Fig. 8
Development of the trunk nervous system in different pre-metamorphic developmental stages of O. fusiformis (14 dpf–21 dpf). FMRFamide-LIR (yellow) and 5-HT-LIR (purple), aTub-LIR (cyan), DNA (dark blue). Confocal z-projections and volume renderings of FMRFamide-LIR (b) and aTub-LIR (b). Ventral is left and apical is up in (a) and (b), in (c) ventral is down and apical is left, (e) and (f) which show a view from apical with the ventral side left (e) and down (f). d shows a view from latero-apical with the ventral side left. Stages are given in days post fertilization (dpf). The shape of the esophagus (and intestine) is indicated by white lines. The position of somata clusters showing 5-HT-LIR is indicated with white dotted circles. a 5-HT-LIR of the trunk nervous system is detectable earliest at 14 dpf. The ventral nerve cord (vn) is represented by four neurites including numerous serial perikarya (inset). Note that the overlap of the 5-HT-LIR and the aTub-LIR causes a white color of the circumesophageal connective (cc). The inset shows an apical view of the ventral nerve cord (vn). b FMRFamide-LIR at 14 dpf is restricted to the two inner parallel neurites and four pairs of perikarya. c At 21 dpf, shortly prior to metamorphosis, the 5-HT-LIR of the ventral nerve cord (vn) is detectable within distinct neurites, serially arranged clusters of somata (white dotted circle) and serial lateral nerves (ln) showing 5-HT-LIR and branching off from the serotonergic cell clusters. Notably, numerous longitudinal nerves (lo) are visible in pre-metamorphic stages. The specimens represent conditions later on observable in juveniles as well. aTub-LIR was hardly detectable due to a dense ciliation of the entire specimen. d A lateral view at 21 dpf reveals several clusters of somata exhibiting 5-HT-LIR. Several lateral nerves (ln) branch off from the ventral nerve cord (vn) at the position of the cell clusters. Note that the posterior part of the ventral cord (vn) is bent under the anterior part and the esophageal region (es) due to the shape of the mitraria. The dotted square indicates the region that is shown in (f) with higher magnification. e An apical view at 21 dpf reveals the presence the dorsal and the ventral parts of the dorsal root of the connective (vpdr, dpdr) and the ventral root of the connective (vr). Furthermore, distinct clusters of serotonergic neurons (sn) along the ventral nerve cord (vn) are detectable. Prominent lateral nerves (ln) branch off from these clusters. The posterior part of the ventral cord (vn) is bent under the anterior one and therefore not visible. f A higher magnification of the posterior part of the ventral nerve cord (vn) at 21 dpf reveals the presence of 4 distinct nerves showing 5-HT-LIR (numbered 1–4). The location of the posterior ventral nerve cord (vn) in the entire animal is shown in (d) and marked with the white dotted square. at, apical tuft; cc, circumesophageal connective; cs, chaetal sac; dpdr, dorsal part of the dorsal root of cc; en, esophageal nerve; es, esophagus; gl, gland; hg, hindgut; ln, lateral nerve; lo, longitudinal nerve; mg, midgut; vn, ventral nerve cord; vpdr, ventral part of the dorsal root of cc;vr, ventral root of the cc. Sale bars = 100 μm (a), 30 μm (b), 50 μm (c–e) and 20 μm (f). The scale bars only refer to the main images, not to the insets