Projections of male-specific receptor neurons in the antennal lobe of the oriental tobacco budworm moth,Helicoverpa assulta: A unique glomerular organization among related species

Abstract

The macroglomerular complex in the primary olfactory center of male moths receives information from numerous pheromone-detecting receptor neurons housed in specific sensilla located on the antennae. We investigated the functional organization of the three glomeruli constituting this complex in Helicoverpa assulta, a unique species among heliothine moths as concerns the composition of the pheromone blend. By tip recordings from the male-specific receptor neurons combined with cobalt-lysine stainings, the axon terminals in the brain were traced and subsequently reconstructed by camera lucida drawings. Some were also reconstructed in a digital form. The results showed that the sensilla could be classified into two functional types. A major category housed two colocalized receptor neurons, one responding to the primary pheromone component cis-9-hexadecenal and the other to the behavioral antagonists cis-9-tetradecenal and cis-9-hexadecenol. Cobalt-lysine applied to this sensillum type consistently resulted in two stained axons, each terminating in one of the two large subunits of the macroglomerular complex: the cumulus or the dorsomedial glomerulus. The second, less frequently appearing sensillum type contained a receptor neuron responding to the second pheromone component, cis-11-hexadecenal. Dye applied to this type resulted in stained axon projections in the ventral glomerulus. In an evolutionary context it is particularly interesting that differences of related heliothine species are reflected in the functional organization of the MGC compartments.

Antennal-lobe tracts in the noctuid moth, Heliothis virescens: new anatomical findings

“…Thus, specific sensory neuron types, randomly distributed in the periphery, project to distinct addresses in the antennal lobe/olfactory bulb. These findings are in full agreement with results from tracing of physiologically characterized receptor neurons in several moth species (Hansson et al 1995;Berg et al 1998Berg et al , 2005Lee et al 2006).…”

Pheromone Reception in Moths

“…Type C sensilla (19%) contained two ORNs (large-spiking one and small-spiking one), with the large-spiking one tuned to Z9-16: Ald and Z9-14:Ald, while the small-spiking one responded to Z11-16: OAc, Z11-16:OH, and Z9-14:Ald. 36,38,39 Similar ORN distributions were also reported in Heliothis subflexa and H. virescens. 39 …”

“…25,35 Various single sensillum recording (SSR) results have indicated that each trichodea sensillum is innervated by the dendrites of two to four ORNs, 24,28,36,37 which also project their axons into the antennal lobe (AL). Three types of non-neuronal cells: trichogen, thecogen, and tormogen cells surround the body of the ORNs.…”

Multiple olfactory receptor neurons and their axonal projections in the antennal lobe of the honeybee Apis mellifera

“…It seems that the dextran, coupled to biotin in our case, is crucial for transport to the axon terminals of the ORNs. So far, the most commonly used technique to study ORN arborization in insects has been labeling with cobalt (cobalt lysine or cobalt chlorite) and subsequent light microscopy (Hansson et al, 1992Boeckh and Tolbert, 1993;Stocker, 1994;Brockmann and Bruckner, 1995;Berg et al, 1998Berg et al, , 2005. Although the quality of staining is comparable in both techniques, the data analysis of cobalt staining of ORNs is limited and thus prone to interpretation errors.…”

“…Comparative neuroanatomical studies in insects revealed that the arrangement of glomeruli in the AL is highly organized. The AL design is species specific (Rospars, 1988;Vickers et al, 1998;Berg et al, 2005;Kleineidam et al, 2005), and functionally corresponding glomeruli are almost invariant in their relative position across individuals (Joerges et al, 1997;Galizia et al, 1999b;Sachse et al, 1999). With the aid of confocal laser-scanning microscopy and computer-aided data analysis, several reference atlases have been made available for comparative and functional investigations of the AL of different insect species (Galizia et al, 1999a;Laissue et al, 1999;Berg et al, 2002;Greiner et al, 2004).…”