Acute Functional Tolerance to Ethanol and Fear Conditioning Are Genetically Correlated in Mice

A major QTL for acute ethanol sensitivity in the alcohol tolerant and non-tolerant selected rat lines

The Alcohol Tolerant and Alcohol Non-Tolerant rats (AT, ANT) were selectively bred for ethanol-induced ataxia as measured on the inclined plane. Here we report on a quantitative trait locus (QTL) study in an F(2) intercross population derived from inbred AT and ANT (IAT, IANT) and a follow-up study of congenics that were bred to examine one of the mapped QTLs. Over 1200 F(2) offspring were tested for inclined plane sensitivity, acute tolerance on the inclined plane, duration of the loss of righting reflex (LORR) and blood ethanol at regain of the righting reflex (BECRR). F(2) rats that were in the upper and lower 20% for inclined plane sensitivity were genotyped with 78 SSLP markers. Significant QTLs for inclined plane sensitivity were mapped on chromosomes 8 and 20; suggestive QTLs were mapped on chromosomes 1, 2 and 3. Highly significant QTLs for LORR duration (LOD = 12.4) and BECRR (LOD = 5.7) were mapped to the same locus on chromosome 1. Breeding and testing of reciprocal congenic lines confirmed the chromosome 1 LORR/BECRR QTL. A series of recombinant congenic sub-lines were bred to fine-map this QTL. Current results have narrowed the QTL to an interval of between 5 and 20 Mb. We expect to be able to narrow the interval to less than 5 Mb with additional genotyping and continued breeding of recombinant sub-congenic lines.

Short-term selection for acute ethanol tolerance and sensitization from an F2 population derived from the high and low alcohol-sensitive selectively bred rat lines

Previous studies have identified quantitative trait loci (QTL) in the inbred high and low alcohol-sensitive rat (IHAS1 and ILAS1) strains. The original development of the strains involved selection for ethanol sensitivity based on duration of the loss of the righting reflex (LORR) after a standard dose of ethanol. This paper confirms some of these QTL using a short-term selection procedure based on the difference between the blood ethanol level at LORR and regain of the righting response. An F(2) population of rats was developed by a reciprocal cross of IHAS1 and ILAS1 rats. Selection for five generations was carried out using delta-blood ethanol concentration (dBEC) as the selection trait, where dBEC=BECLR (BEC at loss of righting reflex)-BECRR (BEC at regain of righting reflex). The lines were labeled tolerant (TOL) or sensitive (SENS). Approximately one-third of the offspring for each generation in each line were genotyped using DNA markers that had been previously found to be linked to QTL on chromosomes 1, 2, 5, 12, and 13. By the fifth generation of selection, the lines showed a very large difference in dBEC, BECRR, and duration of LORR; BECLR showed little segregation during the selection, and latency to lose the righting reflex showed none. IHAS allele frequency increased in the SENS line for markers on chromosomes 1, 5, 12, and 13 while ILAS allele frequency increased in the TOL line. These results were in good agreement with the two previous QTL studies. On chromosome 2, the selection resulted in an accumulation of ILAS alleles in both lines. This study provides independent confirmation of the location of QTL on chromosomes 1, 5, 12, and 13 for ethanol sensitivity. It also suggests that genetic differences in duration of LORR are mediated primarily by the dBEC phenotype.

Does Scopolamine Block the Development of Ethanol-Induced Behavioral Sensitization?

BACKGROUND

The cholinergic system is important in learning processes and probably influences behavioral sensitization to drugs. This study examined the effects of scopolamine (scop), a muscarinic antagonist, on the behavioral sensitization to ethanol (EtOH) stimulant effect in mice.

METHODS

In experiments 1 and 2, male Swiss albino mice received saline or 1.0 mg/kg scop (s.c.) + saline or EtOH (i.p). (1.0 g/kg in experiment 1 and 2.2 g/kg in experiment 2), for 21 days. Locomotor activity (LA) was recorded once a week, being the treatment withdrawn for 7 days after the last test. On the 28th day (challenge 1), they were evaluated under saline or EtOH. In experiment 2, 3 days after the first challenge, they were tested in an open-field arena, under saline or 2.2 g/kg EtOH. Three days after this, mice were tested under saline or 1.0 mg/kg scop in the activity cages.

