Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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Effect of CORT on the basal PS amplitude

CORT (ip, 1 mg/kg, 4 mg/kg and 10 mg/kg) application tended to elevate the amplitude of basal PS induced by a single stimulation. However, no statistical significance (P>0.05) was observed between control and CORT-treated groups.

Effect of CORT on formation of LTP in hippocampal dentate gyrus in anesthetized rats

After delivery of tetanic stimulation (60 Hz, 30 pulses) to the perforant pathway, PS amplitudes in both control and CORT-treated groups were all greatly increased. In control group, the PS amplitudes were elevated 70~80 % higher above the baseline without significant attenuation within 1 h. However, pretreatment with CORT (ip, 1 mg/kg, 4 mg/kg and 10 mg/kg) 1 h before tetanic stimulation does-dependently (P<0.01) reduced the amplitudes of PS evoked in hippocampal dentate gyrus. In addition, administration of CORT dose-dependently reduced the AUC of the time-course potentiation (P<0.01).

Effect of CORT on the Ca2+ currents of VDCC

After spraying CORT (10-6 M, 10-5 M and 10-4 M) to the membrane of hippocampal neurons, Ca2+ currents were instantly facilitated in a dose-dependent manner with maximal elevated amplitudes of 15 %, 42% and 58 % respectively.

CORT-induced facilitation of Ca2+ influx was voltage-independent

In our present study, Ca2+ influx through VDCC at various holding membrane potentials were increased by CORT at the concentration of 10-6 M~10-4 M. However, the elevated amplitudes of Ca2+ currents between CORT-treated and control groups were similar. The ANOVA analysis showed that there was no significant interaction between the membrane potentials and Ca2+ influx through VDCC (F=0.21, P=0.99). Namely, the CORT-facilitated Ca2+ influx was voltage-independent.

Effect of CORT on the synaptic activity

Persistent spraying CORT at dose of 10-4 M to the surface of hippocampal neurons, the mean intervals of synaptic currents were shortened from 498*123 ms to 114*39 ms (P<0.01) while the frequencies of synaptic activity were increased from 3.4*1.3 Hz to 12.9*3.2 Hz (P<0.05). In addition, application of CORT, 10-4 M, reduced the amplitude of synaptic currents from 3.4*1.2 nA to 0.48*0.12 nA (P<0.05), augmented the events of synaptic activity from 1067 to 3024. After addition of TTX, there was almost no synaptic activity. However, application of CORT (10-4 M) induced low-amplitude synaptic currents (0.18*0.09 nA, n=4) with frequency of 4.6*1.0 Hz.

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