Effect Of GABAergic Inhibitory Inputs From Dorsal Nuclei Of Lateral Lemniscus On Acoustic Signal Processing Of Inferior Colliculur Neurons

Processing acoustic information is an important function of the inferior colliculus(IC),as central nucleus in auditory system,it was found that gamma-aminobutyric acid(GABA)ergic inhibition plays a key role in the processing acoustic signal in IC neurons.Dorsal nuclei of lateral lemniscus(DNLL)is one of major source of GABAergic inhibition to IC.The effect of GABAergic inhibitory inputs from DNLL on acoustic signal processing of IC neurons is unclear,and there is few report about the mechanism of GABAergic inhibitory from DNLL regulate the acoustic signal feature detection of IC neurons.In this experiment,we use mice(Mus musculus,Km)and extracellular recording,combine with electrical stimulation and microelectrophoresis technology,to examine the effect of GABAergic inhibitory from DNLL on processing acoustic signals of IC neurons.A total of 114 IC neurons and 57 DNLL neurons were recorded in our experiments.IC neurons can be divided into two groups as unaffected(40/114,35.1%),and inhibited(74/114,64.9%)when we electrical stimulate the DNLL neuron.There were no significant difference in recording depth,the best frequency(BF),the minimum threshold(MT),first spiking latency(FSL),firing duration(FD)between the two groups of IC(unpaired t-test,p>0.05),which suggested that there is no difference in the distribution of these two groups of IC neurons.Each parts of IC may receive the inhibitory input from DNLL.The SC reduced(paired t-test,p<0.001),FSL extended(paired t-test,p<0.001),FD shorted(paired t-test,p<0.01)in the inhibited IC neurons,when we local electrical stimulating the contralateral DNLL neurons.The strongest inhibitory effect occured in the early section of 0?2 ms within the whole firing duration.During bicuculline(BIC)application,the GABAergic inhibitory inputs to recording IC neuron is blocked,and local electrical stimulating DNLL had no longer effect on the response characteristics of IC neurons,which suggested that inhibitory inputs from DNLL to IC were totally GABAergic inhibition.Evaluate by the variation of spike count,42.7 ±13.7%of the inhibitory inputs received by IC neurons is from DNLL.In addition,local electrical stimulating the contralateral DNLL could reduce dynamic range(DR)(paired t-test,p<0.001),increased the slope(paired t-test,p<0.05)of Inhibited IC neurons,indicating that GABAergic inhibition coming from DNLL enhanced the sensitivity of IC neurons about sound intensity.However,the GABAergic inhibition coming from DNLL did not shape the frequency tuning curves(FTC)of IC neurons,which suggested that the GABAergic inhibitory inputs shaping FTC of inhibited IC neurons may come from other auditory nucleus.In the study,the results showed that the ascending inhibitory inputs coming from DNLL to IC were GABAergic inhibition,and the inhibitory effect mainly roles in the early section of IC neurons.The GABAergic inhibition evoked by local electrical stimulation DNLL could enhance the sensitivity of IC neurons about sound intensity,which may paly a role in the processing of enhance acoustic signal.