Dopaminergic neurons in the ventral tegmental area of C57BL/6J and DBA/2J mice differ in sensitivity to ethanol excitation

BACKGROUND: The mesolimbic dopamine pathway that originates in the ventral tegmental area (VTA) is important for the rewarding effects of ethanol. Ethanol has been shown to excite dopaminergic neurons of the VTA, both in vivo and in vitro, in rats. Behavioral differences in the rewarding effects of ethanol have been observed between C57BL/6J and DBA/2J mice. The present electrophysiological study examined the effect of ethanol on individual dopaminergic VTA neurons from these two inbred mouse strains. METHODS: Extracellular single unit recordings of spontaneous action potentials were made from dopaminergic VTA neurons in brain slices from either C57BL/6J or DBA/2J mice. Ethanol (10 to 160 mM) was administered in the superfusate and the mean change in firing rate produced by ethanol was measured. RESULTS: There was no significant difference in basal spontaneous firing rate of dopaminergic VTA neurons between these two mouse strains. Ethanol caused a concentration-dependent increase in the firing rate of neurons from both mouse strains. Ethanol excited dopaminergic VTA neurons from DBA/2J mice more potently than those from C57BL/6J mice. CONCLUSIONS: The difference in sensitivity to ethanol excitation of dopaminergic VTA neurons in C57BL/6J and DBA/2J mice may contribute to differences in their behavioral response to ethanol. The fact that a given concentration of ethanol causes greater excitation of dopaminergic VTA (reward) neurons in DBA/2J mice than in C57BL/6J mice could explain why DBA/2J mice show much stronger place preference conditioning with ethanol. The higher voluntary intake of ethanol by C57BL/6J mice may be partly due to the insensitivity of their dopaminergic VTA neurons that requires them to drink a lot of ethanol to achieve sufficient excitation of reward neurons, whereas DBA/2J mice avoid oral ingestion of ethanol, despite its rewarding effect, because of their aversion to its taste.     

Differential neurosensitivity to the discriminative stimulus properties of ethanol in C57BL/6J and C3H/He mice

BACKGROUND: A large body of evidence suggests that the interoceptive cue associated with ethanol intoxication is complex and dependent on a number of environmental and biological factors. Despite the fact that mice have been widely used to study genetic influences on sensitivity to various actions of ethanol, few studies have used mice to examine sensitivity to the discriminative stimulus effects of ethanol. The purpose of this study was to compare sensitivity to the discriminative stimulus effects of ethanol in two inbred mouse strains, namely C57BL/6J and C3H/He mice. METHODS: Adult male C57BL/6J and C3H/He mice were trained to discriminate between ethanol and saline using a two-lever food reinforcement operant procedure. Once criterion discrimination performance was achieved, dose-response functions were determined from generalization tests. Additional experiments were conducted to determine whether differences in discrimination performance were related to differential blood/brain ethanol levels in the two mouse strains. RESULTS: A greater proportion of C57BL/6J mice acquired the discrimination and required fewer trials to achieve criterion performance compared with C3H/He mice with a 1.0 g/kg ethanol training dose. This deficit in acquisition was overcome when the training dose was increased to 2.0 g/kg for C3H/He mice. In a second experiment, a 1.5 g/kg training dose of ethanol was used for both strains. Again, a greater proportion of C57BL/6J mice acquired the discrimination and required fewer training trials to achieve criterion performance compared with C3H/He mice. Blood ethanol levels did not differ between the strains after administration of the 1.5 g/kg training dose. However, blood and brain ethanol levels did differ between the strains after doses of ethanol were administered that produced equivalent discrimination performance. CONCLUSIONS: Results indicate that ethanol discrimination was more readily acquired and maintained in C57BL/6J mice than C3H/He mice. Ethanol dose-response functions generated from generalization tests also clearly demonstrated greater sensitivity to the discriminative stimulus properties of ethanol in C57BL/6J mice compared with the C3H/He strain. This differential sensitivity to the interoceptive cue produced by ethanol does not seem to be related to learning or pharmacokinetic differences between the two inbred strains.     

