Category Archives: Addiction

Neurobiology of addiction: insight from neurochemical imaging.

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Abstract

“Neuroimaging studies have been crucial in understanding changes in the various neurotransmitter systems implicated in addiction in the living human brain. Predominantly reduced striatal dopamine transmission appears to play an important role in psychostimulant, alcohol and heroin addiction, while addiction to cannabis may be mediated primarily by the endocannabinoid system. However, the study of other neurotransmitter systems likely involved in addiction, for example glutamate, has been limited by the number and quality of available radiotracers, and data on changes in these systems in the most common addictions are emerging only now. Further studies are needed to understand fully how the interplay of various neurotransmitter systems contributes to addiction and to ultimately help to develop more effective treatment approaches.”

http://www.ncbi.nlm.nih.gov/pubmed/22640769

An endocannabinoid hypothesis of drug reward and drug addiction.

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“Pharmacologic treatment of drug and alcohol dependency has largely been disappointing, and new therapeutic targets and hypotheses are needed. There is accumulating evidence indicating a central role for the previously unknown but ubiquitous endocannabinoid physiological control system (EPCS) in the regulation of the rewarding effects of abused substances. Thus an endocannabinoid hypothesis of drug reward is postulated. Endocannabinoids mediate retrograde signaling in neuronal tissues and are involved in the regulation of synaptic transmission to suppress neurotransmitter release by the presynaptic cannabinoid receptors (CB-Rs). This powerful modulatory action on synaptic transmission has significant functional implications and interactions with the effects of abused substances. Our data, along with those from other investigators, provide strong new evidence for a role for EPCS modulation in the effects of drugs of abuse, and specifically for involvement of cannabinoid receptors in the neural basis of addiction. Cannabinoids and endocannabinoids appear to be involved in adding to the rewarding effects of addictive substances, including, nicotine, opiates, alcohol, cocaine, and BDZs. The results suggest that the EPCS may be an important natural regulatory mechanism for drug reward and a target for the treatment of addictive disorders.”

http://www.ncbi.nlm.nih.gov/pubmed/18991888

Endocannabinoid system involvement in brain reward processes related to drug abuse.

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“Cannabis is the most commonly abused illegal drug in the world and its main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC), produces rewarding effects in humans and non-human primates. Over the last several decades, an endogenous system comprised of cannabinoid receptors, endogenous ligands for these receptors and enzymes responsible for the synthesis and degradation of these endogenous cannabinoid ligands has been discovered and partly characterized. Experimental findings strongly suggest a major involvement of the endocannabinoid system in general brain reward functions and drug abuse. First, natural and synthetic cannabinoids and endocannabinoids can produce rewarding effects in humans and laboratory animals. Second, activation or blockade of the endogenous cannabinoid system has been shown to modulate the rewarding effects of non-cannabinoid psychoactive drugs. Third, most abused drugs alter brain levels of endocannabinoids in the brain. In addition to reward functions, the endocannabinoid cannabinoid system appears to be involved in the ability of drugs and drug-related cues to reinstate drug-seeking behavior in animal models of relapse. Altogether, evidence points to the endocannadinoid system as a promising target for the development of medications for the treatment of drug abuse.”

“The endogenous cannabinoid is a recently discovered system that appears to play an important and pervasive role in many types of drug abuse and dependence. Endogenous cannabinoids are neuromodulators that are involved in the signalling of rewarding events and can produce reinforcing and rewarding effects in experimental animals, as they do in humans. Endogenous cannabinoids can also activate other brain systems involved in reward signalling, can modulate the reinforcing and rewarding effects of other non-cannabinoid abused drugs, and are released by drugs of abuse in brain areas involved in reward and reinforcement processes. Accumulating evidence points to the endocannabinoid system as a major target for the development of new pharmacological agents for the treatment of many different types of drug abuse and dependence.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2189556/

Endocannabinoid influence in drug reinforcement, dependence and addiction-related behaviors.

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Abstract

“The endogenous cannabinoid system is an important regulatory system involved in physiological homeostasis. Endocannabinoid signaling is known to modulate neural development, immune function, metabolism, synaptic plasticity and emotional state. Accumulating evidence also implicates brain endocannabinoid signaling in the etiology of drug addiction which is characterized by compulsive drug seeking, loss of control in limiting drug intake, emergence of a negative emotional state in the absence of drug use and a persistent vulnerability toward relapse to drug use during protracted abstinence. In this review we discuss the effects of drug intake on brain endocannabinoid signaling, evidence implicating the endocannabinoid system in the motivation for drug consumption, and drug-induced alterations in endocannabinoid function that may contribute to various aspects of addiction including dysregulated synaptic plasticity, increased stress responsivity, negative affective states, drug craving and relapse to drug taking. Current knowledge of genetic variants in endocannabinoid signaling associated with addiction is also discussed.”

http://www.ncbi.nlm.nih.gov/pubmed/21798285

Marijuana withdrawal and craving: influence of the cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH) genes

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 “While cannabis withdrawal may not include some of the serious medical problems observed with alcohol and opioid withdrawal, it is likely that the symptoms associated with cannabis withdrawal (e.g. negative affect, appetite and sleep disturbance) contribute to the development and intractability of cannabis dependence. In this sense, cannabis withdrawal may be analogous to other, better-understood withdrawal syndromes (e.g. tobacco withdrawal, alcohol withdrawal) that have been the target of intervention efforts. Furthermore, cannabis withdrawal has been described increasingly in terms of the physiological sequelae that coincide with this syndrome, including alterations in dopamine neurotransmission, as well as alterations in other systems.”.

