Pharmacological analysis of ionotropic glutamate and GABA receptor function in neuronal circuits of the zebrafish olfactory bulb

In the olfactory bulb and other brain areas, basic cellular and synaptic properties of individual neurons have been studied extensively in reduced preparations. Nevertheless, it is still poorly understood how intactions between multiple neurons shape spatio-temporal activity patterns and give rise to the computational properties of the the intact circuit. In this thesis, I used pharmacological manipulations of excitatory and inhibitory neurotransmitter receptors to examine the synaptic interactions underlying spontaneous and odor-evoked activity patterns in the intact olfactory bulb of zebrafish. Electrophysiological and one- and two-photon calcium imaging methods were used to record activity from the principal neurons of the OB (mitral cells, MCs), their sensory input, and local interneurons. The combined blockade of AMPA/kainate and NMDA receptors abolished odor-evoked excitation of MCs, indicating that sensory input to the OB is mediated by ionotropic glutamate receptors. Surprisingly, however, the blockade of AMPA/Kainiate receptors alone increased the mean response of MCs and decreased the mean response of interneurons (INs), and the blockade of NMDA receptors caused little or no change in the mean responses of MCs and INs. In addition, antagonists of both glutamate receptor types had diverse effects on the magnitude and time course of individual MC and IN responses and, thus, changed spatio-temporal activity patterns across neuronal populations. The blockade of GABA(A) receptors increased spontaneous and odor evoked firing rates of mitral cells and often induced rhythmic bursting. Moreover, the blockade of, GABA(A) or AMPA/kainate receptors abolished fast oscillatory activity in the local field potential. Blockade of GABA(B) receptors reduced calcium influx in afferent sensory axons and modulated response time courses of mitral cells. These results indicate that (1) IN activity during an odor response depends mainly on AMPA/Kainiate receptor input, (2) interactions between MCs and INs regulate the total OB output activity, (3) AMPA/Kainiate receptors and GABA(A) receptors underly the synchronization of odor-dependent neuronal ensembles and (4) odor-specific patterns of OB output activity are shaped by circuits containing iGlu receptors and GABA receptors. These results provide insights into the mechanisms underlying the processing of odor-encoding activity patterns in the OB

Early visual experience and the receptive-field organization of optic flow processing interneurons in the fly motion pathway

Karmeier K, Tabor R, Egelhaaf M, Krapp HG. Early visual experience and the receptive-field organization of optic flow processing interneurons in the fly motion pathway. Visual neuroscience. 2001;18(1):1-8.The distribution of local preferred directions and motion sensitivities within the receptive fields of so-called tangential neurons in the fly visual system was previously found to match optic flow fields as induced by certain self-motions. The complex receptive-field organization of the tangential neurons and the recent evidence showing that the orderly development of the fly's peripheral visual system depends on visual experience led us to investigate whether or not early visual input is required to establish the functional receptive field properties of such tangential neurons. In electrophysiological investigations of two identified tangential neurons, it turned out that dark-hatched flies which were kept in complete darkness for 2 days develop basically the same receptive-field organization as flies which were raised under seasonal light/dark conditions and were free to move in their cages. We did not find any evidence that the development of the sophisticated receptive-field organization of tangential neurons depends on sensory experience. Instead, the input to the tangential neurons seems to be "hardwired" and the specificity of these cells to optic flow induced during self-motions of the animal may have evolved on a phylogenetical time scale

Noncovalent magnetic control and reversible recovery of graphene oxide using iron oxide and magnetic surfactants

