Further studies on the resistance of mice to myxoviruses

Summary Mice from 16 inbred strains were challenged with neurotropic influenza A virus, strain WSA, in an effort to secure other examples of the occurrence of the genemx. All strains, with the exception of Z/Gw, were fully susceptible. Z/Gw mice showed some degree of resistance probably unrelated tomx.A2G mice were challenged with 12 different virus strains. All influenza viruses used (3 strains of fowl plague, MEL, FM-1, A2/Ann Arbor/2/60 and B/Ann Arbor/3/62) were definitely less virulent for A2G than for control (C3H, A, ICR) mice. Two strains of Newcastle disease virus, and one strain each of rabies, vesicular stomatitis and encephalomyocarditis viruses were of similar virulence for A2G and control mice.The possible bearing of these findings on the epidemiology of influenza is discussed.Work supported by NIH General Research Support Grant FR-05062-03 and Training Grant 5 TI AI 128-04.     

Differences in Measures of Exploration and Fear in MHC-Congenic C57BL/6J and B6-H-2K Mice

MHC-congenic mice prefer to mate with mice of different MHC types and are able to discriminate between MHC-congenic mice by their urine odors, but nothing is known about behavioral differences among MHC-congenic mice. The present experiments examine the strain and sex differences in MHC-congenic C57BL/6J and B6-H-2K mice with respect to exploration and fear motivated behaviors in the elevated plus maze, the elevated zero maze, and the open field. In the elevated plus maze and elevated zero maze, C57BL/6J mice spent more time in the open areas than B6-H-2K mice, suggesting that they were less fearful and more exploratory. No sex differences for exploration were found but male mice defecated more than females in the elevated plus maze. In the open field there were no significant strain or sex differences in measures of exploration or fear. There were no strain differences in the investigation of a novel object placed into the open field, but males investigated the novel object more than females. These results indicate that there are differences in exploratory and fear behavior in MHC-congenic mice that may contribute to mate preferences and that behavioral differences in these mice might be further examined advantageously.     

Tryptophan hydroxylase 2 genotype determines brain serotonin synthesis but not tissue content in C57Bl/6 and BALB/c congenic mice

Tryptophan hydroxylase 2 (TPH2) catalyzes the rate-limiting step in the synthesis of brain serotonin (5-HT). In a previous report, a single nucleotide polymorphism in mTph2 (C1473G) reduced 5-HT synthesis by 55%. Mouse strains expressing the 1473C allele, such as C57Bl/6, have higher 5-HT synthesis rates than strains expressing the 1473G allele, such as BALB/c. Many studies have attributed strain differences to Tph2 genotype without ruling out the potential role of alterations in other genes. To test the role of the C1473G polymorphism in strain differences, we generated C57Bl/6 and BALB/c mice congenic for the Tph2 locus. We found that the 1473G allele reduced 5-HT synthesis in C57Bl/6 mice but had no effect on 5-HT tissue content except for a slight reduction (15%) in the frontal cortex. In BALB/c mice, the 1473C allele increased 5-HT synthesis but again did not affect 5-HT tissue content. At the same time, 5-hydroxyindoleacetic acid (5-HIAA) was significantly elevated in BALB/c congenic mice. In C57Bl/6 mice, there was no effect of genotype on 5-HIAA levels. BALB/c mice had lower expression of monoamine oxidase A and B than C57Bl/6 mice, but there was no effect of Tph2 genotype. On the tail suspension test, escitalopram treatment reduced immobility regardless of genotype. These data demonstrate that the C1473G polymorphism determines differences in 5-HT synthesis rates among strains but only minimally affects 5-HT tissue levels.     

