Dose-response relationship of cytochrome P4501b1 mRNA induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin in livers of C57BL/6J and DBA/2J mice

 The dose-response relationship of cytochrome P4501b1 (Cyp1b1) and Cyp1a1 induction in livers of TCDD-treated female C57BL/6J and DBA/2J mice are described. The animals were treated i.p. with 0.001, 0.01, 0.1, 1, 10 and 50 μg TCDD/kg for 24 h, and Cyp1b1 and Cyp1a1 mRNA expression was analyzed by RT-PCR. In the livers of both mouse strains, the Cyp1b1 and Cyp1a1 mRNA content was increased after TCDD exposure in a dose-dependent manner. These effects were more pronounced in TCDD-responsive C57BL/6J mice than in the less responsive DBA/2J mice, although Cyp1a1 was more responsive to TCDD than Cyp1b1 in both strains. The calculated ED₅₀ values for Cyp1b1 and Cyp1a1 induction in livers of TCDD-treated C57BL/6J mice were 1.3 and 0.08 μg TCDD/kg, respectively. The corresponding values for half-maximal induction response in livers of DBA/2J mice were 3.4 μg TCDD/kg for Cyp1b1 and 1.5 μg TCDD/kg for Cyp1a1. These results show that Cyp1b1 mRNA expression is less inducible by TCDD than Cyp1a1. Both genes are highly inducible in TCDD-responsive C57BL/6J mice expressing the high affinity arylhydrocarbon receptor (Ah receptor), suggesting that Cyp1b1, like Cyp1a1, is a potential Ah receptor-regulated gene. Received: 8 December 1995/Accepted: 6 February 1996     

Nicotine-produced relearning deficit in C57BL/6J and DBA/2J mice

Acute nicotine administration has been shown to influence the acquisition and retention of learning tasks. In order to investigate the many possible behavioral and pharmacological effects of nicotine, a modified 2×2 statedependent learning design was used to assess nicotine's effects on active avoidance learning. Male and female mice of the C57BL/6J (C57) and DBA/2J (DBA) inbred strains were injected with a control solution or with 0.5, 1.0, or 2.0 mg/kg nicotine 5 min before the start of training and, following a 24-h period, 5 min before retraining. Nicotine had no effect on the acquisition of the learning task but, depending on strain and sex, did have an effect on relearning. Relearning in the C57 males was unaffected by nicotine injection, whereas the most prominent effect of nicotine in the C57 females and the DBA males and females was a retrieval deficit. The prevalence of a nicotine-induced retrieval deficit in the present experiment suggests that those mechanisms underlying the retrieval of previously learned information are, in part, mediated or modulated by perturbations within nicotine-sensitive areas of the central nervous system.     

Modulation of cytochrome P450 1 (Cyp1) by vanadium in hepatic tissue and isolated hepatocyte of C57BL/6 mice

The objective of the current study was to investigate the effect of vanadium (V⁵⁺) on Cyp1 expression and activity in C57BL/6 mice liver and isolated hepatocytes. For this purpose, C57BL6 mice were injected intraperitoneally with V⁵⁺ (5 mg/kg) in the absence and presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (15 μg/kg) for 6 and 24 h. Furthermore, isolated hepatocytes from C57BL6 mice were treated with V⁵⁺ (5, 10, and 20 μM) in the absence and presence of TCDD (1 nM) for 3, 6, 12, and 24 h. In vivo, V⁵⁺ alone did not significantly alter Cyp1a1, Cyp1a2, or Cyp1b1 mRNA, protein, or catalytic activity levels. Upon co-exposure to V⁵⁺ and TCDD, V⁵⁺ significantly potentiated the TCDD-mediated induction of the Cyp1a1, Cyp1a2, and Cyp1b1 mRNA, protein, and catalytic activity levels at 24 h. In vitro, V⁵⁺ decreased the TCDD-mediated induction of Cyp1a1 mRNA, protein, and catalytic activity levels. Furthermore, V⁵⁺ significantly inhibited the TCDD-induced AhR-dependent luciferase activity. V⁵⁺ also increased serum hemoglobin (Hb) levels in animals treated for 24 h. Upon treatment of isolated hepatocytes with Hb alone or in the presence of TCDD, there was an increase in the AhR-dependent luciferase activity. When isolated hepatocytes were treated for 2 h with V⁵⁺ in the presence of TCDD, followed by replacement of the medium with new medium containing Hb, there was further potentiation to the TCDD-mediated effect. The present study demonstrates that there is a differential modulation of Cyp1a1 by V⁵⁺ in C57BL/6 mice livers and isolated hepatocytes and demonstrates Hb as an in vivo specific modulator.     

