The relationship between ethanol-induced locomotor activation and narcosis in long-sleep and short-sleep mice

No effect of prenatal alcohol exposure on activity in three inbred strains of mice

AIMS

Prenatal exposure to alcohol can have adverse effects on the developing fetus. Two of the hallmarks of children exposed to alcohol prenatally are attention deficits and hyperactivity. While hyperactivity has been observed in rats following prenatal ethanol exposure, few studies have examined these effects in mice. The present study investigated the effects of prenatal ethanol exposure on activity in mice from three inbred strains: C57BL/6 (B6), Inbred Long Sleep (ILS) and Inbred Short Sleep (ISS).

METHODS

On Days 7 through 18 of gestation, mice were intragastrically intubated twice daily with either 3.0 g/kg ethanol (E) or an isocaloric amount of maltose-dextrin (MD); non-intubated control (NIC) litters were also generated. Offspring activity was monitored at 30, 60, 90 and 150 days of age.

RESULTS

While results showed no effects of prenatal ethanol exposure on any measures of activity, we did observe differences in baseline activity among the strains. ISS mice were more active than B6 and ILS for all activity measures except stereotypy; B6 mice had higher measures of stereotypy than ILS and ISS. Younger mice were more active than older mice. The only sex effects were on measures of stereotypy, where males had higher scores.

CONCLUSIONS

Mice are an excellent organism to study genetic influences on many phenotypes. However, our study and others have shown few effects of prenatal ethanol exposure on behavior in mice. It appears as if the prenatal period in mice, corresponding to organogenesis, is not a sensitive period for producing behavioral deficits following ethanol exposure. It is likely that the first 2 weeks postnatally, corresponding to the brain growth spurt, are more sensitive for producing behavioral effects.

QTL Mapping for Low-Dose Ethanol Activation in the LXS Recombinant Inbred Strains

BACKGROUND

Most mouse quantitative trait loci (QTLs) for behavioral traits have been mapped using populations of mice derived from C57BL/6J (B6) and DBA/2J (D2). It is also important to identify QTLs for behavior in populations derived from other progenitors. We report results from QTL mapping for low-dose (ethanol) locomotor activation (LDA) using the recently developed LXS recombinant inbred (RI) strains, derived from Inbred Long Sleep (ILS) and Inbred Short Sleep (ISS) progenitors. The LXS RI panel has additional genetic variation, and greater power due to a larger number of strains, compared with other RI panels and strain crosses.

METHODS

Mice were tested using a 3-day protocol in which activity levels were monitored for 15 minutes each day. On day 1, baseline activity was recorded; on day 2, mice were injected with saline before testing; and on day 3, mice were injected with 1.8 g/kg ethanol and tested.

RESULTS

Several suggestive QTLs were found, on chromosomes 2, 3, 4, 7, 8, 12, and 13; 3 of these QTLs were sex-specific.

CONCLUSIONS

Two apparently novel LDA QTLs were identified, on chromosomes 4 and 8. The other QTLs appear to replicate previously identified LDA QTLs. These replicated QTLs will be pursued in subsequent studies designed to identify candidate genes.

Open field activity and EtOH activation of gamma-PKC null mutants

Null mutants of the neural-specific gamma-isotype of protein kinase C (gamma-PKC) have demonstrated differential responses to acute administration of ethanol in comparison with wild-type animals. Previous studies have shown that the mutants are less sensitive to ethanol-induced loss of righting response. Null mutants also consume more ethanol and exhibit less behavioral inhibition. In order to determine if these sensitivity differences extend to ethanol activation of locomotor activity in an open-field arena, baseline activity and the effect of two low doses of ethanol were assessed in gamma-PKC null mutants and wild-type littermates. Null mutants demonstrated higher levels of baseline activity than did their wild-type counterparts. Further analysis revealed that a 1.0 g/kg dose of ethanol increased locomotor activity in males and females of both genotypes, whereas only null mutant males were activated by a 1.25 g/kg ethanol dose. The current study demonstrates that male gamma-PKC null mutants exhibit increased sensitivity to activating doses of ethanol in contrast to previous findings of decreased sensitivity to higher, depressive doses. This reflects the pleiotropic effects of the gamma-PKC null mutation on the behavioral effects of ethanol.

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.