Murine model of Kawasaki disease induced by mannoprotein-beta-glucan complex, CAWS, obtained from Candida albicans

Intraperitoneal administration of CAWS (water-soluble extracellular polysaccharide fraction obtained from the culture supernatant of Candida albicans) to mice induces coronary arteritis similar to Kawasaki disease. We analyzed differences in the production of cytokines involved in the occurrence of coronary arteritis among mouse strains, C3H/HeN, C57BL/6, DBA/2 and CBA/J. The incidence of arteritis was 100% in C57BL/6, C3H/HeN and DBA/2 mice, but only 10% in CBA/J mice. The coronary arteritis observed in DBA/2 mice was the most serious, with several mice expiring during the observation period. The CAWS-sensitive strains revealed increased levels of IL-6 and IFN-gamma during the course of a specific response to CAWS by spleen cells. In contrast, IL-10 levels were observed to increase markedly in CAWS-resistant CBA/J mice, but not the CAWS-sensitive strains. However, TNF-alpha levels were more elevated only in DBA/2 mice. The difference in disease development and cytokine production strongly suggests that the genetic background of the immune response to CAWS contributes to the occurrence of coronary arteritis.     

Role of genotype in the development of locomotor sensitization to alcohol in adult and adolescent mice: comparison of the DBA/2J and C57BL/6J inbred mouse strains

Background: Animal models that explore differential sensitivity to the effects of acute and repeated exposure of alcohol (ethanol) may be influenced by both the developmental and genetic profile of the population. Therefore, we sought to compare the influence of ontogeny on sensitivity to ethanol‐induced locomotor stimulation and on the induction of locomotor sensitization to this effect across 2 inbred strains of mice; the ethanol consuming C57BL/6J and the ethanol avoiding DBA/2J strains. Methods: C57BL/6J and DBA/2J adults (postnatal day [PD] 60 to 80) and adolescents (PD 30 ± 2) were assessed for basal activity, acute response to 2.0 g/kg ethanol, and the expression of locomotor sensitization following repeated administration of 2.5, 3.0, or 3.5 g/kg ethanol. Results: Basal activity was different across development for the C57BL/6J, but not DBA/2J, with adult B6 mice showing persistently greater baseline activity. Adolescents of both strains were more sensitive than adults to acute ethanol‐induced locomotor stimulation; adults exhibited a decrease in their acute response across the testing session. Adolescent DBA/2J mice developed less ethanol sensitization compared to adults, with significant sensitization observed only following repeated administration of the lowest ethanol dose (2.5 g/kg), whereas DBA/2J adults sensitized to all doses. Age did not influence the development of ethanol sensitization for the C57BL/6J strain, as both adults and adolescents displayed a sensitized response following all ethanol doses. Conclusions: These results suggest that the developmental pattern of locomotor sensitivity to ethanol is unique to the genotypic profile of the animal model.     

Discriminative stimulus effects of ethanol in C57BL/6J and DBA/2J inbred mice

BACKGROUND: Two of the most widely used mouse strains for studying the behavioral effects of ethanol are C57BL/6J (B6) and DBA/2J (D2) mice. These strains exhibit marked differences in behavioral and physiological responses to ethanol. The subjective discriminative stimulus effects of ethanol may play a role in ethanol abuse, but the discriminative stimulus profile of ethanol has not been compared in B6 and D2 mice. Examination of the discriminative stimulus effects of ethanol in B6 and D2 mouse strains may enhance our understanding of the relationship between the subjective effects of ethanol and other ethanol-induced behavioral effects. METHODS: Twelve adult male C57BL/6J mice and 12 male DBA/2J mice were trained to discriminate 1.5 g/kg ethanol from saline in daily 15 min, milk-reinforced operant sessions. After training, ethanol substitution and response-rate suppression dose response curves were determined for ethanol, midazolam, diazepam, pentobarbital, pregnanolone, 4,5,6,7-Tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), dizocilpine, and morphine. RESULTS: D2 mice learned the ethanol discrimination significantly more quickly than did B6 mice. Ethanol, midazolam, pregnanolone, and dizocilpine fully substituted for ethanol in both strains. Pentobarbital was more potent in producing ethanol-like discriminative stimulus effects in D2 than B6 mice. Midazolam and diazepam were significantly more potent in suppressing response rates in D2 than B6 mice. Morphine failed to substitute for ethanol in either strain, but the ED50 for morphine suppression of responding was significantly lower in B6 than D2 mice. CONCLUSIONS: The initial stimulus effects of 1.5 g/kg ethanol may be more salient in D2 than B6 mice. This does not appear to result from differences in the neurotransmitter systems that mediate ethanol's discriminative stimulus effects. In both strains, gamma-aminobutyric acid-positive modulators and a noncompetitive NMDA antagonist substituted for ethanol. However, strain differences did exist in the potency of gamma-aminobutyric acid-positive modulators and morphine for suppressing operant responding.     