Differential responsiveness to cocaine in C57BL/6J and DBA/2J mice

 The present study compared cocaine-induced hyperlocomotion and cocaine IV self-administration in DBA/2J and C57BL/6J mice. In the locomotor activity experiment, these strains were tested for hyperlocomotion after IP cocaine injection (0–60.0 mg/kg), using a Digiscan Animal Activity Monitoring System. In the cocaine IV self-administration experiment, they were compared for their ability to acquire and maintain cocaine self-administration in operant chambers with levers as the manipulanda. Animals were first trained to respond for food as a reinforcer (condensed milk solution); they were then submitted to surgical IV insertion of an indwelling catheter, and required to respond for IV cocaine (0.25–4.0 mg/kg per injection) as a reinforcer. DBA/2J mice showed significantly higher maximal cocaine-induced hyperlocomotion, more rapid acquisition of cocaine self-administration, and significantly lower rates of cocaine self-administration. Cocaine concentration in the brains of DBA/2J and C57BL/6J mice failed to differ following IP injection, suggesting that distribution factors were not involved in the differential responses to cocaine. Although not conclusive, this pattern of effects may suggest that cocaine has greater reinforcing efficacy in DBA/2J mice, confirming genetic make-up as a determinant factor in cocaine taking behavior. Received: 6 October 1997 / Final version: 4 January 1998     

Dimethylarsinic acid modulates the aryl hydrocarbon receptor-regulated genes in C57BL/6 mice: in vivo study

1.?Dimethylarsinic acid (DMA(V)) is the major metabolite of inorganic arsenic in human body. Thus we investigated the effect of DMA(V) on the alteration of phase I (typified by Cyp1a) and phase II (typified by Nqo1) AhR-regulated genes in vivo. C57BL/6 mice received DMA(V) (13.3?mg/kg, i.p.) with or without TCDD (15?μg/kg, i.p.), thereafter the liver, lung, and kidney were harvested at 6 and 24?h post-treatment.

2.?Results demonstrated that DMA(V) has no significant effect on Cyp1a mRNA and protein expression or catalytic activity in the liver. On the other hand, DMA(V) significantly potentiated the TCDD-mediated induction of Cyp1a mRNA and protein expression, with a subsequent potentiation of catalytic activity in the lung. Moreover, DMA(V) significantly inhibited the TCDD-mediated induction of Cyp1a mRNA and protein expression with subsequent inhibition of catalytic activity in the kidney.

3.?Regarding to phase II AhR-regulated genes, DMA(V) has no significant effect on Nqo1 mRNA and protein expression, or activity neither in the liver, lung, or kidney.

4.?In conclusion, the present work demonstrates for the first time that DMA(V) modulates AhR-regulated genes in a tissue- and enzyme-specific manner. This modulation may play a crucial role in arsenic-induced toxicity and carcinogenicity.     

