. Here, we present a protocol to evaluate the importance of projection neurons from the MEC to the basolateral amygdala (BLA) (MEC-BLA neurons) in mice during context-induced retrieval of morphine withdrawal memory using a conditioned place aversion (CPA) model. We describe steps for surgical procedure and behavioral experiments. Then, we detail procedures of immunofluorescence staining and image analysis. For complete details on the use and execution of this protocol, please refer to Fu et al.1.

Inhibition of the glutamatergic PVT-NAc projections attenuates local anesthetic-induced neurotoxic behaviors

INTRODUCTION

Local anesthetic-induced neurotoxicity contributes to perioperative nerve damage; however, the underlying mechanisms remain unclear. Here, we investigated the role of the paraventricular thalamus (PVT)-nucleus accumbens (NAc) projections in neurotoxicity induced by ropivacaine, a local anesthetic agent.

METHODS

Ropivacaine (58 mg/kg, intraperitoneal administration) was used to construct the local anesthetic systemic toxicity (LAST) mice model. We first identified neural projections from the PVT to the NAc through the expression of a retrograde tracer and virus. The inhibitory viruses (rAAV-EF1α-DIO-hm4D(Gi)-mCherry-WPREs: AAV2/retro and rAAV-CaMKII-CRE-WPRE-hGh: AAV2/9) were injected into the mice model to assess the effects of the specific inhibition of the PVT-NAc pathway on neurological behaviors in the presence of clozapine-N-oxide. The inhibition of the PVT-NAc pathway was evaluated by immunofluorescence staining of c-Fos-positive neurons and Ca2+ signals in CaMKIIa neurons.

RESULTS

We successfully identified a circuit connecting the PVT and NAc in C57BL/6 mice. Ropivacaine administration induced the activation of the PVT-NAc pathway and seizures. Specific inhibition of NAc-projecting CaMKII neurons in the PVT was sufficient to inhibit the neuronal activity in the NAc, which subsequently decreased ropivacaine-induced neurotoxicity.

CONCLUSION

These results reveal the presence of a dedicated PVT-NAc circuit that regulates local anesthetic-induced neurotoxicity and provide a potential mechanistic explanation for the treatment and prevention of LAST.

Comparative effects of arecoline, caffeine, and nicotine on transcription level in the nucleus accumbens of mice

Though widely consumed, current research on the neural mechanisms of arecoline, caffeine, and nicotine remains limited, and the similarities and differences of these substances on the nervous system are still not clear. This study used RNA-seq to analyze the gene expression in the nucleus accumbens (NAc) of mice, and compared the behavioral changes through open field and conditioned place preference (CPP), exploring the effects of different psychoactive substances at transcriptional and behavioral levels. Gene Ontology enrichment analysis revealed that nicotine and caffeine significantly alter biological processes related to synaptic function, and KEGG pathway analysis showed that the differentially expressed genes in the nicotine-treated group were significantly more enriched in pathways related to substance dependence, with arecoline showing the least enrichment. Furthermore, only acute caffeine treatment significantly increased mouse activity, and only nicotine induced CPP. These results provided a scientific basis for evaluating arecoline, caffeine, and nicotine on the nervous system.

The glutamatergic projections from the PVT to mPFC govern methamphetamine-induced conditional place preference behaviors in mice

BACKGROUND

Drug addiction is closely related to the dysregulation of complex neural circuits. However, the neural connections underlying the symptoms of methamphetamine (METH)-induced addiction have yet to be elucidated.

METHODS

We conducted ΔFosB (Delta FBJ murine osteosarcoma viral oncogene homolog B) associated immunofluorescence and electrophysiological recording experiments to measure the neural activity of paraventricular thalamus (PVT) neurons in METH treated mice. Then, the METH-mediated conditional place preference (CPP) behaviors were evaluated after chemogenetic manipulation of PVT neurons. Additionally, the neural projection from PVT to medial prefrontal cortex (mPFC) was verified through Adeno-associated virus (AAV) mediating neural tracing method, and its role on METH-mediated CPP behaviors was determined using chemogenetic and neural ablation strategies.

RESULTS

We found that glutamatergic neurons in PVT were activated by METH. Activating the glutamatergic neurons in PVT promoted the METH-mediated CPP behaviors, while inhibiting these neurons attenuated the CPP behaviors. Moreover, we observed PVT neurons showed robust neuronal projections to mPFC, activation of the mPFC→projecting neurons in PVT or the afferent terminals in mPFC derived from PVT enhanced METH-mediated CPP performance, and ablating the mPFC neurons receipting neural projection from PVT impeded these increased METH-mediated CPP phenotypes.

LIMITATIONS

The underlying molecular mechanism of the dysfunctional PVT neurons after METH treatment and the PVT neurons regulating the activity of mPFC target neurons remains unclear.

CONCLUSIONS

These results shed light on that PVT is a key METH addiction-controlling nucleus, and PVT → mPFC projection regulated METH-mediated CPP behaviors, which could serve as a vital pathway for morbidity and treatment for METH-mediated addiction.

Classification of psychedelics and psychoactive drugs based on brain-wide imaging of cellular c-Fos expression

Psilocybin, ketamine, and MDMA are psychoactive compounds that exert behavioral effects with distinguishable but also overlapping features. The growing interest in using these compounds as therapeutics necessitates preclinical assays that can accurately screen psychedelics and related analogs. We posit that a promising approach may be to measure drug action on markers of neural plasticity in native brain tissues. We therefore developed a pipeline for drug classification using light sheet fluorescence microscopy of immediate early gene expression at cellular resolution followed by machine learning. We tested male and female mice with a panel of drugs, including psilocybin, ketamine, 5-MeO-DMT, 6-fluoro-DET, MDMA, acute fluoxetine, chronic fluoxetine, and vehicle. In one-versus-rest classification, the exact drug was identified with 67% accuracy, significantly above the chance level of 12.5%. In one-versus-one classifications, psilocybin was discriminated from 5-MeO-DMT, ketamine, MDMA, or acute fluoxetine with >95% accuracy. We used Shapley additive explanation to pinpoint the brain regions driving the machine learning predictions. Our results suggest a unique approach for characterizing and validating psychoactive drugs with psychedelic properties.

GABAergic Neurons in the Central Amygdala Promote Emergence from Isoflurane Anesthesia in Mice

BACKGROUND

Recent evidence indicates that general anesthesia and sleep-wake behavior share some overlapping neural substrates. γ-Aminobutyric acid-mediated (GABAergic) neurons in the central amygdala have a high firing rate during wakefulness and play a role in regulating arousal-related behaviors. The objective of this study was to investigate whether central amygdala GABAergic neurons participate in the regulation of isoflurane general anesthesia and uncover the underlying neural circuitry.

METHODS

Fiber photometry recording was used to determine the changes in calcium signals of central amygdala GABAergic neurons during isoflurane anesthesia in Vgat-Cre mice. Chemogenetic and optogenetic approaches were used to manipulate the activity of central amygdala GABAergic neurons, and a righting reflex test was used to determine the induction and emergence from isoflurane anesthesia. Cortical electroencephalogram (EEG) recording was used to assess the changes in EEG spectral power and burst-suppression ratio during 0.8% and 1.4% isoflurane anesthesia, respectively. Both male and female mice were used in this study.

