- [Show abstract] [Hide abstract] ABSTRACT: 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.
- [Show abstract] [Hide abstract] ABSTRACT: The immediate early genes (IEGs) have been suggested to be implicated in mechanisms of addiction, as well as in learning and memory processes. fosB, which belongs to IEG, has been reported to have pleiotropic impact on response to psychoactive drugs, as well as motivational and stress-related behaviours. In the present study, we used mice with constitutive knock-out of fosB in order to study fosB role in mouse phenotype. We studied rewarding properties of morphine (10mg/kg i.p.) in conditioned place preference (CPP) paradigm. Additionally, we studied fosB role in spatial memory and spatial working memory using elevated plus maze model of spatial learning (EPMSL) and delayed non-match to place task (DNMTP). In further studies, locomotor, depressive-like and anxiety-like behaviours were measured. Rewarding effects of morphine in fosB -/- mice were abolished whereas spatial learning was impaired. On the other hand, we found no significant differences in locomotor activity, depression-like and anxiety-like behaviours. In summary, our results indicate that mice lacking fosB are less sensitive to rewarding properties of morphine and display spatial memory impairment and suggest involvement of fosB and its proteins in motivational aspects of reinforcers as well as in learning and memory processes.
- [Show abstract] [Hide abstract] ABSTRACT: alpha-Synuclein is a presynaptic protein proposed to serve as a negative regulator of dopaminergic neurotransmission. Recent research has implicated alpha-synuclein in chronic neuroadaptations produced by psychostimulant and opiate use, as well as in genetically determined susceptibility to alcoholism in humans. The aim of our study was to characterize the changes in alpha-synuclein expression after short-term abstinence from chronic alcohol drinking in mice. Male C57BL/6J mice were allowed to drink increasing concentrations of alcohol in the two-bottle choice procedure. Then the mice were given constant access to an 8% alcohol solution and water for 32 days, and were sacrificed 2 h, 24 h or 48 h after alcohol withdrawal. RT-PCR, in situ hybridization and Western blotting techniques were used to measure alpha-synuclein mRNA and protein levels in the brain and blood. alpha-Synuclein protein levels were elevated by up to 80% in the amygdala of mice withdrawn from alcohol for 24 h or 48 h. No changes in alpha-synuclein levels were found in the mesencephalon or striatum/accumbens. The levels of alpha-synuclein mRNA remained unchanged in all brain regions examined (the striatum, nucleus accumbens, amygdala, substantia nigra, ventral tegmental area). alpha-Synuclein mRNA was up-regulated in the whole blood 48 h after alcohol withdrawal. The accumulation of alpha-synuclein in the amygdala, observed in this study, seems to be a common feature of alcohol and opiate abstinence. This finding suggests a role of alpha-synuclein in common neuroadaptations produced by long-term alcohol and drug use. Although alpha-synuclein expression in the blood seems unrelated to that in the brain, it may serve as a peripheral biomarker of chronic alcohol consumption.
- [Show abstract] [Hide abstract] ABSTRACT: The proteins of Fos family are a potential candidate to link molecular mechanisms of morphine action with behavioural effects such as morphine-induced reward, dependence and tolerance. We used both male and female mice lacking fosB gene to study its contribution to morphine effects. Morphine analgesia (tail-flick test) and hypothermia were studied using morphine at cumulative doses in morphine-naive and morphine-tolerant (tolerance induced by 24 h prior 100 mg/kg morphine administration) mice. FosB -/- mice, as compared to fosB +/+ mice, developed enhanced tolerance to morphine-induced analgesia. No effects of genotype or gender on tolerance to morphine-induced hypothermia were observed. These results suggest that fosB may be involved in the development of tolerance to morphine analgesia but not hypothermia. The gender study implicates that lack of FosB proteins in female fosB -/- mice enhanced morphine analgesic potency. In conclusion, we show that fosB gene is important to analgesia but not hypothermia phenotype indicating its role in morphine effects.
- [Show abstract] [Hide abstract] ABSTRACT: The present study was designed to investigate the involvement of opioidergic component as well as to study GABAergic mechanisms in the expression of heroin discrimination. Male Wistar rats were trained to discriminate heroin (0.5 mg/kg, i.p.) from saline (i.p.) in a two-choice water reinforced fixed ratio (FR) 20 drug discrimination paradigm. In substitution tests, heroin (0.0625-0.5 mg/kg) and morphine (0.5-2 mg/kg, i.p.) evoked a dose-dependent generalization for the drug lever-responding, while muscimol (1 mg/kg, i.p., a GABA(A) receptor agonist) produced a weak partial substitution (ca. 48% heroin-lever responding). Neither tiagabine (2.5 mg/kg, i.p.; a GABA reuptake inhibitor), vigabatrin (75-150 mg/kg, i.p.; an irreversible inhibitor of GABA transaminase), nor baclofen (0.5 mg/kg, i.p.; a GABA(B) receptor agonist) substituted for heroin. In combination studies, the stimulus effects produced by heroin (0.5 mg/kg) or morphine (2 mg/kg) were dose-dependently blocked by opioid receptor antagonists naltrexone (0.1-1 mg/kg, i.p.), and naloxone (0.5-1 mg/kg, i.p.). The peripherally-acting naloxone methiodide at a dose of 1 mg/kg, i.p. did not alter, while at a dose of 10 mg/kg that penetrates across the blood-brain barrier, it reduced the stimulus effects of heroin or morphine. Pretreatment with tiagabine (2.5-5 mg/kg) produced a rightward shift of a heroin dose-response curve, while vigabatrin (75-300 mg/kg), baclofen (0.5-2.5 mg/kg) or muscimol (0.5-2 mg/kg) given prior to heroin (0.0625-0.5 mg/kg) failed to alter heroin discrimination. Our findings confirm previous studies on the significance of mu-opioidergic mechanisms in the expression of heroin discrimination and add the observation that selective inhibition of GABA reuptake, but not inhibition of GABA transaminase or direct stimulation of GABA(A) and GABA(B) receptors, can decrease the overall effects of heroin.