Towards area wide management of insect vectored viruses of tomatoes in the Bowen district.

The Bowen region of Northern Queensland is an important winter production area for tomatoes in Australia. There are three economically important viruses in the region that affect tomato, Tomato yellow leaf curl virus (TYLCV), Tomato spotted wilt virus (TSWV) and Potato leafroll virus (PLRV), which are vectored by whiteflies, thrips and aphids, respectively. An area wide management approach is required to lower the primary inoculum throughout the district. To this end, we undertook investigations into the virus incidence and alternative hosts for the virus and vectors in different cropping regions throughout the district, as well as local management options such as insecticide application and possible non-host cover crops for the wet-season break in production. The initial incidence of Potato leafroll virus was very high, most probably due to abnormal weather patterns for the district, and has ceased to be a problem. Tomato yellow leaf curl virus is a continual problem even at the beginning of the season, indicating large reservoir host(s) in the environment. Only four alternative hosts have been identified: Stachytarpheta jamaicensis (TSWV), Solanum americanum (PLRV and TYLCV) Trianthema portulacastrum (TYLCV), and Amaranthus viridis(TLYCV). Different insecticide and application options were trialled for protection against Tomato yellow leaf curl virus, with the best possible option yielding marketable fruit more than ninety percent of a resistant hybrid. A trial of yield vs time of infection of TYLCV found that whitefly exclusion for 6 weeks post-transplant yielded an average increase of nearly three kilograms of marketable fruit per plant. A number of pulse crops have been confirmed as non-hosts of tomato yellow leaf curl for use as cover crops in the wet-season break. Most of the production has moved to dual resistant TYLCV/TSWV hybrids, though an area wide management program still needs to be established to reduce the primary inoculum throughout the district, giving growers more varietal options, especially early in the season.

Changes during development in transport processes of the blood-brain barrier.

The permeability of the blood-brain barrier to several classes of compounds was studied in rats between the ages of 15 days and 9 weeks. 14C-labelled test substances were injected simultaneously with two reference isotopes, 3H2O and 113mIn-labelled EDTA, into the common carotid artery followed by decapitation 10 s later. There was evidence that a monocarboxylic acid transport system in 15 to 23 day-old rats had a capacity at least six times greater than that present in adult animals. L-Lactate and acetate showed the highest permeability. At all ages there was a constant ratio between L-lactate and (-)D-3-hyroxybutyrate values. D-Glucose permeability increased with age, while that of several amino acids tested was the same in young and adult rats.

Regional brain blood flow, blood volume, and haematocrit values in the adult rat.

Measurements of red cell volume, plasma volume, and tissue haematocrit (Hct) were made in 14 brain regions in adult rats using 51Cr-tagged red cells and 125I-labeled human serum albumin. The mean large vessel (systemic artery) Hct was 41.8, total body Hct was 35.3, and of the brain regions, the lowest value (septal nucleus) was 25.91 and the highest (visual cortex) was 32.05. The lowest blood volume was 6.29 microliters g-1 (caudate putamen) and the highest was 14.44 microliters g-1 (inferior colliculus). There was a significant difference between regions in both blood volume and tissue blood Hct. When brain regions were ranked in order of blood volume, this did not coincide with the order for blood flow.

Tracer 2-deoxyglucose kinetics in brain regions of rats given kainic acid.

The initial distribution of tracer amounts of 2-deoxyglucose between plasma and brain tissue, relative to native glucose, and the rate of accumulation of 2-deoxyglucose-6-phosphate were determined in brain regions of rats given kainic acid intravenously. Regional plasma flow was measured in a comparable group of animals. A previously described compartmental model was used to obtain estimates of rates of glucose transport and of glucose phosphorylation. Both rates were significantly increased in entorhinal cortex, hippocampus, amygdala, and septal nucleus. From measured brain tissue and plasma glucose concentrations, glucose fluxes were also calculated in terms of either irreversible or reversible Michaelis-Menten kinetics. In all brain regions of control rats and in six of the ten regions studied in rats given kainic acid, rates of glucose transport calculated in terms of the Michaelis-Menten models were consistent with those estimated by the tracer 2-deoxyglucose procedure. However, in the four regions in which glucose metabolism was stimulated, rates of glucose transport calculated from the behaviour of tracer 2-deoxyglucose were considerably higher than rates calculated from measured concentrations of glucose in plasma and brain tissue using Michaelis-Menten models. The possibility is considered that in those regions that are metabolically stimulated by kainate, there is an increasing asymmetry between the luminal and abluminal membranes of the capillary endothelium in the permeability to glucose and its analogs. An alternative proposal is that in the model used to analyse the tracer 2-deoxyglucose data, the assumption of a rapid mixing of tracer throughout the endogenous pool of tissue glucose prior to phosphorylation becomes invalid. The discrepancies between tracer and native glucose in these particular regions of rats given kainate are consistent with an apparent metabolic compartmentation. The influence of kainate on plasma flow was found to differ regionally, with flow in entorhinal cortex, hippocampus, and amygdala being unchanged. There is some evidence for increased rates of glycolysis relative to oxidative metabolism in these regions.