Multiple cross mapping (MCM) markedly improves the localization of a QTL for ethanol-induced activation

This study examines the use of multiple cross mapping (MCM) to reduce the interval for an ethanol response QTL on mouse chromosome 1. The phenotype is the acute locomotor response to a 1.5-g/kg i.p. dose of ethanol. The MCM panel consisted of the six unique intercrosses that can be obtained from the C57BL/6J (B6), DBA/2J (D2), BALB/cJ (C) and LP/J (LP) inbred mouse strains (N > or = 600/cross). Ethanol response QTL were detected only with the B6xD2 and B6xC intercrosses. For both crosses, the D2 and C alleles were dominant and decreased ethanol response. The QTL information was used to develop an algorithm for sorting and editing the chromosome 1 Mit microsatellite marker set (http://www.jax.org). This process yielded a cluster of markers between 82 and 85cM (MGI). Evidence that the QTL was localized in or near this interval was obtained by the analysis of a sample (n = 550) of advanced cross heterogenous stock animals. In addition, it was observed that one of the BXD recombinant inbred strains (BXD-32) had a recombination in the interval of interest which produced the expected change in behavior. Overall, the data obtained suggest that the information available within existing genetic maps coupled with MCM data can be used to reduce the QTL interval. In addition, the MCM data set can be used to interrogate gene expression data to estimate which polymorphisms within the interval of interest are relevant to the QTL.

Ethanol-induced activation and rapid development of tolerance may have some underlying genes in common

Ethanol exerts biphasic effects on behavior, stimulant at low doses and depressant at higher doses. In the present study we used two mouse genetic models to investigate the relationships among activating and depressant responses to alcohol. The first model was a panel of nine isogenic genotypes. FAST and SLOW mice, selectively bred for high and low ethanol-induced motor activation, respectively, were used as a second model. We used loss of righting reflex to assess initial sensitivity and acute functional tolerance to a hypnotic dose of ethanol (3 g/kg, 20% v/v). Blood ethanol concentration at the onset of loss of righting reflex was used as an estimate of initial sensitivity, while the difference between concentration values at the recovery and loss of righting represented an acute functional tolerance score. Mean initial sensitivity and acute functional tolerance values of the nine strains were correlated with a previously obtained measure of ethanol-induced locomotor activation. Activation correlated significantly with both initial sensitivity (rg = 0.80; P < 0.05) and acute functional tolerance (rg = 0.77; P < 0.05). Thus, inbred genotypes that were activated more by a low dose of ethanol were also more sensitive to and developed more acute tolerance to a high dose. FAST mice had initial sensitivity values similar to those of SLOW mice, but developed more pronounced tolerance, indicating that ethanol-induced activation and acute functional tolerance may be regulated by some common genetic mechanisms. In summary, these results supported a genetic association between ethanol-induced activation and rapid development of tolerance.

Neurobiological responses to ethanol in mutant mice lacking neuropeptide Y or the Y5 receptor

We have previously shown that voluntary ethanol consumption and resistance are inversely related to neuropeptide Y (NPY) levels in NPY-knockout (NPY -/-) and NPY-overexpressing mice. Here we report that NPY -/- mice on a mixed C57BL/6Jx129/SvEv background showed increased sensitivity to locomotor activation caused by intraperitoneal (ip) injection of 1.5 g/kg of ethanol, and were resistant to sedation caused by a 3.5-g/kg dose of ethanol. In contrast, NPY -/- mice on an inbred 129/SvEv background consumed the same amount of ethanol as wild-type (WT) controls at 3%, 6%, and 10% ethanol, but consumed significantly more of a 20% solution. They exhibited normal locomotor activation following a 1.5-g/kg injection of ethanol, and displayed normal sedation in response to 2.5 and 3.0 g/kg of ethanol, suggesting a genetic background effect. Y5 receptor knockout (Y5 -/-) mice on an inbred 129/SvEv background showed normal ethanol-induced locomotor activity and normal voluntary ethanol consumption, but displayed increased sleep time caused by 2.5 and 3.0 g/kg injection of ethanol. These data extend previous results by showing that NPY -/- mice of a mixed C57BL/6Jx129/SvEv background have increased sensitivity to the locomotor activation effect caused by a low dose of ethanol, and that expression of ethanol-related phenotypes are dependent on the genetic background of NPY -/- mice.

