Expectation effects on brain dopamine responses to methylphenidate in cocaine use disorder

Brain dopamine responses to ultra-processed milkshakes are highly variable and not significantly related to adiposity in humans

Ultra-processed foods high in fat and sugar may be addictive, in part, due to their purported ability to induce an exaggerated postingestive brain dopamine response akin to drugs of abuse. Using standard [11C]raclopride positron emission tomography (PET) displacement methods used to measure brain dopamine responses to addictive drugs, we measured postingestive striatal dopamine responses to an ultra-processed milkshake high in fat and sugar in 50 young, healthy adults over a wide body mass index range (BMI 20-45 kg/m2). Surprisingly, milkshake consumption did not result in significant postingestive dopamine response in the striatum (p=0.62) nor any striatal subregion (p>0.33) and the highly variable interindividual responses were not significantly related to adiposity (BMI: r=0.076, p=0.51; %body fat: r=0.16, p=0.28). Thus, postingestive striatal dopamine responses to an ultra-processed milkshake were likely substantially smaller than many addictive drugs and below the limits of detection using standard PET methods.

Translational models of addiction phenotypes to advance addiction pharmacotherapy

Alcohol and substance use disorders are heterogeneous conditions with limited effective treatment options. While there have been prior attempts to classify addiction subtypes, they have not been translated into clinical practice. In an effort to better understand heterogeneity in psychiatric disorders, the National Institute for Mental Health Research Domain Criteria (RDoC) has challenged scientists to think beyond diagnostic symptoms and to consider the underlying features of psychopathology from a neuroscience-based framework. The field of addiction has grappled with this approach by considering several key constructs with the potential to capture RDoC domains. This critical review will focus on the efforts to apply translational models of addiction phenomenology in human clinical samples, including their relative strengths and weaknesses. Opportunities for forward and reverse translation are also discussed. Deep behavioral phenotyping using neuroscience-informed batteries shows promise for a better understanding of the clinical neuroscience of addiction and advancing precision medicine for alcohol and substance use disorders.

Repeated methamphetamine administration produces cognitive deficits through augmentation of GABAergic synaptic transmission in the prefrontal cortex

Methamphetamine (METH) abuse is associated with the emergence of cognitive deficits and hypofrontality, a pathophysiological marker of many neuropsychiatric disorders that is produced by altered balance of local excitatory and inhibitory synaptic transmission. However, there is a dearth of information regarding the cellular and synaptic mechanisms underlying METH-induced cognitive deficits and associated hypofrontal states. Using PV-Cre transgenic rats that went through a METH sensitization regime or saline (SAL) followed by 7-10 days of home cage abstinence combined with cognitive tests, chemogenetic experiments, and whole-cell patch recordings on the prelimbic prefrontal cortex (PFC), we investigated the cellular and synaptic mechanisms underlying METH-induce hypofrontality. We report here that repeated METH administration in rats produces deficits in working memory and increases in inhibitory synaptic transmission onto pyramidal neurons in the PFC. The increased PFC inhibition is detected by an increase in spontaneous and evoked inhibitory postsynaptic synaptic currents (IPSCs), an increase in GABAergic presynaptic function, and a shift in the excitatory-inhibitory balance onto PFC deep-layer pyramidal neurons. We find that pharmacological blockade of D1 dopamine receptor function reduces the METH-induced augmentation of IPSCs, suggesting a critical role for D1 dopamine signaling in METH-induced hypofrontality. In addition, repeated METH administration increases the intrinsic excitability of parvalbumin-positive fast spiking interneurons (PV + FSIs), a key local interneuron population in PFC that contributes to the control of inhibitory tone. Using a cell type-specific chemogenetic approach, we show that increasing PV + FSIs activity in the PFC is necessary and sufficient to cause deficits in temporal order memory similar to those induced by METH. Conversely, reducing PV + FSIs activity in the PFC of METH-exposed rats rescues METH-induced temporal order memory deficits. Together, our findings reveal that repeated METH exposure increases PFC inhibitory tone through a D1 dopamine signaling-dependent potentiation of inhibitory synaptic transmission, and that reduction of PV + FSIs activity can rescue METH-induced cognitive deficits, suggesting a potential therapeutic approach to treating cognitive symptoms in patients suffering from METH use disorder.

