Hippocampal Neurogenesis as a Critical Target of Neurotoxicants Contained in Foods

Increased spontaneous activity and progressive suppression of adult neurogenesis in the hippocampus of rat offspring after maternal exposure to imidacloprid

Imidacloprid (IMI) is a widely used neonicotinoid insecticide that poses risks for developmental neurotoxicity in mammals. The present study investigated the effects of maternal exposure to IMI on behaviors and adult neurogenesis in the hippocampal dentate gyrus (DG) of rat offspring. Dams were exposed to IMI via diet (83, 250, or 750 ppm in diet) from gestational day 6 until day 21 post-delivery on weaning, and offspring were maintained until adulthood on postnatal day 77. In the neurogenic niche, 750-ppm IMI decreased numbers of late-stage neural progenitor cells (NPCs) and post-mitotic immature granule cells by suppressing NPC proliferation and ERK1/2-FOS-mediated synaptic plasticity of granule cells on weaning. Suppressed reelin signaling might be responsible for the observed reductions of neurogenesis and synaptic plasticity. In adulthood, IMI at ≥ 250 ppm decreased neural stem cells by suppressing their proliferation and increasing apoptosis, and mature granule cells were reduced due to suppressed NPC differentiation. Behavioral tests revealed increased spontaneous activity in adulthood at 750 ppm. IMI decreased hippocampal acetylcholinesterase activity and Chrnb2 transcript levels in the DG on weaning and in adulthood. IMI increased numbers of astrocytes and M1-type microglia in the DG hilus, and upregulated neuroinflammation and oxidative stress-related genes on weaning. In adulthood, IMI increased malondialdehyde level and number of M1-type microglia, and downregulated neuroinflammation and oxidative stress-related genes. These results suggest that IMI persistently affected cholinergic signaling, induced neuroinflammation and oxidative stress during exposure, and increased sensitivity to oxidative stress after exposure in the hippocampus, causing hyperactivity and progressive suppression of neurogenesis in adulthood. The no-observed-adverse-effect level of IMI for offspring behaviors and hippocampal neurogenesis was determined to be 83 ppm (5.5-14.1 mg/kg body weight/day).

Suppression of neurogranin expression by disruption of epigenetic DNA methylation in hippocampal mature granule cells after developmental exposure to neurotoxicants in rats

We previously performed comprehensive analyses of genes hypermethylated promoter regions and downregulated transcripts in the hippocampal dentate gyrus (DG) of rats upon weaning at postnatal day (PND) 21 after developmental exposure to 6-propyl-2-thiouracil (PTU), valproic acid, and glycidol (GLY), all of which are known to show irreversible effects on hippocampal neurogenesis in adulthood on PND 77. Here, we selected neurotransmitter and neurogenesis-related genes for validation analysis of methylation and expression. As a result, Nrgn by GLY and Shisa7, Agtpbp1, and Cyp46a1 by PTU underwent DNA hypermethylation and sustained downregulation. Immunohistochemical analysis of candidate gene products revealed that the number of neurogranin (NRGN)+ granule cells was decreased in the ventral DG by GLY on PND 21 and 77 and by PTU on PND 21. Among the samples of developmental or 28-day young adult-age exposure to known developmental neurotoxicants in humans, i.e., lead acetate, ethanol, and aluminum chloride, a decrease of NRGN+ cells by ethanol was also observed on PND 77 after developmental exposure. Double immunohistochemistry analysis revealed that NRGN was expressed in mature granule cells, and a similar immunoreactive cell distribution was found for phosphorylated calcium/calmodulin-activated protein kinase, a NRGN downstream molecule. After developmental PTU exposure, the number of activity-regulated cytoskeleton-associated protein+ granule cells was also profoundly decreased in the ventral DG in parallel with the decrease in NRGN+ cells on PND 21. These results suggest that NRGN is a potential marker for suppression of synaptic plasticity in mature granule cells in the ventral DG.

