ß2* nAChR sensitivity modulates acquisition of cocaine self-administration in male rats.

Signaling through nicotinic acetylcholine receptors (nAChRs) plays a role in cocaine reward and reinforcement, suggesting that the cholinergic system could be manipulated with therapeutics to modulate aspects of cocaine use disorder (CUD). We examined the interaction between nAChRs and cocaine reinforcement by expressing a hypersensitive ß2 nAChR subunit (ß2Leu9'Ser) in the ventral tegmental area of male Sprague Dawley rats. Compared to control rats, ß2Leu9'Ser rats acquired (fixed ratio) intravenous cocaine self-administration faster and with greater likelihood. By contrast, ß2Leu9'Ser rats were approximately equivalent to controls in their intake of cocaine on a progressive ratio schedule of reinforcement, suggesting differential effects of cholinergic signaling depending on experimental parameters. Like progressive ratio cocaine SA, ß2Leu9'Ser rats and controls did not differ significantly in food SA assays, including acquisition on a fixed ratio schedule or in progressive ratio sessions. These results highlight the specific role of high-affinity, heteropentameric ß2* (ß2-containing) nAChRs in acquisition of cocaine SA, suggesting that mesolimbic acetylcholine signaling is active during this process.

ß2 nAChR Activation on VTA DA Neurons Is Sufficient for Nicotine Reinforcement in Rats.

Mesolimbic nicotinic acetylcholine receptor (nAChRs) activation is necessary for nicotine reinforcement behavior, but it is unknown whether selective activation of nAChRs in the dopamine (DA) reward pathway is sufficient to support nicotine reinforcement. In this study, we tested the hypothesis that activation of ß2-containing (ß2*) nAChRs on VTA neurons is sufficient for intravenous nicotine self-administration (SA). We expressed ß2 nAChR subunits with enhanced sensitivity to nicotine (referred to as ß2Leu9'Ser) in the VTA of male Sprague Dawley (SD) rats, enabling very low concentrations of nicotine to selectively activate ß2* nAChRs on transduced neurons. Rats expressing ß2Leu9'Ser subunits acquired nicotine SA at 1.5 µg/kg/infusion, a dose too low to support acquisition in control rats. Saline substitution extinguished responding for 1.5 µg/kg/inf, verifying that this dose was reinforcing. ß2Leu9'Ser nAChRs also supported acquisition at the typical training dose in rats (30 µg/kg/inf) and reducing the dose to 1.5 µg/kg/inf caused a significant increase in the rate of nicotine SA. Viral expression of ß2Leu9'Ser subunits only in VTA DA neurons (via TH-Cre rats) also enabled acquisition of nicotine SA at 1.5 µg/kg/inf, and saline substitution significantly attenuated responding. Next, we examined electrically-evoked DA release in slices from ß2Leu9'Ser rats with a history of nicotine SA. Single-pulse evoked DA release and DA uptake rate were reduced in ß2Leu9'Ser NAc slices, but relative increases in DA following a train of stimuli were preserved. These results are the first to report that ß2* nAChR activation on VTA neurons is sufficient for nicotine reinforcement in rats.

Relapse-like behavior and nAChR sensitization following intermittent access nicotine self-administration.

Many tobacco smokers consume nicotine intermittently, but the underlying mechanisms and neurobiological changes associated with intermittent nicotine intake are unclear. Understanding intermittent nicotine intake is a high priority, as it could promote therapeutic strategies to attenuate tobacco consumption. We examined nicotine intake behavior and neurobiological changes in male rats that were trained to self-administer nicotine during brief (5 min) trials interspersed with longer (15 min) drug-free periods. Rats readily adapted to intermittent access (IntA) SA following acquisition on a continuous access (ContA) schedule. Probabilistic analysis of IntA nicotine SA suggested reduced nicotine loading behavior compared to ContA, and nicotine pharmacokinetic modeling revealed that rats taking nicotine intermittently may have increased intake to maintain blood levels of nicotine that are comparable to ContA SA. After IntA nicotine SA, rats exhibited an increase in unreinforced responses for nicotine-associated cues (incubation of craving) and specific alterations in the striatal proteome after 7 days without nicotine. IntA nicotine SA also induced nAChR functional upregulation in the interpeduncular nucleus (IPN), and it enhanced nicotine binding in the brain as determined via [11C]nicotine positron emission tomography. Reducing the saliency of the cue conditions during the 5 min access periods attenuated nicotine intake, but incubation of craving was preserved. Together, these results indicate that IntA conditions promote nicotine SA and nicotine seeking after a nicotine-free period.

