Prefrontal Dopamine D1 and D2 Receptors Regulate Dissociable Aspects of Decision Making via Distinct Ventral Striatal and Amygdalar Circuits

Mesolimbic dopamine D2 receptors and neural representations of subjective value

The process by which the value of delayed rewards is discounted varies from person to person. It has been suggested that these individual differences in subjective valuation of delayed rewards are supported by mesolimbic dopamine D2-like receptors (D2Rs) in the ventral striatum. However, no study to date has documented an association between direct measures of dopamine receptors and neural representations of subjective value in humans. Here, we examined whether individual differences in D2R availability were related to neural subjective value signals during decision making. Human participants completed a monetary delay discounting task during an fMRI scan and on a separate visit completed a PET scan with the high affinity D2R tracer [18 F]fallypride. Region-of-interest analyses revealed that D2R availability in the ventral striatum was positively correlated with subjective value-related activity in the ventromedial prefrontal cortex and midbrain but not with choice behavior. Whole-brain analyses revealed a positive correlation between ventral striatum D2R availability and subjective value-related activity in the left inferior frontal gyrus and superior insula. These findings identify a link between a direct measure of mesolimbic dopamine function and subjective value representation in humans and suggest a mechanism by which individuals vary in neural representation of discounted subjective value.

The Abused Inhalant Toluene Impairs Medial Prefrontal Cortex Activity and Risk/Reward Decision-Making during a Probabilistic Discounting Task

Inhalant (e.g., toluene) misuse is linked to behavioral and cognitive deficits in humans, yet preclinical studies of the effect of inhalants on higher-order cognition are limited. We addressed this gap in the literature by examining the effect of toluene vapor exposure on risk/reward decision-making in male and female Sprague-Dawley rats using a probabilistic discounting task. In this task, rodents chose a risky/large reward or a safe/small reward, with the odds of risky reinforcement descending or ascending throughout the test session. We observed a dose-dependent, sex-independent deficit in behavioral flexibility during probabilistic discounting caused by acute toluene exposure. Rats exposed to toluene vapor during adolescence and tested as adults performed comparably to air-treated controls and were susceptible to the effects of an acute toluene challenge. These behavioral flexibility deficits observed suggests dysfunctional medial prefrontal cortex (mPFC) activity. To address this hypothesis, we virally expressed the genetically encoded calcium sensor GCaMP6f in glutamatergic mPFC neurons and monitored calcium transients in real-time using in vivo fiber photometry. mPFC activity peaked before either lever press during free-choice trials in toluene- and air-treated animals. During forced-choice trials, GCaMP6f transients shifted from pre-risky to pre-safe choice, an effect mitigated by acute toluene exposure. mPFC activity decreased during rewarded trials, with larger decreases following risky/large wins compared with safe/small wins. Toluene-treated animals also had decreased mPFC activity during rewarded trials, but there was no distinction between risky/large wins and safe/small wins. These results provide physiological evidence for mPFC-dependent behavioral deficits caused by toluene.SIGNIFICANCE STATEMENT Inhalants (e.g., toluene) are an understudied class of drugs of abuse that cause devastating behavioral and cognitive deficits in humans. Understanding the neurobiological interactions of toluene vapor using animal models is important for developing effective treatment strategies for inhalant addicts. Here we find that toluene vapor reduces behavioral flexibility in rodents making risk/reward-based decisions. The medial prefrontal cortex (mPFC) drives behavioral flexibility during this type of decision-making and we show that toluene reduces the ability of mPFC neurons to track optimal choices as reward probabilities change. Toluene also reduces these neurons' ability to distinguish between small and large rewards. A combination of these factors likely leads to the impaired performance in probabilistic discounting following acute toluene exposure.

Metabotropic glutamate receptor subtype 3 gates acute stress-induced dysregulation of amygdalo-cortical function

Stress can precipitate or worsen symptoms of many psychiatric disorders by dysregulating glutamatergic function within the prefrontal cortex (PFC). Previous studies suggest that antagonists of group II metabotropic glutamate (mGlu) receptors (mGlu₂ and mGlu₃) reduce stress-induced anhedonia through actions in the PFC, but the mechanisms by which these receptors act are not known. We now report that activation of mGlu₃ induces long-term depression (LTD) of excitatory transmission in the PFC at inputs from the basolateral amygdala. Our data suggest mGlu₃-LTD is mediated by postsynaptic AMPAR internalization in PFC pyramidal cells, and we observed a profound impairment in mGlu₃-LTD following a single, 20-min restraint stress exposure. Finally, blocking mGlu₃ activation in vivo prevented the stress-induced maladaptive changes to amydalo-cortical physiology and motivated behavior. These data demonstrate that mGlu₃ mediates stress-induced physiological and behavioral impairments and further support the potential for mGlu₃ modulation as a treatment for stress-related psychiatric disorders.

