Insect photoperiodism and circadian clocks: models and mechanisms.

Photoperiodic clocks allow organisms to predict the coming season. In insects, the seasonal adaptive response mainly takes the form of diapause. The extensively studied photoperiodic clock in insects was primarily characterized by a "black-box" approach, resulting in numerous cybernetic models. This is in contrast with the circadian clock, which has been dissected pragmatically at the molecular level, particularly in Drosophila. Unfortunately, Drosophila melanogaster, the favorite model organism for circadian studies, does not demonstrate a pronounced seasonal response, and consequently molecular analysis has not progressed in this area. In the current article, the authors explore different ways in which identified molecular components of the circadian pacemaker may play a role in photoperiodism. Future progress in understanding the Drosophila circadian pacemaker, particularly as further output components are identified, may provide a direct link between the clock and photoperiodism. In addition, with improved molecular tools, it is now possible to turn to other insects that have a more dramatic photoperiodic response.

Spatio-temporal and kinematic analysis of pointing movements performed by cerebellar patients with limb ataxia.

Three patients with cerebellar limb ataxia and three age-matched controls performed arm-pointing movements towards a visual stimulus during an experimental procedure using a double-step paradigm in a three-dimensional space. Four types of trajectories were defined: P1, single-step pointing movement towards the visual stimulus in the initial position S1; P2, double-step pointing movement towards S1; P3, double-step straight pointing movement towards the second position S2; and P4, double-step pointing movement towards S2 with an initial direction towards S1. We found that the cerebellar patients, as well as the controls, were able to modify their motor programs, but with impaired timing, severe anomalies in the direction and amplitude of the changed movement trajectories and alteration of the precision of the pointing movements.

[Guillain-Barré syndrome of axonal type, Campylobacter jejuni infection and anti-ganglioside GM1 antibodies]. / Syndrome de Guillain-Barré de type axonal, infection à Campylobacter jejuni et anticorps anti-ganglioside GM1.

Infection by Campylobacter jejuni (C. jejuni) has been reported in 17 to 55 p. 100 of the GBS. The "axonal" GBS has been recently attributed to such an association. It is characterized by rapid progression to severe widespread paralysis, respiratory failure, poor and delayed recovery. The acute "axonal" form of Guillain-Barré syndrome has been and remains a matter of controversy. A typical case of GBS with serological evidence of recent C. jejuni infection and increased antibodies to GM1 is reported. An immune mechanism remains most likely. Recent studies have suggested the hypothesis of "shared epitope" between C. jejuni and peripheral nervous system cell (Gal beta 1-3 N Acetylgalactosamine epitope). Such a cross-reactivity could provoke a severe form of GBS with a poor recovery in some predisposed hosts (antiganglioside antibodies, HLA "immunogenic" groups such as B8, B35 or DR3).

[Cognition disorders and parkinsonian syndrome: diffuse Lewy body disease?]. / Troubles cognitifs et syndrome parkinsonien: maladie a corps de Lewy diffus?.

A 68 year old man developed progressive cognitive impairment with an akinetic-rigid syndrome which was atypically responsive to levodopa. The patient died after 18 months and the postmortem examination showed typical Lewy bodies in the substantia nigra and pale bodies in the cortex which were unlabelled by ubiquitin antibodies. This case is particular by the neuropathological examination (no immunoreactivity to antibodies against ubiquitin) and by the abnormal response to treatment (dystonia). These two aspects are discussed.

Planning and execution of pointing movements in cerebellar patients.

Twelve patients with cerebellar dysfunction including a limb ataxia and 12 age-matched controls performed pointing movements with an arm. In one condition, the task was a simple reaction time (RT) movement directed toward a spatially defined target. The other two conditions involved choice tasks in which the amplitude and direction of movement were varied. The variables recorded were: movement latency determined by measuring the RT, duration of movement and the terminal accuracy of pointing as reflected in the movement time (MT), pointing surfaces (PS), and systematic errors. RTs and MTs were found to be significantly longer in cerebellar patients than in controls. In both groups the choice RT increased significantly as compared to simple RT, but no significant difference between patients and controls was found for the mean increase of the choice RT as compared with the mean increase for simple RT. A strong correlation between MTs and PSs was found in the controls. The cerebellar patients showed no correlation between MTs and PSs. The results are discussed in relation to the ability in cerebellar patients to program and execute voluntary movements.

Bilateral and side-related reaction time impairments in patients with unilateral cerebral lesions of a medial frontal region involving the supplementary motor area.

Human subjects (nine patients with unilateral brain lesions of a medial frontal region involving the supplementary motor area, SMA, and 10 controls) performed two reaction time (RT) tasks in response to the presentation of a luminous signal: an aimed movement towards a spatially defined target involving hand lifting and pointing with the index finger, and a no-aimed movement consisting of the hand lifting phase completed by the stabilization of the limb posture without any pointing. When compared with controls, the patients exhibited a bilateral RT increase which was more pronounced in the hand contralateral to the lesion. Moreover, comparison between the two tasks showed that this contralateral RT impairment was more marked in the no-aiming than in the aiming task. These results suggest that unilateral lesions of a medial frontal region involving the SMA cause two types of RT impairment in these motor tasks. The first may concern a supramotor function which acts bilaterally and initiates the motor programme of the limb movement as the first step of preparatory processes. The second component of this RT impairment would concern a supplementary motor function which consists of the feed forward control of the coupling between the hand lifting and the appropriate posture, just before the triggering of the limb movement. This interpretation leads to the hypothesis that the SMA region, and the medial motor system in general, may have a dual motor function.

[Quantitative approach of postural asynergia in cerebellar diseases]. / Approche quantitative de l'asynergie posturale en pathologie cérébelleuse.

In his original description of cerebellar asynergia, Babinski, in 1899, presented a patient with cerebellar dysfunction performing a backward upper trunk bending. When the patient tried to bend his head and trunk, his lower limbs stayed almost motionless, because the associated flexion of the knee and hip, usually observed in a normal subject, did not take place. To reassess the possibility that asynergia may actually be a symptom of cerebellar dysfunction, a combined kinematic and electromyographic (EMG) analysis of the upper-trunk bending was performed on 3 patients suffering from progressive cerebellar ataxia of late onset and showing a significant atrophy of the vermis on MRI examination. Compared with 3 age and sex-matched control subjects, a significant slowing down of the upper-trunk displacement and a marked reduction of the associated displacement of hip and knee was observed. EMG recordings of three pairs of antagonistic muscles at trunk level (rectus abdominis, erectores spinae), at thigh level (vastus lateralis, semi membranosus), and at leg level (tibialis anterior, gastrocnemius lateralis), showed that the reciprocal activation pattern characteristic of a normal fast movement was absent at the thigh level in the cerebellar patients. This lack of reciprocal activation of the thigh muscles during the upper-trunk bending might explain the reduction of the compensatory displacement of the hip and knee. It might also represent an essential feature of cerebellar dysfunction in provoking axial asynergia between the upper-trunk, which is the moving segment, and the leg, which is the supporting segment during equilibrium control and during whole body displacement.