Learning Specific And Non-specific Synaptic Plasticity In Hippocampal CA1 During Reward Associative Learning

Hippocampus,directly related to the function of learning and memory,is a critical brain area for the online acquisition and early storage of memory.The hippocampal plasticity in the process of learning and memory is essential to understanding the memory function of the brain.Long-term potentiation(LTP)and long-term inhibition(LTD)of neural circuits have been considered as the neural basis of learning and memory.As a result,there are many studies on the role of LTP in learning and memory,and most of them are focused on observing the hippocampal synaptic plasticity after learning through in vivo extracellular electrophysiological recording or in vitro experiments.Learning has been proven capable of inducing neural plastic activities(such as LTP).However,only a small number of studies have reported the occurrence of LTP during the learning process.In our previous laboratory studies,we did find that LTP was produced on the learning-specific synaptic pathway during rewarding associative learning.Interestingly,several studies have reported that,in isolated brain slices,LTP was observed in synapses that were not directly stimulated other than those directly stimulated,which was known as heterosynaptic plasticity.We are curious whether heterosynaptic plasticity occurs in hippocampal CA1 during the learning process.In this thesis,we used a reward associative learning paradigm with tone as conditioned stimulus(CS)and water as unconditioned stimulus(US),and performed extracellular electrophysiological records on head-fixed awake mice to reveal the synaptic and heterosynaptic plasticity in hippocampal CA1 during learning process.We found that,with the progress of learning,LTP was induced induced by CS,that is,the synaptic plasticity modification was established in the processing pathway of memory-related information.In addition,electrical stimulation(ES)of Schaffer lateral branches was conducted to induces field postsynaptic response(fPSP)during learning.We found that fPSP induced by ES was not affected by preceding CS with short intervals,which shows neural pathway stimulated by ES,independent of the signal transmission pathway of CS,is non-learning-specific.Our further analysis shows that,with the process of learning,synaptic plasticity also occurs in the nonlearning-specific pathway stimulated by ES,in addition to the learningspecific pathway.In conclusion,during reward associative learning,there is a general potentiation of both learning-specific and non-specific synapses in hippocampal CA1.