Machine learning discriminates P2X7-mediated intracellular calcium sparks in human-induced pluripotent stem cell-derived neural stem cells

Adenosine triphosphate (ATP) is an extracellular signaling molecule that mainly affects the pathophysiological situation in the body and can be sensed by purinergic receptors, including ionotropic P2X7. Neuronal stem cells (NSCs) remain in adult neuronal tissues and can contribute to physiological processes via activation by evoked pathophysiological situations. In this study, we revealed that human-induced pluripotent stem cell-derived NSCs (iNSCs) have ATP-sensing ability primarily via the purinergic and ionotropic receptor P2X7. Next, to develop a machine learning (ML)-based screening system for food-derived neuronal effective substances and their effective doses, we collected ATP-triggered calcium responses of iNSCs pretreated with several substances and doses. Finally, we discovered that ML was performed using composite images, each containing nine waveform images, to achieve a better ML model (MLM) with higher precision. Our MLM can correctly sort subtle unidentified changes in waveforms produced by pretreated iNSCs with each substance and/or dose into the positive group, with common mRNA expression changes belonging to the gene ontology signatures.

Comparison of the effect of glyphosate and glyphosate-based herbicide on hippocampal neurogenesis after developmental exposure in rats

Increasing evidence indicates that glyphosate (GlyP)-based herbicides (GBHs) induce developmental neurotoxicity. The present study investigated the developmental exposure effect of GlyP and GBH on hippocampal neurogenesis in rats. Dams were treated from gestational day 6 to day 21 post-delivery on weaning with a diet containing 1.5% or 3.0% GlyP or drinking water with 1.0% GBH (containing 0.36% GlyP). Dams in the 1.5%-GlyP, 3.0%-GlyP, and GBH groups received 1.04, 2.16, and 0.25 g GlyP/kg body weight (BW)/day during gestation, and 2.27, 4.65, and 0.58 g GlyP/kg BW/day during lactation, respectively. On weaning, 3.0% GlyP- and GBH-exposed offspring decreased the BW, and the latter also decreased the brain weight. Both compounds suppressed neural progenitor cell proliferation in the neurogenic niche, and GlyP-exposed offspring showed a decreased number of TUBB3⁺ immature granule cells. In contrast, both compounds increased the number of ARC⁺ granule cells, suggesting increased synaptic plasticity. Both compounds downregulated antioxidant genes (Cat and Sod2) in the dentate gyrus, suggestive of increased sensitivity to oxidative stress, which might be related to the suppression of neurogenesis. At the adult age, GBH alone sustained decreases in body and brain weights. Both compounds increased hippocampal malondialdehyde levels and upregulated Cat in the dentate gyrus, suggesting induction of oxidative stress. Both compounds upregulated Casp9, and GBH increased neural progenitor cell apoptosis, suggesting disruption of neurogenesis related to oxidative stress. GBH increased the number of COX2⁺ granule cells, and both compounds upregulated Arc, suggesting increased synaptic plasticity. These results suggest that GlyP and GBH might cause similar effects on disruption of neurogenesis accompanying compensatory responses and induction of oxidative stress responses through the adult age in the hippocampus. However, effects on adult age were more evident with GBH, suggesting that the surfactants contained in GBH might have contributed to the enhanced neurotoxicity of GlyP, similar to the enhanced general toxicity.

Comparative study on detectability of learning and memory disorder between two water maze tests commonly used in juvenile rat toxicity studies using isoflurane inhaled rat model

Evaluation of learning and memory is crucial in juvenile animal toxicity studies (JAS) during the development of CNS active drugs, but there are no currently recommended test methods. We compared the ability of the Morris water maze (MWM) and the Biel water maze (BWM) to detect learning and memory disorder (LMD) using rats inhaled isoflurane (IFN). Rats were treated with 1% IFN using inhalation on postnatal day (PND) 7 for 6 h. All rats were subjected to the MWM on PND 33 and the BWM on PND 55/57 (Experiment 1), or the BWM on PND 32/33 and the MWM on PND 54/55 (Experiment 2). On PND 70, the brain was weighed and then neurohistopathology was conducted. There were no IFN-related changes in clinical signs and body weight. In the tests beginning on PND 32/33, the MWM clearly detected IFN-related LMD in both sexes whereas the BWM detected LMD only in males. With an additional benefit of a simpler procedure, the MWM was considered superior to the BMW for JAS. LMD was not detected in both mazes tested from PND 54/55/57, which was considered due to weak effect and/or recovery of brain function with growth. Single IFN inhalation on PND 7 was considered useful as positive control to induce LMD caused by postnatal exposure in rats, but stronger treatment regimens was recommended.

