Genetic selection for nicotine activity in mice correlates with conditioned place preference

Variability in nicotine conditioned place preference and stress-induced reinstatement in mice: Effects of sex, initial chamber preference, and guanfacine

Relapse to smoking occurs at higher rates in women compared with men, especially when triggered by stress. Studies suggest that sex-specific interactions between nicotine reward and stress contribute to these sex differences. Accordingly, novel treatment options targeting stress pathways, such as guanfacine, an α2-adrenergic receptor agonist, may provide sex-sensitive therapeutic effects. Preclinical studies are critical for elucidating neurobiological mechanisms of stress-induced relapse and potential therapies, but rodent models of nicotine addiction are often hindered by large behavioral variability. In this study, we used nicotine conditioned place preference to investigate stress-induced reinstatement of nicotine preference in male and female mice, and the effects of guanfacine on this behavior. Our results showed that overall, nicotine induced significant place preference acquisition and swim stress-induced reinstatement in both male and female mice, but with different nicotine dose-response patterns. In addition, we explored the variability in nicotine-dependent behaviors with median split analyses and found that initial chamber preference in each sex differentially accounted for variability in stress-induced reinstatement. In groups that showed significant stress-induced reinstatement, pretreatment with guanfacine attenuated this behavior. Finally, we evaluated neuronal activation by Arc immunoreactivity in the infralimbic cortex, prelimbic cortex, anterior insula, basolateral amygdala, lateral central amygdala and nucleus accumbens core and shell. Guanfacine induced sex-dependent changes in Arc immunoreactivity in the infralimbic cortex and anterior insula. This study demonstrates sex-dependent relationships between initial chamber preference and stress-induced reinstatement of nicotine conditioned place preference, and the effects of guanfacine on both behavior and neurobiological mechanisms.

Natural genetic variability of the neuronal nicotinic acetylcholine receptor subunit genes in mice: Consequences and confounds

Recent human genetic studies have identified genetic variants in multiple nicotinic acetylcholine receptor (nAChR) subunit genes that are associated with risk for nicotine dependence and other smoking-related measures. Genetic variability also exists in the nAChR subunit genes in mice. Most studies on mouse nAChR subunit gene variability to date have focused on Chrna4, the gene that encodes the α4 nAChR subunit and Chrna7, the gene that encodes the α7 nAChR subunit. However, genetic variability exists for all nAChR genes in mice. In this review, we will describe what is known about nAChR subunit gene polymorphisms in mice and how it relates to variability in nAChR expression and function in brain. The relationship between nAChR genetic variability in mice and the effects of nicotine on several behavioral and physiological measures also will be discussed. In addition, an overview of the contribution of other genetic variation to nicotine sensitivity in mice will be provided. Finally, the potential for natural genetic variability to confound and/or modify the results of studies that utilize genetically engineered mice will be considered. As an example of the ability of a natural genetic variant to modify the effect of an engineered mutation, data will be presented that demonstrate that the effect of Chrna5 deletion on oral nicotine intake is dependent upon naturally occurring variant alleles of Chrna4. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Initial responses to the first dose of nicotine in novel smokers: the role of exposure to environmental smoking and genetic predisposition

BACKGROUND

Sensitivity to initial smoking constitutes an early predictor of the risk of dependence. We investigated the role of exposure to smoking (by parents, siblings, and peers) and reward-related candidate gene polymorphisms (OPRM1 A118G, DRD2 TaqlA and DRD4 bp VNTR) in adolescents' responses to initial smoking.

METHODS

We used cross-sectional survey data and saliva samples from 171 Dutch students who had never inhaled on a cigarette (mean age: 13.9 years). The outcome measure was adolescents' self-reported responses to initial smoking.

RESULTS

Exposure to peer smoking was associated with increased liking (OR = 1.74, CI = 1.13-2.70) and more pleasant sensations (β = .21, p = .01). Exposure to maternal smoking was associated with less unpleasant sensations (β = -.20, p = .01). Adolescents carrying the G-variant of the OPRM1 A118G polymorphism were more likely to report liking (OR = 2.50, CI = 1.09-5.73) and adolescents homozygous for the C-variant of the DRD2 TaqlA polymorphism reported less unpleasant sensations (β = .18, p = .04).

