Pathologic characterization of hypotensive C57BL/6J-agt: angiotensinogen-deficient C57BL/6J mice

Most studies on preconception diagnosis published so far have used polymerase chain reaction (PCR) analysis to identify single gene defects. Although fluorescent DNA probes have been used to obtain a partial cytogenetic diagnosis of aneuploidies in first polar bodies without defined chromosome structures, the analysis of structural chromosome anomalies in the interphase nucleus is not adequate. We describe a procedure to obtain first polar body chromosome complements from hamster and human oocytes. In 63.6% (105 of 165) of hamster first polar bodies the chromosome complement showed a defined chromosome morphology and in 94.1% (16 of 17) of human oocytes fixed after follicular puncture it was possible to obtain high quality, well spread chromosome complements. First polar body chromosomes are fuzzy and shorter than oocyte chromosomes, but fluorescent in-situ hybridization results obtained in human first polar bodies clearly show that it is possible to detect whole chromosomes, centromeres and unique sequences, including the terminal regions of small chromosomes. This suggests that in fresh oocytes, DNA loss resulting from apoptotic chromosome fragmentation has not yet occurred. Using the procedure described, first polar bodies could be used to analyse the meiotic segregation of maternal structural abnormalities and to detect numerical chromosome anomalies in humans.     

Nonshivering thermogenesis during acute cold exposure in adult and aged C57BL/6J mice

In C57BL/6J adult and aged mice, housed at room temperature (22.5 +/- 1 degrees C), we measured O2 consumption and CO2 production and calculated metabolic heat production under conditions of anesthesia and myorelaxation during acute cold stimulation when body temperature was lowered 7.5 degrees C below control level. An independent group of mice was subjected to a three hour partial physical restraint at 6 degrees C and concentration of uncoupling protein (thermogenin) was measured in interscapular brown adipose tissue mitochondria at different times after cold exposure. Heat production under anesthesia and myorelaxation was about 57-66% lower than in nonanesthetized conditions, but increased significantly during cold stimulation in both age groups. Under anesthesia and myorelaxation before and during cold stimulation aged mice produced about 20% more heat than adult mice. Because in these experiments all sources of facultative thermogenesis, except nonshivering, were suppressed by anesthesia and myorelaxation, and because brown adipose tissue is the major source of nonshivering thermoproduction, we concluded that aged mice housed at room temperature have an increased thermogenesis in brown adipose tissue. This conclusion was also supported by the finding that the concentration of uncoupling protein measured in the mitochondria of brown adipose tissue after single cold exposure was significantly higher in aged than in adult mice. Therefore, we propose that the lower, cold-induced, heat production typically observed in nonanesthetized aged mice may reflect reduced thermogenic capacity of skeletal muscles. While aged mice have less brown adipose tissue than adult animals, the remaining brown adipose tissue may compensate by increasing the concentration of uncoupling protein.     

Interval timing accuracy and scalar timing in C57BL/6 mice.

In many species, interval timing behavior is accurate—appropriate estimated durations—and scalar—errors vary linearly with estimated durations. Whereas accuracy has been previously examined, scalar timing has not been clearly demonstrated in house mice (Mus musculus), raising concerns about mouse models of human disease. The authors estimated timing accuracy and precision in C57BL/6 mice, the most used background strain for genetic models of human disease, in a peak-interval procedure with multiple intervals. Both when timing 2 intervals (Experiment 1) or 3 intervals (Experiment 2), C57BL/6 mice demonstrated varying degrees of timing accuracy. An important finding was that, both at the individual and group levels, their precision varied linearly with the subjective estimated duration. Further evidence for scalar timing was obtained using an intraclass correlation statistic. This is the first report of consistent, reliable scalar timing in a sizable sample of house mice, thus validating the peak-interval procedure as a valuable technique, the intraclass correlation statistic as a powerful test of the scalar property, and the C57BL/6 strain as a suitable background for behavioral investigations of genetically engineered mice modeling disorders of interval timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Varenicline ameliorates nicotine withdrawal-induced learning deficits in C57BL/6 mice.

