Medial Nucleus Accumbens Shell Research Articles

Foxp2 Is Required for Nucleus Accumbens-mediated Multifaceted Limbic Function

The forkhead box protein P2 (Foxp2), initially identified for its role in speech and language development, plays an important role in neural development. Previous studies investigated the function of the Foxp2 gene by deleting or mutating Foxp2 from developmental stages. Little is known about its physiological function in adult brains. Although Foxp2 has been well studied in the dorsal striatum, its function in the nucleus accumbens (NAc) of the ventral striatum remains elusive. Here, we examine the physiological function of Foxp2 in NAc of mouse brains. We conditionally knocked out Foxp2 by microinjections of AAV-EGFP-Cre viruses into the medial shell of NAc of Foxp2 floxed (cKO) mice. Immunostaining showed increased c-Fos positive cells in cKO NAc at basal levels, suggesting an abnormality in Foxp2-deficient NAc cells. Unbiased behavioral profiling of Foxp2 cKO mice showed abnormalities in limbic-associated function. Foxp2 cKO mice exhibited abnormal social novelty without preference for interaction with strangers and familiar mice. In appetitive reward learning, Foxp2 cKO mice failed to learn the time expectancy of food delivery. In fear learning, Foxp2 cKO mice exhibited abnormal increases in freezing levels in response to tone paired with foot shock during fear conditioning. The extinction of the fear response was also altered in Foxp2 cKO mice. In contrast, conditional knockout of Foxp2 in NAc did not affect locomotion, motor coordination, thermal pain sensation, anxiety- and depression-like behaviors. Collectively, our study suggests that Foxp2 has a multifaceted physiological role in NAc in the regulation of limbic function in the adult brain.

Inactivation of phosphodiesterase-4B gene in rat nucleus accumbens shell by CRISPR/Cas9 or positive allosteric modulation of the protein affects the motivation to chronically self-administer nicotine

Large scale human genome wide association studies (GWAS) have identified a growing pool of genes associated with cigarette smoking. One of the most prominent, phosphodiesterase-4B (PDE4B), has been associated with multiple smoking phenotypes. Although PDE4B modulates the half-life of neuronal cAMP, its precise role in smoking behaviors is unknown. To address this knowledge gap, we used a reverse translational approach. We inactivated PDE4B in bilateral medial nucleus accumbens shell (NAcs) neurons by injecting AAV containing a specific gRNA in female transgenic Cas9+ Long Evans rats. These rats then were given 23-h chronic access to nicotine intravenous self-administration (IVSA) under a schedule of increasing fixed ratios (FR). With the increased effort required at FR7, nicotine SA (i.e. active presses and drug infusions) declined significantly in controls, whereas it was maintained in the mutagenized group. A progressive ratio (PR) study also showed significantly greater cumulative nicotine infusions in the PDE4B-edited group. Hence, we hypothesized that enhanced PDE4B protein activity would reduce nicotine IVSA. A positive allosteric modulator, 2-(3-(4-chloro-3-fluorophenyl)-5-ethyl-1H-1,2,4-triazol-1-yl)-N-(3,5-dichlorobenzyl)acetamide (MR-L2), was microinfused into NAcs bilaterally at FR3 or FR5; in both cohorts, MR-L2 acutely reduced nicotine IVSA. In summary, these studies show that the activity of PDE4B regulates the capacity of NAcs to maintain nicotine IVSA in face of the cost of increasing work. This finding and the results of the PR study indicate that PDE4B affects the motivation to obtain nicotine. These reverse translational studies in rats provide insight into the motivational effects of NAcs PDE4B that advance our understanding of the smoking behaviors mapped in human GWAS.

An Ascending Excitatory Circuit from the Dorsal Raphe for Sensory Modulation of Pain.

