Helen M. Kamens

Sex differences in voluntary oral nicotine consumption by adolescent mice: a dose-response experiment.

Recent studies with adolescent rodents offer valuable information regarding the neurochemical and behavioral effects of adolescent nicotine exposure. One hundred twenty-one male and 125 female adolescent (35 days of age) C57BL/6J mice were tested for voluntary nicotine consumption by providing 24-h access to both saccharin-only (SAC) and one of six nicotine-containing solutions [10, 25, 50, 75, 100, 200 ug (-)-freebase nicotine/ml in 2% SAC] in the home cage for 7 days. Although males and females drank similar volumes (ml) of nicotine, the female mice consumed more nicotine adjusted for body weight (mg/kg) and as a percentage of total fluid intake than did the male mice. In contrast, there was no sex difference in overall serum cotinine levels (adjusted for liver weight). For all mice, nicotine consumption and serum cotinine levels increased in a dose-dependent manner, and the volume of nicotine intake (ml), percent nicotine intake, and nicotine dosage (mg/kg) on the last day of the experiment were positively correlated with cotinine levels. Cotinine levels were inversely related to body weight only for females. Sex differences in nicotine consumption, but not in cotinine levels, suggest sex differences in pharmacokinetic processes that may contribute to oral nicotine consumption behavior during periadolescence.

Gene expression differences in mice divergently selected for methamphetamine sensitivity

AbstractIn an effort to identify genes that may be important for drug-abuse liability, we mapped behavioral quantitative trait loci (bQTL) for sensitivity to the locomotor stimulant effect of methamphetamine (MA) using two mouse lines that were selectively bred for high MA-induced activity (HMACT) or low MA-induced activity (LMACT). We then examined gene expression differences between these lines in the nucleus accumbens, using 20 U74Av2 Affymetrix microarrays and quantitative polymerase chain reaction (qPCR). Expression differences were detected for several genes, including Casein Kinase 1 Epsilon (Csnkle), glutamate receptor, ionotropic, AMPA1 (GluR1), GABA B1 receptor (Gabbr1), and dopamine- and cAMP-regulated phosphoprotein of 32 kDa (Darpp-32). We used the www.WebQTL.org database to identify QTL that regulate the expression of the genes identified by the microarrays (expression QTL; eQTL). This approach identified an eQTL for Csnkle on Chromosome 15 (LOD=3.8) that comapped with a bQTL for the MA stimulation phenotype (LOD=4.5), suggesting that a single allele may cause both traits. The chromosomal region containing this QTL has previously been associated with sensitivity to the stimulant effects of cocaine. These results suggest that selection was associated with (and likely caused) altered gene expression that is partially attributable to different frequencies of gene expression polymorphisms. Combining classical genetics with analysis of whole-genome gene expression and bioinformatic resources provides a powerful method for provisionally identifying genes that influence complex traits. The identified genes provide excellent candidates for future hypothesis-driven studies, translational genetic studies, and pharmacological interventions.

Sensitivity to psychostimulants in mice bred for high and low stimulation to methamphetamine

Methamphetamine (MA) and cocaine induce behavioral effects primarily through modulation of dopamine neurotransmission. However, the genetic regulation of sensitivity to these two drugs may be similar or disparate. Using selective breeding, lines of mice were produced with extreme sensitivity (high MA activation; HMACT) and insensitivity (low MA activation; LMACT) to the locomotor stimulant effects of acute MA treatment. Studies were performed to determine whether there is pleiotropic genetic influence on sensitivity to the locomotor stimulant effect of MA and to other MA‐ and cocaine‐related behaviors. The HMACT line exhibited more locomotor stimulation in response to several doses of MA and cocaine, compared to the LMACT line. Both lines exhibited locomotor sensitization to 2 mg/kg of MA and 10 mg/kg of cocaine; the magnitude of sensitization was similar in the two lines. However, the lines differed in the magnitude of sensitization to a 1 mg/kg dose of MA, a dose that did not produce a ceiling effect that may confound interpretation of studies using higher doses. The LMACT line consumed more MA and cocaine in a two‐bottle choice drinking paradigm; the lines consumed similar amounts of saccharin and quinine, although the HMACT line exhibited slightly elevated preference for a low concentration of saccharin. These results suggest that some genes that influence sensitivity to the acute locomotor stimulant effect of MA have a pleiotropic influence on the magnitude of behavioral sensitization to MA and sensitivity to the stimulant effects of cocaine. Further, extreme sensitivity to MA may protect against MA and cocaine self‐administration.