RESULTS

The calcium signals of central amygdala GABAergic neurons decreased during the induction of isoflurane anesthesia and were restored during the emergence. Chemogenetic activation of central amygdala GABAergic neurons delayed induction time (mean ± SD, vehicle vs . clozapine-N-oxide: 58.75 ± 5.42 s vs . 67.63 ± 5.01 s; n = 8; P = 0.0017) and shortened emergence time (385.50 ± 66.26 s vs . 214.60 ± 40.21 s; n = 8; P = 0.0017) from isoflurane anesthesia. Optogenetic activation of central amygdala GABAergic neurons produced a similar effect. Furthermore, optogenetic activation decreased EEG delta power (prestimulation vs . stimulation: 46.63 ± 4.40% vs . 34.16 ± 6.47%; n = 8; P = 0.0195) and burst-suppression ratio (83.39 ± 5.15% vs . 52.60 ± 12.98%; n = 8; P = 0.0003). Moreover, optogenetic stimulation of terminals of central amygdala GABAergic neurons in the basal forebrain also promoted cortical activation and accelerated behavioral emergence from isoflurane anesthesia.

CONCLUSIONS

The results suggest that central amygdala GABAergic neurons play a role in general anesthesia regulation, which facilitates behavioral and cortical emergence from isoflurane anesthesia through the GABAergic central amygdala-basal forebrain pathway.

Sexually dimorphic dopaminergic circuits determine sex preference

Sociosexual preference is critical for reproduction and survival. However, neural mechanisms encoding social decisions on sex preference remain unclear. In this study, we show that both male and female mice exhibit female preference but shift to male preference when facing survival threats; their preference is mediated by the dimorphic changes in the excitability of ventral tegmental area dopaminergic (VTADA) neurons. In males, VTADA projections to the nucleus accumbens (NAc) mediate female preference, and those to the medial preoptic area mediate male preference. In females, firing-pattern (phasic-like versus tonic-like) alteration of the VTADA-NAc projection determines sociosexual preferences. These findings define VTADA neurons as a key node for social decision-making and reveal the sexually dimorphic DA circuit mechanisms underlying sociosexual preference.

Thalamic opioids from POMC satiety neurons switch on sugar appetite

High sugar-containing foods are readily consumed, even after meals and beyond fullness sensation (e.g., as desserts). Although reward-driven processing of palatable foods can promote overeating, the neurobiological mechanisms that underlie the selective appetite for sugar in states of satiety remain unclear. Hypothalamic pro-opiomelanocortin (POMC) neurons are principal regulators of satiety because they decrease food intake through excitatory melanocortin neuropeptides. We discovered that POMC neurons not only promote satiety in fed conditions but concomitantly switch on sugar appetite, which drives overconsumption. POMC neuron projections to the paraventricular thalamus selectively inhibited postsynaptic neurons through mu-opioid receptor signaling. This opioid circuit was strongly activated during sugar consumption, which was most notable in satiety states. Correspondingly, inhibiting its activity diminished high-sugar diet intake in sated mice.

Adiponectin receptor 1-mediated basolateral amygdala-prelimbic cortex circuit regulates methamphetamine-associated memory

The association between drug-induced rewards and environmental cues represents a promising strategy to address addiction. However, the neural networks and molecular mechanisms orchestrating methamphetamine (MA)-associated memories remain incompletely characterized. In this study, we demonstrated that AdipoRon (AR), a specific adiponectin receptor (AdipoR) agonist, inhibits the formation of MA-induced conditioned place preference (CPP) in MA-conditioned mice, accompanied by suppression of basolateral amygdala (BLA) CaMKIIα neuron activity. Furthermore, we identified an association between the excitatory circuit from the BLA to the prelimbic cortex (PrL) and the integration of MA-induced rewards with environmental cues. We also determined that the phosphorylated AMPK (p-AMPK)/Cav1.3 signaling pathway mediates the modulatory effects of AdipoR1 in PrL-projecting BLA CaMKIIα neurons on the formation of MA reward memories, a process influenced by physical exercise. These findings highlight the critical function of AdipoR1 in the BLACaMKIIα→PrLCaMKIIα circuit in regulating MA-related memory formation, suggesting a potential target for managing MA use disorders.

Adolescent morphine exposure induced long-term cognitive impairment and prefrontal neurostructural abnormality in adulthood in male mice

Opioids abuse in adolescence is becoming a pressing public health issue. While evidence suggests that exposure to opioids during adolescence leads to lasting alterations in brain development, the long-term cognitive implications in adulthood remain uncertain. We developed a male mouse model of adolescent morphine exposure and used the 5-choice serial reaction time task (5-CSRTT), along with the open field, novel object recognition, Y maze and Barnes maze tests, to assess changes in cognitive behavior. We found that exposure to morphine during adolescence led to deficits in multidimensional cognitive functions in mice, including attention, information processing speed, and behavior inhibition. Notable, these impairments persisted into adulthood. Furthermore, the morphine-exposed mice exhibited decreased learning efficiency and spatial memory. Adolescent morphine exposure also induced significant and persistent morphological changes and synaptic abnormalities in medial prefrontal cortex (mPFC) neurons, which may be responsible for cognitive impairments in adulthood. Together, our study suggests that opioid exposure during adolescence profoundly affects cognitive development and emphasizes that opioid-induced disruption of neurons in adolescence may link mPFC-associated cognitive impairments in adulthood.

Classification of psychedelics and psychoactive drugs based on brain-wide imaging of cellular c-Fos expression

Psilocybin, ketamine, and MDMA are psychoactive compounds that exert behavioral effects with distinguishable but also overlapping features. The growing interest in using these compounds as therapeutics necessitates preclinical assays that can accurately screen psychedelics and related analogs. We posit that a promising approach may be to measure drug action on markers of neural plasticity in native brain tissues. We therefore developed a pipeline for drug classification using light sheet fluorescence microscopy of immediate early gene expression at cellular resolution followed by machine learning. We tested male and female mice with a panel of drugs, including psilocybin, ketamine, 5-MeO-DMT, 6-fluoro-DET, MDMA, acute fluoxetine, chronic fluoxetine, and vehicle. In one-versus-rest classification, the exact drug was identified with 67% accuracy, significantly above the chance level of 12.5%. In one-versus-one classifications, psilocybin was discriminated from 5-MeO-DMT, ketamine, MDMA, or acute fluoxetine with >95% accuracy. We used Shapley additive explanation to pinpoint the brain regions driving the machine learning predictions. Our results support a novel approach for characterizing and validating psychoactive drugs with psychedelic properties.

