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Fig. 3 | BMC Biology

Fig. 3

From: The visual pathway in sea spiders (Pycnogonida) displays a simple serial layout with similarities to the median eye pathway in horseshoe crabs

Fig. 3

First-order sensory processing centers in the protocerebrum of E. spinosa. Immunolabeled samples shown either in MIP (B,EH) or in blend mode (C). Yellow arrowheads mark the optic nerve branch targeting the antero-median neuropil. Red arrowheads point to the optic nerve branch entering the central brain neuropil. A 3D-reconstructed volume rendering of part of the eyes and their R-cell axon bundles that merge dorsal to the brain, μCT scan, lateral view. Stippled brackets indicate the positions of the brain areas depicted in BF. B, C Tubulin (TUB, green) and synapsin (SYN, magenta) immunolabeling. B Extended horizontal section. Asterisks mark tubulin-rich spherical bodies in the anterior soma cortex. C Oblique lateral view of volume rendering with clipping planes applied. The star indicates the area where the optic nerve enters the soma cortex. D Histological cross section. Note the darker staining of the antero-median neuropil, underlain by the less distinct antero-median tract. E Tubulin (magenta) and proctolin (PROC, green) immunolabeling, extended cross section. F Tubulin (magenta) and allatostatin (AST, green) immunolabeling, extended cross section. G Tubulin (magenta), synapsin (gray), and orcokinin (ORCO, green) immunolabeling, extended mid-sagittal section. Synapsin signal omitted in the right image. Note synapsin signal along the antero-median tract, which comprises also some orcokinin-ir neurites to the arcuate body. H Tubulin (magenta) and serotonin (5HT, green) immunolabeling, mid-sagittal section. Note serotonin-ir neurites in the antero-median tract. The solid oval highlights an antero-dorsal cluster of serotonin-ir neurons that project their primary neurites directly into the central brain neuropil. Abbreviations: AB – arcuate body; AE – anterior eye; AMN – antero-median neuropil; AMT – antero-median tract; BR – brain; BRN – brain neuropil; LT – lateral thickening; ONV – optic nerve; PE – posterior eye; PNV – proboscis nerve; RTA – R-cell axons; SVD – sub-visual domain; VN – visual neuropil

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