Connexin36 RNA Expression in the Cochlear Nucleus of the Echolocating Bat, Eptesicus fuscus

The echolocating bat is used as a model for studying the auditory nervous system because its specialized sensory capabilities arise from general mammalian auditory percepts such as pitch and sound source localization. These percepts are mediated by precise timing within neurons and networks of the lower auditory brainstem, where the gap junction protein Connexin36 (CX36) is expressed. Gap junctions and electrical synapses in the central nervous system are associated with fast transmission and synchronous patterns of firing within neuronal networks. The purpose of this study was to identify areas where CX36 was expressed in the bat cochlear nucleus to shed light on auditory brainstem networks in a hearing specialist animal model.

We investigated the distribution of CX36 RNA throughout the cochlear nucleus complex of the echolocating big brown bat, Eptesicus fuscus, using in situ hybridization. As a qualitative comparison, we visualized Gjd2 gene expression in the cochlear nucleus of transgenic CX36 reporter mice, species that hear ultrasound but do not echolocate.

In both the bat and the mouse, CX36 is expressed in the anteroventral and in the dorsal cochlear nucleus, with more limited expression in the posteroventral cochlear nucleus. These results are generally consistent with previous work based on immunohistochemistry.

Our data suggest that the anatomical substrate for CX36-mediated electrical neurotransmission is conserved in the mammalian CN across echolocating bats and non-echolocating mice.