Linking fine-scale behaviour to the hydraulic environment shows behavioural responses in riverine fish

BACKGROUND

Fish migration has severely been impacted by dam construction. Through the disruption of fish migration routes, freshwater fish communities have seen an incredible decline. Fishways, which have been constructed to mitigate the problem, have been shown to underperform. This is in part due to fish navigation still being largely misunderstood. Recent developments in tracking technology and modelling make it possible today to track (aquatic) animals at very fine spatial (down to one meter) and temporal (down to every second) scales. Hidden Markov models are appropriate models to analyse behavioural states at these fine scales. In this study we link fine-scale tracking data of barbel (Barbus barbus) and grayling (Thymallus thymallus) to a fine-scale hydrodynamic model. With a HMM we analyse the fish's behavioural switches to understand their movement and navigation behaviour near a barrier and fishway outflow in the Iller river in Southern Germany.

METHODS

Fish were tracked with acoustic telemetry as they approached a hydropower facility and were presented with a fishway. Tracking resulted in fish tracks with variable intervals between subsequent fish positions. This variability stems from both a variable interval between tag emissions and missing detections within a track. After track regularisation hidden Markov models were fitted using different parameters. The tested parameters are step length, straightness index calculated over a 3-min moving window, and straightness index calculated over a 10-min window. The best performing model (based on a selection by AIC) was then expanded by allowing flow velocity and spatial velocity gradient to affect the transition matrix between behavioural states.

RESULTS

In this study it was found that using step length to identify behavioural states with hidden Markov models underperformed when compared to models constructed using straightness index. Of the two different straightness indices assessed, the index calculated over a 10-min moving window performed better. Linking behavioural states to the ecohydraulic environment showed an effect of the spatial velocity gradient on behavioural switches. On the contrary, flow velocity did not show an effect on the behavioural transition matrix.

CONCLUSIONS

We found that behavioural switches were affected by the spatial velocity gradient caused by the attraction flow coming from the fishway. Insight into fish navigation and fish reactions to the ecohydraulic environment can aid in the construction of fishways and improve overall fishway efficiencies, thereby helping to mitigate the effects migration barriers have on the aquatic ecosystem.

Agricultural contaminants in amphibian breeding ponds: Occurrence, risk and correlation with agricultural land use

Anthropogenic pressure such as agricultural pollution globally affects amphibian populations. In this study, a total of 178 different compounds from five agrochemical groups (i.e. antimicrobial drugs residues (ADRs), coccidiostats and anthelmintics, heavy metals, mycotoxins and pesticides) were determined monthly, from March until June 2019 in 26 amphibian breeding ponds in Flanders, Belgium. Furthermore, a possible correlation between the number and concentration of selected contaminants that were found and the percentage of arable land within a 200 m radius was studied. Within each group, the highest detected concentrations were obtained for 4-epioxytetracycline (0.422 μg L^-1), levamisole (0.550 μg L^-1), zinc (333.1 μg L^-1), 3-acetyldeoxynivalenol (0.013 μg L^-1), and terbuthylazine (38.7 μg L^-1), respectively, with detection frequencies ranging from 1 (i.e. 3-acetyldeoxynivalenol) to 26 (i.e. zinc) out of 26 ponds. Based on reported acute and chronic ecotoxicological endpoints, detected concentrations of bifenthrin, cadmium, copper, cypermethrin, hexachlorobenzene, mercury, terbuthylazine, and zinc pose a substantial ecological risk to aquatic invertebrates such as Daphnia magna and Ceriodaphnia dubia, which both play a role in the food web and potentially in amphibian disease dynamics. Additionally, the detected concentrations of copper were high enough to exert chronic toxicity in the gray treefrog (Hyla versicolor). The number of detected compounds per pond ranged between 0 and 5 (ADRs), 0 - 2 (coccidiostats and anthelmintics), 1 - 7 (heavy metals), 0 - 4 (mycotoxins), and 0 - 12 (pesticides) across the four months. Furthermore, no significant correlation was demonstrated between the number of detected compounds per pond, as well as the detected concentrations of 4-epioxytetracycline, levamisole, copper, zinc, enniatin B and terbuthylazine, and the percentage of arable land within a 200 m radius. For heavy metals and pesticides, the number of compounds per pond varied significantly between months. Conclusively, amphibian breeding ponds in Flanders were frequently contaminated with agrochemicals, yielding concentrations up to the high μg per liter level, regardless of the percentage surrounding arable land, however showing temporal variation for heavy metals and pesticides. This research also identifies potential hazardous substances which may be added to the European watch list (CD 2018/408/EC) in the future.

