Genetic Modulation of Initial Sensitivity to Δ9-Tetrahydrocannabinol (THC) Among the BXD Family of Mice

Cannabinoid receptor 1 activation by the major psychoactive component in cannabis, Δ9-tetrahydrocannabinol (THC), produces motor impairments, hypothermia, and analgesia upon acute exposure. In previous work, we demonstrated significant sex and strain differences in acute responses to THC following administration of a single dose (10 mg/kg, i.p.) in C57BL/6J (B6) and DBA/2J (D2) inbred mice. To determine the extent to which these differences are heritable, we quantified acute responses to a single dose of THC (10 mg/kg, i.p.) in males and females from 20 members of the BXD family of inbred strains derived by crossing and inbreeding B6 and D2 mice. Acute THC responses (initial sensitivity) were quantified as changes from baseline for: 1. spontaneous activity in the open field (mobility), 2. body temperature (hypothermia), and 3. tail withdrawal latency to a thermal stimulus (antinociception). Initial sensitivity to the immobilizing, hypothermic, and antinociceptive effects of THC varied substantially across the BXD family. Heritability was highest for mobility and hypothermia traits, indicating that segregating genetic variants modulate initial sensitivity to THC. We identified genomic loci and candidate genes, including Ndufs2, Scp2, Rps6kb1 or P70S6K, Pde4d, and Pten, that may control variation in THC initial sensitivity. We also detected strong correlations between initial responses to THC and legacy phenotypes related to intake or response to other drugs of abuse (cocaine, ethanol, and morphine). Our study demonstrates the feasibility of mapping genes and variants modulating THC responses in the BXDs to systematically define biological processes and liabilities associated with drug use and abuse.

Behavioral and Metabolome Differences between C57BL/6 and DBA/2 Mouse Strains: Implications for Their Use as Models for Depression- and Anxiety-Like Phenotypes

Mouse models are widely used to study behavioral phenotypes related to neuropsychiatric disorders. However, different mouse strains vary in their inherent behavioral and molecular characteristics, which needs to be taken into account depending on the nature of the study. Here, we performed a detailed behavioral and molecular comparison of C57BL/6 (B6) and DBA/2 (DBA) mice, two inbred strains commonly used in neuropsychiatric research. We analyzed anxiety-related and depression-like traits, quantified hippocampal and plasma metabolite profiles, and assessed total antioxidant capacity (ΤAC). B6 mice exhibit increased depression-like and decreased anxiety-related behavior compared to DBA mice. Metabolite level differences indicate alterations in amino acid, nucleotide and mitochondrial metabolism that are accompanied by a decreased TAC in B6 compared to DBA mice. Our data reveal multiple behavioral and molecular differences between B6 and DBA mouse strains, which should be considered in the experimental design for phenotype, pharmacological and mechanistic studies relevant for neuropsychiatric disorders.

Comparison of response to LPS-induced sepsis in three DBA/2 stocks derived from different sources

Sepsis, one of the most fatal diseases in the world, is known to culminate in multiple organ failure due to an uncontrolled inflammatory response. Hence, the use of animal models in sepsis research is very important to study complex immune responses. The current study was undertaken to compare commercial stocks with KFDA stocks of DBA/2 mice as an animal model for sepsis study. To compare responses of DBA/2 mice to lipopolysaccharides (LPS)-induced sepsis, we measured altered characteristics of various factors associated with sepsis, including survival curves, organ failure and inflammatory response, in DBA/2Korl stock and two commercial stocks (DBA/2A and DBA/2B). Survival rates after LPS exposure were similar for DBA/2Korl and DBA/2B; however, for times over 20 h, survival rates were reduced and concentration dependent in DBA/2A. In order to evaluate multiple organ failure caused by sepsis, H&E stains were evaluated for liver and spleen tissues obtained in the early (2 h) and later (20 h) stages after exposure to LPS; no significant differences were observed between the three stocks. mRNA and protein levels of proinflammatory cytokines were assessed for evaluating inflammatory reactions, and were found to increase in a dose-dependent manner in most DBA/2 mice after LPS treatment. However, no changes were observed in the mRNA levels of proinflammatory cytokines at 20 h after LPS exposure in the DBA/2A stock. The induction of inflammation-mediated factors by LPS exposure did not induce alterations in the mRNA levels of COX-2 and iNOS in all three DBA/2 stocks. Our results indicate that response of DBA/2Korl to LPS-induced sepsis is similar to the two commercial DBA/2 stocks, thus representing its potential as a useful biological resource established in Korea.