Tier-2 studies on monocrotaline immunotoxicity in C57BL/6 mice

Monocrotaline (MCT) is a member of a class of naturally occurring phytotoxins known as pyrrolizidine alkaloids, and is a toxicological concern to both man and his livestock. The purpose of these studies was to evaluate the effect of a 14-day oral MCT (0–100 mg/kg per day) exposure on the functional integrity of various immunocyte effector systems in C57BL/6 mice, as well as to investigate potential mechanisms for its immunotoxicity. Decreases in lymphoid organ weights and cellularity, and resident peritoneal exudate cell (PEC) number were only observed after exposure to the highest dose of 100 mg/kg MCT. This dose also inhibited NK cell cytotoxicity, while the total number of NK lytic units per spleen was decreased (−53%) after exposure to 50 mg/kg MCT. Following i.p. injection of SRBC, the percentage of PEC macrophages containing engulfed SRBC was significantly increased in MCT-exposed mice, while the percentage of large vacuolated (activated) macrophages was decreased in a dose-dependent manner. Exposure to MCT significantly decreased the total number of Ig+ cells without altering the number of CD4+ and CD8+ cells. The antibody responses (PFC/10⁶ spleen cells) to two T cell-independent antigens, TNP-LPS and DNP-Ficoll, were significantly decreased at all MCT doses, and the degree of suppression of both responses was identical at coincident doses. MCT exposure (25 mg/kg) significantly suppressed the blastogenic response to the T cell mitogen concanavalin A (−38%), and to the B cell mitogen lipopolysaccharide (−58%). These results indicate that exposure to MCT can alter the functional integrity of various immune effector responses in a dose-dependent manner, and suggest that the B cell may be a relatively more sensitive target of MCT immunotoxicity compared to T cells, macrophages and NK cells.     

Comparison of 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated hepatotoxicity in C57BL/6J and DBA/2J mice

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined by clinical chemistry and liver histopathology in Ah-responsive C57BL/6J (C57) and Ah-nonresponsive DBA/2J (DBA) mice. Hepatotoxicity was assessed at 1, 3, and 7 d following a single ip injection of TCDD at doses that maximally induce hepatic aryl hydrocarbon hydroxylase (AHH) activity (3 micrograms/kg for C57 and 30 micrograms/kg for DBA mice) and at doses approaching the LD50 (150 micrograms/kg for C57 and 600 micrograms/kg for DBA mice). Histological examination of liver sections was found to be a more sensitive detection method for TCDD-induced hepatic changes than clinical chemistry analyses. Dramatic differences in the development and type of liver injury were observed between TCDD-treated C57 and DBA mice. C57 mice given 3 micrograms TCDD/kg developed mild to moderate hepatic lipid accumulation in the absence of both inflammation and necrosis. Severe fatty change and mild inflammation and necrosis occurred in C57 mice that received 150 micrograms TCDD/kg. In contrast, DBA mice exposed to 30 micrograms TCDD/kg developed hepatocellular necrosis and inflammation without any fatty change. Only slight hepatic lipid accumulation occurred with some necrosis and inflammation in DBA mice given 600 micrograms TCDD/kg. The Ah locus may play a role in determining the sensitivity of C57 mice to the steatotic effects of TCDD.     

Ethanol preexposure increases ethanol self-administration in C57BL/6J and DBA/2J mice

Genetic variables are thought to interact with environmental factors, such as alcohol exposure history, to produce individual differences in alcohol abuse and alcoholism. The objective of this study was to test the potential interaction between genetic predisposition to consume alcohol and alcohol pretreatment on subsequent self-administration. To accomplish this goal, four groups of mice from the ethanol-avoiding DBA/2J (D2) and ethanol-preferring C57BL/6J (B6) inbred strains were exposed to saline, acute ethanol (2 g/kg), or chronic intermittent ethanol (1 or 2 g/kg) intraperitoneal (i.p.) injections. Locomotor activity was monitored after each injection. After preexposure, animals were given a two-bottle choice test with various concentrations of ethanol/sucrose vs. sucrose or ethanol vs. water for 4 days at each concentration. Then, all animals were challenged with a 2.0 g/kg ethanol i.p. injection and locomotor activity was assessed. Acute and chronic ethanol pretreatment increased locomotor activity in response to a challenge dose of ethanol (2 g/kg) in D2 mice but had no effect on B6 mice. Prior exposure to ethanol altered the amount of ethanol consumed in a mouse strain-dependent manner. D2 mice showed a positive relationship between ethanol intake and dose or duration of ethanol preexposure. B6 mice preexposed to ethanol consumed more ethanol than naive animals, independent of dose or duration of exposure. During the last phase of self-administration testing, D2 mice exposed to chronic ethanol (2 g/kg) consumed as much ethanol as B6 from the same pretreatment condition. After a history of ethanol self-administration, saline control mice from the D2 strain showed equal locomotor activation as compared to D2 mice that were pretreated with ethanol injections. B6 mice showed no change in locomotor activity after ethanol self-administration or injection. These results demonstrate that genetic predisposition to avoid alcohol (D2 mice) can be modified by a history of preexposure and that a predisposition to prefer alcohol (B6 mice) may be also amenable to influence by drug history. In general, the results of this study suggest that genetic factors may interact with previous exposure to ethanol to modify ethanol self-administration.     