Ethanol's effects on operant responding: differentiating reinforcement efficacy and motor performance

The purpose of this study was to examine the effects of ethanol on operant responding in rats. Drugs may affect response rates by several mechanisms, including altering motor performance or sensitivity to reinforcement. These two processes can be dissociated by applying a quantitative model of reinforced responding the response-strength equation, to response rates obtained during multiple variable-interval (VI) schedules of reinforcement. This equation has two fitted parameters. One (k) is thought to measure changes in motor performance, and the other (Re) is thought to measure changes in reinforcement efficacy. In experimental sessions, rats earned sucrose reinforcement on a seven-component multiple VI operant schedule. The average intervals varied from 108 to 3 s and provided reinforcement rates from 30 to 1200/h. Following stable baseline performance, rats were injected intraperitoneally prior to sessions with different doses of ethanol: 0.0, 0.3, 0.6. and 0.9 g/kg. Low to moderate doses of ethanol (0.3 and 0.6 g/kg) significantly decreased response rates on several of the VI schedules but did not alter either of the fitted parameters, suggesting that these doses of ethanol did not affect motor performance or sensitivity to reinforcement. The 0.9 g/kg dose decreased responding maintained by many of the VI schedules and significantly increased the Re parameter, suggesting that the sucrose became relatively less efficacious in ethanol compared to vehicle sessions. This relatively high dose of ethanol, however, did not alter responding maintained by the richest reinforcement schedule, and it did not affect motor performance as defined by the k parameter. These results suggest that, within this paradigm, ethanol affects motivation to respond rather than ability to respond.

Different levels of [3H]MK-801 binding in long-sleep and short-sleep lines of mice

The long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differential sensitivity to the hypnotic effects of ethanol. Several studies suggest that excitatory amino acid receptor systems are involved in these genetically determined differences in sensitivity to ethanol. The experiments described in this article examine further the potential role of NMDA excitatory amino acid receptors in genetically determined differences in hypnotic sensitivity to ethanol by measuring [3H]MK-801 binding in eight brain regions of LS and SS lines of mice. Significantly greater levels of binding were found in SS hippocampus and striatum. Binding levels in the remaining brain regions revealed no significant between-line differences. Affinity differences between regions were seen but no between-line differences in affinity were found in any brain region. These findings lend support to the hypothesis that differences in NMDA receptor systems are part of the genetically determined biochemistry that produces differential hypnotic sensitivity to ethanol in LS and SS mice.

Effects of ethanol, MK-801, and chlordiazepoxide on locomotor activity in different rat lines: dissociation of locomotor stimulation from ethanol preference

Several lines of research have suggested a link between the reward value of a drug and its ability to stimulate locomotion. One goal of the present study was to determine whether ethanol preferentially stimulates locomotor activity in lines of rat that show a preference for ethanol. A secondary goal was to determine the extent to which the benzodiazepine-like and NMDA antagonistic action of ethanol accounted for its effect on locomotor activity. To meet these goals, the effects of varying doses of ethanol (0.125-1.0 g/kg), MK-801 (0.1-0.3 mg/kg), and chlordiazepoxide (0.3-3 mg/kg) on locomotor activity were studied in several lines of rats that had been habituated to the testing procedure. The effect of low doses of ethanol on motor activity in the Alcohol-Preferring (P) and Fawn-Hooded rats, which show a strong ethanol preference, were similar to those of the alcohol-nonpreferring (NP), Flinders Sensitive Line, and Flinders Resistant Line rats. Only the Flinder Resistant Line rats showed a small, but significant increase in locomotor activity after the administration of ethanol. The highest dose of ethanol (1.0 g/kg) produced locomotor depression in all lines except the P and NP lines, which were not tested at this dose. These findings do not support a link between locomotor stimulation by ethanol and ethanol preference. In contrast, all lines exhibited locomotor stimulation after moderate (0.1-0.3 mg/kg) doses of MK-801, but did not exhibit increases in activity following any dose of chlordiazepoxide. These data indicate that the profiles of activity after MK-801 and chlordiazepoxide were distinct from that of ethanol in the various rat lines.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic influences on locomotor activating effects of ethanol and sodium pentobarbital

The paradoxical capability of sedative-hypnotics to produce behavioral disinhibition varies among genotypes. In DBA/2 mice ethanol (ETOH) produced strong locomotor stimulation with the peak of the biphasic curve at 1.5 g/kg IP. C57BL/6 mice showed no activation, and F1S were intermediate. These characterizations held for a variety of behavioral indices derived from 15 min tests, such as distance, speed, and rest time, at doses in the 0-2.0 g/kg range. Analogous studies with sodium pentobarbital (0-40 mg/kg) yielded a similar pattern of strain differences in locomotor stimulation. In contrast, loss of righting reflex durations (60 mg/kg PENTO, IP) were similar in the two strains, indicating dissociation of activating and sedative effects. In complementary studies, long- and short-sleep mice, which were bred for differences in soporific effects of ETOH, showed similar activation profiles at ETOH doses up to 1.5 g/kg and PENTO doses up to 30 mg/kg. These studies provide support for an hypothesis of common genetic control of the activation effect for ETOH and PENTO.

