Nadia F. McMillan
B.A. Johns Hopkins University, 2009

2nd Year Medical Student

Advisor: TBD

Department: School of Medicine

Graduate Program: TBD

Title:  Reciprocal Connectivity Between the Central Nucleus of the Inferior Colliculus and the Dorsal Cochlear Nucleus of the CBA/CaJ Mouse

Advisor: David Ryugo, Department of Otolaryngology, Johns Hopkins University

Abstract (undergraduate):

Michael A. Muniak¹, Vikas N. Kodali¹, Makoto Tanigawa¹, Catherine J. Connelly¹, Kristyna Hnizda¹, Nadia F. McMillan¹,
Tan Pongstaporn², David K. Ryugo¹,^2
1Johns Hopkins University, ²Garvan Institute of Medical Research

       Recent observations suggest that descending projections in the brain outnumber ascending ones (Winer and LaRue,1987; Jones, 2000), but few reports have been published that describe the synaptic organization of these projections. Descending pathways are an essential element of sensory systems, and may facilitate the real-time modification of neural responses to external stimuli at any stage from periphery to cortex. In the auditory system, the cochlear nucleus (CN) is key because it initiates all ascending pathways, including a direct contralateral projection to the inferior colliculus (IC). Studies of descending projections in rat and guinea pig suggest that colliculo-cochlear nucleus projections originating in the central nucleus of the IC (CNIC) terminate bilaterally and topographically in the dorsal CN (DCN, Caicedo and Herbert, 1993; Malmierca et al., 1996). We have confirmed this projection in the CBA/CaJ mouse by using multiunit recordings and dye injections in the CNIC. The frequency of the IC injection site matches the frequency location in the DCN as determined by a 3-D frequency atlas created for the mouse CN (Muniak et al., 2011). Moreover, by applying anterograde (dextran amines) and retrograde (beta subunit of cholera toxin) tracer injections in CNIC, we were able to demonstrate that anterogradely labeled descending projections form bouton contacts in close proximity to retrogradely labeled cells in the contralateral DCN. This relationship suggests that the descending pathway from CNIC terminates on the same DCN neurons from which the ascending projections originate. If such synaptic connectivity is verified using electron microscopy, it would provide a direct pathway for modulating ascending auditory information, and could be involved in “egocentric feedback” enhancing signal discrimination and/or underlying selective attention.

Publications:
(pre-MSTP publications indicated with an *)

*"Abernathy’s Surgical Secrets." Crisostomo PR, McMillan A, Meldum DR. Lung Transplantation(Chapter), pp 439-444. In "Surgical Secrets", Sixth Edition, Eds. Harken and Moore, Mosby, 2008.