Varenicline, a partial agonist for α4β2 nicotinic acetylcholine receptors (nAChRs) and full agonist for α7 nAChRs, has been approved for the treatment of smoking cessation. Although recent clinical trials support the efficacy of varenicline for managing global nicotine withdrawal symptoms and for smoking cessation, its effects on animal models of specific withdrawal-associated behaviors have not been tested. The present study evaluated the effects of varenicline on contextual fear conditioning and its effects on nicotine (6.3 mg/kg/day) withdrawal-induced deficits in contextual fear conditioning. Varenicline (0.01, 0.1, 1.0 mg/kg) had no effect on contextual fear conditioning when administered alone, but (0.1 mg/kg) prevented nicotine withdrawal-associated deficits in contextual fear conditioning. These data demonstrate, for the first time, that varenicline reverses nicotine withdrawal-induced deficits in an animal model and suggest that varenicline may be effective at treating nicotine withdrawal-associated deficits in learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Metabolic studies on haloperidol and its tetrahydropyridine analog in C57BL/6 mice

The neuroleptic agent haloperidol (HP) is biotransformed in humans to a pyridinium metabolite, HPP+, that displays neurotoxic properties resembling those of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-derived neurotoxic pyridinium metabolite MPP+. We report here that HP and its tetrahydropyridine dehydration product 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6- tetrahydropyridine (HPTP) are metabolized in vivo by the MPTP-susceptible C57BL/6 mouse to several pyridinium metabolites including HPP+ and the 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-hydroxybutyl]pyridinium species RHPP+, the pyridinium species corresponding to reduced haloperidol (RHP), a major circulating metabolite of HP. Atmospheric pressure ion-spray (API) mass spectral data also suggest the formation of fluorophenyl ring-hydroxylated derivatives of these two pyridinium metabolites. Furthermore, HPLC tracings reveal the presence of HPP+, RHPP+, and two phenolic pyridinium metabolites in brain tissue extracts of HPTP, but not HP, treated mice. The neurotoxic potential of MPTP-type pyridinium species suggests that these metabolites may contribute to some of the neurological disorders observed in humans undergoing chronic HP treatment.     

A major gene affecting age-related hearing loss in C57BL/6J mice

A major gene responsible for age-related hearing loss (AHL) in C57BL/6J mice was mapped by analyses of a (C57BL/6J x CAST/Ei) x C57BL/6J backcross. AHL, as measured by elevated auditory-evoked brainstem response (ABR) thresholds, segregated among backcross mice as expected for a recessive, primarily single-gene trait. Both qualitative and quantitative linkage analyses gave the same genetic map position for the AHL gene (Ahl on chromosome 10, near D10Mit5. Marker assisted selection was then used to produce congenic lines of C57BL/6J that contain different CAST-derived segments of chromosome 10. ABR test results and cochlear histopathology of aged progenitors of these congenic lines are presented. Ahl is the first gene causing late-onset, non-syndromic hearing loss that has been reported in the mouse.     

A study examining intravenous ethanol-conditioned place preference in C57BL/6J mice

The reinforcing effects of intravenous (I.V.) ethanol were examined in C57BL/6J (C57) mice with a conditioned-place-preference (CPP) paradigm. Before CPP testing, adult mice underwent jugular catheterization. On the following day, subjects were acclimated to a two-compartment CPP chamber. A 15-min nondrug pretest was conducted to determine compartment preference. For the treatment group, I.V. ethanol [30% (v/v), 3.4 microl/min, 25 min] was paired with the nonpreferred compartment, whereas I.V. saline was paired with the preferred compartment. The control group received I.V. saline in both compartments. Two conditioning sessions were conducted per day (0900 and 1500), and the order of the infusions was counterbalanced across subjects. The drug-free posttest was identical to the pretest, except that it occurred on the day after the final drug/compartment pairing. The entire procedure required 6 days. After just two pairings with ethanol, with a cumulative ethanol dose of only 0.82 g/kg/day, significant CPP was noted in the treatment group, whereas no change in compartment preference was noted for the control group. A separate group of C57 mice were trained to discriminate intraperitoneal ethanol (1.5 g/kg) from saline using a two-lever drug discrimination paradigm. After training was complete, these mice also underwent jugular catheterization. Substitution testing was conducted with I.V. ethanol [30% (v/v), 6.4 microl/min, 12 min] and saline. The results indicate that the subjective effects of ethanol did not differ according to the route of administration. Together, these experiments provide evidence that ethanol is rewarding for C57 mice, as indexed by ethanol CPP, and that the subjective effects of intravenously and intraperitoneally administered ethanol are similar.     

