The human nucleus accumbens is highly susceptible to G protein down-regulation by methamphetamine and heroin

Determination of the Relationship Between Craving and 4-repeat Allele of DRD4 Gene Polymorphism in the Early Withdrawal Period of Alcohol Use Disorders

OBJECTIVE

Alcohol use disorder (AUD) is a disease with chronic relapses. Risk factors of craving, which is thought to be one of the predictors of relapse, have been studied for a long time. The DRD4 gene is located on chromosome 11p and has a 48-base pair variable number of tandem repeat (VNTR) polymorphisms in the 3rd exon. This study aimed to investigate if a relationship existed between craving and DRD4 VNTR polymorphism and to determine the predictors of craving.

METHODS

A total of 125 patients with AUD were included in the study. The sociodemographic data form, the Michigan Alcoholism Screening Test (MAST), the Obsessive Compulsive Drinking Scale (OCDS), and the Penn Alcohol Craving Scale (PACS) were applied to the patients. Polymerase chain reaction (PCR) was used to determine the DRD4 VNTR variant of all participants in the peripheral blood sample.

RESULTS

In the 4R/4R homozygous group, it was found that the age at first alcohol use was higher and the scores of the OCDS on the seventh day were lower, but this relationship could not be demonstrated in further statistical analyses. In the stepwise linear regression model, the age at first alcohol use, MAST score, duration of AUD, and delirium tremens history were found to be the predictors of craving.

CONCLUSION

DRD4 VNTR polymorphism does not play a role as a predictor of craving. A decrease in age at first alcohol use, an increase in the MAST score, and the presence of delirium tremens were found to be the predictors of craving among the participants of this study.

Normal glutathione levels in autopsied brain of chronic users of heroin and of cocaine

BACKGROUND

Animal studies suggest that exposure to either of the two widely used drugs of abuse, heroin or cocaine, causes depletion of the antioxidant, reduced glutathione, a hallmark of oxidative stress, in the brain. However, the relevance of the animal findings to the human is uncertain and clinical trials with the antioxidant GSH precursor n-acetylcysteine have produced mixed results in cocaine dependence.

METHODS

Our major objective was to compare glutathione levels, determined by an HPLC-coulometric procedure, in autopsied brain of chronic heroin (n = 11) and cocaine users (n = 9), who were positive for the drugs in the brain, to those of matched controls (n = 16). Six brain regions were examined, including caudate, hippocampus, thalamus and frontal, temporal and insular cortices.

RESULTS

In contrast to experimental animal findings, we found no statistically significant difference between mean levels of reduced or oxidized glutathione in the drug user vs. control groups. Moreover, no correlation was found between levels of drugs in the brain and those of glutathione.

CONCLUSIONS

Acknowledging the many generic limitations of an autopsied human brain study and the preliminary nature of the findings, our data nevertheless suggest that any oxidative stress caused by heroin or cocaine in chronic users of the drugs might not be sufficient to cause substantial loss of stores of glutathione in the human brain, at least during early withdrawal. These findings, requiring replication, might also have some relevance to future clinical trials employing glutathione supplement therapy as an anti-oxidative strategy in chronic users of the two abused drugs.

Pattern recognition analysis of proton nuclear magnetic resonance spectra of postmortem cerebrospinal fluid from rats with drug-induced seizure or coma

Cerebrospinal fluid (CSF) is routinely subjected to gross evaluation in postmortem investigations; however, its use in chemical evaluations has not been fully realized. Analysis of nuclear magnetic resonance (NMR) spectra with pattern recognition methods was applied to CSF samples. Rats were treated with pentylenetetrazol (PTZ) to induce seizure or pentobarbital (PB) to induce coma, and postmortem CSF was collected after CO₂ gas euthanization. Pattern recognition analysis of the NMR data was performed on individual postmortem CSF samples. The aim of this study was to determine if pattern recognition analysis of NMR data could be used to classify the rats according to their drug treatment. The applicability of NMR data with pattern recognition analysis using postmortem CSF was also assessed. Partial Least Squares-Discriminant Analysis (PLS-DA) score plots indicated that the PTZ, PB, and NS (control) groups were clustered and clearly separated. PLS-DA correlation loading plots showed respective spectral and category variances of 41% and 42% for factor 1, and 17% and 27% for factor 2. Thus, factors 1 and 2 together described 58% (41%+17%) and 69% (42%+27%) of the variation, respectively. NMR study of postmortem CSF has the potential to be utilized as both a novel forensic neurochemistry method and in the clinical setting.