Induction of antigen-specific Th1-type immune responses by gamma-irradiated recombinant Brucella abortus RB51

Brucella abortus strain RB51 is an attenuated rough mutant used as the live vaccine against bovine brucellosis in the United States and other countries. We previously reported the development of strain RB51 as a bacterial vaccine vector for inducing Th1-type immune responses against heterologous proteins. Because safety concerns may preclude the use of strain RB51-based recombinant live vaccines, we explored the ability of a gamma-irradiated recombinant RB51 strain to induce heterologous antigen-specific immune responses in BALB/c mice. Exposure of strain RB51G/LacZ expressing Escherichia coli beta-galactosidase to a minimum of 300 kilorads of gamma radiation resulted in complete loss of replicative ability. These bacteria, however, remained metabolically active and continued to synthesize beta-galactosidase. A single intraperitoneal inoculation of mice with 10(9) CFU equivalents of gamma-irradiated, but not heat-killed, RB51G/LacZ induced a beta-galactosidase-specific Th1-type immune response. Though no obvious differences were detected in immune responses to B. abortus-specific antigens, mice vaccinated with gamma-irradiated, but not heat-killed, RB51G/LacZ developed significant protection against challenge with virulent B. abortus. In vitro experiments indicated that gamma-irradiated and heat-killed RB51G/LacZ induced maturation of dendritic cells; however, stimulation with gamma-irradiated bacteria resulted in more interleukin-12 secretion. These results suggest that recombinant RB51 strains exposed to an appropriate minimum dose of gamma radiation are unable to replicate but retain their ability to stimulate Th1 immune responses against the heterologous antigens and confer protection against B. abortus challenge in mice.     

Genetic differences in response properties of rostral ventromedial medulla neurons to the μ-opioid receptor agonist DAMGO in mouse inbred strains

Background

Opioid sensitivity varies among individuals. Although opioids can act partly in the rostral ventromedial medulla (RVM), which has a major role in pain perception, individual differences in the functions of the RVM in response to opioids have not been elucidated. Pain-related behavior among inbred mouse strains may reflect individual differences in sensitivity to pain. We therefore investigated the changes in action potentials of RVM neurons in response to opioid in different mouse strains.

Methods

Two inbred strains of mice (A/J and CBA/J) were used. Their behavior to noxious stimuli was measured after intracerebroventricular injection of the μ-opioid receptor agonist, DAMGO. Using an in vivo extracellular recording technique, action potentials from single RVM neurons and their functional type (ON-like, OFF-like, or NEUTRAL-like cell) were identified. Evoked responses of the RVM neurons to noxious stimuli were recorded before and after DAMGO administration.

Results

The behavioral study showed that the dose-dependent antinociceptive effect in the A/J strain was significantly stronger than in the CBA/J strain. The electrophysiological study showed that the number of inhibitory OFF-like cells in A/J mice was significantly larger than in CBA/J mice (P < 0.01), and that the evoked responses of neurons of A/J mice were inhibited significantly more than in CBA/J mice both for ON-like and OFF-like cells (P < 0.01).

Conclusions

The strain differences in the physiological properties of RVM neurons corresponded to the behavioral strain differences. Genetic differences may contribute to the interindividual variation seen in opioid-induced analgesia.     

Analysis of behavioral and hippocampal variation in congenic albino and pigmented BALB mice

Mice of the BALB/c strain are widely used in behavioral research in spite of the albino condition, which can obscure brain-behavior relationships. We have developed a pigmented BALB strain, congenic to BALB/c, which could be more appropriate for neurogenetic studies that aim at identifying the effects of neurological mutations on behavior. Comparison of inbred albino and pigmented congenic BALB arising from the same litters provides a valuable tool for detecting the consequences of the albino mutation on behavioral performances. Preliminary results presented here show that the albino condition does not interfere with the development and patterns of connectivity of mossy fibers in the hippocampus. On the other hand, obvious coat color-linked differences appear for locomotor activity and defecation scores in the open field, pigmented mice being unexpectedlyl less active and more reactive than albino, as if better vision increased their reactions to a novel, anxiogenic environment. Finally, pigmented mice do not show better performances in the radial maze, which confirms that the inability of BALB mice for spatial learning in a highly demanding version of this task cannot be attributed to their inability to process visual information.     

