Behavioral effects of adult male mice induced by low-level acetamiprid, imidacloprid, and nicotine exposure in early-life.

Introduction: Acetamiprid (ACE) and imidacloprid (IMI), the neonicotinoid chemicals, are widely used as pesticides because of their rapid insecticidal activity. Although these neonicotinoids exert very low toxicity in mammals, the effects of early, low-level, chronic exposure on the adult central nervous system are largely unclear. This study investigated the effects of low-level, chronic neonicotinoids exposure in early life on the brain functions of adult mice, using environmentally relevant concentrations. Methods: We exposed mice to an acceptable daily intake level of neonicotinoids in drinking water during the prenatal and postnatal periods. Additionally, we also exposed mice to nicotine (NIC) as a positive control. We then examined the effects on the central nervous system in adult male offspring. Results: In the IMI and NIC exposure groups, we detected behavior that displayed impairment in learning and memory. Furthermore, immunohistochemical analysis revealed a decrease in SOX2 (as a neural stem cell marker) and GFAP (as an astrocyte marker) positive cells of the hippocampal dentate gyrus in the IMI and NIC exposure groups compared to the control group. Discussion: These results suggest that exposure to neonicotinoids at low levels in early life affects neural circuit base formation and post-maturation behavior. Therefore, in the central nervous system of male mice, the effects of low-level, chronic neonicotinoids exposure during the perinatal period were different from the expected effects of neonicotinoids exposure in mature animals.

Immunohistochemical analysis of the vimentin filaments in Sertoli cells is a powerful tool for the prediction of spermatogenic dysfunction.

The close interaction between male germ cells and Sertoli cells, a type of somatic cell found in the seminiferous tubules of mammalian testis, is essential for the normal progression of spermatogenesis in mammals. Vimentin is an intermediate filament protein that primarily provides mechanical support, preserves cell shape, and maintains the nuclear position, and it is often used as a marker to identify Sertoli cells. Vimentin is known to be involved in many diseases and aging processes; however, how vimentin is related to spermatogenic dysfunction and the associated functional changes is still unclear. In a previous study, we reported that vitamin E deficiency affected the testes, epididymis, and spermatozoa of mice, accelerating the progression of senescence. In this study, we focused on the Sertoli cell marker vimentin and explored the relationship between the cytoskeletal system of Sertoli cells and spermatogenic dysfunction using testis tissue sections that caused male reproductive dysfunction with vitamin E deficiency. The immunohistochemical analysis showed that the proportion of the vimentin-positive area in seminiferous tubule cross-sections was significantly increased in testis tissue sections of the vitamin E-deficient group compared with the proportion in the control group. The histological analysis of testis tissue sections from the vitamin E-deficient group showed that vimentin-positive Sertoli cells were greatly extended from the basement membrane, along with an increased abundance of vimentin. These findings suggest that vimentin may be a potential indicator for detecting spermatogenic dysfunction.

Behavioral effects induced by the oral administration of acetamiprid in male mice during the postnatal lactation period or adulthood.

Acetamiprid (ACE), a neonicotinoid chemical, is widely used as a pesticide due to its rapid insecticidal activity. Although neonicotinoids exert very low toxicity in mammals, the effects of early exposure to neonicotinoids on the adult central nervous system are poorly understood. This study investigated the effects of ACE exposure in early life on brain function in adult mice. We exposed male C57BL/6N mice to ACE (10 mg/kg) orally when they were two (postnatal lactation) or 11 weeks old (adult). We examined the effects of ACE on the central nervous system using the mouse behavioral test battery, consisting of the open field test, light/dark transition test, elevated plus-maze test, contextual/cued fear conditioning test, and pre-pulse inhibition test at 12-13 weeks old. In the mouse behavioral test battery, learning memory abnormalities were detected in the mature treatment group. In addition, learning memory and emotional abnormalities were detected in the postnatal lactation treatment group. These results suggest that the behavioral effects of postnatal lactation treatment with ACE were qualitatively different from the behavioral abnormalities in the mature treatment group.

Exposure to bisphenol A or its phenolic analogs during early life induces different types of anxiety-like behaviors after maturity in male mice.

