The effects of ethanol and Ro 15-4513 on elevated plus-maze and rotarod performance in long-sleep and short-sleep mice

Assessment of Acute Motor Effects and Tolerance Following Self-Administration of Alcohol and Edible ∆9 -Tetrahydrocannabinol in Adolescent Male Mice

BACKGROUND

Cannabinoids and their principle psychoactive target, the cannabinoid type 1 receptor (CB1R), impact a number of alcohol-related properties, and although alcohol and cannabis are often co-used, particularly in adolescence, few animal models of this phenomenon exist. We modeled the co-use of alcohol and ∆⁹ -tetrahydrocannabinol (THC) in adolescent mice using ingestive methods popular during this developmental period in humans, namely binge-drinking and edible THC. With this model, we assessed levels of use, acute effects, and tolerance to each substance.

METHODS

Adolescent male C57BL/6J mice had daily, limited access to 1 of 2 edible doughs (THC or control), to 1 of 2 fluids (ethanol (EtOH) or water), and in 1 of 2 orders (dough-fluid or fluid-dough). Home cage locomotor activity was recorded both during access and after access. On the day following the final access session, a subset of mice were assessed for functional and metabolic tolerance to alcohol using accelerating rotarod and blood EtOH concentrations, respectively. The remaining mice were assessed for tolerance to THC-induced hypothermia, and whole-brain CB1R expression was assessed in all mice.

RESULTS

EtOH intake was on par with levels previously reported in adolescent mice. Edible THC was well-consumed, but consumption decreased at the highest dose provided. Locomotor activity increased following EtOH intake and decreased following edible THC consumption, and edible THC increased fluid intake in general. The use of alcohol produced neither functional nor metabolic tolerance to an alcohol challenge. However, the use of edible THC impaired subsequent drug-free rotarod performance and was associated with a reduction in THC's hypothermic effect.

CONCLUSIONS

Adolescent mice self-administered both alcohol and edible THC to a degree sufficient to acutely impact locomotor activity. However, only edible THC consumption had lasting effects during short-term abstinence. Thus, this adolescent co-use model could be used to explore sex differences in self-administration and the impact substance co-use might have on other domains such as mood and cognition.

Atp1a2 contributes modestly to alcohol-related behaviors

Atp1a2 has been previously studied for anxiety, learning and motor function disorders, and fear. Since Atp1a2 has been shown to be involved in anxiety and this behavior is a known risk factor for developing alcoholism, we have been investigating Atp1a2 for its potential role in responses to alcohol. This study utilized Atp1a2 knockout mice; Atp1a2 heterozygous mice, with half the amount of protein compared to wild-type mice, were used because Atp1a2 homozygous null mice die shortly after birth. The alcohol-related behavioral experiments performed were loss of righting reflex (LORR), acute alcohol withdrawal measured by handling-induced convulsions (HIC), drinking in the dark (DID), open-field activity (OFA), and elevated plus-maze (EPM). LORR was a 2-day test that measures acute alcohol sensitivity, and rapid and acute functional tolerance (AFT). HIC was a 3-day test to measure alcohol withdrawal, DID was a 4-day test which measures voluntary alcohol consumption, and OFA and EPM measured anxiety with alcohol exposure. The effect of genotype on alcohol metabolism was also examined. There was a genotype effect on rate of alcohol metabolism, but only in males. There was no effect on alcohol withdrawal severity. The Atp1a2 heterozygous mice consumed more alcohol than wild-type mice in the DID test, although only in males. In addition, only males were observed to show rapid tolerance in the LORR test while only female heterozygous mice showed a pretreatment effect on AFT. Alcohol exposure had a greater anxiolytic effect in the heterozygous mice compared to wild-type mice, although, again, there were sex effects with only males showing the effect in OFA and only females in the EPM. Although the behavioral results were mixed, there does appear to be a connection between anxiety and alcohol. Overall, the results suggest that Atp1a2 does contribute to alcohol-related behaviors, although the effect is modest with a clear dependence on sex.

