Study On Synaptic Plasticity Of Diabetic Rats Learning And Memory Ability Obstacle

ObjectiveThe impact of diabetes on memory function is an important medical problem. SD rats is used in this study, from the level of learning and memory behavior to the synaptic plasticity of key brain areas regarding learning and memory (hippocampal PP-DG pathway), study the synaptic plasticity mechanisms of learning and memory function in SD rats which reduced by diabetes.Based on the behavior of rats with spatial memory characteristics and the change of synaptic plasticity in the PP-DG pathway including long-term potentiation (LTP), long-term Depression(LTD) and paired pulse facility(PPF) and so on, study the reduction of spatial memory ability of SD rats with STZ-induced and high fat diet mixed STZ-induced and the mechanism of synaptic plasticity.Methods1. Experimental animals:70 SD rats, initial body weight is (180±20) g.2. The SD rats were randomly divided into 3 groups:Control group, STZ-induced diabetic group and high fat diet mixed STZ-induced diabetic group. Use streptozotocin (STZ) intraperitoneal injection and the mixed high fat diet to build STZ-induced and high fat diet mixed STZ-induced diabetic rat model. In total,10 rats in control group,30 rats in STZ-induced diabetic group and 30 rats in high fat diet mixed STZ-induced diabetic group.3. Perform Morris water maze learning and memory behavior tests for 3 groups of rats respectively, study the influence of STZ-induced and high fat diet mixed STZ-induced diabetes on spatial memory ability and the spatial associative memory ability.(1) Place navigation test:Perform 4 days continuous training for 3 groups of rats, each time the rats were put into the water separately from the calibration point in quadrant?,?,?of the water maze to find the platform under the water. (2) Spatical probe experiment:Remove the platform, put the rats of 3 groups which had been trained above into the water one by one from Quadrant I and record the trajectory of rat movement and the corresponding parameters within 120s.(3) Spatial association memory test:Removed platform, put the rats of 3 groups into the water one by one from quadrant IV and record the trajectory of rat movement and the corresponding parameters within 120s.4. After Morris water maze test, select 15 rats in each modol group which show poor spatial memory ability to perform LTP, LTD, PPF tests in hippocampus PP-DG pathway together with the control group.(l)Use urethane to anesthesia the rats and fix the head of rat on the stereotaxic apparatus. Place the stimulating electrodes into the rat's entorhinal Perfrant Path (PP), placed recording electrodes in hippocampal dentate gyrus (DG). Stimulation output signal from the stimulator can reach stimulation electrodes to via isolation, recording electrodes record extracellular field excitatory postsynaptic potentials (fEPSP) and the postsynaptic population spike (PPS), the signal pass the patch-clamp amplifier. Input/output (I/O) curve was detected.(2) Paired-pulse facilitation (PPF) Record:Select 50% of the maximum population spike (PS) amplitude of the stimulus intensity as conditioned stimulus (CS) strength. After PS stabilize 20 mins, use double-pulse stimulation, the interval choose 30-100 ms, pulse width choose 150?s, frequency choose 0.5 Hz, stimulus intensity choose conditioned stimulus intensity. Record 5 times for each interval, calculating the ratio of PS2 and PS1.(3) Long-term potentiation (LTP) record:After PS stabilized, use CS to stimulate and record 30 mins as a baseline. When do LTP experiments, choose the high frequency stimulus(HFS), use 20 200Hz pulse as a group, intervals choose 2s, a total of 10 groups, use 75% of the maximum intensity of PS amplitude as stimulation intensity. After HFS, switch to the conditioned stimulus and record 60 mins.