Relationships between extraction and metabolism of glucose, blood flow, and tissue blood volume in regions of rat brain.

Studies were made on the relationships between the rate of glucose metabolism, the transport of glucose between plasma and brain, cerebral blood flow, and blood content. Conscious control rats were compared with rats with intense tremors induced with cismethrin. The influence of plasma glucose concentration was studied by fasting some animals overnight prior to the induction of tremors. Mean plasma glucose was 8.83 mM in controls, 12.57 mM in fed rats with tremors, and 4.94 mM in rats fasted overnight prior to induction of tremors. Of 12 brain regions studied, nine showed an increased rate of glucose utilization in both fed and fasted trembling rats. Cerebellum had the highest percentage increase (200%). Rates of unidirectional glucose influx in fed trembling rats were significantly greater than those in controls in eight regions. In fasted animals, rates were the same as in controls, except in cerebellum, where it was 1.6 times higher. These high rates of glucose influx at low plasma glucose concentrations were indicative of a change in kinetic parameters of glucose transport. Unidirectional glucose influx rates were transformed to estimates of maximal transport rates (Tmax), based on the Michaelis-Menten equation. Average plasma glucose concentrations in regional capillaries (c) were calculated and shown to be maintained at values close to arterial plasma glucose concentrations (Ca), in all brain regions of each group. In trembling rats, Tmax for each brain region was higher than that in controls. In fasted rats with tremors, Tmax was higher in several brain regions than in fed rats. Tmax in cerebellum was 3.37, 4.71, and 7.89 mumol g-1 min-1 in control, fed trembling, and fasted trembling rats, respectively. Blood flow increased significantly in all regions in rats with tremors and was higher in fasted than in fed animals. There was only a weak correlation between blood flow and Tmax. Blood content of several regions increased in rats with tremors, and there was a strong correlation between Tmax and tissue blood volume. Results are consistent with localized regulatory links between blood flow, capillary surface area, and glucose transport in response to metabolic demand and hypoglycaemia. These involve changes in the linear velocity of blood through capillaries and in the extent of capillary recruitment.

Studies on the relationship between cerebral glucose transport and phosphorylation using 2-deoxyglucose.

Regional rates of blood-brain glucose transfer and phosphorylation have been measured in anaesthetized fasted and conscious fed and fasted rats using a dual-label 2-deoxyglucose technique that exploits differences in the early-time distribution of analogue and native glucose between blood and brain. Regional cerebral blood flow was also measured in comparable groups of rats. Estimates of glucose influx in the anaesthetized group were compared with those calculated from previously published kinetic constants obtained using [14C]D-glucose as tracer. The close agreement of these two sets of results served to validate estimates of influx obtained using the glucose analogue. Comparisons between all three groups showed that regional rates of glucose influx were maintained at levels appropriate to the rate of cerebral glucose phosphorylation. This occurred despite wide variations in plasma glucose concentration. The results indicate that at least two factors are involved in the adaptation of glucose supply to meet metabolic demand. One is related to blood flow, and probably reflects changes in the surface area of the capillary endothelium perfused. The second involves changes in the blood-brain barrier permeability to glucose and could reflect changes in the density of functioning glucose transporters within capillary endothelial cell membranes.

A two-compartment description and kinetic procedure for measuring regional cerebral [11C]nomifensine uptake using positron emission tomography.

