Mercury methylation and demethylation by periphyton biofilms and their host in a fluvial wetland of the St. Lawrence River (QC, Canada)

Wetlands in large rivers are important sites of production of the neurotoxin methylmercury (MeHg), and the periphyton growing on wetland macrophytes are increasingly recognized as key players in this production and transfer in food webs. Information is lacking about mercury methylation (Km) and demethylation (Kd) rates in periphytic biofilms from the Northern Hemisphere, as well as about the drivers of net MeHg production, hampering ecosystem modeling of Hg cycling. Mercury methylation and demethylation rates were measured in periphytic biofilms growing on submerged plants in a shallow fluvial lake located in a temperate cold region (St. Lawrence River, Quebec, Canada). Incubations were performed in situ within macrophyte beds using low-level spikes of (199)HgO and Me(200)Hg stable isotopes as tracers. A direct relationship was observed between Km (0.002 to 0.137 d(-1)) and [MeHg] in periphyton. A similar relationship was found between Kd (0.096 to 0.334 d(-1)) and [inorganic Hg]. Periphyton of Lake St. Pierre reached high levels of net MeHg production that were two orders of magnitude higher than those found in local sediment. This production varied through the plant growing season and was mainly driven by environmental variables such as depth of growth, available light, dissolved oxygen, temperature, plant community structure, and productivity of the habitat.

Revisiting hippocampal sclerosis in mesial temporal lobe epilepsy according to the "two-hit" hypothesis

Hippocampal sclerosis (HS) is the most common neuropathological pattern observed in pharmacoresistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy syndrome. However, its pathophysiological mechanisms and neuropathological consequences on seizures remain mostly unresolved. The new international classification of hippocampal sclerosis aims at standardizing its description to allow comparisons between different clinical studies. However, several aspects are not considered in this classification (granule cell dispersion, sprouting, glial modifications…). In this chapter, we discuss these different features associated with hippocampal sclerosis in perspective with the "two-hit" hypothesis and propose mechanisms that could be involved in the modulation of some specific neuropathological aspects like early life stress, hyperthermic seizures, brain lesions or hormonal modifications.

Spatio-temporal variations in biomass and mercury concentrations of epiphytic biofilms and their host in a large river wetland (Lake St. Pierre, Qc, Canada)

Within wetlands, epiphytes and macrophytes play an important role in storage and transfer of metals, through the food web. However, there is a lack of information about spatial and temporal changes in their metal levels, including those of mercury (Hg), a key priority contaminant of aquatic systems. We assessed total mercury (THg) and methylmercury (MeHg) concentrations of epiphyte/macrophyte complexes in Lake St. Pierre, a large fluvial lake of the St. Lawrence River (Québec, Canada). THg and MeHg concentrations were ten fold higher in epiphytes than in macrophytes. THg concentrations in epiphytes linearly decreased as a function of the autotrophic index, suggesting a role of algae in epiphyte Hg accumulation, and % of MeHg in epiphytes reached values as high as 74%. Spatio-temporal variability in THg and MeHg concentrations in epiphytes and macrophytes were influenced by water temperature, available light, host species, water level, dissolved organic carbon and dissolved oxygen.

Methanogens: principal methylators of mercury in lake periphyton

Mercury methylation and demethylation rates were measured in periphyton biofilms growing on submerged plants from a shallow fluvial lake located along the St. Lawrence River (Quebec, Canada). Incubations were performed in situ within macrophytes beds using low-level spikes of (199)HgO and Me(200)Hg stable isotopes as tracers. To determine which microbial guilds are playing a role in these processes, methylation/demethylation experiments were performed in the absence and presence of different metabolic inhibitors: chloramphenicol (general bacteriostatic inhibitor), molybdate (sodium molybdate, a sulfate reduction inhibitor), BESA (2-bromoethane sulfonic acid, a methanogenesis inhibitor), and DCMU (3-(3,4-dichlorophenyl)-1,1 dimethyl urea, a photosynthesis inhibitor). Active microbes of the periphytic consortium were also characterized using 16S rRNA gene sequencing. Methylation rates in the absence of inhibitors varied from 0.0015 to 0.0180 d(-1) while demethylation rates ranged from 0.083 to 0.217 d(-1), which corresponds to a net methylmercury balance of -0.51 to 1.28 ng gDW periphyton(-1) d(-1). Methylation rates were significantly decreased by half by DCMU and chloramphenicol, totally inhibited by BESA, and were highly stimulated by molybdate. This suggests that methanogens rather than sulfate reducing bacteria were likely the primary methylators in the periphyton of a temperate fluvial lake, a conclusion supported by the detection of 16S rRNA gene sequences that were closely related to those of methanogens. This first clear demonstration of methanogens' role in mercury methylation in environmental periphyton samples expands the known diversity of microbial guilds that contribute to the formation of the neurotoxic substance methylmercury.

