[Correlation between enhanced anoxic tolerance induced by hypoxic preconditioning and the stability of mitochondrial membrane potential in cultured hypothalamic cells]

The relationship between enhanced anoxic tolerance induced by hypoxic preconditioning and mitochondrial membrane potential (MMP) was studied in cultured hypothalamic cells. Dynamic changes in MMP were monitored by confocal laser scanning microscopy and expression of B-cell lymphoma/leukemia-2 (bcl-2) was examined by flowcytometry. Hypoxic preconditioning increased the cell survival rate and decreased the lactate dehydrogenase leakage under acute anoxia, in addition to maintaining MMP at a relatively higher level and inducing bcl-2 overexpression during anoxia. The results suggest that hypoxic preconditioning can enhance the tolerance of hypothalamic cells to anoxia, and the underlying mechanism may be related to increased stability of MMP. Overexpression of bcl-2 induced by hypoxic preconditioning may play a role in sustaining the stability of MMP.

[Hypoxic preconditioning enhances hypoxic tolerance of hippocampal neurons and synaptic function of rat]

Hypoxic preconditioning with different simulated altitudes (3,000 m and 5,000 m) was performed on Wistar rats and the evoked population spikes were recorded from the hippocampal slices of these rats. The results showed that the appearance of hypoxic injury potential (HIP) and the disappearance of presynaptic volley (PV) were significantly delayed in response to acute lethal hypoxia. HIP and PV delay became more apparent when the hypoxic preconditioning altitude was increased from 3,000 m to 5,000 m. After reoxygenation, the recovery rate of PV in hypoxic preconditioning groups at 3,000 m and 5,000 m was apparently higher than that of control. The above results suggest that hypoxic preconditioning of animals in vivo increases hypoxic tolerance of hippocampal neurons.

[Effects of intermittent hypoxia on long-term potentiation in hippocampal dentate gyrus of rat]

AIM

To investigate the effects of intermittent hypoxia on the hippocampal synaptic plasticity in rat.

METHODS

The evoked potentials were recorded extracellularly, then the LTP were induced by tetanic stimulation in rat hippocampal dentate gyrus.

RESULTS

Compared with control group, the amplitude of LTP was significantly reduced in hippocampus of rat treated with intermittent hypoxia.

CONCLUSIONS

The present results suggest that the hippocampal synaptic plasticity could be decreased by the treated of intermittent hypoxia.

[Effects of hypoxic preconditioning on anoxic tolerance and IL-1 beta expression in cultured rat hippocampal neurons]

AIM

To study the effects of hypoxic-preconditioning on anoxia-tolerance and IL-1 beta expression in cultured rat hippocampal neurons after anoxia.

METHODS

12 day cultured hippocampal neurons in control and hypoxic-preconditioning group were exposed to anoxic environment(0.9 L/LN2 + 0.1 L/LCO2) for 2, 4, 8 and 12 h. The neurons were immunocytochemically stained using the anti-serum against rhIL-1 beta, The number of survival neurons and the mean optical density (OD) of IL-1 beta expression were investigated.

RESULTS

The morphological changes and IL-1 beta expression induced by acute anoxia in hypoxic-preconditioning neurons were significantly less than those in control. The number of survival neurons was higher in the hypoxia-preconditioning group than that in control group after acute hypoxia.

CONCLUSION

Hypoxia-preconditioning can induce the development of anoxia-tolerance in cultured hippocampal neurons. The decreased IL-1 beta in hippocampal neurons may be an adaptive reaction to acute anoxia.

[The different responses to anoxia in cultured CA1 and DG neurons from newborn rats]

Tissue culture from hippocampal CA1 or dentate gyrus (DG) region was established on the basis of previous neuronal culture technique. The viability, intracellular calcium concentration and brain-derived neurotrophic factor (BDNF) mRNA expression of the two kinds of neurons after anoxia were observed in the counting in the confocal microscopic field and in situ hybridization. It is found that DG neurons are not only more resistant to anoxia, but also have a stronger ability to keep calcium homeostasis and to express BDNF mRNA than CA1 neurons.

