| Learning and memory are two interrelated neural activity. Learning is ability of animal. Animals do exercise and rely on the experience which gained to change their behavior to adapt to the surroundings neural activity process. The memory of animals is the form of information storage. The memory of animals relay on neural activity. The memory can be divided into declarative memory and non-declarative memory. However, all memory neural circuits are involved in the limbic system. The hippocampus is part of the limbic system, which plays an important role in learning and memory neuronal activity.Since1950, scientists have noticed that the relationship between the hippocampus and learning and memory. If the region of hippocampus in the brain was damaged, injured patients often exhibit learning and memory deficits. After years of research, a lot of evidence that the hippocampus is to help humans deal with the main area of the long-term learning and the memory of sound and light, taste and events (declarative memory). The close relationship between hippocampus and learning memory ascribes the mechanism of the activity of nerve cells in the hippocampus.The nervous system consists of two classes of cell, the neuron and glial cell. Neurons are essential for nervous system function. But studies over past decade are raising the awareness about the diversity active roles played by glial cells in the nervous system. The scientists focus on the neurons that play an important role in the nervous system for a considerable time, but ignore the glial cells more than10times higher than the neurons. Glial cells consist of astrocytes, oligodendrocytes, microglia cells. Recent studies have shown that glial cells in the nervous system are not just a supporting partner of the neurons. They are a great help to neurons with its nutritional support functions. They also have effects on the chemical synapses between neurons signal propagation. For example, the pathway of the astrocytic response to neuronal firing is via the activation of metabotropic glutamate receptors on the astrocytes, leading to the production of inositol triphosphate, a second messenger, and to the ensuing calcium release from the endoplasmic reticulum membrane in astrocytes. IP3receptor which is coupled to glutamate receptor is activated too. Then the calcium is released from endoplasmic reticulum in glial cells so that elevated intracellular calcium concentration. The high concentration of calcium ions could activate CaMK II, which can trigger astrocytes to release glutamate, ATP, PRO-BDNF and mature BDNF and so on. These signaling molecules can be passed to the neurons, which affecting the synaptic efficacy of neurons. Chemical synapses also serve to amplify neuronal signals, so that even a small presynaptic nerve terminal can alter the response of a large postsynaptic cell. Such as glutamate released from glial cells which activate the synaptic NMDA receptor, which will be able to activate the postsynaptic membrane, so that the postsynaptic membrane depolarization is happened. The postsynaptic membrane depolarization leads to enhance the postsynaptic membrane of neurons excitatory synaptic current (EPSC) and excitatory postsynaptic potential (EPSP).There is still debate that neurotransmitter that glial calcium activity-dependent release involved in the synaptic plasticity. The focus of the debate lies not in glial cells calcium signal generation and glial transmitter release. Glial neurotransmitter transmission mechanism is calcium-dependent and glial neurotransmitter play an important role in synaptic plasticity. Thus we use IP3R2-KO mice which calcium signaling is silence in glial cells to further clarify whether glial cells by calcium-dependent release of neurotransmitters to regulate synaptic transmission to affect learning and memory function in synaptic the role of plasticity.IP3is short for inositol1,4,5-triphosphate. Phosphatidylinositol signaling pathway is an important signal transduction pathway in cellular. Extracellular signaling molecules is binding with G protein-coupled receptor on the cell surface, which activate phospholipase C (PLC-beta) in the plasma membrane.4,5diphosphate on the plasma membrane phosphatidylinositol hydrolysis (PIP2) into inositol1,4,5-inositol triphosphate (IP3) and diacylglycerol (DG) that are the two second messenger, so that the cells extracellular signal transfer into intracellular signaling. Intracellular IP3is binding to the IP3receptor of the endoplasmic reticulum (ER). Thereby opening calcium channels increase the intracellular calcium ion concentration, and further activate various types of protein that is dependent on calcium ions. IP3receptor can regulate the release of intracellular calcium, and is widely expressed in mammalian cells. IP3receptor consists of four subunits, according to the composition of the subunits, IP3receptor can be divided into three subtypes:IP3R1, IP3R2, IP3R3. Their three subtypes were ITPR1, ITPR2, ITPR3gene encoding synthesis. The existing article reported that the affinity between three subtypes of receptor and IP3is not the same:IP3R2> IP3R1> IP3R3. The affinity between IP3R2receptor and IP3is stronger than IP3R1and IP3R3receptor. And IP3R2are mainly distributed in the glial cells in the hippocampal region. Since IP3R2play an important role in the mechanism that regulation