A Presynaptic Gain Control Mechanism Fine-Tunes Olfactory Behavior

Self Cite

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197

The role of classical neurotransmitters in the transfer and processing of olfactory information is well established in many organisms. Neuropeptide action, however, is largely unexplored in any peripheral olfactory system. A subpopulation of local interneurons (LNs) in the Drosophila antannal lobe is peptidergic, expressing Drosophila tachykinins (DTKs). We show here that olfactory receptor neurons (ORNs) express the DTK receptor (DTKR). Using twophoton microscopy, we found that DTK applied to the antennal lobe suppresses presynaptic calcium and synaptic transmission in the ORNs. Furthermore, reduction of DTKR expression in ORNs by targeted RNA interference eliminates presynaptic suppression and alters olfactory behaviors. We detect opposite behavioral phenotypes after reduction and over expression of DTKR in ORNs. Our findings suggest a presynaptic inhibitory feedback to ORNs from peptidergic LNs in the antennal lobe.olfactory behavior ͉ presynaptic inhibition ͉ tachykinin ͉ two-photon imaging I n Drosophila, odor detection begins when odor molecules activate olfactory receptor neurons (ORNs) in the antennae and maxillary palps. Each of the ORNs expresses only 1 or a few members of a large family of odorant receptor genes (1-4). These ORNs propagate activity to neurons with dendrites in the glomerular compartments of the antennal lobe; each glomerulus receives inputs from ORNs that express the same odorant receptor (1, 3, 5, 6). In the glomeruli, the activity is read by second-order neurons, designated projection neurons (PNs), which relay information to higher olfactory centers in the brain (7).Inhibitory circuits in the glomeruli, mediated by local interneurons (LNs), play a key role in modulating glomerular signal activity. Presynaptic GABAergic inhibition of the ORNs has been shown in both Drosophila (8, 9) and in mammals (10-12). Conversely, cholinergic LNs in the Drosophila antennal lobe have been suggested to increase and redistribute odor-evoked activity at low odor concentrations (13,14).In addition to GABA and acetylcholine it is likely that certain neuropeptides are used as neuromodulators in the antennal lobe circuitry of insects (15, 16), as also suggested in the olfactory bulb in mammals (17,18). One neuropeptide gene that has been implicated in olfactory processing is dtk (19), a gene encoding 5 tachykinin-related peptides, DTKs (20). The DTKs are expressed in Ϸ150 neurons in the Drosophila brain, and in the antennal lobe glomeruli, there are extensive DTK-immunoreactive arborizations derived from a subset of antennal lobe LNs (21). Two DTK receptors, DTKR and NKD, have been identified in Drosophila (22, 23) and 1 of these, DTKR, is strongly expressed in antennal lobe glomeruli (24). Behavioral evidence for a role of DTKs in olfaction was obtained from analysis of flies where dtk expression was knocked down globally using RNA interference (RNAi); these flies displayed diminished odor sensitivity (19).To gain insight into the neuromodulation provided by the DTK signaling system in the antennal lob...

Section: Discussionsupporting

confidence: 53%

“…Presynaptic GABAergic inhibition of the ORNs has been shown in both Drosophila (8,9) and in mammals (10)(11)(12). Conversely, cholinergic LNs in the Drosophila antennal lobe have been suggested to increase and redistribute odor-evoked activity at low odor concentrations (13,14).…”

mentioning

confidence: 99%

Presynaptic peptidergic modulation of olfactory receptor neurons in Drosophila

Ignell

Root

Birse

et al. 2009

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167

197

“…Signal transduction has been implicated in the regulation of behavior across disparate taxa (21), and several genes on the All Eusocial gene list in this category have known roles in behavior and neuronal function, including metabotropic GABA-B receptor subtype 1 (22). Our results provide further evidence that signal transduction may be a general target of selection during behavioral evolution.…”

