Histamine immunofluorescence in the optic lobe of <i>Papilio xuthus</i>.

<p><b>A</b>: Horizontal section. Histamine immunoreactivity was detected in the lamina (La), medulla (Me), lobula (Lo), and lobula plate (LP). The first optic chiasma (1.OC) was weakly labeled. Asterisk indicates a cluster of remnant larval stemmata, which exhibits strong histamine immunoreactivity. <b>B</b>: Enlarged image of a part of the lamina synaptic layer in A. Short visual fiber endings express histamine immunoreactivity. <b>C–E</b>: Lamina cross section, double-labeled with anti-histamine (magenta in C,E) and anti-synapsin (green in D,E). Images are single optical sections of 0.5 µm thickness. Dotted oval in D encloses a single cartridge profile. Histamine immunostaining is distributed widely within cartridges, and in some places it is concentrated in discontinuous ring-like structures (arrows in C). Arrowheads in E point at colocalizations of histamine- and synapsin immunoreactivities. <b>F–H</b>: Horizontal section through the medulla, double-labeled with anti-histamine (magenta in F,H) and anti-synapsin (green in G,H). The numbers in G indicate medulla layers visualized by anti-synapsin labeling. Anti-histamine strongly labeled axon projections that invade layers 1–3 and terminate in layer 4 of the medulla. The terminal specializations correspond to those of long visual fibers (R1, 2 and 9). Proximal layers 6–8 are widely and sparsely supplied with numerous fine immunoreactive fibers. 2.OC, second optic chiasma. Scale bar = 100 µm in A; 50 µm in B; 10 µm in E (applies to C,D); 50 µm in H (applies to F,G).