heroin and preproenkephalin

Opiate-induced alterations in the gene expression of the opioid propeptides prodynorphin (PDYN) and proenkephalin (PENK) in the brain have previously been described. However, there are no studies examining opioid propeptide system alterations due to long-lasting heroin self-administration. In our study, using in situ hybridization, we measured PDYN and PENK mRNA levels in the dorsal striatum, central nucleus of amygdala (CEA), and nucleus accumbens (NAcc) shell and core in rats after 6 weeks of heroin self-administration (fixed ratio 5, 0.02 mg/kg/infusion of heroin i.v.) and their respective saline or heroin "yoked" control. Our results show an increase in the PDYN mRNA level in the CEA and NAcc shell and no changes of PENK gene expression after heroin self-administration. In addition, to dissociate pharmacological effects of heroin from those produced by motivational processes driving active heroin intake on the PDYN and PENK gene expression, we compared effects of response-dependent (contingent) and response-independent (noncontingent--"yoked" heroin control) heroin administration. We found no differences between contingent and noncontingent groups of rats. In conclusion, our results indicate neuroadaptations in the PDYN but not PENK gene expression in rat limbic forebrain during heroin self-administration. We show that such changes depend on direct pharmacological actions of heroin rather than contingent heroin intake. These neuroalterations probably occur as an adaptation to long-lasting heroin exposure and may underlie changes leading to compulsive drug use and addiction.

Topics: Amygdala; Analgesics, Opioid; Animals; Behavior, Animal; Brain; Conditioning, Operant; Corpus Striatum; Enkephalins; Extinction, Psychological; Gene Expression; Heroin; In Situ Hybridization; Male; Nucleus Accumbens; Protein Precursors; Rats; Rats, Sprague-Dawley; Reinforcement Schedule; RNA, Messenger; Self Administration; Time Factors

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

Cannabis use is a hypothesized gateway to subsequent abuse of other drugs such as heroin. We currently assessed whether Delta-9-tetrahydrocannabinol (THC) exposure during adolescence modulates opiate reinforcement and opioid neural systems in adulthood. Long-Evan male rats received THC (1.5 mg/kg intraperitoneally (i.p.)) or vehicle every third day during postnatal days (PNDs) 28-49. Heroin self-administration behavior (fixed ratio-1; 3-h sessions) was studied from young adulthood (PND 57) into full adults (PND 102). THC-pretreated rats showed an upward shift throughout the heroin self-administration acquisition (30 microg/kg/infusion) phase, whereas control animals maintained the same pattern once stable intake was obtained. Heightened opiate sensitivity in THC animals was also evidenced by higher heroin consumption during the maintenance phase (30 and 60 microg/kg/infusion) and greater responding for moderate-low heroin doses (dose-response curve: 7.5, 15, 30, 60, and 100 microg/kg/injection). Specific disturbance of the endogenous opioid system was also apparent in the brain of adults with adolescent THC exposure. Striatal preproenkephalin mRNA expression was exclusively increased in the nucleus accumbens (NAc) shell; the relative elevation of preproenkephalin mRNA in the THC rats was maintained even after heroin self-administration. Moreover, mu opioid receptor (muOR) GTP-coupling was potentiated in mesolimbic and nigrostriatal brainstem regions in THC-pretreated animals. muOR function in the NAc shell was specifically correlated to heroin intake. The current findings support the gateway hypothesis demonstrating that adolescence cannabis exposure has an enduring impact on hedonic processing resulting in enhanced opiate intake, possibly as a consequence of alterations in limbic opioid neuronal populations.

Topics: Analgesics, Non-Narcotic; Analgesics, Opioid; Analysis of Variance; Animals; Animals, Newborn; Benzoxazines; Dose-Response Relationship, Drug; Dronabinol; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Gene Expression Regulation; Guanosine 5'-O-(3-Thiotriphosphate); Heroin; In Situ Hybridization; Limbic System; Male; Morpholines; Naphthalenes; Neurons; Piperidines; Protein Precursors; Pyrazoles; Radioligand Assay; Rats; Rats, Long-Evans; Reinforcement, Psychology; Rimonabant; Self Administration; Sulfur Isotopes; Tritium

To determine whether there are factors during apparent rapid heroin overdose death that affect agonal state and thus brain pH (index of hypoxia) that can influence neurobiological systems linked to drug abuse.. Brain specimens and autopsy/medical reports were investigated in subjects dying from heroin overdose (n=70) and compared to normal controls (n=45) as well as suicide victims (n=31) with a documented rapid cause of death. Detailed autopsy material was characterized as to positive and negative respiratory distress in relation to brain pH; drug toxicity and other demographic information was also evaluated. In situ hybridization histochemistry was used to study mRNA expression levels of dopamine (e.g., D2 receptor, dopamine transporter) and opioid (e.g., proenkephalin) related markers in various structures in relation to brain pH.. Brain pH was generally reduced in heroin overdose cases versus normal and suicide subjects. There was, however, significant variation in heroin overdose deaths related to differences in respiratory distress that differentially altered brain pH levels. Various factors such as vomit inhalation, resuscitation, pulmonary embolism and suffocation contributed to positive respiratory distress. Elevated brain pH was observed in heroin overdose with positive alcohol toxicity suggesting potentiated alcohol-induced rapidity of heroin deaths. mRNA expression levels of the dopamine-related genes and proenkephalin were positively correlated with brain pH.. Respiratory distress contributes to variations in the acute agonal state during heroin overdose death that differentially alters brain pH levels and significantly impacts mRNA levels. Such findings should be considered for postmortem molecular/neurochemical neurobiological studies of opiate abusers.

Topics: Adolescent; Adult; Aged; Autopsy; Brain Chemistry; Central Nervous System Depressants; Drug Overdose; Enkephalins; Ethanol; Female; Heroin; Humans; Hydrogen-Ion Concentration; In Situ Hybridization; Male; Middle Aged; Prevalence; Protein Precursors; Receptors, Dopamine D2; Respiratory Distress Syndrome; RNA, Messenger; Suicide