Behavioral and neurobiological changes in C57BL/6 mice exposed to cuprizone.

C57BL/6 mice were given 0.2% cuprizone (CPZ) for 2 to 6 weeks while controls ate the same diet without CPZ. At various time points the animals were subjected to behavioral tests and their brains were analyzed. Mice exposed to CPZ for 2 and 3 weeks displayed more climbing behavior and lower prepulse inhibition, suggesting an increase in central nervous system activity and impaired sensorimotor gating. In addition, they showed lower activities of monoamine oxidase and dopamine beta hydroxylase in the hippocampus and prefrontal cortex, and had higher dopamine but lower norepinephrine levels in the prefrontal cortex. Mice exposed to CPZ for 4 to 6 weeks had less social interaction, which is an animal correlate of social withdrawal of patients with schizophrenia. Also, these CPZ-exposed mice showed evident brain demyelination, myelin break down, and loss of oligodendrocytes. At all time points the CPZ-exposed mice spent more time in the open arms of an elevated plus maze and exhibited spatial working memory impairment. These data are in line with evidence from human studies suggesting a putative role of white matter abnormality in the pathophysiology of schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction between BTBR and C57BL/6J genomes produces an insulin resistance syndrome in (BTBR x C57BL/6J) F1 mice

Insulin resistance is a common syndrome that often precedes the development of noninsulin-dependent diabetes mellitus (NIDDM). Both diet and genetic factors are associated with insulin resistance. BTBR and C57BL/6J (B6) mice have normal insulin responsiveness and normal fasting plasma insulin levels. However, a cross between these two strains yielded male offspring with severe insulin resistance. Surprisingly, on a basal diet (6.5% fat), the insulin resistance was not associated with fasting hyperinsulinemia. However, a 15% fat diet produced significant hyperinsulinemia in the male mice (twofold at 10 weeks; P < .05). At 10 weeks of age, visceral fat contributed approximately 4.3% of the total body weight in the males versus 1.8% in females. In the males, levels of plasma triacylglycerol and total cholesterol increased 40% and 30%, respectively, compared to females. Plasma free fatty acid concentrations were unchanged. Oral glucose tolerance tests revealed significant levels of hyperglycemia and hyperinsulinemia 15 to 90 minutes after oral glucose administration in the male mice. This was particularly dramatic in males on a 15% fat diet. Glucose transport was examined in skeletal muscles in (BTBR x B6)F1 mice. In the nonhyperinsulinemic animals (females), insulin stimulated 2-deoxyglucose transport 3.5-fold in the soleus and 2.8-fold in the extensor digitorum longus muscles. By contrast, glucose transport was not stimulated in the hyperinsulinemic male mice. Hypoxia stimulates glucose transport through an insulin-independent mechanism. This is known to involve the translocation of GLUT4 from an intracellular pool to the plasma membrane. In the insulin-resistant male mice, hypoxia induced glucose transport as effectively as it did in the insulin-responsive mice. Thus, defective glucose transport in the (BTBR x B6)F1 mice is specific for insulin-stimulated glucose transport. This is similar to what has been observed in muscles taken from obese NIDDM patients. These animals represent an excellent genetic model for studying insulin resistance and investigating the transition from insulin resistance in the absence of hyperinsulinemia to insulin resistance with hyperinsulinemia.     

