High intensity interval training exercise increases dopamine D2 levels and modulates brain dopamine signaling

Background

Previous research has outlined the health benefits of exercise including its therapeutic potential for substance use disorders (SUD). These data have already been utilized and it is now common to find exercise as part of SUD treatment and relapse prevention programs. However, we need to better understand different exercise regimens and determine which would be the most beneficial for SUDs. Recently, high intensity interval training (HIIT) has gained attention in comparison with aerobic and resistance exercise. Little is known regarding the neurobiological mechanisms of HIIT, including its effects on dopamine signaling and receptor levels in the brain. The present study examined the effects of chronic HIIT exercise on dopamine signaling as measured by dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and tyrosine hydroxylase (TH) quantification in the brains of male and female rats as measured by [3H] SCH 23390 and [3H] spiperone autoradiography, and TH-immunoreactive optical density values.

Methods

Rats were separated in two groups: sedentary and HIIT exercise. Exercise was on a treadmill for 30 min daily (10 3 min cycles) for six weeks with progressive speed increased up to 0.8 mph (21.5 m/min).

Results

Results showed for D2R-like binding, a significant effect across the ventral caudate putamen (V CPU) between sexes, such that mean D2R-like binding was 14% greater for males than females. In the nucleus accumbens shell (Nac Shell), the HIIT Exercise rats showed 16% greater D2R-like binding as compared to the sedentary rats. No significant effects of HIIT exercise were found across groups for brain D1R-like binding levels or TH expression.

Conclusion

These results suggest that HIIT exercise can modulate dopamine signaling by way of increased D2R. These findings support the premise that HIIT exercise plays an important role in dopamine signaling and, may provide a potential mechanism for how HIIT exercise can impact the brain and behavior.

Neurogenetics and Epigenetics of Loneliness

Loneliness, an established risk factor for both, mental and physical morbidity, is a mounting public health concern. However, the neurobiological mechanisms underlying loneliness-related morbidity are not yet well defined. Here we examined the role of genes and associated DNA risk polymorphic variants that are implicated in loneliness via genetic and epigenetic mechanisms and may thus point to specific therapeutic targets. Searches were conducted on PubMed, Medline, and EMBASE databases using specific Medical Subject Headings terms such as loneliness and genes, neuro- and epigenetics, addiction, affective disorders, alcohol, anti-reward, anxiety, depression, dopamine, cancer, cardiovascular, cognitive, hypodopaminergia, medical, motivation, (neuro)psychopathology, social isolation, and reward deficiency. The narrative literature review yielded recursive collections of scientific and clinical evidence, which were subsequently condensed and summarized in the following key areas: (1) Genetic Antecedents: Exploration of multiple genes mediating reward, stress, immunity and other important vital functions; (2) Genes and Mental Health: Examination of genes linked to personality traits and mental illnesses providing insights into the intricate network of interaction converging on the experience of loneliness; (3) Epigenetic Effects: Inquiry into instances of loneliness and social isolation that are driven by epigenetic methylations associated with negative childhood experiences; and (4) Neural Correlates: Analysis of loneliness-related affective states and cognitions with a focus on hypodopaminergic reward deficiency arising in the context of early life stress, eg, maternal separation, underscoring the importance of parental support early in life. Identification of the individual contributions by various (epi)genetic factors presents opportunities for the creation of innovative preventive, diagnostic, and therapeutic approaches for individuals who cope with persistent feelings of loneliness. The clinical facets and therapeutic prospects associated with the current understanding of loneliness, are discussed emphasizing the relevance of genes and DNA risk polymorphic variants in the context of loneliness-related morbidity.

