Target identification and validation in brain reward dysfunction

Hypothesizing in the Face of the Opioid Crisis Coupling Genetic Addiction Risk Severity (GARS) Testing with Electrotherapeutic Nonopioid Modalities Such as H-Wave Could Attenuate Both Pain and Hedonic Addictive Behaviors

In the United States, amid the opioid overdose epidemic, nonaddicting/nonpharmacological proven strategies are available to treat pain and manage chronic pain effectively without opioids. Evidence supporting the long-term use of opioids for pain is lacking, as is the will to alter the drug-embracing culture in American chronic pain management. Some pain clinicians seem to prefer classical analgesic agents that promote unwanted tolerance to analgesics and subsequent biological induction of the "addictive brain". Reward genes play a vital part in modulation of nociception and adaptations in the dopaminergic circuitry. They may affect various sensory and affective components of the chronic pain syndromes. The Genetic Addiction Risk Severity (GARS) test coupled with the H-Wave at entry in pain clinics could attenuate pain and help prevent addiction. The GARS test results identify high-risk for both drug and alcohol, and H-Wave can be initiated to treat pain instead of opioids. The utilization of H-Wave to aid in pain reduction and mitigation of hedonic addictive behaviors is recommended, notwithstanding required randomized control studies. This frontline approach would reduce the possibility of long-term neurobiological deficits and fatalities associated with potent opioid analgesics.

Pre-clinical models of reward deficiency syndrome: A behavioral octopus

Individuals with mood disorders or with addiction, impulsivity and some personality disorders can share in common a dysfunction in how the brain perceives reward, where processing of natural endorphins or the response to exogenous dopamine stimulants is impaired. Reward Deficiency Syndrome (RDS) is a polygenic trait with implications that suggest cross-talk between different neurological systems that include the known reward pathway, neuroendocrine systems, and motivational systems. In this review we evaluate well-characterized animal models for their construct validity and as potential models for RDS. Animal models used to study substance use disorder, major depressive disorder (MDD), early life stress, immune dysregulation, attention deficit hyperactivity disorder (ADHD), post traumatic stress disorder (PTSD), compulsive gambling and compulsive eating disorders are discussed. These disorders recruit underlying reward deficiency mechanisms in multiple brain centers. Because of the widespread and remarkable array of associated/overlapping behavioral manifestations with a common root of hypodopaminergia, the basic endophenotype recognized as RDS is indeed likened to a behavioral octopus. We conclude this review with a look ahead on how these models can be used to investigate potential therapeutics that target the underlying common deficiency.

Review: brain neurobiology of gambling disorder based on rodent models

Different literature reviews of gambling disorder (GD) neurobiology have been focused on human studies, others have focused on rodents, and others combined human and rodent studies. The main question of this review was: which are the main neurotransmitters systems and brain structures relevant for GD based on recent rodent studies? This work aims to review the experimental findings regarding the rodent´s neurobiology of GD. A search in the Pub Med database was set (October 2012-October 2017) and 162 references were obtained. After screening, 121 references were excluded, and only 41 references remained from the initial output. More, other 25 references were added to complement (introduction section, neuroanatomical descriptions) the principal part of the work. At the end, a total of 66 references remained for the review. The main conclusions are: 1) according to studies that used noninvasive methods for drug administration, some of the neurotransmitters and receptors involved in behaviors related to GD are: muscarinic, N-methyl-D-aspartate (NMDA), cannabinoid receptor 1 (CB₁), cannabinoid receptor 2 (CB₂), dopamine 2 receptor (D₂), dopamine 3 receptor (D₃), and dopamine 4 receptor (D₄); 2) moreover, there are other neurotransmitters and receptors involved in GD based on studies that use invasive methods of drug administration (eg, brain microinjection); example of these are: serotonin 1A receptor (5-HT_1A), noradrenaline receptors, gamma-aminobutyric acid receptor A (GABA_A), and gamma-aminobutyric acid receptor B (GABA_B); 3) different brain structures are relevant to behaviors linked to GD, like: amygdala (including basolateral amygdala (BLA)), anterior cingulate cortex (ACC), hippocampus, infralimbic area, insular cortex (anterior and rostral agranular), nucleus accumbens (NAc), olfactory tubercle (island of Calleja), orbitofrontal cortex (OFC), medial prefrontal cortex (mPFC), prefrontal cortex (PFC) - subcortical network, striatum (ventral) and the subthalamic nucleus (STN); and 4) the search for GD treatments should consider this diversity of receptor/neurotransmitter systems and brain areas.

