Search

The evolution of animal behaviour is poorly understood.sup.1,2. Despite numerous correlations between interspecific divergence in behaviour and nervous system structure and function, demonstrations of the genetic basis of these behavioural differences remain rare.sup.3-5. Here we develop a neurogenetic model, Drosophila sechellia, a species that displays marked differences in behaviour compared to its close cousin Drosophila melanogaster.sup.6,7, which are linked to its extreme specialization on noni fruit (Morinda citrifolia).sup.8-16. Using calcium imaging, we identify olfactory pathways in D. sechellia that detect volatiles emitted by the noni host. Our mutational analysis indicates roles for different olfactory receptors in long- and short-range attraction to noni, and our cross-species allele-transfer experiments demonstrate that the tuning of one of these receptors is important for species-specific host-seeking. We identify the molecular determinants of this functional change, and characterize their evolutionary origin and behavioural importance. We perform circuit tracing in the D. sechellia brain, and find that receptor adaptations are accompanied by increased sensory pooling onto interneurons as well as species-specific central projection patterns. This work reveals an accumulation of molecular, physiological and anatomical traits that are linked to behavioural divergence between species, and defines a model for investigating speciation and the evolution of the nervous system. A neurogenetic model, Drosophila sechellia--a relative of Drosophila melanogaster that has developed an extreme specialization for a single host plant--sheds light on the evolution of interspecific differences in behaviour., Author(s): Thomas O. Auer [sup.1] , Mohammed A. Khallaf [sup.2] , Ana F. Silbering [sup.1] , Giovanna Zappia [sup.1] , Kaitlyn Ellis [sup.3] , Raquel Álvarez-Ocaña [sup.1] , J. Roman [...]

N,N-Diethyl- meta-toluamide (DEET) is the most widely used insect repellent, but it requires repeated application at high, potentially harmful, concentrations, which is prohibitively impractical and costly in the countries suffering [...]

Abstract Background Odors are represented by specific spatio-temporal activity patterns in the olfactory bulb of vertebrates and its insect analogue, the antennal lobe. In honeybees inhibitory circuits in the AL are involved in the processing of odors to shape afferent odor responses. GABA is known as an inhibitory transmitter in the antennal lobe, but not all interneurons are GABAergic. Therefore we sought to analyze the functional role of the inhibitory transmitter histamine for the processing of odors in the honeybee AL. Results We optically recorded the representation of odors before, during and after histamine application at the input level (estimated from a compound signal), and at the output level (by selectively measuring the projection neurons). For both, histamine led to a strong and reversible reduction of odor-evoked responses. Conclusion We propose that histamine, in addition to GABA, acts as an inhibitory transmitter in the honeybee AL and is therefore likely to play a role in odor processing.

The article presents a study to determine the complementary function and integrated wiring of the evolutionarily distinct drosophila olfactory subsystems that expresses the ionotropic receptors (IRs) and odorant receptors (Ors) by using a comprehensive comparative analysis. The study conducts a systematic analysis of the neuroanatomical and physiological properties of IR olfactory circuits, which provide insights into the contrasting origins and function of these olfactory subsystems.

Trace conditioning is a form of classical conditioning, where a neutral stimulus (conditioned stimulus, CS) is associated with a following appetitive or aversive stimulus (unconditioned stimulus, US). Unlike classical delay conditioning, in trace conditioning there is a stimulus-free gap between CS and US, and thus a poststimulus neural representation (trace) of the CS is required to bridge the gap until its association with the US. The properties of such stimulus traces are not well understood, nor are their underlying physiological mechanisms. Using behavioral and physiological approaches, we studied appetitive olfactory trace conditioning in honeybees. Wefound that single-odor presentation created a trace containing information about odor identity. This trace conveyed odor information about the initial stimulus and was robust against interference by other odors. Memory acquisition decreased with increasing CS-US gap length. The maximum learnable CS-US gap length could be extended by previous trace-conditioning experience. Furthermore, acquisition improved when an additional odor was presented during the CS-US gap. Using calcium imaging, we tested whether projection neurons in the primary olfactory brain area, the antennal lobe, contain a CS trace. We found odor-specific persistent responses after stimulus offset. These post-odor responses, however, did not encode the CS trace, and perceived odor quality could be predicted by the initial but not by the post-odor response. Our data suggest that olfactory trace conditioning is a less reflexive form of learning than classical delay conditioning, indicating that odor traces might involve higher-level cognitive processes. [ABSTRACT FROM AUTHOR]

