Circadian Organization of the Neuroendocrine System of an Adult Insect, Rhodnius Prolixus (STÄL) (HEMIPTERA)

Circadian clocks synchronize with external environmental cycles and regulate rhythms throughout the organism, creating an internal temporal organization of cellular and physiological processes. In the model insect Rhodnius prolixus the prothoracicotropic hormone (PTTH)-ecdysteroid axis is a central component of the larval circadian system. However, PTTH is considered a larval hormone and its only known target, the ecdysteroid-producing prothoracic glands, are absent in adults. Here, PTTH is demonstrated to be present in adult female Rhodnius and its synthesis and release during the period of egg development and oviposition were shown to fluctuate with a daily rhythm that is controlled by the circadian clock in the brain. Ecdysteroids are also present during this time and their levels in hemolymph and ovaries undergo synchronous daily variations that are likewise under clock control. Ovaries are the only adult tissue examined that both contained and released ecdysteroids. It is inferred that the ovaries generate the rhythm of ecdysteroids in the hemolymph. The parallel patterns of PTTH and ecdysteroid release suggest these processes are related and it is tempting to speculate that the PTTH-ecdysteroid axis persists in the adult leading to the orchestration of complex adult-specific processes, such as egg development and oviposition

Modulation of nociception and pain by attention and stress

Les facteurs psychologiques tels que l'hypnose, l'émotion, le stress et l’attention exercent un effet modulant puissant sur la nociception et la douleur. Toutefois, l’influence de l'attention sur la nociception et la douleur, ainsi que les mécanismes neuronaux sous-jacents, ne sont pas clairs. La littérature actuelle sur la modulation attentionnelle des réponses spinales nociceptives, telles que mesurées par le réflexe RIII, et de la perception de l’intensité de la douleur est discordante et souvent contradictoire. Ce mémoire fournit un nouveau cadre pour examiner la modulation du réflexe RIII et de la douleur par l’attention. Une tâche de discrimination sensorielle a été décomposée en trois composantes attentionnelles : la vigilance, l’orientation, et le contrôle exécutif. Auparavant, la nature multidimensionnelle de l’attention fut largement ignorée dans la littérature. Nous démontrons que les composantes attentionnelles ont des effets modulatoires distincts sur la nociception et la douleur et suggérons que ceci représente une partie de la confusion présente dans la littérature. En prenant compte du stress indépendamment, nous démontrons, pour la première fois, que le stress inhibe la modulation attentionnelle du réflexe RIII ce qui indique une interaction et dissociation de la modulation des réponses nociceptives par l’attention et le stress. Ces résultats importants clarifient, en grande partie, les contradictions dans la littérature, puisque les tâches cognitives produisent souvent des augmentations du stress ce qui confond l’interprétation des résultats. De plus, la tâche de discrimination inclut des stimuli visuels et somatosensoriels et révèle que l’influence de l'attention sur la douleur est spatialement spécifique tandis que la modulation attentionnelle de la nociception est spécifique à la modalité des stimuli, au moins en ce qui concerne les modalités examinées. A partir de ces résultats, un nouveau modèle de la modulation attentionnelle des processus de la douleur, basée sur les composantes attentionnelles, a été proposé. Celui-ci est appuyé par la littérature et fournit une explication systématique et intégratrice des résultats antérieurement contradictoires. De plus, à partir de ce modèle, plusieurs mécanismes neuronaux ont été proposés pour sous-tendre la modulation attentionnelle de la nociception et de la douleur.Psychological factors such as hypnosis, emotion, stress, and attention produce powerful modulatory effects on nociception and pain. However, the influence of attention on nociception and pain and the underlying neural mechanism responsible are unclear. The current literature on attentional modulation of spinal nociceptive responses, as measured by the RIII reflex, and pain perception (pain intensity) is inconsistent and often contradictory. The present thesis provides a new component-based framework for the examination of attentional modulation of the RIII reflex and pain. A delayed-discrimination task was decomposed into the three components of attention – namely alerting, orienting, and executive control (sensory working memory). Previously, the multidimensional nature of attention was largely ignored in the pain literature. We show that each component of attention exerts a distinct modulatory effect on nociception and pain and suggest that this accounts for some of the confusion in the literature. By considering stress separately, we demonstrate for the first time that stress blocks attentional modulation of the RIII reflex, indicating an interaction and dissociation of attention- and stress-mediated modulation of spinal nociceptive responses. This important finding clarifies much of the disagreement in the literature, since cognitive tasks often induce increases in stress that consequently confound interpretation. Additionally, both visual and somatosensory stimuli were included in the discrimination task, revealing that the influence of attention on pain intensity is spatially-specific whereas attentional modulation of nociception is modality-specific, at least for the modalities investigated. From these findings a component-based model for the attentional modulation of pain processes is proposed. This model is substantially supported by the literature and provides a meaningful and cohesive explanation of the seemingly contradictory results across studies. Moreover, this model suggests potential neural mechanisms underlying the attentional modulation of pain

Pre-ingestive effects of tannins on the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)

The spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), is considered the most important pest threatening the coniferous forests of eastern North America. Its major hosts are balsam fir ( Abies balsamea ), white spruce ( Picea glauca ), red spruce ( Picea rubens ), and black spruce ( Picea mariana ), all of which contain defensive compounds including tannins. Tannins are known to act as feeding deterrents, digestibility reducers, and toxins in numerous insect species and specifically to reduce growth and survival in the spruce budworm. Using two-choice feeding tests, it was discovered that hydrolysable tannins act as a feeding deterrent and condensed tannins extracted from white spruce act as a phagostimulant for the spruce budworm. To my knowledge, this is the first time condensed tannins have been demonstrated to be phagostimulatory in any insect. It was shown that both types of tannins function via different mechanisms: spruce tannins directly stimulate feeding whereas tannic acid interferes with sucrose detection. A dose-response relationship was demonstrated for both types of tannin. Concentrations of defensive compounds and of tannins are affected by certain forest management techniques. Polar extracts from foliage sampled from 3 different thinning regimes were investigated for their affect on spruce budworm feeding, again using the two-choice feeding tests. Differences between trees appear to be more important than the effects of the thinning treatments but more data are necessary in order to make any firm conclusions. Tannin concentrations should be considered in forest management aimed at controlling spruce budworm populations