Distribution, excretion, and metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J, DBA/2J, and B6D2F1/J mice

The strains of mice, C57BL/6J, DBA/2J, and B6D2F1/J, have been used as models to study the mechanism of action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The distribution, excretion, and metabolism of this compound was studied in male C57BL/6J, DBA/2J, and B6D2F1/J mice following the intraperitoneal administration of radiolabeled TCDD at a dose of 10 micrograms/kg. In all strains, the liver and adipose tissue were the major sites for the accumulation of 3H-TCDD, with more 3H-TCDD being distributed to the livers of the C57BL/6J and B6D2F1/J strains as compared to the DBA/2J strain. While in all strains the feces were the major route of elimination, the total amount of 3H-TCDD-derived radioactivity excreted in the feces amounted to approximately 72% of the original dose in the C57BL/6J and B6D2F1/J strains whereas this was only 54% in the DBA/2J strain. The half-lives for the cumulative excretion of radioactivity in the feces were similar in all strains. The half-life for the excretion of radioactivity in the urine was considerably greater in the DBA/2J strain as compared to the C57BL/6J and B6D2F1/J strains. The estimated half-lives for the total cumulative excretion of 3H-TCDD-derived radioactivity by all routes was 11.0, 24.4, and 12.6 days for the C57BL/6J, DBA/2J, and B6D2F1/J strains, respectively. Greater than 85% of the total radioactivity excreted in urine, bile, and feces from all three mouse strains was present as metabolites of TCDD.     

Diet-induced obesity and cardiovascular regulation in C57BL/6J mice

1. In the present study, we determined the effect of diet-induced obesity on cardiovascular and metabolic regulation in mice at standard laboratory temperatures (ambient temperature (Ta) = 22 degrees C) and during exposure to thermoneutrality (Ta = 30 degrees C). 2. Male C57BL/6J (B6) mice fed a high-fat diet (HFF; n = 17) or chow (CHW; n = 14) for 15 weeks were surgically instrumented with telemetry devices, housed in metabolic chambers and assigned to either control or atenolol treatment (25 mg/kg per day in drinking water) to determine the effects of obesity on baseline cardiovascular function and on the responses to thermoneutrality and 24 h fasting. Mean arterial pressure (MAP), heart rate (HR), arterial pressure and HR variability (time and frequency domain), oxygen consumption (VO2) and locomotor activity were determined. 3. The HFF mice exhibited increased bodyweight (+10.6 +/- 4.1 g), moderate light period hypertension (+8.6 +/- 2.6 mmHg), no difference in HR and increased HR variability at standard laboratory temperature compared with CHW controls. Atenolol produced less of a decrease in HR in HFF mice (-42 +/- 10 b.p.m.) compared with CHW controls (-73 +/- 15 b.p.m.). Acute exposure to thermoneutrality (Ta = 30 degrees C) reduced HR similarly in both HFF and CHW mice (approximately 175 b.p.m.), but reduced MAP less in HFF than in CHW mice (-7.3 +/- 2.5 and -15.2 +/- 1.0 mmHg), respectively. Atenolol treatment had only minor effects on the HR response to thermonuetrality (-114 +/- 13 and -129 +/- 8 b.p.m. in HFF and CHW mice, respectively). The HFF mice displayed greater fasting-induced reductions in light period MAP than did CHW mice (-10.0 +/- 1.1 vs-3.1 +/- 3.5 mmHg, respectively), whereas HR was decreased equally in both groups. Fasting-induced increases in HR variability were attenuated in HFF mice. 4. We conclude that diet-induced obesity produced generally minor changes in cardiovascular regulation in B6 mice at baseline, some of which are distinct from the effects of diet-induced obesity in larger animal models. In contrast, acute variations in Ta or caloric availability produce pronounced alterations in cardiovascular function in either lean or obese mice, which are generally evident after atenolol and, thus, presumably not due exclusively to variation in cardiac sympathetic activity. Interestingly, the degree of obesity induced hypertension was augmented when mice were studied at thermonuetrality. The results suggest an important unrecognized role for vagal tone in the regulation of cardiovascular function in mice and support the need for considerable caution when using mouse models of obesity to examine regulation of cardiovascular function. We argue that mouse physiology studies should be performed in thermoneutral conditions.     

