Diversity and wiring variability of visual local neurons in the Drosophila medulla M6 stratum.
Bottom Line: Based on the segregation of putative dendrites and axons, these local neurons were classified into two families, directional and nondirectional.Neurotransmitter immunostaining suggested a signal routing model in which some visual information is relayed by directional M6-LNs from the anterior to the posterior M6 and all visual information is inhibited by a diverse population of nondirectional M6-LNs covering the entire M6 stratum.Our findings suggest that the Drosophila medulla M6 stratum contains diverse LNs that form repeating functional modules similar to those found in the vertebrate inner plexiform layer.
Affiliation: Institute of Biotechnology and Department of Life Science, National Tsing Hua University, Hsinchu, 30013, Taiwan.Show MeSH
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Mentions: The nondirectional M6-LNs (n = 47) shared the common feature of spatially mixed dendrites and axons. These nondirectional M6-LNs were also highly variable in their morphology and spatial location. By aligning individual neurons with similar morphology into the common M6 retinotopic model, we found that nondirectional M6-LNs could be segregated into seven clusters, each cluster covering one distinct M6 subarea or domain (Fig. 5; in what follows, the seven clusters will be numbered 1–7 and neurons in them named as M6-LNn, where n is cluster number). Within each domain, individual neurons covered similar numbers, but different identities, of retinotopic columns, with extensive areal overlapping (Fig. 6A–C). Thus, together, but not individually, nondirectional M6-LNs with similar morphologies are likely covering all the retinotopic columns within each M6 domain (Fig. 6D–F). This is supported by the observation that arborizations from two sister M6-LN1s (Fig. 6G) or two sister M6-LN2s (Fig. 6H) in the same brain covered the same M6 domain as a single M6-LN1 (Fig. 5A) or a single M6-LN2 (Fig. 5B). We found that two sister M6-LN3s covered 91 columns in M6 (Fig. 6I), which is larger than but not twice as large as the coverage of a single of M6-LN3 (60.7 ± 5.0 columns; Table2), indicating a partial overlap and complementary coverage of retinotopic columns.
Affiliation: Institute of Biotechnology and Department of Life Science, National Tsing Hua University, Hsinchu, 30013, Taiwan.