Neuronal architecture of the antennal lobe in Drosophila melanogaster

Abstract

Computer reconstruction of the antennal lobe of Drosophila melanogaster has revealed a total of 35 glomeruli, of which 30 are located in the periphery of the lobe and 5 in its center. Several prominent glomeruli are recognizable by their location, size, and shape; others are identifiable only by their positions relative to prominent glomeruli. No obvious sexual dimorphism of the glomerular architecture was observed. Golgi impregnations revealed: (1) Five of the glomeruli are exclusive targets for ipsilateral antennal input, whereas all others receive afferents from both antennae. Unilateral amputation of the third antennal segment led to a loss of about 1000 fibers in the antennal commissure. Hence, about 5/6 of the approximately 1200 antennal afferents per side have a process that extends into the contralateral lobe. (2) Afferents from maxillary palps (most likely from basiconic sensilla) project into both ipsi- and contralateral antennal lobes, yet their target glomeruli are apparently not the same as those of antennal basiconic sensilla. (3) Afferents in the antennal lobe may also stem from pharyngeal sensilla. (4) The most prominent types of interneurons with arborizations in the antennal lobe are: (i) local interneurons ramifying in the entire lobe, (ii) unilateral relay interneurons that extend from single glomeruli into the calyx and the lateral protocerebrum (LPR), (iii) unilateral interneurons that connect several glomeruli with the LPR only, (iv) bilateral interneurons that link a small number of glomeruli in both antennal lobes with the calyx and LPR, (v) giant bilateral interneurons characterized by extensive ramifications in both antennal lobes and the posterior brain and a cell body situated in the midline of the suboesophageal ganglion, and (vi) a unilateral interneuron with extensive arborization in one antennal lobe and the posterior brain and a process that extends into the thorax. These structural results are discussed in the context of the available functional and behavioral data.

Target neuron prespecification in the olfactory map of Drosophila

“…Figure 3c summarizes the`landmark' glomeruli (see Methods) that are innervated by anterodorsal projection neurons (green) or lateral projection neurons (red). In the 54 anterodorsal neuroblast and 25 lateral neuroblast clones we examined, we found no exception to this rule, despite the fact that there is no obvious relationship between the positions of projection neuron cell bodies and their glomeruli 4 . These observations indicate that the neuroblast from which a projection neuron is derived restricts its glomerular choice and consequently the subset of olfactory information that it can carry further into the brain.…”

“…Projection neurons of the Drosophila antennal lobe send dendrites into glomeruli and axons to higher brain centres 4 , thereby transferring this odour map further into the brain. Here we use the MARCM method 5 to perform a systematic clonal analysis of projection neurons, allowing us to correlate lineage and birth time of projection neurons with their glomerular choice.…”

“…About 1,300 ORNs expressing 40±60 different receptors 2,6,7 project their axons to 40±50 individually identi®able glomeruli of the antennal lobe 8 (equivalent to the mammalian olfactory bulb 9 ). Information leaves the antennal lobe through an estimated 150 projection neurons (equivalent to mammalian mitral/tufted cells), whose cell bodies are located at the periphery of the antennal lobe 4,10 (Fig. 2b).…”

Diverse Expression and Distribution ofShakerPotassium Channels during the Development of theDrosophilaNervous System

“…The antennal nerve is formed by two bundles of mechanosensory and chemosensory fibers that move together from the antenna until they reach the brain, where they split into two tracks. One bundle is the olfactory track, which terminates at the antennal lobe; the other is the antennal mechanosensory and motor center track, which bypasses the antennal lobe terminating at the mechanosensory region of the deuterocerebrum (Stocker RF et al, 1990). Accordingly, we have identified these labeled fibers as part of the antennal mechanosensory and motor center track.…”

The anatomical pathways for antennal sensory information in the central nervous system of the cricket, Gryllus bimaculatus

“…LH). Previously the projection patterns of AL-PNs have been investigated in a wide variety of insects (fly: Stocker et al, 1990;cockroach: Malun et al, 1993;moth: Homberg et al, 1988, Rø et al, 2007; honeybee: Kirschner et al, 2006;ant: Zube et al, 2008). As in the other species studied we found in the cricket that the IACT was more frequently and more intensely stained.…”