Role of dopamine receptors subtypes, D1-like and D2-like, within the nucleus accumbens subregions, core and shell, on memory consolidation in the one-trial inhibitory avoidance task

The dose-dependent effect of the D2R agonist quinpirole microinjected into the ventral pallidum on information flow in the limbic system

The ventral pallidum (VP) receives its primary inputs from the nucleus accumbens (NAC) and the basolateral amygdala (BLA). We demonstrated recently that in the VP, the D2 DA receptor (D2R) agonist quinpirole dose-dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. In the VP, D2R can be found both on NAC and BLA terminals. According to our hypothesis, quinpirole microinjected into the VP can facilitate memory consolidation via modulation of synaptic plasticity on NAC and/or BLA terminals. The effect of intra-VP quinpirole on BLA-VP and NAC shell-VP synapses was investigated via a high frequency stimulation (HFS) protocol. Quinpirole was administered in three doses into the VP of male Sprague-Dawley rats after HFS; controls received vehicle. To examine whether an interaction between the NAC shell and the BLA at the level of the VP was involved, tetrodotoxin (TTX) was microinjected into one of the nuclei while stimulating the other nucleus. Our results showed that quinpirole dose-dependently modulates BLA-VP and NAC shell-VP synapses, similar to those observed in inhibitory avoidance and spatial learning, respectively. The lower dose inhibits BLA inputs, while the larger doses facilitates NAC shell inputs. The experiments with TTX demonstrates that the two nuclei do not influence each others' evoked responses in the VP. Power spectral density analysis demonstrated that independent from the synaptic facilitation, intra-VP quinpirole increases the amplitude of gamma frequency band after NAC HFS, and BLA tonically suppresses the NAC's HFS-induced gamma facilitation. In contrast, HFS of the BLA results in a delayed, transient increase in the amplitude of the gamma frequency band correlating with the LTP of the P1 component of the VP response to BLA stimulation. Furthermore, our results demonstrate that the BLA plays a prominent role in the generation of the delta oscillations: HFS of the BLA leads to a gradually increasing delta frequency band facilitation over time, while BLA inhibition blocks the NAC's HFS induced strong delta facilitation. These findings demonstrate that there is a complex interaction between the NAC shell region and the VP, as well as the BLA and the VP, and support the important role of VP D2Rs in the regulation of limbic information flow.

No evidence that post-training dopamine D2 receptor agonism affects fear generalization in male rats

BACKGROUND

The neurotransmitter dopamine plays an important role in the processing of emotional memories, and prior research suggests that dopaminergic manipulations immediately after fear learning can affect the retention and generalization of acquired fear.

AIMS

The current study focuses specifically on the role of dopamine D2 receptors (D2Rs) regarding fear generalization in adult, male Wistar rats, and aims to replicate previous findings in mice.

METHODS

In a series of five experiments, D2R (ant)agonists were injected systemically, immediately after differential cued fear conditioning (CS+ followed by shock, CS- without shock). All five experiments involved the administration of the D2R agonist quinpirole at different doses versus saline (n = 12, 16, or 44 rats/group). In addition, one of the studies administered the D2R antagonist raclopride (n = 12). One day later, freezing during the CS+ and CS- was assessed.

RESULTS

We found no indications for an effect of quinpirole or raclopride on fear generalization during this drug-free test. Importantly, and contradicting earlier research in mice, the evidence for the absence of an effect of D2R agonist quinpirole (1 mg/kg) on fear generalization was substantial according to Bayesian analyses and was observed in a highly powered experiment (N = 87). We did find acute behavioral effects in line with the literature, for both quinpirole and raclopride in a locomotor activity test.

CONCLUSION

In contrast with prior studies in mice, we have obtained evidence against a preventative effect of post-training D2R agonist quinpirole administration on subsequent fear generalization in rats.

Region-specific activation in the accumbens nucleus by itch with modified scratch efficacy in mice - a model-free multivariate analysis

Itch is a protective/defensive function with divalent motivational drives. Itch itself elicits an unpleasant experience, which triggers the urge to scratch, relieving the itchiness. Still, it can also result in dissatisfaction when the scratch is too intense and painful or unsatisfactory due to insufficient scratch effect. Therefore, it is likely that the balance between the unpleasantness/pleasure and satisfaction/unsatisfaction associated with itch sensation and scratching behavior is determined by complex brain mechanisms. The physiological/pathological mechanisms underlying this balance remain largely elusive. To address this issue, we targeted the "reward center" of the brain, the nucleus accumbens (NAc), in which itch-responsive neurons have been found in rodents. We examined how neurons in the NAc are activated or suppressed during histamine-induced scratching behaviors in mice. The mice received an intradermal injection of histamine or saline at the neck, and the scratching number was analyzed by recording the movement of the bilateral hind limbs for about 45 min after injection. To experimentally manipulate the scratch efficacy in these histamine models, we compared histamine's behavioral and neuronal effects between mice with intact and clipped nails on the hind paws. As expected, the clipping of the hind limb nail increased the number of scratches after the histamine injection. In the brains of mice exhibiting scratching behaviors, we analyzed the expression of the c-fos gene (Fos) as a readout of an immediate activation of neurons during itch/scratch and dopamine receptors (Drd1 and Drd2) using multiplex single-molecule fluorescence in situ hybridization (RNAscope) in the NAc and surrounding structures. We performed a model-free analysis of gene expression in geometrically divided NAc subregions without assuming the conventional core-shell divisions. The results indicated that even within the NAc, multiple subregions responded differentially to various itch/scratch conditions. We also found different clusters with neurons showing similar or opposite changes in Fos expression and the correlation between scratch number and Fos expression in different itch/scratch conditions. These regional differences and clusters would provide a basis for the complex role of the NAc and surrounding structures in encoding the outcomes of scratching behavior and itchy sensations.

