Behavioral effects of long-term oral administration of aluminum ammonium sulfate in male and female C57BL/6J mice

Parkin-mediated mitophagy protects against aluminum trichloride-induced hippocampal apoptosis in mice via the mtROS-NLRP3 pathway

Aluminum is a neurotoxic food contaminant. Aluminum trichloride (AlCl3) causes hippocampal mitochondrial damage, leading to hippocampal injury. Damaged mitochondria can release mitochondrial reactive oxygen species (mtROS) and activate nucleotide-binding oligomerization domain-like receptor-containing 3 (NLRP3) inflammasomes and apoptosis. E3 ubiquitin ligase PARK2 (Parkin)-mediated mitophagy can attenuate mitochondrial damage. However, the role of mitophagy in AlCl3-induced mice hippocampal damage and its regulatory mechanism remain elusive. First, C57BL/6 N mice were treated with 0, 44.825, 89.65, and 179.3 mg/kg body weight AlCl3 drinking water for 90 d. Apoptosis, NLRP3-inflammasome activation and mitochondrial damage were increased in AlCl3-induced hippocampal damage. In addition, Parkin-mediated mitophagy peaked in the middle-dose group and was slightly attenuated in the high-dose group. Subsequently, we used wild-type and Parkin knockout (Parkin-/-) mice to investigate the AlCl3-induced hippocampal damage. The results showed that Parkin-/- inhibited mitophagy, and aggravated AlCl3-induced mitochondrial damage, NLRP3-inflammasome activation, apoptosis and hippocampal damage. Finally, we administered MitoQ (mtROS inhibitor) and MCC950 (NLRP3 inhibitor) to AlCl3-treated Parkin-/- mice to investigate the mechanism of Parkin-mediated mitophagy. The results showed that inhibition of mtROS and NLRP3 attenuated hippocampal NLRP3-inflammasome activation, apoptosis, and damage in AlCl3-treated Parkin-/- mice. These findings indicate that Parkin-mediated mitophagy protects against AlCl3-induced hippocampal apoptosis in mice via the mtROS-NLRP3 pathway.

Suppression of DNA Double-Strand Break Formation by DNA Polymerase β in Active DNA Demethylation Is Required for Development of Hippocampal Pyramidal Neurons

Genome stability is essential for brain development and function, as de novo mutations during neuronal development cause psychiatric disorders. However, the contribution of DNA repair to genome stability in neurons remains elusive. Here, we demonstrate that the base excision repair protein DNA polymerase β (Polβ) is involved in hippocampal pyramidal neuron differentiation via a TET-mediated active DNA demethylation during early postnatal stages using Nex-Cre/Polβ ^fl/fl mice of either sex, in which forebrain postmitotic excitatory neurons lack Polβ expression. Polβ deficiency induced extensive DNA double-strand breaks (DSBs) in hippocampal pyramidal neurons, but not dentate gyrus granule cells, and to a lesser extent in neocortical neurons, during a period in which decreased levels of 5-methylcytosine and 5-hydroxymethylcytosine were observed in genomic DNA. Inhibition of the hydroxylation of 5-methylcytosine by expression of microRNAs miR-29a/b-1 diminished DSB formation. Conversely, its induction by TET1 catalytic domain overexpression increased DSBs in neocortical neurons. Furthermore, the damaged hippocampal neurons exhibited aberrant neuronal gene expression profiles and dendrite formation, but not apoptosis. Comprehensive behavioral analyses revealed impaired spatial reference memory and contextual fear memory in adulthood. Thus, Polβ maintains genome stability in the active DNA demethylation that occurs during early postnatal neuronal development, thereby contributing to differentiation and subsequent learning and memory.SIGNIFICANCE STATEMENT Increasing evidence suggests that de novo mutations during neuronal development cause psychiatric disorders. However, strikingly little is known about how DNA repair is involved in neuronal differentiation. We found that Polβ, a component of base excision repair, is required for differentiation of hippocampal pyramidal neurons in mice. Polβ deficiency transiently led to increased DNA double-strand breaks, but not apoptosis, in early postnatal hippocampal pyramidal neurons. This aberrant double-strand break formation was attributed to active DNA demethylation as an epigenetic regulation. Furthermore, the damaged neurons exhibited aberrant gene expression profiles and dendrite formation, resulting in impaired learning and memory in adulthood. Thus, these findings provide new insight into the contribution of DNA repair to the neuronal genome in early brain development.