A three-factor model of common early onset psychiatric disorders: temperament, adversity, and dopamine

Commonly comorbid early onset psychiatric disorders might reflect the varying expression of overlapping risk factors. The mediating processes remain poorly understood, but three factors show some promise: adolescent externalizing traits, early life adversity, and midbrain dopamine autoreceptors. To investigate whether these features acquire greater predictive power when combined, a longitudinal study was conducted in youth who have been followed since birth. Cohort members were invited to participate based on externalizing scores between 11 to 16 years of age. At age 18 (age 18.5 ± 0.6 y.o.), 52 entry criteria meeting volunteers had a 90-min positron emission tomography scan with [¹⁸F]fallypride, completed the Childhood Trauma Questionnaire, and were assessed with the Structured Clinical Interview for DSM-5. The three-factor model identified those with a lifetime history of DSM-5 disorders with an overall accuracy of 90.4% (p = 2.4 × 10^-5) and explained 91.5% of the area under the receiver operating characteristic curve [95% CI: .824, 1.000]. Targeting externalizing disorders specifically did not yield a more powerful model than targeting all disorders (p = 0.54). The model remained significant when including data from participants who developed their first disorders during a three-year follow-up period (p = 3.5 × 10^-5). Together, these results raise the possibility that a combination of temperamental traits, childhood adversity, and poorly regulated dopamine transmission increases risk for diverse, commonly comorbid, early onset psychiatric problems, predicting this susceptibility prospectively.

Real time monitoring of dopamine release evoked by mitragynine (Kratom): An insight through electrochemical sensor

BACKGROUND

Mitragynine, the major indole alkaloid from Mitragyna speciosa has been reported previously to possess abuse liability. However, there are insufficient data suggesting the mechanism through which this pharmacological agent causes addiction.

AIMS

In this study, we investigated the effects of mitragynine on dopamine (DA) level and dopamine transporter (DAT) expression from the rat's frontal cortex.

METHODS

DA level was recorded in the brain samples of animals treated with acute or repeated exposure for 4 consecutive days with either vehicle or mitragynine (1 and 30 mg/kg) using electrochemical sensor. Animals were then decapitated and the brain regions were removed, snap-frozen in liquid nitrogen and immediately stored at -80 °C. DA level was quantified using Enzyme linked immunosorbent assay (ELISA) kits and DAT gene expression was determined using quantitative real time polymerase chain reaction (RT-qPCR).

RESULTS/OUTCOME

Mitragynine (1 and 30 mg/kg) did not increase DA release following acute treatment, however, after repeated exposure at day 4, mitragynine significantly and dose dependently increased DA release in the frontal cortex. In this study, we also observed a significant increase in DAT mRNA expression at day 4 in group treated with mitragynine (30 mg/kg).

CONCLUSION/INTERPRETATION

Data from this study indicates that mitragynine significantly increased DA release when administered repeatedly, increased in DAT mRNA expression with the highest tested dose (30 mg/kg). Therefore, the rewarding effects observed after mitragynine administration could be due to its ability to increase DA content in certain areas of the brain especially the frontal cortex.

Drug induced stuttering: pharmacovigilance data

Background: Stuttering is a speech disorder characterized by poor fluency of speech despite the speech production organs being normal. Numerous factors contribute to stuttering, and it may also be an iatrogenic effect of certain drugs. The aim of this study was to investigate the association between stuttering and drug exposure.Research design and methods: We investigated the association between drugs and stuttering. We analyzed reports in the World Health Organization global individual case safety reports database (Vigibase) up to 31 May 2020 with the MedDRA lower level terms 'stutter' and 'stuttering.' The association between a drug and the occurrence of the adverse drug reaction was estimated by disproportionality analysis. Reporting odds ratios (ROR) were calculated with 95% confidence intervals.Results: In total, 724 notifications were identified using the MedDRA terms selected. The main drugs implicated were methylphenidate (ROR = 19.58; 95% CI: 13.3-28.8), topiramate (ROR = 12.5; 95% CI: 7.1-22.1), olanzapine (ROR = 12; 95% CI: 8-17.9) and golimumab (ROR = 10.2; 95% CI: 5.5-19.1).Conclusions: When stuttering occurs in a patient treated by drugs affecting neurotransmission, a drug-induced origin of the stutter should be considered.