Products used in daily life contain multiple chemicals capable of inducing endocrine disruption in animals, including humans. One such typical substance is bisphenol A (BPA). BPA has been widely used in epoxy resins and polycarbonate plastics and can exert several adverse effects. Furthermore, given their structural similarity to BPA, phenolic analogs of BPA, i.e., synthetic phenolic antioxidants (SPAs), are considered to exhibit similar toxicity; however, the effects of early SPA exposure on the adult central nervous system remain poorly clarified. In the present study, we aimed to evaluate and compare the neurobehavioral effects of early life exposure to BPA and two selected SPAs, 4,4'-butylidenebis (6-tert-butyl-m-cresol) (BB) and 2,2'-methylenebis (6-tert-butyl-p-cresol) (MB). We exposed mice to low levels of these chemicals through drinking water during prenatal and postnatal periods. Subsequently, we examined the adverse effects of these chemicals on the central nervous system using a mouse behavioral test battery, comprising the open field test, light/dark transition test, elevated plus-maze test, contextual/cued fear conditioning test, and prepulse inhibition test, at 12-13 weeks old. Based on the behavioral analysis, SPAs, like BPA, may cause affective disorders even at low doses, although qualitative differences were noted in anxiety-related behaviors. In conclusion, our findings could be valuable for clarifying the potential adverse developmental risks of SPA exposure in early life.

Behavioural effects in mice orally exposed to domoic acid or ibotenic acid are influenced by developmental stages and sex differences.

The structure of the brain is dramatically altered during the critical period. Physiological substances (neurotransmitters, hormones, etc.) in the body fluctuate significantly before and after sexual maturation. Therefore, the effect of chemical exposure on the central nervous system often differs depending on the developmental stage and sex. We aimed to compare the behavioural effects that emerged from the administration of chemicals to mice of different life stages (immature or mature) and different sex (male or female). We administered mice with domoic acid (DA), a marine poison, and ibotenic acid (IA), found in poisonous mushrooms. These excitatory amino acids act as agonists for glutamate and are potent neurotoxins. Interestingly, the behavioural effects of these chemicals were completely different. Following DA administration, we observed memory deficits only in groups of male mice treated at maturity. Following IA administration, we observed deviations in emotional behaviour in groups of male mice treated at both immaturity and maturity. In contrast, few characteristic changes were detected in all groups of females. Our results support the theory that the behavioural effects of chemical administration vary considerably with developmental stages and sex. In conclusion, our findings promote better understanding of individual differences in excitatory chemical-induced neurotoxicity and provide evidence for future risk strategies and treatments.

Visualizing the spatial localization of ciclesonide and its metabolites in rat lungs after inhalation of 1-µm aerosol of ciclesonide by desorption electrospray ionization-time of flight mass spectrometry imaging.

Inhaled ciclesonide (CIC), a corticosteroid used to treat asthma that is also being investigated for the treatment of corona virus disease 2019, hydrolyzes to desisobutyryl-ciclesonide (des-CIC) followed by reversible esterification when exposed to fatty acids in lungs. While previous studies have described the distribution and metabolism of the compounds after inhalation, spatial localization in the lungs remains unclear. We visualized two-dimensional spatial localization of CIC and its metabolites in rat lungs after administration of a single dose of a CIC aerosol (with the mass median aerodynamic diameter of 0.918-1.168 µm) using desorption electrospray ionization-time of flight mass spectrometry imaging (DESI-MSI). In the analysis, CIC, des-CIC, and des-CIC-oleate were imaged in frozen lung sections at high spatial and mass resolutions in negative-ion mode. MSI revealed the coexistence of CIC, des-CIC, and des-CIC-oleate on the airway epithelium, and the distribution of des-CIC and des-CIC-oleate in peripheral lung regions. In addition, a part of CIC independently localized on the airway epithelium. These results suggest that distribution of CIC and its metabolites in lungs is related to both the intended delivery of aerosols to pulmonary alveoli and peripheral regions, and the potential deposition of CIC particles on the airway epithelium.

Effect of vitamin E deficiency on spermatogenesis in mice and its similarity to aging.

Vitamin E (VE) plays numerous important roles in mammals because of its antioxidant activity. As a result, VE deficiency (VED) leads to the dysfunction of central nervous, reproductive, and immune systems. However, few studies have reported the effects of VED on the male reproductive system. In this study, we investigated the effects of VED on male reproductive function and examined its relationship to involution in the male reproductive system with aging. We fed a VED or control diet to 4-week-old mice for 12 or 24 weeks. Following the histopathological analysis of reproductive organs, we found seminiferous tubules with exfoliation in the VED groups, and its frequency was significantly increased compared with the controls. Additionally, in the epididymis, a decrease in spermatozoa and an increase in apoptotic germ cells were observed in the VED groups compared with the controls. By Papanicolaou staining, we also found an increase in the proportion of sperm with abnormal morphology in the VED groups compared with the controls. These reproductive effects induced by VED were highly similar to one aspect of those observed in aged mice. Our findings demonstrate that the aging of the male reproductive system may be accelerated because of the impaired in vivo antioxidant capacity induced by VED.

