A revamped rat reference genome improves the discovery of genetic diversity in laboratory rats.

The seventh iteration of the reference genome assembly for Rattus norvegicus-mRatBN7.2-corrects numerous misplaced segments and reduces base-level errors by approximately 9-fold and increases contiguity by 290-fold compared with its predecessor. Gene annotations are now more complete, improving the mapping precision of genomic, transcriptomic, and proteomics datasets. We jointly analyzed 163 short-read whole-genome sequencing datasets representing 120 laboratory rat strains and substrains using mRatBN7.2. We defined ∼20.0 million sequence variations, of which 18,700 are predicted to potentially impact the function of 6,677 genes. We also generated a new rat genetic map from 1,893 heterogeneous stock rats and annotated transcription start sites and alternative polyadenylation sites. The mRatBN7.2 assembly, along with the extensive analysis of genomic variations among rat strains, enhances our understanding of the rat genome, providing researchers with an expanded resource for studies involving rats.

Inactivation of phosphodiesterase-4B gene in rat nucleus accumbens shell by CRISPR/Cas9 or positive allosteric modulation of the protein affects the motivation to chronically self-administer nicotine.

Large scale human genome wide association studies (GWAS) have identified a growing pool of genes associated with cigarette smoking. One of the most prominent, phosphodiesterase-4B (PDE4B), has been associated with multiple smoking phenotypes. Although PDE4B modulates the half-life of neuronal cAMP, its precise role in smoking behaviors is unknown. To address this knowledge gap, we used a reverse translational approach. We inactivated PDE4B in bilateral medial nucleus accumbens shell (NAcs) neurons by injecting AAV containing a specific gRNA in female transgenic Cas9+ Long Evans rats. These rats then were given 23-h chronic access to nicotine intravenous self-administration (IVSA) under a schedule of increasing fixed ratios (FR). With the increased effort required at FR7, nicotine SA (i.e. active presses and drug infusions) declined significantly in controls, whereas it was maintained in the mutagenized group. A progressive ratio (PR) study also showed significantly greater cumulative nicotine infusions in the PDE4B-edited group. Hence, we hypothesized that enhanced PDE4B protein activity would reduce nicotine IVSA. A positive allosteric modulator, 2-(3-(4-chloro-3-fluorophenyl)-5-ethyl-1H-1,2,4-triazol-1-yl)-N-(3,5-dichlorobenzyl)acetamide (MR-L2), was microinfused into NAcs bilaterally at FR3 or FR5; in both cohorts, MR-L2 acutely reduced nicotine IVSA. In summary, these studies show that the activity of PDE4B regulates the capacity of NAcs to maintain nicotine IVSA in face of the cost of increasing work. This finding and the results of the PR study indicate that PDE4B affects the motivation to obtain nicotine. These reverse translational studies in rats provide insight into the motivational effects of NAcs PDE4B that advance our understanding of the smoking behaviors mapped in human GWAS.

Sex and heredity are determinants of oral oxycodone self-administration in 36 Inbred Rat Strains: correlations with behavioral tests of anxiety and novelty-seeking.

Most individuals affected in the national epidemic of oxycodone abuse began taking oral oxycodone by prescription. We studied vulnerability to oxycodone intake in a rat model of oral drug self-administration (SA), since pharmacokinetics affect abuse potential. Females (33 inbred strains) and males (26) obtained oxycodone at increasing concentrations in operant sessions (FR5; 1-16-h) followed by extinction and reinstatement. Active spout licks were greater in females than males during 4-h and 16-h sessions (p< 0.001 for all). Across all stages of oxycodone SA, intake/session was greater in females (p<0.001). Both sexes escalated intake during 16-h extended access vs 4-h sessions (p<2e-16). Intake and active licks varied greatly by strain. The heritability (h2) of active licks/4-h at increasing oxycodone dose was larger in males (h2 females: 0.30-0.39 vs. males: 0.41-0.53). Under a progressive ratio schedule, breakpoints differed by strain (p<2e-16) and by sex in some strains (p=0.018). For cue-induced reinstatement, active licks were greater in females than males (p<0.001). Behavior in naive rats was assessed using elevated plus maze (EPM), open field (OF) and novel object interaction. (NOI) tests. We correlated these behaviors with 28 parameters of oxycodone SA. EPM-defining traits were most commonly associated with SA in both sexes, whereas more OF and NOI traits were SA-associated in males. Overall, sex and heredity are major determinants of the motivation to take and seek oxycodone, which escalates during extended access. The correlation of EPM, a measure of anxiety, with multiple SA parameters indicates the influence of pleiotropic genes.