Multi-residue analysis of 20 mycotoxins including major metabolites and emerging mycotoxins in freshwater using UHPLC-MS/MS and application to freshwater ponds in flanders, Belgium

Mycotoxins are known for their negative impact on human and animal health as they frequently contaminate food and feed products from crop origin that are consumed by humans and animals. Furthermore, mycotoxins can leach out of plant tissue, to be transported through runoff water into nearby ponds where they can exert negative effects on aquatic organisms, such as fish, amphibians and zooplankton. The overall goal of this study was to develop a SPE-UHPLC-MS/MS method for the detection and quantification of multiple mycotoxins in amphibian breeding ponds. The method was validated and yielded acceptable within-run and between-run apparent recoveries and precision, as well as good linearity. Matrix effects (i.e. 75.7-109.6%, ≤ 17.8% RSD) were evaluated using water from 20 different ponds in Flanders, Belgium. By incorporating internal standards, overall results improved and adequate precision values (i.e. ≤ 15%) were obtained according to the EMA guideline. Additionally, extraction recovery (n = 3) was evaluated, yielding good results for all mycotoxins (i.e. 75.3-109.1%, ≤15% RSD), except for AME (i.e. 6.7 ± 0.7%), which implied the need for a matrix-matched calibration curve. Detection sensitivity was in the low nanograms per liter range. Storage stability experiments indicated that sample storage at 4 °C in amber glass bottles and analysis performed within 96 h after sampling was sufficient to avoid loss by degradation for all compounds, excluding β-ZAL and β-ZEL, for which analysis within 24 h is more indicated. The method was successfully applied to water samples originating from 18 amphibian breeding ponds situated across Flanders. Overall, enniatins B, B1 and A1 were most commonly detected at maximum concentrations of 6.9, 3.3 and 2.6 ng L^-1, respectively, followed by detection of beauvericin (1.1 ng L^-1 and < 1 ng L^-1), alternariol monomethyl ether (< 10 ng L^-1), HT2-toxin (< 40 ng L^-1), zearalenone (< 25 ng L^-1) and α-zearalanol (< 10 ng L^-1). We believe that this method will boost further research into the dynamics and ecotoxicological impact of mycotoxins in aquatic environments.

Highly sensitive multi-residue analysis of veterinary drugs including coccidiostats and anthelmintics in pond water using UHPLC-MS/MS: application to freshwater ponds in Flanders, Belgium

Veterinary drugs, such as coccidiostats and anthelmintics are routinely administered in extensive animal husbandry, finding their way into the aquatic environment through urine and/or feces of treated animals kept outdoors or by the application of contaminated liquid manure on agricultural fields and subsequent mechanisms of surface run-off, leaching and drift. Several of these compounds are known to exert acute and chronic toxicity effects on aquatic organisms, and can lead to changes in biodiversity and ecosystem functioning. The overall objective of this research was to develop, validate and apply a highly sensitive, multi-residue SPE-UHPLC-MS/MS method for the determination of 12 coccidiostats, registered as a feed supplement or veterinary medicine in Europe and three regularly used anthelmintics, in pond water, often functioning as amphibian habitat. Sample extraction was optimized using a fractional factorial resolution design. Pond water filtration efficiency (i.e. 80-118%, ≤25% RSD) and matrix effects (i.e. 72-119%, ≤39% RSD) were evaluated using water from respectively 3 and 20 different ponds in Flanders. By incorporating internal standards, overall results improved and adequate precision values (i.e.≤15%) were obtained according to the EMA guidelines. Acceptable within-run and between-run apparent recoveries, satisfactory precision as well as good linearity were demonstrated according to the CD 2002/657/EC, SANTE/12682/2019 and VICH 49 guidelines, except for robenidine for which the between-day precision was between 21.0 and 34.5%. Sample storage stability studies indicated that storage at 4 °C and analysis performed within 96 hours after sampling was sufficient to avoid loss by degradation for all compounds, excluding robenidine. Values for the limit of detection (LOD) and quantification (LOQ) were in nanograms per liter, which was essential for the environmental application of this novel method. The method was successfully applied on grab water samples from the water surface of 18 different ponds across Flanders, Belgium, detecting amprolium and levamisole at concentrations below the LOQ of 2.5 ng L^-1 and at 250.0 ng L^-1 or below the LOQ of 250.0 ng L^-1, respectively. In conclusion, our newly developed method may provide insights about the contamination status of amphibian breeding ponds.

Multi-class analysis of 46 antimicrobial drug residues in pond water using UHPLC-Orbitrap-HRMS and application to freshwater ponds in Flanders, Belgium

Increasing anthropogenic pressure and agricultural pollution raises concerns regarding antimicrobial resistance and biodiversity loss in aquatic environments. In order to protect and restore water resources and biodiversity, antimicrobial drug residues should be monitored in all aquatic environments including pond water. Consequently, the objective of this research was to develop and validate a novel multi-residue method for the simultaneous quantification of 46 targeted human and veterinary antimicrobial drugs in pond water. A suitable extraction method based on solid-phase extraction (SPE) was developed, assisted by a fractional factorial design. A broad polarity range of compounds was covered (log P from -4.05 to 4.38), including major representatives of the following classes: sulfonamides, tetracyclines, quinolones, macrolides, lincosamides, nitrofurans, penicillins, cephalosporins, diaminopyrimidines, pleuromutilins and phenicols. All analytes were separated using ultra-high performance liquid chromatography (UHPLC) and detected in full-scan by Orbitrap high resolution mass spectrometry (Orbitrap-HRMS). Good linearity was obtained for all compounds with R² ≥ 0.993 and goodness-of-fit coefficient (g) ≤ 11.56%. Method detection limits ranged from 10 to 50 ng L^-1 and method quantification limits were 50 ng L^-1 for all compounds. Acceptable values were obtained for within-day and between-day apparent recoveries (i.e. between 50 and 120%), precision (< 30% and < 45%) and measurement uncertainty (< 50%). Targeted analysis of 18 freshwater ponds throughout Flanders was performed to demonstrate the applicability of the newly developed UHPLC-HRMS method. Overall, 20 antimicrobial drugs were detected with highest concentrations observed for tetracyclines and their transformation products ranging between 51 and 248 ng L^-1. Finally, suspect screening was performed suggesting the presence of 14 additional pharmaceuticals including 3 antimicrobial degradation products (e.g. apo-oxytetracycline, amoxicillin penicilloic acid and penilloic acid) and 11 pesticides.

