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H Condé

Publications and source records attributed to H Condé.

At least 19 recordsLinked to original sources
PubMed1998

The role of the pedunculopontine tegmental nucleus in relation to conditioned motor performance in the cat. I. Context-dependent and reinforcement-related single unit activity.

The activity of the pedunculopontine tegmental nucleus (PPTg) neurons was recorded in three unrestrained cats operantly conditioned to perform a lever-release movement. The movement had to be initiated either rapidly after a (click) stimulus in a simple reaction-time paradigm or had to be delayed after the same stimulus in trials identified by a tone cue. Successful trials were rewarded by a food pellet. A total of 107 neurons were recorded with microelectrodes. Brief spike neurons (mean duration: 0.7 ms) and broad spike neurons (mean duration: 2 ms) presumed to be cholinergic were detected. Of the 73 neurons localized in the PPTg area, 53 had brief spikes and 20 broad spikes. Changes in activity most commonly occurred very early after the stimulus or during the reinforcement process. Most neurons with brief spikes exhibited very early excitation after the stimulus and reinforcement-related activity. These neurons had a mean activity of 23.7 impulses/s in the period preceding the stimulus. The onset of activation after the stimulus had a latency of 8.6+/-6.9 ms (mean+/-SD), with a range of 4-35 ms. In trials where the movement had to be delayed after the stimulus, the early activation disappeared or was considerably reduced, showing that it was context-dependent. A small proportion of neurons with brief spikes initially decreased activity after the stimulus, but with a latency >9 ms. All the neurons with broad spikes, except one, had reinforcement-related activity. Half of them showed exclusively reinforcement-related activity, the other half also early activation after the stimulus. These neurons were about half as active in the period preceding the stimulus occurrence than the neurons with brief spikes. The early context-dependent activation is discussed in relation to the excitatory projection of PPTg neurons on the subthalamic nucleus. The reinforcement-related activity, preferentially evidenced in broad spike neurons presumed to be cholinergic, is speculated to be associated with cholinergic projection of PPTg neurons to the dopaminergic neurons of the substantia nigra. Finally, the role of PPTg in the ongoing control of motor performance and reinforcement processes is discussed in relation to the basal ganglia circuitry.

Action Potentials↗
PubMed1998

The role of the pedunculopontine tegmental nucleus in relation to conditioned motor performance in the cat. II. Effects of reversible inactivation by intracerebral microinjections.

The effects of reversible pharmacological manipulation of the neuronal activity in the pedunculopontine tegmental nucleus (PPTg) on the performance of a conditioned movement was studied in two freely moving cats. The microinjections were given in regions where, in the same subjects, we had previously identified neurons with context-dependent early activity after a trigger stimulus and with reinforcement-related activity. The subjects were conditioned to perform a forelimb-flexion movement controlled by a simple reaction-time task. In addition, one subject was trained to execute the same flexion movement, but delayed after the trigger stimulus. Food pellets were used as the reinforcer. Lidocaine injections (1 microl of 2% solution, injected over a 6-min period) induced a transient arrest of performance within minutes. The cessation of performance could be preceded by behavioral signs such as meowing, attempt to escape from the experimental booth, licking, or stereotyped posture. No rotational behavior could be observed. The effects of lidocaine could be mimicked in one subject by an extinction procedure. Muscimol injections (two injections of 0.2 microg in 1 microl, tested in one subject) also induced arrest of performance, but the return to pre-injection level of performance could not be obtained within the time of the test session. The quantitative analysis of reaction times and of inter-trial intervals showed that altering PPTg activity affected inter-trial intervals, but only slightly affected the reaction times. It is speculated that the PPTg is involved in the reinforcement process related to selecting the appropriate motor program.

Animals↗
PubMed1997

Correlations between activity of pallidal neurons and motor parameters.

