Impact of the natural hormonal milieu on ventral striatal responses to appetitive cigarette smoking cues: A prospective longitudinal study

Background

The female sex hormones estradiol (E) and progesterone (P) galvanize the ventral striatal reward pathway. E elevates ventral striatal dopamine and accelerates drug-cued reinstatement, while P has opposing 'protective' effects on drug-related behavior. We hypothesize that women may exhibit greater ventral striatal responses to smoking cues (SCs) during the late follicular phase of the menstrual cycle (MC) when E is high and unimpeded by P, and reduced responses during the late luteal phase when P is high.

Methods

To test our hypothesis, 24 naturally cycling cigarette-dependent women completed functional magnetic resonance (fMRI) sessions over the course of 3 MCs at select time points to reflect the early follicular (low E and P; LEP, control condition), late follicular (high E, low P; HE) and mid-luteal (high E, high P; HEP) MC phases. During fMRI sessions (counterbalanced by phase), women were exposed to a SC versus nonSC audio-visual clip. Ovulation was verified for each MC, and hormone levels were acquired prior to sessions.

Results

Contrasts within conditions showed that ventral striatal brain responses to SCs versus nonSCs were negligible during LEP and greater during HE (p=0.009) and HP (p=0.016). Contrasts across conditions showed that HE and HEP had greater responses than LEP (p=0.005), and HE had greater responses than HEP (p=0.049).

Conclusions

Results support and extend our retrospective cross-sectional study of the influence of the hormonal milieu on SC reactivity. Results are clinically relevant as they may guide novel, hormonally-informed and immediately translatable treatment strategies that can potentially reduce relapse in naturally cycling women.

Mine or Ours? Neural Basis of the Exploitation of Common-Pool Resources

Why do people often exhaust unregulated common (shared) natural resources but manage to preserve similar private resources? To answer this question, in this study we combine a neurobiological, economic and cognitive modeling approach. Using functional magnetic resonance imaging on 50 participants, we show that a sharp decrease of common and private resources is associated with deactivation of the ventral striatum, a brain region involved in the valuation of outcomes. Across individuals, when facing a common resource, ventral striatal activity is anticorrelated with resource preservation (less harvesting), whereas with private resources the opposite pattern is observed. This indicates that neural value signals distinctly modulate behavior in response to the depletion of common vs private resources. Computational modeling suggested that overharvesting of common resources was facilitated by the modulatory effect of social comparison on value signals. These results provide an explanation of people’s tendency to over-exploit unregulated common natural resources.

Differential reinforcement learning responses to positive and negative information in unmedicated individuals with depression

Major depressive disorder (MDD) is characterized by behavioral and neural abnormalities in processing both rewarding and aversive stimuli, which may impact motivational and affective symptoms. Learning paradigms have been used to assess reinforcement encoding abnormalities in MDD and their association with dysfunctional incentive-based behavior, but how the valence and context of information modulate this learning is not well understood. To address these gaps, we examined responses to positive and negative reinforcement across multiple temporal phases of information processing. While undergoing functional magnetic resonance imaging (fMRI), 47 participants (23 unmedicated, predominantly medication-naïve participants with MDD and 24 demographically-matched HC participants) completed a probabilistic, feedback-based reinforcement learning task that allowed us to separate neural activation during motor response (choice) from reinforcement feedback and monetary outcome across two independent conditions: pursuing gains and avoiding losses. In the gain condition, MDD participants showed overall blunted learning responses (prediction error) in the dorsal striatum when receiving monetary outcome, and reduced responses in ventral striatum for positive, but not negative, prediction error. The MDD group showed enhanced sensitivity to negative information, and symptom severity was associated with better behavioral performance in the loss condition. These findings suggest that striatal responses during learning are abnormal in individuals with MDD but vary with the valence of information.

Neural Responsivity to Reward versus Punishment Shortly after Trauma Predicts Long-term Development of Post-Traumatic Stress Symptoms

BACKGROUND

Processing negative and positive valenced stimuli involve multiple brain regions including the amygdala and ventral striatum (VS). Post-Traumatic Stress Disorder (PTSD) is often associated with hyper-responsivity to negatively valenced, yet recent evidence also points to deficient positive valence functioning. It is yet unclear what is the relative contribution of such opposing valence processing shortly after trauma to the development of chronic PTSD.

