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Page 14 of 24 Neuroimmunol Neuroinflammation 2019;6:15 I http://dx.doi.org/10.20517/2347-8659.2019.019

SOD1 G93A mice, further validating the C5a-C5aR1 signalling axis as a potential therapeutic target to slow
disease progression in MND.

19. Gap junction network within an olfactory sensory unit for colony identification in the
Japanese carpenter ant: 3D structure and putative function

Tatsuya Uebi, Mamiko Ozaki

Department of Biology, Graduate School of Science, Kobe University, Kobe, Japan

The environment is filled with chemical information, and animals, including human beings, have developed
adaptive chemosensory systems. It is thought that the chemical information is integrated in the brain before
making a decision. Here, I talk about a complicated olfactory sensory system of a tiny insect, the carpenter
ant, Camponotus japonicus, because we recently found an information integration network at this very
peripheral system. For colony identification, worker ants utilize a colony-specific body odor consisting a
characteristic blend of cuticular hydrocarbons (CHCs) as a social pheromone. C. japonicus workers appeal
to their own colony identification with the colony-specific body odor comprising 18 species-specific CHCs.
Thus, the accurate difference detection among such colony-specific body odors of workers is indispensable
for their social life while inaccurate difference detection is sometimes fatal in competition among colonies.
The body odor CHCs is sensed in a particular type of olfactory organ called Sensilla basiconica on the
antennae. The number of S. basiconica responding to own colony’s CHCs was significantly smaller than that
responding to other colony’s CHCs. This suggests that the very peripheral tiny sensory system possesses a
whole basic machinery for colony identification via odor difference detection. To investigate the functional
design of this type of sensilla, we observed its ultra-structures, using a serial block-face scanning electron
microscope (SBF-SEM). Based on the serial images of 352 cross sections of SBF-SEM, we reconstructed a
3D model of the sensillum. This model reveals that each S. basiconica houses > 100 unbranched dendritic
processes, which extend from the same number of olfactory receptor neurons (ORNs). The dendritic
processes have characteristic beaded-structures and form a twisted bundle within the sensillum. At the
beaded-structures, the cell membranes of the processes are closely adjacent in the interdigitated profiles,
suggesting functional interactions via gap junctions (GJs). Immunohistochemistry with anti-innexin
(invertebrate GJ protein) antisera revealed positive labeling in the antennae of C. japonicus. Innexin 3, one
of the five antennal innexin subtypes, was detected as a dotted signal within the S. basiconica as a sensory
organ for colony identification. The fluorescence intensity of innexin 3 shows a characteristic twin-peak-
distribution similar to the distribution of adhesion regions at beaded-structures. These morphological
results suggest that the beaded-structure provides a platform for functional connection among ORNs via
close apposition of membranes and ORNs form an electrical network via GJs between dendritic processes.
To reveal the function of the ORNs network via GJs, we examined a simplified mathematical simulation
for the inter-dendritic neural network based on cable theory and proposed possible modification of its
responsiveness to virtual stimulation. The mathematical simulation showed that the information network
acts as a “stronger-input-spread or weaker-input-cut filter” in a GJ-distribution-dependent manner. This
novel “filter” supports that ORNs in the S. basiconica generate few impulses when they respond to own
colony’s CHCs (weak stimulation) and generate many impulses when they respond to other colony’s CHCs
(strong stimulation). Therefore, the ORN network via GJs possibly contributes to the distinct identification
of colony-specific blends of CHCs.