Differences in effective connectivity between dyslexic children and normal readers during a pseudoword reading task: an fMRI study.

PURPOSE: This fMRI study investigated phonological and lexicosemantic processing in dyslexic and in chronological age- and reading level-matched children in a pseudoword reading task. MATERIALS AND METHODS: The effective connectivity network was compared between the three groups using a structural model including the supramarginal cortex (BA 40; BA: Brodmann area), fusiform cortex (BA 37) and inferior frontal cortex (BA 44/45) areas of the left hemisphere. RESULTS: The results revealed differences in connectivity patterns. In dyslexic patients, in contrast with chronological age- and reading level-matched groups, no causal relationship was demonstrated between BA 40 and BA 44/45. However, a significant causal relationship was demonstrated between BA 37 and BA 44/45 both in dyslexic children and in the reading level-matched group. CONCLUSIONS: These findings were interpreted as evidence for a phonological deficit in developmental dyslexia.

[Effects of the monosaccharide derivative 8RN-DAGal on the putative P-type calcium channel expressed in Xenopus oocytes]. / Effets du dérivé monosaccharidique 8RN-DAGal sur un courant calcique apparenté au type P exprimé dans l'ovocyte de Xénope.

P-type calcium channels are expressed in Xenopus oocytes after injection of rat cerebellar mRNA. The FTX and omega-Aga-IVa toxins extracted from Agelenopsis aperta venom are known to inhibit the activity of this channel. The present results demonstrate that 8RN-DAGal is also a antagonist of P-type calcium channels. The inhibition of the current, obtained with Ba2+, as charge carrier, is voltage dependent.

[Structure-activity relationship of a new family of calcium antagonist molecules derived from monosaccharides]. / Relations structure-activité d'une nouvelle famille de molécules antagonistes calciques derivées de monosaccharides.

The Ca++ antagonist effects of new drugs derived from monosaccharides were tested in the rat duodenal muscle preparation in vitro. The structure-activity relationship shows that: 1. The monoacetonide products (nR-O-MAG and nR-S-MAG) with alkyl chain from 8 to 9 C atoms induce a maximal reduction of muscular tonus and contraction. 2. The inhibitory effect rapidly decreases when the alkyl chain has a number of C atoms smaller than 7 or larger than 9. 3. The diacetonide (DAG) and acetonide (G) products induce an inhibition of less extent. 4. The Ca++ antagonist effect is very slightly changed by the type of heteroatom (O or S) linking the alkyl chain to the monosaccharide. 5. The type of monosaccharide affects the Ca++ antagonist activity.

Mapping of serotonin-like immunoreactivity in the ventral nerve cord of crayfish.

Whole-mount immunohistochemical technique using antibody to serotonin (5-HT) had been used to map presumptive serotoninergic structures in the ventral abdominal and thoracic nerve cord of crayfish Procambarus clarkii. 5-HT immunoreactivity was detected in more than 30 cell bodies, numerous fibers and peripheral nerve endings of root plexus and neuropilar regions. Immunoreactive fibers are arranged in 3 pairs of rostrocaudal bundles. The median (MFB) and the lateral fiber bundles run longitudinally through the entire thoracic and abdominal nerve cord (first thoracic T1 to sixth abdominal A6 ganglia). The central (CFB) fiber bundles extend only from the subesophageal to the fourth thoracic ganglia. In the 4 anterior thoracic ganglia (T1-T4), two lateroposterior cell bodies send their major processes in the ipsilateral MFB. In the fifth thoracic (T5) and first abdominal (A1) ganglia, the pattern of reactive structures is similar. Two large anterior cells which send a single prominent process to join the ipsilateral MFB and 4 smaller posterior cells. In other abdominal ventral ganglia, immunoreactive structures are smaller and less labeled. Cell bodies are displayed in two kinds of arrangement giving the appearance of two distinct homogeneous groups of ganglia: an anterior group (A2-A3-A4) that contained two pairs of small neurons and a posterior group (A5-A6) that contained only a large unpaired medial neuron. These results were discussed in relation to the serotonin-like immunoreactivity pattern previously described in lobster by Beltz and Krawitz.

Arsenazo III transients and calcium current in a normally non-spiking neuronal soma of crayfish.

Arsenazo III was used to investigate Ca2+ transients in the normally non-excitable soma of the motor giant neurones of the crayfish Procambarus clarkii. Two kinds of regenerative potentials could be obtained depending on membrane potential conditioning: a fast spike after a pre-hyperpolarization to -90 mV and a slow action potential after a pre-depolarization to -50 mV. Only the second of these was accompanied by an Arsenazo III transient. In voltage-clamped, somata injected, with tetraethylammonium chloride, an absorbance change could be obtained by pulsing the membrane potential above -44 mV. The relationship between absorbance change and potential peaked between 0 and +10 mV then fell off to zero at ca. +150 mV. Changes in light absorbance studied using double-pulse protocols suggested that the inactivation of Ca2+ entry was predominantly mediated by the intracellular free Ca2+ concentration. External application of 1 mM-CdCl2 abolished both the absorbance changes and the (Ca2+) inward current. The voltage dependence of this current was similar to that of the absorbance change. For positive membrane potential the current-voltage relationship showed a voltage-dependent conductance property, the origin of which is discussed.

Gap-like junctions between neuron cell bodies and glial cells of crayfish.

Data reported up to now on neuron-glia relationships, show that neuron cell bodies and glial cells are separated by a narrow intercellular cleft which is considered as the microenvironment of the nervous system, and where neuron-glia exchange occurs. We present here evidence that neuron perikarya and ensheathing glial cells of the abdominal ganglia of the crayfish communicate through gap-like junctions. These junctions could constitute short circuits for ionic exchange between neuron perikarya and glial cells, probably with some degree of electrotonic coupling between neurons and glia. In the preparation described here, the intercellular cleft would play only a secondary role in neuron-glia communication.

[Short and long term depression of neuromuscular transmission in crayfish]. / Dépressions à court et à long terme de la transmission neuromusculaire chea l'Ecrevisse

Following single excitation of the abdominal giant motoneuron of crayfish, an important depression of neuro-muscular transmission is observed for about 15 mn. The time course of recovery is not modified even after low frequency (1/30 Hz) repetitive stimulation. Recovery curves obtained for different Mg++ concentration in physiological solutions show two phases of depression: short-term depression which is largely reduced in high Mg++ concentrations - thus probably depending on transmitter depletion in motoneuron terminals - long-term depression which is not modified by changing Mg++ concentration and seems to be independent of depletion.