DEVELOPMENT OF PIGMENT-DISPERSING HORMONE-LIKE IMMUNOREACTIVITY IN THE BRAIN OF THE LOCUST SCHISTOCERCA-GREGARIA - COMPARISON WITH IMMUNOSTAINING FOR UROTENSIN-I AND MAS-ALLATOTROPIN

The development of peptide phenotypes in the lamina and accessory medu lla of the locust brain (Schistocerca gregaria) was studied using anti sera against pigment-dispersing hormone (PDH), urotensin I, and Mas-al latotropin. PDH-like immunoreactivity was first detected as 45% of emb ryonic 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 embryo genesis, innervated all major targets in the brain. At 65% of embryoge nesis, two additional cell groups near the lamina (PDFLa cells) were i mmunostained; they appeared to connect the lamina to the medulla. Loca l neurons of the lamina and accessory medulla had somata adjacent to t he PDFLa and PDFMe cells and exhibited urotensin-I-like immunostaining and Mas-allatotropin-like immunostaining, respectively. Immunostainin g 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 bec ame immunostained at 70% and 100% of embryogenesis, respectively. The results suggest a developmental role for PDH-related peptides during p athfinding of the PDFMe projection neurons; such a function can be exc luded for peptides related to urotensin I and Mas-allatotropin in loca l neurons of the lamina and accessory medulla. The developmental migra tion of PDFMe- and Mas-allatotropin-immunostained cells from the centr al brain into the optic lobe suggests a central-brain origin of the ac cessory medulla.