Role of dopamine D1 receptor in the modulation of memory consolidation by passive and self-administered heroin and associated conditioned stimuli

It has been proposed that opiates modulate memory consolidation, but recent work has indicated that this effect may be mediated by how the drug is experienced (i.e., passive injections vs. self-administration). Because the dopamine (DA) D1 receptor is involved in processing of learning signals and attribution of salience to events experienced by an organism, two studies in male Sprague-Dawley rats tested the effect of blocking this receptor on modulation of memory consolidation by passive and self-administered heroin, in addition to conditioned memory modulation by heroin-paired cues. Using the object location memory task, Study 1 employed SCH23390 (0, 0.05, 0.10 mg/kg, SC) to modulate enhancement of memory consolidation induced by post-training injections of heroin (1 mg/kg, SC) as well as by exposure to the environment paired with heroin injections (6 pairings, 1 h each, 1 mg/kg). Study 2 was conducted in rats that could self-administer heroin (0.05 mg/kg/infusion, IV) and tested whether SCH23390 (0 and 0.1 mg/kg, SC) could prevent memory modulation induced by a change in schedule of self-administration (from fixed to variable ratio). It was found that while repeated passive injections of heroin retained their enhancing effect on memory, when self-administered, heroin enhanced consolidation of object location memory only at the beginning of self-administration and after a change in schedule. Importantly, SCH23390 blocked memory modulation by heroin when passively administered and when the drug was self-administered on a novel schedule. SCH23390 also blocked conditioned memory modulation induced by post-training exposure to heroin-paired cues. Taken together, these results suggest that modulation of memory consolidation by unconditioned and conditioned opiate reinforcers involve a D1-dependent mechanism of salience attribution linked to the anticipation of drug effects.

Enhancement of memory consolidation by an avoidance conditioned stimulus: Modulation by the D3 receptor

Conditioned stimuli (CS) paired with foot-shock can enhance memory consolidation. Because the dopamine D3R has been implicated in mediating various responses to CSs, the current study explored its potential role in modulation of memory consolidation by an avoidance CS. Male Sprague-Dawley rats trained to avoid foot-shocks in a two-way signalled active avoidance task (8 sessions, 30 trials per session, 0.8 mA foot-shock) were pre-treated with the D3R antagonist NGB-2904 (Vehicle, 0.1 or 5 mg/kg) and exposed to the CS immediately after the sample phase of an object recognition memory task. Discrimination ratios were assessed 72 h later. Immediate, but not delayed (6 h), post-sample exposure to the CS enhanced object recognition memory and this effect was dose-dependently blocked by NGB-2904. Control experiments with the beta-noradrenergic receptor antagonist propranolol (10 or 20 mg/kg) and D2R antagonist pimozide (0.2 or 0.6 mg/kg) indicated that NGB-2904 targeted post-training memory consolidation. Exploring the pharmacological selectivity of the D3R effect, it was found that: 1) 5 mg/kg NGB-2904 blocked conditioned memory modulation produced by post-sample exposure to a "weak" CS (one day of avoidance training) and concurrent stimulation of catecholamine activity by 10 mg/kg bupropion; 2) post-sample exposure to a "weak" CS and concurrent administration of the D3R agonist 7-OH-DPAT (1 mg/kg) enhanced consolidation of object memory. Finally, because 5 mg/kg NGB-2904 had no effect on modulation by avoidance training in the presence of foot-shocks, the findings herein support the hypothesis that the D3R plays an important role in modulation of memory consolidation by CSs.

Extended amygdala, conditioned withdrawal and memory consolidation

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

Maternal Morphine Exposure and Post-Weaning Social Isolation Impair Memory and Ventral Striatum Dopamine System in Male Offspring: Is an Enriched Environment Beneficial?

Maternal opioids abuse has some deleterious consequences on next generations. Besides, children's rearing conditions can affect the behavioral states and brain plasticity in their later life. In the present study, we investigated the effects of maternal morphine (MOR) treatment and post-weaning rearing conditions on memory, pain threshold, and the ventral striatum dopaminergic activity in male offspring. Female Wistar rats were treated twice daily either with escalating doses of MOR or with normal saline (NS) one week before mating, during pregnancy and lactation. After weaning, the male pups were assigned to six groups and then raised for an 8-week period under three different conditions: standard (STD), isolated (ISO) or enriched environment (EE). The behavioral tests, including passive avoidance task, novel object recognition, and tail-flick test, were also performed. Moreover, the ventral striatum dopamine's content (DA), mRNA expressions of dopamine receptor 1(D1R) and dopamine receptor 2 (D2R), and dopamine transporter (DAT) were evaluated. The obtained data showed that maternal MOR exposure and post-weaning social isolation could dramatically impair memory in offspring, while EE could reverse these adverse outcomes. Moreover, results of tail flick latency indicated the increased pain threshold in EE animals. At molecular level, maternal MOR injections and social isolation reduced DA levels and altered expressions of D1R, D2R, and DAT within the ventral striatum of these male offspring. However, post-weaning EE partially buffered these changes. Our finding signified the effects of maternal MOR exposure and social isolation on the behaviors and neurochemistry of brain in next generation, and it also provided evidence on reversibility of these alterations following EE.

Analysis of memory modulation by conditioned stimuli

Conditioned stimuli (CS) have multiple psychological functions that can potentially contribute to their effect on memory formation. It is generally believed that CS-induced memory modulation is primarily due to conditioned emotional responses, however, well-learned CSs not only generate the appropriate behavioral and physiological reactions required to best respond to an upcoming unconditioned stimulus (US), but they also serve as signals that the US is about to occur. Therefore, it is possible that CSs can impact memory consolidation even when their ability to elicit conditioned emotional arousal is significantly reduced. To test this, male Sprague–Dawley rats trained on a signaled active avoidance task were divided into “Avoider” and “Non-Avoider” subgroups on the basis of percentage avoidance after 6 d of training. Subgroup differences in responding to the CS complex were maintained during a test carried out in the absence of the US. Moreover, the subgroups displayed significant differences in stress-induced analgesia (hot-plate test) immediately after this test, suggesting significant subgroup differences in conditioned emotionality. Importantly, using the spontaneous object recognition task, it was found that immediate post-sample exposure to the avoidance CS complex had a similar enhancing effect on object memory in the two subgroups. Therefore, to our knowledge, this is the first study to demonstrate that a significant conditioned emotional response is not necessary for the action of a predictive CS on modulation of memory consolidation.

