preproenkephalin and Substance-Related-Disorders

People with a genetic predisposition for substance abuse have defects in genes for the opioid peptides and receptors. A high number of polymorphisms have been detected in the mu-opioid receptor, some of which result in pharmacological alterations. The opioid peptide proopiomelanocortin proved extraordinarily rich in mutations that often lead to severe phenotypical consequences. Prodynorphin displays a polymorphic regulation of transcription. Variants of the mu- and the delta-opioid receptor showed positive associations with opiate and/or alcohol addiction in some studies. However, these associations were weak, indicating a small contribution of the opioid system to these disorders.

Topics: Alleles; beta-Endorphin; Enkephalins; Genetic Predisposition to Disease; Humans; Polymorphism, Genetic; Protein Precursors; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Substance-Related Disorders

Striatal enkephalin and dynorphin opioid systems mediate reward and negative affect, respectively, relevant to addiction disorders. We examined polymorphisms of proenkephalin (PENK) and prodynorphin (PDYN) genes in relation to heroin abuse and gene expression in the human striatum and the relevance of genetic dopaminergic tone, critical for drug reward and striatal function. Heroin abuse was significantly associated with PENK polymorphic 3' UTR dinucleotide (CA) repeats; 79% of subjects homozygous for the 79-bp allele were heroin abusers. Such individuals tended to express higher PENK mRNA than the 81-bp homozygotes, but PENK levels within the nucleus accumbens (NAc) shell were most strongly correlated to catecholamine-O-methyltransferase (COMT) genotype. Control Met/Met individuals expressed lower PENK mRNA than Val carriers, a pattern reversed in heroin users. Up-regulation of NAc PENK in Met/Met heroin abusers was accompanied by impaired tyrosine hydroxylase (TH) mRNA expression in mesolimbic dopamine neurons. In contrast to PENK, no association was detected between PDYN genotype (68-bp repeat element containing one to four copies of AP-1 binding sites in the promoter region) and heroin abuse, although there was a clear functional association with striatal PDYN mRNA expression: an increased number of inducible repeats (three and four) correlated with higher PDYN levels than adult or fetal subjects with noninducible (one and two) alleles. Moreover, PDYN expression was not related to COMT genotype. Altogether, the data suggest that dysfunction of the opioid reward system is significantly linked to opiate abuse vulnerability and that heroin use alters the apparent influence of heritable dopamine tone on mesolimbic PENK and TH function.

Topics: Adult; Analgesics, Opioid; Autopsy; Brain; Dopamine; Enkephalins; Female; Gene Expression Regulation; Heroin; Humans; Male; Neuropeptides; Nucleus Accumbens; Protein Precursors; Receptors, Opioid, mu; Substance-Related Disorders; Tyrosine 3-Monooxygenase

CART peptide is a peptidergic neurotransmitter that is expressed in brain regions involved in critical biological processes such as feeding and stress, and in areas associated with drug reward and abuse including the dopamine-rich nucleus accumbens (NAcc), which can be considered part of the basal ganglia. Because CART has been shown to colocalize with substance P, a marker of the basal ganglia direct pathway, we now test for colocalization with other markers of the direct pathway to determine if CART colocalizes with dynorphin and dopamine D1 receptors. In the NAcc, CART peptide immunoreactivity (IR) was colocalized with prodynorphin-IR in neurons. Approximately 80.1% of CART-IR cells colocalized with prodynorphin-IR, while only 27.6% of prodynorphin-IR neurons contained CART-IR, suggesting that CART cells are a subset of dynorphin cells. In contrast, only about 25% of CART-IR cell bodies demonstrated dopamine D1 receptor-IR. Because dynorphin and D1 receptors are markers for the basal ganglia direct pathway, from the NAcc to the basal ganglia output nuclei, and because CART significantly colocalizes with these markers, some CART neurons are part of the direct pathway or some comparable pathway in the accumbens. The presence of CART in NAcc neurons and the fact that NAcc projection neurons have extensive local collaterals suggest that CART may have effects in both terminal and cell body regions of the accumbens and may therefore affect information processing in the NAcc by modulating accumbal neurons.

Topics: Animals; Cocaine; Enkephalins; Male; Microscopy, Fluorescence; Models, Biological; Nerve Tissue Proteins; Neurons; Neuropeptides; Nucleus Accumbens; Peptides; Protein Precursors; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Substance-Related Disorders

Drugs abused by humans are thought to activate areas in the ventral striatum of the brain that engage the organism in important adaptive behaviors, such as eating. In support of this, we report here that striatal regions of sugar-dependent rats show alterations in dopamine and opioid mRNA levels similar to morphine-dependent rats. Specifically, after a chronic schedule of intermittent bingeing on a sucrose solution, mRNA levels for the D2 dopamine receptor, and the preproenkephalin and preprotachykinin genes were decreased in dopamine-receptive regions of the forebrain, while D3 dopamine receptor mRNA was increased. While morphine affects gene expression across the entire dopamine-receptive striatum, significant differences were detected in the effects of sugar on the nucleus accumbens and adjacent caudate-putamen. The effects of sugar on mRNA levels were of greater magnitude in the nucleus accumbens than in the caudate-putamen. These areas also showed clear differences in the interactions among the genes, especially between D3R and the other genes. This was revealed by a novel multivariate analysis method that identified cooperative interactions among genes, specifically in the nucleus accumbens but not the caudate-putamen. Finally, a role for these cooperative interactions in a load-sharing response to perturbations caused by sugar was supported by the finding of a different pattern of correlations between the genes in the two striatal regions. These findings support a major role for the nucleus accumbens in mediating the effects of naturally rewarding substances and extend an animal model for studying the common substrates of drug addiction and eating disorders.