"TO BE OR NOT TO BE" GWAS Ends the Controversy about the DRD2 Gene as a Determinant of Reward Deficiency Syndrome (RDS)

Since 1990, there have been thousands of published studies on addiction psychiatry. Several from Blum et al showed the clinical relevance of the Genetic Addiction Risk Severity (GARS) test in identifying risk for reward deficiency behaviors in cohorts from polysubstance abuse and pain clinics, post-surgical bariatrics, and DWI offenders facing prison time. Since Blum et al first published in JAMA (1990) concerning the association of the DRD2 gene polymorphism and severe alcoholism, reactions have been mixed. More recently, however, a meta-analysis of 62 studies showed a significant association between DRD2 rs1800497 and Alcohol Use Disorder (AUD). Other studies from Yale University showed that a haplotype block of the DRD2 gene A1 allele was associated with AUD and heroin dependence. GWAS studies of depression and suicide in 1.2 million veterans confirmed the first psychiatric candidate gene study finding from Blum et al 1990; a significant association between the minor DRD2 allele, Taq A1 and severe alcoholism. Additionally, the DRD2 rs1800497 is robustly associated with suicidal behaviors. Furthermore, DNA polymorphic alleles underlying substance use disorder (SUD) with multiple substances were mapped via chromatin refolding, revealing that the DRD2 gene and associated polymorphism(s) as the top gene signal. Based on these investigations, we conclude that GWAS should end the controversy about the DRD2 gene being one determinant of Reward Deficiency Syndrome (RDS) first reported in 1996.

Understanding Attentional Functioning in Adult Attention Deficit Hyperactivity Disorder-Could This Improve Diagnostic Specificity?

The diagnostic criteria for attention deficit hyperactivity disorder (ADHD) reflect the behavioural and functional outcomes of cognitive processes. Historically they have been based on external observations and lack specificity: clinical cohorts of children meeting diagnostic criteria show that around 40% may also meet diagnostic criteria for oppositional defiant disorder (ODD). We have proposed a clinical model to explain this: the Mental Effort Reward Imbalances model of ADHD (MERIM). This model views the lower levels of task completion that underlie several of the diagnostic criteria for ADHD as being due to a summation of deficits in executive functioning and reward processing. The subjective experience of inadequate reward from task completion may explain the reduced motivation, negativity, and oppositional attitude associated with ODD. The hypothesis for this study is that descriptions of affected individuals' attentional characteristics could be more specific for the executive functioning deficits associated with ADHD than the current symptom-based approaches. To test whether this might be usable in practice, we conducted a workshop that aimed to characterise in depth the patterns of attention experienced by adults with ADHD and how they impact functioning. Three main patterns were described: (1) complete lapses in attention; (2) partial attention to a task; (3) attending to multiple tasks and distractions, either simultaneously or in rapid sequence. All of these resulted in reduced productivity. They also described strategies for managing their attention deficits. Some people used distractions positively, to stimulate the mind to remain active and engaged rather than losing focus. Multi-tasking could also achieve this by providing higher levels of stimulation, however, the stimulation could itself become a distraction. Interest or stress might maintain engagement; extremes could sometimes lead to hyperfocusing, which was typically infrequent but could be highly productive. Focusing on executive functions may improve diagnostic sensitivity, as the current criteria fail to identify people who function adequately due to their use of strategies that mitigate the effects of their attentional deficits. Such people may present with secondary depression or anxiety rather than clear, behavioural symptoms of ADHD. With further development, the approach described in this paper may provide a more simple and fundamental way of recognising ADHD within the community. In the longer term, focusing more specifically on executive functions may provide cohorts with a 'purer' form of ADHD for scientific study.

The Role of Impulsivity and Reward Deficiency in "Liking" and "Wanting" of Potentially Problematic Behaviors and Substance Uses

A few studies have examined the changes in substance- and behavior-related "wanting" and "liking" of human subjects, the key properties of Incentive Sensitization Theory (IST). The aim of this study was to examine the dissociation between "wanting" and "liking" as a function of usage frequency, intensity, and subjective severity in individuals across four substances (alcohol, nicotine, cannabis, and other drugs) and ten behaviors (gambling, overeating, gaming, pornography use, sex, social media use, Internet use, TV-series watching, shopping, and work). Also, the potential roles of impulsivity and reward deficiency were investigated in "wanting," "liking," and wellbeing. The sex differences between "wanting" and "liking" were also examined. Based on our findings using structural equation modeling with 749 participants (503 women, M age = 35.7 years, SD = 11.84), who completed self-report questionnaires, "wanting" increased with the severity, frequency, and intensity of potentially problematic use, while "liking" did not change. Impulsivity positively predicted "wanting," and "wanting" positively predicted problem uses/behaviors. Reward deficiency positively predicted problem uses/behaviors, and both impulsivity and problem uses/behaviors negatively predicted wellbeing. Finally, women showed higher levels of "wanting," compared to men. These findings demonstrate the potential roles of incentive sensitization in both potentially problematic substance uses and behaviors.