The unique charging properties of graphene oxide (GO) are exploited in the preparation of a range of noncovalent magnetic GO materials, using microparticles, nanoparticles, and magnetic surfactants. Adsorption and desorption are controlled by modification of pH within a narrow window of <2 pH units. The benefit conferred by using charge-based adsorption is that the process is reversible, and the GO can be captured and separated from the magnetic nanomaterial, such that both components can be recycled. Iron oxide (Fe₂O₃) microparticles form a loosely flocculated gel network with GO, which is demonstrated to undergo magnetic compressional dewatering in the presence of an external magnetic field. For composites formed from GO and Fe₂O₃ nanoparticles, it is found that low Fe₂O₃:GO mass ratios (<5:1) favor flocculation of GO, whereas higher ratios (>5:1) cause overcharging of the surfaces resulting in restabilization. The effectiveness of the GO adsorption and magnetic capture process is demonstrated by separating traditionally difficult-to-recover gold nanoparticles (<i>d</i> ≈ 10 nm) from water. The fully recyclable nature of the assembly and capture process, combined with the vast adsorption capacity of GO, presents obvious and appealing advantages for applications in decontamination and water treatment

Magnetically Responsive Materials based on Polymeric Ionic Liquids and Graphene Oxide for Water Clean-up

Hypothesis Owing to attractive interactions between negatively charged graphene oxide (GO) and a paramagnetic cationic polyelectrolyte (polyallydimethylammonium chloride with a FeCl4− counterion (Fe-polyDADMAC) it should be possible to generate magnetic materials. The benefit of using charge-based adsorption is that the need to form covalently linked magnetic materials is offset, which is expected to significantly reduce the time, energy and cost to make such responsive materials. These systems could have a wide use and application in water treatment. Experiments Non-covalent magnetic materials were formed through the mixing of Fe-pDADMAC and GO. A systematic study was conducted by varying polymer concentration at a fixed GO concentration. UV–Vis was used to confirm and quantify polymer adsorption onto GO sheets. The potential uses of the systems for water purification were demonstrated. Findings Fe-polyDADMAC adsorbs to the surface of GO and induces flocculation. Low concentrations of the polymer (20 mmol/L) induce restabilization. Difficult-to-recover gold nanoparticles can be separated from suspensions as well as the pollutant antibiotic tetracycline. Both harmful materials can be magnetically recovered from the dispersions. This system therefore has economical and practical applications in decontamination and water treatment

Pattern formation in drying blood drops

Funder: Australian Government Research Training Program (RTP) Scholarship.Funder: HaemokinesisPatterns in dried droplets are commonly observed as rings left after spills of dirty water or coffee have evaporated. Patterns are also seen in dried blood droplets and the patterns have been shown to differ from patients afflicted with different medical conditions. This has been proposed as the basis for a new generation of low-cost blood diagnostics. Before these diagnostics can be widely used, the underlying mechanisms leading to pattern formation in these systems must be understood. We analyse the height profile and appearance of dispersions prepared with red blood cells (RBCs) from healthy donors. The red cell concentrations and diluent were varied and compared with simple polystyrene particle systems to identify the dominant mechanistic variables. Typically, a high concentration of non-volatile components suppresses ring formation. However, RBC suspensions display a greater volume of edge deposition when the red cell concentration is higher. This discrepancy is caused by the consolidation front halting during drying for most blood suspensions. This prevents the standard horizontal drying mechanism and leads to two clearly defined regions in final crack patterns and height profile. This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’

Spontaneous Self-Assembly of Thermoresponsive Vesicles Using a Zwitterionic and an Anionic Surfactant.

Spontaneous formation of vesicles from the self-assembly of two specific surfactants, one zwitterionic (oleyl amidopropyl betaine, OAPB) and the other anionic (Aerosol-OT, AOT), is explored in water using small-angle scattering techniques. Two factors were found to be critical in the formation of vesicles: surfactant ratio, as AOT concentrations less than equimolar with OAPB result in cylindrical micelles or mixtures of micellar structures, and salt concentration, whereby increasing the amount of NaCl promotes vesicle formation by reducing headgroup repulsions. Small-angle neutron scattering measurements reveal that the vesicles are approximately 30-40 nm in diameter, depending on sample composition. Small-angle X-ray scattering measurements suggest preferential partitioning of OAPB molecules on the vesicle inner layer to support vesicular packing. Heating the vesicles to physiological temperature (37 °C) causes them to collapse into smaller ellipsoidal micelles (2-3 nm), with higher salt concentrations (≥10 mM) inhibiting this transition. These aggregates could serve as responsive carriers for loading or unloading of aqueous cargoes such as drugs and pharmaceuticals, with temperature changes serving as a simple release/uptake mechanism.Australian Research Council Future Fellowship (FT160100191) to Rico Tabor. and a Discovery Early Career Research Award (DE190100531) to Andrew Clulow