RESULTS

Acutely, EtOH and scop did not alter the LA. However, when both drugs were coadministered, a significant reduction was observed. During the treatment, tolerance to the depressor effect was developed and behavioral sensitization observed only in the saline + 2.2 EtOH group. In challenge 1, the groups scop + 1.0 EtOH, saline + 2.2 EtOH, and scop + 2.2 EtOH presented higher levels of LA than that of the control groups. However, in challenge 2, conducted in a different setting, no differences between groups were observed. In challenge 3, when the animals received scop, both groups pretreated with 2.2 g/kg EtOH (saline + 2.2 EtOH and scop + 2.2 EtOH groups) presented higher levels of activity suggesting an interaction between EtOH and scop.

CONCLUSIONS

Although the coadministration of scopolamine had impaired the observation of sensitization on the 21st day test, when the group scop + EtOH was challenged with scop + EtOH, it seems that the scop just masked the observation, but did not impair the development, of the EtOH-sensitization observed in the challenge with EtOH alone. The higher levels of LA in groups pretreated with EtOH only in the cages but not in the open-field arena confirm the importance of environmental factors, such as the context of drug administration and testing.

Rapid ethanol tolerance mediated by adaptations in acute tolerance in inbred mouse strains

It has been postulated that decreased acute sensitivity to ethanol is an important genetically-mediated risk factor for the development of alcoholism. Previous work in mice and rats has indicated that ethanol sensitivity can be reduced in a genotype-dependent manner by a single dose of ethanol 24 h prior to testing, so-called 'rapid' tolerance. The current studies were undertaken to determine if the observed rapid tolerance was mediated by alterations in initial sensitivity or acute functional tolerance (AFT), the two primary components of acute sensitivity. Separate groups of C57BL/6, DBA/2, ILS, and ISS inbred mouse strains were administered a single pretreatment dose of saline or ethanol (5 g/kg). The original and modified versions of the loss of righting reflex test, ethanol-induced hypothermia, and ataxia on a stationary dowel rod were tested 24 h later. Dependent on the test and strain, varying degrees of rapid tolerance were observed; a pronounced sensitization was detected in one case. There was a concomitant increase in the rate and/or magnitude of AFT with little change in initial sensitivity suggesting that rapid tolerance was mediated primarily by alterations in AFT. This conclusion may have implications for the contribution of acute sensitivity to human alcoholism.

Is behavioral sensitization to ethanol associated with contextual conditioning in mice?

Behavioral sensitization to drugs of abuse seems to involve learning processes. In mice, ethanol-induced locomotor sensitization is potentiated by repeated pairing of ethanol (EtOH) injections and the testing chamber. The present study aimed to test: (1). the association between the performance in a contextual conditioning task and the development of behavioral sensitization to EtOH in mice; (2). whether EtOH sensitization would be expressed in a different testing environment. Male albino Swiss mice (n=72) were initially submitted to a contextual fear conditioning task. After 2 weeks without manipulation, the animals received daily i.p. injections of 2.2 g/kg EtOH (n=52) or saline (n=20), for 21 days. They were tested weekly for locomotor activity in activity cages. After 1 week of withdrawal, all mice received 2.2 g/kg EtOH and had their locomotor activity recorded in an open-field. According to the locomotor behavior displayed along the 21-day treatment, EtOH-treated mice were classified as sensitized (n=15) or non-sensitized (n=15). When these subgroups and saline-treated mice were compared for the freezing response in the conditioning test, sensitized mice displayed a greater freezing time than non-sensitized mice. When challenged with EtOH in the open-field, none of the EtOH-treated subgroups expressed behavioral sensitization. These results suggest that the development of EtOH sensitization seems to be positively associated with contextual learning, and further confirms that the expression of sensitization is highly dependent on contextual cues.