Characterizing the multi-dimensional reaction dynamics of dihalomethanes using XUV-induced Coulomb explosion imaging.

Site-selective probing of iodine 4d orbitals at 13.1 nm was used to characterize the photolysis of CH2I2 and CH2BrI initiated at 202.5 nm. Time-dependent fragment ion momenta were recorded using Coulomb explosion imaging mass spectrometry and used to determine the structural dynamics of the dissociating molecules. Correlations between these fragment momenta, as well as the onset times of electron transfer reactions between them, indicate that each molecule can undergo neutral three-body photolysis. For CH2I2, the structural evolution of the neutral molecule was simultaneously characterized along the C-I and I-C-I coordinates, demonstrating the sensitivity of these measurements to nuclear motion along multiple degrees of freedom.

Inactivation of phosphodiesterase-4B gene in rat nucleus accumbens shell by CRISPR/Cas9 modulates the motivation to chronically self-administer nicotine.

Large scale human genome wide association studies (GWAS) have identified a growing pool of genes associated with cigarette smoking. One of the most prominent, phosphodiesterase-4B (PDE4B), has been associated with multiple smoking phenotypes. Although PDE4B modulates the half-life of neuronal cAMP, its precise role in smoking behaviors is unknown. To address this knowledge gap, we used a reverse translational approach. We inactivated PDE4B in bilateral medial nucleus accumbens shell (NAcs) neurons by injecting AAV containing a specific gRNA in female transgenic Cas9+ Long Evans rats. These rats then were given 23-hour chronic access to nicotine intravenous self-administration (IVSA) under a schedule of increasing fixed ratios (FR). With the increased effort required at FR7, nicotine SA (i.e. active presses and drug infusions) declined significantly in controls, whereas it was maintained in the mutagenized group. A progressive ratio (PR) study also showed significantly greater cumulative nicotine infusions in the mutant group. Hence, we hypothesized that enhanced PDE4B protein activity would reduce nicotine IVSA. A positive allosteric modulator,2-(3-(4-chloro-3-fluorophenyl)-5-ethyl-1H-1,2,4-triazol-1-yl)-N-(3,5-dichlorobenzyl)acetamide (MR-L2), was microinfused into NAcs bilaterally at FR3 or FR5; in both cohorts, MR-L2 acutely reduced nicotine IVSA. In summary, these studies show that the activity of PDE4B regulates the capacity of NAcs to maintain nicotine IVSA in face of the cost of increasing work. This finding and the results of the PR study indicate that PDE4B affects the motivation to obtain nicotine. These reverse translational studies in rats provide insight into the motivational effects of NAcs PDE4B that advance our understanding of the smoking behaviors mapped in human GWAS.

A revamped rat reference genome improves the discovery of genetic diversity in laboratory rats.

The seventh iteration of the reference genome assembly for Rattus norvegicus-mRatBN7.2-corrects numerous misplaced segments and reduces base-level errors by approximately 9-fold and increases contiguity by 290-fold compared to its predecessor. Gene annotations are now more complete, significantly improving the mapping precision of genomic, transcriptomic, and proteomics data sets. We jointly analyzed 163 short-read whole genome sequencing datasets representing 120 laboratory rat strains and substrains using mRatBN7.2. We defined ~20.0 million sequence variations, of which 18.7 thousand are predicted to potentially impact the function of 6,677 genes. We also generated a new rat genetic map from 1,893 heterogeneous stock rats and annotated transcription start sites and alternative polyadenylation sites. The mRatBN7.2 assembly, along with the extensive analysis of genomic variations among rat strains, enhances our understanding of the rat genome, providing researchers with an expanded resource for studies involving rats.

Estimating the abundance of the critically endangered Baltic Proper harbour porpoise (Phocoena phocoena) population using passive acoustic monitoring.