Distribution and excretion of 2,3,7,8-tetrachlorodibenzofuran in C57BL/6J and DBA/2J mice

The distribution and excretion of the toxic pollutant, 2,3,7,8-tetrachlorodibenzofuran (TCDF), was studied in male C57BL/6J and DBA/2J mice (22–29 g). [¹⁴C]TCDF was administered iv at a dose of 0.1 μmmol/kg. The liver was the major site of TCDF accumulation, with more TCDF in the livers of C57BL/6J mice compared to DBA/2J mice. TCDF had a half-life of approximately 1.8 days in the livers of both strains. At 7 hr and 1 day, respectively, radioactivity was redistributed to adipose tissue of C57BL/6J mice and DBA/2J mice. The terminal $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of TCDF in adipose tissue of C57BL/6J mice was 1.1 days, whereas it was 6.8 days in DBA/2J mice; the sixfold longer half-life in DBA/2J mice may be related to the approximately 36% greater adipose tissue content of this strain which may sequester more TCDF. More than 80 and 55% of the dose was excreted in the feces of C57BL/6J and DBA/2J mice, respectively, within 10 days as polar metabolites. The whole body half-life of TCDF was 2 days in C57BL/6J and 4 days in DBA/2J mice. Thus, DBA/2J mice sequester more of the TCDF dose in adipose tissue, accounting for a relatively slower rate of clearance and lower concentrations of TCDF at the putative target site(s) for toxic action.     

Genetic differences in intravenous cocaine self-administration between C57BL/6J and DBA/2J mice

In experiment 1, two different strains of mice [C57BL/6J (B6) and DBA/2J (D2)] were allowed to nosepoke for 5 µl intravenous (IV) infusions during 2-h daily sessions. Two nosepoke holes were available, only one of which was reinforced on an FR-3 schedule with a 10-s time-out indicated by a light inside the reinforced nosepoke hole. During the first nine sessions, infusions were saline. On subsequent sessions, mice acquired nosepoking for 0.5 mg/kg cocaine. Finally, all mice were extinguished by again receiving only saline infusions. Cocaine acted as a reinforcer in both strains. In experiment 2, different mice from the same two strains were allowed to acquire nosepoking for IV cocaine at one of three unit doses (0.5, 1.0, or 2.0 mg/kg). Although there were no effects of unit dose on rate of acquisition, B6 mice were faster in acquiring self-administration behavior than were D2 mice. Experiment 3 assessed behavior in the same mice, after acquisition had occurred. D2 mice nosepoked at a lower rate at asymptote than did B6 mice, but with a higher preference for the cocaine reinforced hole. Unit doses of cocaine were then manipulated within subjects, from 0.125 to 2.0 mg/kg per infusion. Higher doses yielded lower response rates than lower doses, both between and within subjects. Behavior in D2 mice relative to B6 mice also appeared to be shifted to the left of the dose-response curve measured within-subjects. Together, these findings indicate that although cocaine serves as a reinforcer in both strains, there are genetic differences in the pattern of cocaine self-administration between these two mouse strains.     

Genetic differences in 2-aminofluorene pharmacokinetics between intact C57BL/6J and A/J mice

Studies of genetically determined differences in arylamine acetylation with the model carcinogen 2-aminofluorene in C57BL/6J and A/J inbred mouse strains showed that individual differences in the pharmacokinetics of 2-aminofluorene were dependent on differences in 2-aminofluorene N-acetyltransferase activity in liver and blood. Elimination rates of 2-aminofluorene from blood of mice administered a single ip dose of 30, 50, or 100 mg/kg of 2-aminofluorene were dose-dependent in both strains. At a dose of 100 mg/kg, the average rate of 2-aminofluorene elimination was approximately three times faster in rapid acetylator (C57BL/6J) mice than in slow acetylator (A/J) mice (0.36 +/- 0.02 hr-1 vs. 0.12 +/- 0.02 hr-1), and that in B6AF1 mice was intermediate (0.24 +/- 0.02 hr-1) to the parental lines. These results support previous observations that acetylation of arylamines is controlled by intermediate dominant inheritance of two major alleles at a single locus. Comparison of the average rate of elimination of 2-aminofluorene from blood of the congenic mouse line, A.B6-NATr, (0.27 +/- 0.05 hr-1) which has the rapid acetylator allele placed on the A/J background provided evidence that modifying genes of the A/J mouse significantly reduced the effect of the rapid acetylator allele on the rate of 2-aminofluorene elimination. A trend was observed toward a greater apparent volume of distribution for 2-aminofluorene in A/J than in C57BL/6J mice.     