The dorsal raphe nucleus (DRN) is an important nucleus in pain regulation. However, the underlying neural pathway and the function of specific cell types remain unclear. Here, we report a previously unrecognized ascending facilitation pathway, the DRN to the mesoaccumbal dopamine (DA) circuit, for regulating pain. Chronic pain increased the activity of DRN glutamatergic, but not serotonergic, neurons projecting to the ventral tegmental area (VTA) (DRNGlu-VTA) in male mice. The optogenetic activation of DRNGlu-VTA circuit induced a pain-like response in naive male mice, and its inhibition produced an analgesic effect in male mice with neuropathic pain. Furthermore, we discovered that DRN ascending pathway regulated pain through strengthened excitatory transmission onto the VTA DA neurons projecting to the ventral part of nucleus accumbens medial shell (vNAcMed), thereby activated the mesoaccumbal DA neurons. Correspondingly, optogenetic manipulation of this three-node pathway bilaterally regulated pain behaviors. These findings identified a DRN ascending excitatory pathway that is crucial for pain sensory processing, which can potentially be exploited toward targeting pain disorders.

The activity-regulated cytoskeleton-associated protein, Arc, functions in the nucleus accumbens shell to limit multiple triggers of cocaine-seeking behaviour.

Use of addictive substances like cocaine produces enduring associations between the drug experience and cues in the drug-taking environment. In individuals with a substance use disorder (SUD) and attempting to remain abstinent, these powerful drug-cue associations can trigger a return to active drug use, but the molecular mechanisms regulating drug-cue associations remain poorly understood. The activity-regulated cytoskeleton-associated protein (Arc) is induced by cocaine in the nucleus accumbens (NAc), an important brain reward region, but Arc's NAc function in SUD-related behaviour remains unclear. We show here that cocaine self-administration (SA) in rats produced a significant upregulation of Arc protein in both the core and shell subregions of the NAc. Subregion-specific Arc reduction (shRNA) in the medial NAc Shell enhanced both context-associated and cue-reinstated cocaine seeking, but without altering the motivation to work for cocaine, the sensitivity to the reinforcing effects of cocaine or the ability of cocaine priming to reinstate drug seeking. In contrast, we observed no effects of Arc knockdown in the NAc core on any aspect of cocaine SA, extinction or reinstated cocaine seeking, suggesting that Arc functions within the medial NAc shell, but not NAc core, to limit the strength of drug-context and drug-cue associations that promote cocaine-seeking behaviour.

A glutamatergic DRN–VTA pathway modulates neuropathic pain and comorbid anhedonia-like behavior in mice

Chronic pain causes both physical suffering and comorbid mental symptoms such as anhedonia. However, the neural circuits and molecular mechanisms underlying these maladaptive behaviors remain elusive. Here using a mouse model, we report a pathway from vesicular glutamate transporter 3 neurons in the dorsal raphe nucleus to dopamine neurons in the ventral tegmental area (VGluT3DRN→DAVTA) wherein population-level activity in response to innocuous mechanical stimuli and sucrose consumption is inhibited by chronic neuropathic pain. Mechanistically, neuropathic pain dampens VGluT3DRN → DAVTA glutamatergic transmission and DAVTA neural excitability. VGluT3DRN → DAVTA activation alleviates neuropathic pain and comorbid anhedonia-like behavior (CAB) by releasing glutamate, which subsequently promotes DA release in the nucleus accumbens medial shell (NAcMed) and produces analgesic and anti-anhedonia effects via D2 and D1 receptors, respectively. In addition, VGluT3DRN → DAVTA inhibition produces pain-like reflexive hypersensitivity and anhedonia-like behavior in intact mice. These findings reveal a crucial role for VGluT3DRN → DAVTA → D2/D1NAcMed pathway in establishing and modulating chronic pain and CAB.

Sex and cell-specific gene expression in corticolimbic brain regions associated with psychiatric disorders revealed by bulk and single-nuclei RNA sequencing