Topics: Animals; Brain; Down-Regulation; Enkephalins; Feeding and Eating Disorders; Gene Expression; Gene Expression Profiling; Male; Morphine; Neural Pathways; Nucleus Accumbens; Opioid Peptides; Protein Precursors; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Receptors, Dopamine D3; Reward; RNA, Messenger; Substance-Related Disorders; Sucrose; Tachykinins; Up-Regulation

The involvement of dynorphin on Delta-9-tetrahydrocannabinol (THC) and morphine responses has been investigated by using mice with a targeted inactivation of the prodynorphin (Pdyn) gene. Dynorphin-deficient mice show specific changes in the behavioral effects of THC, including a reduction of spinal THC analgesia and the absence of THC-induced conditioned place aversion. In contrast, acute and chronic opioid effects were normal. The lack of negative motivational effects of THC in the absence of dynorphin demonstrates that this endogenous opioid peptide mediates the dysphoric effects of marijuana.

Topics: Analgesia; Analgesics, Opioid; Animals; Avoidance Learning; Behavior, Animal; Brain Chemistry; Dronabinol; Dynorphins; Enkephalins; Female; Gene Targeting; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Mutant Strains; Morphine; Motivation; Motor Activity; Narcotics; Pain Measurement; Protein Precursors; Receptors, Opioid, kappa; Spatial Behavior; Substance-Related Disorders

Chronic administration of morphine or cocaine affects opioid gene expression. To better understand the possible existence of common neuronal pathways shared by different classes of drugs of abuse, we studied the effects of methamphetamine on the gene expression of the opioid precursor prodynorphin and on the levels of peptide dynorphin A in the rat brain. Acute (6 mg/kg, intraperitoneally, i.p.) and chronic (6 mg/kg, i.p. for 15 days) methamphetamine markedly raised prodynorphin mRNA levels in the hypothalamus, whereas no effect was observed in the hippocampus. Dynorphin A levels increased after chronic treatment in the hypothalamus and in the striatum, whereas no significant changes were detected after acute treatment. These results indicate that methamphetamine affects prodynorphin gene expression in the hypothalamus, which may be an important site (also for its relevant neuroendocrine correlates) for opioidergic mechanisms activated by addictive drugs.

Topics: Animals; Brain; Dynorphins; Enkephalins; Gene Expression Regulation; Hippocampus; Hypothalamus; Male; Methamphetamine; Protein Precursors; Rats; Rats, Sprague-Dawley; Substance-Related Disorders; Time Factors; Visual Cortex

Topics: Animals; Central Nervous System Stimulants; Corpus Striatum; Dopamine Agonists; Dopamine Antagonists; Dynorphins; Enkephalins; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Genes, Immediate-Early; Glutamic Acid; Neurons; Neuropeptides; Protein Precursors; Receptors, Dopamine D1; Receptors, Dopamine D2; Substance-Related Disorders; Transcription, Genetic

The modulation by selective dopamine receptor antagonists of the effects of "binge' cocaine (3 x 15 mg kg-1 day-1, i.p., for 3 days after 11 days of adaptation to saline injections) on preproenkephalin, preprodynorphin, kappa opioid receptor and dopamine transporter mRNAs was determined. Administration of cocaine was preceded by daily single injections of a D1 (SCH 23390; 2 mg kg-1) or the D2 (sulpiride; 50 mg kg-1) dopamine receptor antagonist. The D1, and not the D2, antagonist blocked cocaine-induced preprodynorphine and preproenkephalin increases in the caudate-putamen. Sulpiride alone, and sulpiride plus cocaine, increased preproenkephalin mRNA. Dopamine transporter mRNA levels showed a cocaine treatment-antagonist interaction. These data indicate that this administration paradigm elevates both preprodynorphin and preproenkephalin mRNAs by a D1-dependent mechanism not requiring D2 activation.

Topics: Analysis of Variance; Animals; Benzazepines; Brain; Carrier Proteins; Cocaine; DNA Primers; Dopamine Antagonists; Dopamine Plasma Membrane Transport Proteins; Drug Administration Schedule; Dynorphins; Enkephalins; Male; Membrane Glycoproteins; Membrane Transport Proteins; Nerve Tissue Proteins; Polymerase Chain Reaction; Protein Precursors; Rats; Rats, Inbred F344; Receptors, Opioid, kappa; RNA, Messenger; Substance-Related Disorders; Sulpiride; Transcription, Genetic

Other workers have established that cocaine injections increase the levels of dynorphin peptides in the caudate putamen and substantia nigra of the rat brain. Using a quantitative solution hybridization protection assay for mRNA, we detected a significant increase in the concentration of prodynorphin mRNA in caudate putamen extracts of rats injected with cocaine following a 'binge' administration pattern designed to mimic human cocaine abuse. Increased prodynorphin mRNA was observed at the earliest time-point studied (50 h) and the lowest dose (10 mg/kg/day) of cocaine tested and persisted through the 14 day period studied. No prodynorphin mRNA was detected in the substantia nigra.

Topics: Animals; Brain; Caudate Nucleus; Cocaine; Drug Administration Schedule; Enkephalins; Humans; Male; Organ Specificity; Protein Precursors; Putamen; Rats; Rats, Inbred F344; RNA; RNA, Messenger; Substance-Related Disorders; Time Factors