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Neural coding of sensory input is a major unsolved issue in neuroscience. Current experimental methods rely on neural activity recording or visualization following sensory stimulation. Most of them, however, do not include behavioral correlates on the actual perception by the animal. We present a novel approach to address olfaction and coding in adult Drosophila. Sensory input was selectively blocked in two subsets of sensory neurons that project to different, albeit overlapping, groups of central targets, by means of tetanus toxin expressed under the control of the yeast transcription factor Gal4. Glomeruli DL1, DL2, VM1, and VM4 were tested following stimulation with benzaldehyde, ethyl acetate, propionic acid, butanol, or acetone at various concentrations. The behavioral response was found to be modified in an odorant-specific and a concentration-dependent manner. Sensory input to DL2 and, to a minor extent, VM1 and/or VM4, appear to be required for benzaldehyde perception, while acetone is processed through DL1. None of these glomeruli, however, seem necessary for butanol perception. In addition, sexual differences were observed for some stimuli. These results demonstrate the behavioral relevance of odor representation as maps of glomerular activity generated in the antennal lobes following specific sensory input. The strategy used here should be useful to characterize olfactory coding, as new and selective Gal4 lines become available., (Copyright 2003 Wiley Periodicals, Inc. J Neurobiol 56: 1-12, 2003)

The olfactory system of several holometabolous insect species undergoes anatomical changes after eclosion of the imago, following those occurring during metamorphosis. In parallel, odor experience and learning performance also evolve with age. Here, we analyze the case of adult Drosophila females. Synaptogenesis in the antennal lobe (AL) starts in late pupa and continues during the first days of adult life, at the same time as the behavioral response to odors matures. Individual olfactory glomeruli (DM6, DM2, and V) display specific growth patterns between days 1 and 12 of adult life. Experience can modify the olfactory pathway both structurally and functionally as shown by adaptation experiments. The modifications associated with this form of nonassociative learning seem to take place at a critical age. Exposure to benzaldehyde at days 2-5 of adult life, but not at 8-11, causes behavioral adaptation as well as structural changes in DM2 and V glomeruli. Altered levels in intracellular cAMP, caused by dunce and rutabaga mutants, do not affect the normal changes in glomerular size, at least at day 6 of development, but they prevent those elicited by experience, establishing a molecular difference between glomerular changes of intrinsic versus environmental origin. Taken together, these data demonstrate an imprinting-like phenomenon in the olfactory pathway of young Drosophila adults, and illustrate its glomerulus-specific dynamics., (Copyright 2003 Wiley Periodicals, Inc. J Neurobiol 56: 13-23, 2003)

The processing of odorant signals is performed, in the olfactory bulb of vertebrates or in the antennal lobe of insects, by different types of neurons which display specific morphological and functional features. The present work characterizes the morphogenesis of the main neuronal types which participate in olfactory discrimination in the adult honeybee (Apis mellifera). Neurons were stained intracellularly with Lucifer yellow at different stages of pupal development and in the adult, and imaged by laser scanning confocal microscopy. Attending to branching patterns, all pupal neurons could be attributed to morphological types previously established in the adult. Given the functional importance of intraglomerular dendritic arbors in the processing of olfactory information, the study focused on their development. The two main classes, dense and sparse intraglomerular arbors, display adultlike features as early as the second day of pupal development. However, morphometric measurements and confocal observations show that their general pattern undergoes continuous maturation processes until late pupal stages and after emergence of the adult. Among these, the results point out a pruning of dendritic branches in sparse arbors, but not in dense arbors.