Adult‐like complexity of the larval antennal lobe of D. melanogaster despite markedly low numbers of odorant receptor neurons

Abstract

We provide a detailed analysis of the larval head chemosensory system of Drosophila melanogaster, based on confocal microscopy of cell-specific reporter gene expression in P[GAL4] enhancer trap lines. In particular, we describe the neuronal composition of three external and three pharyngeal chemosensory organs, the nerve tracts chosen by their afferents, and their central target regions. With a total of 21 olfactory and 80 gustatory neurons, the sensory level is numerically much simpler than that of the adult. Moreover, its design is different than in the adult, showing an association between smell and taste sensilla. In contrast, the first-order relay of the olfactory afferents, the larval antennal lobe (LAL), exhibits adult-like features both in terms of structure and cell number. It shows a division into approximately 30 subunits, reminiscent of glomeruli in the adult antennal lobe. Taken together, the design of the larval chemosensory system is a "hybrid," with larval-specific features in the periphery and central characteristics in common with the adult. The largely reduced numbers of afferents and the similar architecture of the LAL and the adult antennal lobe, render the larval chemosensory system of Drosophila a valuable model system, both for studying smell and taste and for examining the development of its adult organization.

Sensory determinants of behavioral dynamics in Drosophila thermotaxis

“…We followed the axons of the three thermosensory neurons and found that they run parallel to the axons of the 21 ORNs along the antennal nerve (Movie S4). Each olfactory neuron innervates a distinct glomerulus within the larval antennal lobe (LAL) (27,28). The three thermosensory neurons do not innervate olfactory glomeruli, but glomeruli in a region posterior and slightly dorsal to the LAL (Fig.…”

The molecular basis of CO 2 reception in Drosophila

“…Anterior regions of larvae were dissected (Institut für Zoologie, Regensburg, Germany) and mounted in PBS containing 50% glycerol. Adult brains were dissected and prepared as described (38). Samples were immunostained with nc82 monoclonal antibody (a gift from Alois Hofbauer).…”

Induction of cAMP Response Element-Binding Protein-Dependent Medium-Term Memory by Appetitive Gustatory Reinforcement inDrosophilaLarvae

“…The larval olfactory system is significantly simpler than the adult system with only 21 odorant receptor neurons (Python and Stocker, 2002;Kreher et al, 2005;Ramaekers et al, 2005). To find chemicals that are suitable for larval learning assays, we first examined 30 odorants for naive larval chemotactic behavior and classified them in four groups based on their attractiveness (Table 1).…”

“…Third, our paradigm is free from odor discriminative task. Because the larval olfactory system is considerably simpler than the adult system (Python and Stocker, 2002;Kreher et al, 2005;Ramaekers et al, 2005), simultaneous discrimination of different odors could complicate animal responses, although other studies used two-odor paradigms (Aceves-Piña and Heisenberg et al, 1985;Tully et al, 1994a;Dukas, 1998;Scherer et al, 2003;Gerber et al, 2004a;Hendel et al, 2005;Michels et al, 2005;Neuser et al, 2005). Finally, because only a single odor is applied to larvae during training, the simple design of our paradigm may be of use in imaging of neural representation of the conditioned odor in the brain during learning and memory.…”

“…In addition, recent studies have revealed straightforward organization of the larval olfactory system with only 21 olfactory receptor neurons targeting the 21 antennal lobe glomeruli, from which projection neurons target the larval MB calyx that consists of ϳ28 glomeruli (Python and Stocker, 2002;Kreher et al, 2005;Ramaekers et al, 2005).…”