Distinct roles of excitatory and inhibitory neurons in the medial prefrontal cortex in the expression and reconsolidation of methamphetamine-associated memory in male mice

Methamphetamine, a commonly abused drug, is known for its high relapse rate. The persistence of addictive memories associated with methamphetamine poses a significant challenge in preventing relapse. Memory retrieval and subsequent reconsolidation provide an opportunity to disrupt addictive memories. However, the key node in the brain network involved in methamphetamine-associated memory retrieval has not been clearly defined. In this study, using the conditioned place preference in male mice, whole brain c-FOS mapping and functional connectivity analysis, together with chemogenetic manipulations of neural circuits, we identified the medial prefrontal cortex (mPFC) as a critical hub that integrates inputs from the retrosplenial cortex and the ventral tegmental area to support both the expression and reconsolidation of methamphetamine-associated memory during its retrieval. Surprisingly, with further cell-type specific analysis and manipulation, we also observed that methamphetamine-associated memory retrieval activated inhibitory neurons in the mPFC to facilitate memory reconsolidation, while suppressing excitatory neurons to aid memory expression. These findings provide novel insights into the neural circuits and cellular mechanisms involved in the retrieval process of addictive memories. They suggest that targeting the balance between excitation and inhibition in the mPFC during memory retrieval could be a promising treatment strategy to prevent relapse in methamphetamine addiction.

Neural and molecular investigation into the paraventricular thalamus for chronic restraint stress induced depressive-like behaviors

INTRODUCTION

Disturbance of neural circuits and chronic stress contribute to depression onset. Given the crucial role of paraventricular nucleus of thalamus (PVT) in emotional behaviors, however, the specific neural and molecular mechanism of PVT in depression still unclear.

OBJECTIVE

Our study aim to explore the neural and molecular mechanism of PVT in depression.

METHODS

In the present study, we utilize behavioral tests,chemogenetics, RNA-sequence, molecular profiling and pharmacological approaches to investigate the role of PVT in depression.

RESULTS

We observed that CamkIIα neurons in PVT were inactivated by chronic restraint stress (CRS) with reduced c-Fos positive neurons. Activation of PVTCamkIIα neurons displayed antidepressant-like effect in both naive and CRS mice, whereas inhibition or ablation of these neurons is sufficient to trigger depressive-like behaviors. Moreover, we found that activating PVT → Nucleus accumbens (NAc) circuit attenuated depressive-like behaviors induced by CRS, while inhibiting this circuit directly caused behavioral deficits in mice. Intriguingly, artificially enhancing PVT → Central amygdala (CeA) pathway failed to alleviate depressive-like behaviors. Importantly, increased expression of neuropeptide Y (NPY) and depressive-like behaviors induced by CRS could be ameliorated via antidepressant treatment, manipulation of PVTCamkIIα neurons (or PVT → NAc circuit) and NPY inhibitor.

CONCLUSION

Taken together, our study uncovered that PVT regulated depressive-like behaviors via PVT → NAc circuit together with NPY, thus shedding light on potential target for preventing depression and promoting clinical translation.

Treadmill exercise training inhibits morphine CPP by reversing morphine effects on GABA neurotransmission in D2-MSNs of the accumbens-pallidal pathway in male mice

Relapse is a major challenge in the treatment of drug addiction, and exercise has been shown to decrease relapse to drug seeking in animal models. However, the neural circuitry mechanisms by which exercise inhibits morphine relapse remain unclear. In this study, we report that 4-week treadmill training prevented morphine conditioned place preference (CPP) expression during abstinence by acting through the nucleus accumbens (NAc)-ventral pallidum (VP) pathway. We found that neuronal excitability was reduced in D2-dopamine receptor-expressing medium spiny neurons (D2-MSNs) following repeated exposure to morphine and forced abstinence. Enhancing the excitability of NAc D2-MSNs via treadmill training decreased the expression of morphine CPP. We also found that the effects of treadmill training were mediated by decreasing enkephalin levels and that restoring opioid modulation of GABA neurotransmission in the VP, which increased neurotransmitter release from NAc D2-MSNs to VP, decreased morphine CPP. Our findings suggest the inhibitory effect of exercise on morphine CPP is mediated by reversing morphine-induced neuroadaptations in the NAc-to-VP pathway.

Distinct Thalamo-Subcortical Circuits Underlie Painful Behavior and Depression-Like Behavior Following Nerve Injury

Clinically, chronic pain and depression often coexist in multiple diseases and reciprocally reinforce each other, which greatly escalates the difficulty of treatment. The neural circuit mechanism underlying the chronic pain/depression comorbidity remains unclear. The present study reports that two distinct subregions in the paraventricular thalamus (PVT) play different roles in this pathological process. In the first subregion PVT posterior (PVP), glutamatergic neurons (PVPGlu) send signals to GABAergic neurons (VLPAGGABA) in the ventrolateral periaqueductal gray (VLPAG), which mediates painful behavior in comorbidity. Meanwhile, in another subregion PVT anterior (PVA), glutamatergic neurons (PVAGlu) send signals to the nucleus accumbens D1-positive neurons and D2-positive neurons (NAcD1→D2), which is involved in depression-like behavior in comorbidity. This study demonstrates that the distinct thalamo-subcortical circuits PVPGlu→VLPAGGABA and PVAGlu→NAcD1→D2 mediated painful behavior and depression-like behavior following spared nerve injury (SNI), respectively, which provides the circuit-based potential targets for preventing and treating comorbidity.

Cellular and circuit architecture of the lateral septum for reward processing

The lateral septum (LS) is composed of heterogeneous cell types that are important for various motivated behaviors. However, the transcriptional profiles, spatial arrangement, function, and connectivity of these cell types have not been systematically studied. Using single-nucleus RNA sequencing, we delineated diverse genetically defined cell types in the LS that play distinct roles in reward processing. Notably, we found that estrogen receptor 1 (Esr1)-expressing neurons in the ventral LS (LSEsr1) are key drivers of reward seeking via projections to the ventral tegmental area, and these neurons play an essential role in methamphetamine (METH) reward and METH-seeking behavior. Extended exposure to METH increases the excitability of LSEsr1 neurons by upregulating hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, thereby contributing to METH-induced locomotor sensitization. These insights not only elucidate the intricate molecular, circuit, and functional architecture of the septal region in reward processing but also reveal a neural pathway critical for METH reward and behavioral sensitization.

The nucleus accumbens in reward and aversion processing: insights and implications

The nucleus accumbens (NAc), a central component of the brain's reward circuitry, has been implicated in a wide range of behaviors and emotional states. Emerging evidence, primarily drawing from recent rodent studies, suggests that the function of the NAc in reward and aversion processing is multifaceted. Prolonged stress or drug use induces maladaptive neuronal function in the NAc circuitry, which results in pathological conditions. This review aims to provide comprehensive and up-to-date insights on the role of the NAc in motivated behavior regulation and highlights areas that demand further in-depth analysis. It synthesizes the latest findings on how distinct NAc neuronal populations and pathways contribute to the processing of opposite valences. The review examines how a range of neuromodulators, especially monoamines, influence the NAc's control over various motivational states. Furthermore, it delves into the complex underlying mechanisms of psychiatric disorders such as addiction and depression and evaluates prospective interventions to restore NAc functionality.

