Lead Can Inhibit NMDA-,K^+-,QA/KA-Induced Increases in Intracellular Free Ca^(2+) in Cultured Rat Hippocampal Neurons

Objective To examine the effects of Pb2+ on N-methyl-D-aspartate (NMDA)-, K+- and quisqualate(QA)/kainite(KA)-induced increases in intracellular free calcium concentration ([Ca2+],) in cultured fetal rat hippocampal neurons in order to explain the cognitive and learning deficits produced by this heavy metal. Methods Laser scanning confocal microscopy was used. Results The results clearly demonstrated that adding Pb2+ before or after NMDA/glycine stimulation selectively inhibited the stimulated increases in [Ca2+], in a concentration-dependent manner. In contrast, Pb2+ treatment did not markedly affect increases in [Ca2+], induced by an admixture of QA and KA. The minimal inhibitory effect of Pb2+ occurred at 1 μmol/L, and more than seventy percent abolition of the NMDA-stimulated increase in [Ca2+]; was observed at 100 Jμmoll/L Pb2+. Evaluation of Pb2+-induced increase in [Ca2+], response to elevating extracellular concentrations of NMDA, glycine or calcium revealed that Pb2+ was a noncompetitive antagonist of both NMDA and glycine, and a competitive antagonist of Ca2+ at NMDA receptor channels. In addition. Pb2+ inhibited depolarization-evoked increases in [Ca2+], mediated by K+ stimulation(30μmol/L). indicating that Pb2+ also depressed the voltage-dependent calcium channels. Also, the results showed that Pb2+ appeared to be able to elevate the resting levels of [Ca2+|, in cultured neurons, implying a reason for Pb2+-enhanced spontaneous release of several neurotransmitters reported in several previous studies. Conclusion Lead can inhibit NMDA-. K+-, QA/KA-jnduced increases in intracellular [Ca2+], in cultured hippocampal neurons.

Comparison of the severity of injury of hippocampal neuron in rats induced by simulated push-pull maneuver at various degrees

BACKGROUND： Push-pull effect is often caused during maneuver, and the changes of unconsciousness induced can affect or damage cerebral neurons at various degrees. OBJECTIVE： To observe the effect of simulated push-pull maneuver at various degrees on injury of hippocampal neurons in rats and analyze its phase effect. DESIGN： Randomized control study.SETTING ： Physiological Department of Jilin Medical College.MATERIALS： A total of 40 healthy male Wistar rats, of clean grade, weighting 205-300 g, aged 3-4 months, were randomly divided into control group （n=4） and three push-pull experimental groups, including ＋2 Gz group （intensity： -2 Gz to ＋2 Gz, n=12）, ＋6 Gz group （-6 Gz to ＋6 Gz, n=12） and ＋8 Gz group （-8 Gz to ＋8 Gz, n=12）.METHODS： The experiment was completed in the Physiological Department of Jilin Military Medical College from March 2002 to May 2003. ① Rats in the experimental groups were put at the specially rolling arm of animal centrifugal machine. Then, they were pushed and pulled with ±2 Gz, ±6 Gz and ±8 Gz, respectively. The jolt was 1 Gz/s. However, rats in control group were not treated with any ways. ② Stroke index and neurological evaluation were performed on rats in the experimental groups at 0.5, 6 and 24 hours after push-pull. Stroke index was 25 points in total. The higher the scores were, the severer the cerebral injury was. Neurological evaluation was 10 points in total. The higher the scores were, the severer the nerve injury was. ③ Hippocampal tissue in brain of rats were selected to cut into sections at each time points, and form and distribution of neurons were observed in hippocampal areas with HE staining. Degrees of neuronal injury in hippocampal CA1 area were assayed after push-pull at various degrees with electron microscope. ④ Measurement data were compared with t test.MAIN OUTCOME MEASURES：① Stroke index and neurological evaluation; ② form and distribution of neurons in hippocampal areas;③ degrees of neuronal injury in hippocampal CA1 area.RESULTS： A total of 40 rats were involved in the final analysis. ① Stroke index and neurological evaluation of rats in experimental groups： At 30 minutes and 6 hours after push-pull exposure, stroke index and neurological evaluation were higher in ±6Gz group and ±8 Gz group than those in control group （P 〈 0.01）, especially at 6 hours after push-pull exposure, those in ±8 Gz group were the highest at each time points [（11.00±2.16）, （5.75±1.70） points]. At 24 hours after exposure, those were decreased as compared with those within the former two time points, but the values were still higher than those in control group （P 〈 0.05-0.01）. ② Results of HE staining： At 6 and 24 hours after exposure, partially neuronal degeneration was observed in pyramidal layer in ±6 Gz group and ±8 Gz group, including crenation of neurons, tdangle or polygon, and karyopycnosis, especially the injury in ±8 Gz group was the most obvious at 6 hours after exposure. ③ Results of ultrastructure with electron microscope： Partially neuronal degeneration at various degrees was observed in hippocampal CA1 area in ±2 Gz group at 6 hours after exposure and in ±6 Gz group and ±8 Gz group at 6 and 24 hours after exposure. At 6 hours after exposure, nucleus of hippocampal neurons in ±8 Gz group was irregular and umbilication. Caryotin was aggregated, nuclear matrix was swelled and disorder, and vacuolation was also observed. Rough endoplasmic reticulum was expanded, mitochondrium was swelled, and crista was disappeared.CONCLUSION： ① Push-pull cannot damage hippocampal neurons of rats in ±2 Gz group. ② Exposure can cause injury of hippocampal neurons of rats in ±6Gz group and ±8 Gz group, especially the injury is the severest at 6 hours after exposure in ±8 Gz group and relieves gradually 24 hours later.