Duration Selectivity Of Inferior Collicular Neurons With Auditory Behavior-related Response Patterns And Effect Of Neural Inhibition On The Responses

Sound duration is one of the basic parameters of the auditory signal,and it is also one of the parameters that the constant frequency-frequency modulation(CF-FM)bat actively changes during the process of echolocation.How single-on(SO)and double-on(DO)neurons in inferior colliculus(IC)identify the sound duration and selectively filter the sound duration,and the role of neural inhibition in the formation of response patterns were still unclear.In this study,we were used vivo extracellular recording,and free-field acoustic stimulation to investigate SO and DO neurons in IC of pratt's roundleaf bats(Hipposideros pratti).The main results obtained in the present study are as follows:1.A total of 314 neurons(N=314)were obtained,and they were divided into SO and DO neurons based on their response to CF-FM stimulation.The responses and duration selectivity of 140(N=140/314)neurons were measured by CF and CF-FM sounds stimulation at 10 and 20 dB(MT+10 dB,MT+20 dB)above minimum threshold(MT).According to their response patterns to CF-FM stimulus,they may be classified into SO(N=91,65%)and DO(N=49,35%)neurons.The duration selectivity of SO neurons under CF stimulation is divided into short-pass(SP),long-pass(LP),band-pass(BP),all-pass(AP)or non-duration-selectivity type,and irregular(irregular)type;when stimulated with CF-FM sound,the proportion of duration selectivity SO neurons increased from 60%(N=55/91)to 79%(N=72/91),indicating that the FM component plays an important role in the duration selectivity formation of the neurons,it is may be caused by the interaction of the inputs caused by the two acoustic components that converge projected onto the recording neuron.The duration selectivity of DO neurons under CF acoustic stimulation was the same as that of the above SO neurons,also showed as band-reject(BR)type;when stimulated with CF-FM,the proportion of duration selectivity increased from 51%(N=25/49)to 61%(30/49)under CF stimulation,indicating that FM sound component may effectively increase the duration selectivity of DO neurons.2.Comparing and analyzing the best duration(BD)of SP and BP neurons in SO and DO neurons and the width of duration-tuning(DW)at 50%of maximal response.The results showed that when the sound stimulus changes from CF to CF-FM,the mean BDs of unaffected BP-type SO neurons was reduced from 16.0±7.3 to 8.8±4.5 ms(p<0.05),indicate the duration selectivity of these neurons on behavior-related CF-FM sound stimulation is more accurate.In addition,under the condition of CF-FM sound stimulus,the BDs of unaffected SP-type DO neurons was significantly decreased compared with that of SP-type SO neurons(5.6±4.0 vs.8.5±2.4 ms;p<0.05);DW of unaffected SP-and BP-type DO neurons was significantly increased compared to the same type of SO neurons under CF-FM stimulus(SP:23.3 ± 8.4 vs.34.91±4.1 ms;BP:21.1 ± 6.6 vs.33.0±6.0 ms);DW of unaffected BP type DO neurons was significantly increased in CF-FM sound stimulus compared with CF sound stimulus(SP:21.1 ±4.7±8.4 vs.34.9±4.1 ms;BP:14.1 ±8.5 vs.33.0±6.0 ms).These results suggested that the biological functions of duration selectivity SO and DO neurons are different and there may be involved in performing different echolocation tasks during each stage of hunting.3.When CF and CF-FM sounds stimulus intensity is increased from MT+10 dB to MT+20 dB,the ratio of duration selectivity SO neurons was significantly decreased,while the mean BD of SP and BP types is also significantly reduced(p<0.0001).For DO neurons,the ratio of duration selectivity decreased significantly only when the intensity of CF sound stimulus increased,and the mean BD of the SP and BP types did not significantly change with the increase of the intensity(p>0.05);for the CF-FM stimulation The intensity tolerance is also stronger than CF.These results indicate that duration selectivity DO neurons are more tolerant to the increased CF-FM stimulation intensity than SO neurons.4.The first-spike latency(FSL)of SO and DO neurons was further analyzed by plotting the duration-latency function curve.The results indicate that the coincidence detection or anti-coincidence mechanism is also applicable to explain the mechanism of duration selectivity formation of SO and DO neurons.The effect of FM component may be involved in the formation of duration selectivity of SO and DO neurons5.The complete data of 71(71/198)neurons(SO:55;DO:16)before and after the application of gamma-aminobutyric acid A(GABAA)receptor antagonist bicuculline(Bic)under CF and CM-FM sound stimulus were studied and analyzed.(1)65%(N=26/55)SO neurons exhibited that response duration and number of impulses were significantly increased under the two sound stimulation conditions.About 6%(3/55)of SO response pattern of SO neurons could be transformed into DO response pattern.The response pattern of partial DO neurons to the CF component of CF-FM sound changes from phase-type to sustaind(N=5/12)or phase-burst(N=7/12);and their(N=12/12)response patterns of the FM acoustic components changed from phase-type to phase-burst type;and their number of responses to the two sound components both increased significantly.In addition,in 29%(N=16/55)SO neurons,the response patterns,response duration,and the numbers of impulses,as well as FSL was not affected by Bic.These results suggest that GABAergic inhibition plays an important role in the the formation of duration selectivity and response patterns involved in most of the SO and DO neurons.(2)During the application of Bic under CF and CM-FM sound stimulation condition,about 71%(39/55)of SO neurons and 44%(7/16)of DO neurons showed a significant decrease in FSL;moreover,FSL of 31%(5/16)DO neurons was significantly reduced only during the application of Bic under CF sound stimulation.It is suggested that the short-latency inhibitory input that occurs before or coincident with the arrival of the excitatory input is GABAA inhibitory input and can eliminate the depolarization and delayed action potential of these neurons to varying degrees.(3)About 75%(12/16)of the DO neurons during the application of Bic,mean percent changes in impulses of neurons elicited by the CF sound component is significantly higher than elicited by the FM sound component.However,approximately 25%(4/16)of DO neurons only showed changes in the response pattern of elicited by the FM sound component,and the number of impulses increased accordingly,but there was no significant change in the FSL.Therefore,it is suggested that the effect of GABAergic inhibition on CF and FM sound components in CF-FM sound is different.(4)It is further showed that in the IC the inhibition accepted by SO and DO neurons is different,the inhibited degree of GABAergic inhibition in the SO neurons was obviously stronger than in the DO neurons6.Superoxide dismutase(SOD)in the auditory system has been shown to be associated with a decline in the age-related function of animal ICs.The association between the superoxide dismutase 2(SOD2)gene C47T polymorphism and noise-induced hearing loss(NIHL)was first studied by meta analysis.In the subgroup analysis by ethnicity,the SOD2 C47T polymorphism was significantly associated with NIHL in the recessive model of the Chinese population.