Nucleus accumbens volume as a predictor of anxiety symptom improvement following CBT and SSRI treatment in two independent samples

Structural variations of neural regions implicated in fear responses have been well documented in the pathophysiology of anxiety and may play an important role in treatment response. We examined whether gray matter volume of three neural regions supporting fear and avoidance responses [bilateral amygdala, nucleus accumbens (NAcc), and ventromedial prefrontal cortex (PFC)] predicted cognitive-behavioral therapy (CBT) and selective serotonin reuptake inhibitor (SSRI) treatment outcome in two independent samples of patients with anxiety disorders. Study 1 consisted of 81 adults with anxiety disorders and Study 2 included 55 children and adolescents with anxiety disorders. In both studies, patients completed baseline structural MRI scans and received either CBT or SSRI treatment. Clinician-rated interviews of anxiety symptoms were assessed at baseline and posttreatment. Among the adult sample, greater pre-treatment bilateral NAcc volume was associated with a greater reduction in clinician-rated anxiety symptoms pre-to-post CBT and SSRI treatment. Greater left NAcc volume also predicted greater decreases in clinician-rated anxiety symptoms pre-to-post CBT and SSRI treatment among youth with current anxiety. Across studies, results were similar across treatments, and findings were maintained when adjusting for patient's age, sex, and total intracranial brain volume. We found no evidence for baseline amygdala or ventromedial PFC volume serving as treatment predictors across the two samples. Together, these findings provide promising support for the role of NAcc volume as an objective marker of anxiety treatment improvement that spans across development. Future studies should clarify the specific mechanisms through which NAcc volume exerts its therapeutic effects.

Cell-type and projection-specific dopaminergic encoding of aversive stimuli in addiction

Drug addiction is a major public health concern across the world for which there are limited treatment options. In order to develop new therapies to correct the behavioral deficits that result from repeated drug use, we need to understand the neural circuit dysfunction that underlies the pathophysiology of the disorder. Because the initial reinforcing effects of drugs are dependent on increases in dopamine in reward-related brain regions such as the mesolimbic dopamine pathway, a large focus of addiction research has centered on the dysregulation of this system and its control of positive reinforcement and motivation. However, in addition to the processing of positive, rewarding stimuli, there are clear deficits in the encoding and valuation of information about potential negative outcomes and how they control decision making and motivation. Further, aversive stimuli can motivate or suppress behavior depending on the context in which they are encountered. We propose a model where rewarding and aversive information guides the execution of specific motivated actions through mesocortical and mesolimbic dopamine acting on D1- and D2- receptor containing neuronal populations. Volitional drug exposure alters the processing of rewarding and aversive stimuli through remodeling of these dopaminergic circuits, causing maladaptive drug seeking, self-administration in the face of negative consequences, and drug craving. Together, this review discusses the dysfunction of the circuits controlling different types of aversive learning as well as how these guide specific discrete behaviors, and provides a conceptual framework for how they should be considered in preclinical addiction models.

Effects of pharmacological inhibition of dopamine receptors on memory load capacity

Memory capacity (MC) refers to the limited capacity of working memory and is defined as the number of elements that an individual can remember for a short retention interval. MC is impaired in many human pathologies, such as schizophrenia and ageing. Fronto-striatal dopamine regulates working memory, through its action on dopamine D1- and D2-like receptors. Human and rodent studies have suggested that MC is improved by D2 dopamine receptor agonists. Although D1 receptors have been crucially involved in the maintenance of working memory during delay, their role in regulating the capacity of WM remains poorly explored. In this study, we tested the effects of systemic injection of the D1-like and D2-like receptor antagonists, SCH 23390 and Haloperidol respectively, on MC in mice. For this, we used a modified version of the object recognition task, the Different/Identical Objects Task (DOT/IOT), which allows the evaluation of MC in rodents. The results showed a negative interaction between the dose of both drugs and the number of objects that could be remembered. The doses of SCH 23390 and Haloperidol that impaired novel object discrimination in the highest memory load condition were about 4 and 3 time lower, respectively, of those impairing performance in the lowest memory load condition. However, while SCH 23390 specifically impaired memory load capacity, the effects of Haloperidol were associated to impairment in exploratory behaviors. These findings may help to predict the cognitive side effects induced by Haloperidol in healthy subjects.

Dissociable roles of the nucleus accumbens D1 and D2 receptors in regulating cue-elicited approach-avoidance conflict decision-making

RATIONALE

Approach and avoidance decisions are made when an animal experiences a state of motivational conflict inflicted by stimuli imbued with both positive and negative valences. The nucleus accumbens (NAc), a site where valenced information and action selection converge, has recently been found to be critically involved in the resolution of approach-avoidance conflict. However, the individual roles of the region's dopamine receptor D1 (D1R)- and D2 (D2R)-expressing medium spiny neurons (MSNs) in regulating conflict resolution have not been well established.

OBJECTIVES

Here, we examined the roles of NAc D1R and D2R in cue-elicited approach-avoidance decision-making.

METHODS

Using a conditioned mixed-valence conflict paradigm, rats were initially trained in a radial maze to associate separate visuotactile cues with sucrose reward, foot shock punishment, and no outcome. Following acquisition of the cue-outcome associations, rats were subjected to a conditioned approach-avoidance conflict scenario, in which they were presented with a maze arm containing a superimposition of the reward and punishment cues, and another arm containing neutral cues.

RESULTS

Post-training intra-NAc D1R antagonism (SCH23390) led to an avoidance of the arm containing the mixed-valence cue over the neutral arm, whereas intra-NAc D2R antagonism (sulpiride) resulted in rats exhibiting a preference for the mixed-valence arm.

CONCLUSION

Our results suggest that NAc D1R and D2R exert differential control over decision-making involving cue-elicited approach-avoidance conflict resolution.