Proteostasis in Huntington's disease: disease mechanisms and therapeutic opportunities

Many neurodegenerative diseases are characterized by impairment of protein quality control mechanisms in neuronal cells. Ineffective clearance of misfolded proteins by the proteasome, autophagy pathways and exocytosis leads to accumulation of toxic protein oligomers and aggregates in neurons. Toxic protein species affect various cellular functions resulting in the development of a spectrum of different neurodegenerative proteinopathies, including Huntington's disease (HD). Playing an integral role in proteostasis, dysfunction of the ubiquitylation system in HD is progressive and multi-faceted with numerous biochemical pathways affected, in particular, the ubiquitin-proteasome system and autophagy routes for protein aggregate degradation. Unravelling the molecular mechanisms involved in HD pathogenesis of proteostasis provides new insight in disease progression in HD as well as possible therapeutic avenues. Recent developments of potential therapeutics are discussed in this review.

A high-fat diet combined with food deprivation increases food seeking and the expression of candidate biomarkers of addiction

A mouse model has been developed to study the effect of dietary fat combined with food deprivation periods on palatable food seeking and on the expression of three potential addiction biomarkers in the nucleus accumbens: fumarate hydratase (FH), ATP synthase subunit alpha (ATP5a1) and transketolase (TKT). Forty C57BL/6 J male mice, four-week old, were fed either with a high-fat (HF) diet or standard diet along the experiment. After 3 weeks of differential feeding, animals underwent a two-week training period of two daily sessions where visual cues were paired either to palatable food (chocolate cereals) or no food at all. This training was prolonged one more week with similar, one daily sessions preceded by 12 hours of food deprivation. A behavioural test was finally conducted where mice were confined for 30 minutes either in food unpaired compartments or in compartments previously paired with cereals, but now with empty food trays. Total activity during this behavioural test and serum corticosterone levels right after it were similar in all experimental groups. Mice tested in food-paired compartments showed a marked preference for the empty food tray that gradually disappeared in standard diet-fed individuals but persisted in HF-fed mice. HF-fed mice also overexpressed FH, ATP5a1 and TKT, which positively correlated with the persistence of preference for the empty food tray. It is suggested that HF diets combined with food deprivation may enhance food seeking behaviours while upregulating FH/ATP5a1/TKT, which are further envisaged as biomarkers of addiction.

Human ventromedial prefrontal lesions alter incentivisation by reward

Although medial frontal brain regions are implicated in valuation of rewards, evidence from focal lesions to these areas is scant, with many conflicting results regarding motivation and affect, and no human studies specifically examining incentivisation by reward. Here, 19 patients with isolated, focal damage in ventral and medial prefrontal cortex were selected from a database of 453 individuals with subarachnoid haemorrhage. Using a speeded saccadic task based on the oculomotor capture paradigm, we manipulated the maximum reward available on each trial using an auditory incentive cue. Modulation of behaviour by motivation permitted quantification of reward sensitivity. At the group level, medial frontal damage was overall associated with significantly reduced effects of reward on invigorating saccadic velocity and autonomic (pupil) responses compared to age-matched, healthy controls. Crucially, however, some individuals instead showed abnormally strong incentivisation effects for vigour. Increased sensitivity to rewards within the lesion group correlated with damage in subgenual ventromedial prefrontal cortex (vmPFC) areas, which have recently become the target for deep brain stimulation (DBS) in depression. Lesion correlations with clinical apathy suggested that the apathy associated with prefrontal damage is in fact reduced by damage at those coordinates. Reduced reward sensitivity showed a trend to correlate with damage near nucleus accumbens. Lesions did not, on the other hand, influence reward sensitivity of cognitive control, as measured by distractibility. Thus, although medial frontal lesions may generally reduce reward sensitivity, damage to key subregions paradoxically protect from this effect.

A Shared Molecular and Genetic Basis for Food and Drug Addiction: Overcoming Hypodopaminergic Trait/State by Incorporating Dopamine Agonistic Therapy in Psychiatry

This article focuses on the shared molecular and neurogenetics of food and drug addiction tied to the understanding of reward deficiency syndrome. Reward deficiency syndrome describes a hypodopaminergic trait/state that provides a rationale for commonality in approaches for treating long-term reduced dopamine function across the reward brain regions. The identification of the role of DNA polymorphic associations with reward circuitry has resulted in new understanding of all addictive behaviors.