The Journal of Neuroscience, August 15, 2001, 21(16):6264-6273
Increasing the Number of Synapses Modifies Olfactory
Perception in Drosophila
Angel
Acebes and
Alberto
Ferrús
Instituto Cajal, Consejo Superior de Investigaciones
Científicas, Madrid E-28002, Spain
The Drosophila mutant gigas produces
an enlargement of postmitotic cells caused by additional rounds of DNA
replication. In neurons, the mutant cell establishes more synapses than
normal. We have taken advantage of this feature to study the effect of synapse number on odorant perception. Mosaic adults were generated in
which one antenna was homozygous for gigas, whereas the
contralateral side served as an internal control. Morphological
analysis indicates that the number and type of sensory afferents
forming the mutant antenna, as well as their projection to the
olfactory glomeruli, are normal. In contrast, the volume of identified
glomeruli increases to a variable extent, and mutant sensory neurons
branch profusely. The number of synapses, estimated in the ventral
(V) glomerulus that receives ipsilateral afferents only, is
increased twofold to threefold. Large-dense-core vesicle-containing
terminals that probably modulate olfactory centers are identified in
the V glomerulus. Their number and size are not modified by the mutant
input. Sensory transduction, measured by electroantennograms, is normal
in amplitude and kinetics. In odorant tests, however, the profile of
the behavioral response to ethyl acetate shows attractive responses to
concentrations to which sibling controls remain indifferent
(10
8 and
107 v/v). In addition, the
intensity of the response is augmented both at attractive and repulsive
odorant concentrations with respect to that of controls. These results
demonstrate that increased synapse number in the sensory neurons can
modify the behavior of the organism, allowing a higher sensitivity of perception.
Key words:
olfaction; sensory perception; gigas; synapse
number; olfactory glomeruli; Drosophila
Copyright © 2001 Society for Neuroscience 0270-6474/01/21166264-10$05.00/0
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