| Abstract #582, Date 2/16/99, Session R3, Poster (B82) |
| Ascending projections of the cochlear nucleus in the Egyptian fruit bat (Rousettus aegyptiacus) |
| *K.A. Hutson, M.L. Kieber (Univ. of Toledo) |
Recently we have investigated whether environmental pressures leading to differing auditory “lifestyles” among bats have also led to variation in basic hearing abilities, and to differing or specialized brains. Behavioral investigations of the Egyptian fruit bat (Rousettus aegyptiacus) suggest that the hearing range and sound localization abilities of this species do not differ significantly from those found in other small mammals with similar head size. Furthermore, the cytoarchitectural organization of auditory brainstem structures in this species does not reveal any significant deviations from the general mammalian plan. Nonetheless, the genus Rousettus is unique among Chiroptera. While not reliant on echolocation as a foraging strategy, members of this genus use a crude form of echolocation (tongue “clicks”) to assist in navigation. To further investigate the possibility of neurological specialization, we have begun to use standard tract tracing techniques to examine the central auditory pathways in the Egyptian fruit bat. Here we present our findings on the ascending projections of their cochlear nucleus. Brainstem projections originating from the Egyptian fruit bat’s cochlear nucleus (CN) were studied using anterograde transport of BDA injected into CN via glass micropipettes. Overall, the pattern of anterograde labeling was similar to that seen in other mammals. As expected, the CN projects bilaterally to innervate many auditory brainstem structures. Contralateral targets heavily labeled include MTB, VTB, MSO, LSO, CN, VLL, LL, DLL, and IC. The heaviest ipsilateral projections were to LTB, LSO, and MSO. Though less abundant, the CN also projects ipsilaterally to VLL, ILL, DLL, and IC. Of these ascending projections, two do not conform to the general mammalian plan, and may represent neurological specialization in the Egyptian fruit bat: the extent of the ipsilateral projection to VLL, and perhaps more importantly, the robust nature of the commissural projection to the contralateral CN (see Kieber and Hutson, this meeting). |