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 co mbinatorial manner within the olfactory bulb of vertebrates or the antennal lobe (AL) of insects. Here, we optically measured glomerular calcium activ ities in vivo in the honeybee Apis mellifera during olfactory stimulation w ith 36 pure chemicals differing systematically in carbon chain length (C-5- 10) and functional group (aldehyde, ketone, alcohol, carboxylic acid and al kane). We show their glomerular representations in 38 morphologically ident ified glomeruli out of the honeybee's 160. We measured the molecular recept ive 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 wi th similar response spectra are often direct neighbours. The results allow conclusions about the interactions between olfactory receptors and odour mo lecules, and about the AL network.