Alcohol Suppresses Tonic GABAA Receptor Currents in Cerebellar Granule Cells in the Prairie Vole: A Neural Signature of High-Alcohol-Consuming Genotypes

BACKGROUND

Evidence indicates that the cerebellum plays a role in genetic predilection to excessive alcohol (ethanol [EtOH]) consumption in rodents and humans, but the molecular mechanisms mediating such predilection are not understood. We recently determined that EtOH has opposite actions (enhancement or suppression) on tonic GABAA receptor (GABAA R) currents in cerebellar granule cells (GCs) in low- and high-EtOH-consuming rodents, respectively, and proposed that variation in GC tonic GABAA R current responses to EtOH contributes to genetic variation in EtOH consumption phenotype.

METHODS

Voltage-clamp recordings of GCs in acutely prepared slices of cerebellum were used to evaluate the effect of EtOH on GC tonic GABAA R currents in another high-EtOH-consuming rodent, prairie voles (PVs).

RESULTS

EtOH (52 mM) suppressed the magnitude of the tonic GABAA R current in 57% of cells, had no effect in 38% of cells, and enhanced the tonic GABAA R current in 5% of cells. This result is similar to GCs from high-EtOH-consuming C57BL/6J (B6) mice, but it differs from the enhancement of tonic GABAA R currents by EtOH in low-EtOH-consuming DBA/2J (D2) mice and Sprague Dawley (SD) rats. EtOH suppression of tonic GABAA R currents was not affected by the sodium channel blocker, tetrodotoxin (500 nM), and was independent of the frequency of phasic GABAA R-mediated currents, suggesting that suppression is mediated by postsynaptic actions on GABAA Rs, rather than a reduction of GABA release. Finally, immunohistochemical analysis of neuronal nitric oxide synthase (nNOS; which can mediate EtOH enhancement of GABA release) demonstrated that nNOS expression in the GC layer of PV cerebellum was similar to the levels seen in B6 mice, both being significantly reduced relative to D2 mice and SD rats.

CONCLUSIONS

Combined, these data highlight the GC GABAA R response to EtOH in another species, the high-EtOH-consuming PV, which correlates with EtOH consumption phenotype and further implicates the GC GABAA R system as a contributing mechanism to high EtOH consumption.

Negative allosteric modulation of GABAA receptors inhibits facilitation of brain stimulation reward by drugs of abuse in C57BL6/J mice

RATIONALE

There is an emerging body of evidence that implicates a crucial role of γ-aminobutyric acid subtype A (GABAA) receptors in modulating the rewarding effects of a number of abused drugs. Modulation of GABAA receptors may therefore represent a novel drug-class independent mechanism for the development of abuse treatment pharmacotherapeutics.

OBJECTIVES

We tested the hypothesis that the GABAA receptor benzodiazepine-site (BDZ) negative modulator Ro15-4513 would reduce the reward-related effects of three pharmacologically dissimilar drugs; toluene vapor, d-methamphetamine, and diazepam using intracranial self-stimulation (ICSS) in mice. We also examined whether Ro15-4513 attenuated dopamine release produced by d-methamphetamine in an in vivo microdialysis procedure.

RESULTS

Ro15-4513 abolished ICSS reward facilitation produced by all three abused drugs at Ro15-4513 doses which had no effect on ICSS when administered alone. In contrast, the BDZ antagonist flumazenil only attenuated the ICSS-facilitating effects of diazepam. Administration of the same dose of Ro15-4513 which abolished drug-facilitated ICSS produced a 58 % decrease in d-methamphetamine-stimulated dopamine in the nucleus accumbens of mice relative to d-methamphetamine alone.

CONCLUSIONS

These results demonstrate that negative modulation of GABAA receptors can produce profound reductions in reward-related effects of a diverse group of drugs that activate the mesolimbic reward pathway through different mechanisms. These data suggest that pharmacological modulation of GABAA receptors may represent a viable pathway for the development of drug abuse pharmacotherapies.