There are sex-specific differences in the prevalence, symptomology and course of psychiatric disorders. However, preclinical models have primarily used males, such that the molecular mechanisms underlying sex-specific differences in psychiatric disorders are not well established. In this study, we compared transcriptome-wide gene expression profiles in male and female rats within the corticolimbic system, including the cingulate cortex, nucleus accumbens medial shell (NAcS), ventral dentate gyrus and the basolateral amygdala (n=22-24 per group/region). We found over 3000 differentially expressed genes (DEGs) in the NAcS between males and females. Of these DEGs in the NAcS, 303 showed sex-dependent conservation DEGs in humans and were significantly enriched for gene ontology terms related to blood vessel morphogenesis and regulation of cell migration. Single nuclei RNA sequencing in the NAcS of male and female rats identified widespread sex-dependent expression, with genes upregulated in females showing a notable enrichment for synaptic function. Female upregulated genes in astrocytes, Drd3+MSNs and oligodendrocyte were also enriched in several psychiatric genome-wide association studies (GWAS). Our data provide comprehensive evidence of sex- and cell-specific molecular profiles in the NAcS. Importantly these differences associate with anxiety, bipolar disorder, schizophrenia, and cross-disorder, suggesting an intrinsic molecular basis for sex-based differences in psychiatric disorders that strongly implicates the NAcS. This work was supported by funding from the Hope for Depression Research Foundation (MJM).

Disentangling the role of NAc D1 and D2 cells in hedonic eating

Overeating is driven by both the hedonic component (‘liking’) of food, and the motivation (‘wanting’) to eat it. The nucleus accumbens (NAc) is a key brain center implicated in these processes, but how distinct NAc cell populations encode ‘liking’ and ‘wanting’ to shape overconsumption remains unclear. Here, we probed the roles of NAc D1 and D2 cells in these processes using cell-specific recording and optogenetic manipulation in diverse behavioral paradigms that disentangle reward traits of ‘liking’ and ‘wanting’ related to food choice and overeating in healthy mice. Medial NAc shell D2 cells encoded experience-dependent development of ‘liking’, while D1 cells encoded innate ‘liking’ during the first food taste. Optogenetic control confirmed causal links of D1 and D2 cells to these aspects of ‘liking’. In relation to ‘wanting’, D1 and D2 cells encoded and promoted distinct aspects of food approach: D1 cells interpreted food cues while D2 cells also sustained food-visit-length that facilitates consumption. Finally, at the level of food choice, D1, but not D2, cell activity was sufficient to switch food preference, programming subsequent long-lasting overconsumption. By revealing complementary roles of D1 and D2 cells in consumption, these findings assign neural bases to ‘liking’ and ‘wanting’ in a unifying framework of D1 and D2 cell activity.

A Nucleus Accumbens Tac1 Neural Circuit Regulates Avoidance Responses to Aversive Stimuli

Neural circuits that control aversion are essential for motivational regulation and survival in animals. The nucleus accumbens (NAc) plays an important role in predicting aversive events and translating motivations into actions. However, the NAc circuits that mediate aversive behaviors remain elusive. Here, we report that tachykinin precursor 1 (Tac1) neurons in the NAc medial shell regulate avoidance responses to aversive stimuli. We show that NAcTac1 neurons project to the lateral hypothalamic area (LH) and that the NAcTac1→LH pathway contributes to avoidance responses. Moreover, the medial prefrontal cortex (mPFC) sends excitatory inputs to the NAc, and this circuit is involved in the regulation of avoidance responses to aversive stimuli. Overall, our study reveals a discrete NAc Tac1 circuit that senses aversive stimuli and drives avoidance behaviors.

Increased sucrose consumption in mice gene-targeted for Vmat2 selectively in NeuroD6-positive neurons of the ventral tegmental area.

Ventral tegmental area (VTA) dopamine (DA) neurons are implicated in reward processing, motivation, reward prediction error, and in substance use disorder. Recent studies have identified distinct neuronal subpopulations within the VTA that can be clustered based on their molecular identity, neurotransmitter profile, physiology, projections and behavioral role. One such subpopulation is characterized by expression of the NeuroD6 gene, and projects primarily to the nucleus accumbens medial shell. We recently showed that optogenetic stimulation of these neurons induces real-time place preference while their targeted deletion of the Vmat2 gene caused altered response to rewarding substances, including ethanol and psychostimulants. Based on these recent findings, we wanted to further investigate the involvement of the NeuroD6-positive VTA subpopulation in reward processing. Using the same NeuroD6Cre+/wt ;Vmat2flox/flox mice as in our prior study, we now addressed the ability of the mice to process sucrose reward. In order to assess appetitive behavior and motivation to obtain sucrose reward, we tested conditional knockout (cKO) and control littermate mice in an operant sucrose self-administration paradigm. We observed that cKO mice demonstrate higher response rates to the operant task and consume more sucrose rewards than control mice. However, their motivation to obtain sucrose is identical to that of control mice. Our results highlight previous observations that appetitive behavior and motivation to obtain rewards can be served by distinct neuronal circuits, and demonstrate that the NeuroD6 VTA subpopulation is involved in mediating the former, but not the latter. Together with previous studies on the NeuroD6 subpopulation, our findings pinpoint the importance of unraveling the molecular and functional role of VTA subpopulations in order to better understand normal behavior and psychiatric disease.