Sex-specific behavioral and thalamo-accumbal circuit adaptations after oxycodone abstinence

Opioid use disorder is marked by a progressive change in the motivation to administer the drug even in the presence of negative consequences. After long periods of abstinence, the urge to return to taking the drug intensifies over time, known as incubation of craving. Conditioned responses to drug-related stimuli, can acquire motivational properties and exert control over motivated behaviors leading to relapse. Although, preclinical data suggest that the behavioral expression of opioid use is similar between male and female rodents, we do not have conclusive results on sex differences on craving and relapse across abstinence periods. Here, we investigated the effects of abstinence from oxycodone self-administration on neurotransmission in the paraventricular thalamus (PVT) to nucleus accumbens shell (NAcSh) pathway in male and female rats. Using optogenetics and ex vivo electrophysiology, we assessed synaptic strength and glutamate release probability in this pathway, as well as NAcSh medium spiny neurons (MSN) intrinsic excitability, in slices from rats which were subjected to either 1 (acute) or 14 (prolonged) days of forced abstinence after self-administration. Our results revealed no sex differences in oxycodone self-administration or somatic withdrawal symptoms following acute abstinence. However, we found a sex-specific enhancement in cue-induced relapse after prolonged, but not acute, abstinence from oxycodone self-administration, with females exhibiting higher relapse rates. Notably, prolonged abstinence led to similar increases in synaptic strength at PVT-NAcSh inputs compared to saline controls in both sexes, which was not observed after acute abstinence. Thus, prolonged abstinence results in a time-dependent increase in PVT-NAcSh synaptic strength and sex-specific effects on cue-induced relapse rates. These findings suggest that prolonged abstinence leads to significant synaptic changes, contributing to heightened relapse vulnerability, highlighting the need for targeted therapeutic strategies in opioid use disorder.

A subset of dopamine receptor-expressing neurons in the nucleus accumbens controls feeding and energy homeostasis

Orchestrating complex behaviors, such as approaching and consuming food, is critical for survival. In addition to hypothalamus neuronal circuits, the nucleus accumbens (NAc) also controls appetite and satiety. However, specific neuronal subtypes of the NAc that are involved and how the humoral and neuronal signals coordinate to regulate feeding remain incompletely understood. Here we decipher the spatial diversity of neuron subtypes of the NAc shell (NAcSh) and define a dopamine receptor D1-expressing and Serpinb2-expressing subtype controlling food consumption in male mice. Chemogenetics and optogenetics-mediated regulation of Serpinb2+ neurons bidirectionally regulate food seeking and consumption specifically. Circuitry stimulation reveals that the NAcShSerpinb2→LHLepR projection controls refeeding and can overcome leptin-mediated feeding suppression. Furthermore, NAcSh Serpinb2+ neuron ablation reduces food intake and upregulates energy expenditure, resulting in reduced bodyweight gain. Our study reveals a neural circuit consisting of a molecularly distinct neuronal subtype that bidirectionally regulates energy homeostasis, providing a potential therapeutic target for eating disorders.

Pannexin-1 channel inhibition alleviates opioid withdrawal in rodents by modulating locus coeruleus to spinal cord circuitry

Opioid withdrawal is a liability of chronic opioid use and misuse, impacting people who use prescription or illicit opioids. Hyperactive autonomic output underlies many of the aversive withdrawal symptoms that make it difficult to discontinue chronic opioid use. The locus coeruleus (LC) is an important autonomic centre within the brain with a poorly defined role in opioid withdrawal. We show here that pannexin-1 (Panx1) channels expressed on microglia critically modulate LC activity during opioid withdrawal. Within the LC, we found that spinally projecting tyrosine hydroxylase (TH)-positive neurons (LCspinal) are hyperexcitable during morphine withdrawal, elevating cerebrospinal fluid (CSF) levels of norepinephrine. Pharmacological and chemogenetic silencing of LCspinal neurons or genetic ablation of Panx1 in microglia blunted CSF NE release, reduced LC neuron hyperexcitability, and concomitantly decreased opioid withdrawal behaviours in mice. Using probenecid as an initial lead compound, we designed a compound (EG-2184) with greater potency in blocking Panx1. Treatment with EG-2184 significantly reduced both the physical signs and conditioned place aversion caused by opioid withdrawal in mice, as well as suppressed cue-induced reinstatement of opioid seeking in rats. Together, these findings demonstrate that microglial Panx1 channels modulate LC noradrenergic circuitry during opioid withdrawal and reinstatement. Blocking Panx1 to dampen LC hyperexcitability may therefore provide a therapeutic strategy for alleviating the physical and aversive components of opioid withdrawal.

Pivotal role of orexin signaling in the posterior paraventricular nucleus of the thalamus during the stress-induced reinstatement of oxycodone-seeking behavior

BACKGROUND

The orexin (OX) system has received increasing interest as a potential target for treating substance use disorder. OX transmission in the posterior paraventricular nucleus of the thalamus (pPVT), an area activated by highly salient stimuli that are both reinforcing and aversive, mediates cue- and stress-induced reinstatement of reward-seeking behavior. Oral administration of suvorexant (SUV), a dual OX receptor (OXR) antagonist (DORA), selectively reduced conditioned reinstatement of oxycodone-seeking behavior and stress-induced reinstatement of alcohol-seeking behavior in dependent rats.

AIMS

This study tested whether OXR blockade in the pPVT with SUV reduces oxycodone or sweetened condensed milk (SCM) seeking elicited by conditioned cues or stress.

METHODS

Male Wistar rats were trained to self-administer oxycodone (0.15 mg/kg, i.v., 8 h/day) or SCM (0.1 ml, 2:1 dilution [v/v], 30 min/day). After extinction, we tested the ability of intra-pPVT SUV (15 µg/0.5 µl) to prevent reinstatement of oxycodone or SCM seeking elicited by conditioned cues or footshock stress.

RESULTS

The rats acquired oxycodone and SCM self-administration, and oxycodone intake correlated with signs of physical opioid withdrawal, confirming dependence. Following extinction, the presentation of conditioned cues or footshock elicited reinstatement of oxycodone- and SCM-seeking behavior. Intra-pPVT SUV blocked stress-induced reinstatement of oxycodone seeking but not conditioned reinstatement of oxycodone or SCM seeking or stress-induced reinstatement of SCM seeking.

CONCLUSIONS

The results indicate that OXR signaling in the pPVT is critical for stress-induced reinstatement of oxycodone seeking, further corroborating OXRs as treatment targets for opioid use disorder.

Paraventricular Thalamus Neuronal Ensembles Encode Early-life Adversity and Mediate the Consequent Sex-dependent Disruptions of Adult Reward Behaviors

Early-life adversity increases risk for mental illnesses including depression and substance use disorders, disorders characterized by dysregulated reward behaviors. However, the mechanisms by which transient ELA enduringly impacts reward circuitries are not well understood. In mice, ELA leads to anhedonia-like behaviors in males and augmented motivation for palatable food and sex-reward cues in females. Here, the use of genetic tagging demonstrated robust, preferential, and sex-specific activation of the paraventricular nucleus of the thalamus (PVT) during ELA and a potentiated reactivation of these PVT neurons during a reward task in adult ELA mice. Chemogenetic manipulation of specific ensembles of PVT neurons engaged during ELA identified a role for the posterior PVT in ELA-induced aberrantly augmented reward behaviors in females. In contrast, anterior PVT neurons activated during ELA were required for the anhedonia-like behaviors in males. Thus, the PVT encodes adverse experiences early-in life, prior to the emergence of the hippocampal memory system, and contributes critically to the lasting, sex-modulated impacts of ELA on reward behaviors.

