DEVELOPMENT OF AN IDENTIFIED SEROTONERGIC NEURON IN THE ANTENNAL LOBEOF THE MOTH AND EFFECTS OF REDUCTION IN SEROTONIN DURING CONSTRUCTIONOF OLFACTORY GLOMERULI

Each olfactory (antennal) lobe of the moth Manduca sexta contains a si ngle serotonin (5-HT) immunoreactive neuron whose processes form tufte d arbors in the olfactory glomeruli. To extend our present understandi ng of the intercellular interactions involved in glomerulus developmen t to the level of an individual, identified antennal lobe neuron, we f irst studied the morphological development of the 5-HT neuron in the p resence and absence of receptor axons. Development of the neuron's glo merular tufts depends, as it does in the case of other multiglomerular neurons, on the presence of receptor axons. Processes of the 5-HT neu ron are excluded from the region in which the initial steps of glomeru lus construction occur and thus cannot provide a physical scaffolding on which the array of glomeruli is organized. Because the neuron's pro cesses are present in the antennal lobe neuropil throughout postembryo nic development, 5-HT could prov ide signals that influence the patter n of development in the lobe. By surgically producing 5-HT-depleted an tennal lobes, we also tested the importance of 5-HT in the constructio n of olfactory glomeruli. Even in the apparent absence of 5-HT, the gl omerular array initiated by the receptor axons was histologically norm al, glial cells migrated to form glomerular borders, and receptor axon s formed terminal branches in their normal region within each glomerul us. In some cases, 5-HT-immunoreactive processes from abnormal sources entered the lobe and formed the tufted intraglomerular branches typic al of most antennal lobe neurons, suggesting that local cues strongly influence the branching patterns of developing antennal lobe neurons. (C) 1995 John Wiley & Sons, Inc.