Colin N. Haile

Acquisition and maintenance of intravenous cocaine self-administration in Lewis and Fischer inbred rat strains.

Lewis and Fischer inbred rat strains differ in behavioral and biochemical responses to psychoactive drugs: Lewis rats show greater behavioral responses to psychoactive drugs than Fischer rats and they fail to show biochemical adaptations in the mesolimbic dopamine system after chronic drug exposure, in contrast to Fischer and outbred rats. This suggests that Fischer and Lewis rats may differ in the initial, reinforcing effects of psychoactive drugs, but not in responses seen after the exposure that occurs with maintenance of drug-reinforced behavior. Thus, the present study tested whether these strains differ in acquisition or maintenance of intravenous cocaine self-administration. Acquisition of cocaine self-administration was examined in separate groups that were allowed 15 days to acquire the operant at one of three cocaine doses (0.25, 0.5, or 1.0 mg/kg/infusion). Compared to Fischer rats, Lewis rats acquired cocaine self-administration after fewer training trials and at lower doses. After maintenance, both strains showed characteristic extinction responding with saline substitution and dose-related responding to cocaine, although Fischer rats tended to show higher response rates. Finally, cocaine plasma levels, obtained after an intravenous cocaine infusion (1.0 mg/kg), showed no strain differences suggesting that the strain difference in acquisition was not due to cocaine pharmacokinetics. These strain differences in acquisition of cocaine self-administration may be related to reported strain differences in the mesolimbic dopamine system. Further, because acquisition of drug self-administration is an animal model of vulnerability to drug addiction, these inbred strains may be useful to study factors underlying such vulnerability.

BDNF Levels and Genotype are Associated with Antipsychotic-Induced Weight Gain in Patients with Chronic Schizophrenia

Recent evidence suggests that centrally released brain-derived neurotrophic factor (BDNF) modulates eating behavior and metabolism that is responsible for body weight fluctuation. BDNF also may play an important role in the therapeutic action of antipsychotic medications. We investigated whether the Val66Met polymorphism of the BDNF gene affected weight gain after long-term antipsychotic treatment in schizophrenia. The polymorphism was genotyped in 196 Chinese patients with schizophrenia on long-term antipsychotic medication. Serum BDNF was measured in all patients and 50 normal controls. Mean body mass index (BMI) change was evaluated retrospectively by means of clinical records. The results showed that there was a significant relationship between the three BDNF Val/Met genotypes and mean BMI gain, with genotype having a strong effect on BMI gain in male but not female patients. BDNF levels were significantly lower in patients than normal controls, and negatively correlated with BMI gain in female but not male patients. Our results suggest that variation in the BDNF gene may be a risk factor for weight gain in male patients with schizophrenia on long-term antipsychotic treatment, and decreased BDNF levels may be associated with weight gain in females.

Blockade of melanocortin transmission inhibits cocaine reward

Melanocortins and the melanocortin‐4 receptor (MC4‐R) are enriched in the nucleus accumbens, a brain region that has been implicated in the rewarding action of cocaine and other drugs of abuse. In the present study we use a number of rat behavioral models to show that infusion of a melanocortin peptide antagonist into the nucleus accumbens blocks the reinforcing, incentive motivational, and locomotor sensitizing effects of cocaine. We also show that locomotor responses to repeated cocaine exposure are completely blocked in MC4‐R null mutant mice and reduced in Agouti mice that overexpress an endogenous inhibitor of melanocortins in the brain. The results also demonstrate that cocaine administration increases the expression of MC4‐R in the nucleus accumbens and striatum, and that MC4‐R is co‐localized with prodynorphin in medium spiny neurons in the nucleus accumbens. Together, these findings indicate that the behavioral actions of cocaine are dependent on activation of MC4‐R, and suggest that upregulation of this receptor by drug exposure may contribute to sensitization of these behavioral responses. Modulation of cocaine reward is a novel action of the melanocortin–MC4‐R system and could be targeted for the development of new medications for cocaine addiction.

