Nutrient dynamics at the sediment-water interface in a Mediterranean lagoon (Thau, France): influence of biodeposition by shellfish farming activities.

The Thau Lagoon, a French Mediterranean shallow lagoon, is a site where extensive shellfish farming occurs. The aim of the present work is to evaluate the role of this activity on nutrient exchange at the sediment-water interface in relation to organic matter (OM) sedimentation and degradation. Two stations inside (C5) and outside (C4) of the shellfish farming areas were sampled at three seasons. Porewater chemistry surveys and calculated diffusive fluxes were used to evaluate the trophic status of the Thau lagoon. Quantitative (Particulate Organic Carbon) as well as qualitative OM (Hydrogen Index, Carbohydrates) analyses were performed on sediments to assess OM characteristics. Results emphasized that surficial sediments at C5 are always more enriched in OM. Porewater nutrient concentrations are 10-20 times higher at C5 than at C4. In June 2003, the porewater profiles exhibit a sharp gradient at the bottom waters, indicating a hypereutrophic status, leading to an anoxic crisis.

Chemical characterization of porewaters in an intertidal mudflat of the Seine estuary: relationship to erosion-deposition cycles.

A seasonal field study was carried out in the Seine estuary to determine the chemistry of sediment porewaters using the 'peeper' technique and changes in the elevation of the mudflats using the 'Altus' technique. This approach allowed us to evaluate the release of nutrients and to link these releases to the sediment hydrodynamics. Our results show that nutrient and organic matter cycling in a Seine estuary mudflat exhibits a seasonal behaviour, which is mainly influenced by variations in hydrodynamics. Sediments, rich organic matter, were input during floods and they were mineralized during summer and autumn, releasing nutrients and dissolved organic carbon into the sediment porewaters. The nutrient release, including ammonium, is mainly linked to the mineralization of organic matter, while the release of phosphate is delayed. The delay could be the result of phosphate association with organic matter and/or its co-precipitation with calcium and iron.

Subthalamic stimulation in Parkinson disease: with or without anesthesia?

OBJECTIVE: To study the effects of general anesthesia on the postoperative outcome of patients with Parkinson disease (PD) who underwent surgery using bilateral placement of stimulating electrodes within the subthalamic nucleus (STN). DESIGN: Retrospective analysis. SETTING: Hôpital de la Salpêtrière, Paris, France. PATIENTS: Fifteen PD patients who underwent bilateral implantation of electrodes within the STN received general anesthesia because of severe anxiety, poorly tolerated off-period dystonia, or respiratory difficulties. These patients were compared with 15 patients matched for age, disease duration, and parkinsonian motor disability who underwent the same neurosurgical procedure under local anesthesia. MAIN OUTCOME MEASURE: Motor disability scores. RESULTS: After surgery, the severity of parkinsonian motor disability was markedly improved in both groups of patients. Compared with patients who were under local anesthesia during the operation, the residual parkinsonian motor score under stimulation (with ["on"] or without ["off"] levodopa) and the intensity of stimulation were higher in patients who were under general anesthesia during the operation. CONCLUSIONS: Although the improvement of parkinsonian motor disability is greater in PD patients who receive local anesthesia during surgery, general anesthesia can be performed in patients unable to tolerate prolonged states without levodopa.

Effects of high-frequency stimulation on subthalamic neuronal activity in parkinsonian patients.

BACKGROUND: High-frequency stimulation of the subthalamic nucleus (STN) is a neurosurgical alternative to medical treatment in levodopa-responsive forms of Parkinson disease. The mechanism of action of STN stimulation remains controversial, although an inhibition of overactive STN neurons has been postulated. OBJECTIVE: To determine the effects of high-frequency STN stimulation on the neuronal activity of STN neurons in Parkinson disease patients. PATIENTS: Single-unit recordings of the neuronal activity of the STN were obtained before, during, and after the application of intra-STN electrical stimulation in 15 Parkinson disease patients. Changes in firing frequency and pattern were analyzed using various combinations of stimulus frequency (range, 14-140 Hz). RESULTS: Stimulation at a frequency greater than 40 Hz applied within the STN significantly decreased the firing frequency and increased the burst-like activity in the firing pattern of STN neurons. An aftereffect was observed in cells that had been totally inhibited during high-frequency stimulation. CONCLUSION: The beneficial effects of high-frequency stimulation result from a change in the firing pattern of cellular discharge and a blockade of the spontaneous overactivity of STN neurons.

Subthalamic stimulation in Parkinson disease: intraoperative predictive factors.

BACKGROUND: High-frequency stimulation of the subthalamic nucleus (STN) is an effective treatment for advanced forms of Parkinson disease. Postoperative improvement of motor parkinsonian disability is known to depend on patient selection and surgical targeting. OBJECTIVE: To determine which clinical and electrophysiological variables evaluated during the operation predict the postoperative clinical outcome of patients with Parkinson disease treated by bilateral high-frequency stimulation of the STN. METHODS: Intraoperative clinical and electrophysiological data obtained in 41 patients with Parkinson disease who underwent bilateral implantation of electrodes for STN stimulation were correlated with the improvement in parkinsonian disability assessed 6 months after the operation. RESULTS: The extent of STN neuronal activity recorded along the trajectory of the therapeutic electrode had no effect on the postoperative clinical outcome. The intraoperative improvement in segmental akinesia, but not rigidity, was predictive of the postoperative improvement in parkinsonian motor disability and reduction in daily levodopa-equivalent dosage. Parkinsonian motor disability scores assessed after surgery were lower in patients with intraoperative stimulation-induced dyskinesias than in those without stimulation-induced dyskinesias. CONCLUSION: The improvement of segmental akinesia and the observation of dyskinesias provoked by stimulation during the operation predict the best postoperative effects of bilateral STN stimulation on parkinsonian motor disability.

Compulsions, Parkinson's disease, and stimulation.

Pathophysiological models suggest that obsessive compulsive disorder (OCD) might be associated with dysfunctions in cortico-striato-pallido-thalamo-cortical neuronal circuits. We implanted subthalamic electrodes to alleviate parkinsonian symptoms in two patients who had Parkinson's disease and a history of severe OCD. Parkinsonian disability improved postoperatively in both patients, and 2 weeks after the procedure, their compulsions had disappeared and obsessive symptoms improved (58% improvement for patient 1 on the Yale-Brown obsessive compulsive scale, 64% for patient 2). The improvements in these two patients suggest that high-frequency stimulation could improve function in the subcortical-limbic circuitry in patients with severe OCD.