| The response or dischrge pattern of a central auditory neuron is its basic property and can be also used to encode multiparameters of the sound signal such as coding the duration and pattern of a sound stimulus. In previous studies on the response patterns and duration selectivities, the used methods were basically extracellular recording, but in vivo whole cell patch clamp and intracellular recording were used in a few studies. The mechanism underlying these response properties of the auditory neurons is not completely clear until now. Therefore, the experiment was performed on the inferior colliculus (IC) of mice (Mus musculus, Km) using in vivo intracellular recording and probed the response patterns and duration selectivities of IC neurons to pure tone stimuli and the mechanism underlying shaping response patterns and forming duration selectivities of IC neurons. The results and findings were obtained in present study as following:1. Under stimulation conditions of fixed sound amplitude and best frequency sound, we recorded the the rensponse patterns of IC neurons to pure tones (BF sounds) of 40, 120,200 and 300 ms and analyzed the response pattern of 120 ms sound stimulus among the patterns obtained by the sounds of different durations. Total of 66 neurons were isolated from ICs of 18 mice. The ranges of recoding depth (μm), BF (kHz) and resting potential (RP) (mV) of these neurons were 151-1871 (792.9±354.1),8～38 (13.9±4.7) and-57～-15 (-19.7±12.1), respectively. 58 neurons among these neurons generated action potentials (AP) to BF sound stimuli and their response patterns could be classified into phasic (n=24,41.4%), phasic burst (n=8,13.8% ), phasic-pauser (n=1,1.7%), pauser (n=4,6.9%), chopper (n=2,3.4%), tonic (n=14,24.1% ) and sound-evoked inhibitory style (n=5,8.6%). The responses of remaining 8 neurons were the excitatory post-synaptic potential (EPSP) (n=4) and inhibitory post-synaptic potential (IPSP) (n=4). These results demonstrated that inhibition involve in the forming and shaping process of most IC neurons'discharge pattern, during the process inhibition play a sculpting or carving effect and the local neural circuit formed within IC or the auditory nuclei of sub-IC was its structural base.2. Under stimulation conditions of fixed sound amplitude and best frequency sound with different durations (2,5,7,10,15,20,30,40,50,60,70,80,100,120,160,200 ms), total 118 neurons were isolated from ICs of 30 mice and the ranges of recoding depth (μm), BF (kHz) and RP (mV) of these neurons were 175～1974 (880.8±443.4),7～44 (13.9±4.7) and-91～-16 (-26.4±14.3).99 of 118 neurons neurons had complete data.89 of 99 neurons generated action potentials (AP) to BF sound stimuli with different durations and the remaining 10 neurons generated EPSP (n=3) and IPSP (n=7), respectively. According to the responses of 99 neurons to different sound durations, they could be categorized into duration selective neurons (n=54) such as long pass (LP, n=32, 32.3%), short pass (SP, n=14,14.1%) and band pass (BP, n=8,8.1%) and non-duration selective neuron, all pass (n=45,45.5%), respectively. On the other hand, we observe the response patterns of SP, BP and AP neurons were basically phasic and phasic burst while that of LP neurons were involved in pauser, chopper and tonic. These results demonstrated that the neurons also could represent and encode the sound duration with PSPs except for AP. The interaction between excitatory and inhibitory inputs to synapse, complex temporal integration and neuron's response patern possibly took part in the formation of neuron's duration selectivity.
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