Knowing the abundance of a population is a crucial component to assess its conservation status and develop effective conservation plans. For most cetaceans, abundance estimation is difficult given their cryptic and mobile nature, especially when the population is small and has a transnational distribution. In the Baltic Sea, the number of harbour porpoises (Phocoena phocoena) has collapsed since the mid-20th century and the Baltic Proper harbour porpoise is listed as Critically Endangered by the IUCN and HELCOM; however, its abundance remains unknown. Here, one of the largest ever passive acoustic monitoring studies was carried out by eight Baltic Sea nations to estimate the abundance of the Baltic Proper harbour porpoise for the first time. By logging porpoise echolocation signals at 298 stations during May 2011-April 2013, calibrating the loggers' spatial detection performance at sea, and measuring the click rate of tagged individuals, we estimated an abundance of 71-1105 individuals (95% CI, point estimate 491) during May-October within the population's proposed management border. The small abundance estimate strongly supports that the Baltic Proper harbour porpoise is facing an extremely high risk of extinction, and highlights the need for immediate and efficient conservation actions through international cooperation. It also provides a starting point in monitoring the trend of the population abundance to evaluate the effectiveness of management measures and determine its interactions with the larger neighboring Belt Sea population. Further, we offer evidence that design-based passive acoustic monitoring can generate reliable estimates of the abundance of rare and cryptic animal populations across large spatial scales.

Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime.

Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10-100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH*, PAH+* and PAH2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH2+ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.

Sex and heredity are determinants of drug intake in a novel model of rat oral oxycodone self-administration.

The steady rise in prescription opioids such as oxycodone has led to a virulent epidemic of widespread abuse and deaths in the United States; approximately 80% of affected individuals initiate the habitual use of oxycodone by using prescription oral oxycodone. Given the importance of drug pharmacokinetics in determining abuse potential, we designed an oral operant oxycodone self-administration (SA) procedure in rats to model drug intake by most human users/abusers of oxycodone. Key aspects of the model include limited initial drug intake followed by increasing drug concentrations during extended 4-h sessions on alternating days. Sex and genetic predisposition are major determinants of human opiate abuse. Therefore, we studied females in seven inbred strains (WLI, WMI, LEW, DSS, F344, BN and SHR) and both sexes in three of these strains. All strains increased intake across serially increasing doses (0.025-0.2 mg/ml; p < 0.001): the range of intakes at the final concentration of oxycodone was 0.72 ± 0.17-4.84 ± 1.42 mg/kg (mean ± SEM) - a 6.7-fold difference across strains. In LEW, WLI and WMI strains, oxycodone intake increased significantly across all sessions in both sexes. However, in LEW and WMI male rats but not WLI, daily oxycodone intake was significantly lower across all 4-h sessions than females (p < 0.005). The estimated heritability in oxycodone intake was in the range of 0.21-0.41. In summary, our novel operant oral oxycodone SA model captures the strong abuse potential of oral oxycodone and shows dose, sex and strain-specific drug intake that is significantly dependent on heredity.

Allosteric Modulation of GABAA Receptors in Rat Basolateral Amygdala Blocks Stress-Enhanced Reacquisition of Nicotine Self-Administration.

Stress is a major determinant of relapse to smoked tobacco. In a rat model, repeated stress during abstinence from nicotine self-administration (SA) results in enhanced reacquisition of nicotine SA, which is dependent on the basolateral amygdala (BLA). We postulate that repeated stress during abstinence causes hyperexcitability of the BLA principal output neurons (PNs) due to disinhibition of the PNs from reduced inhibitory regulation by local GABAergic interneurons. To determine if enhanced GABAergic regulation of the BLA PNs can lessen the effects of stress on nicotine intake, positive allosteric modulators (PAMs) of GABAA receptors were infused into the BLA immediately prior to reacquisition of nicotine SA. Three selective PAMs [NS 16085 (binds the benzodiazepine site on α2/α3 GABAA); DCUK-OEt (binds a novel, benzodiazepine site on α1 or α5, ß2 or ß3, γ2 or δ GABAA); DS2 (binds exclusively to δ GABAA] with varied GABAA subunit specificities abolished the stress-induced amplification of nicotine taking during reacquisition. These studies indicate that highly selective PAMS targeting α3 or δ subunit-containing GABAA in the BLA may be effective in ameliorating the stress-induced relapse to smoked tobacco during abstinence from cigarettes.

High-pressure developments for resonant X-ray scattering experiments at I16.