of glial cell calcium concentration. IP3R2likely will affect synaptic transmission and learning and memory in the knockout mouse.The strength of synaptic connections in the nervous system is variable, not fixed. This variability is referred to as neuronal plasticity. The plasticity of synapses in the nervous system influences of the external environment information. Neuronal plasticity is often considered to have a close relationship with learning and memory function. LTD (long terms-depression) and LTP (long terms-potential) are known to be mainly two forms of neural synaptic plasticity. LTD is a lasting reduce synaptic efficacy of stimulation. LTD could be happened in many regions of the brain. There are different types of mechanism in the central nervous system, the type of neural circuits is the same. In the hippocampus region, we can induce LTD two loops:CA3neurons project to the CA1neurons; and DG nerve project onto the CA3neural on neural circuits. The mechanisms of the two neural circuits are not exactly the same. Relationship between LTD and learning and memory function was positively correlated or negatively correlated, there is still controversial. In recent years, studies of professor Yutian Wang have shown that LTD in hippocampal region is helpful to the consolidation of spatial memory. And LTD is happened in vivo or from the brain slices, which need to activate the NMDA receptor, then cause AMPA receptors. Professor Zhang Xia published that cannabinoid CB1receptor-mediated hippocampal LTD by regulating glial cells led to working memory impairment mentioned in the article. The cannabinoid CB1receptor can give rise to glial cells release the glutamate to the synapses. Then glutamate can activate the NMDA receptor and AMPA receptors on the postsynaptic membrane. Result in LTD is happened in vivo, which eventually leading to impaired working memory function in mice. Results from many studies showed that LTD is certainly important influence on the function of learning and memory. This problem is still controversial on the induced LTD favorable or damage on the function of learning and memory. The article published by Professor Zhang Xia expounds that the glial cells of the hippocampus can mediate the formation of LTD, which further affect the expression function of learning and memory on experimental animals. Therefore, we suppose that calcium wave in the glial is disappeared as result of lack of IP3R2in hippocampal glial cells of IP3R2-KO mice, which decreases the synaptic neurotransmitter (such as ATP, reduce glutamate, GABA) released form glial cells. Synaptic neurotransmitter can affects the formation of hippocampus LTD, which could affect the hippocampal-mediated the function of learning and memory, such as working memory, spatial memory and long-term memory.Therefore, we first detected electrophysiological on the hippocampal CA3-CA1region. From the experimental result can be seen that LTD (long terms-depression) is significant difference between IP3R2-WT mouse and IP3R2-KO mouse. LTD on the hippocampal of IP3R2-KO mouse is impaired, which is significance difference with IP3R2-WT mouse. Proved by experiments, we found that the IP3R2-WT mouse which hippocampal CA3-CA1LTD is not impairment (n=7), compared with IP3R2-KO mouse hippocampal CA3-CA1LTD is impairment (n=6). LTD was induced by LFS on the IP3R2-WT and IP3R2-KO mouse hippocampal CA3-CA1region. After LFS, fEPSP amplitude gradually is reduced during10min～20min. Compared to the baseline fEPSP amplitude, transgenic mice exhibited no significant difference was measured in the fEPSP amplitude, which is showed LTD damage. These results expound that calcium concentration in the glial cells has an important regulatory role in neurons LTD. And using whole-cell patch-clamp technique, we observed the spontaneous excitatory postsynaptic current (sEPSC). Compared to the wild type mice, transgenic mice exhibited no significant difference was measured in the amplitude and frequency of sEPSCs. The electrophysiologic findings indicate knockout IP3R2does not cause configuration or structure of synaptic being changes in the brain. But IP3R2gene is knocked out in the glial cells that will lead to alter releases neurotransmitters from glial cells.As already mentioned, there is still controversial that the relationship between LTD with function of learning and memory is a positive correlation or negative correlation. In this experiment, we further zoological experiments associated with learning and memory to detect the IP3R2-WT and IP3R2-KO mice whether there are differences on the function of learning and memory. IP3R2-KO mice observed LTD damaged on the zoological experiments showed learning and memory function is enhanced or weakened, to determine the impact of LTD on learning and memory. So we did the Morris water maze and Y-maze animal behavioral experiments.To verify the significance of calcium concentration in the glial cells on the function of learning and memory of the hippocampus, we performed Morris water maze and Y maze.Morris water maze:British psychologist Morris (1981),80years in the20th century, the early design and applied to an experimental brain learning and memory mechanisms of means. Morris and his colleagues used rats in the search target opaque pool of water and milk mixture containing rat hippocampus and other brain damage after