The Auditory Plasticity And Relationship With Persistent Activity Of Layer V Neurons In The Primary Auditory Cortex Of Mice

Auditory system of human or animal can modulate its structure and function with learning and experience to accommodate the complex sound environment,which is called auditory plasticity.In vivo studies have found that after conditioned training,the frequency response area of pyramidal neurons in primary auditory cortex(AI)varied,and it is modulated by the cholinergic system.How the electrophysiological properties of AI neurons changed during this learning process is still unknown.Previous experiments have indicated that persistent activity(PA)is the representation of learning-induced plasticity,and in vitro studies in our lab found that PA can be induced in AI neurons.The mechanism and related behavioral experiments are lack.Therefore,in this study,we try to explore the electrophysiological properties and persistent activities of neurons in layer V of the primary auditory cortex(AI-L5)in conditioned mice.The results are as follows:(1)After conditioned training,the half-width of action potential of the conditioned group was significantly prolonged than that of the control group(p<0.001).Further analysis showed that the rise time and fall time of AI-L5 neurons of the conditioned group were significantly longer than those of the control group(both p<0.001).After performed correlation analysis between electrophysiological properties and fear response,the half-width of action potential was positively correlated with the freezing index(r=0.5,p<0.05).There were no significant diffeerences in other electrophysiological properties between the control group and the conditioned group,such as the resting membrane potential,input resistance,time constant,threshold potential,active threshold,threshold intensity,AP amplitude(all p>0.05).(2)Compared to the control group,the AI-L5 neurons of conditioned group have fewer spikes,prolonged first spike latency and interspike interver to 500 ms depolarizing current from 100 to 300 pA(all p<0.05).(3)After bath infusion carbachol(CCh),the resting membrane potential of the AI-L5 neurons in the control group and the conditioned group were significantly depolarized,the input resistance were significantly increased,the active threshold were significantly reduced,and the threshold intensity were significantly reduced(all p<0.05).However,the membrane potential of AI-L5 neurons in conditioned group was more depolarized,the input resistance was higher and threshold intensity was lower than those in control group(all p<0.05).The results showed that the AI-L5 neurons in conditioned group are more sensitive to CCh after auditory plasticity.(4)AI-L5 neurons in the control group could not induce PA(0/27),while 48%of AI-L5 neurons in the conditioned group could induce PA(12/25).After the infusion of CCh activated cholinergic receptor,23.8%of the control group AI-L5 neurons could induce PA(5/21),and 76.5%of the AI-L5 neurons in the conditioned group could induce PA(13/17).The results showed that the proportion of PA was higher in the AI-L5 neurons of conditioned group.Some AI-L5 neurons in the conditioned group appeared cluster-burst PA,but the AI-L5 neurons in the control group did not appear clustered PA.To sum up,after conditioned training,the AI-L5 neurons have relatively lower spikes and prolonged action potentials,which may be associated with the suppression of IK.AI-L5 neurons in the conditioned group had a higher proportion of PA,and some of them appeared cluster-burst PA,indicating that PA was the representation of auditory plasticity induced by learning at the cellular level.