Mouse Strain Differences in Oral Operant Ethanol Reinforcement under Continuous Access Conditions

The present experiment examined ethanol setf-administration in C57BL/6J (C57) and DBA/2J (DBA) mice using a continuous access operant procedure. Adult male C57 and DBA mice were initially trained to perform a lever press response to obtain access to 10% w/v sucrose solution. Subsequently, the mice were placed in operant chambers on a continuous (23 hr/day) basis with access to food (FR1), 10% v/v ethanol (FR4), and water from a sipper tube. C57 mice displayed greater rates of responding on the ethanol-associated lever compared with DBA mice. Responding on the food lever was the same in both strains, but DBA mice consumed greater amounts of water. C57 mice consistently displayed both prandial and nonprandial episodes (bouts) of ethanol responding. DBA mice did not respond for ethanol in bouts. Following 50 consecutive sessions, ethanol concentration was altered every 5 days. Response patterns were determined using 0, 5, 10, 20, and 30% v/v ethanol concentrations. C57 mice displayed concentration-dependent responding on the ethanol lever showing that ethanol was functioning as an effective reinforcer in this strain. In contrast, responding on the ethanol lever by DBA mice did not change as a function of ethanol concentration. Saccharin (0.2% w/v) was subsequently added to the ethanol mixture, and responding was examined at 0, 5, 10, and 20% ethanol concentrations. Overall, ethanol lever responding was increased in both strains. As before, C57 mice showed higher levels of ethanol responding, compared with DBA mice. C57 mice also showed higher responding for saccharin alone. These results are consistent with findings that suggest orally administered ethanol is a more effective reinforcer in C57 mice than in DBA mice. Furthermore, C57 mice engage in ethanol-reinforced responding over a broader range of conditions than DBA mice.     

Influence of dose and route of inoculation and of mouse strain on the production of interleukin 2 in mice infected with Mycobacterium lepraemurium

In order to evaluate the influence of route and dose of inoculation on interleukin 2 (IL2) production, C57BL/6 mice were infected either intravenously (I.V.) or subcutaneously (S.C.) with 10(5) or 10(8) Mycobacterium lepraemurium. The role of genetic factors on the production of IL2 during M. lepraemurium infection, was investigated in 7 inbred mouse strains (C57BL/6, DBA/2, F1 (C57BL/6 X DBA/2), DBA/1, BALB/c, CBA and A/J) after I.V. infection with 10(7) M. lepraemurium. At different times after M. lepraemurium inoculation, the number of AFB within the spleens of infected mice was counted and the ability of Con A-activated spleen cells to produce IL2 was studied. In S.C. inoculated C57BL/6 mice the increase in footpad thickness was measured during the progression of infection. After one month of infection heavily infected C57BL/6 mice (10(8) bacilli) showed an early and strong deficiency of IL2 production, regardless of the route of inoculation, whereas mice infected with a lower dose (10(5) bacilli) did not. In S.C. infected mice the decrease of IL2 production was observed when the footpad enlargement reached to the plateau phase. The data obtained from the numeration of AFB within the spleens of infected mice allowed to rank the infected mouse strains into 2 separated groups according to the pattern of the Bcg gene expression. An IL2 deficiency was only observed in C57BL/6, DBA/1, (C57BL/6 X DBA/2)F1 and DBA/2 infected mouse strains. No evident correlation could be shown between splenic IL2 activity upon Con A stimulation and the number of AFB recovered from the spleens of these 7 inbred mouse strains.     