Neuronal and behavioural abnormalities in striatal function in DARPP-32- mutant mice

We investigated the role of the protein phosphatase inhibitor, dopamine‐ and cAMP‐regulated phosphoprotein of 32 kDa (DARPP‐32), in the expression of striatal neuropeptides and in biochemical and behavioural responses to repeated cocaine administration, using DARPP‐32 knock‐out mice. The striatum of DARPP‐32‐mutant mice showed heightened substance‐P‐like immunoreactivity, but normal levels of other neuropeptides. Repeated cocaine administration increased levels of ΔFosB, a Fos family transcription factor, in the striatum of wild‐type mice, and this increase was abolished in DARPP‐32‐mutant mice. Cocaine (20 mg/kg) acutely induced the same level of locomotor activity in the mutant and wild‐type mice, but the mutants showed a higher rate of locomotor sensitization to repeated cocaine exposures. These data show that DARPP‐32 is involved in regulating substance P expression in the striatonigral pathway, and in biochemical and behavioural plasticity with chronic administration of cocaine.

Genome-wide DNA methylation analysis in alcohol dependence

Genetic, epigenetic, and environmental factors influence the development of alcohol dependence (AD). Recent studies have shown that DNA methylation markers in peripheral blood may serve as risk markers for AD. Yet a genome‐wide epigenomic approach investigating the role of DNA methylation in AD has yet to be performed. We conducted a population‐based, case‐control study of genome‐wide DNA methylation to determine if alterations in gene‐specific methylation were associated with AD in a Chinese population. Using the Illumina Infinium Human Methylation27 BeadChip, we assessed gene‐specific methylation in over 27 000 CpG sites from DNA isolated from lymphocytes in 63 male AD in‐patients and 65 male healthy controls. Using a multi‐factorial statistical model, we observed differential methylation between cases and controls at multiple CpG sites with the majority of the methylated CpG sites being hypomethylated. Analyses with the online gene set analysis toolkit WebGestalt revealed that the genes of interest were enriched in multiple biological processes involved in AD development. Gene Ontology function annotation showed that stress, immune response and signal transduction were highly associated with AD. Further analysis by the Kyoto Encyclopedia of Genes and Genomes revealed associations with multiple pathways involved in metabolism through cytochrome P450, cytokine–cytokine receptor interaction and calcium signaling. Associations with canonical pathways previously shown to be involved in AD were also observed, such as dehydrogenases 1A (ADH1A), ADH7, aldehyde dehydrogenases 3B2 (ALDH3B2) and cytochrome P450 2A13. We present evidence that alterations in DNA methylation may be associated with AD, which is consistent with epigenetic theory.

Pharmacogenetic Treatments for Drug Addiction: Alcohol and Opiates

Aims: Psychiatric pharmacogenetics involves the use of genetic tests that can predict the effectiveness of treatments for individual patients with mental illness such as drug dependence. This review aims to cover these developments in the pharmacotherapy of alcohol and opiates, two addictive drugs for which we have the majority of our FDA approved pharmacotherapies. Methods: We conducted a literature review using Medline searching terms related to these two drugs and their pharmacotherapies crossed with related genetic studies. Results: Alcohols physiological and subjective effects are associated with enhanced β-endorphin release. Naltrexone increases baseline β-endorphin release blocking further release by alcohol. Naltrexones action as an alcohol pharmacotherapy is facilitated by a putative functional single nucleotide polymorphism (SNP) in the opioid mu receptor gene (Al18G) which alters receptor function. Patients with this SNP have significantly lower relapse rates to alcoholism when treated with naltrexone. Caucasians with various forms of the CYP2D6 enzyme results in a ‘poor metabolizer’ phenotype and appear to be protected from developing opioid dependence. Others with a “ultra-rapid metabolizer” phenotype do poorly on methadone maintenance and have frequent withdrawal symptoms. These patients can do well using buprenorphine because it is not significantly metabolized by CYP2D6. Conclusions: Pharmacogenetics has great potential for improving treatment outcome as we identify gene variants that affect pharmacodynamic and pharmacokinetic factors. These mutations guide pharmacotherapeutic agent choice for optimum treatment of alcohol and opiate abuse and subsequent relapse.

Pharmacogenetic Treatments for Drug Addiction: Cocaine, Amphetamine and Methamphetamine