Differential regional cerebral uptake of (18)F-fluoro-2-deoxy-D-glucose in Alzheimer's disease and frontotemporal dementia at initial diagnosis

In this paper, the cerebral uptake of (18)F-fluoro-2-deoxy-D-glucose (FDG) was studied in a relatively small group of patients suffering from either clinically diagnosed Alzheimer's disease (AD) or frontotemporal dementia during the initial differential diagnostic workup. The image analysis was done visually and semiquantitatively using three different reference regions. Visual analysis confirmed earlier literature findings on the distribution of decreased FDG uptake and demonstrated prevalent asymmetric patterns in both groups. Only semiquantitative analysis using the sensorimotor cortex as a reference region confirmed the visual findings. Moreover, there were no differences in medial temporal lobe activities between both groups, and there was no correlation of medial temporal lobe activity with dementia severity. In the AD group, a correlation of parietal FDG uptake with MMSE scores was found.

Impact of land-use on macroinvertebrate communities in the Zwalm river basin

For determining the impact of land-use on the aquatic ecosystem in a river basin, a Geographic Information System (GIS) has been used to integrate the main impact factors at different scales. The headwaters and streams of the Zwalm River basin (Flanders, Belgium), which is part of the Scheldt river basin, were selected as study site. A river ecological database was developed based on physical-chemical and biological monitoring. The research focussed on three zones within this Zwalm River basin, each characterized by different land-uses and by consequence different types of pollution, mainly of diffuse origin. The impact was measured by means of the biological diversity, the Belgian Biotic Index and a key macroinvertebrate taxon. For measuring, assessing and managing the impact of land-use on biological communities, an integrated and multidisciplinary approach will be necessary.

Development of river ecosystem models for Flemish watercourses: case studies in the Zwalm river basin

Only recently, modelling has been accepted as an interesting and powerful tool to support river quality assessment and management. The 'River Invertebrate Prediction and Classification System' (RIVPACS), based on statistical modelling, was one of the first and best known systems in this context. RIVPACS was developed to classify macroinvertebrate community types and to predict the fauna expected to occur in different types of watercourses, based on a small number of environmental variables. The prediction is essentially a static 'target' of the fauna to be expected at a site with stated environmental features, in the absence of environmental stress. Therefore this system is rather limited to apply in river assessment and management. Models that offer a prediction of faunal responses to changes in environmental features (e.g. changes in discharge regime, dissolved oxygen level, ...) would be of considerable value for river management. In this context, models based on classification trees, artificial neural networks and fuzzy logic were developed and applied to predict macro-invertebrate communities in the Zwalm river basin located in Flanders, Belgium. Structural characteristics (meandering, substrate type, flow velocity, ...) and physical-chemical variables (dissolved oxygen, pH, ...) were used as inputs to predict the presence or absence of macroinvertebrate taxa in the headwaters and brooks of the Zwalm river basin. In total, data from 60 measurement sites were available. Reliability and particular strengths and weaknesses of these techniques were compared and evaluated. Classification trees performed in general well to predict the absence or presence of the different macroinvertebrate taxa and allowed also to deduct general relations from the dataset. Models based on artificial neural networks (ANNS) were also good in predicting the macroinvertebrate communities at the different sites. Sensitivity analyses related to ANNs allowed to study the impact of the input variables on the presence or absence of macroinvertebrate taxa and to determine the major variables that affect the ecosystem quality and should be taken under direct consideration in the management of river basins. Performance of the fuzzy logic models was significantly related to the methods that were used to set up the membership functions and the reliability of the information that was available. Fuzzy logic did not perform as well as the other two techniques with regard to short term predictions. Fuzzy logic appeared to be better and more robust for long term predictions, because of the easy and pragmatic integration of general expert knowledge and data derived rules in the transparent inference engine. The overall conclusion of our study is that all three techniques, classification trees, artificial neural networks and fuzzy logic appeared to be reliable to predict macroinvertebrate communities in polluted streams.

Optimisation of the discrete conductivity and dissolved oxygen monitoring using continuous data series obtained with automated measurement stations

During the last five years, research on the relation between pollution loads and ecological river water quality has been done on the Dender river. In addition to biological sampling of macroinvertebrates and fish, automated measurement stations were used too to investigate the spatio-temporal variability of physical-chemical water pollution. This study on on-line water quality data collection is based on a measurement campaign during March-April 2000 with two automated measurement stations at two different sites: the flow control weirs at Geraardsbergen and Denderleeuw. These measurement stations contain sensors for temperature, turbidity, conductivity, pH, redoxpotential and dissolved oxygen. Short wave radiation as well as rainfall were monitored by means of pyranometers and rain gauges. A refrigerated sampler with 24 bottles allowed to take samples for additional laboratory analyses. In this study, continuous measurements of two physical-chemical parameters, conductivity and dissolved oxygen, were analysed to evaluate the adequacy of the current monitoring frequency in Flanders. Analysis showed that discrete conductivity measurements can be sufficient for trend detection, but the measuring frequency must be highly increased from one measurement per month to at least 8 measurements. Continuous measurements for conductivity are preferred because extreme values are obtained as well. For dissolved oxygen, a single measurement per month in not enough. The percentage of dissolved oxygen showed a strong diurnal variation with maxima in the late afternoon (photosynthesis) and minima at night (respiration). This parameter also differed significantly from day to day. Continuous measurements are therefore necessary for a reliable assessment of the dissolved oxygen budget of surface waters. When using discrete measurements for dissolved oxygen, a set time should be introduced to eliminate diurnal variation.

