Fig. 1.

Schematic diagrams showing Drosophila (a) and cockroach (b) cerebral cells expressing PERIOD (redrawn from [23, 125]). a In Drosophila, there are seven main groups of neurons. Three groups (DN1, DN2, and DN3) are located in the dorsal region, and the remaining four (LNd, l-LNv, s-LNv, and LPN) are located laterally. The s-LNv and l-LNv express a neuropeptide, PDF. l-LNvs have their processes in the optic lobe and send their axonal projection to the contralateral optic lobe through the posterior optic tract (POT). s-LNvs have axonal projection to the dorsomedial region of the protocerebrum. b In the cockroach, Blattera germanica, three groups of neurons are located in the optic lobe (G-I, G-II, and G-III) and three groups in the dorsal protocerebrum (G-IV, G-V, and G-VI). There is another group (G-D) in the deutocerebrum. PDF is coexpressed in G-I, -II, -III, -IV and -D cells. OL Optic lobe, Pr protocerebrum, De deutocerebrum