Journal of Neurophysiology, Vol 64, Issue 6 1861-1872, Copyright © 1990 by APS
Spectral sensitivities of elementary color-coded neurons in butterfly larva
T. Ichikawa
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan.
1. Response properties and spectral sensitivities of a functional class of
medulla neurons that received dominant input from a single stemma in the
swallowtail butterfly larva were examined with regard to neutral and
chromatic backgrounds. 2. Eight types of neurons were dominated by a
dichromatic stemma with blue and green receptors. Six showed specific
color-opponent responses mediated by two receptors on different
backgrounds; one showed strong color opponency because of fairly balanced
antagonistic input on the neutral (dark and white) background; the other
five usually had weak or concealed color opponency on a neutral background
but became strongly color opponent when appropriate chromatic illumination
was present on the background. The most complex neuron gave excitatory
responses on a dark background, inhibitory responses on a white background,
and color-opponent responses on a chromatic (yellow) background. 3. The
remaining two types of neurons dominated by the dichromatic stemma showed
non-color-opponent and broad action spectra ascribable to a synergistic
effect of the two classes of photoreceptors. 4. All eight types of neurons
dominated by a trichromatic stemma (with UV, blue, and green receptors)
were color opponent. Five showed strong color-opponent responses with the
mediation of the three classes of receptors or only two (UV and green) on a
neutral background. The others revealed distinct color opponency in the
presence of UV or green illumination on the background. 5. The larval
medulla neurons described may form parallel, elementary color-coded
channels in the medulla neuropile to combine the outputs of the different
color receptors in a single visual unit (stemma) into specific
color-opponent signals. They probably correspond to columnar relay neurons
in the medulla of the adult insects with a compound eye.