Ventral Subiculum Inputs to Nucleus Accumbens Medial Shell Preferentially Innervate D2R Medium Spiny Neurons and Contain Calcium Permeable AMPARs.

Ventral subiculum (vSUB) is the major output region of ventral hippocampus (vHIPP) and sends major projections to nucleus accumbens medial shell (NAcMS). Hyperactivity of the vSUB-NAcMS circuit is associated with substance use disorders and the modulation of vSUB activity alters drug seeking and drug reinstatement behavior in rodents. However, to the best of our knowledge, the cell type-specific connectivity and synaptic transmission properties of the vSUB-NAcMS circuit have never been directly examined. Instead, previous functional studies have focused on total ventral hippocampal (vHIPP) output to NAcMS without distinguishing vSUB from other subregions of vHIPP, including ventral CA1 (vCA1). Using ex vivo electrophysiology, we systematically characterized the vSUB-NAcMS circuit with cell type- and synapse-specific resolution in male and female mice and found that vSUB output to dopamine receptor type-1 (D1R) and type-2 (D2R) expressing medium spiny neurons (MSNs) displays a functional connectivity bias for D2R MSNs. Furthermore, we found that vSUB-D1R and vSUB-D2R MSN synapses contain calcium-permeable AMPA receptors in drug-naive mice. Finally, we find that, distinct from other glutamatergic inputs, cocaine exposure selectively induces plasticity at vSUB-D2R synapses. Importantly, we directly compared vSUB and vCA1 output to NAcMS and found that vSUB synapses are functionally distinct and that vCA1 output recapitulated the synaptic properties previously ascribed to vHIPP. Our work highlights the need to consider the contributions of individual subregions of vHIPP to substance use disorders and represents an important first step toward understanding how the vSUB-NAcMS circuit contributes to the etiologies that underlie substance use disorders.SIGNIFICANCE STATEMENT Inputs to nucleus accumbens (NAc) dopamine receptor type 1 (D1R) and D2R medium spiny neurons (MSNs) are critically involved in reward seeking behavior. Ventral subiculum (vSUB) provides robust synaptic input to nucleus accumbens medial shell (NAcMS) and activity of this circuit is linked to substance use disorders. Despite the importance of the vSUB to nucleus accumbens circuit, the functional connectivity and synaptic transmission properties have not been tested. Here, we systematically interrogated these properties and found that basal connectivity and drug-induced plasticity are biased for D2R medium spiny neurons. Overall, we demonstrate that this circuit is distinct from synaptic inputs from other brain regions, which helps to explain how vSUB dysfunction contributes to the etiologies that underlie substance use disorders.

Hippocampal-evoked inhibition of cholinergic interneurons in the nucleus accumbens.

SUMMARYCholinergic interneurons (ChIs) in the nucleus accumbens (NAc) play a central role in motivated behaviors and associated disorders. However, while the activation of ChIs has been well studied in the dorsal striatum, little is known about how they are engaged in the NAc. Here, we find that the ventral hippocampus (vHPC) and the paraventricular nucleus of the thalamus (PVT) are the main excitatory inputs to ChIs in the NAc medial shell. While the PVT activates ChIs, the vHPC evokes a pronounced pause in firing through prominent feedforward inhibition. In contrast to the dorsal striatum, this inhibition reflects strong connections onto ChIs from local parvalbumin interneurons. Our results reveal the mechanisms by which different long-range inputs engage ChIs, highlighting fundamental differences in local connectivity across the striatum.

Corticotropin releasing factor (CRF) systems: Promoting cocaine pursuit without distress via incentive motivation.

