The swift increase in alcohol metabolism (SIAM) in four inbred strains of mice

Overview of mouse assays of ethanol intoxication

There are many behavioral assays to assess sensitivity to ethanol intoxication in mice. Most are simple to implement, and are sensitive to a particular dose range of ethanol. Most reflect genetic influences, and each test appears to reflect the contribution of a relatively distinct collection of genes. This genetic heterogeneity implies that no single test can claim to capture the construct "ethanol intoxication" completely. Depending on the test, and when measurements are made, acute functional tolerance to even a single dose of ethanol must be considered as a contributing factor. Whether or not a test is conducted in naïve mice or as part of a test battery can influence sensitivity, and do so in a strain-dependent manner. This unit reviews existing tests and recommends several.

Rates of ethanol metabolism decrease in sons of alcoholics following a priming dose of ethanol

Rapid changes in rates of ethanol metabolism in response to acute ethanol administration have been observed in animals and humans. To examine whether this phenomenon might vary by risk for alcoholism, 23 young men with a positive family history of alcoholism (family history positive [FHP]) were compared to 15 young men without a family history of alcoholism (family history negative [FHN]). Rates of ethanol metabolism were measured in all subjects first after an initial ethanol dose (0.85 g/kg) and then, several hours later, a second dose (0.3 g/kg), and the two rates were compared. The two groups of subjects were similar in their histories of ethanol consumption. FHP subjects demonstrated faster initial rates of ethanol metabolism, 148+/-36 mg/kg/h, compared to FHN subjects, 124+/-18 mg/kg/h, P=.01. However, FHN subjects increased their rate of metabolism by 10+/-27% compared to a decrease of -15+/-24% in FHP subjects, P=.007. Fifty-two percent of the FHP and none of the FHN subjects exhibited a decline in metabolic rate of 20% or more, P=.0008. Since a significant proportion of FHP subjects exhibited a decrease in the second rate of ethanol metabolism, these preliminary data might help to partly explain why FHP individuals differ in their sensitivity to ethanol and are more likely to develop alcohol dependence.

Schedule-induced ethanol self-administration in DBA/2J and C57BL/6J mice

BACKGROUND

The purpose of these experiments was to provide an initial investigation into ethanol self-administration elicited in the schedule-induced polydipsia (SIP) paradigm.

METHODS

Mature male mice were food deprived to between 80 and 85% of their baseline weight and received 20 daily 1 hr SIP test sessions in which a food pellet (20 mg) was delivered on a fixed-time 60 sec schedule. In different groups, the acquisition of drinking 5% (v/v) ethanol solution (experiment 1) or water (experiment 2) was recorded along with other behaviors that occurred in the test chambers.

RESULTS

Results indicated that C57BL/6J mice drank significantly more ethanol than DBA/2J mice and that C57 mice achieved blood alcohol concentrations as high as 300 mg/dl. Blood alcohol concentrations were consistently correlated with g/kg ethanol intake. The groups did not differ in consumption of water. SIP test sessions using higher concentrations of ethanol (10-20% v/v, experiment 1) or sucrose solutions (0.1-2% w/v, experiment 2) then were performed. Group differences in ethanol consumption were maintained at all ethanol concentrations. Although DBAs drank more of a low concentration of sucrose (0.1%), when expressed as g/kg, sucrose intake was equivalent in the two strains at all concentrations. Analysis of the time course of drinking clearly showed that this behavior was adjunctive in nature.

CONCLUSION

These results demonstrate the effectiveness of this procedure in inducing ethanol self-administration and its utility for investigating the genetic bases of vulnerability toward excessive ethanol consumption.

Role of alcohol dehydrogenase in the swift increase in alcohol metabolism (SIAM). Studies with deer mice deficient in alcohol dehydrogenase

Previous studies have shown that rates of ethanol metabolism increase markedly 2-4 hr after the administration of ethanol in rats and in four inbred strains of mice. This phenomenon, called the swift increase in alcohol metabolism (SIAM), also exists in humans. To determine whether alcohol dehydrogenase (ADH) is necessary for the SIAM response, we compared ethanol metabolism in two strains of the deer mouse, Peromyscus maniculatus. One strain lacks alcohol dehydrogenase (ADH-negative), whereas the other strain has normal ADH levels (ADH-positive). Rates of ethanol elimination were determined after a single intraperitoneal injection of ethanol at different doses (0.5 to 3.0 g/kg) and also after both strains were exposed to various levels of ethanol vapor for 4 hr. The ADH-positive strain exhibited up to a 72% increase in the rate of ethanol elimination after exposure to ethanol vapor compared to the ethanol-injected controls. In contrast, treatment with ethanol vapor did not alter rates of ethanol elimination in the ADH-negative strain. These data demonstrate clearly that ADH is required for SIAM in the deer mouse. In addition, in both the ADH-positive and the ADH-negative strain, rates of ethanol elimination increased in both the ethanol-injected and vapor-treated groups 2- to 3-fold as the dose of ethanol was increased from 100 to 500 mg/100 ml. Thus, it is concluded that this "concentration effect" of ethanol on rates of ethanol metabolism does not involve ADH in the . deer mouse.

Genetic considerations in the effects of ethanol in mice. II. A trans-acting inducibility regulator(s) affecting alcohol dehydrogenase (ADH) activity

The inducibility of alcohol dehydrogenase (ADH) has been recognized in different systems including maize, Drosophila, and mice. Our earlier results showed strain-specific ADH responses to chronic ethanol administration relative to matched littermate controls in mice. For this study we used two strains which showed "induction" (BALB/c and S.W.) and two strains which showed "repression" (C57BL/6J and 129/ReJ) to produce three sets of F1 hybrids and their reciprocals and one set (BALB/c X C57BL/6J) of recombinant inbred (RI) lines. The ADH properties of the resulting genotypes were again evaluated following 15% ethanol treatment in drinking water (2 weeks) in relation to their littermate matched controls in replicated trials. Our F1 results suggest complete dominance for induction over repression at the phenotypic level, and the two repressed strains showed complementation. No significant differences were observed in the reciprocal F1's and all pairs of a given genotype-treatment combination yielded consistent results. The 1:1 segregation of RI lines suggests a single gene difference for ADH inducibility between BALB/c and C57BL/6J. These findings suggest the presence of a trans-acting inducibility regulator(s) for ADH which may or may not represent a single locus. Variability for such regulatory elements may provide an explanation for the commonly observed individual differences in natural populations for response to alcohol including alcohol metabolism.