CONCLUSION

Although preliminary, these findings suggest that exposure to environmental smoking and polymorphisms in the OPRM1 and DRD2 gene may affect initial sensitivity to nicotine, an early phenotype of the risk of dependence. In the future, collaborative efforts to combine data from multiple studies in meta-analyses are needed to improve accuracy of estimated effects in genetic studies.

Nine generations of selection for high and low nicotine intake in outbred Sprague-Dawley rats

Previous animal studies have revealed significant involvement of genetics in nicotine intake; however, the extent of the genetic contribution to this behavior has not been well addressed. We report the first study of nine generations of selection for high and low voluntary nicotine intake in outbred Sprague-Dawley rats. Bidirectional mass selection resulted in progressively greater nicotine consumption in the high nicotine-preferring line but no decrease in nicotine intake in the low nicotine-preferring line across generations. Our estimated realized heritability for high voluntary nicotine intake is 0.26 vs close to zero for low voluntary nicotine intake. In contrast, we found no differences between the lines across generations for saccharine intake. These selected lines may provide useful animal models for identifying susceptibility and resistance genes and variants for controlling voluntary nicotine intake in rodents, although we recognize that more generations of selection of these two lines and independent replication of our selection for high and low nicotine-preferring lines are needed.

Mouse models for studying genetic influences on factors determining smoking cessation success in humans

Humans differ in their ability to quit using addictive substances, including nicotine, the major psychoactive ingredient in tobacco. For tobacco smoking, a substantial body of evidence, largely derived from twin studies, indicates that approximately half of these individual differences in ability to quit are heritable genetic influences that likely overlap with those for other addictive substances. Both twin and molecular genetic studies support overlapping influences on nicotine addiction vulnerability and smoking cessation success, although there is little formal analysis of the twin data that support this important point. None of the current datasets provides clarity concerning which heritable factors might provide robust dimensions around which individuals differ in ability to quit smoking. One approach to this problem is to test mice with genetic variations in genes that contain human variants that alter quit success. This review considers which features of quit success should be included in a comprehensive approach to elucidate the genetics of quit success, and how those features may be modeled in mice.

Empirical support for a multi-dimensional model of sensations experienced by youth during their initial smoking episodes

AIMS

To examine the dimensionality of sensations experienced during initial tobacco smoking.

DESIGN

Cross-sectional survey.

SETTING

Thirteen secondary schools located in British Columbia, Canada.

PARTICIPANTS

Data from 1187 adolescents who responded 'yes' to the question: 'Have you ever tried cigarette smoking, even one or two puffs?'.

MEASUREMENTS

Participants answered questions about their demographic characteristics, tobacco smoking history and sensations experienced during their initial smoking episodes.

FINDINGS

The sensations appear to represent the following three separate but modestly correlated dimensions: a pleasant dimension defined by feeling good and relaxed; an unpleasant dimension defined by coughing, feeling sick and nervous; and a 'buzz' dimension defined by feeling high and dizzy. The three factors made statistically significant contributions to the prediction of transition to regular smoking (defined as having smoked at least 100 cigarettes in one's life-time) after adjusting for age, sex and age at first puff.

CONCLUSIONS

The results suggest that three relatively distinct physiological systems appear to explain the relationship between initial smoking sensations and probability of becoming a regular smoker. Researchers examining sensations experienced during initial tobacco smoking episodes should consider using a three-dimensional profile of symptoms composed of pleasant, unpleasant and buzz dimensions.

