NeuroFIG 18: Commissures in the tail.

Anterior is to the right in all images.
A. The two lumbar ganglia are connected to the preanal ganglion (PAG) by lumbar commissures on the ventral side and to the DC by dorsolateral commissures on the dorsal side. The three dorsorectal ganglion neurons grow their processes ventrally toward the PAG via the left- and right-side dorsorectal commissures.
B. Right and left lumbar commissures (arrows). Dorsorectal commissures are not visible at this epifluorescent image of a transgenic animal expressing the unc119::GFP panneural reporter, right lateral oblique view. Magnification, 400x. (Strain source: CGC.)
C. DA9, a VNC motor neuron situated in the PAG, sends its posteriorly directed process to the DC via lumbar and dorsolateral commissures (arrow). Epifluorescent image from a transgenic animal expressing the itr1pB::GFP reporter gene, right lateral view. Magnification, 600x. (Strain source: H. Baylis and N. Gower.) (Left inset) Graphic rendition of the same neuron.
D. DVB is located in the DRG and sends its process to the PAG via a left-sided dorsorectal commissure (arrow). Epifluorescent image from a transgenic animal expressing unc-47delta::GFP, right lateral view. Magnification, 600x. (Strain source: Y. Jin and O. Hobert.) (Right inset) Schematic rendition of the same neuron.
E. Organization of tail commissures and the preanal region in newly hatched L1, filleted dorsal view. Processes from PVQ, PHA, PHB, LUA, and PVC neuron pairs assemble into two fascicles that pass between the hypodermis and ventral body wall muscles to reach the VNC. The PVR process travels within the right-side fascicle. The posteriorly directed processes from DA8 and DA9 also run within these fascicles on the left and right sides, respectively. At the preanal region, the anteriorly directed processes meet and reassort with processes from dorsorectal neurons (DVA, DVC), head ganglia interneurons (AVA, AVD, AVG, AVH, AVJ, AVK, AVL), and PAG neurons (PVT, PVP, DD6, DA8, DA9). As they extend anteriorly, they make en passant synapses with their neighbors in the preanal region and the VNC (not shown). PHA and PHB axons and LUA processes end in the preanal region. (SD) Subdorsal; (SV) subventral; (IN) head interneuron processes; (R) rectum. (Based on Hedgecock et al., 1985.)

Click on picture for full resolution image.