Some Comparative Aspects of Auditory Brainstem Cytoarchitecture in Echolocating Mammals: Speculations on the Morphological Basis of Time-Domain Signal Processing
A number of studies have described the gross morphology and general hypertrophy of the auditory brainstem nuclei in Cetacea and Chiroptera (See Henson, 1970 for review; Zvorykin, 1959, 1963). However, there have been only a few attempts to describe the cytoarchitecture of the auditory brainstem in detail (Osen & Jansen, 1965; Schweizer, 1981; Zook & Casseday, 1982) or to make comparisons of brainstem auditory cytoarchitecture between echolocating species of bats and marine mammals. We will begin here to take a closer look at the auditory brainstem of a number of microchiropteran and odontocete cetacean species, initially focusing upon a few distinctive cytoarchitectonic patterns found in three cell groups: the anteroventral cochlear nucleus (AVCN), the medial nucleus of the trapezoid body (MNTB) and the ventral nucleus of the lateral lemniscus (VNLL). In some species of bat and dolphin, cells in these nuclei form orderly rows or columns that are more uniformly aligned than is found in most nonecholocating mammals. In the two dolphin species examined, rows of cells perpendicular or at an angle to the fibers of the trapezoid body are present in the caudal part of the AVCN and in the MNTB. Within the VNLL in some bat species there is a distinctive alignment of cell soma, in columns rather than rows, parallel to fiber bundles.
KeywordsInferior Colliculus Cochlear Nucleus Bottlenose Dolphin Caudal Part Eighth Nerve
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