α4-Containing GABA(A) Receptors are Required for Antagonism of Ethanol-Induced Motor Incoordination and Hypnosis by the Imidazobenzodiazepine Ro15-4513

Alcohol (ethanol) is widely consumed for its desirable effects but unfortunately has strong addiction potential. Some imidazobenzodiazepines such as Ro15-4513 are able to antagonize many ethanol-induced behaviors. Controversial biochemical and pharmacological evidence suggest that the effects of these ethanol antagonists and ethanol are mediated specifically via overlapping binding sites on α4/δ-containing GABA_A-Rs. To investigate the requirement of α4-containing GABA_A-Rs in the mechanism of action of Ro15-4513 on behavior, wildtype (WT) and α4 knockout (KO) mice were compared for antagonism of ethanol-induced motor incoordination and hypnosis. Motor effects of ethanol were tested in two different fixed speed rotarod assays. In the first experiment, mice were injected with 2.0 g/kg ethanol followed 5 min later by 10 mg/kg Ro15-4513 (or vehicle) and tested on a rotarod at 8 rpm. In the second experiment, mice received a single injection of 1.5 g/kg ethanol ± 3 mg/kg Ro15-4513 and were tested on a rotarod at 12 rpm. In both experiments, the robust Ro15-4513 antagonism of ethanol-induced motor ataxia that was observed in WT mice was absent in KO mice. A loss of righting reflex (LORR) assay was used to test Ro15-4513 (20 mg/kg) antagonism of ethanol (3.5 g/kg)-induced hypnosis. An effect of sex was observed on the LORR assay, so males and females were analyzed separately. In male mice, Ro15-4513 markedly reduced ethanol-induced LORR in WT controls, but α4 KO mice were insensitive to this effect of Ro15-4513. In contrast, female KO mice did not differ from WT controls in the antagonistic effects of Ro15-4513 on ethanol-induced LORR. We conclude that Ro15-4513 requires α4-containing receptors for antagonism of ethanol-induced LORR (in males) and motor ataxia.

Genetic structure of the LXS panel of recombinant inbred mouse strains: a powerful resource for complex trait analysis

The set of LXS recombinant inbred (RI) strains is a new and exceptionally large mapping panel that is suitable for the analysis of complex traits with comparatively high power. This panel consists of 77 strains-more than twice the size of other RI sets--and will typically provide sufficient statistical power (beta = 0.8) to map quantitative trait loci (QTLs) that account for approximately 25% of genetic variance with a genomewide p < 0.05. To characterize the genetic architecture of this new set of RI strains, we genotyped 330 MIT microsatellite markers distributed on all autosomes and the X Chromosome and assembled error-checked meiotic recombination maps that have an average F2-adjusted marker spacing of approximately 4 cM. The LXS panel has a genetic structure consistent with random segregation and subsequent fixation of alleles, the expected 3-4 x map expansion, a low level of nonsyntenic association among loci, and complete independence among all 77 strains. Although the parental inbred strains-Inbred Long-Sleep (ILS) and Inbred Short-Sleep (ISS)--were derived originally by selection from an 8-way heterogeneous stock selected for differential sensitivity to sedative effects of ethanol, the LXS panel is also segregating for many other traits. Thus, the LXS panel provides a powerful new resource for mapping complex traits across many systems and disciplines and should prove to be of great utility in modeling the genetics of complex diseases in human populations.

Interaction of mazindol with alcohol in mice

Combined anorectic-alcohol misuse is a prevalent problem in Brazil. In order to understand better the interactive effects of ethanol (EtOH) and mazindol (MZ), we examined the effects of EtOH (1.2 g/kg) and MZ (5.0 mg/kg) given alone or in combination, on mouse behaviour. The results indicate that EtOH plus MZ induces a significantly greater increase in locomotor activity of mice than either constituent alone. However, no such interactive effect was detected in the place preference and in the plus-maze test of anxiety. MZ given alone was found to increase the locomotor activity and to possess rewarding effects as measured in the place preference conditioning. At the dose selected, EtOH alone showed anxiolytic and rewarding effects. These results provide some evidence of increased behavioural effects in mice due to combinations of EtOH and MZ. These findings suggest that a major determinant of combined anorectic-alcohol misuse may be the increased stimulating effects produced by such combination.

