Identifying Clinical Phenotypes in People Who Are Hispanic/Latino With Chronic Low Back Pain: Use of Sensor-Based Measures of Posture and Movement, Pain, and Psychological Factors.

OBJECTIVE: The aim of this study was to identify clinical phenotypes using sensor-based measures of posture and movement, pain behavior, and psychological factors in Hispanic/Latino people with chronic low back pain (CLBP). METHODS: Baseline measures from an ongoing clinical trial were analyzed for 81 Hispanic/Latino people with CLBP. Low back posture and movement were measured using commercial sensors during in-person testing and 8 hours of ecological monitoring. Magnitude, frequency, and duration of lumbar movements, sitting and standing postures were measured. Movement-evoked pain was assessed during in-person movement testing. Psychological measures included the Pain Catastrophizing Scale and the Fear Avoidance Beliefs Questionnaire. Random forest analysis was conducted to generate 2 groups and identify important variables that distinguish groups. Group differences in demographics, pain, psychological, and posture and movement variables were examined using t-tests and chi-square analyses. RESULTS: Two subgroups of Hispanic/Latino people with CLBP were identified with minimal error (7.4% misclassification ["out-of-bag" error]). Ecological posture and movement measures best distinguished groups, although most movement-evoked pain and psychological measures did not. Group 1 had greater height and weight, lower movement frequency, more time in sitting, and less time in standing. Group 2 had a greater proportion of women than men, longer low back pain duration, higher movement frequency, more time in standing, and less time in sitting. CONCLUSION: Two distinct clinical phenotypes of Hispanic/Latino people with CLBP were identified. One group was distinguished by greater height and weight and more sedentary posture and movement behavior; the second group had more women, longer duration of low back pain, higher lumbar spine movement frequency, and longer duration of standing postures. IMPACT: Ecological measures of posture and movement are important for identifying 2 clinical phenotypes in Hispanic/Latino people with CLBP and may provide a basis for a more personalized plan of care. LAY SUMMARY: Wearable sensors were used to measure low back posture and movement in Hispanic/Latino people with chronic low back pain. These posture and movement measures helped to identify 2 different clinical subgroups that will give physical therapists more information to better personalize treatment for chronic low back pain in Hispanic/Latino patients.

mPer1 promotes morphine-induced locomotor sensitization and conditioned place preference via histone deacetylase activity.

RATIONALE: Previous studies have shown that repeated exposure to drugs of abuse is associated with changes in clock genes expression and that mice strains with various mutations in clock genes show alterations in drug-induced behaviors. OBJECTIVE: The objective of this study is to characterize the role of the clock gene mPer1 in the development of morphine-induced behaviors and a possible link to histone deacetylase (HDAC) activity. METHODS: In Per1 Brdm1 null mutant mice and wild-type (WT) littermates, we examined whether there were any differences in the development of morphine antinociception, tolerance to antinociception, withdrawal, sensitization to locomotion, and conditioned place preference (CPP). RESULTS: Per1 Brdm1 mutant mice did not show any difference in morphine antinociception, tolerance development, nor in physical withdrawal signs precipitated by naloxone administration compared to WT. However, morphine-induced locomotor sensitization and CPP were significantly impaired in Per1 Brdm1 mutant mice. Because a very similar dissociation between tolerance and dependence vs. sensitization and CPP was recently observed after the co-administration of morphine and the HDAC inhibitor sodium butyrate (NaBut), we studied a possible link between mPer1 and HDAC activity. As opposed to WT controls, Per1 Brdm1 mutant mice showed significantly enhanced striatal global HDAC activity within the striatum when exposed to a locomotor-sensitizing morphine administration regimen. Furthermore, the administration of the HDAC inhibitor NaBut restored the ability of morphine to promote locomotor sensitization and reward in Per1 Brdm1 mutant mice. CONCLUSIONS: Our results reveal that although the mPer1 gene does not alter morphine-induced antinociception nor withdrawal, it plays a prominent role in the development of morphine-induced behavioral sensitization and reward via inhibitory modulation of striatal HDAC activity. These data suggest that PER1 inhibits deacetylation to promote drug-induced neuroplastic changes.