S-[11C]Nomifensine (S-[11C]NMF) is a positron-emitting tracer suitable for positron emission tomography, which binds to both dopaminergic and noradrenergic reuptake sites in the striatum and the thalamus. Modelling of the cerebral distribution of this drug has been hampered by the rapid appearance of glucuronide metabolites in the plasma, which do not cross the blood--brain barrier. To date, [11C]NMF uptake has simply been expressed as regional versus nonspecific cerebellar activity ratios. We have calculated a "free" NMF input curve from red cell activity curves, using the fact that the free drug rapidly equilibrates between red cells and plasma, while glucuronides do not enter red cells. With this free [11C]NMF input function, all regional cerebral uptake curves could be fitted to a conventional two-compartment model, defining tracer distribution in terms of [11C]NMF regional volume of distribution. Assuming that the cerebellar volume of distribution of [11C]NMF represents the nonspecific volume of distribution of the tracer in striatum and thalamus, we have calculated an equilibrium partition coefficient for [11C]NMF between freely exchanging specific and nonspecific compartments in these regions, representing its "binding potential" to dopaminergic or noradrenergic uptake sites (or complexes). This partition coefficient was lower in the striatum when the racemate rather than the active S-enantiomer of [11C]NMF was administered. In the striatum of patients suffering from Parkinson's disease and multiple-system atrophy, the specific compartmentation of S-[11C]NMF was significantly decreased compared with that of age-matched volunteers.

Compartmental analysis of diprenorphine binding to opiate receptors in the rat in vivo and its comparison with equilibrium data in vitro.

The regional binding of the opiate receptor ligand diprenorphine has been examined in rat brain both in vivo and in vitro. The time course of total label in specific brain regions was followed up to 2 h after intravenous bolus injection of [3H]diprenorphine, with or without a pulse chase of unlabelled diprenorphine at 30 min. In addition, total label was measured 30 min after injection of labelled diprenorphine at nontracer concentrations over a range of specific activities. Total data sets for each region were fitted simultaneously to a compartmental model to give estimates of maximal binding capacity (Bmax), the second-order apparent association rate constant, and the first-order dissociation rate constant of the receptor-ligand complex. The model incorporated the use of a reference region with low specific binding (cerebellum). The binding of diprenorphine to rat brain homogenates was measured in vitro under equilibrium conditions at 37 degrees C, pH 7.4, in the presence and absence of naloxone, to give corresponding regional estimates of Bmax and the half-saturation constant Kd. The results showed a close correlation between in vitro and in vivo regional estimates of Bmax over a wide range. There were no significant interregional differences either in Kd in vitro or in the Kd derived from the in vivo analysis, although in vitro and in vivo estimates differed by an order of magnitude. This work was carried out as part of a validation study with a view to the application of the compartmental model to data obtained in vivo in humans using positron emission tomography, when successive studies over a range of specific activities are not feasible.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of cerebral monoamine oxidase B activity using L-[11C]deprenyl and dynamic positron emission tomography.

A tracer kinetic procedure was developed for the measurement of monoamine oxidase type B (MAO-B) activity using L-[11C]deprenyl and positron emission tomography (PET). The kinetic model consisted of two tissue compartments with irreversible binding to the second compartment (three rate constants). In addition, a blood volume component was included. Special attention was given to the accurate measurement of the plasma and whole blood input functions. The method was applied to the measurement of the dose-response curve of a reversible MAO-B inhibitor (Ro 19-6327). From the results, it followed that the rate constant for irreversible binding (k3) appeared to be a better index of MAO-B activity than the net influx constant Ki. Furthermore, regional analysis demonstrated that Ki, but not k3, was flow dependent. This implies that full kinetic analysis is required for an accurate assessment of MAO-B activity.

Macrophage and astrocyte populations in relation to [3H]PK 11195 binding in rat cerebral cortex following a local ischaemic lesion.

PK 11195 is a selective and specific ligand for the peripheral-type benzodiazepine binding site. Its potential for in vivo visualisation of lesioned human brain using positron emission tomography (PET) is currently being assessed. The present study examines the relationship between the temporal development of a local ischaemic lesion with its associated cell populations and the binding of [3H]PK 11195 in rat brain. Unilateral cortical infarcts were induced using the photosensitive dye Rose Bengal. At time intervals from 1 to 7 days after lesioning, the localisation of [3H]PK 11195 binding was determined using in vivo and in vitro autoradiography. Sections adjacent to those used for autoradiography were processed for immunohistochemistry using glial fibrillary acidic protein for astrocytes and ED-1 for macrophages. The results show that the binding of [3H]PK 11195 correlates in both time and spatial localisation with the appearance of macrophages around the lesion. Reactive astrocytes, although present, occupy a separate region in the tissue surrounding the lesion and lie outside the region defined by the [3H]PK 11195 binding. We conclude that the [3H]PK 11195 signal associated with this ischaemic lesion originates primarily from binding to macrophages and that [11C]PK 11195 could be used for imaging acute inflammatory response in human brain using PET.