Sex and Strain Variation in Initial Sensitivity and Rapid Tolerance to Δ9-Tetrahydrocannabinol

Background and Objectives: For cannabis and other drugs of abuse, initial response and/or tolerance to drug effects can predict later dependence and problematic use. Our objective is to identify sex and genetic (strain) differences in initial response and rapid tolerance to Δ9–tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, between highly genetically divergent inbred mouse strains—C57BL/6J (B6) and DBA/2J (D2).

Experimental Approach: Sex and strain responses relative to baseline were quantified following daily exposure (i.p.) to 10 mg/kg THC or vehicle (VEH) over the course of 5 days. Dependent measures included hypothermia (decreased body temperature) and ataxia (decreased spontaneous activity in the open field), and antinociception (increase in tail withdrawal latency to a thermal stimulus). Initial sensitivity to THC was defined as the difference in response between baseline and day 1. Rapid tolerance to THC was defined as the difference in response between days 1 and 2.

Results: B6 exhibited greater THC-induced motor activity suppression and initial sensitivity to ataxia relative to the D2 strain. Females demonstrated greater levels of THC-induced hypothermia and initial sensitivity relative to males. Higher levels of THC-induced antinociception and initial sensitivity were observed for D2 relative to B6. Rapid tolerance to THC was observed for hypothermia and antinociception. Much less tolerance was observed for THC-induced ataxia. D2 exhibited rapid tolerance to THC-induced hypothermia and antinociception at time points associated with peak THC initial response. Likewise, at the peak initial THC response time point, females demonstrated greater levels of rapid tolerance to hypothermic effects relative to males.

Conclusions: Both sex and genetic factors drive variation in initial response and rapid tolerance to the ataxic, antinociceptive, and hypothermic effects of THC. As these traits directly result from THC activation of the cannabinoid receptor 1, gene variants between B6 and D2 in cannabinoid signaling pathways are likely to mediate strain differences in response to THC.

Impaired upregulation of Stat2 gene restrictive to pancreatic β-cells is responsible for virus-induced diabetes in DBA/2 mice

Viral infection is a putative causal factor for the development of type 1 diabetes, but the exact pathogenic mechanism of virus-induced diabetes (VID) remains unclear. Here, to identify the critical factors that regulate VID, we analyzed encephalomyocarditis D (EMC-D) VID-sensitive DBA/2 mice in comparison with resistant B6 mice. EMC-D virus-induced cell death occurred more frequently in DBA/2 β-cells than in B6 β-cells with 100U/ml IFN-β priming in vitro. We therefore purified β-cells using flow cytometry from mice two days after EMC-D virus infection and subjected them to microarray analysis. As a results, innate immune response pathway was found to be enriched in B6 β-cells. The signal transducer and activator of transcription 2 (Stat2) gene interacted with genes in the pathway. Stat2 gene expression levels were lower in DBA/2 mice than in B6 mice, restrictive to β-cells. Moreover, administration of IFN-β failed to upregulate Stat2 gene in DBA/2 β-cells than in those of B6 in vivo. The viral titer significantly increased only in the DBA/2 pancreas. Thus, these provided data suggest that impaired upregulation of Stat2 gene restrictive to β-cells at the early stage of infection is responsible for VID development in DBA/2 mice.

