Effects On Central Nervous System In Offspring Following Drinking Water Sodium Arsenite Intake

PrefaceArsenic intoxication is a public health problem in the world. There are ten provinces to have appeared arsenic intoxication, which damaged seriously the residents health. Arsenic could result in multisystem diseases, including skin, peripheral neuropathy, respiratory system, gastrointestinal system, cardiovascular system, genitourinary system, endocrine and haematological system. In addition , the effects of arsenic toxicity also include changes in behavior, confusion, and memory loss. However, the exact mechanisms of arsenic toxicity on central nervous system remain elusive.To better understand the effect of arsenic on central nervous system, we made arsenic toxicity animal model, to study effects of arsenic exposure from drinking water on development and behavior, learning and memory, observe oxi-dative stress and hispathology changes of offspring rat brain, examined acetyl-choline transmitter, amino acid transmitter and their metabolism enzymes in pups brain to clarity the mechanisms of arsenic - induced central nervous system damage.Methods1. Epidemic investigation of arsenic toxicityAge 6-14 school - age children were randomly selected at A and B villages in Inner Mongolia, in which arsenic concentration of drinking water are separately 0. 16 mg/L and 0. 09 mg/L. Intelligence quotient (IQ) and Reaction Time ( RT) of children were measured.2. Animal model of arsenic toxicityPregnant rats were randomized into four groups. Group 1 received distilled water only as drinking water (control) , the other three groups received 10, 50, 100 mg/L sodium arsenite distilled water solution through drinking water. Preg-* nant rats and pups were exposed to arsenic from gestation day 6 until pups 42 days old. Pups were separately sacrificed at postnatal 0, 28 and 42 day, and cortex, hippocampus were taken.3. Development and behaviorThe early physiological, neurobehavioral, learning and memory of 42 days old pups were measured.4. Measurement of oxidative damageMDA, GSH, GSH - Px in cortex, hippocampus of pups were determined at postnatal 0, 28, 42 day.5. Measurement of neurotransmitter metabolism enzymes activities and mR-NA expressionGlutamine synthetase ( GS) and acetylcholinesterase ( AchE) was measured as the reagent kits and mRNA expression of Glutamate decarboxylase (GAD65, GAD67) and r - aminobutyric acid transferase (GAB A - T) were determined by RT - PCR at postnatal 0, 28, 42 day of pups.6. Histopathology observationHistopathological changes of pups brain were observed under transmission electron microscope at postnatal 42 day.7. Statistical analysisData were processed by Excel and expressed by Mean SD. SPSS 10.0 software was used for the one - way ANOVA. T test was used for analysis of IQ, RT. P values of less than 0.05 were considered significant.Results1. Effects of arsenic exposure on development and behavior, learning and memory in offspring of ratsThe stature and weight of Fl pups in 100 mg/L were lower than that of con-trol group after postnatal day 12. But other physiologic markers (eye opening, pinna detachment, hair growth, tooth growth, et al) were not affected by arsenic. In contrast to the control group, visual placing, acoustic startle and tail suspending of lOOmg/L arsenic were delayed. In bearings water labyrinth tests, the traning times of Fl pups of arsenic exposure groups swimming correctly to the hidden - platform in acquired memory test and memory reservation test were more than that of control group, which showed that learning and memory abilities of Fl pups were affected by arsenic.2. Arsenic - induced oxidative damage of pups brainMDA level of lOOmg/L group Fl pups brain was higher than that of control rats on the postnatal day 0. On the postnatal day 28 and 42, MDA levels in lOOmg/L group Fl pups cortex were also higher than that of control rats, but the difference in hippocampus was not seen. 42 day exposure to arsenic caused significant reduction of GSH on cortex and hippocampus and GSH - Px on hippocampus in 100 mg/L arsenic group compared to control rats. However, the change of GSH level and GSH - Px activities in pups rat brain had not been seen on the postnatal day 0, 28.3. Effects on activities and gene expression of neurotransmitter metabolic enzyme in offspring rats brainOn the postnatal day 0, there were not any significant change on AchE and GS activities and GAD65, GAD67 and GABA - T mRNA expression in arsenic rats compared to control rats. However, GS activities in pups rats cortex showed a significant decrease in 50, 100 mg/L arsenic exposure, and a increase of AchE in 100 mg/L arsenic group rats hippocampus on the postnatal day 28. mRNA expression level of GAD65 in hippocampus and GAD67 in cortex significant increased in 100 mg/L arsenic exposure rats compared to control rats. These changes also appeared on the postnatal day 42.4. Histopathology changes of pups brainUltrastructural pathologic changes of cortex showed vacuolar degeneration of neurons, karyotin aggregating the side of karyotheca, nuclear swollen and hydropic changehydropic degeneration in 50mg/L sodium arsenite rats, and neurons endoplasmic reticulums extremely dilated, free — ribosome disappeared in100 mg/L rats.5. Effects of arsenic exposure on intelligent development of children There was no difference between A and B village children for IQ ( p > 0. 05). Visual simple average RT and visual simple fastest RT of A village children were significantly longer than that of B village children. Auditory simple average RT and auditory simple fastest RT of A village children were significantly longer than that of B village children.Conclusions1. Arsenic exposure from drinking water can impaired neurobehavioral development and abilities of learning and memory in offspring rats.2. Arsenic exposure from drinking water can induced prolong of visual simple RT and auditory simple RT of children, but it was not be seen for the effect of arsenic on children IQ at the concentration 0. 16 and 0. 09 mg/L arsenic.3. Arsenic could penetrate blood - brain barrier and placental barrier to induce lipid peroxidation of pups brain. Compared to control rats, MDA of arsenic exposure group pups brain increased , GSH and GSH - Px decreased.4. Activities of GS, AchE in pups brain were affected by continue arsenic exposure from embryo to poatnatal and mRNA expression of GAD65, GAD67 were potentiated, which resulted in the change of neurotransmitter concentration and disturbance of central nervous system function.5. Arsenic exposure might damage biomembranous structure and result in a series of physiologic and pathologic changes.