Oral exposure to aluminum chloride for 28 days suppresses neural stem cell proliferation and increases mature granule cells in adult hippocampal neurogenesis of young-adult rats

Aluminum (Al), a common light metal, affects the developing nervous system. Developmental exposure to Al chloride (AlCl₃ ) induces aberrant neurogenesis by targeting neural stem cells (NSCs) and/or neural progenitor cells (NPCs) in the dentate gyrus (DG) of rats and mice. To investigate whether hippocampal neurogenesis is similarly affected by AlCl₃ exposure in a general toxicity study, AlCl₃ was orally administered to 5-week-old Sprague Dawley rats at dosages of 0, 4000, or 8000 ppm in drinking water for 28 days. AlCl₃ downregulated Sox2 transcript levels in the DG at the highest dosage and produced a dose-dependent decrease of SOX2⁺ cells without altering numbers of GFAP⁺ or TBR2⁺ cells in the subgranular zone, suggesting that AlCl₃ decreases Type 2a NPCs. High-dose exposure downregulated Pcna, upregulated Pvalb, and altered expression of genes suggestive of oxidative stress induction (upregulation of Nos2 and downregulation of antioxidant enzyme genes), indicating suppressed proliferation and differentiation of Type 1 NSCs. AlCl₃ doses also increased mature granule cells in the DG. Upregulation of Reln may have contributed to an increase of granule cells to compensate for the decrease of Type 2a NPCs. Moreover, upregulation of Calb2, Gria2, Mapk3, and Tgfb3, as well as increased numbers of activated astrocytes in the DG hilus, may represent ameliorating responses against suppressed neurogenesis. These results suggest that 28-day exposure of young-adult rats to AlCl₃ differentially targeted NPCs and mature granule cells in hippocampal neurogenesis, yielding a different pattern of disrupted neurogenesis from developmental exposure.

Ameliorating effect of continuous alpha-glycosyl isoquercitrin treatment starting from late gestation in a rat autism model induced by postnatal injection of lipopolysaccharides

The present study investigated the role of neuroinflammation and brain oxidative stress induced by neonatal treatment with lipopolysaccharides (LPS) on the development of autism spectrum disorder (ASD)-like behaviors and disruptive hippocampal neurogenesis in rats by exploring the chemopreventive effects of alpha-glycosyl isoquercitrin (AGIQ) as an antioxidant. AGIQ was dietary administered to dams at 0.25% or 0.5% (w/w) from gestational day 18 until postnatal day (PND) 21 on weaning and then to pups until the adult stage on PND 77. The pups were intraperitoneally injected with LPS (1 mg/kg body weight) on PND 3. At PND 6, LPS alone increased Iba1+ and CD68+ cell numbers without changing the CD163+ cell number and strongly upregulated pro-inflammatory cytokine gene expression (Il1a, Il1b, Il6, Nfkb1, and Tnf) in the hippocampus, and increased brain malondialdehyde levels. At PND 10, pups decreased ultrasonic vocalization (USV), suggesting the induction of pro-inflammatory responses and oxidative stress to trigger communicative deficits. By contrast, LPS alone upregulated Nfe2l2 expression at PND 6, increased Iba1+, CD68+, and CD163+ cell numbers, and upregulated Tgfb1 at PND 21, suggesting anti-inflammatory responses until the weaning period. However, LPS alone disrupted hippocampal neurogenesis at weaning and suppressed social interaction parameters and rate of freezing time at fear acquisition and extinction during the adolescent stage. On PND 77, neuroinflammatory responses had mostly disappeared; however, disruptive neurogenesis and fear memory deficits were sustained. AGIQ ameliorated most changes on acute pro-inflammatory responses and oxidative stress at PND 6, and the effects on USVs at PND 10 and neurogenesis and behavioral parameters throughout the adult stage. These results suggested that neonatal LPS treatment induced acute but transient neuroinflammation, triggering the progressive disruption of hippocampal neurogenesis leading to abnormal behaviors in later life. AGIQ treatment was effective for ameliorating LPS-induced progressive changes by critically suppressing initial pro-inflammatory responses and oxidative stress.

