Harmful
algal blooms (HABs) caused by cyanobacteria in freshwater
environments produce toxins (e.g., microcystin) that are harmful to
human and animal health. HAB frequency and intensity are increasing
with greater nutrient runoff and a warming climate. Lake spray aerosol
(LSA) released from freshwater lakes has been identified on lakeshores
and after transport inland, including from lakes with HABs, but little
is known about the potential for HAB toxins to be incorporated into
LSA. In this study, freshwater samples were collected from two lakes
in Michigan: Mona Lake during a severe HAB with microcystin concentrations
(>200 μg/L) well above the Environmental Protection Agency
(EPA)
recommended “do not drink” level (1.6 μg/L) and
Muskegon Lake without a HAB (<1 μg/L microcystin). Microcystin
toxins were identified in freshwater, as well as aerosol particles
generated in the laboratory from Mona Lake water by liquid chromatography–tandem
mass spectrometry (LC–MS/MS) at atmospheric concentrations
up to 50 ± 20 ng/m3. Enrichment of hydrophobic microcystin
congeners (e.g., microcystin-LR) was observed in aerosol particles
relative to bulk freshwater, while enrichment of hydrophilic microcystin
(e.g., microcystin-RR) was lower. As HABs increase in a warming climate,
understanding and quantifying the emissions of toxins into the atmosphere
is crucial for evaluating the health consequences of HABs.
Brain-derived neurotrophic factor (BDNF) modulates the synaptic transmission of several monoaminergic neuronal systems, including forebrain dopamine-containing neurons. Recent evidence shows a strong correlation between neuropsychiatric disorders and BDNF hypofunction. The aim of the present study was to characterize the effect of low endogenous levels of BDNF on dopamine system function in the caudate-putamen using heterozygous BDNF (BDNF+/−) mice. Apparent extracellular dopamine levels in the caudate-putamen, determined by quantitative microdialysis, were significantly elevated in BDNF+/− mice compared to wildtype controls (12 vs. 5 nM, respectively). BDNF+/− mice also had a potentiated increase in dopamine levels following potassium (120 mM)-stimulation (10-fold) relative to wildtype controls (6-fold). Slice fast-scan cyclic voltammetry revealed that BDNF+/− mice had reductions in both electrically-evoked dopamine release and dopamine uptake rates in the caudate-putamen. Superfusion of BDNF led to partial recovery of the electrically-stimulated dopamine release response in BDNF+/− mice. Conversely, tissue accumulation of L-3,4-dihydroxyphenylalanine, extracellular levels of dopamine metabolites, and spontaneous locomotor activity were unaltered. Together, this study indicates that endogenous BDNF influences dopamine system homeostasis by regulating the release and uptake dynamics of presynaptic dopamine transmission.
Fast and reliable workflows are needed to quantitate microcystins (MCs), a ubiquitous class of hepatotoxic cyanotoxins, so that the impact of human and environmental exposure is assessed quickly and minimized. Our goal was to develop a high-throughput online concentration liquid chromatography tandem mass spectrometry (LC/MS/MS) workflow to quantitate the 12 commercially available MCs and nodularin in surface and drinking waters. The method run time was 8.5 min with detection limits in the low ng/L range and minimum reporting levels between 5 and 10 ng/L. This workflow was benchmarked by determining the prevalence of MCs and comparing the Adda-ELISA quantitation to our new workflow from 122 samples representing 31 waterbodies throughout Michigan. The frequency of MC occurrence was MC-LA > LR > RR > D-Asp3-LR > YR > HilR > WR > D-Asp3-RR > HtyR > LY = LW = LF, while MC-RR had the highest concentrations. MCs were detected in 33 samples and 13 of these samples had more than 20% of their total MC concentration from MCs not present in US Environmental Protection Agency (US EPA) Method 544. Furthermore, seasonal deviations between the LC/MS/MS and Adda-ELISA data suggest Adda-ELISA cross-reacts with MC degradation products. This workflow provides less than 24-h turnaround for quantification and also identified key differences between LC/MS/MS and ELISA quantitation that should be investigated further.
Cyanotoxins called microcystins (MCs) are highly toxic and can be present in drinking water sources. Determining the structure of MCs is paramount because of its effect on toxicity. Though over 300 MC congeners have been discovered, many remain unidentified. Herein, a method is described for the putative identification of MCs using liquid chromatography (LC) coupled with high-resolution (HR) Orbitrap mass spectrometry (MS) and a new bottom-up sequencing strategy. Maumee River water samples were collected during a harmful algal bloom and analyzed by LC−MS with simultaneous HRMS and MS/ MS. Unidentified ions with characteristic MC fragments (135 and 213 m/z) were recognized as possible novel MC congeners. An innovative workflow was developed for the putative identification of these ions. Python code was written to generate the potential structures of unidentified MCs and to assign ions after the fragmentation for structural confirmation. The workflow enabled the putative identification of eight previously reported MCs for which standards are not available and two newly discovered congeners, MC-HarR and MC-E(OMe)R.
A recently available boron-doped diamond (BDD) working electrode has been developed for use with high-performance liquid chromatography (HPLC) to aid in the detection of molecules with high redox potentials. In this work, we developed a method using a commercially available BDD working electrode for detecting neurotransmitters from two different families with large oxidation potential differences, namely, dopamine (DA) and adenosine (Ado). Hydrodynamic voltammograms were constructed for DA and Ado, and the optimal potentials for the detection of DA and Ado were determined to be +740 and +1200 mV versus a palladium reference electrode, respectively. A working potential of +840 mV was chosen, and the detection range achieved with the BDD electrode for DA and Ado was from low nanomolar to high millimolar levels. To determine the practical function of the BDD electrode, tissue content was analyzed for seven monoamine and two purine molecules, which were resolved in a single run in less than 28 min. Our results demonstrate that the BDD electrode is sensitive and robust enough to detect monoamine and purine molecules from frontal cortex and striatal mouse samples. Using a BDD electrode opens the possibility of exploring multiple classes of neurotransmitters in a single run using electrochemical detection to probe their interactions.
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