A combinatorial model of odor discrimination using a small array of contiguous, chemically defined glomeruli.

The macroglomerular complex (MGC) is a sexually dimorphic array of contiguous glomeruli in male moths, located at the base of the antennal nerve where it enters the primary olfactory processing area of the brain, the antennal lobe. A new three-dimensional reconstruction method was used to map this glomerular array, and images obtained with the laser scanning confocal microscope revealed the precise location and spatial arrangement of the MGC glomeruli in two related species of Heliothine moth. Intracellular recording and staining of projection neurons (PNs) that arborize within the MGC has revealed that information about the two attractive components of the pheromone blend is segregated to different glomeruli in both species. In one species, Helicoverpa zea, a third glomerulus serves as the locus for the processing of odors that antagonize upwind flight. Thus, activation of different but overlapping sets of glomeruli within the MGC may provide a neural substrate for discriminating attractant vs antagonist chemical signals.