Spiking Patterns and Their Functional Implications in the Antennal Lobe of the Tobacco Hornworm \u3cem\u3eManduca sexta\u3c/em\u3e

Bursting as well as tonic firing patterns have been described in various sensory systems. In the olfactory system, spontaneous bursts have been observed in neurons distributed across several synaptic levels, from the periphery, to the olfactory bulb (OB) and to the olfactory cortex. Several in vitro studies indicate that spontaneous firing patterns may be viewed as “fingerprints” of different types of neurons that exhibit distinct functions in the OB. It is still not known, however, if and how neuronal burstiness is correlated with the coding of natural olfactory stimuli. We thus conducted an in vivo study to probe this question in the OB equivalent structure of insects, the antennal lobe (AL) of the tobacco hornworm Manduca sexta. We found that in the moth\u27s AL, both projection (output) neurons (PNs) and local interneurons (LNs) are spontaneously active, but PNs tend to produce spike bursts while LNs fire more regularly. In addition, we found that the burstiness of PNs is correlated with the strength of their responses to odor stimulation – the more bursting the stronger their responses to odors. Moreover, the burstiness of PNs was also positively correlated with the spontaneous firing rate of these neurons, and pharmacological reduction of bursting resulted in a decrease of the neurons\u27 responsiveness. These results suggest that neuronal burstiness reflects a physiological state of these neurons that is directly linked to their response characteristics

Infection of Kissing Bugs with Trypanosoma cruzi, Tucson, Arizona, USA

A survey of triatomine insects found that 41.5% were infected with the causative agent of Chagas disease

Spiking Patterns and Their Functional Implications in the Antennal Lobe of the Tobacco Hornworm Manduca sexta

Bursting as well as tonic firing patterns have been described in various sensory systems. In the olfactory system, spontaneous bursts have been observed in neurons distributed across several synaptic levels, from the periphery, to the olfactory bulb (OB) and to the olfactory cortex. Several in vitro studies indicate that spontaneous firing patterns may be viewed as “fingerprints” of different types of neurons that exhibit distinct functions in the OB. It is still not known, however, if and how neuronal burstiness is correlated with the coding of natural olfactory stimuli. We thus conducted an in vivo study to probe this question in the OB equivalent structure of insects, the antennal lobe (AL) of the tobacco hornworm Manduca sexta. We found that in the moth's AL, both projection (output) neurons (PNs) and local interneurons (LNs) are spontaneously active, but PNs tend to produce spike bursts while LNs fire more regularly. In addition, we found that the burstiness of PNs is correlated with the strength of their responses to odor stimulation – the more bursting the stronger their responses to odors. Moreover, the burstiness of PNs was also positively correlated with the spontaneous firing rate of these neurons, and pharmacological reduction of bursting resulted in a decrease of the neurons' responsiveness. These results suggest that neuronal burstiness reflects a physiological state of these neurons that is directly linked to their response characteristics

Physiology of Visual System of the haematophagous bug Triatoma infestans : a behavioral approach

Se estudiaron algunas propiedades del sistema visual de la vinchuca Triatoma infestans. La cuantificación de la respuesta fototáctica negativa de este insecto permitió: 1) establecer el umbral de sensibilidad de la respuesta a la luz blanca (<0.009 μW/cm²);2) demostrar que esta respuesta muestra una variación diaria, siendo mucho mayor durante la noche que durante el día; 3) demostrar que dicho ritmo es de naturaleza endógena, es decir, independiente de los ciclos luz-oscuridad; 4) demostrar la capacidad de los ocelos para mediar por si mismos la respuesta fototáctica; 5) estudiar la sensibilidad espectral de los ojos compuestos de T. infestans, la que fue establecida entre 357 nm (ultravioleta) y 665 nm (rojo lejano); 6) estudiar la dependencia de esta respuesta con la edad y las mutaciones. Por otra parte, mediante técnicas de morfología funcional se estudió la estructura de las omatidias y sus variaciones según el estado de adaptación y el momento del día. Estas variaciones incluyen movimientos de pigmento pantalla y cambios en la distancia focal, que permiten al ojo adaptarse a las condiciones de luz del ambiente. Estos cambios están bajo control de un oscilador endógeno. Se estudió, además, la interacción entre claves olfativas (presentes en las heces de este insecto) y visuales en el comportamiento de agregación de T. infestans. Los resultados muestran que existe una competencia y/o jerarquía entre las señales de distinta modalidad, dependiente de la composición espectral del estímulo visual. Finalmente, se midieron las condiciones luminosas (intensidad y composición espectral de la luz) en un ambiente natural, las que fueron relacionadas con los resultados presentados en este trabajo de Tesis.Some aspects of the visual system of the haematophagous bug Triatoma infestans were studied. The quantitative analysis of the photonegative response of this insect allowed: 1) to establish the threshold for phototactic sensitivity to white light (<0.009 μW/cm²);2) to demonstrate that this response changes on a daily basis, being more intense during the night than during day hours; 3) to demonstrate that this rhythm is under endogenous control; 4) to demonstrate that ocelli can mediate the phototactic response by themselves; 5) to study the spectral sensitivity of the compound eye, being T. infestans sensitive to a wavelength range between 357 (ultraviolet) and 665 nm (far red); 6) to study the effects of age and mutations in this response. Besides, the morphological analysis allowed to study the structure of the ommatidia of the compound eye and its variations according to the state of adaptation and the daytime. These variations include changes in the distribution of screening pigments and in the focal length, which allow the eye to adapt to the environmental light conditions. These changes showed to be under endogenous control. In addition, the interaction between visual and olfactory cues in the assembling behavior of T. infestans was studied. Results showed that there is a hierarchy between sensory modalities, which depends on the spectral composition of the visual stimuli. Finally, the light conditions (intensity and spectral composition) in a natural environment were measured, and related with the results presented here.Fil:Reisenman, Carolina E.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The neural bases of host plant selection in a Neuroecology framework