Chrna4 A529 knock-in mice exhibit altered nicotine sensitivity

The reasons why people smoke are varied, but research has shown that genetic influences on various aspects of nicotine addiction are a major factor. There also is a strong genetic influence on measures of nicotine sensitivity in mice. Despite the established contribution of genetics to nicotine sensitivity in mice and humans, no naturally occurring genetic variation has been identified that demonstrably alters sensitivity to nicotine in either species. However, one genetic variant has been implicated in altering nicotine sensitivity in mice is a T529A polymorphism in Chrna4, the gene that encodes the nicotinic receptor (nAChR) alpha4 subunit. The Chrna4 T529A polymorphism leads to a threonine to alanine substitution at position 529 of the alpha4 subunit. To more definitively address whether the Chrna4 T529A polymorphism does, in fact, influence sensitivity to nicotine, knock-in mice were generated in which the threonine codon at position 529 was mutated to an alanine codon. Compared with Chrna4 T529 littermate controls, the Chrna4 A529 knock-in mice exhibited greater sensitivity to the hypothermic effects of nicotine, reduced oral nicotine consumption and did not develop conditioned place preference to nicotine. The Chrna4 A529 knock-in mice also differed from T529 littermates for two parameters of acetylcholine-stimulated Rb+ efflux in midbrain: maximal efflux and the percentage of alpha4beta2* receptors with high sensitivity to activation by agonists. Results indicate that the polymorphism affects the function of midbrain alpha4beta2* nAChRs and contributes to individual differences in several behavioral and physiological responses to nicotine thought to be modulated by midbrain alpha4beta2* nAChRs.

Variability in initial nicotine sensitivity due to sex, history of other drug use, and parental smoking

Initial sensitivity to nicotine's effects during early exposure to tobacco may relate to dependence vulnerability. We examined the association of initial nicotine sensitivity with individual difference factors of sex, other drug use history (i.e. cross-tolerance or cross-sensitization), and parental smoking status in young adult nonsmokers (N=131). Participants engaged in 4 sessions, the first 3 to assess the dose-response effects of nasal spray nicotine (0, 5, 10 microg/kg) on rewarding, mood, physiological, sensory processing, and performance effects, and the fourth to assess nicotine reinforcement using a choice procedure. Men had greater initial sensitivity than women to some self-reported effects of nicotine related to reward and incentive salience and to impairment in sensory processing, but men and women did not differ on most other effects. Prior marijuana use was associated with greater nicotine reward, nicotine reinforcement was greater in men versus women among those with prior marijuana use, and having parents who smoked was related to increased incentive salience. However, history of other drug use and parental smoking were not otherwise associated with initial nicotine sensitivity. These findings warrant replication with other methods of nicotine administration, especially cigarette smoking, and in more diverse samples of subjects naïve to nicotine. Yet, they suggest that sex differences in initial sensitivity to nicotine reward occur before the onset of dependence. They also suggest that parental smoking may not increase risk of nicotine dependence in offspring by altering initial nicotine sensitivity, and that cross-tolerance between other drugs and nicotine may not be robust in humans.

Gene and gene by sex associations with initial sensitivity to nicotine in nonsmokers

Genetic variation may influence initial sensitivity to nicotine (i.e. during early tobacco exposure), perhaps helping to explain differential vulnerability to nicotine dependence. This study explored associations of functional candidate gene polymorphisms with initial sensitivity to nicotine in 101 young adult nonsmokers of European ancestry. Nicotine (0, 5, 10 microg/kg) was administered through nasal spray followed by mood, nicotine reward (e.g. 'liking') and perception (e.g. 'feel effects') measures, physiological responses, sensory processing (prepulse inhibition of startle), and performance tasks. Nicotine reinforcement was assessed in a separate session using a nicotine versus placebo spray choice procedure. For the dopamine D4 receptor [DRD4 variable number of tandem repeats (VNTR)], presence of the 7-repeat allele was associated with greater aversive responses to nicotine (decreases in 'vigor', positive affect, and rapid information processing; increased cortisol) and reduced nicotine choice. Individuals with at least one DRD4 7-repeat allele also reported increased 'feel effects' and greater startle response, but in men only. Other genetic associations were also observed in men but not women, such as greater 'feel effects' and anger, and reduced fatigue, in the dopamine D2 receptor (DRD2 C957T single nucleotide polymorphism) TT versus CT or CC genotypes. Very few or no significant associations were seen for the DRD2/ANKK1 TaqIA polymorphism, the serotonin transporter promoter VNTR or 5HTTLPR (SLC6A4), the dopamine transporter 3' VNTR (SLC6A3), and the mu opioid receptor A118G single nucleotide polymorphism (mu opioid receptor polymorphism 1). Although these results are preliminary, this study is the first to suggest that genetic polymorphisms related to function in the dopamine D4, and perhaps D2, receptor may modulate initial sensitivity to nicotine before the onset of dependence and may do so differentially between men and women.