Deconstructing value-based decision making via temporally selective manipulation of neural activity: Insights from rodent models

The ability to choose among options that differ in their rewards and costs (value-based decision making) has long been a topic of interest for neuroscientists, psychologists, and economists alike. This is likely because this is a cognitive process in which all animals (including humans) engage on a daily basis, be it routine (which road to take to work) or consequential (which graduate school to attend). Studies of value-based decision making (particularly at the preclinical level) often treat it as a uniform process. The results of such studies have been invaluable for our understanding of the brain substrates and neurochemical systems that contribute to decision making involving a range of different rewards and costs. Value-based decision making is not a unitary process, however, but is instead composed of distinct cognitive operations that function in concert to guide choice behavior. Within this conceptual framework, it is therefore important to consider that the known neural substrates supporting decision making may contribute to temporally distinct and dissociable components of the decision process. This review will describe this approach for investigating decision making, drawing from published studies that have used techniques that allow temporal dissection of the decision process, with an emphasis on the literature in animal models. The review will conclude with a discussion of the implications of this work for understanding pathological conditions that are characterized by impaired decision making.

Dopamine D2 agonist affects visuospatial working memory distractor interference depending on individual differences in baseline working memory span

The interplay of dopaminergic striatal D1-D2 circuits is thought to support working memory (WM) by selectively filtering information that is to be remembered versus information to be ignored. To test this theory, we conducted an experiment in which healthy participants performed a visuospatial working memory (VSWM) task after ingesting the D2-receptor agonist cabergoline (or placebo), in a randomized, double-blinded, crossover design. Results showed greater interference from distractors under cabergoline, particularly for individuals with higher baseline dopamine (indicated by WM span). These findings support computational theories of striatal D1-D2 function during WM encoding and distractor-filtering, and provide new evidence for interactive cortico-striatal systems that support VSWM capacity and their dependence on WM span.

Dopamine blockade impairs the exploration-exploitation trade-off in rats

In a volatile environment where rewards are uncertain, successful performance requires a delicate balance between exploitation of the best option and exploration of alternative choices. It has theoretically been proposed that dopamine contributes to the control of this exploration-exploitation trade-off, specifically that the higher the level of tonic dopamine, the more exploitation is favored. We demonstrate here that there is a formal relationship between the rescaling of dopamine positive reward prediction errors and the exploration-exploitation trade-off in simple non-stationary multi-armed bandit tasks. We further show in rats performing such a task that systemically antagonizing dopamine receptors greatly increases the number of random choices without affecting learning capacities. Simulations and comparison of a set of different computational models (an extended Q-learning model, a directed exploration model, and a meta-learning model) fitted on each individual confirm that, independently of the model, decreasing dopaminergic activity does not affect learning rate but is equivalent to an increase in random exploration rate. This study shows that dopamine could adapt the exploration-exploitation trade-off in decision-making when facing changing environmental contingencies.

Chronic unpredictable stress promotes cell-specific plasticity in prefrontal cortex D1 and D2 pyramidal neurons

