Genetic-environment analysis of sensitivity and acute tolerance to ethanol in mice

Age differences in the expression of acute and chronic tolerance to ethanol in male and female rats

BACKGROUND

Ontogenetic differences in response to ethanol (EtOH) challenge have been observed under a variety of circumstances, including varying reports of developmental differences in the expression of tolerance to EtOH. The purpose of the present experiment was to further explore potential differences in acute (AT) and chronic (CT) tolerance expression between adolescent and adult, male and female Sprague-Dawley rats, using the social interaction test.

METHODS

AT and CT to the social suppressing effects of a moderate dose of EtOH was assessed in adolescent and adult rats following intraperitoneal injections of 2.0 g/kg EtOH or saline daily for 10 days. At test, adults and adolescents were challenged with 1.0 or 1.25 g/kg EtOH, respectively, with AT and CT assessed at 5 and 25 minutes postinjection using ratios of impairment to brain ethanol concentrations (BrECs) at each time period (CT) and within-session declines in impairment relative to BrECs (AT).

RESULTS

In adolescents, 10 days of EtOH pre-exposure resulted in evidence of CT at 25 minutes postinjection, perhaps associated with an enhanced expression of AT. Among adults, signs of CT were seen at 5 minutes postinjection in adults, and may reflect neuroadaptations unassociated with AT, as with evidence of tolerance emerging only in adult control animals repeatedly exposed to saline injection prior to EtOH challenge on test day. Sex differences in tolerance expression were not observed at either age.

CONCLUSIONS

Our results show ontogenetic differences between adolescents and adults in the short- and long-term neuroadaptations that they express in response to repeated perturbations with EtOH. Together these findings add age of exposure and time of testing within the intoxication period as critical variables to be considered when exploring the complex relationship between AT and CT.

Chronic ethanol intake alters circadian phase shifting and free-running period in mice

Chronic alcohol intake is associated with widespread disruptions in sleep and circadian rhythms in both human alcoholics and in experimental animals. Recent studies have demonstrated that chronic and acute ethanol treatments alter fundamental properties of the circadian pacemaker--including free-running period and responsiveness to photic and nonphotic phase-shifting stimuli--in rats and hamsters. In the present work, the authors extend these observations to the C57BL/6J mouse, an inbred strain characterized by very high levels of voluntary ethanol intake and by reliable and stable free-running circadian activity rhythms. Mice were housed individually in running-wheel cages under conditions of either voluntary or forced ethanol intake, whereas controls were maintained on plain water. Forced ethanol intake significantly attenuated photic phase delays (but not phase advances) and shortened free-running period in constant darkness, but voluntary ethanol intake failed to affect either of these parameters. Thus, high levels of chronic ethanol intake, beyond those normally achieved under voluntary drinking conditions, are required to alter fundamental circadian pacemaker properties in C57BL/6J mice. These observations may be related to the relative ethanol insensitivity displayed by this strain in several other phenotypic domains, including ethanol-induced sedation, ataxia, and withdrawal. Additional experiments will investigate chronobiological sensitivity to ethanol in a range of inbred strains showing diverse ethanol-related phenotypes.

Housing and rank status of male Long-Evans rats modify ethanol's effect on open-field behaviors

RATIONALE

Psychosocial stress is known to alter behavior of rodents. While psychosocial stress may alter the response to some drugs, the response to ethanol (EtOH) has not been evaluated.

OBJECTIVE

To examine open-field behaviors of triad- and singly housed rats treated acutely or voluntarily ingesting EtOH.

METHOD

Triad-housed rats were categorized as dominant, subdominant, or subordinate based on assessments of offensive and defensive behaviors. Open-field behaviors were monitored during a 10-min test in rats voluntarily ingesting a 6% solution of EtOH for 2 weeks (1), and after an i.p. injection of saline, 0.5 or 1.0 g kg(-1) of EtOH (2).

RESULTS

Daily intake of EtOH was highest in subdominant and lowest in dominant rats. Overall, open-field behaviors did not differ between water- and EtOH-consuming triad- or singly housed rats. The 0.5-g kg(-1) dose of EtOH enhanced locomotor activity only in triad-housed rats, center entries primarily in singly housed rats, and head-poke behavior in dominant and singly housed rats. Rearing behavior was not altered by the 0.5-g kg(-1) dose, but in singly housed rats, rearing behavior was depressed by the 1.0-g kg(-1) dose. This larger dose of EtOH had no effect on the other behaviors.

CONCLUSIONS

EtOH's effects on open-field behaviors show behavioral specificity and vary with the subject's housing and/or rank status. EtOH's acute anxiolytic-like effect was primarily evident in singly housed rats.

Comparison of the Onset of Hypoactivity and Anxiety-Like Behavior During Alcohol Withdrawal in Adolescent and Adult Rats

BACKGROUND

Early life alcohol use is associated with increased alcoholism risk. It has been suggested that alterations in the sensitivity of adolescents to the acute effects of ethanol may contribute to this risk by promoting excessive intake. However, an enhanced propensity for developing ethanol dependence or withdrawal-related behavior could also contribute to increased risk. The objective of these studies was to compare the appearance of ethanol withdrawal-related behaviors in adolescent and adult rats.

METHODS

Male Sprague-Dawley rats were exposed to ethanol vapor (12 hr/day) for 12 or 14 days during adolescence or adulthood. In the first study, locomotor activity was assessed after 2, 4, 7, 10, and 14 days of ethanol exposure. In the second study, open field behavior was assessed after 5 or 12 days of ethanol exposure. In follow-up studies, changes in sucrose preference during ethanol withdrawal and motor activity during food restriction were assessed in adolescent rats. Withdrawal assessments were made 7 to 9 hr after daily exposure ended.

RESULTS

Hypoactivity emerged rapidly in adolescent rats during ethanol withdrawal in activity tests, but comparable reductions were not found in adult rats. However, hypoactivity developed in both adolescents and adults in the novel open field. Enhanced anxiety-like behavior in the open field was not observed in either age group during withdrawal. Finally, sucrose preference was unchanged during ethanol withdrawal, and food restriction increased motor activity in adolescent rats.

CONCLUSIONS

These data confirm that symptoms of withdrawal may be differentially expressed in adolescent and adult rats. However, discrepancies in hypoactivity between studies suggest that assessment in a novel versus familiar environment may influence the expression of withdrawal-related behaviors.

Ethanol disrupts fear conditioning in C57BL/6 mice

Ethanol has been demonstrated to disrupt numerous forms of learning. For example, ethanol disrupts fear conditioning in rats. Surprisingly, the opposite result was reported for mice. Because of the importance of mouse models in ethanol research and the predominance of transgenic mice generated on a C57BL/6 background, the present study examined the effects of acute ethanol administration on fear conditioning in C57BL/6 mice. Fear conditioning was chosen because of the apparent contradiction in results between mice and rats, because of its popularity in assessing forebrain-dependent learning and because the task examines two types of learning: (i) the hippocampus-dependent contextual learning and (ii) the hippocampus-independent conditioned stimulus-unconditioned stimulus learning. Dose-response curves were generated for ethanol (0.5, 1.0 and 1.5 g/kg) given on either training day, testing day, or both days. Ethanol, in a dose-dependent manner, disrupted fear conditioning when given on training day or given on both training and testing days. Ethanol given on testing day only did not disrupt fear conditioning. The present results demonstrate that ethanol disrupts fear conditioning in C57BL/6 mice.