ROLE OF THE HEAD IN THE ULTRASTRUCTURAL MIDGUT ORGANIZATION IN RHODNIUS-PROLIXUS LARVAE - EVIDENCE FROM HEAD TRANSPLANTATION EXPERIMENTS AND ECDYSONE THERAPY

Studies on the effects of decapitation, head transplantation and ecdys one therapy on the ultrastructural organization of the midgut in 5th-i nstar larvae of Rhodnius prolixus, were carried out, Control insects h ad a typical and significant organization of the epithelial cells (mai nly microvilli, extracellular membrane layers and basal portion of the epithelial cells) of the midgut (stomach and intestine) during the en tire period of the experiment. However, the host larvae, when decapita ted 1 day after feeding, demonstrated significant changes in the ultra structural organization of the epithelial cells of these compartments. In converse experiments, head transplantations from untreated donors 4-5 days after feeding into headless larvae sustained the ultrastructu ral organization of the epithelial cells in the midgut, Oral therapy w ith ecdysone (5 mu g/mL of blood meal) in decapitated insects signific antly reversed the altered organization of the stomach and intestine. These results point to a brain factor, possibly the prothoracicotropic hormone (PTTH) which stimulates ecdysteroid production in the prothor acic glands, may be a factor responsible, directly or indirectly, for the midgut cell organization in R, prolixus. (C) 1998 Elsevier Science Ltd. All rights reserved.