“These findings may have both etiological and treatment implications. For example, individuals with the CNR1 T/C genotype may be more likely to develop dependence and/or more likely to have trouble establishing abstinence or reducing marijuana use. However, longitudinal studies will be needed to clarify whether this genetic variable actually influences the trajectory of marijuana use/dependence. In addition, treatment studies that incorporate this information are needed to determine whether these (or other) genetic variants may influence treatment outcomes and determine whether alternative treatments may be indicated for these individuals.”

“In conclusion, the cannabis dependence endophenotypes, craving and withdrawal, are important factors in the etiology and treatment of cannabis dependence and, given growing recognition of the underlying physiological sequalae that coincide with long-term cannabis use, these phenotypes are likely to lend themselves to the identification of underlying genetic factors that have direct implications for treatment approaches.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873690/

The genetic basis of the endocannabinoid system and drug addiction in humans.

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“The cannabinoid receptor (CNR1) and the fatty acid amide hydrolase (FAAH) genes are located on chromosomes 6 and 1 in the 6q15 and 1p33 cytogenetic bands, respectively. CNR1 encodes a seven-transmembrane domain protein of 472 amino acids, whereas FAAH encodes one transmembrane domain of 579 amino acids. Several mutations found in these genes lead to altered mRNA stability and transcription rate or a reduction of the activity of the encoded protein. Increasing evidence shows that these functional mutations are related to dependence upon cocaine, alcohol, marijuana, heroin, nicotine and other drugs. One of the most compelling associations is with the C385A single nucleotide polymorphism (SNP), which is found in the FAAH gene. For all of the genetic polymorphisms reviewed here, it is difficult to form overall conclusions due to the high diversity of population samples being studied, ethnicity, the use of volunteers, heterogeneity of the recruitment criteria and the drug addiction phenotype studied. Care should be taken when generalizing the results from different studies. However, many works have repeatedly associated polymorphisms in the CNR1 and FAAH genes with drug-related behaviours; this suggests that these genes should be examined in further genetic studies focusing on drug addiction and other psychiatric disorders.”

http://www.ncbi.nlm.nih.gov/pubmed/21937688

The endocannabinoid system: emotion, learning and addiction.

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“The identification of the cannabinoid receptor type 1 (CB1 receptor) was the milestone discovery in the elucidation of the behavioural and emotional responses induced by the Cannabis sativa constituent Delta(9)-tetrahydrocannabinol. The subsequent years have established the existence of the endocannabinoid system. The early view relating this system to emotional responses is reflected by the fact that N-arachidonoyl ethanolamine, the pioneer endocannabinoid, was named anandamide after the Sanskrit word ‘ananda’, meaning ‘bliss’. However, the emotional responses to cannabinoids are not always pleasant and delightful. Rather, anxiety and panic may also occur after activation of CB1 receptors. The present review discusses three properties of the endocannabinoid system as an attempt to understand these diverse effects. First, this system typically functions ‘on-demand’, depending on environmental stimuli and on the emotional state of the organism. Second, it has a wide neuro-anatomical distribution, modulating brain regions with different functions in responses to aversive stimuli. Third, endocannabinoids regulate the release of other neurotransmitters that may have even opposing functions, such as GABA and glutamate. Further understanding of the temporal, spatial and functional characteristics of this system is necessary to clarify its role in emotional responses and will promote advances in its therapeutic exploitation.”

http://www.ncbi.nlm.nih.gov/pubmed/18422832

Endocannabinoid release from midbrain dopamine neurons: a potential substrate for cannabinoid receptor antagonist treatment of addiction.