Dynamic monitoring of [11C]diprenorphine in rat brain using a prototype positron imaging device.

The present work tests the feasibility of using the most recently developed positron emission tomograph detector technology to image positron-emitting radioligands in small experimental animals. A prototype imaging device, using two opposing multicrystal, high-resolution (approximately 4 mm) block detectors of bismuth germanate to produce a 2-dimensional image in the centre of the field of view, is described. To evaluate the probe's potential as a non-invasive experimental tool, the dynamic regional distribution of the established opiate receptor ligand, [11C]diprenorphine was determined in rat brain following intravenous injection. The distribution of counts in the images was consistent with the localisation of diprenorphine binding sites and the specificity of the signal obtained was confirmed by administration of non-radioactive diprenorphine and naloxone. Although the signal-to-noise ratio was reduced compared with data obtained by post mortem dissection, the dynamic data acquisition capabilities of the system demonstrate the feasibility of monitoring the kinetics of ligand binding in individual animals and encourages further design of a small-diameter detector system with tomographic capabilities.

A method for the simultaneous estimation of regional rates of glucose influx and phosphorylation in rat brain using radiolabeled 2-deoxyglucose.

A procedure is described which allows the simultaneous estimation of the rate of glucose influx from blood to brain and of the rate of glucose phosphorylation in discrete brain regions of the rat. The method is applicable over an experimental period of 5 min and involves sequential i.v. injections of [14C]2-deoxyglucose and [3H]2-deoxyglucose. Arterial blood samples are collected over the experimental period. After 5 min the rat is killed by microwave irradiation to the head and the brain dissected. The data obtained on glucose, 2-deoxyglucose and 2-deoxyglucosephosphate concentrations in plasma and brain are analyzed in terms of a model which relates the kinetics of 2-deoxyglucose uptake and phosphorylation to those of glucose. The model is based on measurements made of the relative rates of unidirectional influx of glucose and 2-deoxyglucose and of their relative fractional rates of phosphorylation.

Brain metabolism and specific transport at the blood-brain barrier after portocaval anastomosis in the rat.

The rapid metabolism of [1-14C]butyrate and [2-14C]pyruvate in the brain was studied after intracarotid injection in control rats and rats given an end-to-side portocaval anastomosis (PCA). At 10 or 50 sec after injection there was a 40-50% lowering of the total amount of radioactivity in the brain of operated rats for both compounds. The percentage distribution of label in various metabolic fractions, e.g. amino acids, was unaltered by PCA. The results from the metabolic studies focused on an impaired transport of short chain monocarboxylic acids between blood and brain in rats with a PCA. The brain uptake index (BUI) of acetate, butyrate, pyruvate and glucose was determined by rapid intracarotid injection of the 14C test compound plus 3H2O as a reference marker. At 3 weeks after PCA, transport of all 3 monocarboxylic acids into brain was reduced by 40-50%. The reduction in [2-14C]pyruvate uptake was absent at one week, but thereafter, up to 50 weeks after operation, was consistently present. Eadie-Hofstee analysis of influx at varying substrate concentrations indicated a reduction in Vmax values of pyruvate and butyrate uptake without changes in Km. The calculated influx rate of glucose in operated rats was reduced in direct proportion to the lowering of plasma glucose. Portocaval anastomosis in the rat induces selective changes on substrates that are transported across the blood-brain barrier via a facilitated transport process.

A study of the kinetic behaviour of glucose based on simultaneous estimates of influx and phosphorylation in brain regions of rats in different physiological states.