Development of short and long-term management options for bergelenput to avoid fish kills caused by algal blooms

Numerous stagnant waters in Flanders are characterized by high nutrient concentrations, leading to severe algal blooms and under critical conditions to fish mortality. In this context, a eutrophicated pond was analysed hydrobiologically during one month in order to develop a management plan for the coming years to restore its ecological stability. Bergelenput (Wevelgem), a former sand pit, is now a nature reserve, currently also used for recreational fishing. During the last decade, incidental fish kills have occurred. The main cause is thought to be nutrient enrichment, enhancing algal blooms. The most probable source of these nutrients is fertiliser runoff from the surrounding fields characterised by intensive agricultural activities. Two possible causes of these fish kills, both associated with algal blooms, were considered during this preliminary study. The first was oxygen depletion of the water caused by algal respiration during the night. The second was related to the presence of Microcystis aeruginosa, a cyanobacterium known to be toxic sometimes and hence responsible for fish kills. Short-term and long-term management options are being developed within the context of this research to rehabilitate the ecosystem.

Recurrent coronary stent thrombosis

A 63-year-old woman with an acute anterior myocardial infarction was treated with primary stent implantation. The absence of coronary artery stenosis and an haematocrit of 58 were indicative of a myeloproliferative disorder and the diagnosis of polycythaemia vera (Vaquez' disease) was confirmed by bone marrow aspiration. The patient had a re-infarction 8 days later. A rescue percutaneous angioplasty was performed for stent thrombosis after unsuccessful thrombolysis. A few hours after sheath removal, a femoral artery thrombosis at the puncture side needed urgent thrombectomy. Finally, a second re-infarction occurred, followed by an irreversible cardiac arrest. Stent thrombosis is a difficult-to-treat complication in patients with polycythaemia vera. If this haematologic disorder is known, primary stent implantation for acute myocardial infarction may not be the first choice in these patients.

57Co-EDTA renal imaging in rats

We studied the synthesis of 57Co-EDTA (Ey = 122 keV), its biodistribution in Wistar rats and its blood and urinary elimination compared with that of 51Cr-EDTA. We added 6 mumol EDTA diluted in 3-5 ml isotonic phosphate buffer (Na2HPO4) to a commercial 57CoCl2 radioactive tracer solution. The incubation period was 15 min. Quality control was performed using TLC and HPLC. Six healthy Wistar rats underwent 57Co-EDTA renography for 30 min. In one rat, additional TLC and HPLC was performed on blood (one sample only) and urine samples (n = 3) obtained 30 min, 30 min, 2 h and 4 h following injection of 18.5 MBq 57Co-EDTA and 51Cr-EDTA respectively. Radioisotope quantification was done by means of a germanium detector. 57Co was chelated to EDTA at high yield (Kstab = 10E36). No free or protein-bound 57Co was found. The ratio of 51Cr-EDTA to 57Co-EDTA remained constant (P = 0.133, n = 4). 57Co-EDTA was rapidly cleared from the blood pool (heart), and prompt and high target-to-background ratios for both kidneys were obtained (mean = 8.4, range = 7-12). At the end of the acquisition, activity remaining in the body excluding kidney and bladder was 45 +/- 5.2%. No specific activity uptake was noted in any other organ or tissue. We conclude that 57Co-EDTA is a promising radioligand for simultaneous clearance and separate renal function estimation. Its preparation is straightforward and, in rats, no free or protein-bound 57Co was found.

55Co-EDTA for renal imaging using positron emission tomography (PET): a feasibility study

The feasibility of imaging renal function with 55Co-ethylene diamine tetraacetic acid (EDTA) and dynamic positron emission tomography was investigated. A group of normal Wistar rats was injected intravenously with 55Co-EDTA and underwent dynamic positron emission tomography (PET) imaging in order to study the biodistribution. The time-activity curves of the heart (blood pool), both kidneys, liver, and bladder were observed. In two animals, blood and urinary clearances of 55Co-EDTA were compared with those for 51Cr-EDTA. In one animal, unilateral reduction in kidney function was induced and the right/left ratio for the kidneys was determined. The time-activity curves showed that 55Co-EDTA cleared rapidly from the blood pool (heart), whereas prompt and high target-to-background ratios for both kidneys were obtained. The entire tracer was cleared from the renal parenchyma by urinary excretion and collection of the activity in the bladder. No specific activity uptake was noticed in any other organ or tissue. The clearances of 55Co-EDTA and 51Cr-EDTA in blood were not significantly different, showing that the nature of the M++ has no influence on the in vivo behavior of EDTA. 55Co can be produced easily by cyclotron irradiation and 55Co-EDTA is a promising physiological tracer for nephrological research using PET.