The difference in the tail-flick latency between C57BL/6 and DBA/2J mice

The tail-flick latency, measured using radiant heat as a noxious stimulus, was significantly shorter in C57BL/6 than in DBA/2J mice, while no significant interstrain differences were observed in the hot-plate test. The experiments in which the animals' tail was painted indicated that the difference in the tail-flick latency between strains was caused by the difference in the color of animal's coat.     

Fear-potentiated startle response in mice: genetic analysis of the C57BL/6J and DBA/2J intercross

The role of genetic factors in the fear-potentiated startle (FPS) response was examined in the inbred C57BL/6J (B6) and DBA/2J (D2) mouse strains. Mice in the D2 strain displayed a significant potentiation in the acoustic startle response (ASR) when presented with a visual condition stimulus (CS) previously paired with an aversive unconditioned stimulus (US). The maximal FPS response was observed following 20 conditioning trials but a near maximal response was noted following as few as five trials. Forty conditioning trials produced a significant reduction in the FPS response that may be related to overtraining. The FPS response in the B6 strain was significantly lower than the D2 strain, regardless of the number of conditioning trials. The contrasting FPS responses were not related to differences in auditory sensitivity known to exist between these strains. Analysis of a full Mendelian cross formed from the B6 and D2 strains found that the FPS response was a highly heritable trait, best described by a simple additive model of inheritance and with a broad-sense heritability of 0.46. The distribution of the FPS response in F2 hybrids formed from the intercross of the D2 and B6 strains was continuous which suggests a multigenic substrate. The light + noise and noise-alone trial types were highly correlated, but no association was detected between the baseline ASR amplitude and the FPS response. Mice from the phenotypic extremes of the F2 distribution displayed FPS responses that were more extreme than either of the progenitor strains. However, both baseline startle amplitude and the salience of auditory stimuli did not differ in these groups. The results of this study confirm an early report by Falls et al. (1997), and provide additional quantitative genetics information necessary for the eventual mapping of the chromosomal regions or genes associated with the FPS response in mice.     

Ethanol vapor self-administration in adult C57BL/6J male mice

To determine if ethanol vapor is reinforcing, chambers with two nose-poke devices were used. First, C57BL/6J mice were trained to nose-poke at one (FR port) and then to hold a nose-poke for at least 1 s at the second (reward port) for 10% sucrose reinforcement. When mice held reward port nose-pokes for > or = 1 s on 95% of session trials, ethanol vapor (0.05%, w/v) or clean air replaced sucrose. In experiment 1, the FR requirement at the FR port was incremented from 1 to 8. Ethanol vapor (n=3) or clean air (n=3) was delivered for 1 s following a single nose-poke at the reward port after completing response requirements at the FR port. Nose-pokes at the FR port increased with increasing FR to maintain ethanol vapor intake, while clean air intake and its associated responding extinguished. In experiment 2, mice (n=4) controlled the duration of ethanol vapor delivery by providing vapor for as long as the mouse held a single poke in the reward port after completing response requirements at the FR port. Nose-pokes at the FR port increased with increasing FR to maintain ethanol vapor intake at the reward port. These findings indicate that ethanol vapor is reinforcing in adult C57BL/6J male mice.     

Accumbens Homer2 overexpression facilitates alcohol-induced neuroplasticity in C57BL/6J mice.