Aberrant IgG isotype generation in mice with abnormal behaviors

BTBR T+tf/J (BTBR) mice were recently cited as a suitable animal model for the study of autism because of their behavioral characteristics and immunological changes similar to those reported from autistic subjects. The BTBR mouse was reported to have significantly higher levels of serum IgG, brain IgG deposits and anti-brain IgG than highly social C57BL/6 mice, suggesting involvement of aberrant immune responses in the occurrence of autism. Up-regulation of IgG production was investigated here, with a focus on the pattern of IgG isotype distribution compared with that in FVB/NJ (FVB) mice, another highly social control strain. The results indicated that levels of serum IgG₁, IgG_2b and IgG₃ in post-natal day 21 BTBR mice was significantly higher than FVB mice, regardless of sex, resulting in higher IgG₁:IgG_2a ratios in BTBR mice than in FVB mice (statistical significance in males). A similar outcome regarding the IgG₁:IgG_2a ratio was observed in culture supernatants of bone marrow cells from these hosts. A presence of brain-reactive IgG in the sera of BTBR was higher than in FVB mice; levels of brain-reactive IgG against whole brain homogenates were higher in BTBR than in FVB mice, with significant differences seen in the striatum and substantia nigra regions. Levels of IgG₁ deposited in the cerebellum, cortex, hippocampus or striatum of both BTBR male and female mice were significantly higher than in FVB counterparts. Overall, these results suggest that alterations in IgG isotype production or deposition in the brain could be implicated in the aberrant immune reactivities of BTBR mice.     

Differential strain‐related tissue immune response to sublethal systemic Aspergillus fumigatus infection in mice

Using a nonlethal systemic Aspergillus fumigatus infection, we have recently shown that similarly efficient elimination of fungus from spleens of prototypic Th1 (C57BL/6) and prototypic Th2 (BALB/c) mice is associated with differential immune responses. In light of these data and given the disseminated character of infection, the aim of the present study is to explore whether there are also strain‐dependent differences in antifungal responses in peripheral tissues of infected mice. Although similar efficiency of conidia removal was noted in liver and kidneys of both strains, BALB/c mice seemed more prone to tissue injury. Compared with other nonlymphoid organs, lungs proved immunologically the most responsive in systemic aspergillosis. Lower numbers of neutrophils and macrophages in the lungs of infected BALB/c mice, delayed and lower (compared with C57BL/6 mice) expression of their oxidative activity, along with late IFN‐γ and upregulated IL‐4 production by lung cells might be responsible for slower elimination of A. fumigatus from the lungs of this mouse strain. The data obtained imply that lungs should be viewed as mandatory organ in evaluation of immune‐mediated antifungal potential of drugs in models of systemic/disseminated infection and that strain differences noted in tissue responses should be taken into account in these settings.     

Increase in aggressiveness of male mice carrying a reciprocal translocation,T(10,13), in the heterozygous state

The agonistic behavior of inexperienced pairs of agouti male mice was determined by counting the bites received from and delivered to the opponent within 24 h. The first 10 min of agonistic encounters was recorded by videotape to analyze the frequency and duration of 10 behavioral traits. Each pair consisted of two F₁ males from the cross of (101/C3H) x NMRI, one of which (test male) was derived from a father carrying a reciprocal translocation, T(10,13), in the heterozygous state, while the other (standard opponent) stemmed from a chromosomally normal father of the same origin. Since the offspring of a heterozygous translocation are segregating into chromosomally normal and translocation mice, the test male was either chromosomally normal or a carrier of the translocation in the heterozygous state. Apart from the translocation, all males were of the same genotypic constitution. Comparing the differences between translocation carriers and chromosomally normal mice relative to their standard opponent, significantly more winners than losers were found among the translocation carriers. The differences of 10 behavioral traits between the test male and his opponent revealed significantly more contacts, pursuits, and attacks and significantly fewer defense and flight responses of the test males when this was a carrier of the heterozygous translocation, T(10,13).Dedicated to Nobel Laureate Professor Dr. Dr. Dr. h.c. mult. Konrad Lorenz on the occasion of his 80th birthday.     