(4) Long-term depression (LTD) Record:After PS stabilized, use CS to stimulate and record 30 mins as a baseline (baseline). When do LTD experiments, choose the low frequency stimulus(LFS), use 900 1 Hz stimulation of the string, each string include 5 to 250 Hz pulses, use CS strength as stimulus intensity. After LFS, switch to the conditioned stimulus and record 60 mins.5. Analyze and discuss of the reduction in learning and memory ability for STZ-induced and high fat diet mixed STZ-induced diabetic rats and mechanisms of synaptic plasticity.Results1. Diabetic rat model validation:Test two diabetic groups at the 1st,7th,14th,28th day after modeling, all blood glucose values are greater than 16.7mmol/L, STZ-induced group average blood glucose at the 28th day is 26.40±3.55 (n= 30) while high fat diet mixed STZ-induced group is 24.85±5.34 (n= 30).2. Morris water maze learning and memory behavior:(1) After 1 month of diabetes modeling, both STZ-induced and high fat diet mixed STZ-induced diabetic rats do not show statistical difference compared with normal control group on spatial memory ability and spatial association memory ability.(2) After 3 months of diabetes modeling, in place navigation experiment, both STZ-induced and high fat diet mixed STZ-induced diabetic rats show longer escape latency compared with the control group, the average value of control group at 4th day is 7.90±3.58 (n= 30), STZ-induced group is 19.02±2.15 (n= 30), high fat diet mixed STZ-induced group is 20.69±3.02 (n= 30), modeling group show statistical difference compared with normal control group (p<0.05). From the second day of experiment, the escape latency of control group is significantly decreased while the diabetic groups decreased slowly.(3) After 3 months of diabetes modeling, in space exploration experiment, if put rats from the trained quadrant I into the water, the swimming time of two diabetic model groups in platform quadrant is short, the first central points and total scores are low. Three above parameter of STZ-induced group are 43.76±10.38 (n= 30),5.33±2.27 (n= 30),2372.11±187.23 (n= 30); High fat diet mixed STZ-induced group are 40.88±14.56 (n= 30),4.85±2.86 (n= 30),2081.67±195.18 (n= 30). The Control group are 69.77±12.36 (n= 30),11.36±2.78 (n= 30),3172.74±250.80 (n= 30). Modeling groups show statistical difference compared with normal control group (p <0.05).If put rats from untrained quadrant?into the water, the platform quadrant swim time, 1 central points and total scores of STZ-induced group are 38.82±9.63 (n= 30),4.86±2.15 (n= 30),2015.98±206.33 (n= 30); High fat diet mixed STZ-induced group are 40.67±11.95 (n= 30),5.31±2.26 (n= 30),2206.85±157.40 (n= 30); Control group are 62.64±10.78 (n= 30),10.57±2.96 (n= 30),2912.63±191.39 (n= 30). All of the values of the modeling groups are lower than the control group, show statistical difference (p<0.05), and the total score of STZ-induced diabetic group is lower than the high fat diet mixed STZ-induced diabetic group.3. The synaptic plasticity in hippocampal PP-DG pathway(1) Waveform of I/O curve:For control group,50% of the maximum intensity of response waveform is 0.35mA. For STZ-induced group,50% of the maximum intensity of response waveform is 0.45mA, For high fat diet mixed STZ-induced group,50%of the maximum response intensity of the waveform is 0.41mA. The overall I/O curves shift to the downward and the right, and the I/O curve shift of STZ-induced group is more further than the high fat diet mixed STZ-induced group compared with the control group.(2) Paired-pulse facilitation (PPF):The enhanced starting point of control group is 35ms, while high fat diet mixed STZ-induced group 37ms and STZ-induced group 42ms. The facilitated strength of 3 rats groups is as below:Control group (204.80±14.57)%(n= 8), high fat diet mixed STZ-induced group (181.79±13.81)%(n= 7), STZ-induced group (172.68±15.02)%(n= 7). Within the pulse interval of 30-100ms, the double-pulse facilitation width of the control group is 65ms, high fat diet mixed STZ-induced group is 63ms and STZ-induced group is 58ms. It can be seen, the double-pulse facilitation intensity of diabetic model groups is lower than in the normal control group, and the facilitation width decreases, with statistical difference (p<0.05). The paired-pulse facilitation intensity of STZ-induced group is more lower.