Exposure to unpredictable environmental stress is widely recognized as a major determinant for risk and severity in neuropsychiatric disorders such as major depressive disorder, anxiety, schizophrenia, and PTSD. The ability of ostensibly unrelated disorders to give rise to seemingly similar psychiatric phenotypes highlights a need to identify circuit-level concepts that could unify diverse factors under a common pathophysiology. Although difficult to disentangle a causative effect of stress from other factors on medial prefrontal cortex (PFC) dysfunction, a wealth of data from humans and rodents demonstrates that the PFC is a key target of stress. The present study sought to identify a model of chronic unpredictable stress (CUS) which induces affective behaviors in C57BL6J mice and once established, measure stress-related alterations in intrinsic excitability and synaptic regulation of mPFC layer 5/6 pyramidal neurons. Adult male mice received 2 weeks of 'less intense' stress or 2 or 4 weeks of 'more intense' CUS followed by sucrose preference for assessment of anhedonia, elevated plus maze for assessment of anxiety and forced swim test for assessment of depressive-like behaviors. Our findings indicate that more intense CUS exposure results in increased anhedonia, anxiety, and depressive behaviors, while the less intense stress results in no measured behavioral phenotypes. Once a behavioral model was established, mice were euthanized approximately 21 days post-stress for whole-cell patch clamp recordings from layer 5/6 pyramidal neurons in the prelimbic (PrL) and infralimbic (IL) cortices. No significant differences were initially observed in intrinsic cell excitability in either region. However, post-hoc analysis and subsequent confirmation using transgenic mice expressing tdtomato or eGFP under control of dopamine D1-or D2-type receptor showed that D1-expressing pyramidal neurons (D1-PYR) in the PrL exhibit reduced thresholds to fire an action potential (increased excitability) but impaired firing capacity at more depolarized potentials, whereas D2-expressing pyramidal neurons (D2-PYR) showed an overall reduction in excitability and spike firing frequency. Examination of synaptic transmission showed that D1-and D2-PYR exhibit differences in basal excitatory and inhibitory signaling under naïve conditions. In CUS mice, D1-PYR showed increased frequency of both miniature excitatory and inhibitory postsynaptic currents, whereas D2-PYR only showed a reduction in excitatory currents. These findings demonstrate that D1-and D2-PYR subpopulations differentially undergo stress-induced intrinsic and synaptic plasticity that may have functional implications for stress-related pathology, and that these adaptations may reflect unique differences in basal properties regulating output of these cells.

Translational tests involving non-reward: methodological considerations

This review is concerned with methods for assessing the processing of unrewarded responses in experimental animals and the mechanisms underlying performance of these tasks. A number of clinical populations, including Parkinson's disease, depression, compulsive disorders, and schizophrenia demonstrate either abnormal processing or learning from non-rewarded responses in laboratory-based reinforcement learning tasks. These effects are hypothesized to result from disturbances in modulatory neurotransmitter systems, including dopamine and serotonin. Parallel work in experimental animals has revealed consistent behavioral patterns associated with non-reward and, consistent with the human literature, modulatory roles for specific neurotransmitters. Classical tests involving an important reward omission component include appetitive extinction, ratio schedules of responding, reversal learning, and delay and probability discounting procedures. In addition, innovative behavioral tests have recently been developed leverage probabilistic feedback to specifically assay accommodation of, and learning from, non-rewarded responses. These procedures will be described and reviewed with discussion of the behavioral and neural determinants of performance. A final section focusses specifically on the benefits of trial-by-trial analysis of responding during such tasks, and the implications of such analyses for the translation of findings to clinical studies.

Postnatal impoverished housing impairs adolescent risk-assessment and increases risk-taking: A sex-specific effect associated with histone epigenetic regulation of Crfr1 in the medial prefrontal cortex

While increasing evidence posits poor decision-making as a central feature of mental disorders, very few studies investigated the effects of early-life stress (ELS) on specific components of reward-related choice behaviors. Risk-taking (RT) involves the exposure to some danger, or negative consequences, in order to achieve a goal-directed behavior. Such behaviors are likely to be preceded by risk-assessment (RA), which is a dynamic cognitive process involving the acquisition of information in potentially dangerous situations. Here, we investigated the effects of being raised in impoverished housing conditions during early life (P2-P9) on RT, RA and dopaminergic and corticotrophinergic gene expression of adolescent male and female mice. Phenotypes were assessed by two protocols: the elevated plus-maze (EPM) and the predator-odor risk-taking (PORT). We found decreased RA in mice exposed to impoverished housing in the absence of a reward (EPM), with a more pronounced effect among females. Moreover, when exposed to a predatory olfactory cue, increased RT was observed in these females in a reward-related task (PORT), as well as decreased HPA axis responsivity. This sex-specific behavioral effect was associated with increased Crfr1 mRNA expression in the medial prefrontal cortex (mPFC) and higher levels of the histone mark H3R2^me2s, a histone modification known to be involved in transcriptional activation, within the promoter of the Crfr1 gene. These findings revealed that ELS exposure can impair the acquisition of environmental information in dangerous situations and increase RT in reward-related scenarios among females, with an important role regarding epigenetic regulation of the Crfr1 gene.

