Descending engagement of brainstem neuronal circuits that govern orofacial motor behaviors

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PROJECT SUMMARY I propose to investigate the neuronal control of orofacial behaviors in rodents. Orofacial behaviors in mature rodents include ingestive behaviors such as licking and chewing, as well as exploratory behaviors, such as sweeping movements of the facial whiskers, or “whisking”, sniffing, and directed nose and head movements. Infants engage in suckling behavior, which involves both exploratory nipple-seeking movements and ingestive sucking movements. The mammalian brainstem contains networks of neurons that control all of these orofacial behaviors, and these networks are directed by other, more rostral parts of the brain that ensure that the associated behaviors are executed in the appropriate context; that is, when the appropriate environmental and internal sensory cues are present. I intend to investigate how these higher-order brain areas influence the appropriate brainstem network modules to implement the animals’ decision to execute an appropriate orofacial motor act. In the mentored phase of the project, I will focus on identifying the neuronal circuit mechanisms that underlie suckling behavior in newborn mice, a topic which, despite its importance for mammalian survival, has been largely ignored by neuroscientists in recent years. To identify neuronal cell-types that are active during suckling, I have been measuring the co-expression of immediate-early-genes along with cell-type specific molecular markers. I can then use the identified neuronal cell-type markers as genetic entry-points to trace the neuronal circuits they comprise. At the same time, I have been developing new viral vector tools to rapidly deliver modern molecular tracers and actuators to the early postnatal mouse brain to probe the mechanisms by which these neuronal circuits code suckling behavior. During the award period, I will use these new tools to (1) map the input/output connectivity of identified suckling-active neuronal populations, and (2) manipulate the activity of these populations in-vivo to determine their roles in generating and maintaining suckling behavior. In the independent phase I will extend my focus to the broader repertoire of ingestive and exploratory orofacial behaviors in adult mice, with the goal of understanding (3) how forebrain inputs to brainstem orofacial pre- motoneurons may gate the expression of these behaviors depending on the environmental and motivational context. Investigating the brainstem modules for such innate motor acts represent an ideal model for studying how networks of connected neurons in the brain control simple behaviors and how nervous systems make decisions. The mentored phase of the project, conducted under the direction of Dr. Catherine Dulac at Harvard University and Dr. Samuel Pfaff at the Salk Institute, outlines a comprehensive plan for the acquisition of a unique combination of technical and professional skills that will enable my transition to an independent research position.