Homer proteins are integral components of the postsynaptic density that are necessary for alcohol-induced neuroplasticity within the nucleus accumbens (NAC). In this report, we describe the effects of chronic alcohol consumption upon NAC Homer expression and investigate the functional consequences of mimicking the alcohol-induced changes in Homer expression vis-à-vis alcohol-induced changes in NAC neurochemistry and behavior. Chronic alcohol consumption under continuous access (3 months; daily intake approximately 11.2+/-1.5 g/kg/day) produced a robust increase in NAC Homer2 protein levels that was apparent at 2 days, 2 weeks, and 2 months following withdrawal from alcohol drinking. The increased Homer2 expression was accompanied by a less enduring elevation in total mGluR1 and NR2b levels that were evident at 2 days and 2 weeks but not at the 2-month time point. Mimicking the alcohol-induced increase in Homer2 levels by viral transfection of NAC neurons in alcohol-preferring C57BL/6J inbred mice enhanced behavioral output for alcohol reinforcement and increased alcohol intake under both preprandial and postprandial conditions. Moreover, NAC Homer2 overexpression facilitated the expression of an alcohol-conditioned place preference, as well as the development of motor tolerance. Finally, NAC Homer2 overexpression facilitated NAC glutamate and dopamine release following an acute alcohol injection and augmented alcohol-induced dopamine and glutamate sensitization, but did not affect NAC gamma-aminobutyric acid levels. Thus, an upregulation in NAC mGluR-Homer2-N-methyl-D-aspartic acid receptor signaling appears to be an important molecular adaptation to alcohol that promotes neuroplasticity facilitating motivational drive for alcohol and the development of alcoholism-related behaviors.     

Potentiated β-cell response to non-glucose stimuli in insulin-resistant C57BL/6J mice

Insulin secretion in response to acetylcholine receptor activation by carbachol in insulin resistance induced by 12 weeks of high-fat diet in C57BL/6J mice is exaggerated. To study whether this persists after a longer period of time and also involves other non-glucose stimuli, we fed C57BL/6J mice a high-fat diet for 24 weeks. Both hyperinsulinemia (341±33 vs. 148±15 pmol/l) and slight hyperglycemia (7.8±0.2 vs. 6.1±0.1 mmol/l) were evident at this time point. The insulinotropic response to high dose carbachol (0.53 μmol/kg; 3403±377 vs. 1595±429 pmol/l), to the glucose analogue, 2-deoxyglucose (6 mmol/kg; 2014±315 vs. 1167±200 pmol/l), to cholecystokinin-8 (15.9 nmol/kg; 499±93 vs. 119±40 pmol/l) and to glucagon-like peptide-1 (32 nmol/kg; 307±86 vs. 71±9 pmol/l), were all exaggerated in mice given high-fat diet. In contrast, the insulin response to glucose was impaired. This shows that insulin resistance is accompanied by a general islet supersensitivity to non-glucose stimuli, which persists over a long period of time.     

PCBs and PBBs: biologic and toxic effects on C57BL/6J and DBA/2J inbred mice

Treatment of genetically inbred "responsive" C57BL/6J and "non-responsive" DBA/2J mice with Aroclor 1254 or fireMaster BP-6 resulted in the induction of hepatic microsomal benzo[a]pyrene hydroxylase only in the former mouse strain and aminopyrine N-demethylase in both strains of mice. In contrast, 3,3',4,4',5-pentachlorobiphenyl and 3,3',4,4'-tetrabromobiphenyl, induced benzo[a]pyrene hydroxylase in both C57BL/6J and DBA/2J but did not enhance aminopyrine N-demethylase in either strain of mouse. Both these coplanar halogenated biphenyls also caused thymic atrophy in the responsive and non-responsive mice and their effects resembled those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Treatment of the inbred mice with several mono-ortho substituted analogs of the coplanar halogenated biphenyls, including 2,3,3',4,4'-pentachloro-, 2,3',4,4',5-pentabromo-, 2,3,3',4,4',5-hexachloro- and 3',4'-dibromo-2,3,4,5-tetrachlorobiphenyl, gave hepatic enzyme-induction results similar to those observed for the commercial halogenated biphenyls. At dose levels of 1500 mumol/kg, most of these compounds caused thymic atrophy in C57BL/6J mice but not in DBA/2J mice. The structure-activity correlations in the mice complement similar studies with the halogenated biphenyls in rats and support the proposed receptor-mediated mechanism for the toxic halogenated aromatics.