The long-term prognosis of hippocampal neurogenesis and behavioral changes of offspring from rats exposed to valproic acid during pregnancy

Aim

In pregnant women with epilepsy, it is essential to balance maternal safety and the potential teratogenicity of anticonvulsants. Recently, growing evidence has indicated that valproic acid (VPA) can produce postnatal congenital malformations and impair cognitive function. However, the mechanisms underlying cognitive dysfunction in long‐term prognoses remain unclear.

Methods

Pregnant Wistar rats received daily intraperitoneal injections of VPA (200 mg/kg/day) from embryonic day 12.5 until birth. On postnatal day (PD) 149, the rats received an injection of bromodeoxyuridine (BrdU). On PD 150, the rats were subjected to the open field (OF), elevated plus‐maze (EPM), and Y‐maze tests. After behavioral testing, perfusion fixation was performed and the brain was dissected for immunohistochemistry.

Results

A significant marked decrease was seen in the number of BrdU‐positive cells in the dentate gyrus of offspring of VPA‐treated dams compared to those of control. However, no significant differences in hyperactivity were found based on the results of the OF test among the offspring on PD 150 of 200 VPA‐treated dams. In addition, no significant differences were seen in the EPM test.

Conclusion

The behavioral abnormality observed in young offspring of VPA‐treated dams was not significantly different from that of controls in adult offspring on PD 150. However, compared with controls, the number of BrdU‐positive cells in VPA‐treated rats was halved. The findings suggest that the behavioral abnormality seems to improve as they grow, even if some structural abnormalities may remain in the central nervous system.

Pregnant Wistar rats received daily intraperitoneal injections of VPA (200 mg/kg/d) from embryonic day 12.5 until birth. On postnatal day (PD) 149, the rats received an injection of bromodeoxyuridine (BrdU). A significant marked decrease was seen in the number of BrdU‐positive cells in the dentate gyrus of offspring of VPA‐treated dams compared to those of control.

Early Life Stress Increases Brain Glutamate and Induces Neurobehavioral Manifestations in Rats

Early life stress (ELS) is associated with an increased risk of developing depression and anxiety disorders. Disturbances of the neurobiological glutamatergic system are implicated in depression; however, the long-term effects of ELS on glutamate (Glu) metabolites remain unclear. Our study used 7T proton magnetic resonance spectroscopy (7T ¹H MRS) to detect metabolic Glu in a rat model to investigate maternal deprivation (MD)-induced ELS. MD was established in Sprague-Dawley rats by periodic separation from mothers and peers. Changes in the hippocampal volume and Glu metabolism were detected by 7T ¹H MRS after testing for depression-like behavior via open field, sucrose preference, and Morris water maze tests. Adult MD offspring exhibited depression-like behavior. Compared to the control, the MD group exhibited reduced ratio of central activity time to total time and decreased sucrose consumption (p < 0.05). MD rats spent less time in the fourth quadrant, where the platform was originally placed, in the Morris water maze test. According to 7T ¹H MRS, hippocampus of MD rats had elevated Glu and glutamate + glutamine (Glu+Gln) levels compared with the control group hippocampi, but Gln, γ-aminobutyric acid (GABA), and glutamate + glutamine (Glu+Gln) in the prefrontal cortex of MD rats showed a downward trend. Depression-like behavior and cognition deficits related to ELS may induce region-specific changes in Glu metabolism in the prefrontal cortex and hippocampus. The novel, noninvasive 7T ¹H MRS-identified associations between Glu levels and ELS may guide future clinical studies.

Prenatal exposure to valproic acid is associated with altered neurocognitive function and neurogenesis in the dentate gyrus of male offspring rats

In pregnant women with epilepsy, it is imperative to balance the safety of the mother and the potential teratogenicity of anticonvulsants, which could cause impairments such as intellectual disability and cleft lip. In this study, we examined behavioral and hippocampal neurogenesis alterations in male offspring of rats exposed to valproic acid (VPA) during pregnancy. Pregnant Wistar rats received daily intraperitoneal injections of VPA (100 mg/kg/day or 200 mg/kg/day) from embryonic day 12.5 until birth. At postnatal day 29, animals received an injection of bromodeoxyuridine (BrdU). At postnatal day 30, animals underwent the open field (OF), elevated plus-maze, and Y-maze tests. After behavioral testing, animals were decapitated, and their brains were dissected for immunohistochemistry. Of the offspring of the VPA200 mothers, 66.6% showed a malformation. In the OF test, these animals showed locomotor hyperactivity. In the elevated plus-maze, offspring of VPA-treated mothers spent significantly more time in the open arms, irrespective of the treatment dose. The number of BrdU-positive cells in the dentate gyrus of the offspring of VPA-treated mothers increased significantly in a dose-dependent manner compared with the control. A significant positive correlation between spontaneous locomotor activity in the OF and BrdU-positive cell counts was observed across groups. In conclusion, VPA administration during pregnancy results in malformations and attention-deficit/hyperactivity disorder-like behavioral abnormalities in the offspring. An increase in cell proliferation in the hippocampus may underlie the behavioral changes observed. Repeated use of high doses of VPA during pregnancy may increase the risk of neurodevelopmental abnormalities dose dependently and should be carefully considered.