Gene expression profiles of multiple brain regions in rats differ between developmental and postpubertal exposure to valproic acid

We have previously reported that the valproic acid (VPA)-induced disruption pattern of hippocampal adult neurogenesis differs between developmental and 28-day postpubertal exposure. In the present study, we performed brain region-specific global gene expression profiling to compare the profiles of VPA-induced neurotoxicity between developmental and postpubertal exposure. Offspring exposed to VPA at 0, 667, and 2000 parts per million (ppm) via maternal drinking water from gestational day 6 until weaning (postnatal day 21) were examined, along with male rats orally administered VPA at 0, 200, and 900 mg/kg body weight for 28 days starting at 5 weeks old. Four brain regions-the hippocampal dentate gyrus, corpus callosum, cerebral cortex, and cerebellar vermis-were subjected to expression microarray analysis. Profiled data suggested a region-specific pattern of effects after developmental VPA exposure, and a common pattern of effects among brain regions after postpubertal VPA exposure. Developmental VPA exposure typically led to the altered expression of genes related to nervous system development (Msx1, Xcl1, Foxj1, Prdm16, C3, and Kif11) in the hippocampus, and those related to nervous system development (Neurod1) and gliogenesis (Notch1 and Sox9) in the corpus callosum. Postpubertal VPA exposure led to the altered expression of genes related to neuronal differentiation and projection (Cd47, Cyr61, Dbi, Adamts1, and Btg2) in multiple brain regions. These findings suggested that neurotoxic patterns of VPA might be different between developmental and postpubertal exposure, which was consistent with our previous study. Of note, the hippocampal dentate gyrus might be a sensitive target of developmental neurotoxicants after puberty.

Disruption of postnatal neurogenesis and adult-stage suppression of synaptic plasticity in the hippocampal dentate gyrus after developmental exposure to sterigmatocystin in rats

Exposure to sterigmatocystin (STC) raises concerns on developmental neurological disorders. The present study investigated the effects of maternal oral STC exposure on postnatal hippocampal neurogenesis of offspring in rats. Dams were exposed to STC (1.7, 5.0, and 15.0 ppm in diet) from gestational day 6 until day 21 post-delivery (weaning), and offspring were maintained without STC exposure until adulthood on postnatal day (PND) 77, in accordance with OECD chemical testing guideline Test No. 426. On PND 21, 15.0-ppm STC decreased type-3 neural progenitor cell numbers in the subgranular zone (SGZ) due to suppressed proliferation. Increased γ-H2AX-immunoreactive (+) cell numbers in the SGZ and Ercc1 upregulation and Brip1 downregulation in the dentate gyrus suggested induction of DNA double-strand breaks in SGZ cells. Upregulation of Apex1 and Ogg1 and downregulation of antioxidant genes downstream of NRF2-Keap1 signaling suggested induction of oxidative DNA damage. Increased p21WAF1/CIP1+ SGZ cell numbers and suppressed cholinergic signaling through CHRNB2-containing receptors in GABAergic interneurons suggested potential neurogenesis suppression mechanisms. Multiple mechanisms involving N-methyl-d-aspartate (NMDA) receptor-mediated glutamatergic signaling and various GABAergic interneuron subpopulations, including CHRNA7-expressing somatostatin+ interneurons activated by BDNF-TrkB signaling, may be involved in ameliorating the neurogenesis. Upregulation of Arc, Ptgs2, and genes encoding NMDA receptors and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors suggested synaptic plasticity facilitation. On PND 77, ARC+ granule cells decreased, and Nos2 was upregulated following 15.0 ppm STC exposure, suggesting oxidative stress-mediated synaptic plasticity suppression. Inverse pattern in gene expression changes in vesicular glutamate transporter isoforms, Slc17a7 and Slc17a6, from weaning might also be responsible for the synaptic plasticity suppression. The no-observed-adverse-effect level of maternal oral STC exposure for offspring neurogenesis was determined to be 5.0 ppm, translating to 0.34-0.85 mg/kg body weight/day.

