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The Antennal Lobes

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Drosophila

Antennal lobes are the first order neuropils of the olfactory chemosensory pathway. They comprise glomeruli - discrete glial bound partitions of neuropil - which are invaded by olfactory receptor terminals.

Glomeruli provide projection neurons. Uniglomerular projections neurons (having dendrites in a single glomerulus) send their axons to the superior lateral protocerebrum on the same side of the brain via the inner antennocerebral tract. Most types of multiglomerular projection neurons (those whose dendrites invade more than one glomerulus) reach the superior lateral protocerebrum via the outer and medial antennocerebral tracts and do not send collaterals to the mushroom body calyces.

Other Insects

Although the projections from the antennal lobes to the brain are similar between different groups of insects, the organization and neuroarchitecture of their antennal lobes can differ markedly. Those of moths and flies are relatively complex. As in honey bees, their glomeruli are uniquely identifiable on the basis of their shape and location within the antennal lobe. Each glomerulus has a complex internal architecture. Each supplies at least three and some as many as seven uniglomerular projection neurons, the axons of which send collaterals to relatively simple and small mushroom bodies.

In the Hymenoptera, ball-like glomeruli are clustered into two to four distinct populations. The internal organization of each glomerulus, regarding the number of its uniglomerular projection neuron dendrites, is simpler than in moths and flies. Each glomerulus provides a pair of projection neurons, the axons of which provide collaterals to complex, large mushroom bodies. A 3-D atlas of the honey bee antennal lobes (provided by Dr. Giovanni Galizia, at the Institute of Neurobiology, Berlin: galizia@zedat.fu-berlin.de) can be compared with similarly generated 3-D maps of the antennal lobes of Drosophila.


Reference

Stocker, R.F.M., Lienhard, C., Borst, A., and K-F. Fischbach (1990) Neuronal architecture of the antennal lobe in Drosophila melanogaster. Cell Tissue Res. 262:9-34 (1996)

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