| Brain-derived neurotrophic factor(BDNF)is an important active substance in the brain,which is involved in the proliferation,regeneration,differentiation,growth,survival,electrophysiology,neurotransmitter transmission and synaptic plasticity of nerve cells,and plays an important role in learning and memory.In songbirds,it was found that BDNF affects the newborn neurons,sex dimorphism and seasonal plasticity of neural structures and song behavior.The song behavior of songbirds is similar to human language function,which is a kind of sensory-motor learning process and an important model for studying learning and memory.The song behavior of songbirds is controlled by a group of song-related nuclei,in which the robust nucleus of the Arcopallium(RA)in the forebrain is the premotor nucleus.The electrophysiological activity of projection neurons in RA is closely related to the characteristics of birdsongs,and the change of its electrophysiological activity will lead to the change of birdsongs.Studies have shown that the injection of BDNF into adult songbird RA can cause changes in structure of birdsong.However,the underlying cytological mechanism remains unclear.It is necessary to confirm whether BDNF influences song behavior by changing excitability,intrinsic membrane properties and synaptic transmission of RA projection neurons.Methods:The whole-cell patch-clamp recording technique and extracellularelectrophysiological recording technique were used to study the effects of BDNF on the excitability,intrinsic membrane properties and excitatory synapse afferent of the premotor nucleus RA projection neurons of adult male zebra finches(a representative species of songbirds)in vitro.Results:1.The results of whole-cell current clamp recording show that BDNF caninduce a small increase in the number of evoked action potentials of RA projection neurons in adult male zebra finches,indicating that BDNF slightly increases the excitability of RA projection neurons,but the change of membrane potential was not significant.The effects of BDNF were blocked by its receptor Trk B(tropomyosin receptor kinase B)antagonist K252 A.In addition,the results show that BDNF had no effect on the input impedance membrane of RA projection neurons.2.The results of whole-cell voltage clamp recording show that BDNF slightly increased mEPSCs' frequency of RA projection neurons in adult male zebra finches,but did not change its amplitude.This effect was blocked by Trk B antagonist K252 A.These results confirm that BDNF enhances excitatory synaptic transmission in RA projection neurons of adult male zebra finches,and suggest that the effect is caused by a presynaptic mechanism.The results also suggest that the enhancement of BDNF on the excitatory synapse transmission in RA projection neurons may be an important reason of the increasement of excitability of RA projection neurons.In addition,BDNF did not affect the rise time,decay time and half-width of mEPSCs.3.The results of field potential recording in vitro show that BDNF slightly increased the amplitude of f EPSP in the HVC-RA pathway in adult male zebra finches,indicating that BDNF slightly enhances the synaptic transmission of HVC-RA pathway in adult male zebra finches.And the effect of BDNF was blocked by Trk B antagonist K252 A.Conclusion:BDNF can enhance the excitatory synaptic afferent and excitability of RA projection neurons through its receptor Trk B,which may be related to the presynaptic mechanism.It is suggested that these induced changes in electrophysiological characteristics of RA projection neurons could be an important mechanism of BDNF regulating song behavior of songbirds.Understanding the neurophysiological regulation of BDNF on song behavior of songbirds can provide important theoretical references for understanding neural activity,the encoding of sensory motor integration and the relationship between brain and behavior,and even human language learning and the solution of some nervous system diseases. |
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