Patterns of cortical activation following motor tasks and psychological-inducing movie cues in heroin users: an fMRI study

OBJECTIVE

Drug abuse and addiction are worldwide health problems. However, few studies have used fMRI to investigate the effect of chronic heroin use on brain activation. This is a study along this line.

METHOD

fMRI positive sites in the brain were recorded during different motor and sensory activities.

RESULTS

Following motor activities, heroin users had more sites globally activated in the brain than in normal volunteers, with ex-heroin users being least reactive. Conversely, a "heroin puffing" movie produced more activation in ongoing-heroin and ex-heroin users than in the normal individuals, whereas a movie with explicit sexual content was less stimulatory in both groups of heroin users compared to normal individuals.

CONCLUSIONS

These significant findings relative to the function of specific brain nuclei are discussed.

Sustained impairment of α2A-adrenergic autoreceptor signaling mediates neurochemical and behavioral sensitization to amphetamine

BACKGROUND

In rodents, drugs of abuse induce locomotor hyperactivity, and repeating injections enhance this response. This effect, called behavioral sensitization, persists months after the last administration. It has been shown that behavioral sensitization to amphetamine develops parallel to an increased release of norepinephrine (NE) in the prefrontal cortex (PFC).

METHODS

Rats and mice were repeatedly treated with amphetamine (1 or 2 mg/kg intraperitoneally, respectively) to obtain sensitized animals. The NE release in the PFC was measured by microdialysis in freely moving mice (n = 55). Activity of locus coeruleus (LC) noradrenergic neurons was determined in anaesthetized rats (n = 15) by in vivo extracellular electrophysiology. The α2A-adrenergic autoreceptor (α2A-AR) expression was assessed by autoradiography on brain slices, and Gαi proteins expression was measured by western blot analysis of LC punches.

RESULTS

In sensitized rats LC neurons had a higher spontaneous firing rate, and clonidine-an α2A-adrenergic agonist-inhibited LC neuronal firing less efficiently than in control animals. Clonidine also induced lower levels of NE release in the PFC of sensitized mice. This desensitization was maintained by a lower density of Gαi1 and Gαi2 proteins in the LC of sensitized mice rather than weaker α2A-AR expression. Behavioral sensitization was facilitated by α2A-AR antagonist, efaroxan, during amphetamine injections and abolished by clonidine treatment.

CONCLUSIONS

Our data indicate that noradrenergic inhibitory feedback is impaired for at least 1 month in rats and mice repeatedly treated with amphetamine. This work highlights the key role of noradrenergic autoreceptor signaling in the persistent modifications induced by repeated amphetamine administration.

Levels of Gsα(short and long), Gα(olf) and Gβ(common) subunits, and calcium-sensitive adenylyl cyclase isoforms (1, 5/6, 8) in post-mortem human brain caudate and cortical membranes: comparison with rat brain membranes and potential stoichiometric relationships