Convergent evidence from alcohol-dependent humans and rats for a hyperdopaminergic state in protracted abstinence.

A major hypothesis in addiction research is that alcohol induces neuroadaptations in the mesolimbic dopamine (DA) system and that these neuroadaptations represent a key neurochemical event in compulsive drug use and relapse. Whether these neuroadaptations lead to a hypo- or hyperdopaminergic state during abstinence is a long-standing, unresolved debate among addiction researchers. The answer is of critical importance for understanding the neurobiological mechanism of addictive behavior. Here we set out to study systematically the neuroadaptive changes in the DA system during the addiction cycle in alcohol-dependent patients and rats. In postmortem brain samples from human alcoholics we found a strong down-regulation of the D1 receptor- and DA transporter (DAT)-binding sites, but D2-like receptor binding was unaffected. To gain insight into the time course of these neuroadaptations, we compared the human data with that from alcohol-dependent rats at several time points during abstinence. We found a dynamic regulation of D1 and DAT during 3 wk of abstinence. After the third week the rat data mirrored our human data. This time point was characterized by elevated extracellular DA levels, lack of synaptic response to D1 stimulation, and augmented motor activity. Further functional evidence is given by a genetic rat model for hyperdopaminergia that resembles a phenocopy of alcohol-dependent rats during protracted abstinence. In summary, we provide a new dynamic model of abstinence-related changes in the striatal DA system; in this model a hyperdopaminergic state during protracted abstinence is associated with vulnerability for relapse.

Clock genes × stress × reward interactions in alcohol and substance use disorders.

Adverse life events and highly stressful environments have deleterious consequences for mental health. Those environmental factors can potentiate alcohol and drug abuse in vulnerable individuals carrying specific genetic risk factors, hence producing the final risk for alcohol- and substance-use disorders development. The nature of these genes remains to be fully determined, but studies indicate their direct or indirect relation to the stress hypothalamo-pituitary-adrenal (HPA) axis and/or reward systems. Over the past decade, clock genes have been revealed to be key-players in influencing acute and chronic alcohol/drug effects. In parallel, the influence of chronic stress and stressful life events in promoting alcohol and substance use and abuse has been demonstrated. Furthermore, the reciprocal interaction of clock genes with various HPA-axis components, as well as the evidence for an implication of clock genes in stress-induced alcohol abuse, have led to the idea that clock genes, and Period genes in particular, may represent key genetic factors to consider when examining gene × environment interaction in the etiology of addiction. The aim of the present review is to summarize findings linking clock genes, stress, and alcohol and substance abuse, and to propose potential underlying neurobiological mechanisms.

Rescue of infralimbic mGluR2 deficit restores control over drug-seeking behavior in alcohol dependence.

A key deficit in alcohol dependence is disrupted prefrontal function leading to excessive alcohol seeking, but the molecular events underlying the emergence of addictive responses remain unknown. Here we show by convergent transcriptome analysis that the pyramidal neurons of the infralimbic cortex are particularly vulnerable for the long-term effects of chronic intermittent ethanol intoxication. These neurons exhibit a pronounced deficit in metabotropic glutamate receptor subtype 2 (mGluR(2)). Also, alcohol-dependent rats do not respond to mGluR(2/3) agonist treatment with reducing extracellular glutamate levels in the nucleus accumbens. Together these data imply a loss of autoreceptor feedback control. Alcohol-dependent rats show escalation of ethanol seeking, which was abolished by restoring mGluR(2) expression in the infralimbic cortex via viral-mediated gene transfer. Human anterior cingulate cortex from alcoholic patients shows a significant reduction in mGluR(2) transcripts compared to control subjects, suggesting that mGluR(2) loss in the rodent and human corticoaccumbal neurocircuitry may be a major consequence of alcohol dependence and a key pathophysiological mechanism mediating increased propensity to relapse. Normalization of mGluR(2) function within this brain circuit may be of therapeutic value.

Inhibition of the casein-kinase-1-ε/δ/ prevents relapse-like alcohol drinking.