Murine coronavirus-induced subacute fatal peritonitis in C57BL/6 mice deficient in gamma interferon

Gamma interferon-deficient (IFN-gamma-/-) mice with a C57BL/6 background were infected intraperitoneally with mouse hepatitis virus strain JHM (JHMV). In contrast to IFN-gamma-+/- and IFN-gamma+/+ mice, JHMV persisted in IFN-gamma-/- mice and induced death during the subacute phase of the infection. Unexpectedly, infected IFN-gamma-/- mice showed severe peritonitis accompanying the accumulation of a viscous fluid in the abdominal and thoracic cavities in the subacute phase. Destructive changes of hepatocytes were not observed. Administration of recombinant IFN-gamma protracted the survival time of IFN-gamma-/- mice after JHMV infection. These results demonstrate that IFN-gamma plays a critical role in viral clearance in JHMV infection. They also show that a resultant persistent JHMV infection induces another form of disease in IFN-gamma-/- mice, which bears a resemblance to feline infectious peritonitis in cats.     

Distinct characteristics of resistance to Borrelia burgdorferi-induced arthritis in C57BL/6N mice

The diazepam-binding inhibitor (DBI) is a 10-kDa highly evolutionarily conserved multifunctional protein. In mammals, one of DBI's functions is in the activation of steroid hormone biosynthesis via binding to a specific outer mitochondrial membrane receptor (benzodiazepine receptor, BZD) and promoting cholesterol transport to the inner membrane. In this work, a multitiered approach was utilized to study the role of this receptor-like activity in ecdysteroidogenesis by larval insect prothoracic glands (PGs). First, both DBI protein and messenger RNA (mRNA) levels were correlated with peak PG ecdysteroid production. In vitro ecdysteroid production was stimulated by the diazepam analogue FGIN 1-27 and inhibited anti-DBI antibodies. The DBI protein was found distributed throughout PG cells, including regions of dense mitochondria, supposed subcellular sites of ecdysteroid synthesis. Finally, a potential mitochondrial BZD receptor in PG cells was demonstrated by photoaffinity labeling. These results suggest an important role for the insect DBI in the stimulation of steroidogenesis by prothoracic glands and indicate that a pathway for cholesterol mobilization leading to the production of steroid hormones appears to be conserved between arthropods and mammals.     

Gene expression in brain during cuprizone-induced demyelination and remyelination

When C57BL/6J mice, 8 weeks of age, received 0.2% Cuprizone in their diet, extensive demyelination in corpus callosum was detectable after 3 weeks, and there was massive demyelination by 4 weeks. As expected, the accumulation of phagocytically active microglia/macrophages correlated closely with demyelination. When Cuprizone was removed from the diet, remyelination was soon initiated; after 6 weeks of recovery, myelin levels were near-normal and phagocytic cells were no longer prominent. Steady-state levels of mRNA for myelin-associated glycoprotein, myelin basic protein, and ceramide galactosyltransferase were already profoundly depressed after 1 week of Cuprizone exposure and were only 10-20% of control values after 2 weeks. Unexpectedly, upregulation of mRNA for these myelin genes did not correlate with initiation of remyelination but rather with accumulation of microglia/macrophages. After 6 weeks of exposure to Cuprizone, mRNA levels were at control levels or higher-in the face of massive demyelination. This suggests that in addition to effecting myelin removal, microglia/macrophages may simultaneously push surviving oligodendroglia or their progenitors toward myelination.     

Dietary isoflavones reduce plasma cholesterol and atherosclerosis in C57BL/6 mice but not LDL receptor-deficient mice

To assess the cardiovascular effects of systemically administered opioid agonists, changes in blood pressure and heart rate were observed after intravenous (i.v.) administration of U50,488H (trans-3,4-dichloro-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeneacetamide), a selective kappa-opioid receptor agonist, and DAMGO (D-Ala2, N-Me-Phe4, Gly5-ol), a selective mu-opioid-receptor agonist. Intravenous administration of U50,488H (1.2 mg/kg) and DAMGO (0.3 mg/kg) to the awake sheep resulted in an immediate increase in blood pressure. The pressor response to U50,488H was accompanied by an increase in heart rate. In contrast, there was no accompanying change in heart rate in response to DAMGO. We hypothesized that the lack of a reflex bradycardia to the pressor responses of both the mu- and kappa-opioid-receptor agonists was due to a blunting of baroreflex-mediated bradycardia. The reflex bradycardia to norepinephrine (0.6 microg/kg/min) was significantly reduced in the presence of DAMGO but not U50,488H. In view of the lack of effect of U50,488H on the baroreflex, we further hypothesized that the tachycardia it elicited was due to an increase in sympathetic activity. Pretreatment with propranolol (0.1 mg/kg) completely blocked the tachycardia elicited by U50,488H. These data suggest that the lack of a reflex bradycardia to the pressor response of DAMGO is due to a blunting of baroreflex-mediated bradycardia. In contrast, the increase in heart rate caused by U50,488H is mediated by sympathetic activation of the heart.     