METHODS

Neurobehavioral indicators of motivational positive vs. negative valence sensitivities were longitudinally assessed in 171 adults (87 females, age=34.19±11.47 years) at 1-, 6-, and 14-months following trauma exposure (TP1, TP2, TP3). Using a gambling fMRI paradigm, amygdala and VS functionality (activity and functional connectivity with the prefrontal cortex) in response to rewards vs. punishments were assessed with relation to PTSD severity at different time-points. The effect of valence processing was depicted behaviorally by the amount of risk taken to maximize reward.

RESULTS

PTSD severity at TP1 was associated with greater neural functionality in the amygdala (but not the VS) towards punishments vs. rewards, and fewer risky choices. PTSD severity at TP3 was associated with decreased neural functionality in both the VS and amygdala towards rewards vs. punishments at TP1 (but not with risky behavior). Explainable machine learning revealed the primacy of VS biased processing, over the amygdala, in predicting PTSD severity at TP3.

CONCLUSIONS

These results highlight the importance of biased neural responsivity to positive relative to negative motivational outcomes in PTSD development. Novel therapeutic strategies early after trauma may thus target both valence fronts.

Association of Inflammatory Activity With Larger Neural Responses to Threat and Reward Among Children Living in Poverty

OBJECTIVE

Children exposed to severe, chronic stress are vulnerable to mental and physical health problems across the lifespan. To explain how these problems develop, the neuroimmune network hypothesis suggests that early-life stress initiates a positive feedback loop between peripheral inflammatory cells and networked brain regions involved in threat and reward processing. The authors sought to test this hypothesis by studying a sample of urban children from diverse socioeconomic backgrounds.

METHODS

The authors examined the basic predictions of the neuroimmune network hypothesis in 207 children (mean age=13.9 years, 63% female; 33% Black; 30% Hispanic), focusing on poverty as a stressor. The children had fasting blood drawn to quantify five inflammatory biomarkers-C-reactive protein, tumor necrosis factor-α, and interleukins-6, -8, and -10-which were averaged to form a composite score. Children also completed two functional MRI tasks, which measured amygdala responsivity to angry facial expressions and ventral striatum responsivity to monetary rewards.

RESULTS

Poverty status and neural responsivity interacted statistically to predict inflammation. Among children living in poverty, amygdala threat responsivity was positively associated with inflammation, and the same was true for ventral striatum responsivity to reward. As children's socioeconomic conditions improved, these brain-immune associations became weaker. In sensitivity analyses, these patterns were robust to alternative measures of socioeconomic status and were independent of age, sex, racial and ethnic identity, and pubertal status. The associations were also condition specific; no interactions were apparent for amygdala responsivity to neutral faces, or striatal responsivity to monetary losses.

CONCLUSIONS

These findings suggest that childhood poverty is associated with accentuated neural-immune signaling, consistent with the neuroimmune network hypothesis.

Association of Prefrontal-Striatal Functional Pathology With Alcohol Abstinence Days at Treatment Initiation and Heavy Drinking After Treatment Initiation

OBJECTIVE

Alcohol use disorder (AUD) is associated with neuroadaptations in brain stress and reward circuits. It is not known whether such neuroadaptations are affected by number of days of alcohol abstinence and whether they influence heavy drinking during the early treatment phase. The authors used a novel functional MRI (fMRI) approach to assess brain responses during sustained exposure to standardized visual stimuli of stressful, alcohol cue, and neutral control images combined with prospective assessment of drinking outcomes during early outpatient treatment, in two related studies.

METHODS

In study 1, 44 treatment-entering patients with AUD and 43 demographically matched healthy control subjects participated in the fMRI experiment to identify dysfunctional responses associated with chronic alcohol abuse. In study 2, 69 treatment-entering patients with AUD were assessed for whether fMRI responses at treatment initiation were influenced by alcohol abstinence and were prospectively predictive of early heavy drinking outcomes.

RESULTS

Relative to control subjects, patients with AUD showed significant hyperreactivity in the ventromedial prefrontal cortex (vmPFC) in response to neutral images, but significant hypoactivation in the vmPFC and ventral striatum in response to stress images and to alcohol cues relative to response to neutral images. In study 2, this specific prefrontal-ventral striatal dysfunction was associated with fewer days of alcohol abstinence and also predicted greater number heavy drinking days during the subsequent 2 weeks of treatment engagement.

CONCLUSIONS

Number of days of alcohol abstinence at treatment initiation significantly affected functional disruption of the prefrontal-striatal responses to stress images and to alcohol cues in patients with AUD, and the severity of this disruption in turn predicted greater heavy drinking during early treatment. Treatments that target this functional prefrontal-striatal pathology could improve early treatment outcomes in AUD.

