The tracheal system of the developing primary olfactory pathway of Manducasexta: tracheae do not play a guidance or targeting role for ingrowing receptor axons

Axons navigate to their targets by detecting signals within the environment through which they are growing. The surfaces of tracheae, which are promin ent features of the insect body plan, could be detected as favorable pathwa ys for sensory axons growing toward the brain. The pattern of the tracheal investment of the adult antennal lobe of the moth Manduca sexta suggested t wo specific possibilities for interaction between tracheae and axons during development: that tracheae might be involved in guiding olfactory receptor axons to their target region of the brain, the antennal lobe; and that tra cheae could provide an address system within the lobe that defines the site s of glomeruli, which are olfactory-axon target areas within the lobe. To d etermine whether tracheae contribute to development of the primary olfactor y pathway, the distribution of tracheae in the adult and developing antenna l lobes was examined with both confocal and electron microscopes. During th e major stages in which axons are growing into the antennal lobe and in whi ch glomeruli are forming, the tracheal investment of the nerve and lobe was found to be minimal. Tracheae thus cannot serve as axon guides or as local address sites for newly forming glomeruli during the initial targeting of receptors onto the antennal lobe. (C) 2001 Elsevier Science Ltd. All rights reserved.