Identification of 5-(1-Methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl)thiophene-2-Carboxamides as Novel and Selective Monoamine Oxidase B Inhibitors Used to Improve Memory and Cognition

Initial work in Drosophila and mice demonstrated that the transcription factor cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) is a master control gene for memory formation. The relationship between CREB and memory has also been found to be true in other species, including aplysia and rats. It is thus well-established that CREB activation plays a central role in memory enhancement and that CREB is activated during memory formation. On the basis of these findings, a phenotypic high-throughput screening campaign utilizing a CRE-luciferase (CRE-Luci) SK-N-MC cell line was performed to identify compounds that enhance transcriptional activation of the CRE promoter with a suboptimal dose of forskolin. A number of small-molecule hits of unknown mechanisms of action were identified in the screening campaign, including HT-0411. Follow-up studies suggested that the CREB activation by HT-0411 is attributed to its specific and selective inhibition of monoamine oxidase B (MAO-B). Further, HT-0411 was shown to improve 24 h memory in rodents in a contextual fear conditioning model. This report describes the lead optimization of a series of 5-(1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl) thiophene-2-carboxamides that were identified as novel, potent, and selective inhibitors of MAO-B. Extensive SAR studies and in vivo behavioral evaluations of this and other related analogue series identified a number of potential clinical development candidates; ultimately, compound 8f was identified as a candidate molecule with high selectivity toward MAO-B (29-56 nM) over MAO-A (19% inhibition at a screening concentration of 50 μM), an excellent profile against a panel of other enzymes and receptors, good pharmacokinetic properties in rodents and dogs, and efficacy in multiple rodent memory models.

Stress-Induced Reduction of Dorsal Striatal D2 Dopamine Receptors Prevents Retention of a Newly Acquired Adaptive Coping Strategy

The inability to learn an adaptive coping strategy in a novel stressful condition leads to dysfunctional stress coping, a marker of mental disturbances. This study tested the involvement of dorsal striatal dopamine receptors in the dysfunctional coping with the Forced Swim test fostered by a previous experience of reduced food availability. Adult male mice were submitted to a temporary (12 days) reduction of food availability [food-restricted (FR)] or continuously free-fed (FF). Different groups of FF and FR mice were used to evaluate: (1) dorsal striatal mRNA levels of the two isoforms of the dopamine D2 receptor (D2S, D2L). (2) Forced Swim-induced c-fos expression in the dorsal striatum; (3) acquisition and 24 h retention of passive coping with Forced Swim. Additional groups of FF mice were tested for 24 h retention of passive coping acquired during a first experience with Forced Swim immediately followed by intra-striatal infusion of vehicle or two doses of the dopamine D2/D3 receptors antagonist sulpiride or the D1/D5 receptors antagonist SCH23390. Previous restricted feeding selectively reduced mRNA levels of both D2 isoforms and abolished Forced Swim-induced c-fos expression in the left Dorsolateral Striatum and selectively prevented 24 h retention of the coping strategy acquired in a first experience of Forced Swim. Finally, temporary blockade of left Dorsolateral Striatum D2/D3 receptors immediately following the first Forced Swim experience selectively reproduced the behavioral effect of restricted feeding in FF mice. In conclusion, the present results demonstrate that mice previously exposed to a temporary reduction of food availability show low striatal D2 receptors, a known marker of addiction-associated aberrant neuroplasticity, as well as liability to relapse into maladaptive stress coping strategies. Moreover, they offer strong support to a causal relationship between reduction of D2 receptors in the left Dorsolateral Striatum and impaired consolidation of newly acquired adaptive coping.

Partial lesion of dopamine neurons of rat substantia nigra impairs conditioned place aversion but spares conditioned place preference

Midbrain dopamine neurons play critical roles in reward- and aversion-driven associative learning. However, it is not clear whether they do this by a common mechanism or by separate mechanisms that can be dissociated. In the present study we addressed this question by testing whether a partial lesion of the dopamine neurons of the rat SNc has comparable effects on conditioned place preference (CPP) learning and conditioned place aversion (CPA) learning. Partial lesions of dopamine neurons in the rat substantia nigra pars compacta (SNc) induced by bilateral intranigral infusion of 6-hydroxydopamine (6-OHDA, 3μg/side) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 200μg/side) impaired learning of conditioned place aversion (CPA) without affecting conditioned place preference (CPP) learning. Control experiments demonstrated that these lesions did not impair motor performance and did not alter the hedonic value of the sucrose and quinine. The number of dopamine neurons in the caudal part of the SNc positively correlated with the CPP scores of the 6-OHDA rats and negatively correlated with CPA scores of the SHAM rats. In addition, the CPA scores of the 6-OHDA rats positively correlated with the tissue content of striatal dopamine. Insomuch as reward-driven learning depends on an increase in dopamine release by nigral neurons, these findings show that this mechanism is functional even in rats with a partial lesion of the SNc. On the other hand, if aversion-driven learning depends on a reduction of extracellular dopamine in the striatum, the present study suggests that this mechanism is no longer functional after the partial SNc lesion.

Dopamine D2 receptors gate generalization of conditioned threat responses through mTORC1 signaling in the extended amygdala

Overgeneralization of conditioned threat responses is a robust clinical marker of anxiety disorders. In overgeneralization, responses that are appropriate to threat-predicting cues are evoked by perceptually similar safety-predicting cues. Inappropriate learning of conditioned threat responses may thus form an etiological basis for anxiety disorders. The role of dopamine (DA) in memory encoding is well established. Indeed by signaling salience and valence, DA is thought to facilitate discriminative learning between stimuli representing safety or threat. However, the neuroanatomical and biochemical substrates through which DA modulates overgeneralization of threat responses remain poorly understood. Here we report that the modulation of DA D2 receptor (D2R) signaling bidirectionally regulates the consolidation of fear responses. While the blockade of D2R induces generalized threat responses, its stimulation facilitates discriminative learning between stimuli representing safety or threat. Moreover, we show that controlled threat generalization requires the coordinated activation of D2R in the bed nucleus of the stria terminalis and the central amygdala. Finally, we identify the mTORC1 cascade activation as an important molecular event by which D2R mediates its effects. These data reveal that D2R signaling in the extended amygdala constitutes an important checkpoint through which DA participates in the control of threat processing and the emergence of overgeneralized threat responses.

Candidate gene study reveals DRD1 and DRD2 as putative interacting risk factors for youth depression

Alterations in the monoaminergic neurotransmission systems are suspected to be involved in the etiology of neuropsychiatric disorders, including depression. The role of these pathways in the risk of developing depressive symptoms during childhood or adolescence is still not completely clear. This study sought to identify putative genetic factors in genes of serotonergic and dopaminergic systems modulating the level of manifestation of depressive symptoms in children and adolescents. We analyzed 170 single nucleotide polymorphisms (SNPs) in 21 candidate dopaminergic and serotonergic genes in a non-clinical sample of 410 Costa Rican participants of ages between 7 and 18 years, assessing the severity of depressive symptoms through the Child Depression Inventory (CDI). Genotypic and haplotypic associations, as well as epistatic effects, were examined. A significant interaction effect was detected between rs1039089 in conjunction with rs877138 located upstream of the dopamine D1 receptor (DRD1) and the dopamine D2 receptor (DRD2) genes respectively, although no evidence was found for any single variant or haplotype related to a differential liability. This newly described genetic interaction among putative regulatory regions of dopamine receptors could affect the level of manifestation of depressive symptoms through an imbalance of D1-D2 heteromers and modulation of cognitive processes.