Endogenous Opioids Are Involved in the Genetically Determined High Preference for Ethanol Consumption

The link between endogenous opioid peptides and the genetic predisposition to preferentially consume ethanol was examined in alcohol preferring C57BL/6J mice compared with the alcohol nonpreferring DBA/2 mice. Concentrations of Met-enkephalin pentapeptide or precursor in various brain regions of potential relevance were not different between the two strains. C57BL/6J mice had a significantly lower pain threshold that could be increased by a selective mu-receptor opioid agonist [D-Ala2, MePhe4, Met(O)5-ol]-enkephalin. Treatment with this drug also decreased ethanol consumption in C57BL/6J mice. Increasing the synaptic half-life of endogenous enkephalins by the enkephalinase inhibitor kelatorphan also decreased ethanol consumption. Assay of endogenous enkephalin degrading activity showed increased enkephalinase activity in striatal issue of C57BL/6J compared with DBA/2 tissue. These results suggest that a relative lack of enkephalin peptides trans-synaptically, possibly resulting from enhanced enkephalin degradation may contribute to increase alcohol consumption in C57BL/6J mice.     

Brain region-specific regulation of urocortin 1 innervation and corticotropin-releasing factor receptor type 2 binding by ethanol exposure

BACKGROUND: Ethanol administration and consumption selectively activates the urocortin 1 (Ucn1)-expressing neurons of the Edinger-Westphal nucleus. We investigated whether repeated ethanol exposure affects Ucn1 and Ucn1-responsive corticotropin-releasing factor type-2 receptors (CRF2). METHODS: Male C57BL/6J and DBA/2J mice were exposed to 2 g/kg ethanol via intraperitoneal injection once per day for 14, seven, or zero days. Ucn1 immunoreactivity was measured in the lateral septum, dorsal raphe, and Edinger-Westphal nucleus. In a separate experiment, C57BL/6J mice were exposed to ethanol for seven, one, or zero days, and CRF2 receptor binding was measured in the lateral septum and dorsal raphe by receptor autoradiography. RESULTS: Ethanol exposure induced parallel changes in Ucn1 immunoreactive terminal fibers in the lateral septum and dorsal raphe of both strains. Seven ethanol exposures but not one ethanol exposure significantly increased CRF2 receptor binding in the dorsal raphe and slightly increased CRF2 receptor binding in the lateral septum. CONCLUSIONS: These results provide evidence that the Ucn1/CRF2 receptor system can be modified by ethanol exposure. They additionally suggest that this system may be involved in behavioral changes during alcoholism.     

Effect of Ethanol Drinking on the Gene Expression of Opioid Receptors, Enkephalinase, and Angiotensin-Converting Enzyme in Two Inbred Mice Strains

There is convincing evidence that genetic factors contribute to the predisposition to alcoholism. In this respect, alcohol-preferring (like C57BL/6 mice) and alcohol-avoiding lines (like DBA/2 mice) of animals served as models in the search for neurobiological substrates of excessive ethanol consumption. One of the systems that is thought to be associated with the incidence of alcoholism is the endogenous opioid system. In the first experiment, basal mRNA levels of μ- and §-opioid receptors, and of opioid-degrading enzymes enkephalinase (neutral endopeptidase 24.11; NEP) and angiotensin-converting enzyme (ACE) in the brain regions of C57BL/6 and DBA/2 mice did not reveal genetically determined differences in these parameters between the two strains. Furthermore, in the brain regions studied, the corresponding enzyme activities of NEP and ACE did not differ significantly between the lines of mice, except for a higher NEP activity in the striatum and olfactoty bulb of DBA/2 mice ( p < 0.01). In the second experiment, C57BL/6 and DBA/2 mice were offered a free choice between water and 10% ethanol solution for 4 weeks and were killed thereafter; from another group, ethanol was removed for 3 days and from a third group ethanol was removed for 3 weeks before killing. In the striatum, a highly significant increase in the ACE mRNA amount was detected after 3 weeks of removal of ethanol in C57BL/6 mice, whereas in DBA/2 mice the §-opioid receptor mRNA level was increased at this time when compared with the corresponding ethanol treatment group. The most striking changes were seen in the hypothalamus, where μ-opioid receptor, ACE, and NEP mRNA amounts markedly decreased after ethanol treatment in both strains. Thus, chronic ethanol intake caused significant changes in the gene expression of distinct components of the endogenous opioid system. These findings further underline an involvement of the opioid system in the effects of ethanol.     

