The cerebellum consists of parallel parasagittal modules that contribute to diverse behaviors, spanning motor to cognitive. Recent work illustrating a role for the anterior interposed nucleus (IntA) in reach control in mice raised questions of its anatomical organization that could confer functional specificity. We employed intersectional cell- and projection- specific labeling methods to map IntA inputs and outputs. In contrast to long-standing dogma of primarily excitatory outputs and restricted inferior olive targeting inhibitory output, we found that inhibitory IntA neurons ramified widely within the brainstem, targeting both motor- and sensory-related nuclei, suggesting potential functional roles in disinhibitory control or predictive sensory cancellation. Using monosynaptic rabies tracing, we then found that excitatory output neurons receive fewer and more precisely organized inputs than inhibitory neurons, which may set them up for distinct computations. Together these data suggest IntA contains at least two distinct output circuits and promise advances in identifying parallel computations of the cerebellum.

The overall object of this project is to create a 3D model of the cerebellum in order to illustrate the anatomical organization of Purkinje neurons, and to provide a better understanding of how they are integrated into other locations of the brain. Because the communication between the cerebrum and cerebellum is a closed system of polysynaptic circuits, understanding the underlying anatomy and physiology is a significant challenge. Classic staining techniques do not have the resolution nor the sophistication to capture the complete organization of the cerebellar cortex, let alone the entire cerebrocerebellar circuit. To overcome this challenge, a more precise staining technique has been developed to understand the complex functional organization of the cerebellum. Using a genetically modified variant of the rabies virus, neural connectivity can be imaged with extreme detail. The rabies is modified so that the glycoprotein required for the trans‐synaptic jump is deleted and replaced with a GFP protein, thus creating the ability to accurately label the connections to a single neuron. As a result of this staining technique, the Purkinje neurons can be traced using the cutting edge tracing software Neurolucida. The traced Purkinje cell somas and their axons can then be rendered in 3D and used for analysis and quantification. Having the ability to visualize the origin of the axons of specific cell types that communicate with the deep cerebellar nuclei in high 3D resolution may begin to provide an understanding of how the input of Purkinje cells is integrated with other excitatory inputs from elsewhere in the brain. Moreover, a 3D model of the cerebellum could also provide a more complete explanation of how the cerebellum quickly and accurately coordinates the inputs and outputs into movement, and is able to predict body movements in space.Support or Funding Informationhttps://www.sciencedirect.com/science/article/pii/0306452284901933This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.