Connexin36 expression in the cochlear nucleus complex of the echolocating bat, Eptesicus fuscus

Gap junctions and electrical synapses in the central nervous system are associated with rapid temporal processing and coincidence detection. Using histology, immunohistochemistry, and in situ hybridization, we investigated the distribution of Connexin36 (Cx36), a protein that comprises neuronal gap junctions, throughout the cochlear nucleus complex of the echolocating big brown bat, Eptesicus fuscus, a species exhibiting extreme behavioral sensitivity to minute temporal changes in ultrasonic echoes. For comparison, we visualized Cx36 expression in the cochlear nucleus of transgenic Cx36 reporter mice, species that hear ultrasound but do not echolocate. We observed Cx36 expression in the anteroventral and dorsal cochlear nucleus, with more limited expression in the posteroventral cochlear nucleus, of both species. Several different morphological cell types were labeled, including globular and spherical bushy, octopus, stellate, and fusiform cells. Labeled Cx36 puncta were also observed. Cx36 expression in the bat was spread throughout a relatively smaller area of the cochlear nucleus than in the mouse, even though the bat cochlear nucleus is hypertrophied. In the bat, the anteroventral cochlear nucleus showed higher percent area label than the dorsal cochlear nucleus, with a trend towards the opposite result in the mouse. The presence of gap junctions appears to be a conserved feature of the mammalian cochlear nucleus and thus not uniquely tied to the temporal hyperacuity of echolocation.