Antecedents and Consequences of Drug Abuse in Rats Selectively Bred for High and Low Response to Novelty.

Antecedents and consequences of drug abuse in rats selectively bred for high and low response to novelty.

Neuropharmacology. 2013 Apr 29;
Flagel SB, Waselus M, Clinton SM, Watson SJ, Akil H

Human genetic and epidemiological studies provide evidence that only a subset of individuals who experiment with potentially addictive drugs become addicts. What renders some individuals susceptible to addiction remains to be determined, but most would agree that there is no single trait underlying the disorder. However, there is evidence in humans that addiction liability has a genetic component, and that certain personality characteristics related to temperament (e.g. the sensation-seeking trait) are associated with individual differences in addiction liability. Consequently, we have used a selective breeding strategy based on locomotor response to a novel environment to generate two lines of rats with distinct behavioral characteristics. We have found that the resulting phenotypes differ on a number of neurobehavioral dimensions relevant to addiction. Relative to bred low-responder (bLR) rats, bred high-responder (bHR) rats exhibit increased exploratory behavior, are more impulsive, more aggressive, seek stimuli associated with rewards, and show a greater tendency to relapse. We therefore utilize this unique animal model to parse the genetic, neural and environmental factors that contribute to addiction liability. Our work shows that the glucocorticoid receptor (GR), dopaminergic molecules, and members of the fibroblast growth factor family are among the neurotransmitters and neuromodulators that play a role in both the initial susceptibility to addiction as well as the altered neural responses that follow chronic drug exposure. Moreover, our findings suggest that the hippocampus plays a major role in mediating vulnerability to addiction. It is hoped that this work will emphasize the importance of personalized treatment strategies and identify novel therapeutic targets for humans suffering from addictive disorders. HubMed – addiction


Ethanol self-administration and nicotine treatment induce brain levels of CYP2B6 and CYP2E1 in African Green monkeys.

Neuropharmacology. 2013 Apr 29;
Ferguson CS, Miksys S, Palmour RM, Tyndale RF

CYP2B6 and CYP2E1 are enzymes responsible for the metabolism of many centrally acting drugs, toxins and endogenous compounds. Human smokers and alcoholics have elevated levels of CYP2B6 and CYP2E1 in certain brain regions, which may contribute to altered drug efficacy, neurotoxicity and metabolic tolerance. The objective of this study was to determine the effects of ethanol self-administration and nicotine treatment, alone and in combination, on brain CYP2B6 and CYP2E1 levels in monkeys. Monkeys were randomized into four groups (N=10/group): an ethanol-only group, a nicotine-only group, an ethanol + nicotine group and a control (no drug) group. Ethanol (10% alcohol in sucrose solution) was voluntarily self-administered by the monkeys and nicotine was given as subcutaneous injections (0.5 mg/kg bid). Immunocytochemistry revealed induction of both CYP2B6 and CYP2E1 protein in certain brain regions and cells within monkey brain as a result of ethanol self-administration, nicotine treatment and combined exposure to both drugs. Immunoblotting analyses demonstrated CYP2B6 induction by ethanol in the caudate, putamen and cerebellum (1.5-3.2 fold, P<0.05), and CYP2E1 induction by nicotine in the frontal cortex and putamen (1.6-2.0 fold, P<0.05). Combined ethanol and nicotine exposure induced CYP2B6 in the caudate, putamen, thalamus and cerebellum (1.4-2.4 fold, P<0.05), and CYP2E1 in the frontal cortex and putamen (1.5-1.8, P<0.05). CYP2B6 and CYP2E1 mRNA levels were unaffected by ethanol or nicotine exposure. In summary, ethanol and nicotine can induce CYP2B6 and CYP2E1 protein in the primate brain, which could potentially result in altered sensitivity to centrally acting drugs and toxins. HubMed – addiction


When a good taste turns bad: Neural mechanisms underlying the emergence of negative affect and associated natural reward devaluation by cocaine.

Neuropharmacology. 2013 Apr 29;
Carelli RM, West EA

An important feature of cocaine addiction in humans is the emergence of negative affect (e.g., dysphoria, irritability, anhedonia), postulated to play a key role in craving and relapse. Indeed, the DSM-IV recognizes that social, occupational and/or recreational activities become reduced as a consequence of repeated drug use where previously rewarding experiences (e.g., food, job, family) become devalued as the addict continues to seek and use drug despite serious negative consequences. Here, research in the Carelli laboratory is reviewed that examined neurobiological mechanisms that may underlie these processes using a novel animal model. Oromotor responses (taste reactivity) were examined as rats learned that intraoral infusion of a sweet (e.g., saccharin) predicts impending but delayed access to cocaine self-administration. We showed that rats exhibit aversive taste reactivity (i.e., gapes/rejection responses) during infusion of the sweet paired with impending cocaine, similar to aversive responses observed during infusion of quinine, a bitter tastant. Critically, the expression of this pronounced aversion to the sweet predicted the subsequent motivation to self-administer cocaine. Electrophysiology studies show that this shift in palatability corresponds to an alteration in nucleus accumbens (NAc) cell firing; neurons that previously responded with inhibition during infusion of the palatable sweet shifted to excitatory activity during infusion of the cocaine-devalued tastant. This excitatory response profile is typically observed during infusion of quinine, indicating that the once palatable sweet becomes aversive following its association with impending but delayed cocaine, and NAc neurons encode this aversive state. We also review electrochemical studies showing a shift (from increase to decrease) in rapid NAc dopamine release during infusion of the cocaine-paired tastant as the aversive state developed, again, resulting in responses similar to quinine infusion. Collectively, our findings suggest that cocaine-conditioned cues elicit a cocaine-need state that is aversive, is encoded by a distinct subset of NAc neurons and rapid dopamine signaling, and promotes cocaine-seeking behavior. Finally, we present data showing that experimentally induced abstinence (30 days) exacerbates this natural reward devaluation by cocaine, and this effect is correlated with a greater motivation to lever press during extinction. Dissecting the neural mechanisms underlying these detrimental consequences of addiction is critical since it may lead to novel treatments that ameliorate negative affective states associated with drug use and decrease the drive (craving) for the drug. HubMed – addiction


Investigational drugs for schizophrenia targeting the dopamine receptor: Phase II trials.

Expert Opin Investig Drugs. 2013 May 3;
Rao NP, Remington G

Introduction: For over half a century now, the dopamine hypothesis has provided the most widely accepted heuristic model linking pathophysiology and treatment in schizophrenia. Despite dopaminergic drugs being available for six decades, this system continues to represent a key target in schizophrenia drug discovery. The present article reviews the scientific rationale for dopaminergic medications historically and the shift in our thinking since, which is clearly reflected in the investigational drugs detailed. Areas covered: We searched for investigational drugs using the key words ‘dopamine,’ ‘schizophrenia,’ and ‘Phase II’ in American and European clinical trial registers (;, published articles using National Library of Medicine’s PubMed database, and supplemented results with a manual search of cross-references and conference abstracts. We provide a brief description of drugs targeting dopamine synthesis, release or metabolism, and receptors (agonists/partial agonists/antagonists). Expert opinion: There are prominent shifts in how we presently conceptualize schizophrenia and its treatment. Current efforts are not as much focused on developing better antipsychotics but, instead, on treatments that can improve other symptom domains, in particular cognitive and negative. This new era in the pharmacotherapy of schizophrenia moves us away from the older ‘magic bullet’ approach toward a strategy fostering polypharmacy and a more individualized approach shaped by the individual’s specific symptom profile. HubMed – addiction