The Dispersion Characteristics Of Efferent Projections In Mouse Motor Cortex

Motor cortex(MC),as an important part of cerebral cortex,participates in motor learning,motor planning and motor control,according to its functions of cortex,which is divided into primary motor cortex(M1)and secondary motor cortex(M2).Neurons in MC project to three brain regions,thalamus(TH),striatum(STR),and spinal cord(SC),to form specific neural circuits.The development of degenerative psychiatric diseases(Amyotrophic lateral sclerosis,Huntington’s disease,and Parkinson’s disease)is closely related.The pattern of MC to downstream one-to-one has been elucidated,and neurons with dispersion projection properties in mice project to two downstream neurons simultaneously.However,it is unclear whether the mouse motor cortex has a dispersion projection pattern to the major downstream brain regions.We believe that the study of the dispersion projection characteristics of the neurons in the mouse motor cortex to the main downstream brain regions will provide valuable reference information for studying the function of neural circuits.In this study,we used an improved retro-AAV/2 virus labeling tool with two different colors,through its retrograde labeling properties along axon terminals,to study the VAL(ventrolateral thalamic nucleus)and VM(ventromedial thalamic nucleus),DLSTR(dorsolateral striatum)and DMSTR(dorsomedial striatum)of the striatum,and motor cortex to subregions of different brain regions,the thalamic VM and striatal DLSTR subregions,thalamic VM and C7(cervical spinal cord segment7),striatal DLSTR and C7 dispersion projection regularity.The results of this study show that:(1)No matter in the projections of mouse MC to different subregions of the same brain region or different brain regions,there are neurons with dispersion properties in the projection neurons.(2)In different subregions of the same brain region,the ratio of dispersion projection neurons in MC to VAL is higher than that of VM projections in total projection neurons,and the ratio of dispersion projection neurons in MC to DLSTR is higher than that of DMSTR projections in total.(3)In different brain regions,there was no significant difference in the ratio of dispersion projection neurons in MC to VM and to DLSTR projections in total projection neurons,but MC to DLSTR compared to C7 projections in total projection neurons.The ratio of neurons was higher,and the ratio of dispersion projection neurons to total projection neurons was higher in MC to C7 than to VM projections.(4)In the projections of MC to DLSTR and DMSTR of the striatum,there is a spatial difference in the distribution of neuronal populations with dispersion properties between M1 and M2.In MC projections to the thalamus and striatum,neuronal populations with dispersion properties were also spatially differentially distributed between M1 and M2.This paper preliminarily explores the rule of diffuse projection in the motor cortex,and lays a foundation for the study of information coding in the motor system through diffuse projection,which is of great significance to the functional research and clinical treatment of motor control neural circuits.