The relationships between the activity of 87 pallidal neurons and parameters characterizing motor performance were analysed quantitatively in six unrestrained cats performing a forelimb flexion movement controlled by a reaction-time paradigm. Three motor variables were considered: the static force exerted when the trigger stimulus occurred, the latency of the force change initiating the liver-release movement and the velocity of the force change. For all the cats, the latency of the change in force was the prevalent parameter in determining the movement onset occurrence. The single-unit activity was quantified on a trial-by-trial basis by measuring the mean firing rate in windows of fixed duration. Both normal (total) and partial linear correlation coefficients were used. Partial correlation coefficients were calculated between the mean firing rate during selected windows and each of the motor parameters. A total of 17% and 9% of all partial correlation coefficients tested (n = 1566) was found to be significantly different from zero, respectively with p < 0.05 and p < 0.01. The mean percentages of explained variation, measured by the square of the correlation coefficient, were 17% (p < 0.05) and 21% (p < 0.01). The 46 pallidal neurons presenting an increase in discharge after the trigger stimulus could be classified in homogeneous subgroups with respect to the signs of the correlations. Representations of the motor programme underlying reaction-time performance evidenced at the pallidal level further substantiate a specific involvement of the basal ganglia in the latency of motor triggering.

Animals↗
PubMed1992

Organization and physiology of the substantia nigra.

A comprehensive review of the literature on the anatomy, electrophysiology and pharmacology of the substantia nigra is presented. A diagram is developed taking into account the interneuronal interactions of neurotransmitters and receptors that control firing rates and neurotransmitter releases. The central features of the diagram are a positive dopaminergic feedforward process and a positive feedback mechanism mediated by extrasynaptic substance P diffusing from striatal terminals to dopaminergic dendrites of the zona compacta neurons. This loop can enhance the transmission of information from the striatum through the pars reticulata output neurons. The loop is controlled at the level of zona compacta neurons by a negative feedback supported by the dendritic release of dopamine and boosted by pedunculopontine activation mediated by muscarinic receptors. The output of the loop is controlled by two negative feedforward processes, both involving GABAergic striatonigral afferents. Application of the model to pharmacological studies of diverse behaviors including seizures, turning, and conditioned behaviors reveals unforseen relationships and may offer insights into, and directions for, further analysis of the mechanisms and functions involved.

Animals↗
PubMed1990

The possible use of a spallation neutron source for neutron capture therapy with epithermal neutrons.

Spallation is induced in a heavy material by 72-MeV protons. The resulting neutrons can be characterized by an evaporation spectrum with a peak energy of less than 2 MeV. The neutrons are moderated in two steps: first in iron and then in carbon. Results from neutron fluence measurements in a perspex phantom placed close to the moderator are presented. Monte Carlo calculations of neutron fluence in a water phantom are also presented under some chosen configurations of spallation source and moderator. The calculations and measurements are in good agreement and show that, for proton currents of less than 0.5 mA, useful thermal-neutron fluences are attainable in the depth of the brain. However, the dose contribution from the unavoidable gamma background component has not been included in the present investigation.

Boron↗
PubMed1989

The production by 72 MeV protons of keV neutrons for 10B neutron capture therapy.

Fast neutrons, produced in a spallation process by 72 MeV protons hitting heavy nuclei, can be moderated down to keV energies, suitable for 10B capture therapy. Measurements of neutron flux from copper and lead targets, after moderation by water and hydrocarbons, have been performed, together with measurements of the fast neutron and gamma-backgrounds. The comparisons with Monte Carlo calculations show good agreement. As neutron fluences up to 10(12) to 10(13)n/cm2 can be produced within a few hours in about 0.5 m target distance the technique seems to be suitable for clinical experiments.

Boron↗
PubMed1983

Cat red nucleus changes of activity during the motor initiation in a reaction time task.