Nucleus Accumbens Shell and mPFC but Not Insula Orexin-1 Receptors Promote Excessive Alcohol Drinking

Addiction to alcohol remains a major social and economic problem, in part because of the high motivation for alcohol that humans exhibit and the hazardous binge intake this promotes. Orexin-1-type receptors (OX1Rs) promote reward intake under conditions of strong drives for reward, including excessive alcohol intake. While systemic modulation of OX1Rs can alter alcohol drinking, the brain regions that mediate this OX1R enhancement of excessive drinking remain unknown. Given the importance of the nucleus accumbens (NAc) and anterior insular cortex (aINS) in driving many addictive behaviors, including OX1Rs within these regions, we examined the importance of OX1Rs in these regions on excessive alcohol drinking in C57BL/6 mice during limited-access alcohol drinking in the dark cycle. Inhibition of OX1Rs with the widely used SB-334867 within the medial NAc Shell (mNAsh) significantly reduced drinking of alcohol, with no effect on saccharin intake, and no effect on alcohol consumption when infused above the mNAsh. In contrast, intra-mNAsh infusion of the orexin-2 receptor TCS-OX2-29 had no impact on alcohol drinking. In addition, OX1R inhibition within the aINS had no effect on excessive drinking, which was surprising given the importance of aINS-NAc circuits in promoting alcohol consumption and the role for aINS OX1Rs in driving nicotine intake. However, OX1R inhibition within the mPFC did reduce alcohol drinking, indicating cortical OXR involvement in promoting intake. Also, in support of the critical role for mNAsh OX1Rs, SB within the mNAsh also significantly reduced operant alcohol self-administration in rats. Finally, orexin ex vivo enhanced firing in mNAsh neurons from alcohol-drinking mice, with no effect on evoked EPSCs or input resistance; a similar orexin increase in firing without a change in input resistance was observed in alcohol-naïve mice. Taken together, our results suggest that OX1Rs within the mNAsh and mPFC, but not the aINS, play a central role in driving excessive alcohol drinking.

Reappraising striatal D1- and D2-neurons in reward and aversion

The striatum has been involved in complex behaviors such as motor control, learning, decision-making, reward and aversion. The striatum is mainly composed of medium spiny neurons (MSNs), typically divided into those expressing dopamine receptor D1, forming the so-called direct pathway, and those expressing D2 receptor (indirect pathway). For decades it has been proposed that these two populations exhibit opposing control over motor output, and recently, the same dichotomy has been proposed for valenced behaviors. Whereas D1-MSNs mediate reinforcement and reward, D2-MSNs have been associated with punishment and aversion. In this review we will discuss pharmacological, genetic and optogenetic studies that indicate that there is still controversy to what concerns the role of striatal D1- and D2-MSNs in this type of behaviors, highlighting the need to reconsider the early view that they mediate solely opposing aspects of valenced behaviour.

Fornix deep brain stimulation circuit effect is dependent on major excitatory transmission via the nucleus accumbens

INTRODUCTION

Deep brain stimulation (DBS) is a circuit-based treatment shown to relieve symptoms from multiple neurologic and neuropsychiatric disorders. In order to treat the memory deficit associated with Alzheimer's disease (AD), several clinical trials have tested the efficacy of DBS near the fornix. Early results from these studies indicated that patients who received fornix DBS experienced an improvement in memory and quality of life, yet the mechanisms behind this effect remain controversial. It is known that transmission between the medial limbic and corticolimbic circuits plays an integral role in declarative memory, and dysfunction at the circuit level results in various forms of dementia, including AD. Here, we aimed to determine the potential underlying mechanism of fornix DBS by examining the functional circuitry and brain structures engaged by fornix DBS.

METHODS

A multimodal approach was employed to examine global and local temporal changes that occur in an anesthetized swine model of fornix DBS. Changes in global functional activity were measured by functional MRI (fMRI), and local neurochemical changes were monitored by fast scan cyclic voltammetry (FSCV) during electrical stimulation of the fornix. Additionally, intracranial microinfusions into the nucleus accumbens (NAc) were performed to investigate the global activity changes that occur with dopamine and glutamate receptor-specific antagonism.

RESULTS

Hemodynamic responses in both medial limbic and corticolimbic circuits measured by fMRI were induced by fornix DBS. Additionally, fornix DBS resulted in increases in dopamine oxidation current (corresponding to dopamine efflux) monitored by FSCV in the NAc. Finally, fornix DBS-evoked hemodynamic responses in the amygdala and hippocampus decreased following dopamine and glutamate receptor antagonism in the NAc.

CONCLUSIONS

The present findings suggest that fornix DBS modulates dopamine release on presynaptic dopaminergic terminals in the NAc, involving excitatory glutamatergic input, and that the medial limbic and corticolimbic circuits interact in a functional loop.

Blocking Dopaminergic Signaling Soon after Learning Impairs Memory Consolidation in Guinea Pigs

Formation of episodic memories (i.e. remembered experiences) requires a process called consolidation which involves communication between the neocortex and hippocampus. However, the neuromodulatory mechanisms underlying this neocortico-hippocampal communication are poorly understood. Here, we examined the involvement of dopamine D1 receptors (D1R) and D2 receptors (D2R) mediated signaling on memory consolidation using the Novel Object Recognition (NOR) test. We conducted the tests in male Hartley guinea pigs and cognitive behaviors were assessed in customized Phenotyper home cages utilizing Ethovision XT software from Noldus enabled for the 3-point detection system (nose, center of the body, and rear). We found that acute intraperitoneal injections of either 0.25 mg/kg SCH23390 to block D1Rs or 1.0 mg/kg sulpiride to block D2Rs soon after acquisition (which involved familiarization to two similar objects) attenuated subsequent discrimination for novel objects when tested after 5-hours in the NOR test. By contrast guinea pigs treated with saline showed robust discrimination for novel objects indicating normal operational processes undergirding memory consolidation. The data suggests that involvement of dopaminergic signaling is a key post-acquisition factor in modulating memory consolidation in guinea pigs.

