An Integrated Micro- and Macroarchitectural Analysis of the Drosophila Brain by Computer-Assisted Serial Section Electron Microscopy
(A–F) Structure of the VNC microvolume. (A) Representative section of VNC stack; profiles of all globular, varicose, and axiform neurites are tinted in shades of green and blue. (B, C) 3D digital model of these processes (B: frontal view; C: fronto-lateral view; red lines in these and other panels show edges of VNC microvolume; yellow dots indicate corner points). Note bundle formed by axiform neurites (arrow in A–C); another bundle of preterminal axons (light green; arrowhead) enters the microvolume from ventro-lateral. Presynaptic sites are colored red. (D) Representative section of VNC microvolume; dendritiform neurites are colored in shades of yellow and brown. (E, F) 3D digital model of all dendritiform processes in frontal view (E) and fronto-lateral view (F). (G–I) Dense overlapping regulon motif. One “primary” presynaptic neurite (“a”; bright green) contacts 12 postsynaptic dendritiform neurites (yellow-brown) at three synapses. Seven other “secondary” presynaptic elements (transparent green) are also presynaptic to these dendrites. Panel G shows representative section in which elements forming part of this motif are shaded; (H) and (I) represent 3D digital models of these elements in frontal view (H) and lateral view (I). In (I), the “primary” axonal element is colored red for better visibility. (J–L) Feed forward motif. The globular neurite (G) has thin branch (Gd) that is postsynaptic to varicose neurite segment (V; arrow in K, L). The dendritiform neurite (D) shown in orange is postsynaptic to both G (arrowhead in J) and V (arrowhead in K). Panels J and K are representative sections of VNC cube where elements of the feed forward motif are highlighted; (L) shows 3D model of motif in lateral view; levels of sections shown in (J) and (K) are indicated. (M) Schematic representation of connectivity encountered in VNC microvolume. (N, O) Schematic representation of feed forward motif and dense overlapping regulon motif, respectively. Scale bar: 1 µm (A, D, G, J, K).