Alcohol Cue-Induced Ventral Striatum Activity Predicts Subsequent Alcohol Self-Administration

BACKGROUND

Human laboratory paradigms are a pillar in medication development for alcohol use disorders (AUD). Neuroimaging paradigms, in which individuals are exposed to cues that elicit neural correlates of alcohol craving (e.g., mesocorticolimbic activation), are increasingly utilized to test the effects of AUD medications. Elucidation of the translational effects of these neuroimaging paradigms on human laboratory paradigms, such as self-administration, is warranted. The current study is a secondary analysis examining whether alcohol cue-induced activation in the ventral striatum is predictive of subsequent alcohol self-administration in the laboratory.

METHODS

Non-treatment-seeking heavy drinkers of East Asian descent (n = 41) completed a randomized, placebo-controlled, double-blind, crossover experiment on the effects of naltrexone on neuroimaging and human laboratory paradigms. Participants completed 5 days of study medication (or placebo); on day 4, they completed a neuroimaging alcohol taste cue-reactivity task. On the following day (day 5), participants completed a 60-minute alcohol self-administration paradigm.

RESULTS

Multilevel Cox regressions indicated a significant effect of taste cue-elicited ventral striatum activation on latency to first drink, Wald χ²  = 2.88, p = 0.05, such that those with higher ventral striatum activation exhibited shorter latencies to consume their first drink. Similarly, ventral striatum activation was positively associated with total number of drinks consumed, F(1, 38) = 5.90, p = 0.02. These effects were significant after controlling for alcohol use severity, OPRM1 genotype, and medication. Other potential regions of interest (anterior cingulate, thalamus) were not predictive of self-administration outcomes.

CONCLUSIONS

Neuroimaging alcohol taste cue paradigms may be predictive of laboratory paradigms such as self-administration. Elucidation of the relationships among different paradigms will inform how these paradigms may be used synergistically in experimental medicine and medication development.

RNA-Seq Analysis of Genetic and Transcriptome Network Effects of Dual-Trait Selection for Ethanol Preference and Withdrawal Using SOT and NOT Genetic Models

BACKGROUND

Genetic factors significantly affect alcohol consumption and vulnerability to withdrawal. Furthermore, some genetic models showing predisposition to severe withdrawal are also predisposed to low ethanol (EtOH) consumption and vice versa, even when tested independently in naïve animals.

METHODS

Beginning with a C57BL/6J × DBA/2J F2 intercross founder population, animals were simultaneously selectively bred for both high alcohol consumption and low acute withdrawal (SOT line), or vice versa (NOT line). Using randomly chosen fourth selected generation (S4) mice (N = 18-22/sex/line), RNA-Seq was employed to assess genome-wide gene expression in ventral striatum. The MegaMUGA array was used to detect genome-wide genotypic differences. Differential gene expression and the weighted gene co-expression network analysis were implemented as described elsewhere (Genes Brain Behav 16, 2017, 462).

RESULTS

The new selection of the SOT and NOT lines was similar to that reported previously (Alcohol Clin Exp Res 38, 2014, 2915). One thousand eight hundred and sixteen transcripts were detected as differentially expressed between the lines. For genes more highly expressed in the SOT line, there was enrichment in genes associated with cell adhesion, synapse organization, and postsynaptic membrane. The genes with a cell adhesion annotation included 23 protocadherins, Mpdz and Dlg2. Genes with a postsynaptic membrane annotation included Gabrb3, Gphn, Grid1, Grin2b, Grin2c, and Grm3. The genes more highly expressed in the NOT line were enriched in a network module (red) with annotations associated with mitochondrial function. Several of these genes were module hub nodes, and these included Nedd8, Guk1, Elof1, Ndufa8, and Atp6v1f.

CONCLUSIONS

Marked effects of selection on gene expression were detected. The NOT line was characterized by higher expression of hub nodes associated with mitochondrial function. Genes more highly expressed in the SOT aligned with previous findings, for example, Colville and colleagues (Genes Brain Behav 16, 2017, 462) that both high EtOH preference and consumption are associated with effects on cell adhesion and glutamate synaptic plasticity.

