Inferior colliculus neurons that express the neuropeptide VIP project to auditory nuclei in the brainstem and thalamus. (P1.9-013)

Objective: To identify the distribution and projection of vasoactive intestinal peptide-expressing (VIP+) cells in the inferior colliculus (IC). Background: The IC is the main hub in the central auditory system, serving a critical role in the ascending and descending auditory pathways. The IC contains three major subdivisions with different functions. The lateral cortex helps localize sounds in space. The dorsal cortex serves auditory attention and vigilance. The central nucleus is involved in the main pathway for sound perception1. We hypothesized that VIP+ cells represent a functional subtype of IC neurons. Design/Methods: We used seven mice genetically engineered to express cre-recombinase and a red fluorescent protein in VIP+ cells. Three mice were used to identify the distribution of VIP+ cells. Five mice were stereotaxically injected with a virus into the left IC for selective labeling of VIP+ cell projection patterns. Four weeks after surgery, mice brains were fixed and sliced horizontally, coronally, or sagittally. Brain sections were viewed on a fluorescence microscope. A computerized system was used to analyze the distribution of VIP+ cells in the IC and to track their projections to IC targets in other brain regions. Results: VIP+ cells are expressed in all three subdivisions of the IC with a majority of the cells being in the dorsal cortex of the IC (>70%). We also found that VIP+ cells project to most major outputs of the IC, contributing to both ascending and descending auditory pathways. Conclusions: VIP+ neurons could contribute to perception, vigilance, and attention. They could play a role in our ability to filter sounds, allowing us to wake up to our crying child but not to a loud truck. Disclosure: Dr. Edelbrock has nothing to disclose. Dr. Beebe has nothing to disclose. Dr. Goyer has nothing to disclose. Dr. Silveira has nothing to disclose. Dr. Roberts has nothing to disclose. Dr. Schofield has nothing to disclose.