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“Substantial evidence suggests that all commonly abused drugs act upon the brain reward circuitry to ultimately increase extracellular concentrations of the neurotransmitter dopamine in the nucleus accumbens and other forebrain areas. Many drugs of abuse appear to increase dopamine levels by dramatically increase the firing and bursting rates of dopamine neurons located in the ventral mesencephalon. Recent clinical evidence in humans and behavioral evidence in animals indicate that cannabinoid receptor antagonists such as SR141716A (Rimonabant) can reduce the self-administration of, and craving for, several commonly addictive drugs. However, the mechanism of this potentially beneficial effect has not yet been identified. We propose, on the basis of recent studies in our laboratory and others, that these antagonists may act by blocking the effects of endogenously released cannabinoid molecules (endocannabinoids) that are released in an activity- and calcium-dependent manner from mesencephalic dopamine neurons. It is hypothesized that, through the antagonism of cannabinoid CB1 receptors located on inhibitory and excitatory axon terminals targeting the midbrain dopamine neurons, the effects of the endocannabinoids are occluded. The data from these studies therefore suggest that the endocannabinoid system and the CB1 receptors located in the ventral mesencephalon may play an important role in regulating drug reward processes, and that this substrate is recruited whenever dopamine neuron activity is increased.”

http://www.ncbi.nlm.nih.gov/pubmed/15878779

Cannabinoid CB1 Receptor Antagonists as Promising New Medications for Drug Dependence

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 “This review examines the development of cannabinoid CB1 receptor antagonists as a new class of therapeutic agents for drug addiction. Abused drugs [alcohol, opiates, Δ9-tetrahydrocannabinol (Δ9-THC), and psychostimulants, including nicotine] elicit a variety of chronically relapsing disorders by interacting with endogenous neural pathways in the brain. In particular, they share the common property of activating mesolimbic dopamine brain reward systems, and virtually all abused drugs elevate dopamine levels in the nucleus accumbens. Cannabinoid CB1 receptors are expressed in this brain reward circuit and modulate the dopamine-releasing effects of Δ9-THC and nicotine. Rimonabant (SR141716), a CB1 receptor antagonist, blocks both the dopamine-releasing and discriminative and rewarding effects of Δ9-THC in animals. Blockade of CB1 receptor activity by genetic invalidation also decreases rewarding effects of opiates and alcohol in animals. Although CB1 receptor blockade is generally ineffective in reducing the self-administration of cocaine in rodents and primates, it reduces the reinstatement of extinguished cocaine-seeking behavior produced by cocaine-associated conditioned stimuli and cocaine-priming injections. Likewise, CB1 receptor blockade is effective in reducing nicotine-seeking behavior induced by re-exposure to nicotine-associated stimuli. Some of these findings have been recently validated in humans. In clinical trials, Rimonabant blocks the subjective effects of Δ9-THC in humans and prevents relapse to smoking in exsmokers. Findings from both clinical and preclinical studies suggest that ligands blocking CB1 receptors offer a novel approach for patients suffering from drug dependence that may be efficacious across different classes of abused drugs.”

“Cannabinoid CB1 Receptor Blockade: A Step Forward in Drug-Dependence Therapy?”

“Despite advances in the understanding of neurobiological and behavioral mechanisms that lead to drug dependence over the last 20 years, no effective treatment is yet available for cocaine or Δ9-THC dependence. Moreover, medications available for ethanol, nicotine, or opioid dependence are ineffective in many subjects. For example, the rate of smoking cessation by subjects entering into clinical trials that combine effective medication and behavioral and cognitive therapy is around 30% at one year; most subjects relapse. Cannabinoid CB1 receptor antagonists represent a potentially useful tool not only for blocking the direct reinforcing effects of Δ9-THC, nicotine, and ethanol, but also for preventing relapse to the use of various drugs of abuse, including cocaine, methamphetamine, and heroin. In addition, environmental stimuli seem to be one of the major factors that can trigger relapse to drug use in abstinent drug abusers. This process is not only critical for psychostimulant abuse, but also for nicotine and heroin abuse, and probably for other drugs of abuse such as ethanol. By reducing the motivational effects of drug-related environmental stimuli, cannabinoid CB1 receptor antagonists might, therefore, provide an effective means for preventing relapse to drug-seeking behavior in abstinent drug abusers, providing a promising new tool for the treatment of dependence on a wide range of abused drugs.”

http://jpet.aspetjournals.org/content/312/3/875.long

Cannabinoid CB1 receptors control conditioned drug seeking.

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Abstract

“Recent developments have implicated cannabinoid CB1 receptors as a novel target for a new class of therapeutic agents used to treat drug addiction. CB1 receptors are expressed in the motivational circuitry of the brain and modulate drug seeking. Blockade of the CB1 receptor is particularly effective in reducing cue-induced reinstatement of drug seeking, an animal analogue of cue-induced relapse in human addicts. These relapse-preventing properties are observed with different classes of abused drug (i.e. psychostimulants, opiates, nicotine and alcohol). In addition, recent evidence indicates a more general role of CB1 receptors in reward-related memories, which is consistent with the proposed role of endocannabinoids in memory-related plasticity. Relapse-preventing actions and inhibitory effects on weight gain were confirmed recently in clinical trials with the CB1 antagonist rimonabant. Collectively, these clinical and preclinical studies suggest that antagonists of CB1 receptors offer a novel approach in the treatment of addictive behaviours.”

http://www.ncbi.nlm.nih.gov/pubmed/15992935