Effects of Natural and Chemically Defined Nutrients on Candida albicans Water-soluble Fraction (CAWS) Vasculitis in Mice

Kawasaki disease (KD) is an inflammatory disease that was identified by Professor Tomisaku Kawasaki in 1961. Candida albicans-derived substances, such as C. albicans water-soluble fraction (CAWS) , induce coronary arteritis similar to KD in mice. CAWS functions as a pathogen-associated molecular pattern (PAMP) by acting as a ligand for dectin-2. A gut-associated immunological system has developed specifically to segregate advantageous and detrimental stimuli, and the microbial flora has been found to markedly affect the development and severity of diseases. We herein investigated whether diet affects the onset and progression of CAWS vasculitis in mice. A standard diet, CE-2, and chemically defined diet, AIN93G, which is free of β-glucan, were used. Although all mice administered with CAWS died, the mean number of survival days was smaller in the AIN93G group because vasculitis was induced earlier than in the CE-2 group. Bacteroides, which are inflammatory flora, were enriched in the microbial flora of the AIN93G group. The results of the present study suggest that diet quality affects not only microbial flora changes, but also the progression of systemic disease.

Changes in Retinal N-Acylethanolamines and their Oxylipin Derivatives During the Development of Visual Impairment in a Mouse Model for Glaucoma

Neurons are especially susceptible to oxidative damage, which is increasingly implicated in neurodegenerative disease. Certain N-acylethanolamines (NAEs) have been shown to protect neurons from oxidative stress. Since glaucoma may be considered a neurodegenerative disorder and the survival of retinal neurons could also be influenced by N-acylethanolamines, our goal was to quantify changes in certain N-acylethanolamine species and their oxylipin derivatives in the retina of a mouse model for glaucoma. We also sought to identify relationships between these and parameters of glaucoma disease development, specifically intraocular pressure, visual acuity, and contrast sensitivity. Five N-acylethanolamine species and three NAE oxylipin derivatives were quantified in retina from young and aged DBA/2Crl mice. N-Acylethanolamines and NAE-oxylipins in retinal extracts were quantified against deuterated standards by isotope dilution gas chromatography-mass spectrometry. Levels (nmol/g dry weight) of N-arachidonoylethanolamine (anandamide; NAE 20:4) were significantly (p = 0.008) decreased in aged (2.875 ± 0.6702) compared to young animals (5.175 ± 0.971). Conversely, the anandamide oxylipin, 15(S)-HETE ethanolamide (15(S)-HETE EA), was significantly (p = 0.042) increased in aged (0.063 ± 0.009) compared to young animals (0.039 ± 0.011). Enzymatic depletion of the anandamide pool by 15-lipoxygenase and consequent accumulation of 15(S)-HETE ethanolamine may contribute to decreased visual function in glaucomatous mice. Since N-acylethanolamines effectively attenuate glaucoma pathogenesis and associated visual impairment, our data provides additional rationale and novel targets for glaucoma therapies.

Strain- and Diet-Related Lesion Variability in Aging DBA/2, C57BL/6, and DBA/2xC57BL/6 F1 Mice

Genetic and environmental factors both play a role in the occurrence of age-related disease. To examine the genetic contribution to the development of spontaneous lesions in aging animals, a complete range of tissues was comprehensively analyzed by histopathology from 180 individually housed ad libitum-fed or 40% calorically restricted 24-month-old male and female mice of 2 parental strains-DBA/2NNia (D2) and C57BL/6NNia (B6)-and the F1 cross B6D2F1/NNia. Several strain- and diet-dependent patterns of lesions were identified. Many lesions were genotype dependent and exhibited recessive phenotypic expression, defined as being common in 1 parental strain but infrequently observed in the F1 cross (eg, glomerulonephritis in B6 mice), while others were maintained from 1 parental strain to the F1 with similar frequencies (eg, reproductive tract leiomyoma in D2 mice). Other lesions were common regardless of genotype (osteoarthritis, periodontitis). Only rare lesions were more common in the F1 but underrepresented in the 2 parental strains. Furthermore, F1 mice had a lower number of overall total lesions and a lower number of tumors than either parental strain. Caloric restriction reduced the total number of lesions and neoplasms regardless of genotype but differentially affected genotype-dependent lesions in B6 and D2 mice, with B6 mice more sensitive to the effects of caloric restriction than D2 mice. In summary, genetics and environmental factors (eg, dietary restriction) both substantially contribute to the pattern of lesions that develop as animals age.