Further studies on genetic variation of hepatosplenic disease and modulation in murine schistosomiasis mansoni

The influence of genetic factors on the modulation of hepatosplenomegaly, portal venous pressure and granuloma size in chronic murine schistosomiasis mansoni was studied. Experiments with congenic mice confirmed previous observations that after 8 weeks of infection these disease manifestations are influenced by non-H-2 genes. During chronic infection (20 weeks compared to 8 weeks of infection), hepatosplenomegaly was minimally altered. Portal venous pressure was found to increase in 129/J and BALB/cJ mice, did not change in C57BL/6J and DBA/2J and decreased in CBA/CaJ mice. Simultaneous measurements of granuloma size delineated two groups: decrease of greater than 40%--C57BL/6J, DBA/2J and CBA/CaJ strains and decrease of less than or equal to 20%--129/J, BALB/cJ and C3H/HeJ mice. There was no consistent correlation between the magnitude or direction of alterations in portal pressure and granuloma size among the various strains studied. Furthermore, these alterations were independent of changes in parasite burden (adult worms or hepatic eggs). This amelioration of disease (modulation) was found to be influenced by a small number of non-H-2 genes.     

Ethanol acceptance as a function of genotype amounts of brain [Met]enkephalin.

Our results indicate a negative correlation between the amount of ethanol (10%) consumed and endogenous levels of brain [Met]enkephalin in C57BL/6J (alcohol-preferring) and DBA/2J (alcohol-nonpreferring) inbred mice strains. Additionally, it was found that 8 wk after 1-day starved groups of both C57BL/6J and DBA/2J mice were challenged with ethanol (10%) for 1-day acceptance, they had significantly lower levels of brain [Met]enkephalin compared with their nonalcohol-treated controls. These results suggest that the brain endogenous peptidyl opiates may play a crucial role in alcohol-seeking behavior.     

Intravenous Ethanol Self-administration in C57BL/6J and DBA/2J Mice

Two strains of mice, C57BL/6J (B6) and DBA/2J (D2) were allowed to self-administer intravenous (iv) ethanol. These two strains were selected because they differ greatly in their preference for drinking ethanol solutions: 86 mice are preferrers, whereas D2 mice are avoiders of ethanol. Of interest was whether these strains would also differ in self-administration of iv ethanol when taste factors presumably do not influence consumption. Mice were trained with either 60, 75, or 90 mg/kg per infusion. Mice from both strains acquired nosepoking for all of these doses on an FR-3 schedule of reinforcement during 2-hr daily sessions. Additionally, mice in both strains acquired an equal preference for nosepoking on the side resulting in ethanol infusions, compared with the side that had no scheduled consequence, although B6 mice took somewhat more ethanol early in training than did D2 mice. Mice in both strains achieved equal levels of responding at the conclusion of training, when response rates had stabilized. A subset of animals were then tested at doses of ethanol ranging from 25 to 125 mg/kg per infusion. Although their responding tended to decrease over time regardless of changes in the unit dose of ethanol, these mice showed lower response rates for higher doses of ethanol, and less responding for saline than for ethanol. Together, these findings imply that iv ethanol has reinforcing properties in both these strains, despite the strain difference in preference for oral ethanol. Self-administration of iv ethanol in mice may prove a valuable addition to existing animal models for the study of ethanol reward.     

