Histaminergic-like immunoreactivity (HA-IR) seen throughout the mid-body region of <i>Leptosynapta clarki</i> juveniles and adults.

<p>A) high concentration of HA-IR neurons in the center of the body wall papillae (c). These neurons project to the radial nerve cord (RNC) (b) and connect in dense bundles (a) (see also D for cross section of RNC); scale bar 100 µm. B) Higher magnification view of RNC and two body wall papillae; ); scale bar 50 µm. Neurons in the papillae have distinct sensory protrusions that reach to the outside of the epithelial layer (C and E; scale bars 50 µm). D) cross section of RNC with projections from body wall papillae sensory neurons to RNC; HA-IR is combined with DIC image which shows the association of histaminergic neurons with latitudinal muscle fibers; scale bar 50 µm. F:G) Sensory neurons of body wall papillae form distinct glomeruli-like structure indicating sites of dense synaptic connections (E). This glomeruli-like structure is visible in G and H; scale bar 25 µm.