Corticotropin releasing factor (CRF) systems in limbic structures are posited to mediate stress-induced relapse in addiction, traditionally by generating distress states that spur drug consumption as attempts at hedonic self-medication. Yet evidence suggests that activating CRF-expressing neurons in the central amygdala (CeA) or nucleus accumbens (NAc) can magnify incentive motivation in absence of distress, at least for sucrose rewards. However, traditional CRF hypotheses in addiction neuroscience are primarily directed toward drug rewards. The question remains open whether CRF systems can similarly act via incentive motivation mechanisms to promote pursuit of drug rewards, such as cocaine. Here we tested whether optogenetic excitation of CRF-containing neurons in either NAc medial shell, lateral CeA, or dorsolateral BNST of transgenic Crh-Cre+ rats would spur preference and pursuit of a particular laser-paired cocaine reward over an alternative cocaine reward, and whether excitation served as a positively-valenced incentive itself, through laser self-stimulation tests. We report that excitation of CRF-containing neurons in either NAc or CeA recruited mesocorticolimbic circuitry to amplify incentive motivation to pursue the laser-paired cocaine: focusing preference on the laser-paired cocaine reward in a two-choice task, and spurred pursuit as doubled breakpoint in a progressive ratio task. Crucially indicating positive-valence, excitation of CRF neurons in NAc and CeA also was actively sought after by most rats in self-stimulation tasks. Conversely, CRF neuronal activation in BNST was never self-stimulated, but failed to enhance cocaine consumption. Collectively, we find that NAc and CeA CRF-containing neurons can amplify pursuit and consumption of cocaine by positively-valenced incentive mechanisms, without any aversive distress.

Inactivation mode of sodium channels defines the different maximal firing rates of conventional versus atypical midbrain dopamine neurons

Two subpopulations of midbrain dopamine (DA) neurons are known to have different dynamic firing ranges in vitro that correspond to distinct projection targets: the originally identified conventional DA neurons project to the dorsal striatum and the lateral shell of the nucleus accumbens, whereas an atypical DA population with higher maximum firing frequencies projects to prefrontal regions and other limbic regions including the medial shell of nucleus accumbens. Using a computational model, we show that previously identified differences in biophysical properties do not fully account for the larger dynamic range of the atypical population and predict that the major difference is that originally identified conventional cells have larger occupancy of voltage-gated sodium channels in a long-term inactivated state that recovers slowly; stronger sodium and potassium conductances during action potential firing are also predicted for the conventional compared to the atypical DA population. These differences in sodium channel gating imply that longer intervals between spikes are required in the conventional population for full recovery from long-term inactivation induced by the preceding spike, hence the lower maximum frequency. These same differences can also change the bifurcation structure to account for distinct modes of entry into depolarization block: abrupt versus gradual. The model predicted that in cells that have entered depolarization block, it is much more likely that an additional depolarization can evoke an action potential in conventional DA population. New experiments comparing lateral to medial shell projecting neurons confirmed this model prediction, with implications for differential synaptic integration in the two populations.

Generation of a DAT-P2A-Flpo mouse line for intersectional genetic targeting of dopamine neuron subpopulations.

SUMMARYDopaminergic projections exert widespread influence over multiple brain regions and modulate various behaviors including movement, reward learning, and motivation. It is increasingly appreciated that dopamine neurons are heterogeneous in their gene expression, circuitry, physiology, and function. Current approaches to target dopamine neurons are largely based on single gene drivers, which either label all dopamine neurons or mark a subset but concurrently label non-dopaminergic neurons. Here, we establish a mouse line with Flpo recombinase expressed from the endogenous Slc6a3 (dopamine active transporter [DAT]) locus. DAT-P2A-Flpo mice can be used together with Cre-expressing mouse lines to efficiently and selectively label dopaminergic subpopulations using Cre/Flp-dependent intersectional strategies. We demonstrate the utility of this approach by generating DAT-P2A-Flpo;NEX-Cre mice that specifically label Neurod6-expressing dopamine neurons, which project to the nucleus accumbens medial shell. DAT-P2A-Flpo mice add to a growing toolbox of genetic resources that will help parse the diverse functions mediated by dopaminergic circuits.