Results from the application of a procedure that allows simultaneous estimation of the rates of glucose transport from blood and of glucose phosphorylation in discrete regions of the brain are given for groups of rats displaying chemically induced motor disturbances. The procedure is based on sequential injections of [14C]- and [3H]-2-deoxyglucose followed a few minutes later by focused microwave irradiation to the head. Control conscious rats were used and rats displaying either whole body tremors, hind-limb rigidity or choreoathetotic movements induced by synthetic pyrethroid compounds. For individual rats estimates of 5 parameters were obtained in up to 16 brain regions. In addition brain tissue and plasma glucose concentrations were determined. The 5 parameters were: (1) rate of total glucose influx from plasma; (2) rate of glucose phosphorylation (equivalent to net influx); (3) rate of glucose efflux; (4) half-life of free glucose in brain; and (5) PS-product expressed as the ratio of the rate of glucose influx to plasma glucose concentration. For each parameter significant differences between regions were found in all groups of animals including conscious controls. The mean values for the somatosensory cortex of control rats were parameter: (1) 2.02 mumol/g/min; (2) 1.11 mumol/g/min; (3) 0.91 mumol/g/min; (4) 0.94 min; and (5) 0.196 ml/g/min. A high correlation was observed between the rate of total glucose influx and the rate of glucose phosphorylation for all brain regions in all groups of rats. This finding is discussed in terms of a synchronized regulatory mechanism on the glucose transport carrier of capillary endothelial cells and on the functional hexokinase Vmax activity within brain cells.

Anatomical mapping of glucose transporter protein and pyruvate dehydrogenase in rat brain: an immunogold study.

The regional and cellular distributions of glucose transporter protein (GT) and pyruvate dehydrogenase (PDH) have been studied with an enhanced immunogold method. The results showed significant amounts of GT in neuropil within regions known to exhibit high demands for glucose whilst neuronal perikarya showed little immunostaining. In contrast PDH immunostaining was most intense in neuronal perikarya. The distributions of these proteins were compared and discussed in relation to existing data on local cerebral glucose utilization and the distribution of other important metabolic enzymes. The results suggest that glucose is transported and metabolised in neuropil and that metabolic products such as pyruvate are transported into the neuronal cell body to undergo further metabolism.

[3H]PK 11195 and the localisation of secondary thalamic lesions following focal ischaemia in rat motor cortex.

The peripheral-type benzodiazepine binding site (PTBBS) ligand, PK 11195, is known to be a marker of damage in the central nervous system, the binding being predominantly to macrophages. Using photochemically induced focal cortical ischaemia as a lesion model in the rat, we have investigated the detection of secondary lesions using [3H]PK 11195 and ex vivo autoradiography. Secondary lesions in the thalamus became apparent during the second week post-lesioning, at a time when [3H]PK 11195 binding around the primary lesion was beginning to subside. Using Brain Browser software, the identity of the labelled thalamic nucleus was confirmed, objectively, as the ventrolateral nucleus, known to have reciprocal connections with the lesioned cortical area. As with the primary lesion, high densities of PTBBS correlated with infiltration of macrophages. Three-dimensional reconstruction of [3H]PK 11195 autoradiograph images showed binding along white matter tracts between the primary and secondary lesions. We conclude that radiolabelled PK 11195 given in vivo can be used in the visualisation of secondary lesions and their associated degenerating tracts.

Changes in regional cerebral blood flow and glucose metabolism associated with symptoms of pyrethroid toxicity.

Regional rates of blood flow (rCBF) and of glucose metabolism (rCMRG) were measured in rats showing symptoms typical of an early stage of the type-2 syndrome of pyrethroid toxicity ie. salivation, chewing, and repetitive head and forelimb movements induced by deltamethrin. rCBF was significantly increased in the fourteen brain regions examined, while rCMRG was increased in thirteen of them. In many of the regions the rate of blood flow became excessive in relation to the rate of glucose utilization. This was notable in areas of cerebral cortex, caudate putamen and hippocampus. Values for blood flow in the cortical regions were remarkably similar to those found in rats showing symptoms typical of the type-1 syndrome of pyrethroid toxicity ie. tremors and heightened startle response induced with cismethrin. Excessive blood flow in cerebral cortex appears to be intrinsic to pyrethroid intoxication and unrelated to specific motor symptoms. By contrast, in cerebellum increases in both rCMRG and rCBF appear to correlate with motor disturbances. Other than in cerebellum, a significant increase in rCBF was of early onset, occurring in animals showing salivation and chewing as the only symptoms after being given deltamethrin. The very high ratio of rCBF/rCMRG found in many brain regions of rats given synthetic pyrethroid compounds is unusual and unexplained.