Aberrant neurogenesis and late onset suppression of synaptic plasticity as well as sustained neuroinflammation in the hippocampal dentate gyrus after developmental exposure to ethanol in rats

Drinking alcohol during pregnancy may cause fetal alcohol spectrum disorder. The present study investigated the effects of maternal oral ethanol (EtOH) exposure (0, 10, or 12.5 % in drinking water) from gestational day 6 until day 21 post-delivery (weaning) on postnatal hippocampal neurogenesis at weaning and in adulthood on postnatal day 77 in rat offspring. At weaning, type-3 neural progenitor cells (NPCs) were decreased in the subgranular zone (SGZ), accompanied by Chrnb2 downregulation and Grin2b upregulation in the dentate gyrus (DG). These results suggested suppression of CHRNB2-mediated cholinergic signaling in γ-aminobutyric acid (GABA)ergic interneurons in the DG hilus and increased glutamatergic signaling through the NR2B subtype of N-methyl-d-aspartate (NMDA) receptors, resulting in NPC reduction. In contrast, upregulation of Chrna7 may increase CHRNA7-mediated cholinergic signaling in immature granule cells, and upregulation of Ntrk2 may cause an increase in somatostatin-immunoreactive ⁽⁺⁾ GABAergic interneurons, suggesting a compensatory response against NPC reduction. Promotion of SGZ cell proliferation increased type-2a NPCs. Moreover, an increase in calbindin-d-29 K⁺ interneurons and upregulation of Reln, Drd2, Tgfb2, Il18, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor subunit genes might participate in this compensatory response. In adulthood, reduction of FOS⁺ cells and downregulation of Fos and Arc suggested suppression of granule cell synaptic plasticity, reflecting upregulation of Tnf and downregulation of Cntf, Ntrk2, and AMPA-type glutamate receptor genes. In the DG hilus, gliosis and hyper-ramified microglia, accompanying upregulation of C3, appeared at weaning, suggesting contribution to suppressed synaptic plasticity in adulthood. M1 microglia increased throughout adulthood, suggesting sustained neuroinflammation. These results indicate that maternal EtOH exposure temporarily disrupts hippocampal neurogenesis and later suppresses synaptic plasticity. Induction of neuroinflammation might initially ameliorate neurogenesis (as evident by upregulation of Tgfb2 and Il18) but later suppress synaptic plasticity (as evident by upregulation of C3 at weaning and Tnf in adulthood).

Identification of gene targets of developmental neurotoxicity focusing on DNA hypermethylation involved in irreversible disruption of hippocampal neurogenesis in rats

We have previously found that maternal exposure to 6‐propyl‐2‐thiouracil (PTU), valproic acid (VPA), or glycidol (GLY) has a sustained or late effect on hippocampal neurogenesis at the adult stage in rat offspring. Herein, we searched for genes with hypermethylated promoter region and downregulated transcript level to reveal irreversible markers of developmental neurotoxicity. The hippocampal dentate gyrus of male rat offspring exposed maternally to PTU, VPA, or GLY was subjected to Methyl‐Seq and RNA‐Seq analyses on postnatal day (PND) 21. Among the genes identified, 170 were selected for further validation analysis of gene expression on PND 21 and PND 77 by real‐time reverse transcription‐PCR. PTU and GLY downregulated many genes on PND 21, reflecting diverse effects on neurogenesis. Furthermore, genes showing sustained downregulation were found after PTU or VPA exposure, reflecting a sustained or late effect on neurogenesis by these compounds. In contrast, such genes were not observed with GLY, probably because of the reversible nature of the effects. Among the genes showing sustained downregulation, Creb, Arc, and Hes5 were concurrently downregulated by PTU, suggesting an association with neuronal mismigration, suppressed synaptic plasticity, and reduction in neural stem and progenitor cells. Epha7 and Pvalb were also concurrently downregulated by PTU, suggesting an association with the reduction in late‐stage progenitor cells. VPA induced sustained downregulation of Vgf and Dpysl4, which may be related to the aberrations in synaptic plasticity. The genes showing sustained downregulation may be irreversible markers of developmental neurotoxicity.