An experimental setup to perform high-pressure resonant X-ray scattering (RXS) experiments at low temperature on I16 at Diamond Light Source is presented. The setup consists of a membrane-driven diamond anvil cell, a panoramic dome and an optical system that allows pressure to be measured in situ using the ruby fluorescence method. The membrane cell, inspired by the Merrill-Bassett design, presents an asymmetric layout in order to operate in a back-scattering geometry, with a panoramic aperture of 100° in the top and a bottom half dedicated to the regulation and measurement of pressure. It is specially designed to be mounted on the cold finger of a 4 K closed-cycle cryostat and actuated at low-temperature by pumping helium into the gas membrane. The main parts of the body are machined from a CuBe alloy (BERYLCO 25) and, when assembled, it presents an approximate height of 20-21 mm and fits into a 57 mm diameter. This system allows different materials to be probed using RXS in a range of temperatures between 30 and 300 K and has been tested up to 20 GPa using anvils with a culet diameter of 500 µm under quasi-cryogenic conditions. Detailed descriptions of different parts of the setup, operation and the developed methodology are provided here, along with some preliminary experimental results.

Basolateral amygdala, nicotinic cholinergic receptors, and nicotine: Pharmacological effects and addiction in animal models and humans.

The amygdala is involved in processing incoming information about rewarding stimuli and emotions that denote danger such as anxiety and fear. Bi-directional neural connections between basolateral amygdala (BLA) and brain regions such as nucleus accumbens, prefrontal cortex, hippocampus, and hindbrain regions regulate motivation, cognition, and responses to stress. Altered local regulation of BLA excitability is pivotal to the behavioral disturbances characteristic of posttraumatic stress disorder, and relapse to drug use induced by stress. Herein, we review the physiological regulation of BLA by cholinergic inputs, emphasizing the role of BLA nicotinic receptors. We review BLA-dependent effects of nicotine on cognition, motivated behaviors, and emotional states, including memory, taking and seeking drugs, and anxiety and fear in humans and animal models. The alterations in BLA activity observed in animal studies inform human behavioral and brain imaging research by enabling a more exact understanding of altered BLA function. Converging evidence indicates that cholinergic signaling from basal forebrain projections to local nicotinic receptors is an important physiological regulator of BLA and that nicotine alters BLA function. In essence, BLA is necessary for behavioral responses to stimuli that evoke anxiety and fear; reinstatement of cue-induced drug seeking; responding to second-order cues conditioned to abused drugs; reacquisition of amplified nicotine self-administration due to chronic stress during abstinence; and to promote responding for natural reward.

Neurogenetic determinants and mechanisms of addiction to nicotine and smoked tobacco.

The single most preventable cause of disease, disability, and death in the United States is tobacco use. Decades of study show that the risk of becoming addicted to smoked cigarettes varies greatly amongst individuals and is heritable, yet environmental factors are also important contributors. In this review, we consider a wide range of methodologies and key published reports that have defined the inheritance of different stages of nicotine-dependent smoking behavior, including preference, initiation, regular use, withdrawal and dependence as well as cessation and relapse. Major findings from both animal and human studies are discussed. Current findings converge primarily on the role of nicotinic cholinergic receptor subunits, although other neurotransmitter systems as well as nicotine metabolism enzymes are implicated. Various stages of nicotine addiction may share common genetic mechanisms, yet several lines of evidence indicate that each stage also has its own unique genetic determinants. Studies on the heritability of smoking initiation demonstrate substantial evidence for gene-environment interaction, although the precise molecular genetic mechanism(s) remains unknown. Considering the relatively few genes identified so far and the small to modest fraction of the variance in risk for a particular smoking phenotype (e.g., smoking initiation in late adolescence) attributable to these genes, a large gap remains to be filled in order to account for the heritability of key phenotypes involved in each stage of addiction to smoked tobacco. Looking forward, new research strategies involving both human and animal studies will produce the fundamental genetic insights that are the foundation for the precision medical treatment of individuals addicted to smoked tobacco.

Three-dimensional imaging of carbonyl sulfide and ethyl iodide photodissociation using the pixel imaging mass spectrometry camera.

The Pixel Imaging Mass Spectrometry (PImMS) camera is used in proof-of-principle three-dimensional imaging experiments on the photodissociation of carbonyl sulfide and ethyl iodide at wavelengths around 230 nm and 245 nm, respectively. Coupling the PImMS camera with DC-sliced velocity-map imaging allows the complete three-dimensional Newton sphere of photofragment ions to be recorded on each laser pump-probe cycle with a timing precision of 12.5 ns, yielding velocity resolutions along the time-of-flight axis of around 6%-9% in the applications presented.

