Cytoarchitecture of auditory system in lower brainstem of the mustache bat, Pteronotus parnellii.

To begin an investigation of the auditory pathways in the brainstem of the mustache bat, we examined the cytoarchitecture of the cochlear nuclei, superior olivary complex, nuclei of the lateral lemniscus, and inferior colliculus. Although all of these auditory centers are hypertrophied in this echolocating bat, only some areas have unusual cytoarchitectural features: 1) In the anterior part of the anteroventral cochlear nucleus we do not find the large spherical cells seen in other mammals; instead, very small spherical cells are found in this area. 2) In the posterior part of the anteroventral cochlear nucleus there is a region containing a homogeneous population of very large multipolar cells. 3) The medial superior olive is unusually large for an animal with a small head. 4) The most striking observations are seen in the lateral lemniscus. The ventral nucleus of the lateral lemniscus has a distinct columnar organization. The intermediate area of the lateral lemniscus contains a large and very distinct nucleus. Each of these cytoarchitectural features distinguishes the auditory system of this bat from that of other mammals. The results raise questions about whether or not there are unique subdivisions in the auditory pathways of echolocating bats. The results also identify these unusual nuclei as candidates to play a role in the special auditory functions related to echolocation.