Optogenetic Dissection of Temporal Dynamics of Amygdala-Striatal Interplay during Risk/Reward Decision Making

Decision making often requires weighing costs and benefits of different options that vary in terms of reward magnitude and uncertainty. Previous studies using pharmacological inactivations have shown that the basolateral amygdala (BLA) to nucleus accumbens (NAc) pathway promotes choice towards larger/riskier rewards. Neural activity in BLA and NAc shows distinct, phasic changes in firing prior to choice and following action outcomes, yet, how these temporally-discrete patterns of activity within BLA→NAc circuitry influence choice is unclear. We assessed how optogenetic silencing of BLA terminals in the NAc altered action selection during probabilistic decision making. Rats received intra-BLA infusions of viruses encoding the inhibitory opsin eArchT and were well trained on a probabilistic discounting task, where they chose between smaller/certain rewards and larger rewards delivered in a probabilistic manner, with the odds of obtaining the larger reward changing over a session (50–12.5%). During testing, activity of BLA→NAc inputs were suppressed with 4- to 7-s pulses of light delivered via optic fibers into the NAc during discrete task events: prior to choice or after choice outcomes. Inhibition prior to choice reduced selection of the preferred option, suggesting that during deliberation, BLA→NAc activity biases choice towards preferred rewards. Inhibition during reward omissions increased risky choice during the low-probability block, indicating that activity after non-rewarded actions serves to modify subsequent choice. In contrast, silencing during rewarded outcomes did not reliably affect choice. These data demonstrate how patterns of activity in BLA→NAc circuitry convey different types of information that guide action selection in situations involving reward uncertainty.

Thalamic afferents to prefrontal cortices from ventral motor nuclei in decision-making

The focus of this literature review is on the three interacting brain areas that participate in decision‐making: basal ganglia, ventral motor thalamic nuclei, and medial prefrontal cortex, with an emphasis on the participation of the ventromedial and ventral anterior motor thalamic nuclei in prefrontal cortical function. Apart from a defining input from the mediodorsal thalamus, the prefrontal cortex receives inputs from ventral motor thalamic nuclei that combine to mediate typical prefrontal functions such as associative learning, action selection, and decision‐making. Motor, somatosensory and medial prefrontal cortices are mainly contacted in layer 1 by the ventral motor thalamic nuclei and in layer 3 by thalamocortical input from mediodorsal thalamus. We will review anatomical, electrophysiological, and behavioral evidence for the proposed participation of ventral motor thalamic nuclei and medial prefrontal cortex in rat and mouse motor decision‐making.

Prefrontal-accumbens opioid plasticity: Implications for relapse and dependence

In addiction, an individual's ability to inhibit drug seeking and drug taking is thought to reflect a pathological strengthening of drug-seeking behaviors or impairments in the capacity to control maladaptive behavior. These processes are not mutually exclusive and reflect drug-induced modifications within prefrontal cortical and nucleus accumbens circuits, however unlike psychostimulants such as cocaine, far less is known about the temporal, anatomical, and cellular dynamics of these changes. We discuss what is known regarding opioid-induced adaptations in intrinsic membrane physiology and pre-/postsynaptic neurotransmission in principle pyramidal and medium spiny neurons in the medial prefrontal cortex and nucleus accumbens from electrophysiological studies and explore how circuit specific adaptations may contribute to unique facets of opioid addiction.

Dopamine Release in Antidepressant-Naive Major Depressive Disorder: A Multimodal [11C]-(+)-PHNO Positron Emission Tomography and Functional Magnetic Resonance Imaging Study

BACKGROUND

Mesolimbic dopamine system dysfunction is believed to contribute to major depressive disorder (MDD), but molecular neuroimaging of striatal dopamine neurotransmission has yielded mixed results, possibly owing to limited sensitivity of antagonist radioligands used with positron emission tomography to assess dopamine release capacity. This study used an agonist radioligand with agonist challenge to assess dopamine release capacity and D₂/D₃ receptor availability in MDD.

METHODS

Twenty-six treatment-naive adults with MDD and 26 healthy comparison participants underwent functional magnetic resonance imaging during a probabilistic reinforcement task, and positron emission tomography with the D₃-preferring ligand [¹¹C]-(+)-PHNO, before and after oral dextroamphetamine. MDD participants then received pramipexole treatment for 6 weeks.