Basolateral amygdala and ventral hippocampus in stress-induced amplification of nicotine self-administration during reacquisition in rat.

RATIONALE: Cigarette smoking remains the leading cause of preventable morbidity and mortality in the USA, although only 3-5 % of quitters are successful for 6-12 months. Stress during abstinence increases the likelihood of relapse to smoking. We recently reported that repeated stress during abstinence from operant nicotine self-administration (SA) amplifies the reacquisition of nicotine SA and affects the diurnal intake of nicotine in rats. Herein, we sought to identify brain regions critical for the expression of stress-enhanced nicotine SA during reacquisition. METHODS: Rats acquired nicotine SA (FR5) with virtually unlimited drug access (23 h/day). During abstinence (8 day), 30 min of restraint stress was applied on days 1, 3, 5, and 7. Beginning day 8, nicotine SA was reacquired over 5 days, and basolateral amygdala (BLA) was inactivated bilaterally or disconnected from nucleus accumbens core (NAcc). Similarly, ventral hippocampus (vHP) was inactivated or disconnected from BLA. RESULTS: Bilateral inactivation (muscimol + baclofen) of BLA or disconnection from NAcc abolished the stress-enhanced reacquisition of nicotine SA without affecting basal levels of nicotine SA. Similarly, bilateral inactivation of vHP or disconnection of vHP and BLA also abolished stress-enhanced reacquisition of nicotine SA. CONCLUSION: BLA, vHP, and functional interactions between BLA-NAcc and vHP-BLA are required for expression of stress-enhanced nicotine SA during reacquisition. However, without stress, these functional interactions are not necessary for reexpression of nicotine SA during reacquisition. Therefore, BLA, vHP, and these regional interactions specifically mediate the effects of repeated stress on the reacquisition of nicotine SA behavior.

Efficacy of a basal bolus insulin protocol to treat prednisolone-induced hyperglycaemia in hospitalised patients.

BACKGROUND/AIM: Few studies have specifically investigated treatment of prednisolone-induced hyperglycaemia. AIM: To determine if a basal bolus insulin (BBI) protocol for inpatient hyperglycaemia is effective in patients prescribed acute prednisolone for an inflammatory disease. METHODS: In a cross-sectional study, 66 patients with type 2 diabetes admitted to a general medical ward and treated with BBI for up to 5 days were studied. Twenty-four patients were taking prednisolone ≥10 mg/day to treat an acute inflammatory disease. The remaining 42 patients were a control group. The primary outcome was mean daily blood glucose level. RESULTS: There were no significant differences in glycosylated haemoglobin (8.1 ± 1.0 vs 8.1 ± 1.6%, P = 0.88), age (77 ± 11 vs 75 ± 14 years, P = 0.57), male sex (63 vs 60%, P = 0.81) or body mass index (30.0 ± 5.3 vs 30.2 ± 11.5 kg/m(2) , P = 0.90) between patients taking prednisolone and controls. Mean daily glucose concentration was higher in patients taking prednisolone than in controls (12.2 ± 0.3 vs 10.0 ± 0.1 mmol/L, P < 0.001). Blood glucose level was higher in patients on prednisolone at 1700 h (14.6 ± 0.6 vs 10.3 ± 0.3 mmol/L, P < 0.001) and 2100 h (14.5 ± 0.6 vs 10.5 ± 0.3 mmol/L, P < 0.001), with no significant differences at 0700 h and 1200 h. These findings occurred despite patients taking prednisolone receiving a higher daily insulin dose than controls (0.67-0.70 vs 0.61-0.65 U/kg, P = 0.001) because of higher doses of ultra-rapid-acting insulin at 1200 h and 1700 h. CONCLUSIONS: Hospitalised patients taking prednisolone had substantial afternoon and evening hyperglycaemia despite receiving BBI via a protocol for inpatient hyperglycaemia. Specific insulin regimens for prednisolone-induced hyperglycaemia are needed that recommend more insulin during this time period.

Quantification and genotyping of lipoprotein lipase in patients with diabetic lipaemia.