Two-year follow-up of Helicobacter pylori infection in C57BL/6 and Balb/cA mice

Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer disease, gastric adenocarcinoma and MALT lymphoma. We previously found high-grade lymphoma after 13 months' H. pylori infection in C57BL/6 mice. In this study we followed H. pylori infection by three different isolates in C57BL/6 and Balb/cA mice for 23 months. Six-week-old C57BL/6 and Balb/cA mice were infected with H. pylori strains 119p (CagA+, VacA+), SS1 (CagA+, VacA+) and G50 (CagA-, VacA-). Mice were followed at 2 weeks, 10 weeks and 23 months post-inoculation (p.i.) by culture, histopathology and serology. Strain G50 was only reisolated from mice 2 weeks p.i. There was no difference in colonization between strain 119p and SS1 at 10 weeks p.i., whereas SS1 gave 100% colonization versus 119p gave 50% 23 months p.i. Interestingly, the inflammation score was higher in mice infected with strain 119p than with SS1 10-week p.i., and there were lymphoepithelial lesions in mice infected with strain 119p and G50 but not with SS1 at 23 months post-infection. Eight mice infected with strains 119p and G50 developed gastric lymphoma (grade 5 and 4). One C57BL/6 mouse infected with strain 119p developed hepatocellular carcinoma after 23 months. Immunoblot showed specific bands of 26-33 kDa against H. pylori in infected mice, and two mice infected with strain SSI reacted with antibodies to the 120 kDa CagA toxin. Conclusion: A reproducible animal model for H. pylori-induced lymphoma and possibly hepatocellular carcinoma is described. Strain diversity may lead to different outcomes of H. pylori infection.     

Characteristics of the blood systems of inbred and noninbred mice

Indices of the peripheral blood and bone marrow were studied in inbred (101/H, CC57W, A2G, CBA/Lac, B6W^V, C57BL/6, ACR) and noninbred mice. Standard norms for the morphological composition of the blood and bone marrow were established. Comparative analysis showed differences in these indices not only between inbred and noninbred mice, but also among animals of the same strain.Central Research Laboratory and Department of Pathophysiology, Tomsk Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR I. V. Toroptsev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 4, pp. 501–503, April, 1978.     

Studies into the mechanisms of strain differences in hippocampus-related behaviors

The heterogeneous mouse stocks HS/Ibg and SABRA/HUC and the inbred strains C57BL/6J, CBA/LAC, and BALB/Crgl were employed in an investigation of strain differences in delayed spontaneous alternation (SA) and eight-arm maze performance (EAM). Intact male mice were tested for SA at age 41 days for 2 consecutive days and for EAM at age 50–54 days, under conditions of water deprivation that commenced on day 43. In SA, BALB mice had a lower score than all other strains on day 1 but differed significantly only from SABRA; performance on day 2 was not consistent with that on day 1. In EAM, HS was first, CBA second, C57 third, SABRA fourth, and BALB fifth. HS was superior to the other strains, while BALB fell far below all other strains in both tests. Except for these two strains, the correlation between the two tests across the other strains was low. A study was undertaken to investigate the role of the hippocampus in the deficits in the performance of BALB mice in the two behaviors. Noradrenergic neurons were transplanted to hippocampus or cortex, and cholinergic neurons to their hippocampus. There were no significant differences in performance between the control and transplanted mice. The possibility was discussed that the behavioral differences are the outcome of variability in the neurotransmitters systems of the hippocampus but probably not the noradrenergic system.     

Induction of Antigen-Specific Th1-Type Immune Responses by Gamma-Irradiated Recombinant Brucella abortus RB51