Natural melatonin ''knockdown'' in C57BL/6J mice: rare mechanism truncates serotonin N-acetyltransferase

Resistance to the anabolic effects of growth hormone (GH) occurs with severe caloric deficit. This study examined whether moderate caloric deficit (50% of daily intake for 7 days) in the adolescent rat exceeds a critical threshold for GH action and whether a combination of GH and insulin-like growth factor I (IGF-I) would have enhanced anabolic effects on the diaphragm (Dia). Five groups of rats (4 wk old) were studied: 1) control (Ctl), 2) nutritionally deprived (ND), 3) ND + GH, 4) ND + IGF-I, and 5) ND + GH + IGF-I. IGF-I was given by continuous infusion (200 microg/day). GH was injected subcutaneously (250 microg every 12 h). Contractile and fatigue properties of the Dia were determined in vitro. Quantitative histochemical methods were used to determine Dia fiber type proportions, cross-sectional areas, and succinate dehydrogenase activities. The body weight of Ctl rats increased 46% compared with 7% in ND animals, whereas that of ND rats receiving growth factors was intermediate. Serum IGF-I levels were reduced 54% in ND animals and maintained with the provision of growth factors. Dia fatigue resistance was improved in ND animals receiving growth factors. There were no differences in Dia contractile properties, fiber type proportions, or succinate dehydrogenase activities across groups. ND resulted in atrophy/growth arrest of all Dia fibers (20-32%) compared with Ctl. Administration of IGF-I and/or GH completely prevented atrophy/growth arrest of all Dia fibers. No additive or synergistic effects were noted. We propose that these growth factors may provide useful short-term adjunctive nutritional support in circumstances in which the provision of optimal nutrition may be delayed or inadequate.     

Macromolecules of the central nervous system and acoustic priming in C57BL/6Bg mice

Short-term cultures of androgen-responsive Shionogi 115 (S115) cells exhibited density-dependent regulation of proliferation rate in the presence or absence of testosterone. The average surface area per cell exposed to the growth medium was inversely proportional to population density. By contrast, long-term cultures (serially passaged in testosterone-containing medium for several months) did not exhibit density-dependent regulation of proliferation rate when grown in testosterone-containing medium. In this medium, cells became elongated and no longer exhibited any obvious decrease in exposed surface area with increasing density. Nevertheless, when subcultured into testosterone-free medium, these cells reverted to an epithelial morphology and exhibited density-dependent regulation of proliferation rate. These relationships suggested that the proliferation rate of cells decreased with density in proportion to the decrease in exposed surface area...     

Differential effects of acrylamide on the degeneration and regeneration of myelinated fibers between C57BL/Ola and C57BL/6J mice after crush injury

Neopterin is a biochemical marker for the activation of the cell-mediated immune system. We measured neopterin, beta 2-microglobulin, and acute phase proteins in 31 HIV-seropositive and -seronegative Zambian patients with tuberculosis, using stored sera that had been obtained at the beginning and at end of antituberculosis treatment. In both HIV-seropositive and -seronegative patients neopterin and acute phase proteins were elevated when tuberculosis was initially diagnosed and fell during treatment. In contrast, the mean beta 2-microglobulin level increased during antituberculous therapy in the HIV-seropositive group. Serum neopterin levels at diagnosis were correlated with other parameters of disease activity (fever, anemia, and weight loss). In both groups, patients with persistently elevated neopterin levels at the end of treatment were more likely to suffer relapse of tuberculosis or other adverse health events in the subsequent follow-up period. Neopterin can be used to monitor the response to antituberculous therapy in both HIV-seropositive and -seronegative patients and may have a prognostic value for the patients' wellbeing in the follow-up period.     

