Neurogenetics of Dopaminergic Receptor Supersensitivity in Activation of Brain Reward Circuitry and Relapse: Proposing “Deprivation-Amplification Relapse Therapy” (DART)

Department of Psychiatry, School of Medicine and McKnight Brain Institute, University of Florida, Gainsville, FL, USA.
Postgraduate Medicine (Impact Factor: 1.7). 11/2009; 121(6):176-96. DOI: 10.3810/pgm.2009.11.2087
Source: PubMed


BACKGROUND AND HYPOTHESIS: It is well known that after prolonged abstinence, individuals who use their drug of choice experience a powerful euphoria that often precipitates relapse. While a biological explanation for this conundrum has remained elusive, we hypothesize that this clinically observed "supersensitivity" might be tied to genetic dopaminergic polymorphisms. Another therapeutic conundrum relates to the paradoxical finding that the dopaminergic agonist bromocriptine induces stronger activation of brain reward circuitry in individuals who carry the DRD2 A1 allele compared with DRD2 A2 allele carriers. Because carriers of the A1 allele relative to the A2 allele of the DRD2 gene have significantly lower D2 receptor density, a reduced sensitivity to dopamine agonist activity would be expected in the former. Thus, it is perplexing that with low D2 density there is an increase in reward sensitivity with the dopamine D2 agonist bromocriptine. Moreover, under chronic or long-term therapy with D2 agonists, such as bromocriptine, it has been shown in vitro that there is a proliferation of D2 receptors. One explanation for this relates to the demonstration that the A1 allele of the DRD2 gene is associated with increased striatal activity of L-amino acid decarboxylase, the final step in the biosynthesis of dopamine. This appears to be a protective mechanism against low receptor density and would favor the utilization of an amino acid neurotransmitter precursor like L-tyrosine for preferential synthesis of dopamine. This seems to lead to receptor proliferation to normal levels and results in significantly better treatment compliance only in A1 carriers. PROPOSAL AND CONCLUSION: We propose that low D2 receptor density and polymorphisms of the D2 gene are associated with risk for relapse of substance abuse, including alcohol dependence, heroin craving, cocaine dependence, methamphetamine abuse, nicotine sensitization, and glucose craving. With this in mind, we suggest a putative physiological mechanism that may help to explain the enhanced sensitivity following intense acute dopaminergic D2 receptor activation: "denervation supersensitivity." Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D2 receptor proliferation occurs (20%-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. Thus, the administration of dopamine D2 agonists would target D2 sensitization and attenuate relapse, especially in D2 receptor A1 allele carriers. This hypothesized mechanism is supported by clinical trials utilizing amino acid neurotransmitter precursors, enkephalinase, and catechol-O-methyltransferase (COMT) enzyme inhibition, which have resulted in attenuated relapse rates in reward deficiency syndrome (RDS) probands. If future translational research reveals that dopamine agonist therapy reduces relapse in RDS, it would support the proposed concept, which we term "deprivation-amplification relapse therapy" (DART). This term couples the mechanism for relapse, which is "deprivation-amplification," especially in DRD2 A1 allele carriers with natural D2 agonist therapy utilizing amino acid precursors and COMT and enkepalinase inhibition therapy.

