Neural processing of chemosensory information from the locust legs [Elektronische Ressource] / (original) (raw)
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Neural processing of chemosensory information from the locust legs
2000
4.1.1 Exteroceptive Organisation and processing 4.1.2 Chemosensory afferent Organisation 4.1.3 Comparison with other insects 4.1.4 Implication for chemosensory processing by the thoracic ganglia of locusts 4.2 Structure and distribution of tarsus sensilla 4.3 Chemosensory stimulation 4.4 Neuronal pathways producing the avoidance reflex 4.5 Behavioural responses to stimulation with chemical solutions 5.0 References 107 List of Abbreviations used Acknowledgements Curriculum Vitae chemoreceptors in Orthoptera (Kendall, 1970; Henning, 1974; White and Chapman, 1990). Almost all-previous behavioural and electrophysiological work on chemoreception in grasshoppers has concentrated on feeding behaviour and the responses of mouthpart sensilla (Haskell and Schoonhoven, 1969; Blaney, 1974, 1975, 1980; Winstanley and Blaney, 1978), yet here too, sensilla, which are provided with a small cone-shaped hair (length 5-10 µm; socket diameter 10 µm; diameter of the hair 4-6 µm). Generally, each sensillum basiconicum is innervated by 5 sensory neurones present below the hair base and surrounded by the enveloping cells one of which is a mechanosensory neuron to responding to mechanical stimuli while the other are chemosensory (White and Chapman, 1990). Basiconic sensilla are widely distributed over the body, including the legs, but are particularly concentrated on the antennae and on the tips of the mouthparts. They are peg-like structures with a shaft that is typically much Although the insect's tarsus plays an important role in contact chemoreception between the insect and its host plant, little attention has been directed the features of its sensilla. Chemoreceptors on the tarsus of the migratory locust could be involved in the recognition of host plants or sites for oviposition. When locusts walk, land or manipulate their food the tarsal pulvilli (pads) make most of the contact with the substrate. The basiconic chemoreceptive sensilla of the tarsal pulvilli should record the chemical composition of the surface but it is not known what the adequate stimuli are and which regular behavioural responses occur.
Journal of Comparative Physiology A, 2005
Chemical stimulation of contact chemoreceptors located on the legs of locusts evokes withdrawal movements of the leg. The likelihood of withdrawal depends on the site of stimulation, in addition to the identity and concentration of the chemical stimulus. A significantly higher percentage of locusts exhibit leg avoidance movements in response to stimulation of distal parts of the leg with any given chemical stimulus compared to proximal sites. Moreover, the percentage of locusts exhibiting avoidance movements is correlated with the density and sensitivity of chemoreceptors on different sites of an individual leg. The effectiveness of chemical stimulation also differs between the fore and hind legs, with NaCl evoking a higher probability of leg withdrawal movements on the foreleg. Moreover, sucrose was less effective than NaCl at evoking withdrawal movements of the foreleg, particularly at low concentrations. The gradients in behavioural responses can be partially attributed to differences in the responsiveness and density of the contact chemoreceptors. These results may reflect the different specialization of individual legs, with the forelegs particularly involved in food selection.
Local and Intersegmental Interneurons with Chemosensory Inputs from the Locust Ovipositor
2015
Sensory afferents from the ovipositors influence the behaviour of locusts before and during egg-laying. Contact chemoreceptors, known as basiconic sensilla in insects, occur dispersed and crowded in fields between mechanosensory receptors on the ovipositor of the female desert locust Schistocerca gregaria and serve to control the chemical features of the substrate before and during oviposition. Responses of contact chemoreceptors to aqueous solutions of salts (NaCl), sugars (glucose), acids (citric acid), oviposition aggregation pheromones (veratrole and acetophenone), alkaloids (quinine and tomatine), and phenolic compounds (salicin) were seen. Higher order processing occurs in local and ascending interneurones of the terminal abdominal ganglion. We focussed on a cluster of interneurons extending in the anterolateral region of the eighth abdominal neuromere. Several have ascending collaterals to more anterior abdominal ganglia. The physiological and morphological differences betwee...
CHEMORECEPTION IN INSECTS AND THE ACTION OF
The unstabilizing action of DDT on many excitable tissues has been firmly established by work in several laboratories (see Roeder and Weiant, 1948, 1951 for references) . However, as Roeder and Weiant demonstrated, not all irritable tissues are equally sensitive.
Most insects have contact chemoreceptors on various surfaces of their body. The relationship between contact chemoreceptors and landing of female moths in the field to find out a suitable place for egg laying is very important to discover a suitable places for the immature and adults to complete their development. This sense of taste can be involved in a number of behaviours, including avoidance, detection and the selection of food and selection of egg-laying sites. Their contact chemoreceptors have only one terminal porous (basiconic sensilla) and five sensory neurons at their base, with one responding to mechanical contact and the others to different classes of attractant or repellent chemicals. Responses to aqueous solutions of salts (NaCl), sugars (glucose), acids (citric acid), oviposition aggregation pheromones (veratrole and acetophenone), alkaloids (quinine and tomatine), and phenolic compounds (salicin) were seen. Higher order processing occurs in local and ascending intern...
Relatively little is still known about the function, types and location of paraproctal sensory systems. This system detects and encodes four different sensory modalities: wind, touch, gustatory and olfactory. The left and right paraproct of the female locusts are located between the dorsal ovipositor, the epiproct and the ninth abdominal sclerite. They are positioned as the most posterior abdominal segments. In the present study, the distribution and the peripheral innervation of the sensory organs on the paraproct has been studied in wholemount preparations by using the cobalt backfill techniques. The paraproct of the female locust bears hair sensilla of three basic types: a) Mechanosensory hairs (bristle or trichoid) each supplied with one sensory cell, b) Dual innervated mechanosensory hairs with a fine cuticular shaft which are restricted to the region near the posterior edges of the outer faces, c) Basiconic hairs which are multimodal receptors which encode both mechanical and chemical contact cues. The morphology and organization of the central projections of chemoreceptors and mechanoreceptors afferent from the paraproct were examined by neurobiocytin staining individual hair afferents. All afferent fibres project in the tenth neuromere of the terminal abdominal ganglion. Projections from single multiply innervated hair sensilla do not segregate with the exception of one afferent of contact chemosensory hairs which terminate only in its segmental neuromere, as was shown for other contact chemoreceptors of the abdomen. It is concluded that these sensilla at the very tip of the abdomen play a major role for mating, for the selection of oviposition sites and during the different oviposition subroutines.
American Zoologist, 2001
SYNOPSIS. Recent studies have investigated the source and target neurons for the diffusible neuronal messenger molecule nitric oxide (NO) in the nervous system of the locust. Here we compare the neuroarchitecture of NO signaling between different sensory systems. The available neuroanatomical data implicate NO in sensory processing for modalities as diverse as mechanoreception, vision, olfaction, gustation and hearing. All respective first-order sensory neuropils are innervated by NOS-containing interneurons. The corresponding sensory receptor neurons lack NOS but seem to express soluble guanylyl cyclase (sGC), the main receptor molecule for NO in the nervous system. The axonal projections of sensory neurons must therefore be considered the primary target of NO in these sensory neuropils. An exception is the antennal olfactory system where sGC is apparently expressed in interneurons, in partial colocalization with NOS.
Neural Control of Gas Exchange Patterns in Insects: Locust Density-Dependent Phases as a Test Case
Plos One, 2013
The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a nonadaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to patterngenerating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30uC. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control.