Differential activating effects of ethanol in C57BL/6Abg and DBA/2Abg mice

A characteristic pattern of ETOH-induced locomotor activation in the DBA/2Abg strain (D2), small activation or sedation in the C57BL/6Abg (B6), and an intermediate position of the F1s was found using a between-group design and 1.5 g/kg ETOH. This pattern was consistent for a variety of behavioral indices not previously examined, including distance, rest time, movement speed and length, as well as the traditional horizontal counts. Using a within-subject, multiple day, repeated-testing procedure, the same three genotypes were also assessed after manipulating drug administration order, where ETOH exposure (1.5 g/kg) was on either the first or second test day. Another experiment examined the effect of lighting level on the response to 1.5 g/kg ETOH using a within-subjects approach. Neither the testing order nor lighting condition had any major influence on the magnitude of activation as measured by locomotor activity (distance). The pattern of additive genotypic influences exhibited by the B6, D2, and F1 mice is remarkably resistant to these contextual and procedural manipulations.

Comparisons of subcolonies of selectively bred long-sleep and short-sleep mice

The Albany subcolony of the selectively bred Long- and Short-Sleep mice was directly compared to the original Colorado colony. As expected from the additional selection applied to the Colorado colony, small differences in the selection phenotype, loss of the righting reflex duration following ethanol treatment, were observed in the Short-Sleep line. However, no colony differences existed in three other indices of ethanol effects. Clear line differences in the shape of the locomotor activity dose-response curve, thermoregulatory effects of ethanol, and ethanol elimination rate replicated earlier findings, but these differences were similar in the two colonies. These data argue for stability of the polygenic control system and provide a picture of remarkable similarity of the two sublines, which were separated by more than 30 generations.

Differences in ethanol-induced behaviors in normal and acatalasemic mice: systematic examination using a biobehavioral approach

In studies designed to further examine the previously reported involvement of catalase in ethanol-induced effects, we attempted to confirm earlier observations by using normal (C3H-N) and acatalasemic (C3H-A) mice. These mice are identical in every respect and differ only in their catalase activity. Data suggested that the application of 3-amino-1,2,4-triazole (AT), a catalase inhibitor, to both substrains of mice resulted in a proportional decrease in motor activity, thus supporting our earlier observations. We also showed that this effect was specific to ethanol because AT did not have any effect on cocaine-induced motor activity in both substrains. Contrary to the effects of ethanol, these substrains did not differ in motor activity in response to cocaine. In an additional study, we observed that acatalasemic mice differed from the normals in their pattern of voluntary ethanol consumption. Acatalasemic mice consumed more ethanol but only when it was presented in the range of concentrations between 12 and 18%. Finally, we also obtained data suggesting that acatalasemic mice have longer duration of sleep time following ethanol administration compared to normals. Catalase activity was measured in both substrains. Results, once again, confirmed earlier data that the substrains differ in this activity and that AT further decreases brain catalase activity in both mice. Finally, when brain homogenates derived from both substrains were incubated with ethanol significant differences in the amount of generated acetaldehyde were found between the two mice strains. Together, these results provide strong support for the involvement of brain catalase in a variety of ethanol-induced behavioral effects.

Genetic correlations among ethanol-related behaviors and neurotensin receptors in long sleep (LS) x short sleep (SS) recombinant inbred strains of mice

Studies were designed to examine the hypothesis that genetic based differences in sensitivity to several behavioral effects of ethanol are mediated, in part, by shared genes and that some of ethanol's actions are mediated by brain neurotensinergic processes. In these studies we have used recombinant inbred (RI) strains of mice derived from Long Sleep (LS/Ibg) and Short Sleep (SS/Ibg) lines of mice. The LS and SS mice were selectively bred to differ in hypnotic sensitivity but also differ in hypothermia and locomotor effects of ethanol. Therefore LS x SS RI strains were used to answer the question whether there are shared genetic influences on these diverse ethanol actions. Moreover, since the LS and SS mice were found to differ in neurotensin (NT) receptor densities in various brain regions, the LS x SS RI strains were used to determine associations between NT receptor densities and ethanol actions. The results showed a significant genetic correlation (r = .38) between hypnotic sensitivity and low-dose locomotor effects of ethanol and indicated multigenetic influences, with estimates of seven, four and three genes being responsible for mediating differences in hypnotic, hypothermic, and locomotor effects of ethanol, respectively. The findings are consistent with one or more genes having pleiotropic effects on these ethanol actions.

