Figure 7

Transmission electron microscopy image showing double immunogold labeling of pigment dispersing factor (PDF) and invertebrate-specific D1-like dopamine receptor (InvD1L) in type II acini of unfed Ixodes ricinus female salivary glands. (A) Cross section of type II acinus detailing the axonal projections arranged around the acinar lumen (L). Insets in A are magnified in (B–E). The PDF-axon (white asterisk) containing large electron-dense vesicles was visualized using 15 nm nanoparticles (black arrows in B), whereas InvD1L-axons (black asterisks) containing electron-lucent vesicles were visualized with 6 nm nanoparticles (empty white arrows, in C–E). An unlabeled axon running close to the PDF-axon (red asterisk in A) containing electron-dense vesicles was also observed. Note that the axons were primarily encapsulated with the plasma membrane of the myoepithelial cell (MC) and terminal projections of ablumenal interstitial cells (AEC, aqua-blue arrows) while less frequent connections with granular cells (yellow squares) were also observed. (F,G) Another region of type II acinus shows three distinct axons running alongside and surrounded by the MC plasma membrane. Inset in F is magnified in (G). A bundle of three axonal processes (InvD1L- 15 nm nanoparticles black arrows; PDF-6 nm nanoparticles white arrows, unlabeled axon, presumed to express SIFamide, is showed by red asterisks) enclosed by the MC in the area of the lumen. Mitochondria (Mt) were evident in both PDF- and InvD1L-axons (G). Bars: 2 μm (A,F), 500 nm (B–E,G).