N-methyl-D-aspartate receptor subunit 1 regulates neurogenesis in the hippocampal dentate gyrus of schizophrenia-like mice

N-methyl-D-aspartate receptor hypofunction is the basis of pathophysiology in schizophrenia. Blocking the N-methyl-D-aspartate receptor impairs learning and memory abilities and induces pathological changes in the brain. Previous studies have paid little attention to the role of the N-methyl-D-aspartate receptor subunit 1 (NR1) in neurogenesis in the hippocampus of schizophrenia. A mouse model of schizophrenia was established by intraperitoneal injection of 0.6 mg/kg MK-801, once a day, for 14 days. In N-methyl-D-aspartate-treated mice, N-methyl-D-aspartate was administered by intracerebroventricular injection in schizophrenia mice on day 15. The number of NR1-, Ki67- or BrdU-immunoreactive cells in the dentate gyrus was measured by immunofluorescence staining. Our data showed the number of NR1-immunoreactive cells increased along with the decreasing numbers of BrdU- and Ki67-immunoreactive cells in the schizophrenia groups compared with the control group. N-methyl-D-aspartate could reverse the above changes. These results indicated that NR1 can regulate neurogenesis in the hippocampal dentate gyrus of schizophrenia mice, supporting NR1 as a promising therapeutic target in the treatment of schizophrenia. This study was approved by the Experimental Animal Ethics Committee of the Ningxia Medical University, China (approval No. 2014-014) on March 6, 2014.

Effect of NMDA on proliferation and apoptosis in hippocampal neural stem cells treated with MK-801

The purpose of the present study was to investigate effects of N-methyl-D-aspartate (NMDA) on proliferation and apoptosis of hippocampal neural stem cells (NSCs) treated with dizocilpine (MK-801). Cultures of hippocampal NSCs were randomly divided into four groups consisting of an untreated control, cells treated with MK-801, NMDA and a combination of MK801 and NMDA (M+N). Proliferative and apoptotic responses for each of the experimental groups were determined by MTS and flow cytometry. The results revealed that MK-801 and NMDA exerted significant effects on hippocampal NSCs proliferation. Cell survival rates decreased in MK-801, NMDA and M+N treated groups compared with the control group. Cells survival rates in NMDA and M+N treated groups increased compared with the MK-801 treated group. MK-801 and NMDA were demonstrated to significantly affect apoptosis in hippocampal NSCs. Total and early stages of apoptosis in MK-801 and NMDA groups significantly increased compared with the control group. Total and early apoptosis of NSCs in the M+N group significantly decreased compared with MK-801 and NMDA groups. Late apoptosis of NSCs in MK-801 and NMDA groups significantly decreased compared with the control group. Late apoptosis of NSCs in the M+N group significantly increased compared with MK-801 and NMDA groups. The present study revealed that MK-801 inhibited proliferation and increased apoptosis in hippocampal NSCs. NMDA may reduce the neurotoxicity induced by MK-801, which may be associated with its activity towards NMDA receptors and may describe a novel therapeutic target for the treatment of schizophrenia.

Inhibitory Effects of Bisphenol-A on Neural Stem Cells Proliferation and Differentiation in the Rat Brain Are Dependent on Wnt/β-Catenin Pathway

Neurogenesis, a process of generation of new neurons, occurs throughout the life in the hippocampus and sub-ventricular zone (SVZ). Bisphenol-A (BPA), an endocrine disrupter used as surface coating for packaged food cans, injures the developing and adult brain. However, the effects of BPA on neurogenesis and underlying cellular and molecular mechanism(s) are still unknown. Herein, we studied the effect(s) of prenatal and early postnatal exposure of low dose BPA on Wnt/β-catenin signaling pathway that controls different steps of neurogenesis such as neural stem cell (NSC) proliferation and neuronal differentiation. Pregnant rats were treated with 4, 40, and 400 μg BPA/kg body weight orally daily from gestational day 6 to postnatal day 21. Both in vivo and in vitro studies showed that BPA alters NSC proliferation and differentiation. BPA impaired NSC proliferation (5'-bromo-2'-deoxyuridine (BrdU(+)) and nestin(+) cells) and neuronal differentiation (BrdU/doublecortin(+) and BrdU/neuronal nuclei (NeuN(+)) cells) in the hippocampus and SVZ as compared to control. It significantly altered expression/protein levels of neurogenic genes and the Wnt pathway genes in the hippocampus. BPA reduced cellular β-catenin and p-GSK-3β levels and decreased β-catenin nuclear translocation, and cyclin-D1 and TCF/LEF promoter luciferase activity. Specific activation and blockage of the Wnt pathway suggested involvement of this pathway in BPA-mediated inhibition of neurogenesis. Further, blockage of GSK-3β activity by SB415286 and GSK-3β small interfering RNA (siRNA) attenuated BPA-induced downregulation of neurogenesis. Overall, these results suggest significant inhibitory effects of BPA on NSC proliferation and differentiation in the rat via the Wnt/β-catenin signaling pathway.