The levels of expression of Gsα(short and long), Gα(olf) and Gβ(common) subunits, and calcium-sensitive adenylyl cyclases isoforms (AC1, 5/6, and 8) in human brain cortical and caudate membranes were quantified by western blot analysis in order to establish their contribution to the patterns of AC functioning. Both areas expressed Gsα(long) (52 kDa) with values ranging from about 1400 ng/mg of membrane protein in cerebral cortex to close to 600 ng/mg of membrane protein in caudate nucleus. In contrast, Gsα(short) and Gsα(olf) were expressed separately, Gsα(short) in cortical membranes with values around 500 ng/mg of membrane protein and Gα(olf) in caudate membranes with values around 1300 ng/mg of membrane protein. Quantitative measurements of Gβ, revealed a similar expression level in cortical and caudate membranes (5444±732 versus 5511±394 ng/mg protein; p=0.966). The B(max) values of GTPγS-dependent [(3)H]-forskolin binding show the following descending order: rat striatal membranes>rat cortical membranes=human caudate membranes>human cortical membranes. Therefore, as measured immunochemically and by [(3)H]-forskolin binding, there seems to be a vast excess of Gsα subunits over catalytic units of AC. The highest levels of AC5/6 expression were detected in caudate membranes. AC8 was little expressed, and there were no significant differences in the relative values between both human brain regions. Finally, the levels of the AC1 isoform were significantly lower in caudate than in cortical membranes. It is concluded that these stoichiometric data contribute nonetheless to explain the significant differences observed in signalling capacities through the AC system in both human brain regions.

Activators of G-protein signaling 3: a drug addiction molecular gateway

Drug addiction is marked by continued drug-seeking behavior despite deleterious consequences and a heightened propensity to relapse not withstanding long, drug-free periods. The enduring nature of addiction has been hypothesized to arise from perturbations in intracellular signaling, gene expression, and brain circuitry induced by substance abuse. Ameliorating some of these aberrations should abate behavioral and neurochemical markers associated with an 'addiction phenotype'. This review summarizes data showing that protein expression and signaling through the nonreceptor activator of G-protein signaling 3 (AGS3) are altered by commonly abused substances in rat and in in-vitro addiction models. AGS3 structure and function are unrelated to the more broadly studied regulator of G-protein signaling family. Thus, the unique role of AGS3 is the focus of this review. Intriguingly, AGS3 protein changes persist into drug abstinence. Accordingly, studies probing the role of AGS3 in the neurochemistry of drug-seeking behavior and relapse are studied in detail. To illuminate this study, AGS3 structure, cellular localization, and function are covered so that an idealized AGS3-targeted pharmacotherapy can be proposed.

Neurobiology of dysregulated motivational systems in drug addiction

The progression from recreational drug use to drug addiction impacts multiple neurobiological processes and can be conceptualized as a transition from positive to negative reinforcement mechanisms driving both drug-taking and drug-seeking behaviors. Neurobiological mechanisms for negative reinforcement, defined as drug taking that alleviates a negative emotional state, involve changes in the brain reward system and recruitment of brain stress (or antireward) systems within forebrain structures, including the extended amygdala. These systems are hypothesized to be dysregulated by excessive drug intake and to contribute to allostatic changes in reinforcement mechanisms associated with addiction. Points of intersection between positive and negative motivational circuitry may further drive the compulsivity of drug addiction but also provide a rich neurobiological substrate for therapeutic intervention.

Sex-dependent effects of periadolescent exposure to the cannabinoid agonist CP-55,940 on morphine self-administration behaviour and the endogenous opioid system

Early cannabinoid consumption may predispose individuals to the misuse of addictive drugs later in life. However, there is a lack of experimental evidence as to whether cannabinoid exposure during adolescence might differently affect opiate reinforcing efficacy and the opioid system in adults of both sexes. Our aim was to examine whether periadolescent chronic exposure to the cannabinoid agonist CP-55,940 could exert sex-dependent effects on morphine reinforcing and the opioid system in adulthood. Morphine reinforcing was studied under a progressive ratio (PR) reinforcement schedule in adult male and female rats that previously acquired morphine self-administration under a fixed ratio 1 (FR1) schedule. Binding levels and functionality of mu-opioid receptors were also evaluated. Periadolescent cannabinoid exposure altered morphine self-administration and the opioid system in adult rats in a sex-dependent manner. CP-55,940-exposed males exhibited higher self-administration rates under a FR1, but not under a PR schedule. In females, CP-55,940 did not modify morphine self-administration under either schedule. Moreover, CP-55,940 also increased mu-opioid receptor levels in the subcallosal streak of pre-treated animals and decreased mu-opioid receptor functionality in the nucleus accumbens shell but again, only in males. Our data indicate that adult male rats exposed to the cannabinoid in adolescence self-administer more morphine than females, but only when the demands required by the schedule of reinforcement are low, which might be related to the decrease in mu-opioid receptor functionality in the NAcc-shell observed in these animals.