Differential sensitivity to the anxiolytic effects of ethanol and flunitrazepam in PKCgamma null mutant mice

Tests of ethanol effects in PKCgamma null mutant mice have indicated that PKCgamma plays a role in initial sensitivity to ethanol-induced sedation, hypothermia, and GABA(A) receptor function and impacts neurochemical pathways mediating anxiety. The present study was undertaken to evaluate whether the decreased sensitivity to ethanol previously observed in these mice generalized to the anxiolytic effects of ethanol. PKCgamma null mutant mice and wild-type controls were tested in the elevated-plus maze, the black/white box, and the mirrored chamber after ethanol (0, 1.0, 1.25, 1.5 g/kg) or flunitrazepam (FNZ) (0, 0.015, 0.03, 0.06 mg/kg). Results indicated that although both genotypes exhibited anxiolytic responses to ethanol in the elevated plus-maze, null mutant mice were less sensitive than wild-type control mice; however, in the black/white box, PKCgamma null mutants were more sensitive than controls to the anxiolytic effects of FNZ. Neither ethanol nor FNZ produced anxiolytic responses in the mirrored chamber for either genotype. These results suggest that PKCgamma differentially mediates anxiolytic responses to ethanol and FNZ and that this relationship interacts with each drug's efficacy in reducing anxiety-related behaviors specific to each of the three mazes.

A proposed test battery and constellations of specific behavioral paradigms to investigate the behavioral phenotypes of transgenic and knockout mice

Behavioral phenotyping of transgenic and knockout mice requires rigorous, formal analyses. Well-characterized paradigms can be chosen from the established behavioral neuroscience literature. This review describes (1) a series of neurological and neuropsychological tests which are effectively used as a first screen for behavioral abnormalities in mutant mice, and (2) a series of specific behavioral paradigms, clustered by category. Included are multiple paradigms for each category, including learning and memory, feeding, analgesia, aggression, anxiety, depression, schizophrenia, and drug abuse models. Examples are given from the experiences of the authors, in applying these experimental designs to transgenic and knockout mice. Extensive references for each behavioral paradigm are provided, to allow new investigators to access the relevant literature on behavioral methodology.

Sensitivity to ethanol-induced ataxia in HOT and COLD selected lines of mice

Studies with inbred strains of mice have suggested that there may be a genetic correlation between strain sensitivities to the ataxic and hypothermic responses to ethanol (EtOH), which would suggest that some genes influence both responses. To test this hypothesis, EtOH sensitivity was determined in replicate lines of mice selectively bred for sensitivity (COLD) or resistance (HOT) to acute ethanol hypothermia. Several tests were used to index ataxia, related traits such as muscle strength, and locomotor activity. The screen test yielded a dose-dependent EtOH-induced decrease in performance that did not differ between the selected lines. Based on the dose-response characteristics of this task, 2.5 g/kg of EtOH was used as the test dose for the remaining experiments. Results from the fixed-speed rotarod and the grid test of motor incoordination also indicated no significant differences between HOT and COLD mice in sensitivity to EtOH impairment. When the selected lines were tested on an accelerating rotarod, COLD mice were impaired by the acute EtOH injection, but HOT mice were unaffected. COLD mice were more sensitive to EtOH-induced decrements in grip strength and locomotor activity. Overall, the results indicated that HOT and COLD mice were only differentially sensitive to EtOH in some tasks related to ataxia, suggesting that some genes must be associated uniquely with EtOH-induced hypothermia or ataxia. The mixed results from the various tests indicate that ataxia can best be conceived as a group of related complex behaviors that cannot be assessed adequately by the use of a single task and that ataxia-related behaviors are influenced by different groups of genes.

Use of transgenics, null mutants, and antisense approaches to study ethanol's actions

Behavioral and biochemical responses mediating ethanol's actions have been difficult to study in humans and animals because of their complex polygenic nature. Recent progress in the creation of new animal models using recombinant DNA technology has provided a set of genetic tools by which the role of specific candidate genes in ethanol's actions can be examined. These techniques include the creation of transgenic and null mutant mice, as well as manipulation of protein synthesis with antisense treatments. These techniques are reviewed, and their potential applications to alcohol research are discussed.