Our evolved unique pleasure circuit makes humans different from apes: Reconsideration of data derived from animal studies

The brain regions tied to pleasure can be triggered by engaging in sex, eating tasty food, watching a movie, accomplishments at school and athletics, consuming drugs, and noble efforts to help the community, the country, and the world. It is noteworthy that research suggests that the latter type of satisfaction, supporting the community, may result in the most substantial positive effects on our immune system. However, these pathways for these effects are not understood. Berridge and Kringelbach have suggested that pleasure is mediated by well-developed mesocorticolimbic circuitry and serves adaptive functions. In affective disorders, anhedonia (lack of pleasure) or dysphoria (negative affect) can result from a breakdown of that hedonic system. Most importantly, human neuroimaging investigations indicate that surprisingly similar circuitry is activated by quite diverse pleasures, suggesting a common neural pathway shared by all rewarding stimuli and behaviors.

Over many years the controversy of dopamine involvement in pleasure/reward has led to confusion in terms, such as trying to separate motivation from pure pleasure (i.e., wanting versus liking). We take the position that animal studies cannot provide real clinical information that is described by self-reports in humans. On November 23^rd, 2017, evidence for our concerns was revealed. A brain system involved in everything from addiction to autism appears to have evolved differently in humans than in apes, as reported by a large research team in the journal Science. To reiterate, the new findings by Sousa et al., also suggest the importance of not over-relying on rodent and even non-human primate studies. Extrapolations, when it comes to the concept of pleasure, dopamine, and reinforcement, are not supported by these data. Human experience and study are now much more critical and important. Extrapolations from non-humans to humans may be more fiction than fact. While this statement is bold it should not at all suggest that animal date is unimportant, that is not the case. It is extremely valuable in many aspects and we must encourage the development of animal models for disease. However, we must be cautious in our interpretation of results without leaping to conclusions that may be explained by follow-up human experiments and subsequent data.

We are further proposing that in terms of overcoming a never –ending battle related to the current drug epidemic, the scientific community should realize that disturbing dopamine homeostasis by taking drugs or having a system compromised by genes or other epigenetic experiences, should be treated by alternative therapeutic modalities, expressed in this article as a realistic key goal. Application of genetic addiction risk (GARS™) testing and pro-dopamine regulation (KB220) should be considered along with other promising technologies including cognitive behavioral therapy, mind fullness, brain spotting and trauma therapy. Basic scientists have worked very hard to dis-entangle pleasure from incentive salience and learning signals in brain reward circuitry, but this work may be limited to animal models and rodents. A different consideration regarding the human reward systems is required.

Stimulants for the Control of Hedonic Appetite

The focus of this paper is treatment of obesity in relation to the management of hedonic appetite. Obesity is a complex condition which may be potentiated by excessive reward seeking in combination with executive functioning deficits that impair cognitive control of behavior. Stimulant medications address both reward deficiency and enhance motivation, as well as suppressing appetite. They have long been recognized to be effective for treating obesity. However, stimulants can be abused for their euphoric effect. They induce euphoria via the same neural pathway that underlies their therapeutic effect in obesity. For this reason they have generally not been endorsed for use in obesity. Among the stimulants, only phentermine (either alone or in combination with topiramate) and bupropion (which has stimulant-like properties and is used in combination with naltrexone), are approved by the United States Food and Drug Administration (FDA) for obesity, although dexamphetamine and methylpenidate are approved and widely used for treating attention deficit hyperactivity disorder (ADHD) in adults and children. Experience gained over many years in the treatment of ADHD demonstrates that with careful dose titration, stimulants can be used safely. In obesity, improvement in mood and executive functioning could assist with the lifestyle changes necessary for weight control, acting synergistically with appetite suppression. The obesity crisis has reached the stage that strong consideration should be given to adequate utilization of this effective and inexpensive class of drug.