Sustained antidepressant effects of ketamine metabolite involve GABAergic inhibition-mediated molecular dynamics in aPVT glutamatergic neurons

Despite the rapid and sustained antidepressant effects of ketamine and its metabolites, their underlying cellular and molecular mechanisms are not fully understood. Here, we demonstrate that the sustained antidepressant-like behavioral effects of (2S,6S)-hydroxynorketamine (HNK) in repeatedly stressed animal models involve neurobiological changes in the anterior paraventricular nucleus of the thalamus (aPVT). Mechanistically, (2S,6S)-HNK induces mRNA expression of extrasynaptic GABAA receptors and subsequently enhances GABAA-receptor-mediated tonic currents, leading to the nuclear export of histone demethylase KDM6 and its replacement by histone methyltransferase EZH2. This process increases H3K27me3 levels, which in turn suppresses the transcription of genes associated with G-protein-coupled receptor signaling. Thus, our findings shed light on the comprehensive cellular and molecular mechanisms in aPVT underlying the sustained antidepressant behavioral effects of ketamine metabolites. This study may support the development of potentially effective next-generation pharmacotherapies to promote sustained remission of stress-related psychiatric disorders.

Rebuilding the behavioral inhibition circuit to prevent opioid relapse

Failure in behavioral suppression is a key feature in substance use disorders, potentially leading to compulsive drug seeking and relapse. In this issue of Neuron, Paniccia et al.1 elucidated a heroin-damaged paraventricular nucleus of the thalamus (PVT)-accumbal circuit and how recovery of PVT function could prevent heroin relapse.

Restoration of a paraventricular thalamo-accumbal behavioral suppression circuit prevents reinstatement of heroin seeking

Lack of behavioral suppression typifies substance use disorders, yet the neural circuit underpinnings of drug-induced behavioral disinhibition remain unclear. Here, we employ deep-brain two-photon calcium imaging in heroin self-administering mice, longitudinally tracking adaptations within a paraventricular thalamus to nucleus accumbens behavioral inhibition circuit from the onset of heroin use to reinstatement. We find that select thalamo-accumbal neuronal ensembles become profoundly hypoactive across the development of heroin seeking and use. Electrophysiological experiments further reveal persistent adaptations at thalamo-accumbal parvalbumin interneuronal synapses, whereas functional rescue of these synapses prevents multiple triggers from initiating reinstatement of heroin seeking. Finally, we find an enrichment of μ-opioid receptors in output- and cell-type-specific paraventricular thalamic neurons, which provide a mechanism for heroin-induced synaptic plasticity and behavioral disinhibition. These findings reveal key circuit adaptations that underlie behavioral disinhibition in opioid dependence and further suggest that recovery of this system would reduce relapse susceptibility.

An ACC-VTA-ACC positive-feedback loop mediates the persistence of neuropathic pain and emotional consequences

The central mechanisms underlying pain chronicity remain elusive. Here, we identify a reciprocal neuronal circuit in mice between the anterior cingulate cortex (ACC) and the ventral tegmental area (VTA) that mediates mutual exacerbation between hyperalgesia and allodynia and their emotional consequences and, thereby, the chronicity of neuropathic pain. ACC glutamatergic neurons (ACCGlu) projecting to the VTA indirectly inhibit dopaminergic neurons (VTADA) by activating local GABAergic interneurons (VTAGABA), and this effect is reinforced after nerve injury. VTADA neurons in turn project to the ACC and synapse to the initial ACCGlu neurons to convey feedback information from emotional changes. Thus, an ACCGlu-VTAGABA-VTADA-ACCGlu positive-feedback loop mediates the progression to and maintenance of persistent pain and comorbid anxiodepressive-like behavior. Disruption of this feedback loop relieves hyperalgesia and anxiodepressive-like behavior in a mouse model of neuropathic pain, both acutely and in the long term.

The Paraventricular Thalamic Nucleus and Its Projections in Regulating Reward and Context Associations

The paraventricular thalamic nucleus (PVT) is a brain region that mediates aversive and reward-related behaviors as shown in animals exposed to fear conditioning, natural rewards, or drugs of abuse. However, it is unknown whether manipulations of the PVT, in the absence of external factors or stimuli (e.g., fear, natural rewards, or drugs of abuse), are sufficient to drive reward-related behaviors. Additionally, it is unknown whether drugs of abuse administered directly into the PVT are sufficient to drive reward-related behaviors. Here, using behavioral as well as pathway and cell-type specific approaches, we manipulate PVT activity as well as the PVT-to-nucleus accumbens shell (NAcSh) neurocircuit to explore reward phenotypes. First, we show that bath perfusion of morphine (10 µM) caused hyperpolarization of the resting membrane potential, increased rheobase, and decreased intrinsic membrane excitability in PVT neurons that project to the NAcSh. Additionally, we found that direct injections of morphine (50 ng) in the PVT of mice were sufficient to generate conditioned place preference (CPP) for the morphine-paired chamber. Mimicking the inhibitory effect of morphine, we employed a chemogenetic approach to inhibit PVT neurons that projected to the NAcSh and found that pairing the inhibition of these PVT neurons with a specific context evoked the acquisition of CPP. Lastly, using brain slice electrophysiology, we found that bath-perfused morphine (10 µM) significantly reduced PVT excitatory synaptic transmission on both dopamine D1 and D2 receptor-expressing medium spiny neurons in the NAcSh, but that inhibiting PVT afferents in the NAcSh was not sufficient to evoke CPP.

Cell-type specific molecular architecture for mu opioid receptor function in pain and addiction circuits

Opioids are potent analgesics broadly used for pain management; however, they can produce dangerous side effects including addiction and respiratory depression. These harmful effects have led to an epidemic of opioid abuse and overdose deaths, creating an urgent need for the development of both safer pain medications and treatments for opioid use disorders. Both the analgesic and addictive properties of opioids are mediated by the mu opioid receptor (MOR), making resolution of the cell types and neural circuits responsible for each of the effects of opioids a critical research goal. Single-cell RNA sequencing (scRNA-seq) technology is enabling the identification of MOR-expressing cell types throughout the nervous system, creating new opportunities for mapping distinct opioid effects onto newly discovered cell types. Here, we describe molecularly defined MOR-expressing neuronal cell types throughout the peripheral and central nervous systems and their potential contributions to opioid analgesia and addiction.

Distinctiveness and continuity in transcriptome and connectivity in the anterior-posterior axis of the paraventricular nucleus of the thalamus

The paraventricular nucleus of the thalamus (PVT) projects axons to multiple areas, mediates a wide range of behaviors, and exhibits regional heterogeneity in both functions and axonal projections. Still, questions regarding the cell types present in the PVT and the extent of their differences remain inadequately addressed. We applied single-cell RNA sequencing to depict the transcriptomic characteristics of mouse PVT neurons. We found that one of the most significant variances in the PVT transcriptome corresponded to the anterior-posterior axis. While the single-cell transcriptome classified PVT neurons into five types, our transcriptomic and histological analyses showed continuity among the cell types. We discovered that anterior and posterior subpopulations had nearly non-overlapping projection patterns, while another population showed intermediate patterns. In addition, these subpopulations responded differently to appetite-related neuropeptides, with their activation showing opposing effects on food consumption. Our studies unveiled the contrasts and the continuity of PVT neurons that underpin their function.