Background: Pharmacogenetics uses genetic variation to predict individual differences in response to medications and holds much promise to improve treatment of addictive disorders. Objectives: To review how genetic variation affects responses to cocaine, amphetamine, and methamphetamine and how this information may guide pharmacotherapy. Methods: We performed a cross-referenced literature search on pharmacogenetics, cocaine, amphetamine, and methamphetamine. Results: We describe functional genetic variants for enzymes dopamine-beta-hydroxylase (DβH), catechol-O-methyltransferase (COMT), and dopamine transporter (DAT1), dopamine D4 receptor, and brain-derived neurotrophic factor (BDNF). A single nucleotide polymorphism (SNP; C-1021T) in the DβH gene is relevant to paranoia associated with disulfiram pharmacotherapy for cocaine addiction. Individuals with variable number tandem repeats (VNTR) of the SLC6A3 gene 3′-untranslated region polymorphism of DAT1 have altered responses to drugs. The 10/10 repeat respond poorly to methylphenidate pharmacotherapy and the 9/9 DAT1 variant show blunted euphoria and physiological response to amphetamine. COMT, D4 receptor, and BDNF polymorphisms are linked to methamphetamine abuse and psychosis. Conclusions: Disulfiram and methylphenidate pharmacotherapies for cocaine addiction are optimized by considering polymorphisms affecting DβH and DAT1 respectively. Altered subjective effects for amphetamine in DAT1 VNTR variants suggest a ‘protected’ phenotype. Scientific Significance: Pharmacogenetic-based treatments for psychostimulant addiction are critical for successful treatment.

Association of clozapine-induced weight gain with a polymorphism in the leptin promoter region in patients with chronic schizophrenia in a Chinese population

Weight gain is a problem commonly encountered with antipsychotic treatment and has become more apparent with increasing use of the newer atypical antipsychotics. The adipocyte-derived hormone, leptin, has been associated with body weight and energy homeostasis, and abnormal regulation of leptin could play a role in weight gain induced by antipsychotics. We investigated whether a leptin gene promoter variant affected weight gain after long-term treatment with clozapine in chronic schizophrenia. Leptin G2548A polymorphism was genotyped in 102 Chinese Han inpatients with chronic schizophrenia treated with clozapine. Weight gains, expressed as change in body mass index (BMI), were monitored after long-term clozapine treatment. We found a significant relationship between the 3 leptin G/A genotypes and mean BMI gain (F2,99 = 3.35, P = 0.039, r2 = 0.09). Moreover, genotype had a strong effect on BMI gain in male (P = 0.004, r2 = 0.16), but not in female patients (P > 0.05). Thus, variation in the leptin gene may be a risk factor for weight gain in male patients with schizophrenia on long-term clozapine treatment.

The novel oxidative stress marker thioredoxin is increased in first-episode schizophrenic patients

Excessive free radical production leading to oxidative stress may be involved in the pathophysiology of schizophrenia. Oxidative stress increases serum thioredoxin (TRX), a redox-regulating protein with antioxidant activity recognized as an oxidative-stress marker. The aim of this study was to assess the clinical significance of serum TRX levels in various stages of schizophrenia. Serum TRX levels were determined using ELISA from 60 never-medicated first-episode and 66 medicated chronic schizophrenia patients and 66 healthy control subjects matched for age and gender. The psychopathology of schizophrenia was assessed by the Positive and Negative Syndrome Scale (PANSS). Our results showed that group comparison between first-episode and chronic patients and control groups revealed significantly increased serum TRX only in first-episode patients. Increased levels of TRX in patients experiencing an acute stage schizophrenic episode was also significantly higher compared to chronic schizophrenic patients on antipsychotic medication. Serum TRX was also positively correlated with positive symptoms of schizophrenia. Our results suggest oxidative stress occurs in an acute stage of schizophrenic episode and may have an important role in pathogenesis and symptomology of schizophrenia. Lower TRX levels in chronic patients treated with antipsychotics may have implications for treatment outcome.

Pharmacotherapeutics directed at deficiencies associated with cocaine dependence: Focus on dopamine, norepinephrine and glutamate

Much effort has been devoted to research focused on pharmacotherapies for cocaine dependence yet there are no FDA-approved medications for this brain disease. Preclinical models have been essential to defining the central and peripheral effects produced by cocaine. Recent evidence suggests that cocaine exerts its reinforcing effects by acting on multiple neurotransmitter systems within mesocorticolimibic circuitry. Imaging studies in cocaine-dependent individuals have identified deficiencies in dopaminergic signaling primarily localized to corticolimbic areas. In addition to dysregulated striatal dopamine, norepinephrine and glutamate are also altered in cocaine dependence. In this review, we present these brain abnormalities as therapeutic targets for the treatment of cocaine dependence. We then survey promising medications that exert their therapeutic effects by presumably ameliorating these brain deficiencies. Correcting neurochemical deficits in cocaine-dependent individuals improves memory and impulse control, and reduces drug craving that may decrease cocaine use. We hypothesize that using medications aimed at reversing known neurochemical imbalances is likely to be more productive than current approaches. This view is also consistent with treatment paradigms used in neuropsychiatry and general medicine.