learning, memory and spatial orientation, and cognitive achieved remarkable results. This device is not only the experimental design is reasonable and the method is simple and practical, but also easy to observe and record the animal into the water to search hidden in the time required by the underwater platform, strategy, and their swimming trajectory, which can be analyzed and inferred animals learning, memory and spatial cognitive ability. Although the first subjects for the rats, but since then the labyrinth system assessment of rodent spatial learning and memory in the classic procedure, widely used in basic and applied research in neurobiology, pharmacology and other fields. It is a more objective measure of animal spatial memory, working memory, and spatial ability to distinguish changes. Morris water maze consist of hidden platform experiment (hidden platform test), space exploration the experimental (Probe trials), visual platform for experimental the (visible platform test)[JJBuccafusco]. Visual platform is designed for experimental detection of external conditions, such as temperature, experiments inside the room furnishings, and hidden platform is designed for experiment detected in experimental animals access to outside information and experience, which is the ability to learn; space exploration, the memory capacity of the experimental detection of experimental animals outside information; such as the impact of the experimental animals.By Morris water maze test on the IP3R2-WT mice and IP3R2-KO mice, we can see learning and memory ability in this experiment. After completion of the hidden platform experiment, the space probe test, visual platform for experiments, we found that IP3R2-KO mice in the hidden platform experiment latency period is shorter than the latency period of IP3R2-WT mice. The result indicates that IP3R2-KO mice’s ability stronger than the ability of IP3R2-WT mice on learning and memory. In the visible platform experiments, there is no difference between IP3R2-WT mice and IP3R2-KO mice on the swimming speed. There is no statistical difference on the latency period. In conclusion, the results of Morris water maze can be seen learning and memory ability of IP3R2-KO mice is stronger than the ability of IP3R2-WT miceY-maze is mainly for learning, working memory and reference memory test. There is a relative complicated experiment:eight-arm maze. In contrast, the Y-maze is simple, feasible and practicality. Y-maze now is commonly used in learning and memory function evaluation. Y-maze consists of three identical arms. According to the analysis of experimental animals to enter the number of times in each arm, the times and the correct number, number of errors, the route parameters can reflect the spatial memory of the experimental animals. Y-maze test model is used to study spatial recognition memory in rodents, relative to the advantages of the passive avoidance experiments:In this maze, drived by curiosity, the rodents explore the different environment in the Y maze. Rodents can learn rules to avoid disadvantages. The Y maze can effectively detect spatial memory of animals. During three-day on the Y maze, there was no statistically significant difference on choice total number between IP3R2-WT mice and IP3R2-KO mice. On the second day of the experiment, correct percentage of IP3R2-WT mice was higher than the percentage of IP3R2-KO mice. There is no significant difference on the third day. In conclusion, these results illustrate that the the IP3R2-WT mice and IP3R2-KO mice learning and memory function is not difference on the Y-maze test.In summary, our current study found that the calcium elevation in the glial cells of IP3R2-KO mice is important for LTD formation on the hippocampal CA1region. Morris water maze experiments show that spatial memory of IP3R2-KO mice is stronger than spatial memory of IP3R2-WT mice. IP3R2-KO mice in the Morris water maze learning and memory ability is stronger than in IP3R2-WT mice. But several regions regularize the function of learning and memory in the brain, such as hippocampus, the prefrontal cortex, amygdala, striatum area. Although the electrophysiological results showed that LTD of IP3R2-KO mouse is impairment on the hippocampal CA1region, it can not be resolved directly that LTD impairment results in spatial memory increase on the IP3R2-KO mice. It will be possible that several areas have been changes in the transgenic mouse brain, and we detected the mouse hippocampal CA1region LTD was impairment only. It is still unclear whether other areas of the brain involved in the regulation of learning and memory function produce changed. So we suspect IP3R2-KO mice CA1region of hippocampus and other brain regions to regulate learning and memory function of the mice. LTD impairment and the results of Morris water maze may be two parallel way. The follow-up of the subject will detect LTD on IP3R2-loxP mice which is specific knock the IP3R2in glial cells of the hippocampal CA1region, and observed the transgenic mice performance of Morris water maze. This topic results suggest that the intracellular calcium concentration of glial cells is increased, which inhibis LTD on the hippocampal CA1region of IP3R2-KO mouse, which is possible to enhance the function of learning and memory in transgenic mice. |
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