Fig. 3. Projection pattern of the sensory fibers in the medial nerve (MN). (A) The axons were stained by forward-filling from the cut end of the MN with tetramethylrhodamine–dextran. The preparation was counterstained with Lucifer Yellow to visualize the boundary of the tissue. Serial confocal optical slices were acquired and projected to a frontal plane. In the image, the tetramethylrhodamine–dextran-stained fibers were superimposed on the counterstained image of the brain. Axons originating from the MN run through the medial half of the antennal nerve (AN) and project into the antennal lobe (AL). (B) Projected AL image of optical sections at 50±20 µm in depth. The image is of the same preparation as that in A, with a high magnification. The macroglomerular complex (MGC) was always stained more densely than the ordinary glomeruli. The axons projecting to the MGC are biased towards the medial MGC; however, those projecting to the ordinary glomeruli distribute homologously to each ordinary glomerulus. (C) The projected image of the thick axons projecting to the antennal mechanosensory and motor center (AMMC; 105±20 µm in depth). Most of the thin axons running from the MN project to the AL anteriorly, and most of the thick axons project to the AMMC, passing through the posterior AL. (D–F) Confocal images of an anterior plane (D; 28 µm in depth), a medial plane (E; 50 µm in depth) and a posterior plane (F; 73 µm in depth) of the MGC. The MGC is composed of two compartments: toroid, which is a donut-shaped structure, and cumulus, which is a disk-shaped structure situated more proximally to the AN input. In both the anterior and the medial planes, the stained axons are biased towards the medial MGC: medial toroid and medial cumulus. In the posterior plane, the stained axons are distributed homologously. OL, optic lobe; cT, central toroid; mT, medial toroid; lT, lateral toroid; mC, medial cumulus; lC, lateral cumulus. Scale bar, 200 µm (A), 100 µm (B,C), 50 µm (D–F).