Fig. 4. Immunofluorescence expression of 5-HT_1Hel and 5-HT_7Hel in the CNS of mature H. trivolvis. 5-HT_1Hel-like immunoreactivity (A) and 5-HT_7Hel-like immunoreactivity (B–F) was observed in select neurites within neuropile (arrows) and neurite tracts (arrowhead) in all ganglia of the CNS. The expression observed in the cerebral ganglia (A and B), pleural ganglia (C and D) and buccal ganglia (E and F) was representative of the pattern seen in all ganglia. Immunoreactivity was not observed in neuronal somata. Scale bar, 30 µm.