Addictive drugs modify neurogenesis, synaptogenesis and synaptic plasticity to impair memory formation through neurotransmitter imbalances and signaling dysfunction

Drug abuse changes neurophysiological functions at multiple cellular and molecular levels in the addicted brain. Well-supported scientific evidence suggests that drugs negatively affect memory formation, decision-making and inhibition, and emotional and cognitive behaviors. The mesocorticolimbic brain regions are involved in reward-related learning and habitual drug-seeking/taking behaviors to develop physiological and psychological dependence on the drugs. This review highlights the importance of specific drug-induced chemical imbalances resulting in memory impairment through various neurotransmitter receptor-mediated signaling pathways. The mesocorticolimbic modifications in the expression levels of brain-derived neurotrophic factor (BDNF) and the cAMP-response element binding protein (CREB) impair reward-related memory formation following drug abuse. The contributions of protein kinases and microRNAs (miRNAs), along with the transcriptional and epigenetic regulation have also been considered in memory impairment underlying drug addiction. Overall, we integrate the research on various types of drug-induced memory impairment in distinguished brain regions and provide a comprehensive review with clinical implications addressing the upcoming studies.

A novel role for astrocytic fragmented mitochondria in regulating morphine addiction

Chronic morphine exposure causes the development of addictive behaviors, accompanied by an increase in neuroinflammation in the central nervous system. While previous researches have shown that astrocytes contribute to brain diseases, the role of astrocyte in morphine addiction through induced neuroinflammation remain unexplored. Here we show that morphine-induced inflammation requires the crosstalk among neuron, astrocyte, and microglia. Specifically, astrocytes respond to morphine-induced neuronal activation by increasing glycolytic metabolism. The dysregulation of glycolysis leads to an increased in the generation of mitochondrial reactive oxygen species and causes excessive mitochondrial fragmentation in astrocytes. These fragmented, dysfunctional mitochondria are consequently released into extracellular environment, leading to activation of microglia and release of inflammatory cytokines. We also found that blocking the nicotinamide adenine dinucleotide salvage pathway with FK866 could inhibit astrocytic glycolysis and restore the mitochondrial homeostasis and effectively attenuate neuroinflammatory responses. Importantly, FK866 reversed morphine-induced addictive behaviors in mice. In summary, our findings illustrate an essential role of astrocytic immunometabolism in morphine induced neural and behavioral plasticity, providing a novel insight into the interactions between neurons, astrocytes, and microglia in the brain affected by chronic morphine exposure.

Genetic Tagging Uncovers a Robust, Selective Activation of the Thalamic Paraventricular Nucleus by Adverse Experiences Early in Life

Background

Early-life adversity (ELA) is associated with increased risk for mood disorders, including depression and substance use disorders. These disorders are characterized by impaired reward-related behaviors, suggesting compromised operations of reward-related brain circuits. However, the brain regions engaged by ELA that mediate these enduring consequences of ELA remain largely unknown. In an animal model of ELA, we identified aberrant reward-seeking behaviors, a discovery that provides a framework for assessing the underlying circuits.

Methods

Employing TRAP2 (targeted recombination in active populations) male and female mice, in which neurons activated within a defined time frame are permanently tagged, we compared ELA- and control-reared mice, assessing the quantity and distribution of ELA-related neuronal activation. After validating the TRAP2 results using native c-Fos labeling, we defined the molecular identity of this population of activated neurons.

Results

We uniquely demonstrated that the TRAP2 system is feasible and efficacious in neonatal mice. Surprisingly, the paraventricular nucleus of the thalamus was robustly and almost exclusively activated by ELA and was the only region distinguishing ELA from typical rearing. Remarkably, a large proportion of ELA-activated paraventricular nucleus of the thalamus neurons expressed CRF1, the receptor for the stress-related peptide, corticotropin-releasing hormone, but these neurons did not express corticotropin-releasing hormone itself.

Conclusions

The paraventricular nucleus of the thalamus, an important component of reward circuits that is known to encode remote, emotionally salient experiences to influence future motivated behaviors, encodes adverse experiences as remote as those occurring during the early postnatal period and is thus poised to contribute to the enduring deficits in reward-related behaviors consequent to ELA.

The Cdk5 inhibitor β-butyrolactone impairs reconsolidation of heroin-associated memory in the rat basolateral amygdala

The persistence of maladaptive heroin-associated memory, which is triggered by drug-related stimuli that remind the individual of the drug's pleasurable and rewarding effects, can impede abstinence efforts. Cyclin-dependent kinase 5 (Cdk5), a neuronal serine/threonine protein kinase that plays a role in multiple neuronal functions, has been demonstrated to be involved in drug addiction and learning and memory. Here, we aimed to investigate the role of cdk5 activity in the basolateral amygdala (BLA) in relapse to heroin seeking, using a self-administration rat model. Male rats underwent 10 days of heroin self-administration training, during which an active nose poke resulted in an intravenous infusion of heroin that was accompanied by a cue. The rats then underwent nose poke extinction for 10 days, followed by subsequent tests of heroin-seeking behaviour. We found that intra-BLA infusion of β-butyrolactone (100 ng/side), a Cdk5 inhibitor, administered 5 min after reactivation, led to a subsequent decrease in heroin-seeking behaviour. Further experiments demonstrated that the effects of β-butyrolactone are dependent on reactivated memories, temporal-specific and long-lasting on relapse of heroin-associated memory. Results provide suggestive evidence that the activity of Cdk5 in BLA is critical for heroin-associated memory and that the specific inhibitor, β-butyrolactone, may hold potential as a substance for the treatment of heroin abuse.

Accumbal-thalamic connectivity and associated glutamate alterations in human cocaine craving: A state-dependent rs-fMRI and 1H-MRS study

Craving is a core symptom of cocaine use disorder and a major factor for relapse risk. To date, there is no pharmacological therapy to treat this disease or at least to alleviate cocaine craving as a core symptom. In animal models, impaired prefrontal-striatal signalling leading to altered glutamate release in the nucleus accumbens appear to be the prerequisite for cocaine-seeking. Thus, those network and metabolic changes may constitute the underlying mechanisms for cocaine craving and provide a potential treatment target. In humans, there is recent evidence for corresponding glutamatergic alterations in the nucleus accumbens, however, the underlying network disturbances that lead to this glutamate imbalance remain unknown. In this state-dependent randomized, placebo-controlled, double-blinded, cross-over multimodal study, resting state functional magnetic resonance imaging in combination with small-voxel proton magnetic resonance spectroscopy (voxel size: 9.4 × 18.8 × 8.4 mm3) was applied to assess network-level and associated neurometabolic changes during a non-craving and a craving state, induced by a custom-made cocaine-cue film, in 18 individuals with cocaine use disorder and 23 healthy individuals. Additionally, we assessed the potential impact of a short-term challenge of N-acetylcysteine, known to normalize disturbed glutamate homeostasis and to thereby reduce cocaine-seeking in animal models of addiction, compared to a placebo. We found increased functional connectivity between the nucleus accumbens and the dorsolateral prefrontal cortex during the cue-induced craving state. However, those changes were not linked to alterations in accumbal glutamate levels. Whereas we additionally found increased functional connectivity between the nucleus accumbens and a midline part of the thalamus during the cue-induced craving state. Furthermore, obsessive thinking about cocaine and the actual intensity of cocaine use were predictive of cue-induced functional connectivity changes between the nucleus accumbens and the thalamus. Finally, the increase in accumbal-thalamic connectivity was also coupled with craving-related glutamate rise in the nucleus accumbens. Yet, N-acetylcysteine had no impact on craving-related changes in functional connectivity. Together, these results suggest that connectivity changes within the fronto-accumbal-thalamic loop, in conjunction with impaired glutamatergic transmission, underlie cocaine craving and related clinical symptoms, pinpointing the thalamus as a crucial hub for cocaine craving in humans.