During the past decade, it has been shown that circadian clock genes have more than a simple circadian time-keeping role. Clock genes also modulate motivational processes and have been implicated in the development of psychiatric disorders such as drug addiction. Recent studies indicate that casein-kinase 1ε/δ (CK1ε/δ)--one of the components of the circadian molecular clockwork-might be involved in the etiology of addictive behavior. The present study was initiated to study the specific role of CK1ε/δ in alcohol relapse-like drinking using the 'Alcohol Deprivation Effect' model. The effect of CK1ε/δ inhibition was tested on alcohol consumption in long-term alcohol-drinking rats upon re-exposure to alcohol after deprivation using a four-bottle free-choice paradigm with water, 5%, 10%, and 20% ethanol solutions, as well as on saccharin preference in alcohol-naive rats. The inhibition of CK1ε/δ with systemic PF-670462 (0, 10, and 30 mg/kg) injections dose-dependently decreased, and at a higher dosage prevented the alcohol deprivation effect, as compared with vehicle-treated rats. The impact of the treatment was further characterized using nonlinear regression analyses on the daily profiles of drinking and locomotor activity. We reveal that CK1ε/δ inhibition blunted the high daytime alcohol intake typically observed upon alcohol re-exposure, and induced a phase shift of locomotor activity toward daytime. Only the highest dose of PF-670462 shifted the saccharin intake daily rhythm toward daytime during treatment, and decreased saccharin preference after treatment. Our data suggest that CK1 inhibitors may be candidates for drug treatment development for alcoholism.

A functional Tph2 C1473G polymorphism causes an anxiety phenotype via compensatory changes in the serotonergic system.

The association of single-nucleotide polymorphisms (SNPs) in the human tryptophan hydroxylase 2 (TPH2) gene with anxiety traits and depression has been inconclusive. Observed inconsistencies might result from the fact that TPH2 polymorphisms have been studied in a genetically heterogeneous human population. A defined genetic background, control over environmental factors, and the ability to analyze the molecular and neurochemical consequences of introduced genetic alterations constitute major advantages of investigating SNPs in inbred laboratory mouse strains. To investigate the behavioral and neurochemical consequences of a functional C1473G SNP in the mouse Tph2 gene, we generated congenic C57BL/6N mice homozygous for the Tph2 1473G allele. The Arg(447) substitution in the TPH2 enzyme resulted in a significant reduction of the brain serotonin (5-HT) in vivo synthesis rate. Despite decreased 5-HT synthesis, we could detect neither a reduction of brain region-specific 5-HT concentrations nor changes in baseline and stress-induced 5-HT release using a microdialysis approach. However, using a [(35)S]GTP-γ-S binding assay and 5-HT(1A) receptor autoradiography, a functional desensitization of 5-HT(1A) autoreceptors could be identified. Furthermore, behavioral analysis revealed a distinct anxiety phenotype in homozygous Tph2 1473G mice, which could be reversed with chronic escitalopram treatment. Alterations in depressive-like behavior could not be detected under baseline conditions or after chronic mild stress. These findings provide evidence for an involvement of functional Tph2 polymorphisms in anxiety-related behaviors, which are likely not caused directly by alterations in 5-HT content or release but are rather due to compensatory changes during development involving functional desensitization of 5-HT(1A) autoreceptors.

Reduced alcohol intake and reward associated with impaired endocannabinoid signaling in mice with a deletion of the glutamate transporter GLAST.