Unit recordings were made in the posterior red nucleus of 4 freely moving cats, performing a conditioned forelimb flexion in response to a sound, in a simple reaction time (RT) paradigm. More than 50% of the recorded neurons (154) were found to be task-related, with marked changes of firing (mostly increases) time-locked with the go-signal (mean latency: 40.8 ms +/- 12 ms SD) and frequency-correlated with the duration of the RT. These RT-correlated changes of firing disappeared or were markedly decreased when the movement was not triggered. Most of the task-related neurons also displayed late changes of firing during the force change, time-locked with the movement. Furthermore, a clear relation was observed between the rubral firing before and after the go-signal and the sensorimotor field of the recorded neuron: the neurons preferentially related to limb or trunk movements discharged with the highest frequency throughout the conditioned sequence and exhibited the best RT-correlated increases of firing during the movement initiation. In contrast, rubral neurons apparently related to head-movements generally discharged with low frequency and commonly exhibited decreases of firing in the initiation period. The changes of rubral firing prior to the motor activity, correlated to the RTs, suggest a command function for the RN, in the triggering of the conditioned motor response.

Animals↗
PubMed1982

Motor command in the ventrolateral thalamic nucleus: neuronal variability can be overcome by ensemble average.

The variability and stationarity of single unit activity and reaction times in a simple reaction time task were investigated by means of unit recordings from the ventrolateral thalamic nucleus in the cat. The study was carried out on eight neurons recorded over many trials and displaying an increase in activity correlated with the performed reaction time. The stationarity of the correlation appeared to be better than that of the unit activity or reaction time taken alone. In this stationary process the neuronal variability is considerable, and the investigator has to use time averages over many trials to be able to extract information from the single unit data. Since the nervous system does not required repeated presentations of a stimulus to trigger a movement, it must be using parallel processing of information throught ensemble averages. A simulation of an ensemble average based upon the data from these eight neurons showed that such a process can be efficient. An evaluation of the number of neurons required to obtain a quasi deterministic neuronal command of the reaction time value, gave the speculative figure of 70. This figure could represent the dimension of the set of neurons with the same characteristics involved in the motor command.

Animals↗
PubMed1982

The rubro-olivary tract in the cat, as demonstrated with the method of retrograde transport of horseradish peroxidase.

The rubro-olivary projection in the cat was investigated by means of the retrograde transport of horseradish peroxidase. After injections in the inferior olive, more than a thousand labelled neurons were found in the ipsilateral red nucleus. These neurons had triangular-shaped cell bodies with an average diameter of 26.4 +/- 7.7 microns (mean +/- S.E.M.) and had few dendrites. Between 85% and 95% of the rubro-olivary neurons were found in the rostral third of the red nucleus (between A 5.5 and A 7). Morphologically, the rubro-olivary neurons are similar to rubro-thalamic neurons. Previous studies with retrograde transport of horseradish peroxidase have failed to demonstrate an extensive projection from the red nucleus to the inferior olive. These results are discussed in relation to our own findings.

Animals↗
PubMed1981

Control of reaction time performance involves the striatum.

Cats were tested for the effect of unilateral cooling of the centre median nucleus of the thalamus (CM) or of the caudate nucleus (Cd) as they performed a simple reaction time schedule. Shortening of reaction time occurred during CM cooling. Lengthening of the reaction time was observed during Cd cooling. Moreover, the Cd cooling was followed after a variable delay of a few minutes by a slowing down of the trial rate, and even by the arrest of performance for the lowest cooling temperature. The subject restarted at will after an arrest period, without motivational or motor disturbances, except for a short period of rotatory behaviour. The arrest period duration was about equal to the arrest period latency. Human subjects suffering from Parkinson's disease were tested with the same reaction time schedule. They showed lengthened reaction times and difficulty to perform reliably more than a ten of trials.

Animals↗
PubMed1979

Activity of ventrolateral thalamic neurons in relation to a simple reaction time task in the cat.

