[Biological roles of trace elements in the brain with special focus on Zn and Fe]. / Rôles biologiques des éléments traces dans le cerveau--exemples du Zn et du Fe.

INTRODUCTION: Many metals like iron (Fe), copper (Cu) or zinc (Zn) fulfil various essential biological functions and are thus vital for all living organisms. For instance, they play important roles in nervous tissue, participating in a wide range of processes such as neurotransmitter synthesis, myelination or synaptic transmission. STATE OF THE ART: As in other tissues, brain cells tightly control the concentration of metals but any excess or deficit can lead to deleterious responses and alter cognitive functions. Of note, certain metals such as Zn, Fe or Cu accumulate in specific brain structures over lifespan and several neurodegenerative diseases are associated with a dysregulation of the homeostatic mechanisms controlling the concentration of these cations. CONCLUSION AND PERSPECTIVES: This review will address some of the cellular and molecular processes controlling the entry and distribution of selected metals (mainly Zn and Fe) in the brain, as well as their roles in synaptic transmission, in the pathogenesis of some neurologic diseases such as Parkinson's disease and Alzheimer's disease, and their impact on cognitive functions.

The genome of Laccaria bicolor provides insights into mycorrhizal symbiosis.

Mycorrhizal symbioses--the union of roots and soil fungi--are universal in terrestrial ecosystems and may have been fundamental to land colonization by plants. Boreal, temperate and montane forests all depend on ectomycorrhizae. Identification of the primary factors that regulate symbiotic development and metabolic activity will therefore open the door to understanding the role of ectomycorrhizae in plant development and physiology, allowing the full ecological significance of this symbiosis to be explored. Here we report the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor (Fig. 1) and highlight gene sets involved in rhizosphere colonization and symbiosis. This 65-megabase genome assembly contains approximately 20,000 predicted protein-encoding genes and a very large number of transposons and repeated sequences. We detected unexpected genomic features, most notably a battery of effector-type small secreted proteins (SSPs) with unknown function, several of which are only expressed in symbiotic tissues. The most highly expressed SSP accumulates in the proliferating hyphae colonizing the host root. The ectomycorrhizae-specific SSPs probably have a decisive role in the establishment of the symbiosis. The unexpected observation that the genome of L. bicolor lacks carbohydrate-active enzymes involved in degradation of plant cell walls, but maintains the ability to degrade non-plant cell wall polysaccharides, reveals the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots. The predicted gene inventory of the L. bicolor genome, therefore, points to previously unknown mechanisms of symbiosis operating in biotrophic mycorrhizal fungi. The availability of this genome provides an unparalleled opportunity to develop a deeper understanding of the processes by which symbionts interact with plants within their ecosystem to perform vital functions in the carbon and nitrogen cycles that are fundamental to sustainable plant productivity.

Transvenous versus perinervous stimulation of the phrenic nerve to assess the diaphragmatic strength in rabbits.

Diaphragmatic strength can be measured by transdiaphragmatic pressure during phrenic nerve stimulation. In order to avoid phrenic nerve dissection, a transjugular approach of the phrenic nerve can be performed. The objective of this study was to verify the identity of perinervous and transvenous techniques of phrenic nerve stimulation to assess diaphragmatic force. In intact (n = 9) or right phrenicotomized (n = 12) rabbits, we compared esophageal pressure (Peso) induced by supramaximal perinervous stimulation of the phrenic nerve with that obtained by transvenous stimulation of the phrenic nerve. Electromyography (EMG) of the thoracic muscles was studied in four animals. We found no difference between Peso induced by perinervous (PNS) and transvenous (TVS) unilateral or bilateral phrenic nerve stimulation. During unilateral stimulation, no EMG activity was recorded in the non stimulated diaphragm, or in the middle part of the esophagus, or in ipsi- and contralateral accessory inspiratory muscles. We conclude that in rabbits, unilateral or bilateral TVS of the phrenic nerve is functionally equivalent to PNS, whatever the side of stimulation; Peso is not altered by esophageal contraction in TVS. Transvenous stimulation can replace perinervous stimulation in experimental studies, when cervical access is difficult.

Selective resection of the phrenic nerve roots in rabbits. Part II: Respiratory effects.

This study evaluates the delayed respiratory consequences of selective resection of one or several roots of the right phrenic nerve in rabbits. A total of 50 animals were operated on according to five modalities of root resection. A total of 11 animals served as control. The breathing pattern was analysed 8 weeks after surgery. Transdiaphragmatic pressure was measured during transjugular supramaximal stimulation of the phrenic nerve, unilaterally or bilaterally and during prolonged tracheal occlusion (PImax). No difference was observed between the esophageal pressure observed during bilateral phrenic nerve stimulation (BilPeso) in control animals when compared to animals with resection of the highest root of the right phrenic nerve (16.2 +/- 1.0 versus 14.5 +/- 1.0 cmH2O (mean +/- SE). Resection of the two highest or of the two lowest roots of the right phrenic nerve resulted in a similar BilPeso (11.3 +/- 0.8 versus 11.1 +/- 1.2 cmH2O). Preservation of only the accessory phrenic nerve (PN) resulted in a low value of BilPeso (9.8 +/- 1.0 cmH2O) similar to that obtained with complete denervation of the right hemidiaphragm. Ventilation and PImax were not different between the denervated or intact rabbits during quiet breathing. We conclude that in rabbits: (1) Diaphragmatic function is preserved after resection of the highest root of the phrenic nerve. (2) Diaphragmatic function is altered if only the APN is preserved.

Respiratory response to CO2 in patients with chronic obstructive pulmonary disease in acute respiratory failure.

The aim of our study was to determine the importance of chemoreceptor stimulation by carbon dioxide in setting the level of ventilation in patients with chronic obstructive pulmonary disease (COPD) in acute respiratory failure. We studied the ventilatory and mouth occlusion pressure (P0.1) responses to CO2 in 25 COPD patients under treatment for episodes of acute respiratory failure, and in 24 normal subjects. Carbon dioxide rebreathing tests were performed in the spontaneously breathing, intubated patients, after arterial blood gases had been quasi-normalized by mechanical ventilation, which allowed us to compare both groups at similar resting arterial carbon dioxide tension (PaCO2) and acid-base status. The slopes of the ventilatory responses were markedly lower in the patients (mean +/- SEM, 1.28 +/- 0.23 versus 12.53 +/- 1.13 l.min-1.kPa-1). The slopes of the P0.1 responses were lower in the patients (0.27 +/- 0.05 versus 0.45 +/- 0.05 kPa.kPa-1), but the absolute P0.1 values were not significantly different from the normals. Increasing PaCO2 from 5.3 to 8 kPa (40 to 60 mmHg) resulted in a mean increase of 34% in ventilation. These results show that CO2 drive is a major determinant of respiratory stimulation in many COPD patients with acute respiratory failure.