Effects of galanin on monoaminergic systems and HPA axis: Potential mechanisms underlying the effects of galanin on addiction- and stress-related behaviors

Like a number of neuropeptides, galanin can alter neural activity in brain areas that are important for both stress-related behaviors and responses to drugs of abuse. Accordingly, drugs that target galanin receptors can alter behavioral responses to drugs of abuse and can modulate stress-related behaviors. Stress and drug-related behaviors are interrelated: stress can promote drug-seeking, and drug exposure and withdrawal can increase activity in brain circuits involved in the stress response. We review here what is known about the ability of galanin and galanin receptors to alter neuronal activity, and we discuss potential mechanisms that may underlie the effects of galanin on behaviors involved in responses to stress and addictive drugs. Understanding the mechanisms underlying galanins effects on neuronal function in brain regions related to stress and addiction may be useful in developing novel therapeutics for the treatment of stress- and addiction-related disorders.

A role for neuronal nicotinic acetylcholine receptors in ethanol-induced stimulation, but not cocaine- or methamphetamine-induced stimulation

RationaleCocaine (COC), ethanol (EtOH), and methamphetamine (MA) are widely abused substances and share the ability to induce behavioral stimulation in mice and humans. Understanding the biological basis of behavioral stimulation to COC, EtOH, and MA may provide a greater understanding of drug and alcohol abuse.ObjectivesIn these studies we set out to determine if neuronal nicotinic acetylcholine receptors were involved in the acute locomotor responses to these drugs, our measure of behavioral stimulation.MethodsA panel of acetylcholine receptor antagonists was used to determine if nicotinic receptors were involved in EtOH- and psychostimulant-induced stimulation. We tested the effect of these drugs in genotypes of mice (FAST and DBA/2J) that are extremely sensitive to this drug effect. To determine which acetylcholine receptor subunits may be involved in this response, relative expression of the α3, α6, β2, and β4 subunit genes was examined in mice selectively bred for high and low response to EtOH.ResultsMecamylamine, but not hexamethonium, attenuated the acute locomotor response to EtOH. The acetylcholine receptor antagonist dihydro-β-erythroidine and methyllycaconitine had no effect on this response. The α6 and β4, but not α3 or β2, subunits of the acetylcholine receptor were differentially expressed between mice bred for extreme differences in EtOH stimulation. Mecamylamine had no effect on psychostimulant-induced locomotor activity.ConclusionsNeuronal nicotinic receptors are involved in EtOH, but not psychostimulant, stimulation. These studies suggest a lack of involvement of some nicotinic receptor subtypes, but more work is needed to determine the specific receptor subtypes involved in this behavior.

Behavioral genetic contributions to the study of addiction-related amphetamine effects

Amphetamines, including methamphetamine, pose a significant cost to society due to significant numbers of amphetamine-abusing individuals who suffer major health-related consequences. In addition, methamphetamine use is associated with heightened rates of violent and property-related crimes. The current paper reviews the existing literature addressing genetic differences in mice that impact behavioral responses thought to be relevant to the abuse of amphetamine and amphetamine-like drugs. Summarized are studies that used inbred strains, selected lines, single-gene knockouts and transgenics, and quantitative trait locus (QTL) mapping populations. Acute sensitivity, neuroadaptive responses, rewarding and conditioned effects are among those reviewed. Some gene mapping work has been accomplished, and although no amphetamine-related complex trait genes have been definitively identified, translational work leading from results in the mouse to studies performed in humans is beginning to emerge. The majority of genetic investigations have utilized single-gene knockout mice and have concentrated on dopamine- and glutamate-related genes. Genes that code for cell support and signaling molecules are also well-represented. There is a large behavioral genetic literature on responsiveness to amphetamines, but a considerably smaller literature focused on genes that influence the development and acceleration of amphetamine use, withdrawal, relapse, and behavioral toxicity. Also missing are genetic investigations into the effects of amphetamines on social behaviors. This information might help to identify at-risk individuals and in the future to develop treatments that take advantage of individualized genetic information.

The α6 nicotinic acetylcholine receptor subunit influences ethanol-induced sedation.