RESULTS

MDD participants had trend-level greater dopamine release capacity in the ventral striatum, as measured by percent change in baseline binding potential relative to nondisplaceable compartment (ΔBP_ND) (-34% vs. -30%; p = .072, d = 0.58) but no difference in D₂/D₃ receptor availability (BP_ND). Striatal and extrastriatal BP_ND and percent change in baseline BP_ND were not significantly associated with blood oxygen level-dependent response to reward prediction error in the ventral striatum, severity of depression and anhedonia, or antidepressant response to pramipexole (response rate = 72.7%).

CONCLUSIONS

[¹¹C]-(+)-PHNO demonstrated high sensitivity to displacement by amphetamine-induced dopamine release, but dopamine release capacity and D₂/D₃ availability were not associated with ventral striatal activation to reward prediction error or clinical features, in this study powered to detect large effects. While a preponderance of indirect evidence implicates dopaminergic dysfunction in MDD, these findings suggest that presynaptic dopamine dysregulation may not be a feature of MDD or a prerequisite for treatment response to dopamine agonists.

Executive functioning: perspectives on neurotrophic activity and pharmacology

Executive functioning is a high-level cognitive ability, regulating other abilities and behaviors to achieve desired goals. A typical executive task can be defined as the capacity to maintain one's attention on the current task, that is, responding only to the correct but not to distractive stimuli. Impairments of executive functions, or executive dysfunctions, have a growing impact on everyday life and academic achievement and are usually an early feature, and one of the core features, in brain injury and memory and behavioral disorders. Furthermore, emerging evidence indicates that memory therapeutics cannot achieve their clinical benefits in cognition if executive dysfunction is not effectively and simultaneously treated. Improvement of executive functions might be achieved through targeting some signaling pathways in the brain, including the brain-derived neurotrophic factor signaling pathways. These agents may be useful either as stand-alone interventions for patients with executive dysfunction and/or psychiatric and memory disorders or as essential adjuncts to drugs that target the underlying pathology in various brain injury and memory and behavioral disorders.

Heterogeneous dopamine signals support distinct features of motivated actions: implications for learning and addiction

Despite decades of research, investigations into effective neural and pharmacological therapies for many drugs of abuse, such as cocaine, have produced no FDA-approved approaches. This difficulty derives from the complexity of substance use disorders, which encompass a variety of behavioral, psychological, and neural circuit-based changes that occur as a result of repeated experience with the drug. Dopamine signaling has been demonstrated to play a key role in several aspects of drug abuse—from mediating its reinforcing properties and drug-seeking to triggering relapse—while also mediating a number of important aspects of normal (nondrug related) motivated behaviors and actions. Real-time recording methods such as in vivo voltammetry, electrophysiology, and calcium imaging demonstrate that the signaling properties of dopamine for motivationally relevant stimuli are highly dynamic and spatiotemporally circumscribed within afferent target regions. In this review, we identify the origins and functional consequences of heterogeneous dopamine release in the limbic system, and how these properties are persistently altered in the drug-experienced brain. We propose that these spatiotemporally parallel dopaminergic signals are simultaneously available to the animal, but that these circuits are impaired following prolonged drug experience by disrupting the location and content of dopamine signals in afferent target regions. These findings are discussed in the context of relapse and pathways to discovering new treatments for addiction disorders.

Conflict and adaptation signals in the anterior cingulate cortex and ventral tegmental area

The integration and utilization of feedback in order to determine which decision strategy to use in different contexts is the core of executive function. The anterior cingulate cortex (ACC) is central to these processes but how feedback is made available to the ACC is unclear. To address this question, we trained rats with implants in the ACC and the ventral tegmental area (VTA), a dopaminergic brain region implicated in feedback processing, in a spatial decision reversal task with rule switching occurring approximately every 12 trials. Following a rule switch, the rats had to shift and sustain responses to the alternative side in order to obtain reward. Partial directed coherence (PDC) models of signal directionality between the ACC and VTA indicated that VTA → ACC communication (near 4 Hz) increased immediately prior to incorrect choices and during post-error decisions. This increase did not occur during correct choices. These data indicate that the VTA provides a feedback-driven, bottom-up modulating signal to the ACC which may be involved in assessing, and correcting for, decision conflict.

