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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.

Both intrinsic (programmed) and extrinsic (non-programmed) factors are thought to play a role in the morphogenesis of neurones in the honeybee antennal lobe (the first relay station in the olfactory pathway) during development. We present here a morphometric and statistical analysis of a large population of pupal honeybee antennal lobe neurones grown in primary culture. Quantitative parameters were used to characterize neuronal shapes. On the basis of such morphometric measurements, an automatic classification allowed three morphological types to be distinguished. Their main characteristics are presented and the role of intrinsic and extrinsic factors in their determination is discussed.