The glomerular code for odor representation is species specific in the honeybee Apis mellifera.

Odors are coded by glomerular activity patterns in the insect antennal lobe (AL) and in the mammalian olfactory bulb. We measured glomerular responses to 30 different odors in the AL of honeybees using calcium-sensitive dyes. By subsequently staining glomeruli and identifying individual glomerular outlines, we were able to compare the patterns between animals. Regardless of whether the odors were mixtures or pure substances, environmental odors or pheromones, their representations were highly conserved among individuals. Therefore, it may be possible to create a functional atlas of the AL in which particular molecular receptive ranges are attributed to each glomerulus.

The spatial representation of chemical structures in the antennal lobe of honeybees: steps towards the olfactory code.

Odours are represented by specific ensembles of activated glomeruli in a combinatorial manner within the olfactory bulb of vertebrates or the antennal lobe (AL) of insects. Here, we optically measured glomerular calcium activities in vivo in the honeybee Apis mellifera during olfactory stimulation with 36 pure chemicals differing systematically in carbon chain length (C-5-10) and functional group (aldehyde, ketone, alcohol, carboxylic acid and alkane). We show their glomerular representations in 38 morphologically identified glomeruli out of the honeybee's 160. We measured the molecular receptive range of identified glomeruli averaging up to 21 individuals. Of the 38 glomeruli measured, 23 show maximal activity in a specific range of chain length. Glomeruli preferentially responding to a functional group are also always broadly tuned to particular chain lengths. Furthermore, glomeruli with similar response spectra are often direct neighbours. The results allow conclusions about the interactions between olfactory receptors and odour molecules, and about the AL network.