AIMS: To determine if diabetic lipaemia is caused by loss of function mutations in the lipoprotein lipase gene, LPL. METHODS: We conducted a case-control study over 2 years in two tertiary care hospitals in South Australia. Six patients with a history of diabetic lipaemia and 12 control subjects, with previous diabetic ketoacidosis and peak triglyceride concentrations < 2.4 mmol/l were included. Participants were well at the time of study investigations. RESULTS: Only one patient with lipaemia had a loss of function mutation in LPL and no functional mutations in APOC2 or GPIHBP1 were identified. The mean lipoprotein lipase concentration was lower in patients with diabetic lipaemia than in control subjects (306 vs. 484 µg/l, P = 0.04). The mean fasting C-peptide concentration was higher in patients with diabetic lipaemia than in control subjects (771 vs. 50 pmol/l; P = 0.001). CONCLUSIONS: Lipoprotein lipase deficiency in patients with a history of diabetic lipaemia was predominantly quantitative, rather than secondary to mutations in LPL, APOC2 or GPIHBP1. The majority of patients with severe hypertriglyceridaemia in diabetic ketoacidosis may have ketosis-prone Type 2, rather than Type 1, diabetes.

Amplified reacquisition of nicotine self-administration in rats by repeated stress during abstinence.

RATIONALE: Quitting smoking is often very challenging, leading to frequent relapse. Exposure to acute and chronic stress during abstinence increases the likelihood of relapse to smoking. In rodents, stress acutely reinstates nicotine seeking after extinction of nicotine self-administration (SA). However, whether reacquisition of nicotine taking is amplified by chronic stress during abstinence from nicotine SA has not been determined in animals. OBJECTIVES: We sought to determine effects of repeated restraint stress during abstinence on reacquisition of nicotine SA. METHODS: Rats acquired nicotine SA (23 h/day) under a fixed-ratio (FR) 5 schedule of reinforcement, which was followed by an abstinence phase. Restraint (0, 2, and 4 times) was administered during abstinence. Animals reacquired nicotine SA, first under a progressive ratio (PR) schedule, beginning immediately after the final stress, followed by an FR5 schedule. In another experiment, reacquisition (FR5) began 24 h after the final stress. No PR testing was conducted. RESULTS: Four restraint stress exposures during abstinence, but not only two, enhanced reacquisition of nicotine SA by increasing nicotine injections under a PR schedule beginning immediately after the final stress (p < 0.05) followed by increasing nicotine intake under an FR5 schedule (p < 0.05). This was observed even when the final stress and reacquisition trial were separated by 24 h. Moreover, repeated stress-induced nicotine taking during the behaviorally inactive phase (i.e., lights on) of the 24-h diurnal cycle. CONCLUSIONS: Chronic (i.e., repeated) stress during abstinence promotes reacquisition of nicotine SA and affects diurnal pattern of nicotine intake.

Protection genes in nucleus accumbens shell affect vulnerability to nicotine self-administration across isogenic strains of adolescent rat.

Classical genetic studies show the heritability of cigarette smoking is 0.4-0.6, and that multiple genes confer susceptibility and resistance to smoking. Despite recent advances in identifying genes associated with smoking behaviors, the major source of this heritability and its impact on susceptibility and resistance are largely unknown. Operant self-administration (SA) of intravenous nicotine is an established model for smoking behavior. We recently confirmed that genetic factors exert strong control over nicotine intake in isogenic rat strains. Because the processing of afferent dopaminergic signals by nucleus accumbens shell (AcbS) is critical for acquisition and maintenance of motivated behaviors reinforced by nicotine, we hypothesized that differential basal gene expression in AcbS accounts for much of the strain-to-strain variation in nicotine SA. We therefore sequenced the transcriptome of AcbS samples obtained by laser capture microdissection from 10 isogenic adolescent rat strains and compared all RNA transcript levels with behavior. Weighted gene co-expression network analysis, a systems biology method, found 12 modules (i.e., unique sets of genes that covary across all samples) that correlated (p<0.05) with amount of self-administered nicotine; 9 of 12 correlated negatively, implying a protective role. PCR confirmed selected genes from these modules. Chilibot, a literature mining tool, identified 15 genes within 1 module that were nominally associated with cigarette smoking, thereby providing strong support for the analytical approach. This is the first report demonstrating that nicotine intake by adolescent rodents is associated with the expression of specific genes in AcbS of the mesolimbic system, which controls motivated behaviors. These findings provide new insights into genetic mechanisms that predispose or protect against tobacco addiction.