ORCID Profile
0000-0002-7634-127X
Current Organisations
University of Queensland
,
University of Southern Queensland
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Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.MCN.2011.02.012
Abstract: Correct wiring of the nervous system during development requires axons to respond appropriately to gradients of attractive and repulsive guidance cues. However, the steepness and concentration of these gradients vary in vivo, for instance, with distance from the target. Understanding how these changing conditions affect the navigation strategies used by developing axons is important for understanding how they are guided over long distances. Previous work has shown that cyclic nucleotide levels determine whether axons are attracted or repelled by steep gradients of the same guidance cue, but it is unknown whether this is also true for shallow gradients. We therefore investigated the guidance responses of rat superior cervical ganglion (SCG) axons in both steep and shallow gradients of nerve growth factor (NGF). In steep gradients we found that cyclic nucleotide-dependent switching occurred, consistent with previous reports. Surprisingly however, we found that in shallow NGF gradients, cyclic nucleotide-dependent switching did not occur. These results suggest that there may be substantial differences in the way axons respond to gradient-based guidance cues depending on where they are within the gradient.
Publisher: Frontiers Media SA
Date: 17-01-2018
Publisher: Elsevier BV
Date: 03-2016
DOI: 10.1016/J.CUB.2016.01.041
Abstract: The tectum has long been known as a hub of visual processing, and recent studies have elucidated many of the circuit-level mechanisms by which tectal neurons filter visual information. Here, we use population-scale imaging of tectal neurons expressing a genetically encoded calcium indicator to characterize tectal responses to non-visual stimuli in zebrafish. We identify ensembles of neurons responsive to stimuli for each of three sensory modalities: vision, audition, and water flow sensation. These ensembles display consistently represented response profiles to our stimuli, and each has a preferred stimulus and salient feature to which it is most responsive. Each sensory modality drives a unique spatial profile of activity in the tectal neuropil, suggesting that the neuropil's laminar structure functionally subserves multiple modalities. The positions of the responsive neurons in the periventricular layer are also distinct across modalities, and very few neurons are responsive to multiple modalities. The cells contributing to each ensemble are highly variable from trial to trial, but ensembles contain "cores" of reliably responsive cells, suggesting a mechanism whereby they could maintain consistency in reporting salient stimulus features while retaining flexibility to report on similar stimuli. Finally, we find that co-presentation of auditory or water flow stimuli suppress visual responses in the tectum.
Publisher: CSIRO Publishing
Date: 2023
DOI: 10.1071/CP22335
Publisher: Wiley
Date: 29-07-2023
DOI: 10.1111/PPA.13777
Abstract: Common root rot (CRR) caused by the soilborne pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus ) is becoming increasingly prevalent worldwide. Identification of CRR is difficult and time‐consuming for human assessors due to the non‐distinctive above‐ground symptoms, with browning of subcrown internodes and roots the most distinguishing symptom of infection. CRR disease has been recognized as a significant disease for cereal crops in many countries. In 2009, CRR in Australia was estimated to cause $30 million average annual yield loss for wheat and $13 million for barley. Recent evidence indicates CRR may be more prevalent than expected in Australian wheat cropping areas due to lack of research on this disease. Low levels of B. sorokiniana survive in the soil for up to 10 years and attack plants at early stages of growth. Therefore, mitigating CRR in wheat and barley may not be practical at the late stages of infection due to lack of effective methods however, early detection might be viable to alleviate the impact of this disease. A comprehensive overview of CRR caused by B. sorokiniana , including disease background, worldwide economic losses, management methods, potential CRR detection using multispectral and hyperspectral sensors and the research focus over the past 50 years is provided in this article. This review paper is expected to provide thorough supplemental information for current studies about CRR and proposes recommendations for whole‐of‐field disease scouting methods to farmers, enabling reduced time and cost for CRR management and increasing wheat and barley production worldwide.
Publisher: University of Queensland Library
DOI: 10.14264/UQL.2016.47
Publisher: Frontiers Media SA
Date: 2015
Publisher: Elsevier BV
Date: 05-2012
DOI: 10.1016/J.NEURON.2012.02.035
Abstract: Correct guidance of axons to their targets depends on an intricate network of signaling molecules in the growth cone. Calcium and cAMP are two key regulators of whether axons are attracted or repelled by molecular gradients, but how these molecules interact to determine guidance responses remains unclear. Here, we constructed a mathematical model for the relevant signaling network, which explained a large range of previous biological data and made predictions for when axons will be attracted or repelled. We then confirmed these predictions experimentally, in particular showing that while small increases in cAMP levels promote attraction large increases do not, and that under some circumstances reducing cAMP levels promotes attraction. Together, these results show that a relatively simple mathematical model can quantitatively predict guidance decisions across a wide range of conditions, and that calcium and cAMP levels play a more complex role in these decisions than previously determined.
Publisher: Springer Science and Business Media LLC
Date: 11-02-2015
Publisher: Proceedings of the National Academy of Sciences
Date: 03-2010
Abstract: Guidance of axons by molecular gradients is crucial for wiring up the developing nervous system. It often is assumed that the unique signature of such guidance is immediate and biased turning of the axon tip toward or away from the gradient. However, here we show that such turning is not required for guidance. Rather, by a combination of experimental and computational analyses, we demonstrate that growth-rate modulation is an alternative mechanism for guidance. Furthermore we show that, although both mechanisms may operate simultaneously, biased turning dominates in steep gradients, whereas growth-rate modulation may dominate in shallow gradients. These results suggest that biased axon turning is not the only method by which guidance can occur.
Publisher: Springer Science and Business Media LLC
Date: 07-10-2016
DOI: 10.1038/SREP34887
Abstract: Sensory coding relies on ensembles of co-active neurons, but these ensembles change from trial to trial of the same stimulus. This is due in part to wide variability in the responsiveness of neurons within these ensembles, with some neurons responding regularly to a stimulus while others respond inconsistently. The specific functional properties that cause neurons to respond more or less consistently have not been thoroughly explored. Here, we have examined neuronal ensembles in the zebrafish tectum responsive to repeated presentations of a visual stimulus, and have explored how these populations change when the orientation or brightness of the stimulus is altered. We found a continuum of response probabilities across the neurons in the visual ensembles, with the most responsive neurons focused toward the spatial centre of the ensemble. As the visual stimulus was made dimmer, these neurons remained active, suggesting higher overall responsiveness. However, these cells appeared to represent the most consistent end of a continuum, rather than a functionally distinct “core” of highly responsive neurons. Reliably responsive cells were broadly tuned to a range of stimulus orientations suggesting that, at least for this stimulus property, tight stimulus tuning was not responsible for their consistent responses.
No related grants have been discovered for Andrew Thompson.