Activation of dopamine D4 receptor inhibits an L-type calcium current in cerebellar granule cells.

The functions of the D4 receptor, a newly cloned D2-like receptor, as well as the identity of cells expressing it, are still poorly defined. Using quantitative polymerase chain reaction we detected the messenger RNA of the D4, but not other D2-like receptor, in cultured granule cells from neonatal rat cerebellum. In these neurons, dopamine reduced high-voltage-activated calcium current, with a pharmacology corresponding to that of the D4 receptor. The response declined from one to three days, when calcium currents were mostly sensitive to nifedipine, to 15 days, when nifedipine-insensitive calcium currents were also present and D4 receptor messenger RNA had declined. The dopamine response was abolished after pretreatment of the cells by pertussis toxin, was potentiated and made irreversible by infusion of guanosine 5'-O-(3-thiotriphosphate) but persisted in the presence of cyclic AMP and isobutylmethylxanthine. These results indicate the presence in the neonatal cerebellum of a functional D4 receptor inhibiting an L-type calcium current, an action involving a Gi/Go protein but independent from adenylate cyclase inhibition.

Operant conditioning of the visual smooth pursuit in young infants.

Smooth pursuit is a complex behaviour which is not considered as totally functional at birth. The lack of maturation of the visuo-motor systems is generally invoked to explain this phenomenon. However, if this oculomotor response is an operant behaviour, an alternate explanation may be found in the absence of previous confrontation with the environmental contingencies. A first group of young infants were placed in situations in which their oculomotor responses could produce an auditory stimulus. In such situations, young infants are able to improve their pursuit. Music was randomly delivered to a second group. No music was delivered to a third group. For the last two groups no augmentation of the proportion of slow movements was observed. Our main conclusion is that visual tracking has the properties of an operant behaviour and may be enhanced at birth. These results will be discussed within the frameworks of the behavioural discrepancy and of the maturationist hypotheses of the ocular motor control.

Quantitative assessment of the static properties of the oculo-motor system by the photo-oculographic technique.

The paper addresses the problems raised by the application of the photo-oculographic technique to the quantification of static orientations of the eye in ophthalmology. Eye orientations are determined from the relative positions of corneal reflex and pupil images. The relationship between the positions of these images and the angular rotations of the eye is studied with an optical model of the anterior chamber of the eye. This model is used to analyse the influence of technical and physiological variables and to evaluate the accuracy of different calibration procedures applicable to clinics.

[Asymmetry of visual perceptive activity of faces and emotional facial expressions]. / Asymétrie dans l'activité perceptive visuelle des visages et des expressions faciales emotionnelles.

Eye movements were studied in 40 right-handed subjects during perception of symmetrical chimerical faces. These movements were recorded using an original system based on a differential optical method for the detection of corneal reflection and of the pupil made shiny. Under basal conditions, the first fixation was usually located in the left visual hemifield. The subjects spent more time gazing at the right hemiface (P less than 0.04). This visuo-spatial asymmetry in favour of the left hemispace was increased when the subject was requested to determine the emotional expressions of a new series of faces (P less than 0.002). Compared with basal conditions, the increase in the percentage of time spent in the left area was significant (P less than 0.035). An analysis performed on the first 3 seconds confirmed and amplified the differences observed. These results can partly be explained by reading habits and exploratory activity for symmetrical shapes. However, activation of the right hemisphere, specialized in the perception of faces and facial expressions, probably influenced visual exploration by drawing attention to the left area and favouring the left visual hemifield.

[Eye controlled microscope used in ophthalmic microsurgery]. / Commande du microscope par le regard appliquée à la microchirurgie ophtalmologique.

This article presents a system of oculomotor control of the microscope used in ophthalmic microsurgery. An eye movement sensor has been integrated within the microscope lens. The information provided by this sensor is used to control the position of the microscope with no alteration of the surgeon's visual functions and no interference with his visual sensori-motor reflexes. Results have been obtained from laboratory experimentations as well as from a series of anterior and posterior segment surgical procedures. They demonstrate the high precision and sensitivity of the gaze control which can be used to compensate for the reduction of the field of vision resulting from the optical magnification of the microscope.