Biometrical genetic analysis of ethanol's psychomotor stimulant effect

Hereditary influences on psychomotor stimulant effects of ethanol (ETOH) were studied in a classical Mendelian cross of DBA/2Abg (D2) and C57BL/6Abg (B6) inbred mouse strains. A dose-response study with nine doses (0-3.5 g/kg ip) indicated that B6 mice lack the activational limb of the biphasic curve (< or = 1.5 g/kg), as assessed in a 15-min test. D2 mice ran greater distances and ran faster, at doses up to 2.5 g/kg. B6 mice showed no increments in speed or distance at these doses that activated D2 mice. Several other indices reinforced the conclusion of ETOH-induced behavioral activation in D2 mice and lack there of in B6 mice (traditional photobeam interruptions--horizontal counts; center distance; vertical movements; inactive time; as well as derived indices of running speed and average length of each movement). The F1, F2, and backcross generations produced dose-response curves that showed additive inheritance of the activational response to doses below 1.5 g/kg. A second study (n = 1446) examined response to 1.5 g/kg with a within-subjects design in the full Mendelian cross. This study verified the completely additive mode of inheritance for the total distance measure suggested in the dose-response study, and showed that sex linkage and sex differences were not present. Narrow sense heritability of the ETOH activation response (indexed by total distance) was calculated at 0.35 and approximately 3 loci were estimated to be responsible for the B6/D2 difference. The other phenotypes (described above) also showed strongly additive genetic control.(ABSTRACT TRUNCATED AT 250 WORDS)

A genetic comparison of behavioral actions of ethanol and nicotine in the mirrored chamber

Human alcoholics are almost invariably heavy users of tobacco, perhaps because both ethanol and nicotine may have anxiolytic activity. However, studies in humans have not uniformly detected anxiolytic effects because significant individual differences in anxiolytic actions of these agents seem to exist. One factor that seems to contribute to these individual differences is tolerance to ethanol. Individuals who are more sensitive to depressant actions of alcohol seem to show anxiolytic actions more readily. Consequently, we examined the relative sensitivities of the ethanol-sensitive (to the anesthetic actions of ethanol) long-sleep (LS) and ethanol-resistant short-sleep (SS) mouse lines to diazepam, ethanol, nicotine, and ethanol-nicotine combinations in the mirrored chamber test. This test measures approach-conflict behavior. Ethanol and nicotine evoked changes in mirrored chamber activities that resembled those elicited by diazepam. These effects were seen at doses that did not markedly affect locomotor activity, thereby suggesting that these changes in behavior represent anxiolytic actions. The LS-SS mice did not differ in sensitivity to diazepam, but the SS were more uniformly responsive to the other drugs. Only the SS showed clear evidence for interactions between ethanol and nicotine. If the changes in mirrored chamber behavior elicited by ethanol, nicotine, and combinations of the two drugs occur because of anxiety reduction, it seems that the SS mouse line is more responsive to anxiolytic actions of these drugs.

Solubilization of benzodiazepine receptors from long- and short-sleep mice

Previous studies have shown that long-sleep (LS) and short-sleep (SS) mice, which were selectively bred for differential responses to the sedative-hypnotic actions of ethanol, also differ in response to several other agents that act at the GABAergic receptor. Binding at cortical benzodiazepine receptors is enhanced differentially by GABA and ethanol in membranes prepared from the two lines of mice with SS receptors enhanced to a greater extent. Heat denaturation studies and other biochemical characterizations of these receptors suggest that the GABAergic receptor complex from the two lines of mice differs. The present study examined whether perturbation of receptor-membrane interactions by treatment with detergent altered either GABA enhancement of [3H]flunitrazepam binding or ethanol enhancement of this binding. Octylglucopyranoside (OCTG), 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS), or deoxycholate solubilization of cortical membranes resulted in a loss of the LS/SS difference in GABA enhancement. Ethanol's effects on binding were altered differently from those of GABA by treatment with OCTG as an increase, not a decrease, in enhancement was observed in both lines of mice. These results suggest that protein-membrane interactions play an important role in mediating LS/SS differences in the allosteric interactions within the GABAergic receptor complex.