Synaptic Plasticity Of Hippocampal CA1 Neurons And Changes In Spontaneous Activity During Initial Storage Of Associative Award Memory

As one of the important brain regions for learning and memory,the hippocampus is responsible for the online acquisition,early storage and consolidation of memory.At present,it is generally believed that synaptic plasticity is an important basis for the realization of learning and memory.In order to understand the synaptic plasticity mechanism of learning and memory,on the one hand,after studying,the neuroplasticity of hippocampus was observed by in vitro experiments,and it was found that learning caused changes in the morphology and functional properties of LTP in hippocampal neurons;In addition,people have also identified neuronal activity encoding memory information in vivo animal experiments,mainly comparing the action potential changes and field potential changes of hippocampal neurons;due to technical difficulties,only a few studies have reported in vivo animal processes.For example,there is a study on synaptic plasticity changes associated with memory acquisition and storage that occur after joint fear memory.Therefore,further exploration of different types of Associative learning(reward and spatial)induced synaptic plasticity differences can help to understand the memory storage mechanism of hippocampus.In this thesis,we used the whole-cell patch clamp technique of head-fixed mice to use the rewarded associative learning behavior paradigm to observe the synaptic mechanisms of sensory information processing and memory coding of hippocampal CA1 pyramidal neurons before and after learning.Our study found that only a small amount(about 23%)of CA1 pyramidal cells were able to produce a membrane potential response to the experimentally selected sound stimulation when the mice were not learning.However,after the sound stimulation was used as the conditional stimulus for the associative learning and the water supply reward was trained for the unconditioned stimulus,the same electrophysiological recording was performed on the anesthetized mice,and the results showed that the membrane potential of the CA1 pyramidal cells stimulated by the sound condition The reaction ratio is greatly increased to about 70%.Moreover,these responses are inhibitory postsynaptic responses with an amplitude of 1.39 ± 0.72 mV with a decrease in the frequency of action potential firing.We further compared the spontaneous membrane potential activity and action potential activity of CA1 pyramidal cells before and after learning.By performing patch-clamp recordings under awake and anesthesia,we found that the resting membrane potential and threshold levels of CA1 pyramidal cells did not change significantly,and the slope of the ascending phase of CA1 pyramidal cells increased significantly after learning.We further analyzed the discharge of CA1 pyramidal cells,and the resulting increase in the frequency of action potentials was mainly due to the increase in the frequency of burst The difference was that the burst composed of more action potentials increased significantly under anesthesia.In the awake state,the burst of less action potential is increased.The experimental results of this paper show that the Associative reward learning induces inhibitory synaptic responses in hippocampal CA1 neurons and changes in membrane intrinsic excitability in CA1 neurons,which provide further insights into the mechanisms of hippocampal neuronal plasticity in understanding hippocampal-dependent associative memory.