Hippocampal dentate gyrus of rat offspring exposed maternally to PTU, VPA, or GLY was subjected to global methylation analysis on PND 21. Genes downregulated on PND 77 were examined. PTU concurrently downregulated Creb, Arc, and Hes5, suggesting an association with the diverse effects on neurogenesis. PTU also concurrently downregulated Epha7 and Pvalb, suggesting an association with progenitor cell reduction. VPA downregulated Vgf and Dpysl4, suggesting an association with the aberrant synaptic plasticity. In contrast, GLY did not induce sustained downregulation.

Continuous exposure to amorphous formula of curcumin from the developmental stage facilitates anti-anxiety-like behavior and fear-extinction learning in rats

An amorphous formula of curcumin (CUR) has shown to enable an improved bioavailability after ingestion. The aim of this study was to investigate the hypothesis that exogenously administered CUR has an advantage in ameliorating post-traumatic stress disorder at low doses. To this end, Long-Evans rats were dietary exposed to CUR at 0.1% or 0.5% from gestational day 6 to postnatal day (PND) 74 or 77. Offspring exposed to 0.1% CUR revealed facilitation of anti-anxiety-like behavior in the open field test and fear-extinction learning tested during PND 62 to 74, increases in hippocampal granule cells expressing immediate-early gene proteins and a decrease in prelimbic cortical neurons expressing phosphorylated extracellular signal-regulated kinase 1/2 after the last trial of the fear-extinction learning test on PND 74. The constitutive gene expression levels of Gria1, Gria2, Grin2d, Slc17a6, and Slc17a7 were altered in the hippocampal dentate gyrus and amygdala on PND 77. These results suggest alterations in synaptic plasticity to strengthen neural circuits in promoting the behavioral effects by 0.1%-CUR. In contrast, 0.5% CUR revealed a lack of any of the changes in behavioral tests that were observed at 0.1%; however, this dose upregulated oxidative stress and neuroinflammation-related genes in the hippocampal dentate gyrus, and increased neural stem cells and proliferation activity of the subgranular zone in the dentate gyrus. These results suggest a possible preventive use of CUR at low doses in mitigating some stress disorders; however, excessively absorbed doses may prevent behavioral changes by inducing neuroinflammation that affects hippocampal neurogenesis involving neural stem cells.

Developmental exposure to diacetoxyscirpenol reversibly disrupts hippocampal neurogenesis by inducing oxidative cellular injury and suppressed differentiation of granule cell lineages in mice

To investigate the developmental exposure effect of diacetoxyscirpenol (DAS) on postnatal hippocampal neurogenesis, pregnant ICR mice were provided a diet containing DAS at 0, 0.6, 2.0, or 6.0 ppm from gestational day 6 to day 21 on weaning after delivery. Offspring were maintained through postnatal day (PND) 77 without DAS exposure. On PND 21, neural stem cells (NSCs) and all subpopulations of proliferating progenitor cells were suggested to decrease in number in the subgranular zone (SGZ) at ≥ 2.0 ppm. At 6.0 ppm, increases of SGZ cells showing TUNEL⁺, metallothionein-I/II⁺, γ-H2AX⁺ or malondialdehyde⁺, and transcript downregulation of Ogg1, Parp1 and Kit without changing the level of double-stranded DNA break-related genes were observed in the dentate gyrus. This suggested induction of oxidative DNA damage of NSCs and early-stage progenitor cells, which led to their apoptosis. Cdkn2a, Rb1 and Trp53 downregulated transcripts, which suggested an increased vulnerability to DNA damage. Hilar PVALB⁺ GABAergic interneurons decreased and Grin2a and Chrna7 were downregulated, which suggested suppression of type-2-progenitor cell differentiation. On PND 77, hilar RELN⁺ interneurons increased at ≥ 2.0 ppm; at 6.0 ppm, RELN-related Itsn1 transcripts were upregulated and ARC⁺ granule cells decreased. Increased RELN signals may ameliorate the response to the decreases of NSCs and ARC-mediated synaptic plasticity. These results suggest that DAS reversibly disrupts hippocampal neurogenesis by inducing oxidative cellular injury and suppressed differentiation of granule cell lineages. The no-observed-adverse-effect level of DAS for offspring neurogenesis was determined to be 0.6 ppm (0.09-0.29 mg/kg body weight/day).

