Multimodal investigation of dopamine D(2)/D(3) receptors, default mode network suppression, and cognitive control in cocaine-use disorder

Neural mechanisms linked to treatment outcomes and recovery in substance-related and addictive disorders

The present review focuses on potential neural mechanisms underlying recovery from psychiatric conditions characterised by impaired impulse control, specifically substance use disorders, gambling disorder, and internet gaming disorder. Existing treatments (both pharmacological and psychological) for these addictions may impact brain processes, and these have been evaluated in neuroimaging studies. Medication challenge and short-term intervention administration will be considered with respect to treatment utility. Main models of addiction (e.g., dual process, reward deficiency syndrome) will be considered in the context of extant data. Additionally, advanced analytic approaches (e.g., machine-learning approaches) will be considered with respect to guiding treatment development efforts. Thus, this narrative review aims to provide directions for treatment development for addictive disorders.

The influence of dopamine autoreceptors on temperament and addiction risk

As a major regulator of dopamine (DA), DA autoreceptors (DAARs) exert substantial influence over DA-mediated behaviors. This paper reviews the physiological and behavioral impact of DAARs. Individual differences in DAAR functioning influences temperamental traits such as novelty responsivity and impulsivity, both of which are associated with vulnerability to addictive behavior in animal models and a broad array of externalizing behaviors in humans. DAARs additionally impact the response to psychostimulants and other drugs of abuse. Human PET studies of D2-like receptors in the midbrain provide evidence for parallels to the animal literature. These data lead to the proposal that weak DAAR regulation is a risk factor for addiction and externalizing problems. The review highlights the potential to build translational models of the functional role of DAARs in behavior. It also draws attention to key limitations in the current literature that would need to be addressed to further advance a weak DAAR regulation model of addiction and externalizing risk.

Neuroimaging correlates of internet gaming disorder: Can we achieve the promise of translating understandings of brain functioning into clinical advances?

Objectives

Here we aimed to consider the neural factors associated with internet gaming disorder (IGD), as well as the associations between these factors and existing treatments for the disorder.

Methods

A narrative review was conducted.

Results

Pharmacological as well as psychological treatments for IGD may be associated with specific changes in multiple brain areas and circuits. In particular, fronto-striatal and subcortical regions and pathways appear relevant to IGD and its treatment.

Conclusions

Neuroimaging holds promise for identifying specific mechanisms underlying IGD interventions. However, to date, firm conclusions are difficult to draw and more research examining neural mechanisms of empirically supported treatments for IGD is needed.

Association of dopamine D2-like and D3 receptor function with initial sensitivity to cocaine reinforcement in male rhesus monkeys

Identifying neurobiological characteristics that predict the development of cocaine use disorder would be of great value in prevention efforts. Because of their importance in mediating the abuse-related effects of cocaine, brain dopamine receptors are logical candidates for investigation. We analyzed data from two recently published studies that characterized availability of dopamine D2-like receptors (D2R) with [11C]raclopride PET imaging and dopamine D3 receptor (D3R) sensitivity with quinpirole-induced yawning in cocaine-naïve rhesus monkeys who subsequently acquired cocaine self-administration and completed a cocaine self-administration dose-effect curve. The present analysis compared D2R availability in several brain areas and characteristics of quinpirole-induced yawning, both acquired when monkeys were drug-naïve, with measures of initial sensitivity to cocaine. D2R availability in the caudate nucleus was negatively correlated with the ED50 of the cocaine self-administration curve, although the significance of this relationship was driven by an outlier and was not present after the outlier was removed. No other significant associations were observed between D2R availability in any examined brain region and measures of sensitivity to cocaine reinforcement. However, there was a significant negative correlation between D3R sensitivity, represented by the ED50 of the quinpirole-induced yawning curve, and the dose at which monkeys acquired cocaine self-administration. We also report no change from baseline D2R availability when a second PET scan was conducted after completion of the dose-effect curves. These data suggest the utility of D3R sensitivity, but not D2R availability, as a biomarker for vulnerability and resilience to cocaine. The well-established relationships between dopamine receptors and cocaine reinforcement in cocaine-experienced humans and animals may require extensive cocaine exposure.

Independent component analysis for internet gaming disorder

Introduction: There is a growing interest in the study of the neurobiological correlates of internet gaming disorder (IGD), and new techniques are beginning to be implemented for this purpose, such as independent component analysis (ICA). Aims: The present narrative review aimed to explore the studies that had used ICA for the study of the different brain networks possibly associated with IGD. Methods: We specifically focussed on three of the main networks: default-mode network, executive-control and salience networks. Results: Most studies have identified alterations in these three brain networks in individuals with IGD, which may be involved in the development and maintenance of this disorder. Conclusion: More studies are needed to deepen an understanding of the specific role of each in the symptomatology and treatment of IGD.

Cellular messenger molecules mediating addictive drug-induced cognitive impairment: cannabinoids, ketamine, methamphetamine, and cocaine

Background

Cognitive impairment is a commonly reported symptom with increasing life spans. Numerous studies have focused on identifying precise targets to relieve or reduce cognitive impairment; however, its underlying mechanism remains elusive. Most patients or animals exposed to addictive drugs exhibit cognitive impairment. Accordingly, the present review discusses the molecular changes induced by addictive drugs to clarify potential mechanisms that mediate cognitive impairments.