Induction of the five urea-cycle enzymes by glucagon in cultured foetal rat hepatocytes.

Foetal hepatocytes obtained from rats at different stages were cultured in order to investigate the inducibility of the five urea-cycle enzymes by glucagon and dibutyryl cyclic AMP (Bt2cAMP). When 18.5-day-old hepatocytes were cultured for 3 days with 10(-7) M glucagon, the activities of carbamoyl phosphate synthetase (CPS), argininosuccinase (ASL) and arginase were increased by 1.4-, 1.8- and 1.9-fold, respectively, as compared to controls. These effects were mimicked by 10(-4) M Bt2cAMP, but the activities of ornithine transcarbamylase (OTC) and argininosuccinate synthetase (ASS) were never changed by the addition of these compounds. Hepatocytes cultured at earlier stages were not responsive to glucagon unless dexamethasone was added simultaneously, suggesting that this steroid might induce some steps necessary for glucagon action. Bt2cAMP was effective as early as day 16.5 without requiring the presence of steroids. In addition, the effect of the cyclic nucleotide appeared additive or synergistic with that of dexamethasone. The simultaneous addition of actinomycin D did not affect the glucagon-induced increase in enzyme levels, thus suggesting a post-transcriptional effect of the hormone on the foetal enzyme activities. Insulin itself did not have any effect on the basal level of the enzyme activities and had only a moderate inhibitory effect on glucagon-induced ASL activity. This slight effect of insulin is in contrast with the marked inhibitory effect of dexamethasone on this enzyme activity that we described previously.

[Evaluation of spatial discrimination performances of newborn infants with the visual pursuit of structured stimuli]. / Evaluation des capacités de discrimination spatiale des enfants nouveau-nés par la poursuite visuelle de stimulus structurés.

Pursuit eye movements have been recorded with the photo-oculographic technique from newborn infants during the presentation of stimulations specific for spatial discrimination functions. 72.5 per cent of 51 subjects whose eye movements have been recorded have successfully followed stimuli of spatial frequency up to 0.4 cycles per degree. Estimations of grating visual acuity are similar to those provided by the preferential looking technique.

Hormonal regulation of two urea-cycle enzymes in cultured foetal hepatocytes.

Foetal-rat hepatocytes were cultured in primary monolayer culture, and activity changes of argininosuccinate synthetase (ASS, EC 6.3.4.5) and argininosuccinase (ASL, EC 4.3.2.1) were followed under defined hormone conditions. In hormone-free medium, cultured cells maintained the enzyme activities at values equal to those of freshly isolated cells for at least 3 days. Continuous addition of dexamethasone produced the development of the two enzyme activities, but only after the first 20h of culture. Under these conditions, urea production by the foetal hepatocytes was concomitantly increased in the culture medium. Pretreatment with dexamethasone for 20h was sufficient to produce the development of ASL activity within the 2 following days. Introduced alone, glucagon induced an increase of ASL activity, but did not affect the ASS activity. The most powerful stimulation of ASS and ASL could be observed in cultured hepatocytes if glucagon and dexamethasone were added simultaneously or sequentially. These results indicated that the development of the receptor complex for the induction of urea-cycle enzymes appears early before birth and established that glucocorticoids amplify the glucagon stimulation of these enzyme activities during foetal life.

Precocious induction of arginase in primary cultures of fetal rat hepatocytes.

Fetal rat hepatocytes were isolated and cultured in primary culture to investigate activity changes of arginase under defined conditions. In hormone-free medium, cultured cells maintained the enzyme activity at levels equal to that of freshly isolated cells for at least 4 d. Arginase activity could be induced by dexamethasone in hepatocytes isolated from 16.5-d-old fetuses although cells were competent to respond to glucagon only at the stage of 18.5 d. The combination of the two hormones induced greater levels of arginase activity than the individual compounds. These findings indicate that glucocorticoid and glucagon receptors appear early and sequentially before birth and reveal that cultured fetal hepatocytes provide a suitable system for the investigation of the role of hormones in the initiation of enzyme synthesis.