A hyperglutamatergic state has been hypothesized to drive escalation of alcohol intake. This hypothesis predicts that an impairment of glutamate clearance through inactivation of the astrocytic glutamate transporter, GLAST (EAAT1), will result in escalation of alcohol consumption. Here, we used mice with a deletion of GLAST to test this prediction. WT and GLAST KO mice were tested for alcohol consumption using two-bottle free-choice drinking. Alcohol reward was evaluated using conditioned place preference (CPP). Sensitivity to depressant alcohol effects was tested using the accelerating rotarod, alcohol-induced hypothermia, and loss of righting reflex. Extracellular glutamate was measured using microdialysis, and striatal slice electrophysiology was carried out to examine plasticity of the cortico-striatal pathway as a model system in which adaptations to the constitutive GLAST deletion can be studied. Contrary to our hypothesis, GLAST KO mice showed markedly decreased alcohol consumption, and lacked CPP for alcohol, despite a higher locomotor response to this drug. Alcohol-induced ataxia, hypothermia, and sedation were unaffected. In striatal slices from GLAST KO mice, long-term depression (LTD) induced by high frequency stimulation, or by post-synaptic depolarization combined with the l-type calcium channel activator FPL 64176 was absent. In contrast, normal synaptic depression was observed after application of the cannabinoid 1 (CB1) receptor agonist WIN55,212-2. Constitutive deletion of GLAST unexpectedly results in markedly reduced alcohol consumption and preference, associated with markedly reduced alcohol reward. Endocannabinoid signaling appears to be down-regulated upstream of the CB1 receptor as a result of the GLAST deletion, and is a candidate mechanism behind the reduction of alcohol reward observed.

Translational magnetic resonance spectroscopy reveals excessive central glutamate levels during alcohol withdrawal in humans and rats.

BACKGROUND: In alcoholism, excessive glutamatergic neurotransmission has long been implicated in the acute withdrawal syndrome and as a key signal for dependence-related neuroplasticity. Our understanding of this pathophysiological mechanism originates largely from animal studies, but human data are needed for translation into successful medication development. METHODS: We measured brain glutamate levels during detoxification in alcohol-dependent patients (n = 47) and in healthy control subjects (n = 57) as well as in a rat model of alcoholism by state-of-the-art ¹H-magnetic magnetic resonance spectroscopy at 3 and 9.4 T, respectively. RESULTS: We found significantly increased glutamate levels during acute alcohol withdrawal in corresponding prefrontocortical regions of treatment-seeking alcoholic patients and alcohol-dependent rats versus respective control subjects. The augmented spectroscopic glutamate signal is likely related to increased glutamatergic neurotransmission because, enabled by the high field strength of the animal scanner, we detected a profoundly elevated glutamate/glutamine ratio in alcohol-dependent rats during acute withdrawal. All dependence-induced metabolic alterations normalize within a few weeks of abstinence in both humans and rats. CONCLUSIONS: Our data provide first-time direct support from humans for the glutamate hypothesis of alcoholism, demonstrate the comparability of human and animal magnetic resonance spectroscopy responses, and identify the glutamate/glutamine ratio as potential biomarker for monitoring disease progression.

Sensorimotor gating, working and social memory deficits in mice with reduced expression of the vesicular glutamate transporter VGLUT1.

Glutamate is the main excitatory neurotransmitter in the central nervous system. A hypoglutamatergic state is believed to play an important role in the pathophysiology of schizophrenia. The release of glutamate in the brain is modulated by a class of vesicular glutamate transporters, VGLUT1-3. Among them, VGLUT1 represents the isoform predominantly expressed in the neocortex and hippocampus. Here we investigated the potential involvement of VGLUT1 deficiency in generating schizophrenia-like abnormalities by testing mice with diminished expression of VGLUT1 in several behavioural tests relevant for schizophrenia. We found behavioural alterations in these mice resembling correlates of schizophrenia, such as working- and social memory impairments and deficits in prepulse inhibition (PPI) of the acoustic startle reflex (ASR), but normal locomotor behaviour under basal conditions. Our data may be important for a better understanding of the contribution of reduced VGLUT1-mediated presynaptic glutamatergic neurotransmission in the generation of several behavioural abnormalities associated with schizophrenia.

Effects of the circadian rhythm gene period 1 (per1) on psychosocial stress-induced alcohol drinking.

