Studies On Bilateral Collicular Interaction Of Modulating The Latency Of Neuron:Whole-Cell Patch Clamp Recording In Brain Slice

The inferior colliculus(IC)plays an important role in the binaural information input as the last level of binaural integration of the subcortical nucleus.At present,the study of the interaction between bilateral ICs is mainly focused on the changes of the acoustic response characteristics of one side of IC neurons by electrical stimulating,local anesthetizing,or cryoloop cooling the other side of IC.And most of these studies focus on the interaction between bilateral ICs on IC neuron fire rate,whereas on the latency of IC neurons are few.In addition,these studies are basically done using in vivo extracellular recording,the relevant synaptic mechanism is not very clear.Moreover,due to in vivo experiments can not completely excluding the involvement of corticofugal system or subcortical pathway that input information to IC,so this study using whole-cell patch clamp recording method to explore the effect of interaction between bilateral ICs on neuronal response latency and its possible synaptic mechanisms in vitro brain slice.The results are demonstrated as follows:1.By electrical stimulating one side of CNIC,we have obtained 87 neurons on the other side of DCIC and CNIC which considered that have synaptic connection.In the voltage clamp mode,three types of synaptic inputs were recorded:only received excitatory input(EPSC,E type),only received inhibitory input(IPSC,I type)and mixed input(EPSC+IPSC,E+I type).The proportion of these three types of neurons were 32.2%(28/87),8%(7/87)and 59.8%(52/87).2.By injecting a depolarized step current(0-150pA)into neurons that are clamped on one side of the IC,and to stimulate the other CNIC simultaneously to explore the excitatory or inhibitory effect of IC neurons on Latency and its possible synaptic mechanisms.In this part,we recorded 53 neurons,and three synaptic inputs types of neurons accounted for 18(E type),4(I type),31(E+I type)respectively.IC neurons response latency is affected degrees cause its received the synaptic inputs of other side.In these neurons,30.2%was shortened(16/53,P<0.001),45.3%was prolonged(24/53,P<0.001)and 24.5%had no change(13/53,P>0.05).There was a certain relationship between the type of synaptic input and the change of latency of the neurons on the recording side.The relationship were as follows:most E-type synaptic input shortened the latency of neurons(72.2%,13/18),Little part no change(22.2%,4/18).There was only an E-type synaptic input that prolonged the latency of neurons(5.6%,1/18);half of type I synaptic input prolonged the latency of neurons(50%,2/4),half did not change(50%,2/4);most E+I type synaptic input prolonged the latency of neurons(67.7%,21/31),and the number of neurons was significantly reduced(9.7%,3/31)Or no change(22.6%,7/31).This latency change is related not only to the type of synaptic input but also to the relative magnitude of excitement and inhibition.For example,neurons with prolonged in response latency,IPSC amplitude is much larger than 150pA,and larger than the EPSC amplitude in E+I synaptic input.For neurons with short or no change in response latency,The amplitude of IPSC is less than 150 pA,and equal to or slightly larger than the amplitude of EPSC in E+I synaptic input.In addition,the change of latency of IC neurons was also due to the change of the sub-threshold depolarization duration of the first action potential(r-0.9989,P<0.0001).3.These three kinds of synaptic input types have a certain distribution trend.E+I type is widely distributed in CNIC and DCIC,E type is relatively concentrated in this two nuclei,I type due to the small number of neurons did not show a clear distribution trend.Overall,The type of synaptic input between the bilateral IC is predominantly E+I.And the interaction between the bilateral IC can change the response latency of most IC neurons.This latency change is related not only to the type of synaptic input but also to the relative magnitude of excitement and inhibition.And the change of latency of IC neurons was also due to the change of the sub-threshold depolarization duration of the first action potential.