[Urea cycle enzyme activities in fetal rat hepatocytes in primary cultures]. / Activités enzymatiques du cycle de l'urée dans les hépatocytes de foetus de rat en culture primaire.

The development of urea synthetizing enzymes, namely argininosuccinate synthetase, argininosuccinase and arginase was studied in fetal Rat liver cells in culture. The enzyme activities were measured in 18.5 days old isolated hepatocytes and could not develop without addition of dexamethasone in the culture medium.

[Comparative study of electrooculographic and photooculographic recordings]. / Etude comparative des enregistrements électro-oculographiques et photo-oculographiques.

The authors present the results of clinical application of a new invasive real time method for ocular movement recording. There is an optical system which measures the gaze direction from the video signals of five reflected corneal dots and pupil image. Their study is based upon 110 simultaneous P.O.G. - E.O.G. recordings of normal beings or patients having various oculomotor troubles. It appears that the heavy odds of such a new method is obvious. It allows to obtain an absolute measurement of eye positions in relation to the basic line whatever the pattern and axis of the moving may be. A quantitative evaluation of all movement parameters is in progress. It still remains to solve the problem of large deviations and the wearing of optical correction during the examination.

[A new technic for recording eye movements by image processing. Principle and method]. / Une nouvelle technique d'enregistrement des mouvements oculaires par traitement d'image. Principe et méthode.

Nowadays, electro-oculography remains the only clinical method for ocular movement recording which is largely used in daily practise, but it has many drawbacks and limits. Till now the photo-oculographic technics have been only applied in laboratory conditions. A new differential photo-oculographic procedure is presented. This optical method is based upon the measurement of gaze direction and ocular movement amplitude from the relative pattern of five reflected corneal dots and pupil image which are located in two different optical plans. The authors relate in detail the recording devices and processing materials for the computerized analysis of video signals. The preliminary results confirm the real advantages of the method which allows to record all sorts of ocular movements in clinical conditions.

[Analysis of vergence movements using differential photo-oculography]. / Analyse des mouvements de vergence par photo-oculographie différentielle.

Analysis of vergence troubles is weight by an heavy handicap. In clinical conditions it is easy to value the static vergence balance with a great lot of tests. On the contrary examination of kinetic vergence pattern is generally neglected. Usually a refixation vergence is a combination of an horizontal convergence-divergence of 5 to 10 degrees with a vertical component of 15 to 20 degrees. It is impossible to do their reliable analysis by kinetic EOG because the unequal transmission of potential towards the orbital rim. The authors give the results obtained by photo-oculographic method perfected by Charlier and Buquet. On all recordings it can be noticed that, in vergence refixation, vertical movements of both eyes are always true congruent saccadic versions, while the horizontal movements are disjunctive, dissociated and unequal. On the vertical axis it seems to be no real kinetic vergence at all, but in some cases only a mere tonic alignment. Such a device is a very good mean to study the vergence troubles in daily practice.

Butyrate blocks the accumulation of CDC2 mRNA in late G1 phase but inhibits both the early and late G1 progression in chemically transformed mouse fibroblasts BP-A31.

Sodium butyrate (6 mM) blocks the resumption of the cell division cycle in serum-deprived chemically transformed Balb/c-3T3 mouse fibroblasts (BP-A31). The inhibition of G1 progression by sodium butyrate is not restricted to a specific mitogenic signaling pathway and is equally effective when tetradecanoyl phorbol acetate (TPA), insulin, or fetal calf serum (FCS) is used as inducer. The inhibitor acts in early as well as late G1 phase as indicated by experiments in which inhibitor was added and withdrawn at different times after restimulation of quiescent cells by FCS. At the gene expression level, sodium butyrate does not affect the inducibility of early cell cycle-related genes (c-myc, c-jun) while blocking the induction of cdc 2 mRNA, a late G1 marker. We conclude that sodium butyrate does not interfere with the growth factor signaling pathways regulating the (early) cell cycle-related gene expression. However, the presence of sodium butyrate early in G1 phase inhibits the cascade of events leading eventually to the expression of late G1-characteristic genes such as cdc2. The antimitogenic activity of sodium butyrate may be related to its interference with an (unknown) process involved in the "mitogenic" cascade.