Reward-Related Neural Correlates of Antisocial Behavior and Callous-Unemotional Traits in Young Men

BACKGROUND

Individuals involved in antisocial behavior often engage in excessive reward-driven behavior even in the face of severe punishments including incarceration. However, the neural mechanisms of reward processing in antisocial behavior have not been examined while considering the heterogeneity of antisocial behavior and specific phases of reward and loss processing. In this study, we investigate the relationship between antisocial behavior, callous-unemotional traits, and neural activity during the anticipation and receipt of rewards and losses.

METHODS

A community sample of 144 low income, racially diverse, urban males at risk for antisocial behavior completed self-report measures, a clinical interview, and an fMRI scan at age 20. Neural response during the anticipation and receipt of monetary rewards and losses was linked to antisocial behavior and callous-unemotional traits using a priori ventral striatum region of interest analyses and exploratory whole brain analyses.

RESULTS

Antisocial behavior, but not callous-unemotional traits, was related to less ventral striatum response during reward anticipation. There were no significant relationships between neural reactivity and antisocial behavior or callous-unemotional traits during reward or loss outcomes. Antisocial behavior was also related to less ventrolateral prefrontal cortex reactivity during reward and loss anticipation.

CONCLUSIONS

These findings support a hypo-reactivity model of reward and loss anticipation in antisocial behavior. Lower striatal reactivity to cues of reward and lower prefrontal-regulatory recruitment during reward and loss anticipation may contribute to maladaptive reward-related behavior found in antisocial behavior.

Intact Ventral Striatal Prediction Error Signaling in Medicated Schizophrenia Patients

BACKGROUND

Midbrain dopaminergic neurons code a computational quantity, reward prediction error (RPE), which has been causally related to learning. Recently, this insight has been leveraged to link phenomenological and biological levels of understanding in psychiatric disorders, such as schizophrenia. However, results have been mixed, possibly due to small sample sizes. Here we present results from two studies with relatively large Ns to assess VS RPE in schizophrenia.

METHODS

In the current study we analyzed data from two independent studies, involving a total of 87 chronic medicated schizophrenia patients and 61 controls. Subjects completed a probabilistic reinforcement-learning task in conjunction with fMRI scanning. We fit each participant's choice behavior to a Q-learning model and derived trial-wise RPEs. We then modeled BOLD signal data with parametric regressor functions using these values to determine whether patient and control groups differed in prediction-error-related BOLD signal modulations.

RESULTS

Both groups demonstrated robust VS RPE BOLD activations. Interestingly, these BOLD activation patterns did not differ between groups in either study. This was true when we included all participants in the analysis, as well as when we excluded participants whose data was not sufficiently fit by the models.

CONCLUSIONS

These data demonstrate the utility of computational methods in isolating/testing underlying mechanisms of interest in psychiatric disorders. Importantly, similar VS RPE signal encoding across groups suggests that this mechanism does not drive task deficits in these patients. Deficits may instead stem from aberrant prefrontal/parietal circuits associated with maintenance and selection of goal-relevant information.

Effects of naltrexone on neural and subjective response to alcohol in treatment-seeking alcohol-dependent patients

BACKGROUND

Positively reinforcing properties of alcohol are in part mediated by activation of the ventral striatum (VS). Alcohol-induced release of endogenous opioids is thought to contribute to this response. Preclinical studies show that the opioid antagonist naltrexone (NTX) can block this cascade, but its ability to do so in treatment-seeking alcoholics has not been examined. Our objective was to study the effects of NTX on alcohol-induced VS activation and on amygdala response to affective stimuli in treatment-seeking alcohol-dependent inpatients.

METHODS

Sixty-three treatment-seeking alcoholics were randomized to receive NTX (50 mg) or placebo (PLC) daily. On Day 7, participants underwent an alcohol cue reactivity session, and craving was measured using the Penn Alcohol Craving Scale. On Day 9, participants received a saline infusion followed by an alcohol infusion and also viewed affective stimuli in a magnetic resonance scanner.

RESULTS

Irrespective of medication treatment condition, the alcohol infusion did not activate the VS in the alcohol-dependent patients. Unexpectedly, VS activation was greater in NTX treated patients than in the PLC group. NTX treated patients also reported increased craving in response to alcohol cue exposure, and increased subjective response to alcohol ("high" and "intoxicated") compared to PLC subjects. No significant effects of alcohol infusion on brain response to affective stimuli were in the NTX or PLC groups.

CONCLUSIONS

Unlike previous findings in social drinkers, a moderate level of intoxication did not activate the VS in treatment-seeking alcoholics. This is likely to reflect tolerance to the positively reinforcing properties of alcohol in this clinical population. Our findings may help explain the efficacy of NTX to reduce heavy drinking, but not to maintain abstinence.