Caffeine protects neuronal cells against injury caused by hyperoxia in the immature brain

Caffeine administered to preterm infants has been shown to reduce rates of cerebral palsy and cognitive delay, compared to placebo. We investigated the neuroprotective potential of caffeine for the developing brain in a neonatal rat model featuring transient systemic hyperoxia. Using 6-day-old rat pups, we found that after 24 and 48h of 80% oxygen exposure, apoptotic (TUNEL(+)) cell numbers increased in the cortex, hippocampus, and central gray matter, but not in the hippocampus or dentate gyrus. In the dentate gyrus, high oxygen exposure led to a decrease in the number of proliferating (Ki67(+)) cells and the number of Ki67(+) cells double staining for nestin (immature neurons), doublecortin (progenitors), and NeuN (mature neurons). Absolute numbers of nestin(+), doublecortin(+), and NeuN(+) cells also decreased after hyperoxia. This was mirrored in a decline of transcription factors expressed in immature neurons (Pax6, Sox2), progenitors (Tbr2), and mature neurons (Prox1, Tbr1). Administration of a single dose of caffeine (10mg/kg) before high oxygen exposure almost completely prevented these effects. Our findings suggest that caffeine exerts protection for neonatal neurons exposed to high oxygen, possibly via its antioxidant capacity.

Prenatal carbofuran exposure inhibits hippocampal neurogenesis and causes learning and memory deficits in offspring

Neurogenesis is a process of generation of new neurons in the hippocampus and associated with learning and memory. Carbofuran, a carbamate pesticide, elicits several neurochemical, neurophysiological, and neurobehavioral deficits. We evaluated whether chronic prenatal oral exposure of carbofuran during gestational days 7-21 alters postnatal hippocampal neurogenesis at postnatal day 21. We found carbofuran treatment significantly decreased bromodeoxyuridine (BrdU) positive cell proliferation and long-term survival in the hippocampus only but not in the cerebellum. We observed a reduced number of transcription factor SOX-2 and glial fibrillary acidic protein (GFAP) colabeled cells, decreased nestin messenger RNA (mRNA) expression, and decreased histone-H3 phosphorylation following carbofuran treatment, suggesting a decreased pool of neural progenitor cells (NPC). Colocalization of BrdU with doublecortin (DCX), neuronal nuclei (NeuN), and GFAP suggested decreased neuronal differentiation and increased glial differentiation by carbofuran. The number of DCX(+) and NeuN(+) neurons, NeuN protein levels, and fibers length of DCX(+) neurons were decreased by carbofuran. Carbofuran caused a significant downregulation of mRNA expression of the neurogenic genes/transcription factors such as neuregulin, neurogenin, and neuroD1 and upregulation of the gliogenic gene Stat3. Carbofuran exposure led to increased BrdU/caspase 3 colabeled cells, an increased number of degenerative neurons and profound deficits in learning and memory processes. The number and size of primary neurospheres derived from the hippocampus of carbofuran-treated rats were decreased. These results suggest that early gestational carbofuran exposure diminishes neurogenesis, reduces the NPC pool, produces neurodegeneration in the hippocampus, and causes cognitive impairments in rat offspring.

Effects of repeated electroconvulsive seizure on cell proliferation in the rat hippocampus

Electroconvulsive therapy (ECT) is known as a successful treatment for severe depression. Despite great efforts, the biological mechanisms underlying the beneficial effects of ECT remain largely unclear. In this study, animals received a single, 10, or 20 applications of electroconvulsive seizure (ECS), and then cell proliferation and apoptosis were investigated in the subgranular zone (SGZ) of the dentate gyrus. We analyzed whether a series of ECSs could induce changes in the dentate gyrus in a dose-response fashion. A single-ECS seizure significantly increased cell proliferation in the SGZ by ∼2.3-fold compared to sham treatment. After 10 ECSs, a significant increase in cell proliferation was observed in the SGZ by ∼2.4-fold compared to sham treatment. Moreover, 10 ECSs induced a significant increase in cell proliferation by 1.3-fold compared to a single-ECS group. However, cell proliferation did not differ between the group with 20 ECSs and sham group. In addition, a significant increase in the number of apoptotic cells was found in the group with 10 ECSs, whereas no significant change in it was found in either a single ECS or 20 ECSs group compared to sham treatment. These findings indicate that the optimal number of treatments and duration of stimulation requires investigation. Further studies are needed to elucidate the intracellular mechanisms underlying both effective and excessive ECT.