Brain levels of neuropeptides in human chronic methamphetamine users

Animal data show that neuropeptide systems in the dopamine-rich brain areas of the striatum (caudate, putamen, and nucleus accumbens) are influenced by exposure to psychostimulants, suggesting that neuropeptides are involved in mediating aspects of behavioral responses to drugs of abuse. To establish in an exploratory study whether levels of neuropeptides are altered in brain of human methamphetamine users, we measured tissue concentrations of dynorphin, metenkephalin, neuropeptide Y, neurotensin, and substance P in autopsied brains of 16 chronic methamphetamine users and 17 matched control subjects. As expected, levels of most neuropeptides were enriched in dopamine-linked brain regions such as the nucleus accumbens and striatum of normal human brain. In contrast to animal findings of increased neuropeptide levels following short-term methamphetamine exposure, striatal neuropeptide concentrations were either normal or moderately decreased in the methamphetamine users. In other examined dopamine-poor cortical and subcortical brain areas, neuropeptide levels were generally either normal or variably reduced. Although the neuropeptide differences might be explained by methamphetamine-induced damage to neuropeptide-containing neurons, our human data are consistent with the possibility that, at least in the human striatum, long-term methamphetamine exposure leads to an adaptive process that is distinct from that which increases neuropeptide levels after acute methamphetamine exposure.

Long-term upregulation of protein kinase A and adenylate cyclase levels in human smokers

Repeated injections of cocaine and morphine in laboratory rats cause a variety of molecular neuroadaptations in the cAMP signaling pathway in nucleus accumbens and ventral tegmental area. Here we report similar neuroadaptations in postmortem tissue from the brains of human smokers and former smokers. Activity levels of two major components of cAMP signaling, cAMP-dependent protein kinase A (PKA) and adenylate cyclase, were abnormally elevated in nucleus accumbens of smokers and in ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of the catalytic subunit of PKA were correspondingly higher in the ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of other candidate neuroadaptations, including glutamate receptor subunits, tyrosine hydroxylase, and other protein kinases, were within normal range. These findings extend our understanding of addiction-related neuroadaptations of cAMP signaling to tobacco smoking in human subjects and suggest that smoking-induced brain neuroadaptations can persist for significant periods in former smokers.

Cocaine and methamphetamine produce different patterns of subjective and cardiovascular effects

The stimulant effects of cocaine and methamphetamine are mediated by changes in synaptic concentrations of brain monoamines; however, the drugs alter monoamine levels via different mechanisms. This study examined the subjective and cardiovascular responses produced by investigational administration of cocaine or methamphetamine, in order to examine the onset and patterns of subjective and cardiovascular responses. Subjects included 14 non-treatment seeking cocaine-dependent and 11 non-treatment seeking methamphetamine-dependent volunteers. As part of ongoing research studies, cocaine and methamphetamine subjects received cocaine (40 mg, IV) or methamphetamine (30 mg, IV), respectively. Subjective and cardiovascular responses were assessed for 30 min and 60 min, respectively. The data reveal significant within groups differences for all subjective effects and cardiovascular effects (p<0.05). Significant between group differences in subjective effects were observed for "Any Drug Effect" (p<.008 for group, and p<.029 for group x time), for "High" (p<.002 for group, and p<.0001 for group x time) and for "Stimulated" (p<.001 for group, and p<.006 for group x time). Significant between group differences in cardiovascular effects were observed for Systolic blood pressure (p<.0001 for group, and p<.002 for group x time), Diastolic blood pressure (p<.0001 for group, though p=NS for group x time), and for Heart Rate (p<.0001 for group, and p<.0001 for group x time). The only difference between the groups for placebo was for heart rate, where there was a significant group x time effect (p<.005). Taken together, the data reveal that the subjective effects of cocaine tended to peak and then decline more rapidly than those produced by methamphetamine. The subjective effects of methamphetamine tended to rise more slowly, and remain elevated longer. Cardiovascular effects of cocaine and methamphetamine had similar onset, but effects of cocaine tended to decline more rapidly. Overall, the results reveal differences in the onset, pattern, and duration of subjective and cardiovascular responses following cocaine or methamphetamine administration in stimulant addicted patients. We predict that these differences may impact drug use and relapse patterns, and may have implications in medications development for these addictive disorders.