Deletion of Prkcz increases intermittent ethanol consumption in mice

BACKGROUND

Prkcz has been identified as a gene whose expression is positively correlated with ethanol (EtOH) consumption in mice and is also induced by EtOH. Two proteins are produced from Prkcz: protein kinase M zeta (PKMζ), which is expressed in the nervous system and protein kinase C zeta (PKCζ), which is expressed in other tissues. We examined Prkcz(-/-) mice that lack PKCζ and PKMζ to investigate the role of this gene in behavioral responses to EtOH.

METHODS

Male Prkcz(-/-) and wild-type littermates were tested for EtOH consumption using 4 procedures: 24-hour intermittent access, 4-hour limited intermittent access, 4-day drinking-in-the-dark, and 24-hour continuous access. We also assessed the acute hypnotic effect of EtOH, EtOH reward, and taste preference for sweet-, bitter-, salty-, and umami-flavored solutions. Finally, we determined whether EtOH could increase PKMζ and PKCζ transcripts and protein expression in wild-type mice using quantitative PCR and Western blot analysis.

RESULTS

Prkcz(-/-) mice consumed more EtOH than their wild-type littermates in both intermittent access procedures, but not in the drinking-in-the-dark or 24-hour continuous access procedures. EtOH exposure increased Prkcz transcripts in cultured PC12 cells, and intermittent EtOH consumption increased PKMζ protein in the ventral striatum of wild-type mice.

CONCLUSIONS

Absence of PKMζ in the brain is associated with increased EtOH intake during procedures that incorporate intermittent consumption sessions every other day. Our data suggest that EtOH induces PKMζ, which acts in a negative feedback loop to limit binge-like EtOH consumption.

Initial evidence that OPRM1 genotype moderates ventral and dorsal striatum functional connectivity during alcohol cues

BACKGROUND

Endogenous opioids and striatal dopamine have been implicated in cue-induced alcohol craving and have been hypothesized to play a role in goal-directed, as opposed to habitual, alcohol use. This initial study examines dorsal and ventral striatal functional connectivity during alcohol-cue processing as a function of the A118G single-nucleotide polymorphism of the mu-opioid receptor (OPRM1) gene.

METHODS

Seventeen individuals with alcohol dependence (6 females; 90% Caucasian; mean age = 29.4) underwent blood oxygen level-dependent functional magnetic resonance imaging, while performing an alcohol taste-cues task. Psychophysiological interaction analyses investigated associations of the OPRM1 genotype with ventral and dorsal striatum functional connectivity, using the ventral striatum and the caudate as the seed region, respectively.

RESULTS

Compared to A-allele homozygotes, G-allele carriers of the OPRM1 gene showed (i) greater activation of the insula and orbitofrontal cortex and (ii) stronger negative fronto-striatal functional connectivity for both ventral and dorsal striatal seed regions during processing of alcohol versus water cues.

CONCLUSIONS

These preliminary findings suggest that, relative to A-allele homozygotes, G-allele carriers show unstable frontal regulation over reward and/or habit-driven inputs from the striatum resulting from greater reward sensitivity combined with limited self-control resources.

Psychosocial problems and recruitment of incentive neurocircuitry: exploring individual differences in healthy adolescents

Maturational differences in brain responsiveness to rewards have been implicated in the increased rates of injury and death in adolescents from behavior-related causes. However, much of this morbidity is related to drug intoxication or other externalizing behaviors, and may be concentrated in a subset of adolescents who are at psychosocial or neurobiological risk. To examine whether individual differences in psychosocial and behavioral symptomatology relate to activation of motivational neurocircuitry, we scanned 26 psychiatrically healthy adolescents using fMRI as they performed a monetary incentive delay task. Overall Problem Density on the Drug Use Screening Inventory (DUSI-OPD) correlated positively with activation of ventral mesofrontal cortex (mFC) during anticipation of responding for rewards (vs responding for no incentive). In addition, DUSI-OPD correlated positively with right ventral striatum recruitment during anticipation of responding to win rewards (vs responding for no incentive or to avoid losses of identical magnitudes). Finally, a psychophysiological interaction (PPI) analysis indicated that increased connectivity between nucleus accumbens and portions of anterior cingulate and mFC as a function of reward prospects also correlated with DUSI-OPD. These findings extend previous reports demonstrating that in adolescents, individual differences in reactivity of motivational neurocircuitry relate to different facets of impulsivity or externalizing behaviors.