Establish An Associative Learning Model Of Medium Difficulty And Examine Changes Of Local Field Potential Reaction To Conditional Stimulus In Hippocampal CA1 During Learning

Learning and memory is a major function of hippocampus,and its realization relies on synaptic plasticity.Hence,the elucidation of synaptic changes in the hippocampal circuit during learning is necessary for understanding hippocampus-dependent learning and memory.For decades,a mass of studies have been conducted on synaptic plasticity,most of which are focused on post-learning synaptic changes,including the postsynaptic density thickening,the shape and number alteration of spines,the increase of neuron excitability,local field potential augmentation,memory-elicited action potential and so forth.But studies on synaptic activity and changes in hippocampus during learning are rarely reported.Here,we established a learning model with medium difficulty,based on which learning-related changes in hippocampal CA1 during the process were preliminarily explored.On the specific requirements of our study,a behavior paradigm was established,in which animals learn an association of sound and water with 100-200 pairing conditioning within 0.5-1 h.Analysis on the test results in the second day after conditioning revealed two groups of animals.First,in the well-tested group,the mice licked water at once they heared the tone.Meanwhile,there was a higher frequency for mice to lick in the correct window than in the other time.Second,not-well-tested group,test results in the second day after conditioning showed a random scatter of licking.And the frequency of licking in the correct window during conditioning was the same as that in the error window.We found that well-tested group,the licking frequency in correct window remains the same during the conditioning,while in error window the licking frequency decline soon and the decline is obvious.The ratio of licking frequency in error window over that in correct window decline soon and the decline is obvious.In not-well-tested group,the licking frequency in correct window and error window both decline;Meanwhile,in a few animals,the licking frequency in correct window remains the same,while in error window,the licking frequency has a late and not obvious decline.The ratio of licking frequency in error window over that in correct window decline late and not obvious.On the basis of the established behaviorism paradigm,local field potential(LFP)in hippocampal CA1 was recorded during conditioning.First,we observed genesis of LTP both in CA1 stratum radiatum(sr)and stratum pyramidale(sp).Second,a compare revealed that the genesis of sp-LTP was statistically earlier than that of sr-LTP,and that the amplitude of sp-LTP was significantly larger.All results suggest that in associative learning hippocampal regions are capable of gradual LTP,and that there may exist a sequence of LTP in these regions.Our study supplies new infromation to further understanding of the mechanisms of hippocampus-dependent learning.