Pharmacological Analysis of Ionotropic Glutamate Receptor Function in Neuronal Circuits of the Zebrafish Olfactory Bulb

Although synaptic functions of ionotropic glutamate receptors in the olfactory bulb have been studied in vitro, their roles in pattern processing in the intact system remain controversial. We therefore examined the functions of ionotropic glutamate receptors during odor processing in the intact olfactory bulb of zebrafish using pharmacological manipulations. Odor responses of mitral cells and interneurons were recorded by electrophysiology and 2-photon Ca2+ imaging. The combined blockade of AMPA/kainate and NMDA receptors abolished odor-evoked excitation of mitral cells. The blockade of AMPA/kainate receptors alone, in contrast, increased the mean response of mitral cells and decreased the mean response of interneurons. The blockade of NMDA receptors caused little or no change in the mean responses of mitral cells and interneurons. However, antagonists of both receptor types had diverse effects on the magnitude and time course of individual mitral cell and interneuron responses and, thus, changed spatio-temporal activity patterns across neuronal populations. Oscillatory synchronization was abolished or reduced by AMPA/kainate and NMDA receptor antagonists, respectively. These results indicate that (1) interneuron responses depend mainly on AMPA/kainate receptor input during an odor response, (2) interactions among mitral cells and interneurons regulate the total olfactory bulb output activity, (3) AMPA/kainate receptors participate in the synchronization of odor-dependent neuronal ensembles, and (4) ionotropic glutamate receptor-containing synaptic circuits shape odor-specific patterns of olfactory bulb output activity. These mechanisms are likely to be important for the processing of odor-encoding activity patterns in the olfactory bulb

Attachment of Salmonella strains to a plant cell wall model is modulated by surface characteristics and not by specific carbohydrate interactions

Background: Processing of fresh produce exposes cut surfaces of plant cell walls that then become vulnerable to human foodborne pathogen attachment and contamination, particularly by Salmonella enterica. Plant cell walls are mainly composed of the polysaccharides cellulose, pectin and hemicelluloses (predominantly xyloglucan). Our previous work used bacterial cellulose-based plant cell wall models to study the interaction between Salmonella and the various plant cell wall components. We demonstrated that Salmonella attachment was favoured in the presence of pectin while xyloglucan had no effect on its attachment. Xyloglucan significantly increased the attachment of Salmonella cells to the plant cell wall model only when it was in association with pectin. In this study, we investigate whether the plant cell wall polysaccharides mediate Salmonella attachment to the bacterial cellulose-based plant cell wall models through specific carbohydrate interactions or through the effects of carbohydrates on the physical characteristics of the attachment surface. Results: We found that none of the monosaccharides that make up the plant cell wall polysaccharides specifically inhibit Salmonella attachment to the bacterial cellulose-based plant cell wall models. Confocal laser scanning microscopy showed that Salmonella cells can penetrate and attach within the tightly arranged bacterial cellulose network. Analysis of images obtained from atomic force microscopy revealed that the bacterial cellulose-pectin-xyloglucan composite with 0.3 % (w/v) xyloglucan, previously shown to have the highest number of Salmonella cells attached to it, had significantly thicker cellulose fibrils compared to other composites. Scanning electron microscopy images also showed that the bacterial cellulose and bacterial cellulose-xyloglucan composites were more porous when compared to the other composites containing pectin. Conclusions: Our study found that the attachment of Salmonella cells to cut plant cell walls was not mediated by specific carbohydrate interactions. This suggests that the attachment of Salmonella strains to the plant cell wall models were more dependent on the structural characteristics of the attachment surface. Pectin reduces the porosity and space between cellulose fibrils, which then forms a matrix that is able to retain Salmonella cells within the bacterial cellulose network. When present with pectin, xyloglucan provides a greater surface for Salmonella cells to attach through the thickening of cellulose fibrils