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    • "This is a very complex mechanism involving epigenetic effects in cases of substance use especially in parental substance abuse. The well-known high risk for relapse in carriers of the DRD2 AI allele (Dahlgren et al., 2011) could be in part due to proposed dopamine receptor supersensitivity (Blum et al., 2009). Furthermore, decreased reward and negative eating behaviors in obesity are accompanied by diminished dopaminergic neurotransmission. "
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    ABSTRACT: Obesity and many well described eating disorders are accurately considered a global epidemic. The consequences of Reward Deficiency Syndrome, a genetic and epigenetic phenomena that involves the interactions of powerful neurotransmitters, are impairments of brain reward circuitry, hypodopaminergic function and abnormal craving behavior. Numerous sound neurochemical and genetic studies provide strong evidence that food addiction is similar to psychoactive drug addiction. Important facts which could translate to potential therapeutic targets espoused in this review include: 1) brain dopamine (DA) production and use is stimulated by consumption of alcohol in large quantities or carbohydrates bingeing; 2) in the mesolimbic system the enkephalinergic neurons are in close proximity, to glucose receptors; 3) highly concentrated glucose activates the calcium channel to stimulate dopamine release from P12 cells; 4) blood glucose and cerebrospinal fluid concentrations of homovanillic acid, the dopamine metabolite, are significantly correlated and 5) 2-deoxyglucose the glucose analogue, in pharmacological doses associates with enhanced dopamine turnover and causes acute glucoprivation. Evidence from animal studies and human fMRI support the hypothesis that multiple, but similar brain circuits are disrupted in obesity and drug dependence and DA-modulated reward circuits are involved in pathologic eating behaviors. Treatment for addiction to glucose and drugs alike, based on a consensus of neuroscience research, should incorporate dopamine agonist therapy, in contrast to current theories and practices that use dopamine antagonists. Until now, powerful dopamine-D2 agonists have failed clinically, due to chronic down regulation of D2 receptors instead, consideration of novel less powerful D2 agonists that up-regulate D2 receptors seems prudent. We encourage new strategies targeted at improving DA function in the treatment and prevention of obesity a subtype of reward deficiency.
    Frontiers in Psychology 09/2014; 5:919. DOI:10.3389/fpsyg.2014.00919 · 2.80 Impact Factor
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    • "Importantly and clinically relevant, haloperidol reduces the number of D2High receptors induced by psychostimulants. In terms of SUD, Blum et al. proposed a neurobiological and neurogenetic mechanism involving supersensitivity of DRD2 [208]. The potential role of dopaminergic polymorphisms and psychiatric disease and SUD have been the subject of intense investigation [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] since the initial findings of Blum et al. on the DRD2 gene and severe alcoholism [24]. "
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    ABSTRACT: The dopamine system has been implicated in both substance use disorder (SUD) and schizophrenia. A recent meta-analysis suggests that A1 allele of the DRD2 gene imposes genetic risk for SUD, especially alcoholism and has been implicated in Reward Deficiency Syndrome (RDS). We hypothesize that dopamine D2 receptor (DRD2) gene Taq1 A2 allele is associated with a subtype of non-SUD schizophrenics and as such may act as a putative protective agent against the development of addiction to alcohol or other drugs of abuse. Schizophrenics with SUD may be carriers of the DRD2 Taq1 A1 allele, and/or other RDS reward polymorphisms and have hypodopaminergic reward function. One plausible mechanism for alcohol seeking in schizophrenics with SUD, based on previous research, may be a deficiency of gamma type endorphins that has been linked to schizophrenic type psychosis. We also propose that alcohol seeking behavior in schizophrenics, may serve as a physiological self-healing process linked to the increased function of the gamma endorphins, thereby reducing abnormal dopaminergic activity at the nucleus accumbens (NAc). These hypotheses warrant further investigation and cautious interpretation. We, therefore, encourage research involving neuroimaging, genome wide association studies (GWAS), and epigenetic investigation into the relationship between neurogenetics and systems biology to unravel the role of dopamine in psychiatric illness and SUD.
    Medical Hypotheses 02/2014; 82(5). DOI:10.1016/j.mehy.2014.02.019 · 1.07 Impact Factor
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    ABSTRACT: Substance use disorders (SUD) are inheritable and the culprit is hypodopaminergic function regulated by reward genes. We evaluated a natural dopaminergic agonist; KB220 intravenous (IV) and oral variants, to improve dopaminergic function in SUD. Our pilot experiment found a significant reduction of chronic symptoms, measured by the Chronic Abstinence Symptom Severity (CASS) Scale. The combined group (IV and oral) did significantly better than the oral-only group over the first week and 30-day follow-up period. Next, the combination was given to 129 subjects and three factors; Emotion, Somatic, and Impaired Cognition, with eigenvalues greater than one were extracted for baseline CASS-Revised (CASS-R) variables. Paired sample t-tests for pre and post-treatment scales showed significant declines (p = .00001) from pre- to post-treatment: t = 19.1 for Emotion, t = 16.1 for Somatic, and t = 14.9 for Impaired Cognition. In a two-year follow-up of 23 subjects who underwent KB220IV therapy (at least five IV treatments over seven days) plus orals for 30+ days: 21 (91%) were sober at six months, 19 (82%) having no relapse; 19 (82%) were sober at one year, 18 (78%) having no relapse; and 21 (91%) were sober two-years post-treatment, 16(70%) having no relapse. We await additional research and advise caution in interpreting these encouraging results.
    Journal of psychoactive drugs 11/2012; 44(5):398-409. DOI:10.1080/02791072.2012.737727 · 1.10 Impact Factor
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