(3) LTP:After 60 mins of high-frequency stimulation, the PS amplitude of the conditioned stimulus amplitude.in control group is (258.93±22.45)%(n= 7), high fat diet mixed STZ-induced group is (203.67±19.86)%(n= 6) and STZ-induced group is (160.12±17.91)%(n= 6).The high fat diet mixed STZ-induced group LTP is 55.26%lower than the Control group, the STZ-induced group LTP is 98.81% lower than the control group, the result of model groups and control group show statistical difference (p<0.05), and the STZ-induced diabetes is more serious.(4) LTD:After 60 mins of low-frequency stimulation, the PS amplitude of the conditioned stimulus amplitude in control group is (106.35±3.51)%(n= 6), high fat diet mixed STZ-induced group is (81.92±9.96)%(n= 5) and STZ-induced group is (67.73±4.35)%(n= 5). The results showed that LTD facilitated in model groups and had statistical difference with control group (p<0.05). The PS amplitude of high fat diet mixed STZ-induced group is 24.43% lower than control group, the PS amplitude of STZ-induced group is 38.62% lower than the control group, so the LTD facilitation range of STZ-induced diabetic group is larger than the high fat diet mixed STZ-induced diabetic group.(5) The range of synaptic plasticity:The synaptic plasticity of control group is 152.58%(n= 6), high fat diet mixed STZ-induced group is 121.75%(n= 5) and STZ-induced group is 92.39% (n= 5). Thus, whether STZ-induced or high fat diet mixed STZ-induced diabetic group have reduced the PP-DG pathway hippocampal synaptic plasticity range of rats, the destruction to synaptic plasticity of STZ-induced diabetic group is more serious, so the range of synaptic plasticity is smaller than the high fat diet mixed STZ-induced diabetic group.ConclusionsThis paper is to study the synaptic plasticity mechanisms of learning and memory ability reduction for diabetic rats. Based on the Morris Water Maze study on spatial memory behavior and synaptic plasticity in hippocampi PP-DG pathway, main conclusions are as follows:1. The impact of diabetes to the spatial learning and memory behavior(1) Thru Morris water maze experiment, after a certain time, both STZ-induced and high fat diet mixed STZ-induced diabetes can lead to the decline of spatial memory and space associated memory ability in rats. (2) Compared with the high fat diet mixed STZ-induced diabetes, the space associated memory ability of STZ-induced diabetic group was destroyed more serious.2. The synaptic plasticity mechanisms of the declining of the learning and memory ability in diabetics rats(1) After having diabetes, the I/O curve of rat hippocampus PP-DG area shift down, the PS amplitude of the responses waveform decreases after same strength of synaptic incentive, this indicate that diabetes makes the synaptic transmission performance degradation.(2) After having diabetes, the paired-pulse facilitation intensity in hippocampus of rats is inhibited significantly, the interval of paired-pulse facilitation is decreased. This indicates diabetes impact hippocampal PP-DG short-term synaptic plasticity may be achieved by inhibiting the release of presynaptic neurotransmitter.(3) Both STZ-induced and high fat diet mixed STZ-induced diabetes can inhibit the formation of hippocampus LTP significantly, can facilitate the phenomenon of hippocampal LTD, the range of synaptic plasticity is reduced, so both STZ-induced and high fat diet mixed STZ-induced diabetes decreased hippocampal long-duration synaptic plasticity in PP-DG pathway.(4) Compared with high fat diet mixed STZ-induced diabetes, the STZ-induced diabetes make a lower paired-pulse facilitation intensity, a greater inhibition of LTP and a greater amplitude of LTD facilitation, a smaller range of synaptic plasticity. Therefore, the destruction of STZ-induced diabetes in hippocampal synaptic plasticity is more serious than high fat diet mixed STZ-induced diabetes.