55Cobalt (Co) as a PET-tracer in stroke, compared with blood flow, oxygen metabolism, blood volume and gadolinium-MRI

Several studies have shown the feasibility of divalent cobalt (Co)-isotopes (55Co and 57Co) in imaging of neuronal damage in stroke, multiple sclerosis, cerebral tumors and traumatic brain injury. Little is known how regional Co uptake relates to other pathophysiological changes after stroke. Therefore, we compared 55Co-PET with functional parameters such as regional cerebral blood flow (rCBF) using C(15)O(2), regional oxygen metabolism (rCMRO(2)) using 15O(2), regional cerebral blood volume (rCBV) and post-gadolinium (Gd) T(1)w-MRI to assess the permeability of the blood-brain-barrier (BBB). Sixteen patients (10 female; six male) aged 43 to 84 (mean 69) years with first ever stroke, as shown by CT or MRI, were examined with 55Co-PET and C(15)O(2)-, 15O(2)- and C(15)O-PET in one single session, in a period varying from 0 to 30 days after stroke-onset. Regions of infarction on C(15)O(2)- and 15O(2)-PET (defined by rCMRO(2)<65% or rCBF<45% of the contralateral value) were subsequently superimposed on the 55Co-PET scan. Clinical status was established using the Orgogozo stroke scale, which was assessed both at day 1 and at discharge (at least 6 weeks after day 1). Accumulation of 55Co was seen in eight out of 16 patients, occurring in areas showing a diminished oxygen metabolism, was only partially related to blood flow, and was located mainly outside the extent of the infarction or luxury perfusion as seen on post-Gd T(1)w-MRI. Statistical analysis showed a negative correlation between the Orgogozo score at discharge and the uptake of radioactive cobalt.

[Methyl-11C]thymidine positron emission tomography in tumoral and non-tumoral cerebral lesions

BACKGROUND

No ideal radiopharmaceutical exists for positron emission tomography (PET) that fulfills all clinical requirements for the study of brain tumors.

PURPOSE

The usefulness of a recently developed PET tracer, [methyl-11C]thymidine ([methyl-11C]TdR) is explored in brain tumors.

PATIENTS AND METHODS

Twenty patients with confirmed tumoral and non-tumoral brain lesions were investigated with [methyl-11C] TdR PET. The 11C activity was visually and quantitatively assessed. In two patients, dynamic scans were performed. The PET findings were compared to those of magnetic resonance imaging (MRI) or computed tomography (CT) of the brain and to the final diagnosis.

RESULTS

Eight out of ten patients with confirmed tumoral lesions or tumor recurrence had increased 11C activity within the lesion. In ten non-tumoral lesions no increased 11C uptake was found. The dynamic PET studies showed that [methyl-11C] TdR first acts as a blood flow tracer, but that later on the uptake of 11C activity is due to labeled metabolites, crossing the blood-brain barrier. Increased tracer activity was only observed in tumoral and not in non-tumoral contrast-enhanced lesions on MRI or CT.

CONCLUSIONS

[Methyl-11C] TdR is not a selective PET radiopharmaceutical for brain tumors, but can be used as a tracer for tumoral blood-brain barrier disruption.

In vivo distribution and identification of 11C-activity after injection of [methyl-11C]thymidine in Wistar rats

[Methyl-11C]thymidine and PET offer an in vivo, noninvasive quantitative approach for studying nucleoside uptake in cells on the condition the fraction of [methyl-11C]thymidine (in deoxyribonucleic acid [DNA] or as DNA precursors) versus the total accumulated activity is known.

METHODS

In a group of normal (n = 6) and a group of tumor-bearing (n = 3) Wistar rats, the biodistribution of 11C-activity was studied dynamically. In a second group of rats (n = 6), the animals were killed at 20 min postinjection and the organs and tissues of interest (liver, heart, brain, duodenum and tumor) were measured for activity and then homogenized. 11C-activity in each fraction (cell debris, protein/ DNA-fraction, lipids and supernatant) was measured. The supernatant was analyzed by high-performance liquid chromatography (HPLC)-radiochromatography for identification of different 11C-labeled compounds.

RESULTS

After venous injection, most of the 11C-activity was rapidly trapped in the liver and in fast-dividing tissue (e.g., duodenum); minor activity was located in the bladder, kidneys, heart and brain. HPLC separation showed that the 11C-activity of the liver tissue consisted of metabolites only. For the duodenum and tumor, at least 55% of the 11C-activity was precipitated in the protein/DNA-fraction and about 60% as DNA precursors (thymidine, 2'-deoxythymidine 5'-monophosphate and 2'-deoxythymidine 5'- triphosphate ) in the supernatant.

CONCLUSION

Despite the in vivo metabolism, major 11C-activity in rapidly dividing tissue consists of [methyl-11C]thymidine incorporated in the DNA. Catabolism takes place mainly in the liver where the degradation products are stored. PET quantification data using [methyl-11C] thymidine can give information about thymidine incorporation in DNA and cell proliferation of tumors.