OBJECTIVE: Circadian and stress-response systems mediate environmental changes that affect alcohol drinking. Psychosocial stress is an environmental risk factor for alcohol abuse. Circadian rhythm gene period 1 (Per1) is targeted by stress hormones and is transcriptionally activated in corticotropin releasing factor-expressing cells. The authors hypothesized that Per1 is involved in integrating stress response and circadian rhythmicity and explored its relevance to alcohol drinking. METHOD: In mice, the effects of stress on ethanol intake in mPer1-mutant and wild-type mice were assessed. In humans, single nucleotide polymorphisms (SNPs) in hPer1 were tested for association with alcohol drinking behavior in 273 adolescents and an adult case-control sample of 1,006 alcohol-dependent patients and 1,178 comparison subjects. In vitro experiments were conducted to measure genotype-specific expression and transcription factor binding to hPer1. RESULTS: The mPer1-mutant mice showed enhanced alcohol consumption in response to social defeat stress relative to their wild-type littermates. An association with the frequency of heavy drinking in adolescents with the hPer1 promoter SNP rs3027172 and with psychosocial adversity was found. There was significant interaction between the rs3027172 genotype and psychosocial adversity on this drinking measure. In a confirmatory analysis, association of hPer1 rs3027172 with alcohol dependence was shown. Cortisol-induced transcriptional activation of hPer1 was reduced in human B-lymphoblastoid cells carrying the risk genotype of rs3027172. Binding affinity of the transcription factor Snail1 to the risk allele of the hPer1 SNP rs3027172 was also reduced. CONCLUSIONS: The findings indicate that the hPer1 gene regulates alcohol drinking behavior during stressful conditions and provide evidence for underlying neurobiological mechanisms.

Circadian disruption and SCN control of energy metabolism.

In this review we first present the anatomical pathways used by the suprachiasmatic nuclei to enforce its rhythmicity onto the body, especially its energy homeostatic system. The experimental data show that by activating the orexin system at the start of the active phase, the biological clock not only ensures that we wake up on time, but also that our glucose metabolism and cardiovascular system are prepared for increased activity. The drawback of such a highly integrated system, however, becomes visible when our daily lives are not fully synchronized with the environment. Thus, in addition to increased physical activity and decreased intake of high-energy food, also a well-lighted and fully resonating biological clock may help to withstand the increasing "diabetogenic" pressure of today's 24/7 society.

Per1(Brdm1) mice self-administer cocaine and reinstate cocaine-seeking behaviour following extinction.

A clear interrelationship between biological rhythms and addiction has emerged from recent preclinical and clinical studies. In particular, the manipulation of the so-called 'clock genes' interferes with the manifestation of drug-related responses. For instance, Period 1 (Per1(Brdm1)) mutant mice do not display behavioural sensitization in response to repeated cocaine administration and do not express cocaine conditioned place preference, in contrast to control littermates. To assess the involvement of the mPer1 gene in a robust model of cocaine reinforcement and relapse-like behaviour, we tested Per1(Brdm1) mutant mice and their littermates for self-administration of several doses (0.06-0.75 mg/kg/infusion) of cocaine, and for reinstatement of an extinguished cocaine-seeking response. Per1(Brdm1) mutant mice did not differ from control littermates in their propensity to self-administer cocaine or to reinstate an extinguished cocaine-seeking behaviour in response to drug-associated cues or cocaine priming. In contrast to our earlier data on Per1(Brdm1) mutant mice in cocaine sensitization and conditioned place preference, this finding does not suggest a relationship between the circadian clock gene mPer1 in cocaine self-administration and reinstatement of cocaine-seeking behaviour. This study adds one further example to the notion that various behavioural tests usually used in addiction research rely on different neurobiological substrates.

Amphetamine regulates NR2B expression in Go2α knockout mice and thereby sustains behavioral sensitization.

The α-subunit of Go2 is a regulator of dopamine (DA) homeostasis. Deletion of the protein results in an imbalance of the direct and indirect DA pathway by reducing D1 and increasing D2 receptors. As a result, cocaine-induced behavioral sensitization is abolished. Here we show that repeated amphetamine injections in Go2α-/- mice induced a similar D1/D2 receptor ratio shift as cocaine but surprisingly the knockouts developed normal behavioral sensitization. DA receptor signaling following either cocaine or amphetamine treatment was also similar in Go2α-/- mice suggesting another mechanism involved in the differential behavioral response. Evidence is increasing that DA-glutamate interactions in the striatum determine psychostimulant action. In this line, repeated amphetamine injections led to a twofold increase in the amount of the NMDA receptor subunit NR2B in Go2α-/- mice resulting in an enhanced inhibition of the indirect DA pathway. This effect is not seen after cocaine treatment. Furthermore, amphetamine but not cocaine treatment maintained the ratio between the glutamate receptor mGluR1/5 interacting proteins Homer and Homer1a in the knockouts thereby sustaining the direct pathway. We conclude that amphetamine provokes behavioral sensitization in Go2α-/- mice by an enhanced inhibition of the indirect pathway without disturbing the direct pathway thereby overcoming the imbalance in the DArgic system.

