Journal of Neuroscience, Vol 9, 2819-2834, Copyright © 1989 by Society for Neuroscience
Differential ascending projections to aural regions in the 60 kHz contour of the mustache bat's inferior colliculus
LS Ross and GD Pollak
Department of Zoology, University of Texas, Austin 78712.
The inferior colliculus of the mustache bat is similar in many respects to
the inferior colliculus of more commonly studied mammals. However, the
isofrequency contour devoted to processing 60 kHz, the dorsoposterior
division (DPD) is greatly expanded, encompassing an area approximately
equal to one-third of the central nucleus. Of particular significance is
that monaural and binaural neurons are segregated in the DPD into 4
spatially distinct aural regions. In this study we exploit the great
enlargement of the 60 kHz region in the central nucleus of the inferior
colliculus (ICc) of the mustache bat to determine the source of ascending
projections to the 4 different aural regions of the DPD. Small
iontophoretic deposits of HRP were made within each of the physiologically
defined aural regions, and the locations and numbers of retrogradely
labeled cells in the auditory brainstem nuclei were determined. Two major
features of collicular organization were found. The first is that each
aural region receives a unique set of projections from a subset of lower
auditory nuclei and thus is distinguished both by its neural response
properties and by the pattern of ascending projections it receives. The
dorsomedial EE region receives inputs primarily from the ipsilateral
intermediate nucleus of the lateral lemniscus (INLL) and ventral nucleus of
the lateral lemniscus (VNLL), and the contralateral ICc. In contrast, the
ventrolateral EE region receives projections from the ipsilateral medial
superior olivary nucleus (MSO), VNLL, and INLL. The inputs to the EI region
originate primarily from the dorsal nucleus of the lateral lemniscus (DNLL)
and lateral superior olivary nucleus (LSO) bilaterally and from the
ipsilateral INLL. The afferents to the EO region include the contralateral
cochlear nucleus, the ipsilateral VNLL and INLL and MSO. The second major
organizational feature is that the binaural nuclei of the brain-stem
project upon the DPD in a more restricted manner than do some of the lower
monaural nuclei, such as the VNLL and INLL, which project in a more
widespread manner. The unique set of projections terminating in each aural
region of the DPD suggests that the neurons should have substantially
different properties, even when neurons in different regions are of the
same general aural type. Moreover, the elucidation of the
micro-organization of the DPD provides insights into the different ways
that binaural properties of DPD neurons are created by the convergence of
inputs from particular subsets of lower auditory nuclei.(ABSTRACT TRUNCATED
AT 400 WORDS)
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