Phosphorus-31 NMR spectrometry of the calf muscles in patients with arterial claudication. Preliminary results

Phosphorus NMR spectrometry allows non-invasive exploration in vivo of certain aspects of muscle energy metabolism. A study was conducted in 10 healthy volunteers and 12 patients with lower limb affections (stage II claudication) to define a precise methodology and to discuss perspectives offered by this new method, in the light of preliminary findings. Changes with time of amplitude of peaks of phosphocreatine (Pcr), inorganic phosphorus (Pi) and ATP, and of intracellular pH, showed that recovery of 80% of resting value of the ratio Pcr/Pi + Pcr after quantified exercise is a very discriminatory parameter correlated with severity of arteriographic findings in patients with claudication.     

Time-course of changes in firing rates and firing patterns of subthalamic nucleus neuronal activity after 6-OHDA-induced dopamine depletion in rats

The subthalamic nucleus (STN) plays a key role in motor control. Disorganization of its neuronal activity is implicated in the manifestation of parkinsonian motor symptoms. The aim of the present work was to study the time-course of changes in the firing activity of STN neurons in a rat model of parkinsonism. Electrophysiological recordings were done in normal rats and four groups of rats at different time points after 6-hydroxydopamine (6-OHDA) microinjection into the pars compacta of substantia nigra (SNc). Results showed a significant decrease in firing rate during the first and second weeks post lesion (5.53+/-0.56 and 7.66+/-0.73 spikes/s, respectively) compared to normal rats (11.13+/-0.59 spikes/s). From the 3rd week after 6-OHDA injection the firing rates returned toward baseline, with an average of 9.71+/-0.51 spikes/s during the 3rd week and 11.13+/-0.71 spikes/s during the 4th week. With regard to firing pattern, the majority of STN cells (90%) discharged regularly or slightly irregularly in normal animals. Only 4% exhibited burst activity and 6% had mixed firing patterns. After SNc-lesion, the percentage of cells exhibiting burst and mixed patterns increased progressively from 35% during the first week to 56% at week 4 post-lesion. In sum, these experiments revealed that the firing rate of STN neurons was altered only transiently following nigral lesions, whereas a progressive and stable change in the firing pattern was observed up to 4 weeks post lesion, suggesting that the persistence of bursts firing more closely relates to the motor pathologies of this rat model of parkinsonism.     

Stereo-electroencephalography methodology: advantages and limits

Since January 1990, 70 patients with medically intractable partial epilepsy underwent a stereo-EEG investigation in our center. We first described technical requirements, and gave an overview of the variety of the explored cerebral regions and implantation patterns realized, pointing out the low rate of morbidity (1.4%). The three-dimensional epileptogenic zone thus defined led to a tailored individualized surgical excision in 60 patients, while 9 are waiting for surgery and the remaining 1 has been excluded (1.4%). Conceptual and technical aspects of the stereo-EEG methodology were discussed in order to underline its peculiarities in the field of "depth recordings", and more generally among the broader group of "invasive" procedures.     

Opposite motor effects of pallidal stimulation in Parkinson's disease

We studied the effects—on parkinsonian signs, on levodopa-induced dyskinesias, and on levodopa response—of acute experimental high-frequency stimulation of the internal pallidum (GPi) during off-drug and on-drug phases. Thirteen quadripolar electrodes were evaluated in 8 patients with Parkinson's disease (PD). Stimulation of the most ventral contacts, lying at the ventral margin of or just below the GPi, led to pronounced improvement in rigidity and a complete arrest of levodopa-induced dyskinesias. The antiakinetic effect of levodopa was also blocked and the patients became severely akinetic. Stimulation of the most dorsal contacts, lying at the dorsal border of the GPi or inside the external pallidum, usually led to the moderate improvement of off-drug akinesia and could also induce dyskinesias in some patients. When using an intermediate contact for chronic stimulation, a good compromise between these opposite effects was usually obtained, mimicking the effect of pallidotomy. We conclude that there are at least two different functional zones within the globus pallidus, at the basis of a different pathophysiology of the cardinal symptoms of PD. The opposite effects may explain the variable results of pallidal surgery reported in the literature and may also largely explain the paradox of PD surgery. A possible anatomical basis for these differential functional effects could be a functional somatotopy within the GPi, with the segregation of the pallidofugal fibers from the outer portion of the GPi, on one hand, forming the ventral ansa lenticularis and from the inner portion of the GPi, on the other hand, forming the dorsal lenticular fasciculus.