The Journal of Neuroscience, March 1, 1999, 19(5):1771-1781
Neural Mapping of Direction and Frequency in the Cricket Cercal
Sensory System
Sussan
Paydar2,
Caitlin
A.
Doan2, and
Gwen A.
Jacobs1
1 Center for Computational Biology, Montana State
University, Bozeman, Montana 59717, and 2 Department of
Molecular and Cell Biology, University of California, Berkeley,
California 94720
Primary mechanosensory receptors and interneurons in the cricket
cercal sensory system are sensitive to the direction and frequency of
air current stimuli. Receptors innervating long mechanoreceptor hairs
(>1000 µm) are most sensitive to low-frequency air currents (<150
Hz); receptors innervating medium-length hairs (900-500 µm) are most
sensitive to higher frequency ranges (150-400 Hz). Previous studies
demonstrated that the projection pattern of the synaptic arborizations
of long hair receptor afferents form a continuous map of air current
direction within the terminal abdominal ganglion (Jacobs and
Theunissen, 1996). We demonstrate here that the projection pattern of
the medium-length hair afferents also forms a continuous map of
stimulus direction. However, the afferents from the long and
medium-length hair afferents show very little spatial segregation with
respect to their frequency sensitivity. The possible functional
significance of this small degree of spatial segregation was
investigated, by calculating the relative overlap between the long and
medium-length hair afferents with the dendrites of two interneurons
that are known to have different frequency sensitivities. Both
interneurons were shown to have nearly equal anatomical overlap with
long and medium hair afferents. Thus, the differential overlap of these
interneurons with the two different classes of afferents was not
adequate to explain the observed frequency selectivity of the
interneurons. Other mechanisms such as selective connectivity between
subsets of afferents and interneurons and/or differences in interneuron
biophysical properties must play a role in establishing the frequency
selectivities of these interneurons.
Key words:
sensory maps; sensory system; insect; functional
neuroanatomy; three-dimensional reconstruction; mechanosensory
receptors
Copyright © 1999 Society for Neuroscience 0270-6474/99/1951771-11$05.00/0
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