Development of morphine-induced tolerance and withdrawal: involvement of the clock gene mPer2.

The present study has been designed to assess specifically the involvement of the clock gene mPer2 in morphine-induced tolerance and withdrawal. At first, we checked the absence of initial differences in the expression of several gene transcripts involved in the development of morphine dependence in Per2(Brdm1) mutant mice and in their respective wild-type (WT) control littermates. Morphine-induced tolerance as well as precipitated withdrawal was then assessed in these mice. The Per2(Brdm1) mutant mice clearly developed less tolerance and showed attenuated withdrawal signs compared to WT. These results show that mPER2 is involved in morphine-induced tolerance and withdrawal.

Circadian regulation of central ethanol sensitivity by the mPer2 gene.

The effect of alcohol is known to vary with the time of the day. Although initially it was suggested that this phenomenon may be due to diurnal differences in ethanol metabolism, more recent studies were contradicting. In the present study, we therefore first set out in assessing the diurnal variations in ethanol sensitivity in mice analysing, concurrently, ethanol elimination rates. Ethanol-induced (3.5 g/kg; intraperitoneal) loss of righting reflex (LORR) duration was thus determined at several Zeitgeber time (ZT) points (ZT5, 11, 17 and 23) in C57BL/6N mice. In parallel, the corresponding ethanol elimination rates were also assessed. The results display the existence of a distinct diurnal rhythm in LORR duration peaking at ZT11, whereas no differences could be observed regarding the elimination rates of alcohol. Successively, we checked the involvement of the clock genes mPer1 and mPer2 in conveying this rhythm in sensitivity, testing LORR and hypothermia at the peak and trough previously observed (ZT5 and ZT11). Per1(Brdm1) mice demonstrate a similar diurnal pattern as control mice, with enhanced LORR durations at ZT11. In contrast, Per2(Brdm1) mice did not exhibit a temporal variation to the depressant effects of ethanol with respect to LORR, revealing a constant high sensitivity to ethanol. The present study reveals a central role of the mPer2 gene in inhibiting alcohol sensitivity at the beginning of the inactive phase.

Cue-induced alcohol-seeking behaviour is reduced by disrupting the reconsolidation of alcohol-related memories.

RATIONALE: In humans, the retrieval of memories associated with an alcohol-related experience frequently evokes alcohol-seeking behaviour. The reconsolidation hypothesis states that a consolidated memory could again become labile and susceptible to disruption after memory retrieval. OBJECTIVES: The aim of our study was to examine whether retrieval of alcohol-related memories undergoes a reconsolidation process. METHODS: For this purpose, male Wistar rats were trained to self-administer ethanol in the presence of specific conditioned stimuli. Thereafter, animals were left undisturbed in their home cages for the following 21 days. Memory retrieval was performed in a single 5-min exposure to all alcohol-associated stimuli. The protein synthesis inhibitor anisomycin, the non-competitive N-methyl-D: -aspartate (NMDA) receptor antagonist MK-801 and acamprosate, a clinically used drug known to reduce a hyper-glutamatergic state, were given immediately after retrieval of alcohol-related memories. The impact of drug treatment on cue-induced alcohol-seeking behaviour was measured on the following day and 7 days later. RESULTS: Administration of both anisomycin and MK-801 reduced cue-induced alcohol-seeking behaviour, showing that memory reconsolidation was disrupted by these compounds. However, acamprosate had no effect on the reconsolidation process, suggesting that this process is not dependent on a hyper-glutamatergic state but is more related to protein synthesis and NMDA receptor activity. CONCLUSIONS: Pharmacological disruption of reconsolidation of alcohol-associated memories can be achieved by the use of NMDA antagonists and protein synthesis inhibitors and may thus provide a potential new therapeutic strategy for the prevention of relapse in alcohol addiction.