Ethanol preference is inversely correlated with ethanol-induced dopamine release in 2 substrains of C57BL/6 mice

BACKGROUND: The C57BL/6 mouse model has been used extensively in alcohol drinking studies, yet significant differences in ethanol preference between substrains exist. Differences in ethanol-induced dopamine release in the ventral striatum could contribute to this variability in drinking behavior as dopamine has been implicated in the reinforcing properties of ethanol. METHODS: A 2-bottle choice experiment investigated the difference in ethanol preference between C57BL/6J and C57BL/6NCrl animals. Microdialysis was used to determine dopamine release and ethanol clearance in these 2 substrains after intraperitoneal injections of 1.0, 2.0 and 3.0 g/kg ethanol or saline. RESULTS: C57BL/6J mice exhibited significantly greater ethanol preference and less ethanol-stimulated dopamine release compared with C57BL/6NCrl mice. The intraperitoneal injections of ethanol caused a significant increase in dopamine in both substrains at all 3 doses with significant differences between substrains at the 2 highest alcohol doses. Saline injections had a significant effect on dopamine release when given in a volume equivalent to the 3 g/kg ethanol dose. Ethanol pharmacokinetics were similar in the 2 substrains at all 3 doses. CONCLUSIONS: Ethanol-induced dopamine release in the ventral striatum may contribute to the differences in alcohol preference between C57BL/6J and C57BL/6NCrl mice.     

Acetaldehyde dehydrogenase (Ahd-2)-Associated DNA Polymorphisms in Mouse Strains with Variable Ethanol Preferences

The genotype-dependent response of mice to ethanol has been well documented. Cytosolic acetaldehyde dehydrogenase (ALDH-2) increases in some strains while decreasing in others with ethanol treatment. Further work suggests that the mRNA for ALDH-2 (Ahd-2 mRNA) levels are altered following ethanol feeding in a strain-dependent fashion. This report identifies differences in Ahd-2 at the genomic DNA level among different strains of mice. Restriction fragment length polymorphisms (RFLPs) associated with the Ahd-2 locus were found for the restriction enzymes EcoRI, HindIII, Pst I and Rsa I. The mouse strains included in this study could be categorized into two groups based on their overall Ahd-2 associated DNA banding patterns. Strains C57BL/6J, C57BL/6J*, C57BL/10J and BALB/c form group 1 while strains C3H/HeJ, C3H/HeSnJ, 129/ReJ, Csb, SW and DBA/2J form group 2. With the exception of BALB/c, group 1 represents alcohol preferring strains while group 2 are alcohol avoiding strains. Additional work will be required to determine the physiological significance (if any) of these RFLPs and their possible relationship to ethanol preference and avoidance.     

Analysis of metallothionein brain gene expression in relation to ethanol preference in mice using cosegregation and gene knockouts

BACKGROUND: Metallothioneins (MTs) are ubiquitously expressed intracellular proteins that bind heavy metals and are involved in cytoprotection against several types of stress agents including chemicals, hormones, and oxidants. We have previously reported 1 isoform, MT-II, as a possible candidate gene for ethanol (EtOH) preference (EP) determination in mice. METHODS: Semiquantitative RT-PCR was used to determine brain mRNA levels of MT-I and MT-III in 4 inbred mouse strains with variable EP. Following this, cosegregation of MT-II brain expression with EP was analyzed in F2 mice from 2 intercrosses (C57BL/6J x BALB/cJ and C57BL/6J x DBA/2J). Studies on MT-I/MT-II knockout (KO) mice were also undertaken to further explore this relationship. RESULTS: Our results suggest that MT-I is responsive to EtOH, with no evidence of basal-level differences between strains. Conversely, MT-III shows no EtOH response, yet indicates a possible strain-specific feature with C57BL/6J having the lowest levels of brain MT-III. Metallothionein-II expression cosegregates with EP in F2 mice from a C57BL/6J (preferring) and DBA/2J (avoiding) intercross. Although F2 mice from a cross with C57BL/6J and BALB/cJ (avoiding) strains follow a similar pattern, the results are not statistically significant. Metallothionein-I/MT-II knockout (MT-KO) mice appear to have smaller litter sizes as well as higher weight compared with controls (129S1/SvImJ) and also show a slight increase in EP. CONCLUSIONS: Metallothionein-II remains the primary candidate of the mouse MT gene family for involvement in EP. Its effect on EP appears to be dependent on the genetic background. Such conclusions are based on results from C57BL/6J, BALB/cJ, DBA/2J, and 129 inbred mouse strains. Evidence also points to shared neural pathways involved in weight gain and obesity. The complex interactions between MT-II, EP, and weight gain/obesity remain to be studied.     