Section: Discussionmentioning

confidence: 52%

Genes involved in convergent evolution of eusociality in bees

Woodard

Fischman

Venkat³

et al. 2011

202

225

Eusociality has arisen independently at least 11 times in insects. Despite this convergence, there are striking differences among eusocial lifestyles, ranging from species living in small colonies with overt conflict over reproduction to species in which colonies contain hundreds of thousands of highly specialized sterile workers produced by one or a few queens. Although the evolution of eusociality has been intensively studied, the genetic changes involved in the evolution of eusociality are relatively unknown. We examined patterns of molecular evolution across three independent origins of eusociality by sequencing transcriptomes of nine socially diverse bee species and combining these data with genome sequence from the honey bee Apis mellifera to generate orthologous sequence alignments for 3,647 genes. We found a shared set of 212 genes with a molecular signature of accelerated evolution across all eusocial lineages studied, as well as unique sets of 173 and 218 genes with a signature of accelerated evolution specific to either highly or primitively eusocial lineages, respectively. These results demonstrate that convergent evolution can involve a mosaic pattern of molecular changes in both shared and lineage-specific sets of genes. Genes involved in signal transduction, gland development, and carbohydrate metabolism are among the most prominent rapidly evolving genes in eusocial lineages. These findings provide a starting point for linking specific genetic changes to the evolution of eusociality. social evolution | social insects | sociogenomics | molecular phylogenetics

“…The activity of ORNs, either excitation or inhibition, provides behaviorally relevant information about odorants such as their identity, concentration, and source. The information transduced by an ORN is processed in the antennal lobe (12,13) and sent via PNs to the mushroom bodies, which are believed to be centers for olfactory learning and memory (14,15).…”

mentioning

confidence: 99%

Post-eclosion odor experience modifies olfactory receptor neuron coding in Drosophila

Iyengar

Chakraborty

Goswami

et al. 2010

Olfactory responses of Drosophila undergo pronounced changes after eclosion. The flies develop attraction to odors to which they are exposed and aversion to other odors. Behavioral adaptation is correlated with changes in the firing pattern of olfactory receptor neurons (ORNs). In this article, we present an information-theoretic analysis of the firing pattern of ORNs. Flies reared in a synthetic odorless medium were transferred after eclosion to three different media: (i) a synthetic medium relatively devoid of odor cues, (ii) synthetic medium infused with a single odorant, and (iii) complex cornmeal medium rich in odors. Recordings were made from an identified sensillum (type II), and the Jensen-Shannon divergence (D JS ) was used to assess quantitatively the differences between ensemble spike responses to different odors. Analysis shows that prolonged exposure to ethyl acetate and several related esters increases sensitivity to these esters but does not improve the ability of the fly to distinguish between them. Flies exposed to cornmeal display varied sensitivity to these odorants and at the same time develop greater capacity to distinguish between odors. Deprivation of odor experience on an odorless synthetic medium leads to a loss of both sensitivity and acuity. Rich olfactory experience thus helps to shape the ORNs response and enhances its discriminative power. The experiments presented here demonstrate an experience-dependent adaptation at the level of the receptor neuron.imaginal conditioning | sensory adaptation | odor imprinting | JensenShannon divergence | chemo receptor tuning O lfaction in the fruit fly, Drosophila melanogaster, is crucial for a variety of behaviors, including associative learning (1, 2), courtship (3), foraging (4), and flight (5, 6). Odorants are detected by approximately 1,300 olfactory receptor neurons (ORNs), which are housed in sensilla on the third antennal segment and individually express one of approximately 50 functional odor receptors in adults (7-9). All ORNs expressing the same olfactory receptor project to one of approximately 50 glomeruli in the antennal lobe, where they synapse with a set of projection neurons (PNs) (10, 11). The activity of ORNs, either excitation or inhibition, provides behaviorally relevant information about odorants such as their identity, concentration, and source. The information transduced by an ORN is processed in the antennal lobe (12, 13) and sent via PNs to the mushroom bodies, which are believed to be centers for olfactory learning and memory (14, 15).Experience-dependent modifiability (i.e., plasticity) of olfactory representation at the level of the central nervous system is well known (2,16,17). Relatively little attention has been paid to long-term changes in sensory neuron activity resulting from odor experiences. It was previously shown that exposure of newly born imago to a particular set of odorants alters their responses to these odors (18,19). The flies develop an attraction to the chemicals to which they are exposed and an av...