Natural Compounds Rosmarinic Acid and Carvacrol Counteract Aluminium-Induced Oxidative Stress

Aluminum accumulation, glutathione (GSH) and malondialdehyde (MDA) concentrations as well as catalase (CAT) and superoxide dismutase (SOD) activities were determined in erythrocytes and brain and liver homogenates of BALB/c mice treated with Al3+ (7.5 mg/kg/day (0.15 LD50) as AlCl3 (37.08 mg/kg/day), whereas HCl (30.41 mg/kg/day) was used as Cl- control, the treatments were performed for 21 days, i.p., in the presence and absence of rosmarinic acid (0.2805 mg/kg/day (0.05 LD50), 21 days, i.g.) or carvacrol (0.0405 mg/kg/day (0.05 LD50), 21 days, i.g.). The treatment with AlCl3 increased GSH concentration in erythrocytes only slightly and had no effect on brain and liver homogenates. Rosmarinic acid and carvacrol strongly increased GSH concentration in erythrocytes but decreased it in brain and liver homogenates. However, AlCl3 treatment led to Al accumulation in mice blood, brain, and liver and induced oxidative stress, assessed based on MDA concentration in the brain and liver. Both rosmarinic acid and carvacrol were able to counteract the negative Al effect by decreasing its accumulation and protecting tissues from lipid peroxidation. AlCl3 treatment increased CAT activity in mice brain and liver homogenates, whereas the administration of either rosmarinic acid or carvacrol alone or in combination with AlCl3 had no significant effect on CAT activity. SOD activity remained unchanged after all the treatments in our study. We propose that natural herbal phenolic compounds rosmarinic acid and carvacrol could be used to protect brain and liver against aluminum induced oxidative stress leading to lipid peroxidation.

Age-related behavioral changes from young to old age in male mice of a C57BL/6J strain maintained under a genetic stability program

AIM

Aging is thought to coincide with gradual and progressive changes in brain function and behavior over the lifetime. Our previous meta-analytic study reported age-related behavioral changes from young to middle age in male C57BL/6J mice. However, the previous study had some limitations that could affect the generalizability of the findings because of the potential influence of genetic and environmental factors on behavior, in addition to a lack of information regarding the behaviors of old-aged mice. Here, to investigate age-related behavioral changes from young to old age in mice, we analyzed the behaviors of male C57BL/6J mice from four different age groups (8, 47, 73, and 99 weeks of age at the beginning of the experiment) from a colony that had been maintained in a genetically controlled condition based on The Jackson Laboratory's Genetic Stability Program in an environmentally controlled animal facility.

METHODS

We used a battery of behavioral tests, including the light/dark transition, open field, elevated plus maze, hot plate, social interaction, rotarod, three-chamber social approach, prepulse inhibition, Porsolt forced swim, T-maze, Barnes maze, tail suspension, and fear-conditioning tests.

RESULTS

Some behavioral changes occurred between young and middle age, and further changes in various behaviors were observed in old age. Decreased locomotor activity and increased anxiety-like behavior were found in old-aged mice compared to those in young and middle-aged mice in the light/dark transition test. Similarly, an age-dependent decrease in locomotor activity was observed in the open field test and the elevated plus maze test, while there was an age-dependent increase in the time spent in the center area in the open field test and there were no significant differences among age groups in behavioral measures of anxiety in the elevated plus maze test. Decreases in motor performance and the auditory startle response were found in middle-aged mice compared to those in young mice. Similar behavioral changes and increased pain sensitivity, decreased social novelty preference, reduced working and spatial memory, and impaired cued fear memory were observed in old-aged mice compared to those in young mice. Prepulse inhibition was higher in middle-aged mice than in young and old-aged mice. Age-related changes in depression-related behavior were dependent on the type of test and the test time period.

