Odor coding is bilaterally symmetrical in the antennal lobes of honeybees (Apis mellifera)

Abstract

The primary olfactory neuropil, the antennal lobe (AL) in insects, is organized in glomeruli. Glomerular activity patterns are believed to represent the across-fibre pattern of the olfactory code. These patterns depend on an organized innervation from the afferent receptor celss, and interconnections of local interneurons. It is unclear how the complex organiation of the AL is achieved ontogenetically. In this study, we measured the functional activity patterns elicited by stimulation with odors in the right and the left AL of the same honeybee (Apis mellifera) using optical imaging of the calcium-sensitive dye calcium green. We show here that these patterns are bilaterally symmetrical (n = 25 bees). This symmetry holds true for all odours tested, irrespective of their role as pheromones or as environmental odours, or wether thes were pure substances or complex blends (n = 13 odours). Therefore, we exclude the activity dependent mechanisms local to one AL determine the functional glomerular activity. This identity is genetically predetermined. ALternatively, if activity dependent processes are involvd, bilateral connections would have shape syymetry, or, temporal constraints could lead to identical patterns on both sides due to their common history of odour exposure.