Voluntary Alcohol Consumption in BXD Recombinant Inbred Mice: Relationship to Alcohol Metabolism

Studies were initiated to characterize behaviorally and biochemically C57BL/6J and DBA/2J inbred mice, as well as BXD Recombinant Inbred (RI) strains derived from them. The C57BL/6J, DBA/2J, and 7 BXD RI strains were tested for voluntary alcohol consumption (VAC) by receiving 4 days of forced exposure to a 10% (w/v) solution of alcohol, followed by 3 weeks of free choice between water and 10% alcohol. Measures of VAC included the absolute intake of alcohol (g/kg), as well as alcohol preference. A wide range of VAC was displayed by the various BXD RI strains with a continuous (rather than bimodal) distribution, indicating that there is likely to be additive effects of several genes involved in regulating alcohol-related behaviors. Kinetic characteristics of aldehyde dehydrogenase and catalase in liver and brain of the C57BL/6J, DBA/2J, and BXD strains of mice were determined to test the hypothesis that the genetic regulation of the levels of alcohol-metabolizing enzymes mediate differences in VAC. Aldehyde dehydrogenase activity was determined spectrophotometrically by observing the change in absorption at 340 nm. Catalase activity was determined by measuring oxygen production with a Yellow Springs Biological Oxygen monitor and oxygen electrode. There was a strong negative relationship between VAC and brain catalase activity in the BXD RI and parental strains. These data suggest that RI strains are likely to be useful genetic models in the examination of quantitative trait loci controlling VAC and other responses to alcohol.     

Ethanol‐Induced Increase of Agouti‐Related Protein (AgRP) Immunoreactivity in the Arcuate Nucleus of the Hypothalamus of C57BL/6J,but not 129/SvJ,Inbred Mice

Background: The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor, pro‐opiomelanocortin (POMC). Previous research has shown that MC receptor (MCR) agonists reduce, and MCR antagonists increase, ethanol consumption in rats and mice. Consistently, genetic deletion of the endogenous MCR antagonist, agouti‐related protein (AgRP), causes reductions of ethanol‐reinforced lever pressing and binge‐like ethanol drinking in C57BL/6J mice. Ethanol also has direct effects on the central MC system, as chronic exposure to an ethanol‐containing diet causes significant reductions of α‐melanocyte stimulating hormone (α‐MSH) immunoreactivity in specific brain regions of Sprague‐Dawley rats. Together, these observations suggest that the central MC system modulates neurobiological responses to ethanol. To further characterize the role of the MC system in responses to ethanol, here we compared AgRP and α‐MSH immunoreactivity in response to an acute injection of saline or ethanol between high ethanol drinking C57BL/6J mice and moderate ethanol drinking 129/SvJ mice. Methods: Mice received an intraperitoneal (i.p.) injection of ethanol (1.5 g/kg or 3.5 g/kg; mixed in 0.9% saline) or an equivolume of 0.9% saline. Two hours after injection, animals were sacrificed and their brains were processed for AgRP and α‐MSH immunoreactivity. Results: Results indicated that acute ethanol administration triggered a dose‐dependent increase in AgRP immunoreactivity in the arcuate (ARC) of C57BL/6J mice, an effect that was not evident in the 129/SvJ strain. Although acute administration of ethanol did not influence α‐MSH immunoreactivity, C57BL/6J mice had significantly greater overall α‐MSH immunoreactivity in the ARC, dorsomedial, and lateral regions of the hypothalamus relative to the 129/SvJ strain. In contrast, C57BL/6J mice displayed significantly lower α‐MSH immunoreactivity in the medial amygdala. Conclusions: The results show that acute ethanol exposure has direct effects on endogenous AgRP activity in ethanol preferring C57BL/6J mice. It is suggested that ethanol‐induced increases in AgRP may be part of a positive feedback system that stimulates excessive binge‐like ethanol drinking in C57BL/6J mice. Inherent differences in α‐MSH immunoreactivity may contribute to differences in neurobiological responses to ethanol that are characteristically observed between the C57BL/6J and 129/SvJ inbred strains of mice.     

