A connectome and analysis of the adult Drosophila central brain

Abstract

The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the evolution of the fly's brain.

Parallel Visual Pathways with Topographic versus Nontopographic Organization Connect the Drosophila Eyes to the Central Brain

“…Nevertheless, it should be noted that the total number of subdomains remains the same in both nomenclatures, with the major difference being the posterior-lateral subdomain (‘lp’), which has been attributed to the central domain (SU-c p ) in our study, as part of the Connectin-positive central neuropil. Based on the connectome reconstruction of the hemibrain dataset ( Scheffer et al, 2020 ), which reports in a total number of 347 MeTu neurons (‘MC61-type’), we estimate 60 MeTu neurons per topographic class (and twice that for MeTu-m cells), assuming an equal innervation of SU subdomains of similar volume. Because we counted 8–12 TuBu neurons from three independent expression lines, we estimate a convergence ratio from MeTu to TuBu neurons of about 8:1 to 5:1.…”

An unbiased template of the Drosophila brain and ventral nerve cord

“…More recently, Xu et al [ 55 ] released the Drosophila “hemibrain” dataset, a focused ion bean scanning electron microscopy (FIBSEM) image volume, along with neuronal reconstructions. We have also created a transformation from our template to the hemibrain dataset and made it publicly available.…”

“…The process we used to create the transform for the hemibrain is similar to that for FAFB. We processed and downsampled a synapse prediction [ 55 ] to create a synthetic synapse density image, which was registered to the template as above. Registration was somewhat more challenging for FAFB, given that the the hemibrain image does not cover the entire brain.…”

Cell types and neuronal circuitry underlying female aggression in Drosophila

“…Drosophila melanogaster provides a good model for dissecting the neuronal circuitry of aggression due to the genetic tools available for targeting and manipulating individual cell types, the availability of extensive connectomic information, and the relative simplicity of its nervous system and behavior ( Bellen et al, 2010 ; Dionne et al, 2018 ; Kravitz and Huber, 2003 ; Scheffer et al, 2020 ; Simpson and Looger, 2018 ; Tirian and Dickson, 2017 ). In male flies, studies investigating the neuronal correlates of aggression have implicated a group of 18–34 cells in the central brain, the P1/pC1 cluster, as well as various neuropeptides and biogenic amines, including neuropeptide F, tachykinin, and octopamine ( Alekseyenko et al, 2019 ; Alekseyenko et al, 2014 ; Asahina, 2018 ; Asahina, 2017 ; Asahina et al, 2014 ; Dierick and Greenspan, 2007 ; Hoopfer et al, 2015 ; Hoyer et al, 2008 ; Ishii et al, 2020 ; Wohl et al, 2020 ; Wu et al, 2020 ; Zhou et al, 2008 ).…”