Initial nicotine sensitivity in humans as a function of impulsivity

RATIONALE

Impulsivity is related to greater risk of nicotine dependence, perhaps by enhancing sensitivity to nicotine's reinforcing and rewarding effects during initial smoking experiences.

OBJECTIVE

We examined the influence of impulsivity characteristics on acute sensitivity to nicotine reward, reinforcement, and other effects in 131 young adult nonsmokers.

MATERIALS AND METHODS

Participants engaged in four sessions: the first three to assess dose-response effects of nasal spray nicotine (0, 5, 10 microg/kg) on reward, as well as mood, physiological, and performance effects, and the fourth to assess nicotine reinforcement using a choice procedure. Five impulsivity factors, derived from factor analysis of self-report (e.g., Barratt Impulsivity Scale, Sensation-Seeking Scale, Novelty seeking) and computer (stop-go, delay discounting, probability discounting) measures of impulsivity, were labeled "novelty seeking", "response disinhibition", "extraversion", "inhibition", and "probability/delay discounting".

RESULTS

The associations of novelty seeking with nicotine reinforcement and reward tended to move in opposite directions by sex, generally being directly related in men but inversely or unrelated in women. Similarly, response disinhibition was associated with reward and some mood responses to nicotine that differed by sex. Extraversion was inversely associated with nicotine reinforcement. Characteristics loading on to the other impulsivity factors had little association with nicotine sensitivity.

CONCLUSIONS

These results are preliminary, but they suggest that characteristics broadly related to impulsivity, especially novelty seeking and response disinhibition, are associated with initial sensitivity to some effects of acute nicotine, including reinforcement and reward, and may do so differentially between men and women.

Chromosomal loci that influence oral nicotine consumption in C57BL/6J x C3H/HeJ F2 intercross mice

Several studies have demonstrated that there are genetic influences on free-choice oral nicotine consumption in mice. In order to establish the genetic architecture that underlies individual differences in free-choice nicotine consumption, quantitative trait loci (QTL) mapping was used to identify chromosomal regions that influence free-choice nicotine consumption in male and female F(2) mice derived from a cross between C57BL/6J and C3H/HeJ mice. These two mouse strains were chosen not only because they differ significantly for oral nicotine consumption, but also because they are at or near phenotypic extremes for all measures of nicotine sensitivity that have been reported. A four-bottle choice paradigm was used to assess nicotine consumption over an 8-day period. The four bottles contained water or water supplemented with 25, 50 or 100 microg/ml of nicotine base. Using micrograms of nicotine consumed per milliliter of total fluid consumed per day as the nicotine consumption phenotype, four significant QTL were identified. The QTL with the largest LOD score was located on distal chromosome 1 (peak LOD score = 15.7). Other chromosomes with significant QTL include central chromosome 4 (peak LOD score = 4.1), proximal chromosome 7 (peak LOD score = 6.1) and distal chromosome 15 (peak LOD score = 4.8). These four QTL appear to be responsible for up to 62% of the phenotypic variance in oral nicotine consumption.

Genetic contributions to addiction

Even the most extreme environmentalists along the nature-nurture continuum in psychology now acknowledge that genes often contribute to individual differences in behavior. Behavioral traits are complex, reflecting the aggregate effects of many genes. These genetic effects are interactive, inter se and with the environments in which they are expressed. Human studies of addictive behaviors have clearly implicated both environmental and genetic influences. This review selects drug dependence as a paradigmatic addiction, and further, concentrates on the extensive literature with genetic animal models. Both traditional studies with inbred strains and selected lines and studies exploiting the new molecularly based technologies of the genomics era are discussed. Future directions for further contribution of animal models studies to our understanding of the brain dysregulations characteristic of addictions are identified.