[Effect of adenosine on intracellular free calcium in cultured rat hippocampal CA1 neurons during anoxia]

Intracellular free Ca2+ concentration ([Ca2+]i) was measured by laser scanning confocal microscope, using Ca2+ indicator Fluo-3 in cultured hippocampal CA1 neurons isolated from newborn rat. The results showed that acute anoxia induced a rapid increase of [Ca2+]i in hippocampal CA1 neurons, and this increase could be attenuated by 100 mumol/L adenosine significantly. This effect of adenosine could be suppressed by adenosine A1 receptor antagonist CPT or potassium channel blockers, 4-AP and glipizide. These results suggest that adenosine activates 4-AP- or ATP-sensitive potassium channels through A1 receptors, and consequently inhibits the [Ca2+]i elevation in hippocampal neurons during anoxia.

Effect of ginsenosides against anoxic damage of hippocampal neurons in culture

AIM

To study the protective effect of ginsenosides (Gin) against anoxic injury in brain cells.

METHODS

On d 12 after plating of the hippocampal cells from newborn rat, the cultures were exposed to anoxic atmosphere (95% N2 + 5% CO2) for 4-24 h. The cellular morphology, survival rate, and effluxes of lactate dehydrogenase (LDH) and K+ from cells were observed.

RESULTS

After 24-h anoxia, the survival rate of cells was decreased from 92% +/- 4% before anoxia to 1.0% +/- 2.0%; the effluxes of LDH and K+ were increased from 2.3 +/- 0.6 U L-1 and 5.56 +/- 0.16 mmol L-1 before anoxia to 36 +/- 5 U L-1 and 8.5 +/- 0.7 mmol L-1, respectively. In the Gin group exposed anoxia for 24 h, the survival rate of cells was 4% +/- 4%; the effluxes of LDH and K+ were 30 +/- 3 U L-1 and 7.9 +/- 0.8 mmol L-1, respectively. All these changes were lower in Gin group than those of control.

CONCLUSION

Under anoxia the cultured hippocampal neurons were seriously damaged, which may be protected by Gin.

[Protective effect of calcitonin gene-related peptide on synaptic function in hippocampal slice during hypoxia]

Rat hippocampal slices placed in two compartments of a dual chamber were immersed in the superfusing artificial cerebrospinal fluid (ACSF) with 95% O2 + 5% CO2. The population spike (PS) and presynaptic fiber volley (PV) were recorded in CA1 pyramidal cells by stimulating Schaffer collateral pathways. Following hypoxia produced by replacing O2 with N2, the PS became gradually diminished and abolished, and in parts of the slices hypoxic injury spikes (HIP) could be observed. When 4 nmol/L beta-calcitonin gene-related peptide (beta-CGRP) -containing ACSF was superfused to the slice before and during hypoxia, the time at which PS began to decrease and got in complete abolishment were both postponed, and HIP were delayed or disappeared. After reoxygenation the recovery rate of PS was obviously higher in slices treated with CGRP than the control slices and the protective effect of CGRP was dose-dependent. In addition, superfusion of CGRP after hypoxia also increased the recovery of PS. These results indicate that (1) the time for the appearance of attenuation and disappearance of PS are varied according to the degree of hypoxia; (2) CGRP has a neuronal protective action against hypoxia.

[Effects of interleukin-1 and interleukin-2 on electrophysiological characteristics of rat hippocampal neurons in culture]

The effects of recombinant human interleukin-1 beta (rhIL-1 beta) and interleukin-2 (rhIL-2) on the cultured rat hippocampal neurons were investigated with intracellular recording and extracellular micropressure ejection techniques. Experimental results showed that all of the neurons tested with rhIL-1 beta (100 U/ml) exhibited a 4.20 +/- 1.86 mV membrane hyperpolarization. 50% of the neurons treated with rhIL-2 (100 U/ml) showed a depolarization of 11.12 +/- 3.71 mV accompanied by bursting activity, while in a still higher concentration (1,000 U/ml) a 3.25 +/- 0.63 mV hyperpolarization was observed. All the above effects of rhIL-1 beta and rhIL-2 on the hippocampal neurons were completely reversible. The membrane resistance of the neurons was not significantly affected by these cytokines. These results suggest that the effects of cytokines IL-1 and IL-2 on the excitability of hippocampal neurons may be a way by which the immune system exerts a regulatory action on hippocampal function.