Segregation of a spontaneous Klrd1 (CD94) mutation in DBA/2 mouse substrains

Current model DBA/2J (D2J) mice lack CD94 expression due to a deletion spanning the last coding exon of the Klrd1 gene that occurred in the mid- to late 1980s. In contrast, DBA/2JRj (D2Rj) mice, crosses derived from DBA/2J before 1984, and C57BL/6J (B6) mice lack the deletion and have normal CD94 expression. For example, BXD lines (BXD1–32) generated in the 1970s by crossing B6 and D2J do not segregate for the exonic deletion and have high expression, whereas BXD lines 33 and greater were generated after 1990 are segregating for the deletion and have highly variable Klrd1 expression. We performed quantitative trait locus analysis of Klrd1 expression by using BXD lines with different generation times and found that the expression difference in Klrd1 in the later BXD set is driven by a strong cis-acting expression quantitative trait locus. Although the Klrd1/CD94 locus is essential for mousepox resistance, the genetic variation among D2 substrains and the later set of BXD strains is not associated with susceptibility to the Influenza A virus PR8 strain. Substrains with nearly identical genetic backgrounds that are segregating functional variants such as the Klrd1 deletion are useful genetic tools to investigate biological function.

Effect of acute swim stress on plasma corticosterone and brain monoamine levels in bidirectionally selected DxH recombinant inbred mouse strains differing in fear recall and extinction

Stress-induced changes in plasma corticosterone and central monoamine levels were examined in mouse strains that differ in fear-related behaviors. Two DxH recombinant inbred mouse strains with a DBA/2J background, which were originally bred for a high (H-FSS) and low fear-sensitized acoustic startle reflex (L-FSS), were used. Levels of noradrenaline, dopamine, and serotonin and their metabolites 3,4-dihydroxyphenyacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were studied in the amygdala, hippocampus, medial prefrontal cortex, striatum, hypothalamus and brainstem. H-FSS mice exhibited increased fear levels and a deficit in fear extinction (within-session) in the auditory fear-conditioning test, and depressive-like behavior in the acute forced swim stress test. They had higher tissue noradrenaline and serotonin levels and lower dopamine and serotonin turnover under basal conditions, although they were largely insensitive to stress-induced changes in neurotransmitter metabolism. In contrast, acute swim stress increased monoamine levels but decreased turnover in the less fearful L-FSS mice. L-FSS mice also showed a trend toward higher basal and stress-induced corticosterone levels and an increase in noradrenaline and serotonin in the hypothalamus and brainstem 30 min after stress compared to H-FSS mice. Moreover, the dopaminergic system was activated differentially in the medial prefrontal cortex and striatum of the two strains by acute stress. Thus, H-FSS mice showed increased basal noradrenaline tissue levels compatible with a fear phenotype or chronic stressed condition. Low corticosterone levels and the poor monoamine response to stress in H-FSS mice may point to mechanisms similar to those found in principal fear disorders or post-traumatic stress disorder.

Postnatal developmental changes in the medial nucleus of the trapezoid body in a mouse model of auditory pathology

Age-related hearing loss (AHL) is a multifactorial disorder characterized by a decline in peripheral and central auditory function. Here, we examined synaptic transmission in DBA/2 mice, which carry the AHL8 gene, at the identifiable glutamatergic synapse in the medial nucleus of the trapezoid body (MNTB), a nucleus in the superior olivary complex critical for acoustic timing. Mice exhibited raised auditory brainstem thresholds by P14, soon after hearing onset. Excitatory postsynaptic currents were prolonged; however, postsynaptic excitability was normal. By P18, high-frequency hearing loss was evident. Coincident with the onset of hearing loss, MNTB principal neurons displayed changes in intrinsic firing properties. These results suggest that changes in transmission in the superior olivary complex are associated with early onset hearing loss.

