Dissection Of Cross-streams Through The Ventral Posteromedial Thalamic Nucleus By Optical Imaging

Neural circuit is the basic unit that constitutes the nervous system of the brain,and plays a very important role in the transmission and processing of neural information.The rodent’s modular whisker sensory system is one of the classic models for studying neural circuits and neural information processing.It is generally believed that rodents perceive external information through whiskers,and convey sensory information to the sensory cortex through two main parallel pathways consisting of the Lemniscal 1 pathway and the extralemniscal pathway.The ventral posteromedial thalamic nucleus(VPM)is an important relay nucleus of two main parallel pathways,which integrates and conveys information from multiple whiskers to the barrel-like structure of the primary somatosensory cortex(S1).However,studies have continued to observe that when the pathway of the multi-whisker information integration of barrel neurons is damaged,barrel neurons still have the functional characteristics of multi-whisker information integration.This means that there may be a neural pathway that mediates the cross-streams when the two main parallel pathways pass through the VPM nuclei.However,as result of the lack of direct evidence,there is still controversy as to whether there is a cross-streams when the two main parallel pathways pass through the VPM nuclei.This study intends to provide evidence for answering these questions from a fine anatomical perspective using optical neuroprojection imaging.A method for obtaining the fine morphology of single VPM neurons by optical imaging was established using the Cre-dependent dual virus system as a neural tracer,and the chemical sectioning fluorescence tomography system(CSFT)and the Neuro GPSTree reconstruction software independently developed by the laboratory to analyzing the downstream output circuit of VPM neurons.At the same time,the upstream input circuit of VPM neurons from trigeminal the trigeminal nucleus spinalis(Sp5i)was analyzed,using retrovirus labeling system with the canine adenovirus type 2.The main research contents are as follows:(1)The study of VPM neurons mediate cross-streams.First,we obtained single-cell projection data of VPM neurons,established a long-range projection map of different VPM neuron projection types in the whole brain,and discovered a new type of VPM neurons projecting to the barrel structure.This result provides anatomical evidence that VPM neurons mediate down cross-streams.Second,we found that Sp5 i neurons project to the dorsomedial section of VPM(VPMdm)in addition to the ventral lateral part of VPM(VPMvl)previously studied.This result provides anatomical evidence that VPM neurons mediate up cross-streams.(2)Morphological characteristics analysis of different VPM neuron projection types.Based on the neuron morphological analysis method,this paper analyzes the morphological and structural characteristics of VPM neurons,and know about VPMvl-cross neurons are consistent with VPMc neurons in the input and output in most brain regions and the interlayer projection pattern of primary somatosensory cortex,are and significantly different from VPMvl-type neurons.In conclusion,single-cell optical imaging was used to investigate the projection patterns of VPM neurons downstream to the cerebral cortex and the projections of Sp5 i neurons to VPM nuclei.The results provide anatomical evidence for the existence of cross-streams in the VPM nuclei for the two major parallel pathways in the whisker sensory system to support VPM neurons mediating the cross-streams.This study may provide a missing connection circuits for barrel neurons to process and integrate external information by whiskers,lay a foundation for further exploration of the function of barrel neural circuits,and also provides an exploratory example for the study of fine neural circuit structure.