Valence and salience encoding by parallel circuits from the paraventricular thalamus to the nucleus accumbens

The anterior and posterior subregions of the paraventricular thalamus (aPVT and pPVT, respectively) play unique roles in learned behaviors, from fear conditioning to alcohol/drug intake, potentially through differentially organized projections to limbic brain regions including the nucleus accumbens medial shell (mNAcSh). Here, we found that the aPVT projects broadly to the mNAcSh and that the aPVT-mNAcSh circuit encodes positive valence, such that in vivo manipulations of the circuit modulated both innately programmed and learned behavioral responses to positively and negatively valenced stimuli, particularly in females. Further, the endogenous activity of aPVT presynaptic terminals in the mNAcSh was greater in response to positively than negatively valenced stimuli, and the probability of synaptic glutamate release from aPVT neurons in the mNAcSh was higher in females than males. In contrast, we found that the pPVT-mNAcSh circuit encodes stimulus salience regardless of valence. While pPVT-mNAcSh circuit inhibition suppressed behavioral responses in both sexes, circuit activation increased behavioral responses to stimuli only in males. Our results point to circuit-specific stimulus feature encoding by parallel PVT-mNAcSh circuits that have sex-dependent biases in organization and function.

Neurons innervating both the central amygdala and the ventral tegmental area encode different emotional valences

Mammals are frequently exposed to various environmental stimuli, and to determine whether to approach or avoid these stimuli, the brain must assign emotional valence to them. Therefore, it is crucial to investigate the neural circuitry mechanisms involved in the mammalian brain's processing of emotional valence. Although the central amygdala (CeA) and the ventral tegmental area (VTA) individually encode different or even opposing emotional valences, it is unclear whether there are common upstream input neurons that innervate and control both these regions, and it is interesting to know what emotional valences of these common upstream neurons. In this study, we identify three major brain regions containing neurons that project to both the CeA and the VTA, including the posterior bed nucleus of the stria terminalis (pBNST), the pedunculopontine tegmental nucleus (PPTg), and the anterior part of the basomedial amygdala (BMA). We discover that these neural populations encode distinct emotional valences. Activating neurons in the pBNST produces positive valence, enabling mice to overcome their innate avoidance behavior. Conversely, activating neurons in the PPTg produces negative valence and induces anxiety-like behaviors in mice. Neuronal activity in the BMA, on the other hand, does not influence valence processing. Thus, our study has discovered three neural populations that project to both the CeA and the VTA and has revealed the distinct emotional valences these populations encode. These results provide new insights into the neurological mechanisms involved in emotional regulation.

The role of NMDA glutamate receptors in the lateral habenula on morphine-induced conditioned place preference in rats

The lateral habenula (LHb) has received special attention due to its role in modulating motivated behavior, stress response, and rewarding and aversive stimuli through monoamine transmission. In the present study, the involvement of the N-methyl-d-aspartate (NMDA) receptors of the LHb in the expression and acquisition phases of morphine-induced conditioned place preference (CPP) was studied in male rats. Bilateral injections of agonist/antagonist (MK-801) of NMDA receptor were performed during the conditioning sessions of the acquisition phase. In other separate groups, drugs were also injected into the LHb before the test session during the expression phase of CPP. A 5-day CPP bias paradigm was used to study the effect of injections of NMDA and MK-801 into the LHb on morphine reward-related behavior. Different doses of NMDA plus morphine reduced the CPP score during the acquisition phase, whereas MK-801 significantly increased conditioning scores during the acquisition phase of CPP. The injection of agonists and antagonists of NMDA receptors in LHb had no significant effect on CPP scores and locomotion during the expression phase of CPP, whereas the motor activity in the acquisition phase was affected by the drugs. The reduction effect of NMDA on the CPP scores during the acquisition phase was blocked by pretreatment with MK-801. Our findings also suggest that NMDA receptors in the LHb may be involved in the acquisition phase of morphine-induced CPP.

Opioid Receptors Modulate Firing and Synaptic Transmission in the Paraventricular Nucleus of the Thalamus

The paraventricular nucleus of the thalamus (PVT) is involved in drug addiction-related behaviors, and morphine is a widely used opioid for the relief of severe pain. Morphine acts via opioid receptors, but the function of opioid receptors in the PVT has not been fully elucidated. Here, we used in vitro electrophysiology to study neuronal activity and synaptic transmission in the PVT of male and female mice. Activation of opioid receptors suppresses the firing and inhibitory synaptic transmission of PVT neurons in brain slices. On the other hand, the involvement of opioid modulation is reduced after chronic morphine exposure, probably because of desensitization and internalization of opioid receptors in the PVT. Overall, the opioid system is essential for the modulation of PVT activities.SIGNIFICANCE STATEMENT Opioid receptors modulate the activities and synaptic transmission in the PVT by suppressing the firing rate and inhibitory synaptic inputs. These modulations were largely diminished after chronic morphine exposure.

Plastic and stimulus-specific coding of salient events in the central amygdala

The central amygdala (CeA) is implicated in a range of mental processes including attention, motivation, memory formation and extinction and in behaviours driven by either aversive or appetitive stimuli1-7. How it participates in these divergent functions remains elusive. Here we show that somatostatin-expressing (Sst+) CeA neurons, which mediate much of CeA functions3,6,8-10, generate experience-dependent and stimulus-specific evaluative signals essential for learning. The population responses of these neurons in mice encode the identities of a wide range of salient stimuli, with the responses of separate subpopulations selectively representing the stimuli that have contrasting valences, sensory modalities or physical properties (for example, shock and water reward). These signals scale with stimulus intensity, undergo pronounced amplification and transformation during learning, and are required for both reward and aversive learning. Notably, these signals contribute to the responses of dopamine neurons to reward and reward prediction error, but not to their responses to aversive stimuli. In line with this, Sst+ CeA neuron outputs to dopamine areas are required for reward learning, but are dispensable for aversive learning. Our results suggest that Sst+ CeA neurons selectively process information about differing salient events for evaluation during learning, supporting the diverse roles of the CeA. In particular, the information for dopamine neurons facilitates reward evaluation.