Acute administration of Δ⁹ tetrahydrocannabinol does not prevent enhancement of sensory gating by clozapine in DBA/2 mice

Despite high rates of marijuana abuse in schizophrenia, the physiological interactions between tetrahydrocannabinol (THC) and antipsychotic medications are poorly understood. A well-characterized feature of schizophrenia is poor gating of the P50 auditory-evoked potential. This feature has been translationally modeled by the DBA/2 mouse, which exhibits poor suppression of the P20-N40 AEP, the rodent analog of the human P50. Previous work has demonstrated that this deficit is reversed by the antipsychotic clozapine. It is unknown, however, if this effect is altered by THC administration. Using a conditioning-testing paradigm with paired auditory stimuli, the effects of clozapine and dronabinol (a pharmaceutical THC formulation) on inhibitory P20-N40 AEP processing were assessed from in vivo hippocampal CA3 recordings in anesthetized DBA/2 mice. The effects of clozapine (0.33 mg/kg) and dronabinol (10 mg/kg) were assessed alone and in combination (0.33, 1 or 1.83 mg/kg clozapine with 10mg/kg dronabinol). Improved P20-N40 AEP gating was observed after acute administration of 0.33 mg/kg clozapine. Co-injection of 0.33 mg/kg clozapine and 10 mg/kg THC, however, did not improve gating relative to baseline. This effect was overcome by higher doses of clozapine (1 and 1.83 mg/kg), as these doses improved gating relative to baseline in the presence of 10 mg/kg THC. 10 mg/kg THC alone did not affect gating. In conclusion, THC does not prevent improvement of P20-N40 gating by clozapine.

Astrocyte Reactivity: A Biomarker for Retinal Ganglion Cell Health in Retinal Neurodegeneration

Retinal ganglion cell (RGC) loss in glaucoma is sectorial in nature and preceded by deficits in axonal transport. Neuroinflammation plays an important role in the pathophysiology of glaucoma in the retina, optic nerve and visual centers of the brain, where it similarly appears to be regulated spatially. In a murine model, we examined the spatial characteristics of astrocyte reactivity (migration/proliferation, hypertrophy and GFAP expression) in healthy retina, retina with two glaucoma-related risk factors (aging and genetic predisposition) and glaucomatous retina and established relationships between these reactivity indices and the spatial organization of astrocytes as well as RGC health. Astrocyte reactivity was quantified by morphological techniques and RGC health was determined by uptake and transport of the neural tracer cholera toxin beta subunit (CTB). We found that: (1) astrocyte reactivity occurs in microdomains throughout glaucomatous retina as well as retina with risk factors for glaucoma, (2) these astrocyte microdomains are primarily differentiated by the degree of retinal area covered by the astrocytes within them and (3) percent retinal area covered by astrocytes is highly predictive of RGC health. Our findings suggest that microdomains of astrocyte reactivity are biomarkers for functional decline of RGCs. Based on current and emerging imaging technologies, diagnostic assessment of astrocytes in the nerve fiber layer could succeed in translating axonal transport deficits to a feasible clinical application.

Spatial regulation of interleukin-6 signaling in response to neurodegenerative stressors in the retina

Neuroinflammation, defined as the induction of immune-related processes within the central nervous system, is recognized as a component of many neurodegenerative disorders, including glaucomatous degeneration of retinal ganglion cells (RGCs). Previous work in vitro identified IL-6 as a potential neuroprotective factor for RGCs, particularly those challenged by glaucoma-related stressors. Here we examined the temporal and spatial characteristics of IL-6 signaling in response to two stressors related to RGC neurodegeneration: age and elevated intraocular pressure (IOP). Using ELISA, immunoblotting, immunolabeling and quantitative microscopy, we measured and compared whole retina and RGC-related expression of IL-6 and IL-6Rα in normal retina (young C57), retina susceptible to glaucomatous neurodegeneration (young DBA/2), aging retina (aged C57) and aging retina challenged by elevated IOP (aged DBA/2). We found that: 1) neurodegenerative stressors induce alterations in whole retina expression of IL-6 and IL-6Rα, 2) these whole retina changes do not reflect the immediate milieu of RGCs, where IL-6 and IL-6Rα expression is spatially variable and 3) the extent and magnitude of this spatial variability is stressor-dependent. Our data provide the first evidence that neurodegenerative stressors produce microenvironments of IL-6 signaling in retina and that the nature and magnitude of spatial regulation is dependent on the identity of the stressor.

Profiling psychomotor and cognitive aging in four-way cross mice

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4 months) and older (23 months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.