A NAc Tac1 Neural Circuit Mediates Aversion

Neural circuits that encode aversive stimuli are essential for motivational regulation and survival in animals. The nucleus accumbens (NAc) plays an important role in predicting aversive events and translating motivations into actions. However, the NAc circuits that mediate aversive behaviors remain elusive. Here, we report that the activity of tachykinin precursor 1 (Tac1) neurons in the NAc medial shell regulates aversive behaviors. Using viral tracing and electrophysiology, we show that NAcTac1 neurons receive excitatory inputs from the medial prefrontal cortex (mPFC) and project inhibitory signals to the lateral hypothalamic area (LH). Moreover, selective optogenetic inhibition and activation of the mPFC glutamatergic neurons (mPFCGlut)→NAc medial shell Tac1 neurons (NAcTac1) →LH glutamatergic neurons (LHGlut) circuit bidirectionally modulate aversive behaviors in mice. Overall, our study reveals a discrete circuit regulating aversion.

Dopamine release and its control over early Pavlovian learning differs between the NAc core and medial NAc shell

Dopamine neurons respond to cues to reflect the value of associated outcomes. These cue-evoked dopamine responses can encode the relative rate of reward in rats with extensive Pavlovian training. Specifically, a cue that always follows the previous reward by a short delay (high reward rate) evokes a larger dopamine response in the nucleus accumbens (NAc) core relative to a distinct cue that always follows the prior reward by a long delay (low reward rate). However, it was unclear if these reward rate dopamine signals are evident during early Pavlovian training sessions and across NAc subregions. To address this, we performed fast-scan cyclic voltammetry recordings of dopamine levels to track the pattern of cue- and reward-evoked dopamine signals in the NAc core and medial NAc shell. We identified regional differences in the progression of cue-evoked dopamine signals across training. However, the dopamine response to cues did not reflect the reward rate in either the NAc core or the medial NAc shell during early training sessions. Pharmacological experiments found that dopamine-sensitive conditioned responding emerged in the NAc core before the medial NAc shell. Together, these findings illustrate regional differences in NAc dopamine release and its control over behavior during early Pavlovian learning.

Effects of pituitary adenylate cyclase-activating polypeptide isoforms in nucleus accumbens subregions on ethanol drinking.

While limited research has implicated the neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), in problematic alcohol use, the brain regions and isoforms involved in this effect remain to be determined. One region that has been found both to exhibit PACAP binding and, separately, to be involved in ethanol drinking is the nucleus accumbens (NAc). Thus, this study sought to characterize the effect of the PACAP isoforms in the NAc on ethanol drinking under the intermittent-access two-bottle-choice paradigm, in male and female Long-Evans rats. With microinjection into the medial NAc shell, PACAP-27 but not PACAP-38 was found to dose-dependently reduce binge-like ethanol drinking. In contrast, the PACAP receptor antagonist, PACAP (6-27), but not PACAP (6-38), enhanced ethanol drinking. This effect of PACAP was substance specific, as neither isoform in the NAc shell affected binge-like sucrose drinking. It was also anatomically specific, as PACAP-38 rather than PACAP-27 suppressed ethanol drinking when injected into the NAc core, and PACAP-27 instead enhanced drinking when injected into the caudal third of the medial NAc shell. Finally, while PACAP-38 in the NAc shell affected stress-related exploratory behavior, reducing time spent in the light chamber of a light-dark box, PACAP-27 did not significantly affect behavior in a light-dark box or open field. Together, these results, showing that PACAP-27 in the NAc shell attenuates binge-like ethanol drinking without affecting select stress-related behaviors, suggest that compounds related to this PACAP isoform should be investigated as potential novel therapeutics for the treatment of alcohol use disorder.

Roles of dopamine and glutamate co-release in the nucleus accumbens in mediating the actions of drugs of abuse.

