Synganglial morphology and neurosecretory centers of adult Amblyomma americanum (L.) (Acari : Ixodidae)

Lone star ticks, Amblyomma americanum (L.), were processed by standard histological means for paraffin embedding, sectioning, and staining by the paraldehyde-fuchsin technique. The synganglion is highly condensed around the esophagus and possesses paired optic, cheliceral, palpal, pedal I-IV nerves, and opisthosomal nerves and a single unpaired esophageal nerve. Although optic nerves were observed leading from the eyes to the protocerebrum, distinct optic ganglia were not seen in any of the preparations examined. The paraldehyde-fuchsin technique revealed 14 neurosecretory centers (11 paired, 3 unpaired) within the synganglion, which are described in relation to the underlying neuropilar structure. A previously undescribed internal subesophageal center that consists of a single cell was observed within a cluster of perikarya lying posteriorly adjacent to the esophagus. A three-dimensional reconstruction of the internal neuropilar structure of the synganglion was made, and the included neurosecretory centers were mapped. Comparisons are made to previous work on other ticks, and physiological relationships are considered.