Selective breeding, congenic strains, and other classical genetic approaches to the analysis of alcohol-related polygenic pleiotropisms

Dimensions of behavioral sensitivities to alcohol in mice are under control of polygenic systems of relatively small size. The mode of inheritance of these phenotypes is frequently additive, with no evidence of dominance, epistasis, or sex linkage. The utility of classical breeding methodologies, such as selection, for assessment of genetic correlations is reviewed. A distinction is drawn between pleiotropisms in these polygenic systems, and the statistical concept of a genetic correlation. Development of congenic strains is argued to be a powerful alternative methodology, heretofore unused in alcohol pharmacogenetics. Using the phenotype of behavioral activation produced by a low dose of ethanol, we describe the production of an activated congenic strain on the non-activated background of the C57BL/6 mouse strain. Through five generations of repeated backcrossing, from a genetically heterogenous stock, "activational" alleles are being successfully transferred to the C57BL/6 background. Theoretical issues in the creation of congenic strains in potentially polygenic systems are covered, including number of effective loci and heritability.

Genetic analyses of the biphasic nature of the alcohol dose-response curve

Ethanol (ETOH)-induced locomotor activation and depression were studied in 23 genotypes of mice. This included a diallel cross of four inbred strains tested with a range of ETOH doses from 0 to 2.75 g/kg. The diversity in shapes of the biphasic ETOH dose-response curves was both qualitative and quantitative, and additive gene action characterized the genetic control of the dose-response curve. Small dominance effects were typically directional in the direction of more activation, or resistance to sedation. No evidence was found for maternal effects, sex linkage, or epistasis. Sex differences were seen in the increased susceptibility of male mice to locomotor sedation at higher ETOH doses. In the diallel cross, there was no correlation between the degree of activation produced by low ETOH doses and sedation produced by higher doses. This indicates that while considerable genetic influences exist for both activational and sedative domains of ETOH effects, these genetic influences are relatively independent.

Locomotor activity responses to ethanol in selectively bred long- and short-sleep mice, two inbred mouse strains, and their F1 hybrids

Locomotor activity responses to sub-hypnotic doses of ethanol (ETOH) were assessed in selected lines of mice (LS and SS), inbred strains, and their F1 hybrids. Data were obtained as photocell beam interruptions in a 15-min test for a dose range of 0 to 2.75 or 3.5 g/kg for LS and SS mice, respectively. Biphasic dose-response curves were obtained for LS and SS mice with the SS mice showing a sedative limb of the dose-response curve shifted to the right. The effects of 2.0 g/kg ETOH were also assessed in a diallel cross of the selected LS/SS lines and C57BL/6Abg and MOLD/RkAbg inbred strains. The 2.0 g/kg dose produced a wide range of responses, from sedation in C57BL/6Abg mice to extreme activation in SS and MOLD/RkAbg mice, and no effect in LS mice. The responses of F1 hybrids reflected a typical pattern of partial dominance, with heterosis in some crosses. When present, dominance was in the direction of greater locomotor activation. These patterns were confirmed by biometrical genetic analysis of the 4 x 4 diallel cross of the two lines and the two inbred strains. The data indicate that loci in addition to those responsible for selection for sedative sensitivity in LS and SS mice can influence locomotor activation produced by sub-hypnotic ETOH doses, and that SS and MOLD mice show locomotor activation for different genetic reasons.