Sex-restricted non-Mendelian inheritance of mouse chromosome 11 in the offspring of crosses between C57BL/6J and (C57BL/6J x DBA/2J)F1 mice

We report on the observation of sex-restricted, non-Mendelian inheritance over a region of mouse Chromosome (Chr) 11, occurring in the offspring of crosses between two commonly used Mus musculus-derived inbred strains, C57BL/6J and DBA/2J. In the surviving backcross progeny of reciprocal matings between (C57BL/6J x DBA/2J)F1 hybrids and the C57BL/6J parental strain, we observed the preferential appearance of C57BL/6J alleles along a region of Chr 11. The deviation from Mendelian predictions was observed only in female offspring from both reciprocal backcrosses, and not in males from either cross. The sex-specificity of the observed non-Mendelian inheritance points to an explanation based on embryonic or neonatal lethality. Our data add to previously obtained evidence for a Chr 11 locus or loci with sex-specific and allele-specific effects on viability.     

Acoustic startle response in young and aging C57BL/6J and CBA/J mice.

C57 mice demonstrate progressive age-related hearing loss during the 1st yr, whereas CBA mice lose little sensitivity through 18 mo of age. The acoustic startle response (ASR) was measured to determine behavioral correlates of aging with and without presbycusis. Stimuli were tone pips with frequencies of 4–24 kHz at intensities of 70–200 dB SPL. ASR thresholds increased with age, and startle amplitudes became smaller. Changes in startle parameters were more pronounced in C57 mice, with middle to high frequencies severely affected. Startle latencies at and above ASR threshold increased with age in C57 mice. CBA data indicate that aging has little effect on ASR parameters; the C57 data show that hearing loss is a cogent factor. ASR parameters of C57 mice are altered to a greater extent than expected, on the basis of the elevations of absolute sensory thresholds, particularly for middle frequencies. Both peripheral and central mechanisms may account for the discrepancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pharmacogenetic differences in audiogenic seizure priming of C57BL/6Bg and DBA/1Bg-asr mice

Susceptibility to audiogenic seizures can be induced in some strains of resistant mice by exposure to an initial auditory stimulus (acoustic priming). Aminooxyacetic acid, hydrazine, glutamic acid, gamma-aminobutyric acid (GABA), cycloheximide, and metyrapone antagonize the acoustic priming of audiogenic seizure susceptibility in C57BL/6Bg mice, whereas only metyrapone attenuates that of DBA/1Bg-asr mice. The strain difference in the effect of AOAA and cycloheximide is correlated with a small, transient fall in level of brain GABA in C57BL/6Bg but not DBA41Bg-asr mice. These findings support our hypothesis that there are at least two neural mechanisms of acoustic priming, each with its own genetic basis and that corticosteroids are required by both mechanisms for the development of primed seizures.     

Plasticity of auditory cortex associated with sensorineural hearing loss in adult C57BL/6J mice

The representation of frequency was mapped in the primary auditory cortex (AI) of C57BL/6J (C57) mice during young adulthood (1.5-2 months) when hearing is optimal, and at 3, 6, and 12 months of age, a period during which progressive, high frequency, sensorineural hearing loss occurs in this strain. Maps were also obtained from CBA/CaJ mice which retain good hearing as they age. In AI of young adult C57 mice and CBA mice, characteristic frequencies (CFs) of multiple-unit clusters were easily identified with extracellular recordings, and a general tonotopic organization was observed from dorsal (high frequency) to ventral and caudal (low frequency). In individual cases there appeared to be deviations from the above tonotopic organization, despite the fact that inbred mice are genetically invariant. As progressive loss of high frequency sensitivity ensued peripherally, a substantially increased representation of middle frequencies was observed in AI. There was no apparent change in the surface area of the auditory cortex despite the elimination of high frequencies, and virtually the entire auditory cortex became devoted to the middle frequencies (especially 10-13 kHz) for which sensitivity remained high. Similar age-related changes were not observed in normal-hearing CBA mice. These findings indicate that plasticity in the representation of frequency in AI is associated with high frequency hearing loss in C57 mice.