Pheromone processing center in the protocerebrum of Bombyx mori revealed by nitric oxide-induced anti-cGMP immunocytochemistry

The antennal lobe (AL) of the male silkworm moth Bombyx mori contains 60 ± 2 ventrally located antennal glomeruli and a dorsal macroglomerular complex (MGC) consisting of three subdivisions. The response patterns of MGC projection neurons (PNs) to pheromonal stimuli correlate with their dendritic arborization in the subdivisions of the MGC. However, the representation of this pheromonal information in the lateral protocerebrum (LPC), which is the target site of the AL PNs, is not well known. We performed nitric oxide (NO)‐induced anti‐cGMP immunohistochemistry and found that the PNs which respond to the major pheromone component (bombykol) express strong immunoreactivity. They project to a specific area, the delta area in the inferior lateral protocerebrum (ΔILPC), which clearly represents the processing center for the major pheromone component. Furthermore, to examine the projection sites in the LPC from each subdivision of the MGC, we performed double‐labeling of each type of MGC‐PNs, combined with NO‐induced anti‐cGMP immunohistochemistry. We revealed that projections from each subdivision of the MGC overlapped or separated in specific regions of the ΔILPC. These results suggest that integration and segregation of pheromone information may occur in the ΔILPC. J. Comp. Neurol. 481:340–351, 2005. © 2004 Wiley‐Liss, Inc.