Figure 5

Serotonin immunoreactivity in the protocerebrum of Speleonectes tulumensis. (A-G) Dorsal view of confocal laser-scans of horizontal vibratome sections (50 μm). (A) Overview of serotonin immunoreactivity (5HT-IR, green) showing the distribution of 5HT-ir cells (sA1, sA2, sB1, sB2). Left brain hemisphere double labeled for acetylated α-tubulin immunoreactivity (TUB-IR, magenta), revealing the position of the hemiellipsoid body (HE). (B) Neurites of sA1 project anteriorly forming a convergence (arrowhead) with neurites from the 5HT-ir domain sd1 (double arrowhead). One branch leaves this convergence anteriorly to more posterior regions of the nervous system (red arrows in B and C), decussating in the center of the brain (double arrowhead in C). Cluster sB1 projects posteriorly into sd9 (yellow arrow in B). (D) Another branch of the convergence in (B) runs medially into a decussation and innervates sd2 (arrowheads). Sd2 is associated to spherical sd3 and sd4-6 (yellow arrowheads). The domains sd4-6 are interconnected by faintly stained longitudinal neurites that decussate at the midline (arrows). (E) Neurites from sd2 run anteriorly to another unpaired midline neuropil (sd7) and further anterior to the paired sd8 (yellow arrow). Additionally, sd4 is interconnected to sd11 (arrows). The lateral positioned sd9 are connected by a heavily labeled commissure (red double arrowheads) composed of neurites of cluster sA2 (see F). (F) Cluster sA2 projects anteriorly into the neuropil forming numerous commissures. The most noticeable one passes sd2 ventrally projecting into the vesicular sd9 (red double arrowheads in E and F). The domain sd9 is interconnected to the more dorsally positioned sd10. Both parts of sd10 are connected via a thin commissure (arrows in F). (G) Projections from cluster sB2 enter the protocerebrum, deflect in a conspicuous loop, grow again laterally and end in the vesicular sd9 (arrows). Abbreviations: HE: hemiellipsoid body; sA1, sA2, sB1, sB2: 5HT-ir cell groups; sd1-11: 5HT-ir domains.