Evidence that genetic differences in habituation and GABAergic mechanisms may be related to sensitivity to ethanol and development of ethanol tolerance in mice

Habituation to a test environment following daily exposure for 5 days was examined in three genetically different strains of mice. C57 animals showed significant habituation to the new environment already on the second day. The habituation of NMRI mice was significant on the third day, whereas CBA mice showed no habituation at all during the experimental period. There was no difference between the animal strains in learning capacity in a passive avoidance test, but CBA mice displayed a significant increase in latency in their performance. When tested for sensitivity to the convulsant actions of GABAergic antagonists, picrotoxin produced seizures at lower doses in CBA as compared to NMRI and C57 mice, whereas there was no difference between the strains in the seizure activity produced by the specific GABA receptor antagonist bicuculline. When the animals were tested for sensitivity to ethanol in a horizontal wire test, ethanol (2 g/kg, IP) produced muscle relaxation in CBA mice whereas the performance of NMRI and C57 was not affected. A large dose of ethanol (4 g/kg, IP) produced a significantly longer sleeping time in CBA mice as compared to NMRI and C57 animals. Ethanol-produced hypothermia was, however, similar in all animals. Environment-dependent development of tolerance to ethanol following daily injections of ethanol for 4 days was examined. C57 mice showed the most rapid development of tolerance towards ethanol's hypnotic actions, whereas CBA mice showed no tolerance to this effect of ethanol. No difference between the strains to the development of tolerance to ethanol's hypothermic effects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinctions among sedative, disinhibitory, and ataxic properties of ethanol in inbred and selectively bred mice

Three different domains of behavioral action of ethanol (ETOH) were examined in a battery of seven inbred strains and in the selectively bred Long-Sleep (LS) and Short-Sleep (SS) mice. Sedative effects were examined with the loss of the righting reflex test at 3.8 g/kg. The variation among inbred strains was only half the size of the difference between LS and SS mice which were selectively bred for extremes in this phenotype; such a result is expected for phenotypes controlled polygenically. Blood ETOH levels at waking from the narcosis also showed a range of differences among the inbred strains that was less than the LS/SS difference. Ataxia was measured with the grid test, and the inbred strains fell into two groups, resembling the highly ataxic LS line, and the less ataxic SS line. Biphasic effects of ETOH on locomotor activity were strongly genotype dependent. Variation in degree of activation/disinhibition produced by doses up to 1.5 g/kg (IP) ranged from no activation, in the C57BL/6Abg strain which was larger than that seen for SS mice. The patterns of strain differences for both ataxia and activation were highly different from the duration of loss of righting reflex measure, suggesting multiple independent genetically based "sensitivities" to ETOH.

Selected mouse lines, alcohol and behavior

The technique of selective breeding has been employed to develop a number of mouse lines differing in genetic sensitivity to specific effects of ethanol. Genetic animal models for sensitivity to the hypnotic, thermoregulatory, excitatory, and dependence-producing effects of alcohol have been developed. These genetic animal models have been utilized in numerous studies to assess the bases for those genetic differences, and to determine the specific neurochemical and neurophysiological bases for ethanol's actions. Work with these lines has challenged some long-held beliefs about ethanol's mechanisms of action. For example, lines genetically sensitive to one effect of ethanol are not necessarily sensitive to others, which demonstrates that no single set of genes modulates all ethanol effects. LS mice, selected for sensitivity to ethanol anesthesia, are not similarly sensitive to all anesthetic drugs, which demonstrates that all such drugs cannot have a common mechanism of action. On the other hand, WSP mice, genetically susceptible to the development of severe ethanol withdrawal, show a similar predisposition to diazepam and phenobarbital withdrawal, which suggests that there may be a common set of genes underlying drug dependencies. Studies with these models have also revealed important new directions for future mechanism-oriented research. Several studies implicate brain gamma-aminobutyric acid and dopamine systems as potentially important mediators of susceptibility to alcohol intoxication. The stability of the genetic animal models across laboratories and generations will continue to increase their power as analytic tools.

Increased stimulatory effect by the combined administration of cocaine and alcohol in mice

Locomotor activity was recorded after 5-30 mg/kg of cocaine in mice pretreated or not with a stimulant dose of ethanol (2.0 g/kg). The increase in locomotion induced by the association of cocaine plus ethanol was significantly larger when compared to either the group injected with only cocaine or only ethanol.

Response variability of ethanol-induced locomotor activation in mice

Mice from a randomly bred strain were divided into two groups according to their locomotor responses to ethanol (0.8-3.0 g/kg): in two thirds of the tested animals ethanol increased locomotor activity (ethanol activated-EA), whereas in the remaining one third it did not (ethanol non-activated-ENA). Both groups did not differ in their locomotor activity after saline administration. Furthermore, EA and ENA mice presented a similar increase in locomotor activity after challenge with 1.0 and 2.0 mg/kg d-amphetamine. Chronic exposure to ethanol increased the ethanol-induced locomotor activation in both EA and ENA groups. The possibility that the lack of responsiveness of ENA mice to ethanol's acute activating effect could be due to a higher sensitivity to the depressant effect of ethanol is discussed.