Mu-opioid receptor-expressing neurons in the paraventricular thalamus modulate chronic morphine-induced wake alterations

Disrupted sleep is a symptom of many psychiatric disorders, including substance use disorders. Most drugs of abuse, including opioids, disrupt sleep. However, the extent and consequence of opioid-induced sleep disturbance, especially during chronic drug exposure, is understudied. We have previously shown that sleep disturbance alters voluntary morphine intake. Here, we examine the effects of acute and chronic morphine exposure on sleep. Using an oral self-administration paradigm, we show that morphine disrupts sleep, most significantly during the dark cycle in chronic morphine, with a concomitant sustained increase in neural activity in the Paraventricular Nucleus of the Thalamus (PVT). Morphine binds primarily to Mu Opioid Receptors (MORs), which are highly expressed in the PVT. Translating Ribosome Affinity Purification (TRAP)-Sequencing of PVT neurons that express MORs showed significant enrichment of the circadian entrainment pathway. To determine whether MOR + cells in the PVT mediate morphine-induced sleep/wake properties, we inhibited these neurons during the dark cycle while mice were self-administering morphine. This inhibition decreased morphine-induced wakefulness but not general wakefulness, indicating that MORs in the PVT contribute to opioid-specific wake alterations. Overall, our results suggest an important role for PVT neurons that express MORs in mediating morphine-induced sleep disturbance.

Global brain c-Fos profiling reveals major functional brain networks rearrangements after alcohol reexposure

Many fundamental questions on alcohol use disorder (AUD) are frequently difficult to address by examining a single brain structure, but should be viewed from the whole brain perspective. c-Fos is a marker of neuronal activation. Global brain c-Fos profiling in rodents represents a promising platform to study brain functional networks rearrangements in AUD. We used a mouse model of alcohol drinking in IntelliCage. We trained mice to voluntarily drink alcohol, next subjected them to withdrawal and alcohol reexposure. We have developed a dedicated image computational workflow to identify c-Fos-positive cells in three-dimensional images obtained after whole-brain optical clearing and imaging in the light-sheet microscope. We provide a complete list of 169 brain structures with annotated c-Fos expression. We analyzed functional networks, brain modularity and engram index. Brain c-Fos levels in animals reexposed to alcohol were different from both control and binge drinking animals. Structures involved in reward processing, decision making and characteristic for addictive behaviors, such as precommissural nucleus, nucleus Raphe, parts of colliculus and tecta stood out particularly. Alcohol reexposure leads to a massive change of brain modularity including a formation of numerous smaller functional modules grouping structures involved in addiction development. Binge drinking can lead to substantial functional remodeling in the brain. We provide a list of structures that can be used as a target in pharmacotherapy but also point to the networks and modules that can hold therapeutic potential demonstrated by a clinical trial in patients.

Distinct reward processing by subregions of the nucleus accumbens

The nucleus accumbens (NAc) plays an important role in motivation and reward processing. Recent studies suggest that different NAc subnuclei differentially contribute to reward-related behaviors. However, how reward is encoded in individual NAc neurons remains unclear. Using in vivo single-cell resolution calcium imaging, we find diverse patterns of reward encoding in the medial and lateral shell subdivision of the NAc (NAcMed and NAcLat, respectively). Reward consumption increases NAcLat activity but decreases NAcMed activity, albeit with high variability among neurons. The heterogeneity in reward encoding could be attributed to differences in their synaptic inputs and transcriptional profiles. Specific optogenetic activation of Nts-positive neurons in the NAcLat promotes positive reinforcement, while activation of Cartpt-positive neurons in the NAcMed induces behavior aversion. Collectively, our study shows the organizational and transcriptional differences in NAc subregions and provides a framework for future dissection of NAc subregions in physiological and pathological conditions.

Neural correlates of recall and extinction in a rat model of appetitive Pavlovian conditioning

Extinction is a fundamental form of inhibitory learning that is important for adapting to changing environmental contingencies. While numerous studies have investigated the neural correlates of extinction using Pavlovian fear conditioning and appetitive operant reward-seeking procedures, less is known about the neural circuitry mediating the extinction of appetitive Pavlovian responding. Here, we aimed to generate an extensive brain activation map of extinction learning in a rat model of appetitive Pavlovian conditioning. Male Long-Evans rats were trained to associate a conditioned stimulus (CS; 20 s white noise) with the delivery of a 10% sucrose unconditioned stimulus (US; 0.3 ml/CS) to a fluid port. Control groups also received CS presentations, but sucrose was delivered either during the inter-trial interval or in the home-cage. After conditioning, 1 or 6 extinction sessions were conducted in which the CS was presented but sucrose was withheld. We performed Fos immunohistochemistry and network connectivity analyses on a set of cortical, striatal, thalamic, and amygdalar brain regions. Neural activity in the prelimbic cortex, ventral orbitofrontal cortex, nucleus accumbens core, and paraventricular nucleus of the thalamus was greater during recall relative to extinction. Conversely, prolonged extinction following 6 sessions induced increased neural activity in the infralimbic cortex, medial orbitofrontal cortex, and nucleus accumbens shell compared to home-cage controls. All these structures were similarly recruited during recall on the first extinction session. These findings provide novel evidence for the contribution of brain areas and neural networks that are differentially involved in the recall versus extinction of appetitive Pavlovian conditioned responding.

Whole-brain tracking of cocaine and sugar rewards processing

Natural rewards, such as food, and sex are appetitive stimuli available for animals in their natural environment. Similarly, addictive rewards such as drugs of abuse possess strong, positive valence, but their action relies on their pharmacological properties. Nevertheless, it is believed that both of these kinds of rewards activate similar brain circuitry. The present study aimed to discover which parts of the brain process the experience of natural and addictive rewards. To holistically address this question, we used a single-cell whole-brain imaging approach to find patterns of activation for acute and prolonged sucrose and cocaine exposure. We analyzed almost 400 brain structures and created a brain-wide map of specific, c-Fos-positive neurons engaged by these rewards. Acute but not prolonged sucrose exposure triggered a massive c-Fos expression throughout the brain. Cocaine exposure on the other hand potentiated c-Fos expression with prolonged use, engaging more structures than sucrose treatment. The functional connectivity analysis unraveled an increase in brain modularity after the initial exposure to both types of rewards. This modularity was increased after repeated cocaine, but not sucrose, intake. To check whether discrepancies between the processing of both types of rewards can be found on a cellular level, we further studied the nucleus accumbens, one of the most strongly activated brain structures by both sucrose and cocaine experience. We found a high overlap between natural and addictive rewards on the level of c-Fos expression. Electrophysiological measurements of cellular correlates of synaptic plasticity revealed that natural and addictive rewards alike induce the accumulation of silent synapses. These results strengthen the hypothesis that in the nucleus accumbens drugs of abuse cause maladaptive neuronal plasticity in the circuitry that typically processes natural rewards.

Nucleus accumbens circuit disinhibits lateral hypothalamus glutamatergic neurons contributing to morphine withdrawal memory in male mice

The lateral hypothalamus (LH) is physiologically critical in brain functions. The LH also plays an important role in drug addiction. However, neural circuits underlying LH involvement of drug addiction remain obscure. In the present study,our results showed that in male mice, during context-induced expression of morphine withdrawal memory, LH glutamatergic neurons played an important role; dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs) projecting from the core of nucleus accumbens (NAcC) to the LH were an important upstream circuit to activate LH glutamatergic neurons; D1-MSNs projecting from the NAcC to the LH activated LH glutamatergic neurons through inhibiting LH local gamma-aminobutyric acid (GABA) neurons. These results suggest that disinhibited LH glutamatergic neurons by neural circuits from the NAcC importantly contribute to context-induced the expression of morphine withdrawal memory.