| 1. |
- Ignell, Rickard, et al.
(författare)
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Juvenile-hormone-mediated plasticity of aggregation behaviour and olfactory processing in adult desert locusts
- 2001
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 204:2, s. 249-259
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Tidskriftsartikel (refereegranskat)abstract
- In desert locusts Schistocerca gregaria, aggregation behaviour is elicited by aggregation pheromones. In this study, we show that the behavioural response to the major and most potent adult aggregation pheromone component, phenylacetonitrile, is age- and juvenile-hormone-dependent. Furthermore, we show that juvenile hormone influences the responsiveness of olfactory interneurons in the antennal lobe to aggregation pheromone, whereas the responsiveness of antennal receptor neurons is not changed. Old locusts and locusts injected with juvenile hormone, in contrast to young locusts and locusts deprived of juvenile hormone through allatectomy, i.e. after surgical removal of the gland producing this hormone, do not display any aggregation behaviour, as indicated by long-term behavioural observations. The lack of positive olfactory-guided behaviour coincides with an impairment of the central olfactory system, which displays a lower number of neurons responding to aggregation pheromone. Indirect and direct actions of juvenile hormone at different levels of the central nervous system may thus contribute to the regulation and modulation of behavioural responsiveness in the locust.
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| 2. |
- Ignell, Rickard
(författare)
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Olfaction in Desert Locusts- Anatomy, Function and Plasticity of the Central Olfactory System
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The anatomy, function and plasticity of the primary olfactory centre, the antennal lobe (AL), of the desert locust Schistocerca gregaria was investigated using a number of neuroanatomical and neurophysiological methods. Anatomical characterisation of the AL in a number of orthopteran species made it possible to deduce a model concerning the evolution of microglomeruli. These neuropil structures, constituting the first relay centres in the olfactory information pathway of the desert locust, seem to have evolved through fragmentation of multicompartmented unique glomeruli elicited by changes in the architecture of olfactory receptor- and projection neurons. The function and plasticity of the AL was investigated by characterising the response characteristics of olfactory projection neurons in 1st, 3rd, 5th and adult solitary and gregarious locusts by means of intracellular recording and staining methods while stimulating with behaviourally relevant odours. This characterisation revealed stage- and phase-dependent plasticity in the olfactory pathway, including changes and differences in response spectra and sensitivity of olfactory projection neurons. These changes were linked with morphological changes within the AL. Plasticity of olfactory information processing and aggregation behaviour in adult gregarious locusts was also studied in relation to age and juvenile hormone (JH) level. Locusts containing a high level of JH, i. e. old locusts and locusts injected with JH, displayed an impairment of the central olfactory system that was reflected in a diminished behavioural response to the main adult aggregation pheromone component, phenylacetonitrile. Locusts containing a low level of JH, on the other hand, displayed a fully functional olfactory system and a positive response to the tested pheromone component. The morphology and ramification pattern of immunocytochemically identified aminergic and neuropeptidergic neurons were investigated as a first step toward unravelling their potential role in olfactory information processing. This study revealed a number of novel interneurons innervating the AL showing immunoreactivity to serotonin, histamine, locustatachykinin, leucokinin and FMRFamide.
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| 3. |
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| 4. |
- Ignell, Rickard, et al.
(författare)
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The Antennal Lobe of Orthoptera - Anatomy and Evolution
- 2001
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Ingår i: Brain, Behavior and Evolution. - : S. Karger AG. - 0006-8977 .- 1421-9743. ; 57:1, s. 1-17
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The first odor-processing neuropils of insects comprise glomeruli, islets of neuropil, that are supplied by olfactory receptor neurons and give rise to efferent axons to higher brain centers. Glomeruli size and organization varies in a taxon-specific manner across the Insecta, suggesting possible correlates between their organization and chemosensory behaviors in different insect groups. Comparative studies of antennal lobe glomeruli within the Orthoptera have been used to infer how the various taxon-specific arrangements of odorant-processing structures (glomeruli) might have evolved. The cellular arrangements in glomeruli have been surveyed using anterograde filling and Golgi impregnation of antennal receptor neurons projecting to the antennal lobe in Stenopelmatidae, Tettigoniidae, Gryllidae, Tetrigidae and Acrididae. These taxa, which represent the two sub-orders of Orthoptera, reveal a high correlation between the neural architecture of the glomeruli and structures within the glomeruli. Using a recent molecular phylogeny of the Orthoptera we have mapped the occurrence of glomerular characteristics to infer the evolution of antennal lobe structures in orthopterans. The functional implications of these results are discussed.
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| 5. |
- Ignell, Rickard, et al.
(författare)
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The maxillary palp sensory pathway of Orthoptera
- 2001
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Ingår i: Arthropod Structure & Development. - 1467-8039. ; 29:4, s. 295-305
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Tidskriftsartikel (refereegranskat)abstract
- Primary sensory projections and arborisations of higher-order neurons associated with the maxillary palps were examined in Tettigoniidae, Gryllidae, Tetrigidae and Acrididae representing the two sub-orders of Orthoptera, Ensifera and Caelifera. Anterograde filling and Golgi impregnation of maxillary receptor neurons revealed two patterns of innervation, the ensiferous and the caeliferous type. In both ensiferans and caeliferans, receptor neurons arborised within the tritocerebrum, the antennal motor- and mechano-sensory centre and the lobus glomerulatus. In ensiferans, additional areas of innervation were found in the lobus glomerulatus and in a previously undescribed neuropil, here referred to as the accessory lobus glomerulatus. In relation to the anatomical data a putative functional segregation of the neuropil into gustatory-, olfactory- and mechano-sensory centres is implied.
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