Macroglomerular complex

Axons of antennal ORCs project through the antennal nerve to enter the brain at the level of the ipsilateral antennal lobe (AL) of the deutocerebrum (52). ORC axons project from the flagellum to targets in the AL, but axons from antennal mechanosensory neurons bypass the AL and project instead to an "antennal mechanosensory and motor center" in the deutocerebrum posteroventral (with respect to the body axis of the animal) to the AL (52, 58, 64). In moths and certain other insect groups, sex-pheromonal information is processed in a prominent male-specific neuropil structure in each AL called the macroglomerular complex (MGC) (16, 52, 64, 65). 

Todd, J. L., Anton, S., Hansson, B. S. and Baker, T. C. (1995). Functional organization of the macroglomerular complex related to behaviourally expressed olfactory redundancy in male cabbage looper moths. Physiological Entomology 20 349-361. 

Hansson B. S., Christensen T. A. and Hildebrand J. G. (1991). Functionally distinct subdivisions of the macroglomerular complex in the antennal lobe of the male sphinx moth Manduca sexta. J. Comp. Neurol. 312, 264—278. 

Figure 24.1 A surface reconstruction of a male antennal lobe of the moth Spodoptera littoralis. The brain was immunostained with synapsin antibody and optically sectioned using a confocal microscope. Stacks of images were integrated with the software Imaris 2,7 (Bitplane AG, Switzerland) on a Silicon Graphics workstation to obtain surface projections of the lobe. The macroglomerular complex (MGC) is located close to the entrance of the antennal nerve. M, medial D, dorsal (modified from Carlsson et at, 2002). B Synaptic organization of the major types of antennal lobe neurons. Sensory neurons (ORNs) make uniglomerular synapses both directly with projection neurons (PNs) and indirectly via local interneurons (LNs). In addition, local interneurons innervate several glomeruli and generally make inhibitory synapses. Cell bodies of PNs and LNs are located within the antennal lobe.

In species using sex-pheromone communication, a sexual dimorphism in glomerular structure has been observed, where a single or a complex of large glomeruli form the macroglomerular complex (MGC). The MGC receives input only from sex-pheromone-sensitive ORNs or neurons sensitive to compounds inhibiting sexual attraction. 

Figure 24.4 Gray-scaled signals of optical recordings of calcium activity from the antennal lobe of the moth Helicoverpa zea. A, B and C show thresholded (>50 percent of maximum) responses to the pheromone components Z11-16 Ald and Z9-16 Ald and a behavioral antagonist Z11-16 Ac, respectively. D A schematic figure of the organization of the macroglomerular complex in H. zea (from Vickers et al., 1998). The position of the glomeruli coincides with the foci of calcium responses, i.e. response to Z11-16 Ald takes place in the cumulus, Z9-16 Ald in the DM-P glomerulus and Z11-16 Ac in the DM-A glomerulus. These activity patterns corroborate the innervation patterns of functionally identified projection neurons (redrawn from Vickers et al., 1998).

Berg B. G., Almaas T. J., Bjaalie J. G. and Mustaparta H. (1998) The macroglomerular complex of the antennal lobe in the tobacco budworm moth Heliothis virescens specified subdivision in four compartments according to information about biologically significant compounds. J. Comp. Physiol. A 183(6), 669-682. 

J.L. Todd, S. Anton, B.S. Hansson B.S and T.C. Baker, Functional organization of the macroglomerular complex related to hehavioraUy expressed olfactory redundancy in male cahhage loopermoth. Physiol. Entomol. 20 (1995) 349-361. 

The extreme sensitivity of the receptor neurons is combined with a most efficient processing of their responses by the central nervous system. Via the axons of the receptor neurons the nerve impulses are conducted to the antennal lobe, the first synaptic station of the central olfactory pathway in insects. The axons of the pheromone receptor neurons terminate on local interneurons and projection neurons (PN) of the macroglomerular complex (MGC) (Hildebrand 1996). The silk moth has... 

Kanzaki, R., Soo, K., Seki, Y., Wada, S. Projections to higher olfactory centres from subdivid-ions of the antennal lobe macroglomerular complex of the male silkmoth. Chem. Senses 28, 113-130 (2003)... 

---