Reduced cortical neurotransmitter receptor complex levels in fetal Down syndrome brain

In this study, cortical receptor complex levels were determined in fetal Down syndrome (DS, trisomy 21) brain. Frontal cortices were obtained from individuals with DS (19th-22nd week of gestation) and controls. Membrane proteins were extracted, assayed on blue native gels and immunoblotted with brain receptor antibodies. Levels of a D1R-containing complex were markedly decreased in male and female cortices of DS individuals. Females with DS had significant reductions of nicotinic acetylcholine receptors α4 and α7, NMDA receptor GluN1 and AMPA receptor GluA1- and GluA3-containing receptor complexes. Levels of other brain receptor complexes (5-hydroxytryptamine 1A, GluA2 and GluR4 receptor-containing complexes) were comparable between the groups of females. Levels of GluA2- and GluA3-containing complexes were significantly increased in males. Decreased levels of D1R complexes in both sexes, along with the significant reduction of α4, α7-containing receptor complexes observed in females, may explain the brain deficits and impaired cognition observed in DS.

Toward sophisticated basal ganglia neuromodulation: Review on basal ganglia deep brain stimulation

This review presents state-of-the-art knowledge about the roles of the basal ganglia (BG) in action-selection, cognition, and motivation, and how this knowledge has been used to improve deep brain stimulation (DBS) treatment of neurological and psychiatric disorders. Such pathological conditions include Parkinson's disease, Huntington's disease, Tourette syndrome, depression, and obsessive-compulsive disorder. The first section presents evidence supporting current hypotheses of how the cortico-BG circuitry works to select motor and emotional actions, and how defects in this circuitry can cause symptoms of the BG diseases. Emphasis is given to the role of striatal dopamine on motor performance, motivated behaviors and learning of procedural memories. Next, the use of cutting-edge electrochemical techniques in animal and human studies of BG functioning under normal and disease conditions is discussed. Finally, functional neuroimaging studies are reviewed; these works have shown the relationship between cortico-BG structures activated during DBS and improvement of disease symptoms.

Positive emotional arousal increases duration of memory traces: different role of dopamine D1 receptor and β-adrenoceptor activation

We investigated the effects of post-training administration of dopamine D1 receptor antagonist SCH 23390 and β-adrenergic receptor antagonist Propranolol on memory retention of an object sampled in a state of positive emotional arousal. Saline-treated mice trained and tested under high emotional/motivational arousal (High) showed discrimination of a novel object both 24 and 96 h post-training. Instead, mice trained and tested under low motivational arousal (Low) were unable to discriminate the novel object 96 h post-training. Both a high (2 mg/kg) and a low (1 mg/kg) dose of Propranolol reduced object discrimination in High mice tested 24 h post-training, whereas neither dose was effective in Low mice. A high dose of SCH 23390 (0.025 mg/kg) reduced discrimination of the novel object in High mice tested both 24 and 96 h post-training, whereas a low dose of the D1 antagonist (0.01 mg/kg) reduced discrimination in High mice tested 96 h post-training and abolished discrimination in Low mice tested 24h after training.

Learning induced epigenetic modifications in the ventral striatum are necessary for long-term memory

Epigenetic modifications such as histone acetylation in cortical or allocortical regions have been shown to be necessary for the formation of long-term memories. Here we investigated whether similar changes were occurring also in the ventral striatum and whether they are necessary for the consolidation of aversive memory. To this purpose we performed immediate post-training focal administrations of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA, 5, 10 or 15 μg/side) or the DNA methyltransferase (DNMT) inhibitor, 5-aza-2'-deoxycytidine (5-AZA, 0.0625 or 0.125 μg/side) in the ventral striatum of mice trained in one-trial inhibitory avoidance task. Intra-ventral striatal SAHA administrations, immediately after training, improved memory retention. Opposite effects were found with 5-AZA. We also found that training in the one-trial inhibitory avoidance is accompanied by increased acetylation of specific residues that can be further increased by intra-VS SAHA administrations. Intra-VS 5-AZA administrations on the other hand reduced training-induced histones acetylation at the same residues. These findings imply the occurrence of histone acetylation in the ventral striatum in order to store aversive memory. Moreover, they suggest that the effects induced by the DNMT inhibitor 5-AZA may at least partially due to blockade of H3 and H4 acetylation. These results suggest that the contemporary activation of similar molecular mechanisms might be needed in different brain regions to enable the formation of long-term memories.

Impairing effect of amphetamine and concomitant ionotropic glutamate receptors blockade in the ventral striatum on spatial learning in mice

RATIONALE

Accumulating evidence supports the involvement of the ventral striatum (VS) in spatial information processing. The multiple cortical glutamatergic and mesolimbic dopaminergic (DAergic) afferences on the same neurons in the ventral striatum provide the neuroanatomical substrate for glutamate and dopamine functional interaction. However, there is little evidence in the literature on how this interaction affects the ability to encode spatial information.

OBJECTIVE

First, we evaluated the effect of intra-VS bilateral infusion of different doses of amphetamine (0.3, 0.75, and 1.5 μg/side) on the ability to detect spatial novelty in mice. Next, we examined the impact produced on the same abilities by intra-VS infusion of ineffective doses of amphetamine (0.3 μg/side) in association with N-methyl-D-aspartate (NMDA) (3.125 ng/side) or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) (0.25 ng/side) receptor antagonist.

RESULTS

The results show that infusion of amphetamine impairs detection of spatial novelty, affecting also exploratory activity and marginally the detection of nonspatial novelty. In contrast, an association of subthreshold doses of amphetamine with NMDA or AMPA receptor antagonists exerted a selective effect on reactivity to a spatial change.

CONCLUSIONS

These findings demonstrate that enhanced DAergic activity in the VS enhances glutamate receptor antagonist-induced impairment in learning and memory.

