| Morphological description: | Fine arborization relay interneurons (FAI) exhibit arborizations within a large portion of the antennal lobe. Most of these neurons cover more than half of the lobe, though they do not always invade the same glomeruli. A region that is spared in most cases is the glomerulus VA1. Typically, all of the FAI processes are of small diameter, which makes the distinction between stem processes and terminal arborizations difficult. One or several fibers leave the lobe in posterior direction just adjacent to the oesophagus, at some distance from the iACT. Due to staining of many other neurons, the projections of these fibers could not be elucidated. Likewise, the position of their cell body remains unknown. Eight of the FAI observed are unilateral. However, mirror symmetric patterns in both antennal lobes (two preparations), suggest that some of the FAI might be bilateral, although the connections between the two lobes remain obscure. The projection targets of FAIs are unknown. Although its extensive arborizations bear some resemblance to the local interneurons, its processes extending from the lobe differentiate it from the local interneurons. FAIs could either be output neurons that carry information from many glomeruli to brain centers distinct from the calyx or the lateral horn or they could represent centrifugal fibers that provide the lobe with central information. |