Contributions of medial prefrontal cortex to decision making involving risk of punishment

The prefrontal cortex (PFC) plays an important role in several forms of cost-benefit decision making. Its contributions to decision making under risk of explicit punishment, however, are not well understood. A rat model was used to investigate the role of the medial PFC (mPFC) and its monoaminergic innervation in a Risky Decision-making Task (RDT), in which rats chose between a small, "safe" food reward and a large, "risky" food reward accompanied by varying probabilities of mild footshock punishment. Inactivation of mPFC increased choice of the large, risky reward when the punishment probability increased across the session ("ascending RDT"), but decreased choice of the large, risky reward when the punishment probability decreased across the session ("descending RDT"). In contrast, enhancement of monoamine availability via intra-mPFC amphetamine reduced choice of the large, risky reward only in the descending RDT. Systemic administration of amphetamine reduced choice of the large, risky reward in both the ascending and descending RDT; however, this reduction was not attenuated by concurrent mPFC inactivation, indicating that mPFC is not a critical locus of amphetamine's effects on risk taking. These findings suggest that mPFC plays an important role in adapting choice behavior in response to shifting risk contingencies, but not necessarily in risk-taking behavior per se.

Chronic Exposure to Methamphetamine Disrupts Reinforcement-Based Decision Making in Rats

The persistent use of psychostimulant drugs, despite the detrimental outcomes associated with continued drug use, may be because of disruptions in reinforcement-learning processes that enable behavior to remain flexible and goal directed in dynamic environments. To identify the reinforcement-learning processes that are affected by chronic exposure to the psychostimulant methamphetamine (MA), the current study sought to use computational and biochemical analyses to characterize decision-making processes, assessed by probabilistic reversal learning, in rats before and after they were exposed to an escalating dose regimen of MA (or saline control). The ability of rats to use flexible and adaptive decision-making strategies following changes in stimulus-reward contingencies was significantly impaired following exposure to MA. Computational analyses of parameters that track choice and outcome behavior indicated that exposure to MA significantly impaired the ability of rats to use negative outcomes effectively. These MA-induced changes in decision making were similar to those observed in rats following administration of a dopamine D2/3 receptor antagonist. These data use computational models to provide insight into drug-induced maladaptive decision making that may ultimately identify novel targets for the treatment of psychostimulant addiction. We suggest that the disruption in utilization of negative outcomes to adaptively guide dynamic decision making is a new behavioral mechanism by which MA rigidly biases choice behavior.

Differential Contributions of Nucleus Accumbens Subregions to Cue-Guided Risk/Reward Decision Making and Implementation of Conditional Rules

The nucleus accumbens (NAc) is a key node within corticolimbic circuitry for guiding action selection and cost/benefit decision making in situations involving reward uncertainty. Preclinical studies have typically assessed risk/reward decision making using assays where decisions are guided by internally generated representations of choice-outcome contingencies. Yet, real-life decisions are often influenced by external stimuli that inform about likelihoods of obtaining rewards. How different subregions of the NAc mediate decision making in such situations is unclear. Here, we used a novel assay colloquially termed the "Blackjack" task that models these types of situations. Male Long-Evans rats were trained to choose between one lever that always delivered a one-pellet reward and another that delivered four pellets with different probabilities [either 50% (good-odds) or 12.5% (poor-odds)], which were signaled by one of two auditory cues. Under control conditions, rats selected the large/risky option more often on good-odds versus poor-odds trials. Inactivation of the NAc core caused indiscriminate choice patterns. In contrast, NAc shell inactivation increased risky choice, more prominently on poor-odds trials. Additional experiments revealed that both subregions contribute to auditory conditional discrimination. NAc core or shell inactivation reduced Pavlovian approach elicited by an auditory CS+, yet shell inactivation also increased responding during presentation of a CS-. These data highlight distinct contributions for NAc subregions in decision making and reward seeking guided by discriminative stimuli. The core is crucial for implementation of conditional rules, whereas the shell refines reward seeking by mitigating the allure of larger, unlikely rewards and reducing expression of inappropriate or non-rewarded actions.SIGNIFICANCE STATEMENT Using external cues to guide decision making is crucial for adaptive behavior. Deficits in cue-guided behavior have been associated with neuropsychiatric disorders, such as attention deficit hyperactivity disorder and schizophrenia, which in turn has been linked to aberrant processing in the nucleus accumbens. However, many preclinical studies have often assessed risk/reward decision making in the absence of explicit cues. The current study fills that gap by using a novel task that allows for the assessment of cue-guided risk/reward decision making in rodents. Our findings identified distinct yet complementary roles for the medial versus lateral portions of this nucleus that provide a broader understanding of the differential contributions it makes to decision making and reward seeking guided by discriminative stimuli.