CONCLUSIONS

This study generally confirmed our previous report regarding age-related behavioral changes from young to middle age and expanded the previous observations by examining the behaviors of old-aged mice. Our results show age-related changes in a wide range of behaviors in mice from young to old age. Most behaviors showed gradual changes with advancing age, but some types of behaviors, such as vertical activity, prepulse inhibition, and depression-related behavior, did not show unidirectional changes with age. These findings provide basic information about the behavioral characteristics of young, middle-aged, and aged male C57BL/6J mice.

Effects of chronic fentanyl administration on behavioral characteristics of mice

Background

Fentanyl, a synthetic opioid categorized as a narcotic analgesic, has a 100‐ to 200‐fold stronger effect than most opioids, such as morphine. Fatal accidents due to chronic use and abuse of fentanyl are a worldwide social problem. One reason for the abuse of fentanyl is its psychostimulant effects that could induce behavioral changes. The effects of chronic fentanyl administration on behavior, however, are unclear.

Methods

Adult male C57BL/6J mice were chronically administered fentanyl (0.03 or 0.3 mg/kg/d i.p.), and various behaviors were assessed using a behavioral test battery.

Results

Mice chronically administered a high dose of fentanyl (0.3 mg/kg/d) exhibited decreased anxiety‐like behavior as assessed by the open field and elevated plus maze tests. On the other hand, interruption of fentanyl administration led to increased anxiety‐like behavior as observed in the light and dark transition test. The hot plate test revealed that chronic administration of fentanyl reduced pain sensitivity. High‐dose chronic fentanyl administration reduced the locomotor stimulatory effects of cocaine. The results, however, failed to reach the threshold for study‐wide statistical significance.

Conclusion

Chronic fentanyl administration induces some behavioral changes in mice. Although further studies are needed to clarify the underlying mechanisms of the behavioral effects of chronic fentanyl administration, our findings suggest that fentanyl is safe under properly controlled conditions.

To investigate the effects of long‐term fentanyl use on brain function, adult male C57BL/6J mice were chronically administered fentanyl (0.03 or 0.3 mg/kg/d ip) and analyzed in a behavioral test battery. Chronic fentanyl administration reduced anxiety‐like behavior, pain sensitivity, and the locomotor stimulatory effects of cocaine in mice. The results, however, failed to reach the threshold for study‐wide statistical significance.

Comprehensive behavioral analysis and quantification of brain free amino acids of C57BL/6J congenic mice carrying the 1473G allele in tryptophan hydroxylase-2

Aim

Tryptophan hydroxylase 2 (Tph2) is a rate‐limiting enzyme for the biosynthesis of 5‐hydroxytryptamine (5‐HT, serotonin). Previous studies have reported that C1473G polymorphism of the murine Tph2 gene leads to decreased 5‐HT levels in the brain and abnormal behavioral phenotypes, such as impaired anxiety‐ and depression‐like behaviors. In this study, to confirm the effect of the C1473G polymorphism on mouse phenotypes, we conducted a comprehensive battery of behavioral tests and measured the amounts of brain free amino acids involved in the production of 5‐HT.

Methods

We obtained C57BL/6J congenic mice that were homozygous for the 1473G allele of Tph2 (1473G) and subjected them and their wild‐type littermates (1473C) to a battery of behavioral tests. Using reverse‐phase high‐performance liquid chromatography (HPLC), we measured the amounts of free amino acids in the 5‐HT and epinephrine synthetic/metabolic pathways in the frontal cortex, hippocampus, striatum, and midbrain.

Results

We failed to detect significant differences between genotypes in depression‐like behaviors, anxiety‐like behaviors, social behaviors, sensorimotor gaiting, or learning and memory, while 1473G mice exhibited a nominally significant impairment in gait analysis, which failed to reach study‐wide significance. In the HPLC analysis, there were no significant differences in the amounts of 5‐HT, dopamine, norepinephrine, and epinephrine in the frontal cortex, hippocampus, striatum, and midbrain.

Conclusion

Our findings do not support the idea that congenic C57BL/6J mice carrying the 1473G allele may represent an animal model of mood disorder under normal conditions without stress.

We assessed the behavioral and biochemical phenotypes of congenic C57BL/6J mice carrying the 1473G allele and failed to identify significant differences between the 1473G allele‐carrying mice and their wild‐type littermates. Thus, our findings do not support the use of 1473G allele‐carrying C57BL/6J mice as an animal model of mood disorder under normal conditions without stress.