Differences in resistance against osmotic challenge among C57BL/6, DBA/2 and their hybrid mice metaphase II (MII) stage oocytes.

Oocytes of B6D2F1 (BDF1) mice are often used as recipients for intracytoplasmic sperm injection because of their cell membrane resistance against capillary penetration. It is assumed that oocytes of BDF1 mice have superior traits because of their hybrid vigour. However, the mechanisms of hybrid vigour are unclear. In this study, we focused on the membrane resistance of MII stage oocytes against changes in extracellular osmotic pressure. As a result, MII stage oocytes of inbred C57BL/6 and DBA/2 mice showed high tolerance in either a hypertonic or a hypotonic environment. Conversely, MII stage oocytes of hybrid BDF1 and D2B6F1 mice showed high tolerance in both hypertonic and hypotonic environments. Therefore, it is considered that MII stage oocytes of hybrid mice have superior traits than those of inbred mice. Our findings demonstrated that the hybrid vigour exists in the form of resistance to extracellular osmotic environment in hybrid MII stage oocytes.

Early-life exposure to low levels of permethrin exerts impairments in learning and memory with the effects on neuronal and glial population in adult male mice.

Permethrin, a pyrethroid chemical, is widely used as a pesticide because of its rapid insecticidal activity. Although permethrin is considered to exert very low toxicity in mammals, the effects of early, low-level, chronic exposure on the adult central nervous system are unclear. In this study, we investigated the effects of low-level, chronic permethrin exposure in early life on the brain functions of adult mice, using environmentally relevant concentrations. We exposed mice to the acceptable daily intake level of permethrin (0.3 ppm) in drinking water during the prenatal and postnatal periods. We then examined the effects on the central nervous system in adult male offspring. In the permethrin group, we detected behavior that displayed incomplete adaptation to a novel environment, as well as an impairment in learning and memory. In addition, immunohistochemical analysis revealed an increase in doublecortin- (an immature neuron marker) positive cells in the hippocampal dentate gyrus in the permethrin exposure group compared with the control group. Additionally, in the permethrin exposure group there was a decrease in astrocyte number in the hilus of the dentate gyrus, and remaining astrocytes were often irregularly shaped. These results suggest that exposure to permethrin at low levels in early life affects the formation of the neural circuit base and behavior after maturation. Therefore, in the central nervous system of male mice, low-level, chronic permethrin exposure during the prenatal and postnatal periods has effects that were not expected based on the known effects of permethrin exposure in mature animals.

Effects of doxorubicin on sperm DNA methylation in mouse models of testicular toxicity.

Testicular toxicity is a frequent adverse effect of cancer chemotherapy that has no effective clinical biomarker. To find new biomarkers, we focused on epigenetic mechanisms in the male germline. We investigated the DNA methylation status of the male germline during testicular toxicity induced by doxorubicin (DXR), a widely used anticancer agent. We established mouse models of early stage testicular toxicity and testicular pre-toxicity by the administration of 0.2 mg/kg and 0.02 mg/kg DXR, respectively, twice weekly for 5 weeks. Histological analysis showed sparse abnormalities in testicular tissue; however, western blotting analysis revealed reduced testicular expression levels of DNA methyltransferases DNMT3a and DNMT3b in both DXR-treated groups. Interestingly, comprehensive sperm DNA methylation analysis using Methyl-CpG binding domain protein-enriched genome sequencing revealed that hypomethylation was the most frequent change induced by DXR. These findings suggest that sperm DNA methylation status may be used as an early diagnostic marker for testicular changes not detected by conventional toxicity analysis.

Prenatal and postnatal exposure to low levels of permethrin exerts reproductive effects in male mice.

Permethrin, a pyrethroid chemical, is widely used as a pesticide because of its rapid insecticidal activity. Although permethrin is considered to exert very low toxicity on mammalian reproductive organs, the effects of early low-level and chronic exposure on adult spermatogenesis are unclear. We exposed mice to environmentally relevant concentrations of permethrin (0, 0.3, and 30ppm) in drinking water during prenatal and postnatal period and examined the effects on the testis in mice offspring when they reached maturity (12 weeks of age). Using methyl green-pyronin staining, we found an abnormal accumulation of RNA in the seminiferous epithelia of mice treated with permethrin; this accumulation may be derived from an enlargement of the residual body. Additionally, permethrin may cause a decline of Sertoli cell functions. Our findings demonstrate that low-level and chronic permethrin exposure during prenatal and postnatal period has distinct effects on male reproductive system in mice.