Cobalt-55 positron emission tomography in recurrent ischaemic stroke

The present study investigates if Cobalt-55 (55Co) positron emission tomography (PET) allows us to distinguish and detect recent, recurrent strokes in patients who had already suffered a previous infarct in the same vascular territory. Fourteen patients with recurrent strokes underwent a 55Co PET scan of the brain. Recently infarcted areas, less than 2 months old, had a high 55Co uptake ratio, whereas infarcts of 6 months to 1 year had an uptake ratio comparable to normal brain tissue. In infarcts older than 2 years the 55Co uptake ratio was decreased compared to the control values. The evolution in 55Co uptake ratios with time can be explained by the dynamics of the inflammatory response within the infarct core. 55Co PET allows to demonstrate stroke recurrence and suggests that single photon emission tomography, using 57Co as the tracer, could be a more easy alternative to be used in routine neurological practice.

The significance of cobalt-55 positron emission tomography in ischemic stroke

Cobalt-55 ((55)Co) has been shown to be an interesting positron emission tomography (PET) tracer that may reflect calcium (Ca) influx in damaged cerebral tissue. Because Ca load is important in the ischemic cascade, the exact meaning of (55)Co PET in stroke patients has to be shown. The present study compares the degree of (55)Co uptake to regional cerebral blood flow (rCBF) and regional cerebral metabolic rate for oxygen (rCMRO(2)) values in brains of patients with ischemic stroke. Eighteen patients with an ischemic event in the middle cerebral artery territory were examined with PET using, in the same session, (55)Co and the (15)O steady state technique. The (55)Co ratio was assessed in ischemic and infarcted regions and compared with the corresponding rCBF and rCMRO(2) values. The average (55)Co ratio is inversely correlated to the rCBF and rCMRO(2) values. Also (55)Co accumulation tends to increase during the weeks after the onset of stroke and decreases down to normal levels after 6 months. The degree of (55)Co uptake corresponds to the severity of the ischemic damage within the first month after stroke. As it increases with time, it probably reflects the Ca accumulation caused by the progression of the inflammatory response within and around the infarct core.

Cobalt-55 positron emission tomography of ipsilateral thalamic and crossed cerebellar hypometabolism after supratentorial ischaemic stroke

Cobalt-55 (55Co) is a positron emission tomography (PET) tracer used to demonstrate brain damage, possibly associated to calcium-mediated processes. The degree of 55Co accumulation correlates with the severity of ischaemia in stroke patients. It is still a matter of debate whether ipsilateral thalamic hypometabolism (ITH) and crossed cerebellar hypometabolism (CCH), occurring after middle cerebral artery (MCA) infarcts, represent only a metabolic depression of these remote regions or can lead to structural damage. The present study investigates whether an increased 55Co influx can be demonstrated with PET in ITH and CCH after MCA infarcts. About half of the patients with ITH and CCH had a significant degree of 55Co uptake in, respectively, the ipsilateral thalamus and the contralateral cerebellar hemisphere. It was observed in patients with severe signs of stroke on admission and poor clinical outcome, and correlated well with the degree of 55Co influx within the supratentorial infarct. The present study demonstrates that ITH and CCH after MCA infarction can represent structural damage in these remote areas that occurs during the second week after stroke onset.

Acetazolamide vasoreactivity in vascular dementia: a positron emission tomographic study

The present study investigates the vasoreactivity of the brain in patients with large infarcts and dementia (multi-infarct dementia; MID) and in patients with microangiopathy, lacunes, white matter changes and dementia (lacunar dementia; LD) using positron emission tomography (PET) and 13NH3 as regional cerebral blood flow (rCBF) tracer. In the control group, an increase in rCBF ranging from 32 to 43% was found in all brain regions after intravenous acetazolamide administration. In both the MID group and the group with multiple infarcts without dementia, moderate loss of vasoreactivity was observed in the frontal, temporal and parietal cortex compared to the control values. Vasoreactivity was severely impaired in all cerebral regions of the LD group and restricted to the thalamus in the group with lacunes and white matter changes without dementia (lacunar stroke; LS). This suggests that global loss of vasoreactivity is not a determining factor in the occurrence of MID, but might be important in LD. The present study shows that loss of the vascular reserve leading to exhausted metabolic reserve of the whole brain is one of the possible mechanisms for the occurrence of vascular dementia.

Drug-induced Brugada syndrome

Survivors of sudden death without structural heart disease and a normal coronary angiogram are often diagnosed with idiopathic ventricular fibrillation (VF). The criteria for idiopathic VF have been reviewed elsewhere. However, a careful analysis of the electrocardiogram (ECG) is essential in the differential diagnosis of unexplained sudden cardiac death. We report two patients with unexplained VF, intermittent right bundle-branch block (RBBB) and ST-segment elevation in the precordial leads V1-V3. This syndrome is named after Brugada who first described a clinical series. This paper stresses the dynamic changes and the spontaneous normalization of the ECG. Class I drugs can unmask this peculiar ECG-pattern and can sometimes precipitate an arrhythmia if they are given chronically. Patients with the diagnosis of idiopathic VF should be screened for intermittent RBBB and ST-segment elevation. Because the syndrome is mostly familial and inherited as an autosomal dominant trait, diagnosis of this entity in a patient has an implication for the screening of family members.