Alcohol and nicotine are often co-used and data from human and animals studies have demonstrated that common genes underlie responses to these two drugs. Recently, the genes that code for the subunits of the nicotinic acetylcholine receptors have been implicated as a common genetic mediator for alcohol and nicotine responses. The mammalian genes that code for the α6 and β3 subunits of the nicotinic acetylcholine receptor (Chrna6 and Chrnb3, respectively) are located adjacent to each other on human and mouse chromosome 8. These subunits have gained attention as potential regulators of drug behaviors because of their expression in the striatum where they have been shown to modulate dopamine release. Human genetic studies have shown that variation in these genes is associated with alcohol phenotypes. In the current experiments, mice lacking the Chrna6 or Chrnb3 gene were tested for three ethanol behaviors: choice ethanol consumption, ataxia, and sedation. Wildtype (WT), heterozygous (HET), and knockout (KO) mice of each strain went through a standard 2-bottle choice drinking paradigm, the balance beam, and the Loss of Righting Reflex (LORR) paradigm. No genotypic effects on any of the 3 behavioral tasks were observed in Chrnb3 animals. While the Chrna6 gene did not significantly influence ethanol consumption (g/kg) or ataxia, mice lacking the α6 subunit took significantly longer to recover their righting reflex than WT animals. These data provide evidence that receptors containing this subunit modulate the sedative effects of ethanol. Further work examining other models of ethanol consumption and behavioral responses to ethanol is needed to fully characterize the role of these receptor subunits in modulating ethanol responses.

The parallel rod floor test: a measure of ataxia in mice

The parallel rod floor test is a new model of ataxia in mice. It allows the simultaneous measurement of ataxia and locomotor activity. This protocol is designed for researchers examining ethanol-induced motor incoordination in mice, but it should be applicable to other sedative/hypnotic drugs and to testing cerebellar mutant mice or mice with engineered genetic defects. This protocol takes 3 d, with the time per day depending on how many animals are tested. The test allows researchers to quantify differences in motor coordination among genotypes of mice that may differ in locomotor activity. Unlike many other methods for assessing incoordination, the parallel rod floor test yields similar patterns of genetic sensitivity across a range of variant forms of the apparatus.

The nicotinic acetylcholine receptor partial agonist varenicline increases the ataxic and sedative-hypnotic effects of acute ethanol administration in C57BL/6J mice.

BACKGROUND The costs associated with alcohol abuse are staggering, therefore much effort has been put into developing new pharmacologic strategies to decrease alcohol abuse. Recently, the nicotinic acetylcholine receptor (nAChR) partial agonist varenicline has been shown to decrease ethanol consumption in both humans and animal models. METHODS We examined the effects of varenicline on the ataxic and sedative-hypnotic effects of ethanol. First, varenicline was administered prior to placement in a locomotor activity chamber to determine whether varenicline influenced baseline locomotor activity. To determine the effect of nicotinic modulation on ethanol-induced motor incoordination, varenicline was administered 30 minutes prior to an acute ethanol injection and then mice were tested on the balance beam, dowel test, or fixed-speed rotarod. To examine ethanols sedative-hypnotic effects, varenicline was administered 30 minutes prior to 4 g/kg ethanol and the duration of loss of righting reflex (LORR) was measured. RESULTS Varenicline markedly reduced baseline locomotor activity in C57BL/6J mice. Varenicline increased ethanol-induced ataxia when measured on the balance beam and dowel test but had no effect when measured on the fixed-speed rotarod. Pretreatment with varenicline increased the duration of LORR. CONCLUSIONS These data provide evidence that nAChRs may be involved in the ataxic and sedative effects of ethanol. It is possible that one mechanism that could contribute to the ability of varenicline to decrease ethanol consumption may be through increasing negative behavioral effects of alcohol.

Nominal association with CHRNA4 variants and nicotine dependence.

Nicotine binds to nicotinic acetylcholine receptors and studies in animal models have shown that α4β2 receptors mediate many behavioral effects of nicotine. Human genetics studies have provided support that variation in the gene that codes for the α4 subunit influences nicotine dependence (ND), but the evidence for the involvement of the β2 subunit gene is less convincing. In this study, we examined the genetic association between variation in the genes that code for the α4 (CHRNA4) and β2 (CHRNB2) subunits of the nicotinic acetylcholine receptor and a quantitative measure of lifetime DSM-IV ND symptom counts. We performed this analysis in two longitudinal family-based studies focused on adolescent antisocial drug abuse: the Center on Antisocial Drug Dependence (CADD, N = 313 families) and Genetics of Antisocial Drug Dependence (GADD, N = 111 families). Family-based association tests were used to examine associations between 14 single nucleotide polymorphisms (SNPs) in CHRNA4 and CHRNB2 and ND symptoms. Symptom counts were corrected for age, sex and clinical status prior to the association analysis. Results, when the samples were combined, provided modest evidence that SNPs in CHRNA4 are associated with ND. The minor allele at both rs1044394 (A; Z = 1.988, P = 0.047, unadjusted P-value) and rs1044396 (G; Z = 2.398, P = 0.017, unadjusted P-value) was associated with increased risk of ND symptoms. These data provide suggestive evidence that variation in the α4 subunit of the nicotinic acetylcholine receptor may influence ND liability.