Brucella abortus strain RB51 is an attenuated rough mutant used as the live vaccine against bovine brucellosis in the United States and other countries. We previously reported the development of strain RB51 as a bacterial vaccine vector for inducing Th1-type immune responses against heterologous proteins. Because safety concerns may preclude the use of strain RB51-based recombinant live vaccines, we explored the ability of a gamma-irradiated recombinant RB51 strain to induce heterologous antigen-specific immune responses in BALB/c mice. Exposure of strain RB51G/LacZ expressing Escherichia coli β-galactosidase to a minimum of 300 kilorads of gamma radiation resulted in complete loss of replicative ability. These bacteria, however, remained metabolically active and continued to synthesize β-galactosidase. A single intraperitoneal inoculation of mice with 10⁹ CFU equivalents of gamma-irradiated, but not heat-killed, RB51G/LacZ induced a β-galactosidase-specific Th1-type immune response. Though no obvious differences were detected in immune responses to B. abortus-specific antigens, mice vaccinated with gamma-irradiated, but not heat-killed, RB51G/LacZ developed significant protection against challenge with virulent B. abortus. In vitro experiments indicated that gamma-irradiated and heat-killed RB51G/LacZ induced maturation of dendritic cells; however, stimulation with gamma-irradiated bacteria resulted in more interleukin-12 secretion. These results suggest that recombinant RB51 strains exposed to an appropriate minimum dose of gamma radiation are unable to replicate but retain their ability to stimulate Th1 immune responses against the heterologous antigens and confer protection against B. abortus challenge in mice.     

Protection against rotavirus shedding after intranasal immunization of mice with a chimeric VP6 protein does not require intestinal IgA

Intranasal immunization of mice with chimeric VP6 and the adjuvant LT(R192G) consistently elicits >95% reductions in fecal rotavirus shedding following challenge. To determine the association between mucosal antibody and protection, we immunized BALB/c wt and J chain knockout (Jch-/-) mice with VP6 and either LT(R192G) or cholera toxin (CT). Both strains developed nearly equal levels of serum rotavirus IgG, but Jch-/- mice, which cannot transport dimeric IgA across epithelial cell surfaces, developed >4-fold higher levels of serum rotavirus IgA. Stool rotavirus IgA was present in wt but undetectable in Jch-/- mice. When challenged with rotavirus strain EDIM, reductions in rotavirus shedding were nearly identical in VP6-immunized wt and Jch-/- mice (i.e., 97% and 92%, respectively; P > 0.01). Th1 CD4 T cell responses were also detected in VP6-immunized animals based on high levels of IFN-gamma and IL-2 found after in vitro VP6 stimulation of spleen cells. Therefore, protection induced by intranasal immunization of mice with VP6 and adjuvant does not depend on intestinal rotavirus IgA antibody but appears to be associated with CD4 T cells.     

Distinct Influences of Neonatal Epidermal Growth Factor Challenge on Adult Neurobehavioral Traits in Four Mouse Strains

Epidermal growth factor (EGF) receptor (ErbB1) signals regulate dopaminergic development and function and are implicated in schizophrenia. We evaluated genetic effects on neurobehavioral changes induced by neonatal EGF administration, using four mouse strains. Subcutaneous EGF administration increased phosphorylation of brain ErbB1 in all strains, although DBA/2 and C57BL/6 mice had lower basal phosphorylation. Neonatal EGF treatment differentially influenced physical and behavioral/cognitive development, depending on mouse strain. Prepulse inhibition was decreased in DBA/2 and C57BL/6 mice but not C3H/He and ddY mice. Locomotor activity was accelerated in DBA/2 mice, but reduced in ddY mice. EGF treatment enhanced fear-learning performance with a tone cue in DBA/2 mice, but decreased performance with tone and context cues in C3H/He and ddY mice, respectively. The strain-dependent behavioral sensitivity was correlated with basal ErbB1 phosphorylation. Genetic components regulating brain ErbB1 signaling strongly influence the direction and strength of behavioral responses stemming from the neonatal neurotrophic perturbation.     

A Genetically Controlled Hippocampal Transmitter System Regulating Exploratory Behavior in Mice

Male C57BL/6 and DBA/2 mice were intrahippocampally microinjected with muscimol (0.5 μg), given 15 min prior to individual 20-min exploration tests in a novel environment, and compared to saline controls. The GABA agonist reduced various exploratory acts and locomotor activity in strain C57BL/6 and increased the scores in DBA/2. In conjunction with similar opposite effects previously found with intra-hippocampal methylscopolamine and naloxone, these findings suggest that the opioid modulation of the hippocampal cholinergic mechanism which facilitates behavioral responses to novelty in mice is effectuated indirectly through an inhibitory GABAergic system. The functioning of these regulatory systems appears to depend on genotype.     

