Development of pigment-dispersing hormone-like immunoreactivity in the brain of the locust Schistocerca gregaria : comparison with immunostaining for urotensin I and Mas-allatotropin

Abstract

The development of peptide phenotypes in the lamina and accessory medulla of the locust brain (Schistocerca gregaria) was studied using antisera against pigment-dispersing hormone (PDH), urotensin I, and Mas-allatotropin. PDH-like immunoreactivity was first detected as 45% of embryonic development in somata at the base of the optic lobe. In the 55% embryo, processes from these neurons (PDFMe cells) extended into the developing accessory medulla and into the lamina and, by 85% of embryogenesis, innervated all major targets in the brain. At 65% of embryogenesis, two additional cell groups near the lamina (PDFLa cells) were immunostained; they appeared to connect the lamina to the medulla. Local neurons of the lamina and accessory medulla had somata adjacent to the PDFLa and PDFMe cells and exhibited urotensin-I-like immunostaining and Mas-allatotropin-like immunostaining, respectively. Immunostaining in these neurons occurred first in their arborizations in the lamina (anti-urotensin I, 50% of embryogenesis) and accessory medulla (anti-Mas-allatotropin, 65% of embryogenesis), whereas their cell bodies became immunostained at 70% and 100% of embryogenesis, respectively. The results suggest a developmental role for PDH-related peptides during pathfinding of the PDFMe projection neurons; such a function can be excluded for peptides related to urotensin I and Mas-allatotropin in local neurons of the lamina and accessory medulla. The developmental migration of PDFMe- and Mas-allatotropin-immunostained cells from the central brain into the optic lobe suggests a central-brain origin of the accessory medulla.