Role of dexamethasone and insulin on the development of the five urea-cycle enzymes in cultured rat foetal hepatocytes.

The activity changes of the urea-cycle enzymes were monitored in cultured foetal hepatocytes after dexamethasone and insulin treatments. Addition of dexamethasone induced the development of carbamoyl-phosphate synthetase, argininosuccinate synthetase, argininosuccinase and arginase activities as soon as day 16.5 of gestation. When insulin was added together with dexamethasone, it markedly inhibited the steroid-induced increase in carbamoyl-phosphate synthetase, argininosuccinate synthetase and argininosuccinase activities.

Changes in levels of argininosuccinate lyase mRNA during induction by glucagon and cyclic AMP in cultured foetal-rat hepatocytes.

During the perinatal period, the activity of the urea-cycle enzyme argininosuccinate lyase (ASL) is regulated by glucocorticoids, glucagon and insulin. In this study, the effects of glucagon and cyclic AMP (cAMP) analogues were examined on the synthesis of ASL and on the level of its corresponding mRNA in cultured foetal hepatocytes. Northern-blot analysis revealed that these agents only gave a transient induction of ASL mRNA amount, which reached a peak at 6 h and declined thereafter. This induction preceded the increase in enzyme activity and amount which could be observed for 2 or 3 days of culture. Stimulation of ASL mRNA accumulation by a combination of cAMP analogues and dexamethasone was additive, indicating that glucocorticoids and cAMP are both necessary to promote hepatocyte differentiation and that inductions could occur via independent pathways. Induction by cAMP analogues could be abolished by actinomycin D, suggesting a control mechanism at the transcriptional level. Puromycin was without effect on ASL mRNA induction by cAMP, indicating that no ongoing protein synthesis was required in the stimulation process.

Expression of argininosuccinate lyase mRNA in foetal hepatocytes. Regulation by glucocorticoids and insulin.

Argininosuccinate lyase (ASL), the fourth enzyme of the urea cycle, belongs to a group of liver enzymes appearing in the late foetal period in the rat. Several hormones, including glucocorticosteroids and insulin have been implicated in the control of the development of this enzyme activity. In this study, the cloned cDNA was used to measure the relative abundance of ASL mRNA in the livers of rats at various stages of perinatal development and in cultured foetal hepatocytes during hormonal manipulations. The ASL mRNA was first detectable on day 15.5 of gestation and increased in amount concomitantly with the rise in the enzyme activity, suggesting that the appearance of enzyme activity reflects the turning on of specific gene transcription. When foetal hepatocytes were exposed to dexamethasone, an increase in ASL mRNA was detected, which was completely abolished by addition of actinomycin D, suggesting a transcriptional effect of the steroid. In contrast, administration of cortisol to foetuses in utero had no effect on the mRNA level, suggesting that the steroid action is inhibited in the intra-uterine environment. Insulin might be the inhibiting factor since it completely repressed the dexamethasone-induced accumulation of ASL mRNA in foetal hepatocytes. These data were confirmed in vivo by experiments using streptozotocin, which produces insulin-depleted foetuses and causes the accumulation of ASL mRNA. This regulation of ASL mRNA by glucocorticoids and insulin could account for the modulation of the enzyme activity observed in vivo and in vitro.

[Differential photo-oculography of vertical and oblique movements]. / Photo-oculographie différentielle des mouvements verticaux et obliques.

Up to now EOG has been the only method used to record ocular movements in daily practice. However such a mean has various drawbacks and limits. It has two main gaps: firstly for vertical movements because the interference discharges related with palpebral movements and blinkings; on the other hand for oblique movements because the unequal transmission of EOG potential towards the orbital rim. The differential photo-oculography perfected by Charlier et Buquet has been fitted and now can be easily used in clinical conditions. With this optical method, it exists a direct relation between the gaze direction and video signals of the eye. The authors point out the reliability of its results not only for horizontal movements, but also for vertical and oblique movements. This method allows a relevant analysis of all kinetic parameters whatever the moving axis may be.