Decreased immunodensities of micro-opioid receptors, receptor kinases GRK 2/6 and beta-arrestin-2 in postmortem brains of opiate addicts

The homologous regulation of opioid receptors, through G protein-coupled receptor kinases (GRKs) and beta-arrestins, is an initial step in the complex molecular mechanisms leading to opiate tolerance and dependence. This study was designed to evaluate in parallel the contents of immunolabeled micro-opioid receptors (glycosylated proteins), two representative GRKs (GRK 2 and GRK 6) and beta-arrestin-2 in brains of opiate addicts who had died of an opiate overdose (heroin or methadone). The immunodensities of micro-opioid receptors were decreased (66 kDa protein: 24%, n=24, P<0.0001; 85 kDa protein: 16%, n=24, P<0.05) in the prefrontal cortex of opiate addicts compared with sex-, age-, and PMD-matched controls. This down-regulation of brain micro-opioid receptors was more pronounced in opiate addicts dying of a heroin overdose (27-30%, n=13) than in those who died of a methadone overdose (5-16%, n=11). In the same brains, significant decreases in the immunodensities of GRK 2 (19%, n=24, P<0.05), GRK 6 (25%, n=24, P<0.002) and beta-arrestin-2 (22%, n=24, P< 0.0005) were also quantitated. In contrast, the content of alpha-internexin (a neuronal marker used as a negative control) was not changed in brains of opiate addicts. In these subjects, there was a significant correlation between the densities of GRK 6 and beta-arrestin-2 (r=0.63, n=24, P=0.001), suggesting that both proteins are regulated in a coordinated manner by opiate drugs in the brain. The results indicate that opiate addiction in humans (tolerant state) is associated with down-regulation of brain micro-opioid receptors and regulatory GRK 2/6 and beta-arrestin-2 proteins. These molecular adaptations may be relevant mechanisms for the induction of opiate tolerance in brains of opiate addicts.

Brain vesicular acetylcholine transporter in human users of drugs of abuse

Limited animal data suggest that the dopaminergic neurotoxin methamphetamine is not toxic to brain (striatal) cholinergic neurons. However, we previously reported that activity of choline acetyltransferase (ChAT), the cholinergic marker synthetic enzyme, can be very low in brain of some human high-dose methamphetamine users. We measured, by quantitative immunoblotting, concentrations of a second cholinergic marker, the vesicular acetylcholine transporter (VAChT), considered to be a "stable" marker of cholinergic neurons, in autopsied brain (caudate, hippocampus) of chronic users of methamphetamine and, for comparison, in brain of users of cocaine, heroin, and matched controls. Western blot analyses showed normal levels of VAChT immunoreactivity in hippocampus of all drug user groups, whereas in the dopamine-rich caudate VAChT levels were selectively elevated (+48%) in the methamphetamine group, including the three high-dose methamphetamine users who had severely reduced ChAT activity. To the extent that cholinergic neuron integrity can be inferred from VAChT concentration, our data suggest that methamphetamine does not cause loss of striatal cholinergic neurons, but might damage/downregulate brain ChAT in some high-dose users. However, the finding of increased VAChT levels suggests that brain VAChT concentration might be subject to up- and downregulation as part of a compensatory process to maintain homeostasis of neuronal cholinergic activity. This possibility should be taken into account when utilizing VAChT as a neuroimaging outcome marker for cholinergic neuron number in human studies.