The evaluation of AZ66, an optimized sigma receptor antagonist, against methamphetamine-induced dopaminergic neurotoxicity and memory impairment in mice

Sigma (σ) receptors have recently been identified as potential targets for the development of novel therapeutics aimed at mitigating the effects of methamphetamine. Particularly, σ receptors are believed to mitigate some of the neurotoxic effects of methamphetamine through modulation of dopamine, dopamine transporters and body temperature. Furthermore, recent evidence suggests that targeting σ receptors may prevent cognitive impairments produced by methamphetamine. In the present study, an optimized σ receptor antagonist, AZ66, was evaluated against methamphetamine-induced neurotoxicity and cognitive dysfunction. AZ66 was found to be highly selective for σ receptors compared to 64 other sites tested. Pretreatment of male, Swiss Webster mice with i.p. dosing of AZ66 significantly attenuated methamphetamine-induced striatal dopamine depletions, striatal dopamine transporter reductions and hyperthermia. Additionally, neurotoxic dosing with methamphetamine caused significant memory impairment in the object recognition test, which was attenuated when animals were pretreated with AZ66; similar trends were observed in the step-through passive avoidance test. Taken together, these results suggest that targeting σ receptors may provide neuroprotection against the neurotoxicity and cognitive impairments produced by methamphetamine.

Dopaminergic Gene Polymorphisms Affect Long-term Forgetting in Old Age: Further Support for the Magnification Hypothesis

Emerging evidence from animal studies suggests that suboptimal dopamine (DA) modulation may be associated with increased forgetting of episodic information. Extending these observations, we investigated the influence of DA-relevant genes on forgetting in samples of younger (n = 433, 20–31 years) and older (n = 690, 59–71 years) adults. The effects of single nucleotide polymorphisms of the DA D2 (DRD2) and D3 (DRD3) receptor genes as well as the DA transporter gene (DAT1; SLC6A3) were examined. Over the course of one week, older adults carrying two or three genotypes associated with higher DA signaling (i.e., higher availability of DA and DA receptors) forgot less pictorial information than older individuals carrying only one or no beneficial genotype. No such genetic effects were found in younger adults. The results are consistent with the view that genetic effects on cognition are magnified in old age. To the best of our knowledge, this is the first report to relate genotypes associated with suboptimal DA modulation to more long-term forgetting in humans. Independent replication studies in other populations are needed to confirm the observed association.

Dopamine-glutamate interplay in the ventral striatum modulates spatial learning in a receptor subtype-dependent manner

The ventral striatum (VS) is characterized by a distinctive neural architecture in which multiple corticolimbic glutamatergic (GLUergic) and mesolimbic dopaminergic (DAergic) afferents converge on the same output cell type (the medium-sized spiny neuron, MSN). However, despite the gateway function attributed to VS and its involvement in action selection and spatial navigation, as well as the evidence of physical and functional receptor-receptor interaction between different members of ionotropic GLUergic and DAergic receptors, there is no available knowledge that such reciprocal interaction may be critical in shaping the ability to learn novel spatial and non-spatial arrangement of stimuli. In this study, it was evaluated whether intra-VS bilateral infusion of either N-methyl-D-aspartate (NMDA) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-selective antagonists may suppress the ability to detect spatial or non-spatial novelty in a non-associative behavioral task. In a second set of experiments, we further examined the hypothesis that VS-mediated spatial information processing may be subserved by some preferential receptor-receptor interactions among specific GLUergic and DAergic receptor subtypes. This was assessed by concomitant intra-VS infusion of the combination between subthreshold doses of either NMDA or AMPA receptor antagonists with individual D1 or D2 receptor blockade. The results of this study highlighted the fact that NMDA or AMPA receptors are differentially involved in processing of spatial and non-spatial novelty, and showed for the first time that preferential NMDA/D1 and AMPA/D2 receptor-receptor functional communication, but not NMDA/D2 and AMPA/D1, is required for enabling learning of novel spatial information in the VS.

Human fear reconsolidation and allelic differences in serotonergic and dopaminergic genes

Fear memory persistence, central for the development and maintenance of anxiety disorders, is partially genetically controlled. Recently, consolidation and reconsolidation processes have been reported to affect fear memory stability and integrity. This study explored the impact of reconsolidation processes and genetic make-up on fear reacquisition by manipulating reconsolidation, using extinction performed outside or inside a reconsolidation interval. Reacquisition measured by skin conductance responses was stronger in individuals that extinguished outside (6 h) than inside (10 min) the reconsolidation interval. However, the effect was predominantly present in val/val homozygotes of the functional val158met polymorphism of the catechol O-methyltransferase (COMT) enzyme and in short-allele carriers of the serotonin-transporter length 5-HTTLPR polymorphism. These results demonstrate that reconsolidation of human fear memory is influenced by dopamine and serotonin-related genes.

Functional correlation between GABAergic and dopaminergic systems of dorsal hippocampus and ventral tegmental area in passive avoidance learning in rats

The aim of the present study was to investigate the existence of possible functional correlation between GABA-A and dopamine (DA) receptors of the dorsal hippocampus and the ventral tegmental area (VTA) in passive avoidance learning. Two guide cannulas were stereotaxically implanted in the CA1 region of the dorsal hippocampus and the VTA of male Wistar rats. In order to measure memory retrieval, the animals were trained in a step-through type passive avoidance task and tested 24 h after training. Post-training intra-CA1 administration of a GABA-A receptor agonist, muscimol (0.01-0.02 μg/rat) dose-dependently impaired memory retrieval. Post-training intra-VTA administration of SCH23390 (a dopamine D1 receptor antagonist; 0.1-0.8 μg/rat) or sulpiride (a D2 receptor antagonist; 0.5-1.5 μg/rat) decreased the inhibitory effect of muscimol (0.02 μg/rat, intra-CA1) on memory retrieval. Intra-VTA administration of the same doses of SCH23390, but not sulpiride, decreased the step-through latencies. On the other hand, post-training administration of muscimol (0.02 μg/rat) into the VTA inhibited memory retrieval. The administration of SCH23390 (0.01-0.2 μg/rat) or sulpiride (0.1-1 μg/rat) into the CA1 region, immediately after training, had no effect on memory retrieval. Furthermore, the amnesic effect of intra-VTA administration of muscimol was significantly decreased by intra-CA1 administration of sulpiride (0.5 and 1 μg/rat, intra-CA1), but not SCH23390. The practical conclusion is that the relationship between the hippocampus and the VTA may regulate memory formation in passive avoidance learning. Also, the correlation between the hippocampus and VTA by a dopaminergic system may be involved in mediating muscimol-induced amnesia.