Evaluation of neurotoxicity and hepatotoxicity effects of acute and sub-acute oral administration of unripe ackee (Blighia sapida) fruit extract

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Acute oral dose of 2000 mg/kg of unripe B. sapida fruit extract (BSE) was toxic to mice.

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Repeated treatment with BSE impaired locomotor function, memory performance and shortened seizure latency in mice.

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Repeated treatment with BSE significantly up-regulate acetylcholinesterase enzyme activity in mice.

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Repeated treatment with BSE elevates oxidative stress in the brain and liver of mice.

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Repeated treatment with BSE showed histopathological evidences of toxicity in mice brain and liver.

Ackee (Blighia sapida) is a commonly eaten fruit that is indigenous to West Africa and Jamaica. Ackee poisoning in young children have been reported in parts of Nigeria due to consumption of the unripe fruits. This study was designed to identify potential mechanisms of acute and sub-acute toxicity of unripe B. sapida fruit extract (BSE).

Acute toxic effect was investigated in mice of either sex administered BSE 2000 mg/kg. The sub-acute toxicity effects were investigated in mice of either sex that received 28 days repeated administration of BSE (100 and 500 mg/kg, p.o.). Locomotor activity and memory performance were measured as well as seizure vulnerability in PTZ-induced model. Liver enzymes were assessed in the serum. Acetylcholinesterase, oxidative stress parameters and histopathological changes were assessed in the brain and liver tissues.

Signs and symptoms of toxicity such as urination, tremor, depressed locomotion and death were observed in acute toxicity test. Sub-acute dosing caused significant impairment in locomotor activity and memory performance in mice. Seizure threshold was shortened in BSE-treated compared to control mice. Brain acetylcholinesterase activity was significantly increased. Alkaline phosphatase (ALP) was significantly elevated in mice that received BSE (500 mg/kg). Furthermore, BSE caused significant increase in oxidative stress expressed in nitrite, malondialdehyde, reduced glutathione and catalase in the brain and liver tissues. Histological staining revealed neuronal damage of brain hippocampus and hepatocellular swelling and necrosis.

Blighia sapida unripe fruit extract increased susceptibility to seizure and impaired locomotor and memory function. The biochemical and histopathological findings revealed potential toxicity mechanisms related to neurotoxicity and hepatotoxicity.

Developmental Exposure to Aluminum Chloride Irreversibly Affects Postnatal Hippocampal Neurogenesis Involving Multiple Functions in Mice

Aluminum (Al) is neurotoxic to adults and also to infants. In this study, we investigated the developmental exposure effect of AlCl3 on postnatal hippocampal neurogenesis. Pregnant mice were administered 0-, 900-, or 1800-ppm AlCl3 via drinking water from gestational day 6 to postnatal day (PND) 21, with their offspring examined on PND 21 and PND 77. On PND 21, GFAP-immunoreactive (+) neural stem cells (NSCs) and p21Cip1/Waf1+ cells were decreased in number in the subgranular zone at 900 and ≥900 ppm, respectively. Pcna transcript level examined at 1800 ppm was decreased in the dentate gyrus. These results suggest induction of compromised cell quiescence that caused impaired self-renewal capacity of NSCs accompanying slowing down of cell cycling, which ultimately resulted in exhaustion of the NSC pool. At 1800 ppm, Reelin+ hilar GABAergic interneurons were also decreased, suggesting a contribution to the NSC reduction. At this dose, TBR2+ or DCX+ progenitor and immature granule cells and PVALB+ interneurons were increased. Moreover, COX-2+ granule cells were increased at ≥900 ppm. These results suggest facilitation of transient progenitor cell proliferation and differentiation during exposure. Moreover, TUNEL+ or Morin-stained granule cells were increased, together with Casp12 transcript upregulation, suggesting induction of Al accumulation-related endoplasmic reticulum stress-mediated granule cell apoptosis. Transcript expression changes on cholinergic and glutamatergic signals and synaptic plasticity suggested contribution to disruptive neurogenesis. The NSC-targeting effects sustained through the adult stage despite no sustained Al-accumulation. These results suggest that developmental AlCl3-exposure irreversibly affects postnatal hippocampal neurogenesis involving multiple functions in mice.

