Lucinda L. Miner

Behavioral phenotypes of inbred mouse strains: implications and recommendations for molecular studies

Abstract Choosing the best genetic strains of mice for developing a new knockout or transgenic mouse requires extensive knowledge of the endogenous traits of inbred strains. Background genes from the parental strains may interact with the mutated gene, in a manner which could severely compromise the interpretation of the mutant phenotype. The present overview summarizes the literature on a wide variety of behavioral traits for the 129, C57BL/6, DBA/2, and many other inbred strains of mice. Strain distributions are described for open field activity, learning and memory tasks, aggression, sexual and parental behaviors, acoustic startle and prepulse inhibition, and the behavioral actions of ethanol, nicotine, cocaine, opiates, antipsychotics, and anxiolytics. Using the referenced information, molecular geneticists can choose optimal parental strains of mice, and perhaps develop new embryonic stem cell progenitors, for new knockouts and transgenics to investigate gene function, and to serve as animal models in the development of novel therapeutics for human genetic diseases.

Strain comparison of nicotine-induced seizure sensitivity and nicotinic receptors

Nicotine-induced seizure sensitivity was assessed in 19 inbred mouse strains. Two routes of drug administration were utilized: acute intravenous (IV) infusion and intraperitoneal (IP) injection. Dose-response curves for sensitivity to IP nicotine-induced seizures were constructed for the 19 inbred strains and a heterogeneous stock (HS/Ibg) of mice. Differences were observed among the strains both in ED50 values and slopes of the dose-response curves following IP injection of nicotine. ST/bJ mice were the most sensitive having an ED50 of 2.34 +/- 0.09 mg/kg nicotine. DBA/1J mice were the most resistant strain with an ED50 value of 6.16 +/- 0.02 m/kg nicotine. Latency to clonic seizure was measured in the 19 inbred mouse strains using the acute IV route of drug administration. Again, ST/bJ mice were the most sensitive and DBA/2Ibg were the most resistant to IV nicotine-induced seizures. Significant correlations were observed between latency to IV nicotine-induced seizures and both ED50 values and the slope of the dose-response curves for IP nicotine-induced seizures. However, the pattern of results differed between the two routes of drug administration. The relationship between seizure sensitivity and nicotinic receptor concentration in three brain regions, cortex, midbrain and hippocampus, was also assessed using alpha-bungarotoxin (BTX) as the ligand. A significant relationship was observed between BTX binding in the three brain regions and sensitivity to IV nicotine-induced seizures such that strains with greater concentrations of BTX binding sites were more sensitive to nicotine-induced seizures than were strains with lower concentrations of BTX binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine Reward and Locomotor Activity in C57BL/6J and 129/SvJ Inbred Mice and Their F1 Cross

Large individual differences exist among mice in their behavioral responses to drugs of abuse, and many of these differences have a substantial genetic basis. The creation of new animal models using recombinant DNA technology has provided new genetic tools for assessing the role of specific candidate genes in drug response. This study presents a characterization of cocaine activation and reward in the two strains used most commonly for production of knockout mice, C57BL/6J and 129/SvJ, and their outcrossed F1 offspring. Using conditioned place preference, the study demonstrates that there are large strain differences in spontaneous locomotor activity and in the rewarding effects of cocaine. The 129/SvJ strain is hypoactive and is very sensitive to the locomotor activating effects of cocaine but does not develop cocaine-conditioned place preference under conditions that yield significant place preference in C57BL/6J mice. These phenotypes are not inherited in a simple additive manner, but rather the F1 generation resembles the C57BL/6J progenitor strain for a number of the behaviors examined.

Retained cocaine conditioned place preference in D1 receptor deficient mice

The role of the D1 dopamine receptor subtype in mediating cocaine effects was examined in mice in which the D1 receptor gene had been ablated by homologous recombination. Cocaine reward was assessed by conditioned place preference experiments using mice which had either one allele (+/-) or both alleles (-/-) of the D1 dopamine receptor gene disrupted and in their wild type (+/+) littermates. Cocaine conditioning resulted in similar increases in preference for drug-paired environments in mice of each of the three genotypes. Cocaine did not alter locomotor activity levels in homozygous, D1 knockout mice -/-, whereas increased activity was noted in both +/+ and +/- animals. These results are consistent with the idea that the D1 receptor is involved in the locomotor stimulant effects of cocaine, but has little role in a major test of the rewarding and reinforcing effects of the drug.

Cocaine reward and MPTP toxicity: alteration by regional variant dopamine transporter overexpression.