Calcium differentially alters behavioral and electrophysiological responses to ethanol in selectively bred mouse lines

Sensitivity to the hypnotic action of ethanol has been found to increase in SS/Ibg (SS) but not in LS/Ibg (LS) mice after intracerebroventricular (icv) administration of calcium. In the present investigation, a correlation was found between calcium-induced changes in behavioral sensitivity and in the sensitivity of cerebellar Purkinje neurons to the depressant effects of locally applied ethanol. Cerebellar Purkinje neuron sensitivity was measured as the dose of ethanol pressure ejected from a multibarreled micropipette required to produce a 50% depression of spontaneous firing rate of single neurons. Administration of 0.2-0.4 mumol calcium chloride into the lateral ventricle of the brain increased the sensitivity of SS but not LS mice to the hypnotic behavioral effect of systemically administered ethanol. Similarly, Purkinje neuron sensitivity to locally applied ethanol was also enhanced in SS but not in LS mice 15 min following administration of calcium (0.25 mumol) icv. Furthermore, locally applied ethanol was more effective in depressing spontaneous Purkinje neuron discharge in SS mice when a 1 mM calcium solution was concomitantly pressure ejected with ethanol from the micropipette. Magnesium chloride did not mimic the effects of calcium on either behavioral or electrophysiological effects of ethanol, suggesting that the action of calcium is not a nonspecific effect of divalent cations. These data suggest that calcium-dependent processes may be involved in behavioral and electrophysiological effects associated with ethanol intoxication. Further research will be required to determine if the genetically selected difference in ethanol sensitivity expressed in LS and SS mice is regulated by calcium mechanisms.

The effects of ethanol on exploration in DBA/2 and C57Bl/6 mice

The effect of ethanol (0.8, 1.6, and 2.4 g/kg) was assessed on the behavior of DBA/2 and C57Bl/6 mice in a holeboard test. Ethanol caused a dose-related decrease in the locomotor activity of the C57Bl/6 mice, and the highest dose also significantly decreased exploratory head-dipping. In contrast ethanol significantly increased the locomotor activity of DBA/2 mice. Only the lowest dose, however, significantly increased exploratory head-dipping, and the highest dose caused a marked decrease in exploration. These results emphasize the importance of distinguishing between the effects of ethanol on locomotor and exploratory activities.

The excitatory effect of ethanol: absence in rats, no tolerance and increased sensitivity in mice

Three questions related to ethanol's stimulating effect (ESE) were studied. The first referred to the reported absence of tolerance to ESE in mice. It was determined whether tolerance would develop if the period of ethanol treatment were extended significantly beyond those normally found in the literature. No evidence of tolerance to ESE was found over a 5-month period of treatment. The second issue related to the possibility that mice not only do not develop tolerance but actually become more responsive to ESE after chronic exposure. A dose of ethanol that acutely did not produce a significant activating effect did induce a marked excitation after the animals were chronically treated with ethanol. Finally, the issue was addressed of whether the absence of ESE in some strains of rats could in part be due to a masking effect by the depressant component of this drug. To test this possibility rats were treated with ethanol for a 4-month period. Tolerance to the depressant effect was observed but no ESE was detected.

An evaluation of the role of ethanol clearance rate in the differential response of long-sleep and short-sleep mice to ethanol

Ethanol (ETOH) clearance rates were determined in Long-Sleep (LS) and Short-Sleep (SS) mice, which were selectively bred for differential soporific response to ETOH. Determination of blood ethanol levels at 45 min intervals following administration of 3.8 g/kg IP indicated that SS mice clear ETOH at a faster rate. Repeatedly sampled mice of each line cleared ETOH more slowly than those where samples were taken only once. A second experiment utilized pairs of LS and SS mice matched on body weight. These were treated with one of several doses of ETOH, and duration of loss of the righting reflex measured for one member of the pair. Blood ETOH levels were determined in samples taken from both members of the pair when the tested member regained the righting reflex. LS mice had small but consistently higher blood ETOH levels in these pairs. The magnitude of the differences between the LS and SS mice in these experiments indicate that clearance rate differences can account for only a small portion of the differences in behavioral responses of these mice to ETOH.