Comprehensive behavioral analysis of indoleamine 2,3-dioxygenase knockout mice

AIM

Indoleamine 2,3-dioxygenase 1 (IDO1) metabolizes the essential amino acid tryptophan into kynurenine derivatives, which are involved in neural activity via the kynurenine pathway (KP). IDO1 is an initial rate-limiting enzyme in the KP and is activated by stress and/or inflammation. The perturbation of IDO1 activity, which causes KP imbalance, is associated with psychiatric and neurological disorders. It has been reported that wild-type (WT) mice under inflammatory conditions show increased anxiety-like behavior and decreased novel object recognition, whereas Ido1 knockout (KO) mice do not display these behaviors. However, the behavioral phenotypes of Ido1 KO mice have not yet been fully examined under non-inflammatory conditions.

METHODS

We subjected Ido1 KO mice to a comprehensive behavioral test battery under normal conditions.

RESULTS

Ido1 KO mice and WT mice showed similar locomotor activity, anxiety-like behavior, social behavior, depression-like behavior, and fear memory. In the T-maze test, Ido1 KO mice exhibited weak but nominally significant impairment in the working memory task of the T-maze, but this result failed to reach study-wide significance.

CONCLUSIONS

Ido1 KO mice did not show any clear behavioral abnormalities under normal conditions. Further studies may be necessary to investigate their behavioral phenotype under inflammatory conditions due to their known roles in inflammation.

Behavioral effects of long-term oral administration of aluminum ammonium sulfate in male and female C57BL/6J mice

Background

Aluminum (Al) is considered to be a neurotoxic metal, and excessive exposure to Al has been reported to be a potential risk factor for neurodegenerative diseases. Al ammonium sulfate is one of the Al compounds that is widely used as a food additive. However, the effects of the oral administration of Al ammonium sulfate on physical development and behavior remain to be examined.

Methods

In this study, we investigated the effects of the administration of Al ammonium sulfate 12‐water dissolved in drinking water (0.075 mg/mL) beginning in adolescence on various types of behavior in adult female C57BL/6J mice through a battery of behavioral tests (low‐dose experiment; Experiment 1). We further examined the behavioral effects of the oral administration of a higher dose of the Al compound in drinking water (1 mg/mL) beginning in the prenatal period on behavior in adult male and female mice (high‐dose experiment; Experiment 2).

Results

In the low‐dose experiment, in which females’ oral intake of Al was estimated to be 0.97 mg Al/kg/d as adults, Al‐treated females exhibited an increase in total arm entries in the elevated plus maze test, an initial decrease and subsequent increase in immobility in the forced swim test, and reduced freezing in the fear conditioning test approximately 1 month after the conditioning session compared with vehicle‐treated females (uncorrected P < .05). However, the behavioral differences did not reach a statistically significant level after correction for multiple testing. In the high‐dose experiment, in which animals’ oral intakes were estimated to be about ten times higher than those in the low‐dose experiment, behavioral differences found in the low‐dose experiment were not observed in high‐dose Al‐treated mice, suggesting that the results of the low‐dose experiment might be false positives. Additionally, although high‐dose Al‐treated females exhibited increased social contacts with unfamiliar conspecifics and impaired reference memory performance, and high‐dose Al‐treated mice exhibited decreases in prepulse inhibition and in correct responses in the working memory task (uncorrected P < .05), the differences in any of the behavioral measures did not reach the significance level after correction for multiple testing.

Conclusion

Our results show that long‐term oral exposure to Al ammonium sulfate at the doses used in this study may have the potential to induce some behavioral changes in C57BL/6J mice. However, the behavioral effects of Al were small and statistically weak, as indicated by the fact that the results failed to reach the study‐wide significance level. Thus, further study will be needed to replicate the results and reevaluate the behavioral outcomes of oral intake of Al ammonium sulfate.

Aluminum (Al) ammonium sulfate was orally administered to C57BL/6J mice (estimated dose of 0.97‐9.78 Al mg/kg/d). Behavioral effects of Al were assessed in a battery of behavioral tests in mice in adulthood. Statistically significant behavioral differences were not found between Al‐ and vehicle‐treated mice.