Discriminative stimulus (DS) properties of nicotine in the C57BL/6 mouse

Previous research conducted in this and other laboratories has examined the role of genetic factors in determining sensitivity to (-)-nicotine in a variety of behavioral and physiological measures in the rat. More recent research further indicates that genetic factors can also influence the level of sensitivity to (-)-nicotine when serving as a discriminative stimulus (DS) in different rat strains. However, there has been little work examining the influence of genotype on the discriminative stimulus (DS) properties of (-)-nicotine in mice, a species that has played a major role in understanding the relationship between genetics and (-)-nicotine pharmacological effects. To further our understanding of the role of genetics and the ability of (-)-nicotine to exert DS control of behavior in the mouse, a group of C57BL/6 mice was trained to discriminate 0.4 mg/kg (-)-nicotine from saline using a two-lever operant procedure. (-)-Nicotine's discriminative stimulus in C57BL/6 mice appears to be similar to that generated in the rat. Results from behavioral tests with other drugs indicated that d-amphetamine exhibited a partial generalization, while (+)-nicotine fully generalized with nicotine. Tests of antagonism with mecamylamine and scopolamine further showed the cholinergic specificity of the (-)-nicotine DS in the mouse; mecamylamine but not scopolamine completely antagonized the (-)-nicotine DS. This work lays the groundwork for future comparisons of different mouse strain's sensitivities to (-)-nicotine's discriminative stimulus as well as using this behavioral model to search for new nicotinic receptor agonists and antagonists.

Measuring reward with the conditioned place preference paradigm: a comprehensive review of drug effects, recent progress and new issues

This review gives an overview of recent findings and developments in research on brain mechanisms of reward and reinforcement from studies using the place preference conditioning paradigm, with emphasis on those studies that have been published within the last decade. Methodological issues of the paradigm (such as design of the conditioning apparatus, biased vs unbiased conditioning, state dependency effects) are discussed. Results from studies using systemic and local (intracranial) drug administration, natural reinforcers, and non-drug treatments and from studies examining the effects of lesions are presented. Papers reporting on conditioned place aversion (CPA) experiments are also included. A special emphasis is put on the issue of tolerance and sensitization to the rewarding properties of drugs. Transmitter systems that have been investigated with respect to their involvement in brain reward mechanisms include dopamine, opioids, acetylcholine, GABA, serotonin, glutamate, substance P, and cholecystokinin, the motivational significance of which has been examined either directly, by using respective agonist or antagonist drugs, or indirectly, by studying the effects of these drugs on the reward induced by other drugs. For a number of these transmitters, detailed studies have been conducted to delineate the receptor subtype(s) responsible for the mediation of the observed drug effects, particularly in the case of dopamine, the opioids, serotonin and glutamate. Brain sites that have been implicated in the mediation of drug-induced place conditioning include the 'traditional' brain reward sites, ventral tegmental area and nucleus accumbens, but the medial prefrontal cortex, ventral pallidum, amygdala and the pedunculopontine tegmental nucleus have also been shown to play important roles in the mediation of place conditioning induced by drugs or natural reinforcers. Thus, although the paradigm has also been criticized because of some inherent methodological problems, it is clear that during the past decade place preference conditioning has become a valuable and firmly established and very widely used tool in behavioural pharmacology and addiction research.

Continued trends in the conditioned place preference literature from 1992 to 1996, inclusive, with a cross-indexed bibliography

In light of the overwhelming response to the previous publication in Neuroscience and Biobehavioral Reviews (1993, 17, 21-41) regarding trends in place conditioning (either preference or aversion), the present work constitutes a five-year follow-up to review the empirical research in this behavioral paradigm from 1992 to 1996, inclusively. The behavioral technique has grown as indicated by the number of publications over the last five years which equals those authored over the 35 years covered by our last survey. The previous work used descriptive statistics to explore topical issues, whereas the present work discusses trends since that time and hopes to provide an exhaustive bibliography of the CPP literature, including articles, published abstracts, book chapters and reviews, as well as providing a cross-index of identified key words/drugs tested.