IMMUNOCYTOCHEMICAL CHARACTERIZATION OF THE ACCESSORY MEDULLA IN THE COCKROACH LEUCOPHAEA-MADERAE

Several lines of evidence suggest that pigment-dispersing hormone-immu noreactive neurons with ramifications in the accessory medulla are inv olved in the circadian system of insects. The present study provides a detailed analysis of the anatomical and neurochemical organization of the accessory medulla in the brain of the cockroach Leucophaea madera e. We show that the accessory medulla is compartmentalized into centra l dense nodular neuropil surrounded by a shell of coarse fibers. It is innervated by neurons immunoreactive to antisera against serotonin an d the neuropeptides allatostatin 7, allatotropin, corazonin, gastrin/c holecystokinin, FMRFamide, leucokinin I, and pigment-dispersing hormon e. Some of the immunostained neurons appear to be local neurons of the accessory medulla, whereas others connect this neuropil to various br ain areas, including the lamina, the contralateral optic lobe, the pos terior optic tubercles, and the superior protocerebrum. Double-label e xperiments show the colocalization of immunoreactivity against pigment -dispersing hormone with compounds related to FMRFamide, serotonin, an d leucokinin I. The neuronal and neurochemical organization of the acc essory medulla is consistent with the current hypothesis for a role of this brain area as a circadian pacemaking center in the insect brain.