Projections of ventral tegmental area dopamine (DA) neurons to the medial shell of the nucleus accumbens have been increasingly implicated as integral to the behavioral and physiological changes involved in the development of substance use disorders (SUDs). Recently, many of these nucleus accumbens-projecting DA neurons were found to also release the neurotransmitter glutamate. This glutamate co-release from DA neurons is critical in mediating the effect of drugs of abuse on addiction-related behaviors. Potential mechanisms underlying the role(s) of dopamine/glutamate co-release in contributing to SUDs are unclear. Nevertheless, an important clue may relate to glutamate's ability to potentiate loading of DA into synaptic vesicles within terminals in the nucleus accumbens in response to drug-induced elevations in neuronal activity, enabling a more robust release of DA after stimulation. Here, we summarize how drugs of abuse, particularly cocaine, opioids, and alcohol, alter DA release in the nucleus accumbens medial shell, examine the potential role of DA/glutamate co-release in mediating these effects, and discuss future directions for further investigating these mechanisms.

Cooperative synaptic and intrinsic plasticity in a disynaptic limbic circuit drive stress-induced anhedonia and passive coping in mice

Stress promotes negative affective states, which include anhedonia and passive coping. While these features are in part mediated by neuroadaptations in brain reward circuitry, a comprehensive framework of how stress-induced negative affect may be encoded within key nodes of this circuit is lacking. Here, we show in a mouse model for stress-induced anhedonia and passive coping that these phenomena are associated with increased synaptic strength of ventral hippocampus (VH) excitatory synapses onto D1 medium spiny neurons (D1-MSNs) in the nucleus accumbens medial shell (NAcmSh), and with lateral hypothalamus (LH)-projecting D1-MSN hyperexcitability mediated by decreased inwardly rectifying potassium channel (IRK) function. Stress-induced negative affective states are prevented by depotentiation of VH to NAcmSh synapses, restoring Kir2.1 function in D1R-MSNs, or disrupting co-participation of these synaptic and intrinsic adaptations in D1-MSNs. In conclusion, our data provide strong evidence for a disynaptic pathway controlling maladaptive emotional behavior.

Desire or Dread from Nucleus Accumbens Inhibitions: Reversed by Same-Site Optogenetic Excitations.

Microinjections of a glutamate AMPA antagonist (DNQX) in medial shell of nucleus accumbens (NAc) can cause either intense appetitive motivation (i.e., 'desire') or intense defensive motivation (i.e., 'dread'), depending on site along a flexible rostrocaudal gradient and on environmental ambience. DNQX, by blocking excitatory AMPA glutamate inputs, is hypothesized to produce relative inhibitions of NAc neurons. However, given potential alternative explanations, it is not known whether neuronal inhibition is in fact necessary for NAc DNQX microinjections to generate motivations. Here we provide a direct test of whether local neuronal inhibition in NAc is necessary for DNQX microinjections to produce either desire or dread. We used optogenetic channelrhodopsin (ChR2) excitations at the same local sites in NAc as DNQX microinjections to oppose relative neuronal inhibitions induced by DNQX in female and male rats. We found that same-site ChR2 excitation effectively reversed the ability of NAc DNQX microinjections to generate appetitive motivation, and similarly reversed ability of DNQX microinjections to generate defensive motivation. Same-site NAc optogenetic excitations also attenuated recruitment of Fos expression in other limbic structures throughout the brain, which was otherwise elevated by NAc DNQX microinjections that generated motivation. However, to successfully reverse motivation generation, an optic fiber tip for ChR2 illumination needed to be located within <1 mm of the corresponding DNQX microinjector tip; that is, both truly at the same NAc site. Thus, we confirm that localized NAc neuronal inhibition is required for AMPA-blocking microinjections in medial shell to induce either positively-valenced 'desire' or negatively-valenced 'dread'.SIGNIFICANCE STATEMENT A major hypothesis posits neuronal inhibitions in nucleus accumbens generate intense motivation. Microinjections in nucleus accumbens of glutamate antagonist, DNQX, which might suppress local neuronal firing, generate either appetitive or defensive motivation, depending on site and environmental factors. Is neuronal inhibition in nucleus accumbens required for such pharmacologically-induced motivations? Here we demonstrate that neuronal inhibition is necessary to generate appetitive or defensive motivations, using local optogenetic excitations to oppose putative DNQX-induced inhibitions. We show that excitation at the same site prevents DNQX microinjections from recruiting downstream limbic structures into neurobiological activation, and simultaneously prevents generation of either appetitive or defensive motivated behaviors. These results may be relevant to roles of nucleus accumbens mechanisms in pathological motivations, including addiction and paranoia.