Late effect of developmental exposure to glycidol on hippocampal neurogenesis in mice: Loss of parvalbumin-expressing interneurons

Developmental exposure to glycidol of rats causes axonal injury targeting axon terminals in dams and transient disruption of late-stage differentiation of hippocampal neurogenesis, accompanying sustained increase in the number of reelin-producing or calretinin-expressing interneurons in offspring. The molecular mechanism of disruptive neurogenesis probably targets the newly generating nerve terminals. We previously found differences between mice and rats in the effects on hippocampal neurogenesis after developmental exposure to the same neurotoxic substances. In the present study, we examined the effects and underlying mechanisms of developmental exposure to glycidol on hippocampal neurogenesis in mice. Glycidol (800 or 1600ppm) was administered in drinking water to mated female mice from gestational day 6 to postnatal day 21. Compared to mice drinking water without glycidol (control), the exposed dams showed axon terminal injury at both concentrations of glycidol. The offspring of the dams that had received 1600ppm glycidol had fewer parvalbumin (PVALB)⁺ γ-aminobutyric acid (GABA)-ergic interneurons and neuron-specific nuclear protein⁺ postmitotic neurons in the hilus of the hippocampal dentate gyrus. Thus, exposure of glycidol to adult mice induced axonal degeneration equivalent to that seen in the rat; however, the target mechanism for the disruption of hippocampal neurogenesis by developmental exposure was different from that in rats, with the hilar neuronal population not affected until adulthood. Considering the role of PVALB⁺ GABAergic interneurons in the brain, developmental glycidol exposure in mice may cause a decline in cognitive function in later life, and involve a different mechanism from that targeting axon terminals in rats.

Late Effect of Developmental Exposure to 3,3'-Iminodipropionitrile on Neurogenesis in the Hippocampal Dentate Gyrus of Mice

The effects of developmental exposure to 3,3'-iminodipropionitrile (IDPN), a neurotoxicant that causes proximal axonopathy, on mouse hippocampal neurogenesis was examined. Pregnant mice were exposed to IDPN at 0, 600, or 1200 ppm in their drinking water from gestational day 6 to postnatal day (PND) 21. On PND 21, male offspring showed increased postmitotic neuron-specific NeuN-immunoreactive⁽⁺⁾ granule cell numbers in the dentate subgranular zone (SGZ) and granule cell layer (GCL) and decreased glutamate receptor gene Grin2d levels in the dentate gyrus at 1200 ppm. On PND 77, decreased numbers were observed for TBR2⁺ progenitor cells in the SGZ at ≥600 ppm and GFAP⁺ stem cells, DCX⁺ progenitor cells and immature granule cells, NeuN⁺ immature and mature granule cells, PCNA⁺ proliferating cells in the SGZ and/or GCL, and immunoreactive cells for ARC or FOS, immediate-early gene products related to neuronal and synaptic plasticity, in the GCL at 1200 ppm. Additionally, at 1200 ppm of IDPN, downregulation of Kit, the gene encoding the stem cell factor (SCF) receptor, and upregulation of Kitl, encoding SCF, were observed in the dentate gyrus. Therefore, maternal IDPN exposure in mice affects neurogenesis involving glutamatergic signals at the end of developmental exposure, with late effects suppressing SGZ cell proliferation, reducing the broad range of granule cell lineage population, which may be responsible for SCF receptor downregulation. The upregulated SCF was likely a feedback response to the decreased receptor level. These results suggest that reduced SCF signaling may cause suppressed neuronal and synaptic plasticity.