Downregulation of neuronal cdk5/p35 in opioid addicts and opiate-treated rats: relation to neurofilament phosphorylation

Neuronal cyclin-dependent kinase-5 (Cdk5) and its neuron-specific activator p35 play a major role in regulating the cytoskeleton dynamics. Since opioid addiction was associated with hyperphosphorylation of neurofilament (NF) in postmortem human brains, this study was undertaken to assess the status of the cdk5/p35 complex and its relation with NF-H phosphorylation in brains of chronic opioid abusers. Decreased immunodensities of cdk5 (18%) and p35 (26-44%) were found in the prefrontal cortex of opioid addicts compared with matched controls. In the same brains, the densities of p25 (a truncated neurotoxic form of p35), phosphatase PP2Ac and mu-calpain were found unaltered. Acute treatment of rats with morphine (30 mg/kg, 2 h) increased the density of cdk5 (35%), but not that of p35, in the cerebral cortex. In contrast, chronic morphine (10-100 mg/kg for 5 days) induced marked decreases in cdk5 (40%) and p35 (47%) in rat brain. In brains of opioid addicts, the density of phosphorylated NF-H was increased (43%) as well as the ratio of phosphorylated to nonphosphorylated NF-H forms (two-fold). In these brains, phosphorylated NF-H significantly correlated with p35 (r=0.58) but not with cdk5 (r=0.03). The results suggest that opiate addiction is associated with downregulation of cdk5/p35 levels in the brain. This downregulation and the aberrant hyperphosphorylation of NF-H proteins might have important consequences in the development of neural plasticity associated with opiate addiction in humans.

Biochemical and molecular studies using human autopsy brain tissue

The use of human brain tissue obtained at autopsy for neurochemical, pharmacological and physiological analyses is reviewed. RNA and protein samples have been found suitable for expression profiling by techniques that include RT-PCR, cDNA microarrays, western blotting, immunohistochemistry and proteomics. The rapid development of molecular biological techniques has increased the impetus for this work to be applied to studies of brain disease. It has been shown that most nucleic acids and proteins are reasonably stable post-mortem. However, their abundance and integrity can exhibit marked intra- and intercase variability, making comparisons between case-groups difficult. Variability can reveal important functional and biochemical information. The correct interpretation of neurochemical data must take into account such factors as age, gender, ethnicity, medicative history, immediate ante-mortem status, agonal state and post-mortem and post-autopsy intervals. Here we consider issues associated with the sampling of DNA, RNA and proteins using human autopsy brain tissue in relation to various ante- and post-mortem factors. We conclude that valid and practical measures of a variety of parameters may be made in human brain tissue, provided that specific factors are controlled.

Repeated cocaine treatment decreases whole-cell calcium current in rat nucleus accumbens neurons