The effects of enriched environment on the behavioral and corticosterone response to methamphetamine in adolescent and adult mice

Methamphetamine alters behavior and the stress response system. Relatively little research has examined the effects of methamphetamine in adolescents and compared these effects to those in adults. Housing in enriched environments has been explored as one way to protect against the effects of methamphetamine, but the findings are conflicting and no study has examined how enriched environment may alter the behavioral and corticosterone responses to methamphetamine in adolescent and adult rodents. We examined the long‐term effects of methamphetamine exposure on anxiety, social behavior, behavioral despair, and corticosterone levels in adolescent and adult mice housed in enriched or isolated environments. Enriched environment did not alter the behavioral or corticosterone response to methamphetamine. Methamphetamine exposure decreased anxiety and increased behavioral despair in adult mice, but methamphetamine did not alter behavior in adolescent mice. There was no effect of methamphetamine on social behavior or corticosterone levels. Our findings demonstrate that the specific environmental enrichment paradigm used in this study was not sufficient to mitigate the behavioral effects of methamphetamine and that adolescent mice are relatively resistant to the effects of methamphetamine compared to adult mice.     

Strain-typical patterns of pregnancy-induced nestbuilding in mice: Maternal and experiential influences

Pregnant C57BL/6J mice incorporate less material into maternal nests and build fewer fully enclosed nests than do pregnant DBA/2J mice. These strain differences are not ameliorated by additional reproductive experience since multiparous animals also exhibit a similar pattern. Reciprocally-crossed hybrid females exhibit DBA-like levels of pregnancy-induced nestbuilding and cross-fostered C57BL and DBA females retain the phenotype of their strain. Experiential and maternal environmental factors apparently are not responsible for strain differences in pregnancy-induced nestbuilding. Differences in ovarian function and/or central neural tissue sensitivity to ovarian hormones may modulate strain differences in pregnancy-induced nestbuilding.     

Prenatal behavior of the C57BL/6J mouse: a promising model for human fetal movement during early to mid-gestation

The study of fetal neurobehavioral development in genetically altered mice promises a significant advance in our understanding of the prenatal origins of developmental disabilities in humans. Despite their importance, little is known about fetal neurobehavioral development in mice. In this study, we observed prenatal behavioral patterns of the C57BL/6J mouse, a common background strain for genetically altered mice, and report their similarity to those observed in the early to mid-gestation human fetus. Fetal offspring from pregnant C57BL/6J dams were observed on the day before birth (E18 of a 19-day gestation). Scoring and analysis of fetal movement included Prechtl's Method for Qualitative Assessment, Interlimb Movement Synchrony, a measure of the temporal relationship between movements of limb pairs, and Behavioral State, quantified through detailed analysis of high and low amplitude limb movements. With the exception of fetal breathing movements, all categories and patterns of behavior typically reported in the early to mid-gestation human fetus were observed in the C57BL/6J mouse fetus. Our results suggest that behavioral analysis of fetal C57BL/6J mice may yield important new insights into early to mid-gestation human behavioral development.     

Passive transfer of immunity of Mycobacterium avium in susceptible and resistant strains of mice.

Naturally susceptible mice (C57BL/6) infected with M. avium (strain Weybridge) developed a population of splenic T cells which, on transfer to syngeneic recipient mice, conferred significant protection against a subsequent challenge inoculum of M. avium. Similar T cells from naturally resistant mice (A/J) did not protect syngeneic recipient mice. Growth of M. avium in donor mice only occurred in the C57BL/6 strain. Replication of M. avium in donor mice was necessary for the development of protective T cells. High numbers of killed mycobacterium did not induce immune T cells. In addition, A/J mice inoculated with increasing numbers of viable M. avium (which still did not replicate) failed to develop protective T lymphocytes. Further studies indicated that no protective T cells were present in the M. avium-infected A/J mouse, although evidence for non-specific immunity in these mice was obtained. In addition, BCG (which grows progressively in A/J mice) stimulated a population of splenic T cells which protected recipient mice from subsequent infection with M. tuberculosis.