Loss of the Ca2+/calmodulin-dependent protein kinase type IV in dopaminoceptive neurons enhances behavioral effects of cocaine.

The persistent nature of addiction has been associated with activity-induced plasticity of neurons within the striatum and nucleus accumbens (NAc). To identify the molecular processes leading to these adaptations, we performed Cre/loxP-mediated genetic ablations of two key regulators of gene expression in response to activity, the Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) and its postulated main target, the cAMP-responsive element binding protein (CREB). We found that acute cocaine-induced gene expression in the striatum was largely unaffected by the loss of CaMKIV. On the behavioral level, mice lacking CaMKIV in dopaminoceptive neurons displayed increased sensitivity to cocaine as evidenced by augmented expression of locomotor sensitization and enhanced conditioned place preference and reinstatement after extinction. However, the loss of CREB in the forebrain had no effect on either of these behaviors, even though it robustly blunted acute cocaine-induced transcription. To test the relevance of these observations for addiction in humans, we performed an association study of CAMK4 and CREB promoter polymorphisms with cocaine addiction in a large sample of addicts. We found that a single nucleotide polymorphism in the CAMK4 promoter was significantly associated with cocaine addiction, whereas variations in the CREB promoter regions did not correlate with drug abuse. These findings reveal a critical role for CaMKIV in the development and persistence of cocaine-induced behaviors, through mechanisms dissociated from acute effects on gene expression and CREB-dependent transcription.

Glutamate receptors on dopamine neurons control the persistence of cocaine seeking.

Cocaine strengthens excitatory synapses onto midbrain dopamine neurons through the synaptic delivery of GluR1-containing AMPA receptors. This cocaine-evoked plasticity depends on NMDA receptor activation, but its behavioral significance in the context of addiction remains elusive. Here, we generated mice lacking the GluR1, GluR2, or NR1 receptor subunits selectively in dopamine neurons. We report that in midbrain slices of cocaine-treated mice, synaptic transmission was no longer strengthened when GluR1 or NR1 was abolished, while in the respective mice the drug still induced normal conditioned place preference and locomotor sensitization. In contrast, extinction of drug-seeking behavior was absent in mice lacking GluR1, while in the NR1 mutant mice reinstatement was abolished. In conclusion, cocaine-evoked synaptic plasticity does not mediate concurrent short-term behavioral effects of the drug but may initiate adaptive changes eventually leading to the persistence of drug-seeking behavior.

Deletion of Go2alpha abolishes cocaine-induced behavioral sensitization by disturbing the striatal dopamine system.

The alpha-subunits of the trimeric Go class of GTPases, comprising the splice variants Go1alpha and Go2alpha, are abundantly expressed in brain and reside on both plasma membrane and synaptic vesicles. Go2alpha is involved in the vesicular storage of monoamines but its physiological relevance is still obscure. We now show that genetic depletion of Go2alpha reduces motor activity induced by dopamine-enhancing drugs like cocaine, as repeated injections of cocaine fail to provoke behavioral sensitization in Go2alpha(-/-) mice. In Go2alpha(-/-) mice, D1 receptor signaling in the striatum is attenuated due to a reduced expression of Golf alpha and Gs alpha. Following cocaine treatment, Go2alpha(-/-) mice have lower D1 and higher D2 receptor amounts compared to wild-type mice. The lack of behavioral sensitization correlates with reduced dopamine levels in the striatum and decreased expression of tyrosine hydroxylase. One reason for the neurochemical changes may be a reduced uptake of monoamines by synaptic vesicles from Go2alpha(-/-) mice as a consequence of a lowered set point for filling. We conclude that Go2alpha optimizes vesicular filling which is instrumental for normal dopamine functioning and for the development of drug-induced behavioral sensitization.