Novel mutations in pyridoxine-dependent epilepsy

PURPOSE

Pyridoxine-Dependent Epilepsy (PDE) is a rare autosomal recessive disease with neonatal seizures resistant to conventional anti-epileptic drugs. This metabolic disease has to be diagnosed early and treated to improve outcome. We report on two new mutations that open new prenatal prospects and suggest a new diagnostic procedure.

CASE REPORT

We describe PDE in a neonate carrying two novel mutations in the ALDH7A1 gene: c.[852_856delCTTAG] + [1230C > A]; p.[(Phe410Leu)] + p.[(Leu285CysfsX26)]. This case also illustrates that diagnosis could have been made without any pyridoxine withdrawal, thanks to the measurement of biomarkers. The patient was successfully treated with pyridoxine supplementation and currently shows normal neurological development.

Influence of hypothermia on the prognostic value of early EEG in full-term neonates with hypoxic ischemic encephalopathy

OBJECTIVE

To determine the prognostic value of early electroencephalograms (EEG) in full-term neonates suffering from hypoxic ischemic encephalopathy (HIE) exposed to whole-body hypothermia (cooled group), compared to neonates treated conventionally (control group).

METHODS

The study included all term neonates born at Grenoble Hospital between 2000 and 2006 with symptoms of HIE. The first two EEGs were reviewed retrospectively and classified according to current electrophysiological criteria. In the cooled group, EEGs were recorded with a mean body temperature of 33°C. Neurological outcome was correlated with EEG pattern.

RESULTS

An EEG inactive or paroxysmal pattern was associated with death in 60% of the controls, while all survivors had neurological sequels. In the cooled group, this EEG pattern was only predictive of death in 40% while survivors had normal examination at 1 year of age. Mild abnormalities on the first EEG correlated with a good prognosis in both groups. The second EEG had a high predictive value, particularly in the cooled group. Persistence of inactivity at 3 days after birth was always associated with death.

CONCLUSIONS

After HIE, the first two EEGs are good prognostic indicators, also in the cooled group. Strong discontinuity in the EEG observed on the first hours after hypothermia induction can be associated with a good outcome.

SIGNIFICANCE

Early Stage 4 EEGs recorded during the hypothermia may not always indicate a poor prognosis in HIE.

A novel microdialysis probe designed for clinical use: potential analytical and therapeutic applications

Significant obstacles to the use of microdialysis in the clinic for diagnostic or therapeutic purposes include the production of dedicated entry port through the skull and the formation of a tract by the insertion of a probe into the parenchyma. We have developed a microdialysis probe that is minimally invasive and can be combined with an intracranial pressure probe, recording electrode, or other intracranial probe, that is minimally invasive. Yet the surface area of this probe is very high, permitting high recovery efficiencies even at relatively high flow rates. This probe design makes possible minimally invasive measurement of the peroxidation product, uric acid, and excitatory amino acids, two analytes that increase in experimental traumatic brain injury in animals. Moreover, its large surface area makes therapeutic applications of microdialysis probes in the brain potentially feasible. A pilot evaluation of the ability of microdialysis to have therapeutic benefit in limiting experimental excitotoxin lesions induced in rat striatum by N-methyl-D-aspartate (NMDA) is reported.