Unrestrained cats performed ballistic forelimb flexion movements triggered by an auditory stimulus (CS) on a simple reaction time (RT) paradigm. During the variable foreperiod the subject was required to hold down a lever and to release it on presentation of the CS. The RTs ranged from 200 to 300 ms. The activity of single neurons of the ventrolateral nucleus of the thalamus (VL) was recorded bilaterally. More than 40% of the 166 units recorded in the VL contralateral to the performing limb presented, after the CS, changes of activity with a latency less than 100 ms and were classified into three types: (1) Twenty-five units had a short latency transient increase of activity 10 to 30 ms after the CS, followed by a longer increase or decrease in activity. Short latency increase as well as subsequent increase of the firing rate were not correlated to the RTs. (2) Twenty-nine units showed a 40-60 ms latency increase of activity which lasted long enough to continue during the forelimb movement. These units displayed a correlation between the RTs and the mean firing rate measured in the 40-100 ms period after the CS. The more the cells were activated, the shorter the RTs. (3) Fifteen units presented a reciprocal pattern of discharge with respect to the type (2) units. The firing rate decreased with latencies ranging from 20 to 90 ms after the CS. Only 14,5% of the 96 units recorded in the VL ipsilateral to the performing limb presented changes of activity starting in the 100 ms period following the CS. Background firing levels as well as phasic activity were rather low compared to those observed contralaterally. Sixteen units showed burst activity while the cat was performing but burst pattern was not time-related to the task. In an unconditioned animal, a very low level of activity and an absence of modulations were observed in both VLs.

Animals↗
PubMed1979

Effects of ventrolateral thalamic nucleus cooling on initiation of forelimb ballistic flexion movements by conditioned cats.

Five cats were trained to perform a forelimb ballistic flexion on a reaction time paradigm including an upper limit of about 400 ms for reinforcement (food pellets). They were implanted with a cyrogenic probe thermically insulated, except at the tip, by a vacuum jacket (outer diameter, 1.1 mm). Four cats had the probe inserted into the ventrolateral thalamic nucleus (VL), contralateral to the moving limb. During cooling they showed increased reaction times, which remained constant throughout daily sessions performed during many weeks, independent of the foreperiod but varying from 25 to 100 ms according to the subject. The temperatures used to upset the reaction times varied from +10 decrees C to -8 degrees C, depending on the localisation of the probe and on the insulation of the silver tip used to prevent nervous tissue reaction, but for each subject the reaction times always increased when the temperature was lowered. The fifth cat, with a probe inserted between VL and the Centre Median, showed a decrease of reaction times on cooling to 0 degrees C and an increase of the reaction times for a cooling at -10 degrees C. For one of the four cats with a probe properly inserted into the VL, strain-gauges were stuck on the lever to measure the latency of the decrease of the pressure exerted by the subject when the subject initiated the forelimb flexion in response to the CS. Reaction times and latencies of pressure changes were closely correlated with the movement onset, and they were equally delayed during cooling. This result demonstrates that it is not by slowing down movement velocity that reaction times are upset during VL cooling but by delaying the movement onset.

Animals↗
PubMed1979

Observations on the orthograde and retrograde transport of horseradish peroxidase in the cat.

Horseradish peroxidase (HRP) was applied to the precruciate cortex of the cat. The peroxidase was either applied directly to the surface or injected by glass micropipettes in single or multiple injections. Retrograde as well orthograde transport was observed by light and electron microscopy in different areas: in the thalamus: the nucleus ventralis lateralis and the nucleus centrum medianum, in the red nucleus and in the spinal cord. The distribution of HRP within the nervous elements of the nuclei: axon terminals and/or perikarya and dendrites, was observed by light and electron microscopy. HRP was present in dendrites and perikarya, indicating retrograde transport, in experiments where damage to the injected nervous tissue could be suspected. However HRP appeared restricted to the nerve endings, indicating orthograde transport, when the damage seemed to be minimal. This effect of injury on retrograde transport of HRP was further confirmed by experiments using bilateral HRP injections and unilateral lesions of the spinal cord to label rubro-spinal cells. Thus retrograde transport of HRP could be induced by lesion in systems where it does not occur normally. The normal intra-axonal transport of HRP appears to be from the perikaryon to the nerve endings. This orthograde transport can be seen under the light microscope and can be confused with faint retrograde labeling.

Animals↗