The hypodopaminergic state ten years after: transcranial magnetic stimulation as a tool to test the dopamine hypothesis of drug addiction

An altered dopamine transmission has been described for different types of addiction for a long time. Preclinical and clinical evidence support the hypodopaminergic hypothesis and underpin the need to increase dopamine transmission to obtain therapeutic benefit. Repetitive transcranial magnetic stimulation (rTMS) of prefrontal cortex shows efficacy in treating some forms of addiction. Recent imaging studies confirmed that the therapeutic effect of rTMS is correlated with an enhancement of dopamine transmission. Novel targets for rTMS are under evaluation to increase its effectiveness in treating addiction, and research is ongoing to find the optimal protocol to boost dopaminergic transmission in the addicted brain. TMS can thus be considered a useful tool to test the dopamine hypothesis of drug addiction and instrumental in the search for addiction therapeutics.

The anticipatory dopamine response in addiction: A common neurobiological underpinning of gambling disorder and substance use disorder?

The dopamine system is associated with reward processes in both gambling disorder and substance use disorder, and may constitute a common neurobiological underpinning in addiction. The present review examines differences and similarities of dopaminergic reward processes in gambling disorder and substance use disorder. First, it is suggested that baseline binding potentials of the dopamine system may not be a common pathway, since substance use disorder is associated with reduced binding potentials, whereas gambling disorder is not. Second, it is suggested that dopaminergic reward response may be not a common pathway, since substance use disorder is associated with a blunted dopamine response toward drugs, while conflicting findings of reward response has been reported in gambling disorder. Instead, it is suggested that the anticpatory dopamine response may constitute a common underpinning of gambling disorder and substance use disorder, which may be associated with increased dopamine activity in both types of disorder, and does not involve the intake of substances. The notion of the anticipatory dopamine response as a common underpinning of gambling disorder and substance use disorder is consistent with dopaminergic models of addictions such as the incentive-sensitization model, the ingrative neurodevelopmental model of vulnerability toward addiction and the reward prediction error model.

Binge alcohol use is not associated with alterations in striatal dopamine receptor binding or dopamine release

BACKGROUND

Previous imaging studies using Positron Emission Tomography (PET) have shown that alcohol use disorder (AUD) is associated with a decrease in dopamine type 2/3 receptor (D_2/3) binding and dopamine transmission. Although binge drinking is a risk factor for future AUD, little is known about the neurobiology of binge drinking in young adults. This study measured D_2/3 receptor binding and stimulant-induced dopamine release using PET and [¹¹C]raclopride in binge drinkers without an AUD.

METHODS

This study included 14 healthy controls (HC) and 14 young adult binge drinkers (BD), aged 18-25. The BD met National Institute on Alcohol Abuse and Alcoholism (NIAAA) criteria for binge drinking and the HC subjects were social drinkers. The subjects were scanned with [¹¹C]raclopride before and after the administration of oral methylphenidate (60 mg) to measure D_2/3 binding and dopamine release.

RESULTS

There was no significant difference in the PET measures of D_2/3 binding or methylphenidate-induced dopamine release between the two groups. There was no significant association between Alcohol Use Disorders Identification Test (AUDIT) scores or 30-day drinking history and the imaging data.

CONCLUSION

In this sample of 18-25-year-old binge drinkers without a diagnosis of a substance use disorder, there were no significant differences in D_2/3 receptor binding potential or methylphenidate-induced dopamine release relative to healthy controls.