Locomotor responses of FAST and SLOW mice to several alcohols and drugs of abuse

Opioid sensitivity in mice selectively bred to consume or not consume methamphetamine

There has been little investigation of genetic factors and associated mechanisms that influence risk for development of methamphetamine (MA) dependence. Selectively bred mouse lines that exhibit high (MAHDR) or low (MALDR) levels of MA intake in a two-bottle choice MA drinking (MADR) procedure provide a genetic tool for this purpose. These lines were used to determine whether opioid sensitivity and MA intake are genetically associated, because opioid-mediated pathways influence some effects of MA. Sensitivity to the analgesic effects of the μ-opioid receptor (MOP-r) agonist fentanyl (0.05, 0.1, 0.2, 0.4 mg/kg) was examined using two acute thermal tests (hot plate and tail flick) and one chronic pain test (magnesium sulfate abdominal constriction). Locomotor stimulant responses to fentanyl (0.05, 0.1, 0.2, 0.4 mg/kg) and morphine (10, 20, 30 mg/kg) were also examined. In addition, MADR was measured in the progenitor strains [(C57BL/6J (B6), DBA/2J (D2)] of the F2 population from which the selected lines were generated. The MADR lines did not differ in sensitivity to the analgesic effects of fentanyl; however, MALDR mice exhibited greater locomotor activation than MAHDR mice to both fentanyl and morphine. D2 mice consumed more MA than B6 mice. The line differences for MA consumption and morphine activation recapitulated B6 and D2 strain differences for these two traits, but not strain differences previously found for opioid analgesic responses. These results support a negative genetic correlation between MA consumption and sensitivity to the stimulant effects of opioids and suggest the involvement of MOP-r regulated systems in MA intake.

Overview of mouse assays of ethanol intoxication

There are many behavioral assays to assess sensitivity to ethanol intoxication in mice. Most are simple to implement, and are sensitive to a particular dose range of ethanol. Most reflect genetic influences, and each test appears to reflect the contribution of a relatively distinct collection of genes. This genetic heterogeneity implies that no single test can claim to capture the construct "ethanol intoxication" completely. Depending on the test, and when measurements are made, acute functional tolerance to even a single dose of ethanol must be considered as a contributing factor. Whether or not a test is conducted in naïve mice or as part of a test battery can influence sensitivity, and do so in a strain-dependent manner. This unit reviews existing tests and recommends several.

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.

Genetic determinants of ethanol reinforcement

In this paper, we present examples of some of the several behaviors which have been taken to indicate the reinforcing efficacy of drugs, including ethanol. Efforts to identify the genetic determinants of these behaviors have employed diverse pharmacogenetic methods. For example, we have used selective breeding to develop mice selected for severe or attenuated ethanol withdrawal and have found that Withdrawal Seizure Prone mice show a greater conditioned preference for ethanol-associated locations than the selected Withdrawal Seizure Resistant line. Similarly, HOT mice, selected for insensitivity to ethanol-induced hypothermia, had greater conditioned place preference after ethanol training than COLD mice, selected for ethanol hypothermic sensitivity. We have also developed selected mouse lines responsive or unresponsive to ethanol-stimulated locomotor activity. These FAST and SLOW lines develop sensitization rather than tolerance to ethanol-induced activity. Using inbred strains of mice, others had shown that strains differed in preference for drinking ethanol solutions. We found that these strains also differed in acceptance of ethanol. Single-gene techniques have been used to show that preference drinking is significantly altered in mutant rodent strains lacking hypothalamic vasopressin, or with nephrogenic diabetes insipidus. In a specific panel of Recombinant Inbred mouse strains, we found that a single gene appeared to control a significant portion of the variance in preference drinking. These examples show that traits putatively related to drug reinforcement show substantial genetic control. Specifically, single-gene methods show promise of identification and mapping of genes related to drug reinforcement.