Strain Differences in Behavioral Inhibition in a Go/No‐go Task Demonstrated Using 15 Inbred Mouse Strains

Background: High levels of impulsivity have been associated with a number of substance abuse disorders including alcohol abuse. Research has not yet revealed whether these high levels predate the development of alcohol abuse. Methods: The current study examined impulsivity in 15 inbred strains of mice (A/HeJ, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, C57L/J, C58/J, CBA/J, DBA/1J, DBA/2J, NZB/B1NJ, PL/J, SJL/J, SWR/J, and 129P3/J) using a Go/No‐go task, which was designed to measure a subject’s ability to inhibit a behavior. Numerous aspects of response to ethanol and other drugs of abuse have been examined in these strains. Results: There were significant strain differences in the number of responses made during the No‐go signal (false alarms) and the extent to which strains responded differentially during the Go and No‐go signals (d′). The rate of responding prior to the cue did not differ among strains, although there was a statistically significant correlation between false alarms and precue responding that was not related to basal activity level. Interstrain correlations suggested that false alarms and rate of responding were associated with strain differences in ethanol‐related traits from the published literature. Conclusions: The results of this study do support a link between innate level of impulsivity and response to ethanol and are consistent with a genetic basis for some measures of behavioral inhibition.     

Maximal testosterone production in Leydig cells from inbred mice relates to the activity of 3 beta-hydroxysteroid dehydrogenase-isomerase

We previously described significant differences in maximal testosterone production by Leydig cells from the following strains of inbred mice: C57BL/10J, C57BL/6J, DBA/2J, and C3H/HeJ. To evaluate whether these differences in maximal testosterone production related to the activities of the steroidogenic enzymes of the smooth endoplasmic reticulum of Leydig cells from these strains, the activities of 3 beta-hydroxysteroid dehydrogenase-isomerase, 17 alpha-hydroxylase, C17-20 lyase, and 17-ketosteroid reductase were measured in homogenates of purified Leydig cells using 3H-labeled substrates and measuring the amounts of 3H products formed. Maximal and basal testosterone production were determined by incubating aliquots of Leydig cells for 2 h in the presence or absence of 30 pM hCG. Maximal testosterone production by Leydig cells from C57BL/10J and C57BL/6J mice was significantly greater than that by Leydig cells from DBA/2J and C3H/HeJ mice. No difference in basal testosterone production was observed among the strains. Among the four enzymes studied, only 3 beta-hydroxysteroid dehydrogenase-isomerase activity was significantly correlated with hCG-stimulated testosterone production by Leydig cells from the four strains of mice. In addition, when equivalent numbers of Leydig cells from each strain were incubated with an equal concentration of [3H]pregnenolone, a similar difference in [3H] testosterone production was observed among the four strains, as was seen with hCG-stimulation. Leydig cells from C57BL/10 and C57BL/6J mice left less [3H]pregnenolone unmetabolized and produced higher amounts of [3H]testosterone than Leydig cells from DBA/2J and C3H/HeJ mice. There was a significant negative correlation between the amount of pregnenolone unmetabolized and the amount of testosterone produced. These data suggest that 3 beta-hydroxysteroid dehydrogenase-isomerase may be important in determining the differences in hCG-stimulated testosterone production by Leydig cells from the four strains of mice.