Main body

We investigated changes in cognitive function using four drugs: cannabinoids, ketamine, methamphetamine, and cocaine. Chronic administration of most addictive drugs reduces overall cognitive functions, such as working, spatial, and long-term recognition memories. Levels of several transcription factors involved in neuronal differentiation, as well as functional components of neurotransmitter receptors in neuronal cells, are reportedly altered. In addition, inflammatory factors showed a generally increasing trend. These impairments could be mediated by neuroinflammation, synaptic activity, and neuronal plasticity.

Conclusion

This review outlines the effects of acute or chronic drug use and potential molecular alterations in the central nervous system. In the central nervous system, addictive drug-induced changes in molecular pathways associated with cognitive function might play a pivotal role in elucidating the pathogenesis of cognitive impairment.

Location, Location, Location: The Expression of D3 Dopamine Receptors in the Nervous System

When the rat D3 dopamine receptor (D3R) was cloned and the distribution of its mRNA examined in 1990-1991, it attracted attention due to its peculiar distribution in the brain quite different from that of its closest relative, the D2 receptor. In the rat brain, the D3R mRNA is enriched in the limbic striatum as opposed to the D2 receptor, which is highly expressed in the motor striatal areas. Later studies in the primate and human brain confirmed relative enrichment of the D3R in the limbic striatum but also demonstrated higher abundance of the D3R in the primate as compared to the rodent brain. Additionally, in the rodent brain, the D3R in the dorsal striatum appears to be co-expressed with the D1 dopamine receptor-bearing striatal neurons giving rise to the direct output striatal pathway, although the picture is less clear with respect to the nucleus accumbens. In contrast, in the primate striatum, the D3R co-localizes with the D2 receptor throughout the basal ganglia as well as in extrastriatal brain areas. The relative abundance of the D3R in the limbic striatum, its output structures, secondary targets, and some of the other connected limbic territories may underpin its role in reward, drug dependence, and impulse control. Selective expression of D3R in the brain proliferative areas may point to its important role in the neural development as well as in neurodevelopmental abnormalities associated with schizophrenia and other developmental brain disorders.

Longitudinal changes in network engagement during cognitive control in cocaine use disorder

BACKGROUND

Cocaine use disorder (CUD) is characterized by poor cognitive control and has limited empirically supported treatment options. Furthermore, an understanding of brain mechanisms underlying CUD is at a relatively early stage. Thus, this study aimed to investigate longitudinal alterations in functional neural networks associated with cognitive control in cocaine use disorder (CUD).

METHODS

Secondary analysis was performed on data from 44 individuals who participated in three randomized clinical trials for CUD and completed an fMRI Stroop task both at baseline and post-treatment. Independent component analysis (ICA) was performed to assess changes in functional network engagement and investigate associations with cocaine-use behaviors. Mixed linear models were performed to test for longitudinal effects on network engagement and relationships with baseline patterns of cocaine use (i.e., past-month frequency and lifetime years of use) and periods of abstinence/use between scans (i.e., percent negative urine toxicology and maximum days of contiguous abstinence).

RESULTS

Six functional networks were identified as being related to cognitive control and/or exhibiting changes in engagement following treatment. Results indicated that engagement of amygdala-striatal, middle frontal and right-frontoparietal networks were reduced over time in CUD. Less change in the amygdala-striatal network was associated with greater lifetime years of cocaine use. Additional analyses revealed that negative toxicology results and achievement of continuous abstinence were associated with greater engagement of the right-frontoparietal network.

CONCLUSIONS

Neural systems that underlie cognitive control may change over time in individuals with CUD. A longer history of cocaine-use may hinder changes in network activity, potentially impeding recovery.

Can pharmacotherapy improve treatment outcomes in people with co-occurring major depressive and cocaine use disorders?

Introduction: Major depressive disorder (MDD) and cocaine use disorder (CUD) are prevalent and frequently co-occur. When co-occurring, the presence of one disorder typically negatively impacts the prognosis for the other. Given the clinical relevance, we sought to examine pharmacotherapies for co-occurring CUD and MDD. While multiple treatment options have been examined in the treatment of each condition individually, studies exploring pharmacological options for their comorbidity are fewer and not conclusive.Areas Covered: For this review, the authors searched the literature in PubMed using clinical query options for therapies and keywords relating to each condition. Then, they described potentially promising pharmacologic therapeutic options based on shared mechanisms between the two conditions and/or results from individual clinical trials conducted to date.Expert opinion: Medications like stimulants, dopamine (D3) receptors partial agonists or antagonists, antagonists of kappa opioid receptors, topiramate, and ketamine could be promising as there is significant overlap relating to reward deficiency models, antireward pathways, and altered glutamatergic systems. However, the available clinical literature on any one of these types of agents is mixed. Additionally, for some agents there is possible concern related to abuse potential (e.g. ketamine and stimulants).