The Relation Of Difference Of Formation Of Fear Memory, Level Of Plasm Corticosteroid And Expression Of NMDA Receptor Subunit In Hippocampus CA1 Area In Two Species Mice

Objective to search for the expressive variation of NMDA receptor subunit inhippocampus CA1 area after formation of fear memory through establishing an experimentalanimal model with fear memory in mice, thereby looking for the mechanism of molecular action.Methods Kunming mice (KM) and C57BL/6 mice were adopted. The irritative train offootplate shock was combined with a tone signal for check the difference of fear memoryformation in different shock intensity and in different species mice, in identical condition training.The stupor response appeared 24-hr after the training represents the formation of fearmemory. Checking Ca²⁺ concentration in brain slice and cultured hippocampus nerve cell byconfocal microscopy using Flou-3/AM as fluorescent probe; Reciping brain tissue and cryostat sectionfor testing the expression of NMDA receptor subunit and c-fos by immunohistochemistry method. serum corticosterone (CORT) was assayed by using HPLC method. Undertaking associtivitycomparison to above results.Results The optimal current intensity inducing a reproducible response was 0.40.6mA in both species mice. In KM trained using 0.4, 0.6, and 0.9mA aversive stimuli,the durations of stupor response were 60.00±57.77 s, 110.00±129.61 s and 101.99±20.38 s respectively; P＞0.05; the highest qualification percentage (30%) was seen in0.6mA group. Using 0.4mA aversive stimulus, the duration was 275.62±36.99s inC57BL/6, which was significantly than that in KM (P＜0.01). All C57BL/6 mice qualified,while only 7.69% in KM (P＜0.01). In KM, serum CORT concentration were (215.453±60.276)μg/L in trained group, significantly higher than that in the control group((101.083±70.266)μg/L, P＜0.01). In C57BL/6, the values were (176.933±38.202)μg/L(108.009±20.452)μg/L respectively, and P＜0.01. In trained KM, stupor responseduration was (36.00±29.292) s, and in trained C57BL/6, the duration was (257.50±36.450) s, which were not correlated to the corresponding serum CORT levels (r=-0.462,P＞0.05 and r=-0.273, P＞0.05 respectively).Conclusionsâ‘ C57BL/6 species mice is more suitable for experimental requisitionin fear stupor response time under stimulation condition of 0.4mA current with sound 70dB and achievement ratio reached above 95%;â‘¡It is not markedly associativity between level of plasm CORT and training achievement, but C57BL/6 species micecoefficient correlation r is -0.462, |r|＞0.3 and＜0.5, that express low-degree negativecorrelation. Corticosterone level of blood plasma is not obviously difference before andafter training between the both spcies mice, that account for that the difference oftraining effect is not relativition with Corticosterone level of blood plasma; but if notdiscrepancy of genetic background affected molecule mechanism of retention ofmemory, required further investigation;â‘¢The expression of NR2B and c-fos weremarkedly increased in hippocampus CA1 area after fear memory was formed, thatsuggest that the level of corticosterone concentration in blood plasm was increased whenstress, that cause facilitation and rigidification of LTP through enhancement of geneexpression in intracellular, thereby retention of fear memory were kept longer time.