Nicotine restores morphine-induced memory deficit through the D1 and D2 dopamine receptor mechanisms in the nucleus accumbens

Involvement of the dopamine D1 and D2 receptors in the nucleus accumbens (NAc) with interaction between morphine and nicotine on inhibitory avoidance (IA) memory was investigated. A step-through type of inhibitory avoidance tasks was used to assess memory in male Wistar rats. The results showed that subcutaneous (s.c.) administration of morphine (7.5 mg/kg) after training decreased retrieval of IA memory in the animals when tested 24 h later. Pre-test administration of the same dose of morphine significantly reversed the deficiency in retrieval. The results also showed that pre-test administration of nicotine (0.2 and 0.4 mg/kg, s.c.) by itself mimicked the effect of pre-test morphine, and lower doses of nicotine (0.1 and 0.2 mg/kg) also improved the effect of a low dose of morphine (2.5 mg/kg) on retrieval of IA memory. Pre-test intra-NAc administration of the dopamine D1 receptor antagonist, SCH 23390 (0.001 and 0.01 µg/rat), and the dopamine D2 receptor antagonist, sulpiride (0.5 and 1 µg/rat) caused no significant effects on IA memory by themselves, but both prevented reinstatement of the retrieval of IA memory by the effective dose of nicotine (0.4 mg/kg). It can be concluded that the dopaminergic mechanism(s) in the NAc is a crosslink for the effect of morphine and nicotine on reinstatement of retrieval of IA memory impaired by post-training administration of morphine.

Mouse models of genetic effects on cognition: relevance to schizophrenia

Cognitive dysfunction is a core feature of schizophrenia. Growing evidence indicates that a wide variety of genetic mutations and polymorphisms impact cognition and may thus be implicated in various aspects of this mental disorder. Despite differences between human and rodent brain structure and function, genetic mouse models have contributed critical information about brain mechanisms involved in cognitive processes. Here, we summarize discoveries of genetic modifications in mice that impact cognition. Based on functional hypotheses, gene modifications within five model systems are described: 1) dopamine (D1, D2, D3, D4, D5, DAT, COMT, MAO); 2) glutamate (GluR-A, NR1, NR2A, NR2B, GRM2, GRM3, GLAST); 3) GABA (α(5), γ(2), α(4), δGABA(A), GABA(B(1)), GAT1); 4) acetylcholine (nAChRβ2, α7, CHRM1); and 5) calcium (CaMKII-α, neurogranin, CaMKKβ, CaMKIV). We also consider other risk-associated genes for schizophrenia such as dysbindin (DTNBP1), neuregulin (NRG1), disrupted-in-schizophrenia1 (DISC1), reelin and proline dehydrogenase (PRODH). Because of the presumed importance of environmental factors, we further consider genetic modifications within the stress-sensitive systems of corticotropin-releasing factor (CRF), brain-derived neurotrophic factor (BDNF) and the endocannabinoid systems. We highlight the missing information and limitations of cognitive assays in genetically modified mice models relevant to schizophrenia pathology.

Dissociable roles of dopamine within the core and medial shell of the nucleus accumbens in memory for objects and place

There is increasing focus on the role of the nucleus accumbens (NAc) in learning and memory, but there is little consensus as to how the core and medial shell subregions of the NAc contribute to these processes. In the current experiments, we used spontaneous object recognition to test rats with 6-hydroxydopamine lesions targeted at the core or medial shell of the NAc on a familiarity discrimination task and a location discrimination task. In the object recognition variant, control animals were able to discriminate the novel object at both 24-hr and 5-min delay. However, in the lesion groups, performance was systematically related to dopamine (DA) levels in the core but not the shell. In the location recognition task, sham-operated animals readily detected the object displacement at test. In the lesion groups, performance impairment was systematically related to DA levels in the shell but not the core. These results suggest that dopamine function within distinct subregions of the NAc plays dissociable roles in the modulation of memory for objects and place.

Modulatory influence of dopamine receptors on consolidation of object recognition memory

The role of dopamine receptors in regulating the formation of recognition memory remains poorly understood. Here we show the effects of systemic administration of dopamine receptor agonists and antagonists on the formation of memory for novel object recognition in rats. In Experiment I, rats received an intraperitoneal (i.p.) injection of vehicle, the selective D1 receptor agonist SKF38393 (1.0 and 5.0mg/kg), or the D2 receptor agonist quinpirole (1.0 and 5.0mg/kg) immediately after training. In Experiment II, rats received an injection of vehicle, the dopamine receptor antagonist SCH23390 (0.1 and 0.05 mg/kg), or the D2 receptor antagonist raclopride (0.5 and 0.1mg/kg) before training, followed by an injection of vehicle or the nonselective dopamine receptor agonist apomorphine (0.05 mg/kg) immediately after training. SKF38393 at 5mg/kg produced an enhancement of novel object recognition memory measured at both 24 and 72 h after training, whereas the dose of 10mg/kg impaired 24-h retention. Posttraining administration of quinpirole did not affect 24-h retention. Apomorphine enhanced memory in rats given pretraining raclopride, suggesting that the effect was mediated by selective activation of D1 receptors. The results indicate that activation of D1 receptors can enhance recognition memory consolidation. Importantly, pharmacological activation of D1 receptors enhanced novel object recognition memory even under conditions in which control rats showed significant retention.

Long-term memory for pavlovian fear conditioning requires dopamine in the nucleus accumbens and basolateral amygdala

The neurotransmitter dopamine (DA) is essential for learning in a Pavlovian fear conditioning paradigm known as fear-potentiated startle (FPS). Mice lacking the ability to synthesize DA fail to learn the association between the conditioned stimulus and the fear-inducing footshock. Previously, we demonstrated that restoration of DA synthesis to neurons of the ventral tegmental area (VTA) was sufficient to restore FPS. Here, we used a target-selective viral restoration approach to determine which mesocorticolimbic brain regions receiving DA signaling from the VTA require DA for FPS. We demonstrate that restoration of DA synthesis to both the basolateral amygdala (BLA) and nucleus accumbens (NAc) is required for long-term memory of FPS. These data provide crucial insight into the dopamine-dependent circuitry involved in the formation of fear-related memory.