Role of Anterior Intralaminar Nuclei of Thalamus Projections to Dorsomedial Striatum in Incubation of Methamphetamine Craving

Relapse to methamphetamine (Meth) seeking progressively increases after withdrawal from drug self-administration (incubation of Meth craving). We previously demonstrated a role of dorsomedial striatum (DMS) dopamine D1 receptors (D1Rs) in this incubation. Here, we studied the role of afferent glutamatergic projections into the DMS and local D1R-glutamate interaction in this incubation in male rats. We first measured projection-specific activation on day 30 relapse test by using cholera toxin b (retrograde tracer) + Fos (activity marker) double-labeling in projection areas. Next, we determined the effect of pharmacological reversible inactivation of lateral or medial anterior intralaminar nuclei of thalamus (AIT-L or AIT-M) on incubated Meth seeking on withdrawal day 30. We then used an anatomical asymmetrical disconnection procedure to determine whether an interaction between AIT-L→DMS glutamatergic projections and postsynaptic DMS D1Rs contributes to incubated Meth seeking. We also determined the effect of unilateral inactivation of AIT-L and D1R blockade of DMS on incubated Meth seeking, and the effect of contralateral disconnection of AIT-L→DMS projections on nonincubated Meth seeking on withdrawal day 1. Incubated Meth seeking was associated with selective activation of AIT→DMS projections; other glutamatergic projections to DMS were not activated. AIT-L (but not AIT-M) inactivation or anatomical disconnection of AIT-L→DMS projections decreased incubated Meth seeking. Unilateral inactivation of AIT-L or D1R blockade of the DMS had no effect on incubated Meth craving, and contralateral disconnection of AIT-L→DMS projections had no effect on nonincubated Meth seeking. Our results identify a novel role of AIT-L and AIT-L→DMS glutamatergic projections in incubation of drug craving and drug seeking.SIGNIFICANCE STATEMENT Methamphetamine seeking progressively increases after withdrawal from drug self-administration, a phenomenon termed incubation of methamphetamine craving. We previously found that D1R-mediated dopamine transmission in the dorsomedial striatum plays a critical role in this incubation phenomenon. Here, we used neuroanatomical and neuropharmacological methods in rats to demonstrate that an interaction between the glutamatergic projection from the lateral anterior intralaminar nuclei of the thalamus to the dorsomedial striatum and local dopamine D1 receptors plays a critical role in relapse to methamphetamine seeking after prolonged withdrawal. Our study identified a novel motivation-related thalamostriatal projection critical to relapse to drug seeking.

Androgen Regulation of the Mesocorticolimbic System and Executive Function

Multiple lines of evidence indicate that androgens, such as testosterone, modulate the mesocorticolimbic system and executive function. This review integrates neuroanatomical, molecular biological, neurochemical, and behavioral studies to highlight how endogenous and exogenous androgens alter behaviors, such as behavioral flexibility, decision making, and risk taking. First, we briefly review the neuroanatomy of the mesocorticolimbic system, which mediates executive function, with a focus on the ventral tegmental area (VTA), nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC). Second, we present evidence that androgen receptors (AR) and other steroid receptors are expressed in the mesocorticolimbic system. Using sensitive immunohistochemistry and quantitative polymerase chain reaction (qPCR) techniques, ARs are detected in the VTA, NAc, mPFC, and OFC. Third, we describe recent evidence for local androgens ("neuroandrogens") in the mesocorticolimbic system. Steroidogenic enzymes are expressed in mesocorticolimbic regions. Furthermore, following long-term gonadectomy, testosterone is nondetectable in the blood but detectable in the mesocorticolimbic system, using liquid chromatography tandem mass spectrometry. However, the physiological relevance of neuroandrogens remains unknown. Fourth, we review how anabolic-androgenic steroids (AAS) influence the mesocorticolimbic system. Fifth, we describe how androgens modulate the neurochemistry and structure of the mesocorticolimbic system, particularly with regard to dopaminergic signaling. Finally, we discuss evidence that androgens influence executive functions, including the effects of androgen deprivation therapy and AAS. Taken together, the evidence indicates that androgens are critical modulators of executive function. Similar to dopamine signaling, there might be optimal levels of androgen signaling within the mesocorticolimbic system for executive functioning. Future studies should examine the regulation and functions of neurosteroids in the mesocorticolimbic system, as well as the potential deleterious and enduring effects of AAS use.