When an animal smells an odor, olfactory sensory neurons generate an activity pattern across olfactory glomeruli of the first sensory neuropil, the insect antennal lobe or the vertebrate olfactory bulb. Here, several networks of local neurons interact with sensory neurons and with output neurons-insect projection neurons, or vertebrate mitral/tufted cells. The extent and form of information processing taking place in these local networks has been subject of controversy. To investigate the role of local neurons in odor information processing we have used the calcium sensorG-CaMPto perform in vivo recordings of odor-evoked spatiotemporal activity patterns in five genetically defined neuron populations of the antennal lobe of Drosophila melanogaster: three distinct populations of local neurons (two GABAergic and one cholinergic), as well as sensory neurons and projection neurons. Odor-specific and concentration dependent spatiotemporal response patterns varied among neuron populations. Activity transfer differed along the olfactory pathway for different glomerulus- odor combinations: we found cases of profile broadening and of linear and complex transfer. Moreover, the discriminability between the odors also varied across neuron populations and was maximal in projection neurons. Discriminatory power increased with higher odor concentrations over a wide dynamic range, but decreased at the highest concentration. These results show the complexity and diversity of odor information processing mechanisms across olfactory glomeruli in the fly antennal lobe. [ABSTRACT FROM AUTHOR]

To understand how odor information is represented and processed in the antennal lobe (AL) of Drosophila melanogaster, we have optically recorded glomerular calcium responses to single odors and odor mixtures from olfactory sensory neurons (OSNs) and projection neurons (PNs). Odor mixtures offer a good tool to analyze odor processing because experimental results can be tested against clear predictions. At the level of the OSNs, the representation of odor mixtures could be predicted from the response patterns of the components in most cases. PN responses to mixtures, however, provide evidences of interglomerular inhibition. Application of picrotoxin (PTX), an antagonist of GABAA-like receptors, enhanced odor responses, modified their temporal course, and eliminated mixture suppression at the PN level. Our results can be best explained by postulating the existence of at least two local networks in the fly AL: a glomerulus specific network, which includes excitatory and inhibitory connections and a PTX sensitive inhibitory global network that acts on all glomeruli with proportional strength to the global AL input. [ABSTRACT FROM AUTHOR]

In the present work, we characterized the effects of serotonin type 3 receptor ligands on recombinant and native alpha 9 alpha 10-containing nicotinic acetylcholine receptors (nAChRs). Our results indicate that the recombinant alpha 9 alpha 10 nAChR shares striking pharmacological properties with 5-HT(3) ligand-gated ion channels. Thus, 5-HT(3) receptor antagonists block ACh-evoked currents in alpha 9 alpha 10-injected Xenopus laevis oocytes with a rank order of potency of tropisetron (IC(50), 70.1 +/- 0.9 nM) > ondansetron (IC(50), 0.6 +/- 0.1 microM) = MDL 72222 (IC(50), 0.7 +/- 0.1 microM). Although serotonin does not elicit responses in alpha 9 alpha 10-injected oocytes, it blocks recombinant alpha 9 alpha 10 receptors in a noncompetitive and voltage-dependent manner (IC(50), 5.4 +/- 0.6 microM). On the other hand, we demonstrate an in vivo correlate of these properties of the recombinant receptor, with those of the alpha 9 alpha 10-containing nAChR of frog saccular hair cells. The possibility that the biogenic amine serotonin might act as a neuromodulator of the cholinergic efferent transmission in the vestibular apparatus and in the organ of Corti is discussed.