Representation of the Glomerular Olfactory Map in the Drosophila Brain

Abstract

We explored how the odor map in the Drosophila antennal lobe is represented in higher olfactory centers, the mushroom body and lateral horn. Systematic single-cell tracing of projection neurons (PNs) that send dendrites to specific glomeruli in the antennal lobe revealed their stereotypical axon branching patterns and terminal fields in the lateral horn. PNs with similar axon terminal fields tend to receive input from neighboring glomeruli. The glomerular classes of individual PNs could be accurately predicted based solely on their axon projection patterns. The sum of these patterns defines an "axon map" in higher olfactory centers reflecting which olfactory receptors provide input. This map is characterized by spatial convergence and divergence of PN axons, allowing integration of olfactory information.

Olfaction in vector-host interactions

“…The synaptic wiring within single glomeruli provides anatomical evidence for discrete processing channels within individual AL glomeruli, in which functionally distinct ORNs converge and make direct synaptic contacts with PNs. Single neuron tracing of PNs in D. melanogaster along with the stereotypic mapping of ORNs in AL glomeruli also provide anatomical support for these types of channels ( Figure 7B, Couto et al 2005, Marin et al 2002. As mentioned above, an odorant stimulus will typically elicit activity in several ORN classes ( Figure 4A), and consequently several processing channels will be activated by any given stimulus (see above).…”

“…The topographic map in the antennal lobe, of at least D. melanogaster, is retained in the higher olfactory centres, the mushroom body and the lateral horn of the protocerebrum (Jefferies et al 2007, Lin et al 2007, Marin et al 2002, Wong et al 2002. Projection neurons that innervate a given glomerulus display stereotypic branching patterns in these centres, whereas projection neurons innervating different glomeruli exhibit very different arborisation patterns.…”

Synaptic Integration of Olfactory Information in Mouse Anterior Olfactory Nucleus

“…An intriguing structural parallel is that olfactory receptor neurons expressing the same olfactory receptor make convergent projections onto second-order neurons, which are located in the antennal lobe of the insect or the MOB of the mammal. Subsequently, these second-order neurons make divergent projections to their respective targets in the insect protocerebrum and the mammalian olfactory cortex, and evidence suggests that multiple second-order neurons with different response properties may converge on a single postsynaptic thirdorder neuron (Zou et al, 2001;Marin et al, 2002;Wong et al, 2002). This extensive pattern of anatomical divergence and convergence between second-and third-order neurons in these systems may facilitate integration of olfactory information, including the combination of multiple odorant features present in complex natural stimuli.…”

Self-organization in the olfactory system: one shot odor recognition in insects

“…In recent work in Drosophila [29,23,55,44] the specificity of PN projections to the MB and the protocerebrum has been investigated. Marin et al [29], e.g., state: "inspection of axon collateral projections of different classes of PNs did not reveal obvious stereotype as compared to the striking stereotype of lateral horn axon branching pattern and terminal fields ." Other authors interpret the data differently such that the situation remains as yet unclear.…”

“…Each receptor cell expresses one receptor type [48], and all cells with the same receptor type project to the same glomeruli [31,46]. As a result, olfactory information seems to be encoded as combinatorial activation patterns of glomeruli in the AL [21,40,11,29]. In locust, these patterns are transformed to spatio-temporal patterns of active projection neurons (PNs) [22,25,50,24,39] which improve the separation of representations of similar odors [42,18,10].…”