Dopamine D1 receptors within the nucleus accumbens (NAc) are intricately involved in the rewarding effects of cocaine and in withdrawal symptoms after cessation of repeated cocaine administration. These receptors couple to a variety of ion channels to modulate neuronal excitability. Using whole-cell recordings from dissociated adult rat NAc medium spiny neurons (MSNs), we show that, as in dorsal striatal MSNs, D1 receptor stimulation suppresses N- and P/Q-type Ca(2+) currents (I(Ca)) by activating a cAMP/protein kinase A/protein phosphatase (PP) signaling system, presumably leading to channel dephosphorylation. We also report that during withdrawal from repeated cocaine administration, basal I(Ca) density is decreased by 30%. Pharmacological isolation of specific I(Ca) components indicates that N- and R-type, but not P/Q- or L-type, currents are significantly reduced by repeated cocaine treatment. Inhibiting PP activity with okadaic acid enhances I(Ca) in cocaine withdrawn, but not control, NAc neurons, suggesting an increase in constitutive PP activity. This suggestion was supported by a significant decrease in the ability of D1 receptor stimulation and direct activation of cAMP signaling to suppress I(Ca) in cocaine-withdrawn NAc neurons. Chronic cocaine-induced reduction of I(Ca) in NAc MSNs will globally impact Ca(2+)-dependent processes, including synaptic plasticity, transmitter release, and intracellular signaling cascades that regulate membrane excitability. Along with our previously reported reduction in whole-cell Na(+) currents during cocaine withdrawal, these findings further emphasize the important role of whole-cell plasticity in reducing information processing during cocaine withdrawal.

Methamphetamine enhances cell-associated feline immunodeficiency virus replication in astrocytes

Human immunodeficiency virus (HIV) infection among substance abusers is on the rise worldwide. Psychostimulants, and in particular methamphetamine (METH), have detrimental effects on the immune system as well as causing a progressive neurodegeneration, similar to HIV infection. Many Lentivirinae, including feline immunodeficiency virus (FIV), penetrate into the central nervous system early in the course of infection with astrocytes serving as a reservoir of chronic brain infection. We demonstrate that the FIV-Maryland isolate infects feline primary and cell line (G355-5)-cultured astrocytes only under cell-associated conditions. Infected astrocytes yielded a new astrocytotropic isolate, capable of cell-free infection (termed FIV-MD-A). This isolate contained four amino acid substitutions in the envelope polyprotein resulting in a change in net charge as compared to FIV-MD. Infection for both isolates was dependent upon a functional astrocyte CXCR4 receptor. Methamphetamine increased significantly FIV replication in feline astrocytes for cell-associated infection only, with no effect on peripheral blood mononuclear cells or astrocytes infected with FIV-MD-A. This viral replication was related to proviral copy number, suggesting the effect of METH is at the viral entry or integration into host genome levels, but not at the translational level. Thus, lentiviral infection of the brain in the presence of the psychostimulant METH may result in enhanced astrocyte viral replication, producing a more rapid and increased brain viral load.

The DRD4 VNTR polymorphism influences reactivity to smoking cues

Recent research has indicated that craving for tobacco can be reliably elicited by exposure to smoking cues, suggesting that cue-elicited craving for tobacco may be a useful phenotype for research on genetic factors related to nicotine dependence. Given the potential role of dopamine in cue-elicited craving, the authors examined whether the DRD4 VNTR polymorphism is associated with cue-elicited craving for tobacco. Participants who were homozygous or heterozygous for the 7 repeat (or longer) allele were classified as DRD4 L, and all other participants were classified as DRD4 S. Participants were exposed to smoking cues before smoking either high-nicotine cigarettes or control cigarettes. Analyses suggested that participants in the L group demonstrated significantly greater craving, more arousal, less positive affect, and more attention to the smoking cues than did the participants in the S group.

Dopamine D1 receptor protein is elevated in nucleus accumbens of human, chronic methamphetamine users

Animal data have long suggested that an adaptive upregulation of nucleus accumbens dopamine D1 receptor function might underlie part of the dependency on drugs of abuse. We measured by quantitative immunoblotting protein levels of dopamine D1 and, for comparison, D2 receptors in brain of chronic users of methamphetamine, cocaine, and heroin. As compared with the controls, brain dopamine D1 receptor concentrations were selectively increased (by 44%) in the nucleus accumbens of the methamphetamine users, whereas a trend was observed in this brain area for reduced protein levels of the dopamine D2 receptor in all three drug groups (-25 to -37%; P < 0.05 for heroin group only). Our data support the hypothesis that aspects of the drug-dependent state in human methamphetamine users might be related to increased dopamine D1 receptor function in limbic brain.