Astrocytes Affect Neuron’s Electrophysiological Responses To Sound In Medial Geniculate Body

Mammalian nervous system contains two kinds of cells, nerve cells (neurons) and glial cells.Among them, astrocytes (astrocyte) is the primary. Studies confirm that astrocytes play an important role in the process of cognition, emotion and feeling, and sports information processing. Medial geniculate body (MGB) is an important replace nuclei of sound transmission in brain,and can be divided into three main partitions:abdominal (ventral division of MGB, MGv), back (dorsal division of MGB, MGd), intermediate (medial division of MGB, MGm). Some researches show that, astrocytes play a role in the processing of central sensory system neuronal plasticity, but in the auditory system,especially the auditory thalamus MGB neurons, the function of astrocytes in neuronal plasticity still has few reports.Objective To study the role of astrocytes in MGB neuronal plasticity.Methods Our study has using SD rats live in different time after unilateral cochlear ablation(ab),by electrophysiological recording techniques, record action potential firing of ab ipsilateral MGB neurons berore and after astrocyte function change by injection fluorocitrate (FC) in the ventricle.We statistics and analysis the changes of firing pattern, the spike counts, the first spike latency(FSL), minimum threshold (MT), frequency tuning curve (FTC) and the best frequency (BF)and so on.Results1 The change of normal group rats MGv neuronal electrical activity before and after injected FC:Compared with the no injection, after FC injection,we can see the MGv neurons spike counts decrease and FSL extend from the raster plot diagram, FTC RIF and tuning curve of FSL directly. Statistic find MT rise, spike counts decrease, FSL extend after injection, the results all have significant statistical differences.2 MGv neuronal electrical activity changes after unilateral cochlear ablation different time periods:in noise stimulation,(1)Firing pattern:the potential waveform of MGv neurons acoustic evoked response of control group is orderliness and regularity. Single acoustic evoked response potential waveform is obviously. Compared with the control group, ab groups acoustically induced reaction potential waveform have varying degree changes and spontaneous discharge increase.Compared in ab groups,we find that ab24h, ab7d, abl4d group,the spontaneous discharge evidently increase.And single acoustic evoked response potential waveform changes, mainly show several continuous and low firing waveform.There are no significant difference between ab groups. (2) MT:compared with control group, MT of MGv neurons of ab groups increased in different degree with the extension of the cochlea ablation time. Compared between each groups of ab,we find that MT of MGv neurons of ab30d group is obviously higher than that of ab4h, ab24h and ab7d group. (3) Spike counts: compared with control group, the spike counts of ab group MGv neuronal occur to varying degrees, among them, the spike counts of ab4h group, ab14d group and ab30d group reduce most obvious. There is no difference between each ab groups. (4) FSL: compared with control group, the FSL of MGv neurons of ab groups are extending in different degree, among them, the group of ab4h, FSL extend the most obvious. Compared between each groups of ab, we found that FSL of ab24h, ab7d, ab14d group and ab30d group MGv neurons is obviously shorter than ab4h group, among them, FSL of ab7d and ab14d group shorten the most obvious, whereas the FSL of ab24h group is longer than abl4d group. The results have significant differences.3 After cochlear ablation different time periods,the electrical activity changes of MGv neurons of ab ipsilateral of rats before and after the FC injection:under the pure tone stimulation, with the extension of cochlear ablation period,the MT, spike counts and FSL of ab ipsilateral MGv neurons have a oppositely change compares with ab early stage. MT and spike counts change results of ab30d group is oppositely in contrast with other groups of ab. FSL of ab7d group, abl4d group, group ab30d group is opposite with ab4h and ab24h group result. (1)MT:comparison in the group, after the injection of drugs FC, MT of ab4h, ab24h, ab7d group and abl4d group higher than no FC injection, while the MT of ab30d group below. Among them, the change of ab14d group is most obvious. Comparison between groups, ab4h and ab7d group compares ab30d, and ab4h group compares abl4d group has significant differences. (2) spike counts:comparison in the group found that after injection drug FC, spike counts of ab4h, ab24h, ab7d group and ab14d group less than no FC injection, while ab30d group more than before FC injection, among them, the ab4h group. Ab24h,ab7d group and ab30d group have most obvious changes. Comparison between groups, the change of ab4h, ab24h, ab7d group and ab14d group, compares with ab30d, ab24h, ab14d group compares with ab7d group, and ab4h group compares with ab24h group all have significant differences. (3) FSL:comparison in the group, after the FC injection, FSL of ab4h, ab24h group overall shorten than no injection, but ab7d, abl4d, ab30d group is extender, among them,the change of ab24h group and ab7d group is most obvious. Comparison between each groups, the change of ab24h group, ab7d and ab30d group compares with ab4h group has a significant difference.4 The study of acoustic response characteristics to different subregions of MGB neurons find:(1) under the pure tone stimulation, spike counts of normal group rats MGm significantly less than MGv and MGd.MT of MGv and MGm higher than the MGd. (2) After inject drugs FC, MGv neurons’s CF move to high frequency sound, and MT increased.But MGd, MGm neurons’s CF and MT remain unchanged.Conclusion1 Astrocytes function change can affect the acoustic response properties of MGv neurons.2 After rats unilateral cochlear ablation, MGv neuronal of the ipsilateral of ab happen plasticity changes.3 Astrocytes function change in different periods of cochlear ablation have different influence.With the time of cochlea ablation time extension, there have a oppositely change compares with ab early stage shows that astrocytes maybe involve in the process of MGv neuronal plasticity.4 Different changes of MGB neurons three partition (MGv, the action of the MGd, MGm) after astrocytes function changed.