Frequency Representation And Tuning Of The Inferior Collicular Neurons Of Mice: Intracellular Recording In Vivo

Frequency of sound is one of the three basic characteristic of the sound, each central auditory neuron can respond to sound within some range of frequency, represent, and code these sound frequencies by different pattern of membrane potential. Because there are some difficulties in using intracellular recording in vivo, previous studies on frequency representation and tuning of sound in central auditory neurons were basically to use electrophysiological method of extracellular recording in vivo, In this study, under free field stimulation condition, we used the method of intracellular recording in vivo and investigated frequency representation and tuning of inferior collicular (IC) neurons in light anesthetized mice (Mus musculus, Km).80 sound sensitive IC neurons were obtained by intracellular recording and frequency representation and tuning of 39 among these neurons were analyzed. The ranges (mean±standard deviation) of recording depth (μm), best frequency (kHz), frequency bandwidth (kHz), and response latency (ms) of 39 neurons were 345～1871 (963±352),5～33 (17.0±8.6),7～47 (30.3±11.7), and 3.5～19.2 (11.2±3.8), respectively.According to responses and representation of neurons to different sound frequencies, they could be classified into four types, i.e.①the neurons (n=9) showed sound frequency representation and tuning property by inhibitory postsynaptic potential (IPSP) and duration of inhibitory action;②the neurons (n=7) showed sound frequency representation and tuning property by excitatory postsynaptic potential (EPSP);③the neurons (n=18) showed sound frequency representation and tuning property by action potential (AP); and④the neurons (n=5) showed sound frequency representation and tuning property by different ways of membrane potentials. On the other hand, the neurons had the shortest latency to best frequency sound stimulus and their latencies also showed some tuning properties, latency changed with frequency changing. By comparison of latencies of first IPSP, EPSP, and AP, the results showed latency (8.8±3.4 ms) of IPSP0.05) between mean amplitudes of IPSP (7.0±3.5 mV) and EPSP (5.3±2.1 mV).These results from intracellular recording demonstrated that three ways, AP, EPSP, and IPSP, could be used in frequency representation and tuning of IC neurons, but their temporal properties were different. The longer duration of IPSP suggested that IC neurons needed longer recovery time from hyper-polarization to resting membrane potential (RP) than from EPSP to RP.