Quantitative genetics and mouse behavior

Quantitative differences are observed for most complex behavioral and pharmacological traits within any population. Both environmental and genetic influences regulate such individual differences. The mouse has proven to be a superb model in which to investigate the genetic basis for quantitative differences in complex behaviors. Genetically defined populations of mice, including inbred strains, heterogeneous stocks, and selected lines, have been used effectively to document these genetic differences. Recently, quantitative trait loci methods have been applied to map the chromosomal regions that regulate variation with the goal of eventually identifying the gene polymorphisms that reside in these regions.

Alcohol tolerance and nicotine cross-tolerance in adolescent mice

The present experiment was designed to evaluate the development of tolerance to alcohol and cross-tolerance to nicotine in adolescent mice. C57BL/6J mice (30-40 days old) were injected IP with alcohol (2.5 g/kg) for 4 consecutive days. A control group received four saline injections. On the test day, all subjects received an alcohol injection. Tolerance to alcohol's hypothermic effect was observed. Mice (male and female) exposed to alcohol for the 4 previous days showed less hypothermic response to an alcohol challenge than animals injected for 4 days with saline and then challenged with alcohol. Tolerance to alcohol's motor incoordinating effects and differences in blood alcohol concentrations were not observed. Thirty days following alcohol treatment, the same mice received a single nicotine injection (1 mg/kg) to assess cross-tolerance. Nicotine's effect on locomotor activity (open field test) and rectal temperature varied as a function of prior adolescent alcohol exposure and gender. Specifically, female mice who had been exposed to alcohol administrations were more resistant to nicotine's effect on locomotion and temperature than saline-treated animals. In summary, these data demonstrate that adolescent mice develop tolerance to some, but not all, alcohol-induced responses, and that female mice are cross-tolerant to nicotine's effects on temperature and activity.

Congenic strains developed for alcohol- and drug-related phenotypes

Quantitative trait loci (QTLs) for many alcohol- and drug-related traits have been mapped using well-accepted mapping techniques. The ultimate goal of gene identification necessitates confirmation of the QTL and reduction of the interval surrounding the QTL; both can be accomplished in congenic strains. These strains carry a chromosomal region introgressed from a donor strain onto the genetic background of a second, recipient strain. Multiple generations of backcrossing reduce the unlinked donor genome to less than 0.1%. Then, phenotypic comparisons between mice congenic for the donor region and controls from the recipient strain allow confirmation of the QTL effect. Animals with recombinations in the donor region can be used to generate interval-specific congenic recombinant lines. Numerous congenic strains are currently being developed in which chromosomal regions carrying QTLs for alcohol- and drug-related traits have been transferred from one strain onto a second strain. The purpose of this review is to summarize the chromosomal regions, donor and recipient strains, and results obtained from these congenics. Most researchers developing such strains are willing to share these resources to facilitate localization of the genetic bases of other phenotypes.

Peptide signaling paths related to intoxication, memory and addiction

Abstract Many peptides bind to G protein-coupled receptors and activate intracellular signaling paths for adaptive cellular responses. The components of these paths can be affected by signals from other neurotransmitters to produce overall integrated results not easily predicted from customary a priori considerations. This intracellular cross-talk among signaling paths provides a "filter" through which long-term tonic signals affect short-term phasic signals as they progress toward the nucleus and induce long-term adaptation of gene expression which provide enduring attributes of acquired memories and addictions. Peptides of the PACAP family provide intracellular signaling that involves kinases, scaffolding interactions, Ca2 + mobilization, and gene expression to facilitate development of tolerance to alcohol and development of associative memories. The peptide-induced enhancement of NMDA receptor responses to extracellular glutamate also may increase behavioral sensitization to the low doses of alcohol that occur at the onset of each bout of drinking. Because many gene products participate in each signaling path, each behavioral response to alcohol is a polygenic process of many steps with no single gene product sufficient to interpret fully the adaptive response to alcohol. Different susceptibility of individuals to alcohol addiction may be a cumulative result of small differences among the many signaling components. Understanding this network of signals may help interpret future "magic bullets" proposed to treat addiction.