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Abstract

The rodent vibrissal system offers an ideal model for studying sensory-motor pathways in the mammalian central nervous system. There has been much consideration to bring insight to the organization of the whisker sensory pathways throughout the rodent brain. However, it is poorly understood how brain-wide whisker motor pathways are organized and how, together with sensory pathways, they constitute a sensory-motor loop that can provide sensory feedback to the whiskers during tactile-based behaviors. It has been previously reported that whisker muscles are directly innervated by vibrissal motor neurons(vMN) located in the lateral area of the Facial Nucleus(FN) and that these vMNs are directly innervated by output neurons of the vibrissal motor cortex (Herfst and Brecht, 2007). It has also been suggested that this vibrissal motor area of the cortex is divided into two segregated regions. 1) A sensory input area called the Transitional Zone (TZ) and 2) a whisker motor output area called vM1 (Smith Alloway, 2013; Matyas et al., 2010). In this study we inject wild type rabies virus into the mystacial pad targeting a single muscle that is wrapped around a whisker follicle. The virus is transported retrogradely across multiple synapses throughout the central nervous system in a time dependent manner (Kelly and Strick, 2000), first labeling vMNs located in the FN and subsequently the hierarchy of pathways that provide input to these motor neurons. Combining this injection method with custom-designed brain-wide imaging techniques and automated somata detection software (Oberlaender et al., 2009), we provide unprecedented quantitative insight to the organization of the whisker motor pathways, setting the stage to investigate how cortex provides sensory feedback to peripheral receptor organs during sensory-motor tasks.