Synthesis of 6-methyl[11C]-2'-deoxyuridine and evaluation of its in vivo distribution in Wistar rats

In this study, 6-methyl-2'-deoxyuridine, an artificial nucleoside, was labeled with 11C in the methyl position. Tissue distribution of 6-methyl[11C]-2'-deoxyuridine was investigated in normal Wistar rats and compared to the behavior of the natural nucleoside [methyl-11C]thymidine. High renal clearance, up to at least 20% of the injected activity, was noticed during the 20 min period following injection. Tissue distribution as determined by dynamic PET studies of both 11C-labeled nucleosides was significantly different for most of the organs.

55Co-PET in stroke: relation to bloodflow, oxygen metabolism and gadolinium-MRI

BACKGROUND

Several studies have shown the feasibility of Co-isotopes (55Co and 57Co) in imaging of neuronal damage in stroke, multiple sclerosis, cerebral tumors and trauma. These studies indicate that Co-isotopes allow visualization of brain pathology related to inflammatory processes, reactive gliosis and cell death. Until now, it is not clear if 55Co accumulation occurs in the core of infarction or in the penumbra. Therefore, in the present study, we compared 55Co-PET with functional parameters such as cerebral bloodflow (rCBF) using C15O2, oxygen metabolism (rCMRO2) using 15O2 and cerebral bloodvolume (CBV) using C15O in PET and with the anatomical parameter Gd-MRI.

PATIENTS AND METHODS

Seventeen patients (11 male; 6 female) age 43 to 84 (mean 69) with middle cerebral artery (mca) stroke, as proven by CT or MRI, were examined with 55Co-PET (0.5-1.0 mCi 55CoCl2), C15O2-, 15O2- and C15O-PET in one session 0-30 days after stroke-onset. Regions of infarction were defined by rCMRO2 being smaller than 65% or rCBF below 45% of the contralateral value and were subsequently superimposed on the cobalt scan. To compare the Cobalt uptake with the Gd-MRI, a realignment program was used that matches the MRI with the bloodflow images. Clinical status was established using the Orgogozo stroke scale at admission and at discharge (at least 6 weeks after admission) and the Barthel index.

RESULTS

Eight patients showed a positive Co-PET scan and were used for further analysis. It appeared that Co accumulates in areas with a diminished oxygen metabolism and with a preserved bloodflow. We found Co-uptake in only a part of the Gd enhanced brain tissue with a tendency to be located peripherally or outside the Gd demarcated brain tissue.

CONCLUSION

The results of the present study suggest that Co accumulates into infarcted brain tissue with a rather preserved flow independently of blood-brain barrier breakdown.

Constitutive flocculation in Saccharomyces cerevisiae through overexpression of the GTS1 gene, coding for a 'Glo'-type Zn-finger-containing protein

The product of the cloned GTS1 gene is characterized by structural features found in transcription factors. It contains one Zn-finger motif (CXXCX16CXXC) situated in the N-terminal end with a high degree of homology to the newly identified 'Glo' family of Zn-finger proteins (Ireland et al., 1994, EMBO J. 13, 3812-3821). The C-terminal end of the protein is characterized by poly (Ala-Gln) and poly-Gln stretches. Poly-Gln are part of trans-acting motifs in known transcription factors. Overexpression of the GTS1 gene results in constitutive flocculation. Whole cell electrophoretic mobility and hydrophobicity of GTS1 overexpressing cells was respectively lower and higher relative to control cells. GTS1-induced flocculation is hardly sensitive to mannose in contrast to FLO1-determined flocculation. Overexpression of the GTS1 gene in a flo1 background does not abolish flocculation, suggesting that the FLO1 gene is not linked with the GTS1 gene in a 'flocculation pathway'.

Crossed cerebellar diaschisis after middle cerebral artery infarction

It is unclear whether crossed cerebellar diaschisis (CCD) is merely an epiphenomenon, as its clinical significance remains uncertain. We retrospectively analysed the positron emission tomographic (PET) findings in 28 patients with a chronic, stable middle cerebral artery (MCA) infarct and in 22 controls, using the steady state technique and 15O. Also, the Orgogozo scores on admission and at the time of the PET examination were compared in the patients with MCA infarction. Based on the asymmetry index and the 95% confidence limits for regional cerebellar blood flow (rCBF) and oxygen consumption (rCMRO2) in the control group, the stroke patients were subdivided in a group with (n = 8) and a group without (n = 20) CCD. The CCD group had lower values of rCMRO2 in the infarct and border areas compared to those of the non-CCD patients. The infarct location within the MCA territory was similar but the size was somewhat larger in the CCC group. The degree of neurological improvement was better in the non-CCD group. Although persistence of CCD has no real clinical significance it appears to be correlated to more severe and widespread ischaemia in the affected MCA territory and to the lack of significant clinical improvement.

Cerebral oxygen metabolism in patients with progressive supranuclear palsy: a positron emission tomography study

To investigate cerebral oxygen metabolism in progressive supranuclear palsy (PSP), 5 patients with a clinical diagnosis of PSP and a variable degree of cognitive deficit were selected for positron emission tomography (PET) of the brain. In 4 of them, a significant decrease in oxygen metabolism was found in all cortical regions, without frontal accentuation. In the group as a whole, this decrease was even slightly more marked in parietal and temporal regions. These findings are not consistent with earlier PET studies that demonstrated frontal targeting of hypometabolism in PSP patients. Part of this discrepancy can be explained by differences in methodology, although the use of different clinical criteria and overlap of PSP with other neurodegenerative diseases must be taken into account. It is concluded that the absence of frontal hypometabolism on PET examination does not exclude the diagnosis of PSP.