Effects of the dopamine/norepinephrine releaser phenmetrazine on cocaine self-administration and cocaine-primed reinstatement in rats.

RATIONALE: Like other monoamine releasers such as D-amphetamine, chronic treatment with phenmetrazine can attenuate cocaine self-administration in monkeys. OBJECTIVES: The present studies extended this finding to rodents and to cocaine-primed reinstatement, a putative laboratory animal model of relapse. METHODS: In experiment 1, rats self-administered food pellets or injections of 0.19 mg/kg cocaine (i.v.) under a progressive-ratio schedule. When responding was stable, subcutaneous osmotic pumps were implanted containing saline or (+)-phenmetrazine (25 or 50 mg/kg per day). In experiment 2, rats self-administered injections of 0.75 mg/kg cocaine under a fixed-ratio 1 schedule in daily 6-h sessions. When responding was stable, rats were removed from the self-administration environment for 7 days and treated continuously with saline, 5 mg/kg per day D-amphetamine or phenmetrazine (25 or 50 mg/kg per day) via osmotic pumps. Rats were then returned to the self-administration context while treatment continued, and responding was extinguished by removing response-contingent stimulus changes and cocaine injections. Once responding was extinguished, reinstatement tests were conducted using cocaine injections (10 mg/kg i.p.). RESULTS: Phenmetrazine decreased self-administration of cocaine, but not food pellets, during the 14-day treatment period; effects persisted for several days after treatment was discontinued. Moreover, cocaine-induced increases in responding during the reinstatement test were attenuated by D-amphetamine and both phenmetrazine doses. CONCLUSIONS: These results extend the study of the effects of phenmetrazine on cocaine self-administration to a rodent model, and provide further support for the use of monoamine releasers as agonist medications for cocaine abuse.

Association between genetic polymorphisms in the prostate-specific antigen gene promoter and serum prostate-specific antigen levels.

BACKGROUND: Recent evidence suggests that genetic variation in the promoter of the prostate-specific antigen (PSA) gene may contribute to individual variation in serum PSA levels. However, polymorphisms associated with variations in PSA levels have not been identified. METHODS: We used the polymerase chain reaction to amplify the promoter region of the PSA genes (nucleotide positions -3873 to -5749 with respect to the start of transcription) of 409 healthy white men at risk for lung disease. Polymerase chain reaction products were sequenced to identify polymorphisms in the PSA gene promoter and to genotype the men for common single nucleotide polymorphisms (SNPs) and were cloned into luciferase reporter constructs to assay PSA promoter activity in human LNCaP prostate cancer cells. Analysis of variance was used to test the association of polymorphism frequencies with mean serum PSA levels. All statistical tests were two-sided. RESULTS: The -4643G/A SNP (G allele) had a 21.2% prevalence and was associated with increases in serum PSA levels (P =.017) and PSA promoter activity (P<.001). The -5412C/T SNP (C allele) had a 22.0% prevalence and was associated with an increase in serum PSA levels (P =.0015). The -5429T/G SNP (G allele) had a 23.0% prevalence, was associated with an increase in serum PSA levels (P =.021), and was in linkage disequilibrium with the -5412C/T SNP. The promoter activity of the -5412 C/-5429 G haplotype was higher than that of the -5412 T/-5429 T haplotype (P<.001). CONCLUSIONS: Genetic variations in the PSA promoter are associated with serum PSA levels in men without prostatic disease. PSA promoter genotype information may help to refine models of PSA cutoff values.