Understanding how animals make use of environmental information to guide behavior is a fundamental problem in the field of neuroscience. Similarly, the field of ecology seeks to understand the role of behavior in shaping interactions between organisms at various levels of organization, including population-, community- and even ecosystem-level scales. Together, the newly emerged field of Neuroecology seeks to unravel this fundamental question by studying both the function of neurons at many levels of the sensory pathway and the interactions between organisms and their natural environment. The interactions between herbivorous insects and their host plants are ideal examples of Neuroecology given the strong ecological and evolutionary forces and the underlying physiological and behavioral mechanisms that shaped these interactions. In this review we focus on an exemplary herbivorous insect within the Lepidoptera, the giant sphinx moth Manduca sexta, as much is known about the natural behaviors related to hostplant selection and the involved neurons at several level of the sensory pathway. We also discuss how herbivore-induced plant odorants and secondary metabolites in floral nectar in turn can affect moth behavior, and the underlying neural mechanisms

Antagonistic effects of floral scent in an insect–plant interaction

In southwestern USA, the jimsonweed Datura wrightii and the nocturnal moth Manduca sexta form a pollinator–plant and herbivore–plant association. Because the floral scent is probably important in mediating this interaction, we investigated the floral volatiles that might attract M. sexta for feeding and oviposition. We found that flower volatiles increase oviposition and include small amounts of both enantiomers of linalool, a common component of the scent of hawkmoth-pollinated flowers. Because (+)-linalool is processed in a female-specific glomerulus in the primary olfactory centre of M. sexta, we hypothesized that the enantiomers of linalool differentially modulate feeding and oviposition. Using a synthetic mixture that mimics the D. wrightii floral scent, we found that the presence of linalool was not necessary to evoke feeding and that mixtures containing (+)- and/or (−)-linalool were equally effective in mediating this behaviour. By contrast, females oviposited more on plants emitting (+)-linalool (alone or in mixtures) over control plants, while plants emitting (−)-linalool (alone or in mixtures) were less preferred than control plants. Together with our previous investigations, these results show that linalool has differential effects in feeding and oviposition through two neural pathways: one that is sexually isomorphic and non-enantioselective, and another that is female-specific and enantioselective

Evolution of Olfactory Receptors Tuned to Mustard Oils in Herbivorous Drosophilidae.

The diversity of herbivorous insects is attributed to their propensity to specialize on toxic plants. In an evolutionary twist, toxins betray the identity of their bearers when herbivores coopt them as cues for host-plant finding, but the evolutionary mechanisms underlying this phenomenon are poorly understood. We focused on Scaptomyza flava, an herbivorous drosophilid specialized on isothiocyanate (ITC)-producing (Brassicales) plants, and identified Or67b paralogs that were triplicated as mustard-specific herbivory evolved. Using in vivo heterologous systems for the expression of olfactory receptors, we found that S. flava Or67bs, but not the homologs from microbe-feeding relatives, responded selectively to ITCs, each paralog detecting different ITC subsets. Consistent with this, S. flava was attracted to ITCs, as was Drosophila melanogaster expressing S. flava Or67b3 in the homologous Or67b olfactory circuit. ITCs were likely coopted as olfactory attractants through gene duplication and functional specialization (neofunctionalization and subfunctionalization) in S. flava, a recently derived herbivore