An unusual case of bilateral virilizing adrenal adenoma co-secreting androgens and cortisol

We report the case of a 68-year-old woman presenting with clinical and biochemical evidence of hyperandrogenism. Imaging studies revealed the presence of a bilateral adrenal tumor. Although there was a predominant secretion of androgens, autonomous production of cortisol was also evidenced on the basis of an inversion of the circadian rhythm of plasma cortisol and an absence of cortisol suppression by dexamethasone. The functional status of both tumors was demonstrated by an iodocholesterol scintigraphy and by an adrenal vein catheterization. Surgical excision of both adrenal tumors was performed and histological examination disclosed no criteria of malignancy. The patient still remains disease-free 3 years after surgery. To our knowledge, this is the second report of the bilateral occurrence of a virilizing adrenal tumor and the first in which the functional characteristics of the tumors are detailed.

[Methyl-carbon-11] thymidine for in vivo measurement of cell proliferation

[Methyl-11C]thymidine and PET provide an in vivo, noninvasive, quantitative approach for studying nucleoside uptake in cells on condition that the fraction of metabolites in the total accumulated activity is known.

METHODS

Using an animal model (Wistar rats), two independent approaches were followed. In the first approach, total accumulated activity in rapidly dividing tissue after intravenous injection of [methyl-11C]thymidine, respectively, [methyl-11C]thymine (first metabolite), was compared. In the second approach, the liver was surgically isolated to avoid thymidine catabolism.

RESULTS

After injection of [methyl-11C]thymidine, tissue activity consists of both labeled thymidine and metabolites, while after injection of [methyl-11C]thymine, it consists only of metabolites. The fraction of metabolites ranged from 9% to 44%. Comparing the specific activity with and without liver function yielded similar results. The calculated amount of metabolites was about 10%.

CONCLUSION

In spite of the intense in vivo catabolism, major activity in rapidly dividing tissue consists of [methyl-11C]thymidine.

Kinetics of [methyl-11C]thymidine in patients with squamous cell carcinoma of the head and neck

Thymidine labelled with a position emitter and imaging by positron emission tomography has been suggested to measure tumour proliferation in vivo non-invasively. The present study presents a compartmental model which describes the behavior of [methyl-11C]thymidine in tumour tissue and allows quantification of the data using a proliferation parameter (PP). In nine patients with squamous cell carcinoma of the head and neck, 11C-activity over the tumour and the adjacent blood vessels was measured. The median PP without correction for blood pool activity was found to be 8.61 10(-4) min(-1). With correction this parameter changed from -14% to +40%. We found no correlation between either sex or tumour differentiation and PP. The described model can be used to quantitate [methyl-11C]thymidine uptake in human tumours. Indivdual correction for tumour blood volume is mandatory.

Late-onset epileptic seizures in patients with leukoaraiosis: a positron emission tomographic study

Leukoaraiosis, found on computed tomographic scans of the brain, is suspected to be of ischemic origin and is frequently associated with progressive decline of cognitive functions in elderly persons. Some of them also develop late-onset epilepsy. The present positron emission tomographic study investigates if these seizures in mentally nonaffected patients with leukoaraiosis are related to an underlying ischemic process. Patients with leukoaraiosis and late-onset seizures have a more important decline of regional blood flow and oxygen consumption in the cortical areas, compared to normal age-matched controls, to patients with cryptogenic symptomatic late-onset epilepsy and to patients with a similar degree of leukoaraiosis but without epilepsy. The present study suggests that both the late-onset seizures and the leukoaraiosis in patients with, at that time, no obvious mental deterioration are premonitory signs of an encephalopathy of unknown origin, possibly leading to cognitive decline.

Ipsilateral thalamic diaschisis after middle cerebral artery infarction

The significance of ipsilateral thalamic diaschisis (ITD) among patients with chronic, stable middle cerebral artery (MCA) infarcts was investigated. Twenty eight subjects with chronic MCA infarction and twenty two normal controls were studied with positron emission tomography (PET), using the steady state technique with 15O. Stroke patients were subdivided into a group with ITD (n = 12) and a group without ITD (n = 16). Patients with ITD had greater decreases of regional blood flow (rCBF) and oxygen consumption (rCMRO2) in the infarcted MCA territory, compared to MCA infarction without ITD. The neurological deficits at the time of PET scanning were similar between both groups. Extent of infarction by CT brain scan appeared more predominant in peri-insular regions of patients with ITD, while in non diaschisis patients infarcts were more widely distributed throughout the MCA territories. Occurrence of ITD and of crossed cerebellar diaschisis (CCD) did not correlate. Occurrence of ITD seems to be linked to diffuse reductions of blood flow and oxygen metabolism in cortical territories of the MCA. Mechanisms of ITD were different from those of CCD.

Positron emission tomographic study of late-onset cryptogenic symptomatic seizures

Ten patients with epilepsy of unknown origin, starting after the age of 50 years, and without clear evidence of cognitive decline were studied with positron emission tomography, using the steady state technique with 15O. Cerebral blood flow and oxygen metabolism were significantly decreased in all cortical areas. No focal areas of hypometabolism were detected. Treatment with phenytoin did not influence the results. It is suggested that late-onset seizures could be the premonitory signs of a progressive encephalopathy of unknown origin.