Fig. 4.

Adult zooids behavioral response is impaired during both the weekly cycle and with age. (A-C) Confocal imaging nervous system stained with anti-alpha tubulin (green) and Hoechst (blue). (A) Dorsal view of an adult zooid. Nerves (arrows) branching from the brain toward the oral siphon are clearly visible. (B) Upper view of the oral siphon populated with primary sensory cells. These mechanoreceptor cells are in epidermis and have both a cilium (dendrite) and an axon directed to the brain. When stimulated they activate the oral siphon sphincter muscle contraction and induce siphon closure. (C) Tentacle, at the base of the oral siphon, with a row of secondary sensory cells (coronal cells). At their base, they form synapses with dendrites belonging to brain neurons. Their stimulation induces the contraction of both body and atrial siphon muscles, leading to expulsion of seawater from the oral siphon. (D and E) Experimental design of the behavioral tests. In the siphon stimulation test (SST) (D) a jet of seawater is used to stimulate the oral siphon primary sensory cells in epidermis. In the tentacle stimulation test (TST) (E), a jet of seawater stimulates the coronal cells of the tentacles. (F) Behavioral response of zooids following TSTs and SSTs performed in days 1.4.6. (G) Comparison of behavioral response of adults from young and old colonies following TSTs performed during the days 1,4,6. ANOVA and post hoc test. P value < 0.05 (*); P value < 0.01 (**); P value < 0.001 (***).