Polygenic factors play important roles in animal models of substance abuse and susceptibility to dopaminergic neurodegeneration. Genetic factors are also likely to contribute to the etiology of human drug abuse disorders, and may alter human vulnerabilities to Parkinsonian neurodegeneration. The dopamine transporter (DAT; SLC6A3) is densely expressed by the dopaminergic midbrain neurons that play central roles in drug reward and is believed to be a primary site of action for cocaine reward. This transporter is necessary for the action of selective dopaminergic neurotoxins, and is uniquely expressed on neurons that are the primary targets of Parkinsonian neurodegeneration. To study possible influences of variant DAT expression on these processes, we have constructed transgenic mice (THDAT) in which tyrosine hydroxylase (TH) promoter sequences drive expression of a rat DAT cDNA variant, increase striatal DAT expression by 20-30%, and provide modest alterations in striatal levels of dopamine and its metabolites. THDAT mice habituate more rapidly to a novel environment than wildtype littermates. These animals display enhanced reward conferred by cocaine, as measured by conditioned place preference. However, locomotor responses to cocaine administration are similar to those of wildtype mice, except at high cocaine doses. THDAT mice display more than 50% greater losses of dopaminergic neurons following a course of MPTP treatment than do wildtype control mice. These results document a model for allelic variation at a gene locus that can exert significant effects in murine models of human substance abuse vulnerability and dopaminergic neurodegeneration.

Genetic influences on acute responses to nicotine and nicotine tolerance in the mouse.

Nineteen inbred mouse strains were tested for their relative sensitivity to nicotines effects on respiratory rate, acoustic startle response, heart rate, Y-maze activity (crosses and rears) and body temperature. Separate animals were tested for their sensitivity to nicotine-induced seizures following IP injection or IV infusion. Dose-response curves were constructed for each measure. Large strain differences were obtained for all of these measures. Nicotines effects on heart rate, Y-maze activity and body temperature segregated together into the various mouse strains whereas seizure sensitivity segregated independently which suggests that these responses are under separate genetic control. Evidence was obtained which suggests that nicotine-induced seizures are regulated, in part, by the number of hippocampal nicotinic receptors measured with alpha-bungarotoxin (BTX). Strain differences in the development of tolerance to nicotine were also observed. Four mouse strains were tested and one of these strains (C3H) did not exhibit tolerance to nicotine. The binding of (3H)nicotine and (125I)BTX increased in the brains of all four mouse strains. These changes may relate to tolerance in some mouse strains, but since C3H mice did not exhibit tolerance even though brain nicotinic receptors changed following chronic treatment, other explanations for the role of receptor changes in tolerance to nicotine must be sought.

Mecamylamine blockade of nicotine responses: Evidence for two brain nicotinic receptors

Mice of two inbred strains, DBA and C3H, were pretreated with mecamylamine before challenge with nicotine. Mecamylamine blocked nicotine-induced seizures, enhanced startle, and alterations in respiratory rate, Y-maze activity, heart rate and body temperature. Mecamylamine blocked nicotine-induced seizures and enhanced startle with IC50 values of less than 0.1 mg/kg. The other nicotine effects were blocked by mecamylamine with IC50 values between 0.8 and 2.3 mg/kg. Strain differences in sensitivity to mecamylamine blockade were also detected. These results suggest that nicotine elicits its effects at two receptors, which may be those labeled with [125I]-alpha-bungarotoxin and with [3H]-nicotine.

Relationship between nicotine-induced seizures and hippocampal nicotinic receptors

A controversy has existed for several years concerning the physiological relevance of the nicotinic receptor measured by alpha-bungarotoxin binding. Using mice derived from a classical F2 and backcross genetic design, a relationship between nicotine-induced seizures and alpha-bungarotoxin nicotinic receptor concentration was found. Mice sensitive to the convulsant effects of nicotine had greater alpha-bungarotoxin binding in the hippocampus than seizure insensitive mice. The binding sites from seizure sensitive and resistant mice were equally affected by treatment with dithiothreitol, trypsin or heat. Thus it appears that the difference between seizure sensitive and insensitive animals may be due to a difference in hippocampal nicotinic receptor concentration as measured with alpha-bungarotoxin binding.

Blending addiction research and practice: Strategies for technology transfer

Consistent with traditional conceptions of technology transfer, efforts to translate substance abuse and addiction research into treatment practice have typically relied on the passive dissemination of research findings. The large gap between addiction research and practice, however, indicates that there are many barriers to successful technology transfer and that dissemination alone is not sufficient to produce lasting changes in addiction treatment. To accelerate the translation of research into practice, the National Institute on Drug Abuse launched the Blending Initiative in 2001. In part a collaboration with the Substance Abuse and Mental Health Services Administration/Center for Substance Abuse Treatments Addiction Technology Transfer Center program, this initiative aims to improve the development, effectiveness, and usability of evidence-based practices and reduce the obstacles to their timely adoption and implementation.

Chromosomal mapping of the psychomotor stimulant effects of cocaine in BXD recombinant inbred mice

To elucidate genes associated with cocaines locomotor stimulant effects, we used recombinant inbred-quantitative trait loci (RI-QTL) analyses to identify chromosomal loci associated with locomotor activity before (baseline) and after cocaine treatment. RI-QTL analyses seek to identify associations between a quantitative measure of a phenotype and one or more previously mapped marker loci across a panel of RI strains. In the present study, 11 BXD RI strains were used to identify several putative QTLs for each phenotype. Both baseline locomotor activity and cocaines locomotor stimulant effects are polygenic, with both unique and overlapping genetic influences. The largest associations for baseline activity were observed on chromosomes 5 and 9 and the largest associations for cocaines psychomotor stimulant effects on chromosomes 3 and 17.