Fig. 2. Global and focused insight into the adult annelid nervous system.

(A) Comparison of uncleared (left) and DEEP-Clear processed (right) bristle worm specimens. (B) Imaging of EGFP signal in photoreceptors of DEEP-Clear–processed pMos{rops::egfp}^vbci2 animals by light-sheet microscopy. Arrowheads indicate projections from the eyes into the central-brain neuropil. Inset shows the XZ projection of the boxed area. (C and D) EGFP⁺ parapodial cell bodies and their projections (arrowheads) into and along the ventral nerve cord as visualized by light-sheet microscopy. (E to G) Anti-acetylated alpha-tubulin (anti-AcTub) immunolabeling revealing the annelid nervous system, visualized either by light-sheet microscopy [(E) whole animal, including the stereotypical trunk nervous system; inset showing major structures of the brain] or confocal microscopy [(F) anterior eye, with photoreceptor cells exhibiting segmentation into outer segments protruding into the central filling mass and basal cell bodies; (G) brain, with the inset showing a magnification of the boxed region of the anterior eye]. The specimen in (G) shows a colabeling by anti-Vasotocin (anti-VT) immunohistochemistry, and arrowheads indicate VT⁺ puncta (putative dense core vesicles) in deep neurite projections. Corresponding VT⁺ cell bodies can be seen in close proximity to the anterior eyes. an, antennal nerve; cb, cell body; fm, filling mass; no, nuchal organ; np, neuropil; os, outer segment; pac, parapodial receptor cells; ae, anterior eye; pe, posterior eye; prc, eye photoreceptor cell; sn.II, segmental nerve II; vnc, ventral nerve cord.