PubMed Health⌕ Search

Biomedical subjects

M Hugon

Publications and source records attributed to M Hugon.

At least 37 records · Page 2Linked to original sources
PubMed1987

Evoked potential changes in rat hippocampal slices under helium pressure.

High pressures of helium affect the physiology of the central nervous system in animals and humans. We examined these effects in rat hippocampal slices. The in vitro preparation displayed a reversible reduction in postsynaptic and antidromic field potentials of CA1 pyramidal cells, but no significant change in the amplitude of the afferent volley. Although the subliminal synaptic response of CA1 neurons was depressed, the ability of these cells to produce population spikes was enhanced. These changes resembled those previously found in vivo in the rat hippocampus. The present results support the hypothesis of a helium pressure-induced depolarization of hippocampal neurons. Other possible mechanisms are discussed.

Animals↗
PubMed1987

A versatile chamber for microphysiologic studies with gas mixtures under high pressure.

A pressure chamber, designed for microelectrode recordings in isolated tissues or organs an capable of withstanding pressures up to 200 bar, is described. The versatility of the vessel allows a wide variety of experimental configurations and several types of studies. It features a complete access, easy visibility, interchangeable tissue bath and micromanipulator modules, as continuous perfusion and temperature control of the preparation under pressure. The ability to move micropipettes in 1-micron steps allows single unit recording on a variety of in vitro preparations at normal or elevated gas pressures. Successful physiologic tests, using the hippocampal slice preparation, are described. The results testify to the reliability of the system and to the usefulness of this in vitro model to study the gas pressure effects on isolated networks of mammalian CNS.

Air Pressure↗
PubMed1985

Postural forearm changes induced by predictable in time or voluntary triggered unloading in man.

Human subjects sitting in a chair were asked to maintain their right forearm in a horizontal position in half supination. The forearm was loaded with a constant weight of one kilogram. Vertical force at the wrist level, angular position of the elbow and EMG activity of biceps, brachio-radialis and triceps muscles were recorded. Unloading was tested under four different conditions, the first two having been used in a previous study (Hugon et al. 1982): Voluntary unloading by the subject's other hand. An "anticipatory" deactivation of the load bearing forearm flexors is observed preventing the elbow rotation of that arm. Unpredictable passive unloading. This results in an upward forearm rotation which provokes the classical "unloading reflex". Two new conditions were tested in the present paradigm: Imposed unloading predictable in time (tone signal preceding unloading by a fixed interval). Unloading being actively triggered when the subject presses a key. Under the two latter conditions, no anticipatory deactivation of the flexor supporting muscles preceding the onset of unloading as in situation A was observed. During the first 120 ms after the onset of unloading, the forearm rotation was the same as in situation B (unpredictable passive unloading). Thereafter, the rotation was smaller in some subjects, apparently due to an ameliorated reflex action. It is concluded that temporal information concerning the precise time of the unloading or the triggering of the load release by a voluntary movement (key press) was not by itself able to induce the anticipatory deactivation of the forearm flexors that was seen with a coordinated voluntary release of the load by the contralateral arm.

Adult↗
PubMed1985

A study of spontaneous and evoked activity in the rat hippocampus under helium-oxygen high pressure.

High pressures affect the physiology of the central nervous system. For a better understanding of this effect, we examined the hippocampal activity in the rat under high pressures (91 bars) of helium-oxygen. Effects of high pressure on hippocampal physiology are: an abnormally sustained 5-8 Hz pattern of spontaneous activity, followed, in some cases, by seizures; a marked decrease in the responses of CA1 pyramidal cells to stimulation of their commissural afferents; and a 50% decrease in the afterdischarge threshold. On the basis of the relatively well understood hippocampal physiology in normobaric conditions, our observations suggest that high pressures induce hypoexcitability of afferents and/or target cells.

Animals↗
PubMed1984

[Proprioceptive proximo-distal relationships between the quadriceps and soleus muscles in man].

Electrical stimulation of femoral nerve modulates voluntary tonic activity o of ipsilateral soleus muscle. Stimulus time-locked inhibitory and facilitatory phases can be distinguished. EMG temporal analysis suggests that early perturbations are correlated with spinal effects of centripetal electrical activity. The inhibitory effects which momentarily abolish voluntary soleus activity are thought to result from quadriceps Ib fibres recruitment. While no heteronymous activity is induced at rest, femoral nerve Ia fibres activation can produce soleus muscle reflex when soleus motor nucleus excitability is increased by voluntary command. Recurrent discharge resulting from soleus reflex response enhances inhibition initially due to quadriceps Ib volley. Secondary effects of isometric quadriceps contraction (and soleus contraction when the femoral stimulus elicits a reflex in this muscle) have their own effects later. These findings suggest that proprioceptive relationships of the two muscular groups are efficient during tonic isometric voluntary command.

Electric Stimulation↗
PubMed1982

Anticipatory postural changes induced by active unloading and comparison with passive unloading in man.

Normal human subjects, sitting in a chair, were required to maintain stable elbow flexion against loads of 0.5 kg or 1.0 kg. Unloading was affected either 'passively' by the experimenter, or 'actively' with the subject's own contralateral arm. Elbow angle, force exerted by the load, and electromyographic activity (EMG) of biceps and triceps muscles of both arms were recorded and averaged. 'Passive' unloading was followed by a reduction of biceps EMG activity, starting 50--80 ms after weight lift, and by an upward deflection of the forearm. With 'active' unloading, however, a reduction of the biceps EMG activity slightly preceded the onset of unloading (0--30 ms). This reduction of the 'actively' unloading arm occurred at about the same time as the activity of the contralateral unloading arm. In this experiment, the unloaded forearm maintained an almost stable position. Thus, the anticipatory adjustment of elbow posture, observed when unloading was performed by the subject, appears to optimize limb stability during the mechanical perturbation.

Action Potentials↗
PubMed1982

The possible mechanisms of the high pressure-induced motor disturbances in the cat.

High pressures elicit a high-frequency tremor (8-12 c/sec) in mammals, the mechanisms of which are still unknown. The present study shows that: (1) in spite of many similarities observed between the EMG characteristics of harmaline-induced tremor and pressure-induced tremor, cerebellar lesions which suppress the harmaline-induced tremor, do not modify the characteristics of the pressure-induced tremor; (2) at depth, the caudal part of the spinal cat (section at T9-T10 spinal level) displays irregular spontaneous EMG activities which can be clonic or rhythmic (4-8 c/sec), and a neuromuscular stretch hyperreflexivity. These data suggest that the origin of the pressure-induced tremor is spinal and neuromuscular rather than cerebellar.

Animals↗
PubMed1982

Patterns of interaction of effects of light metabolically inert gases with those of hydrostatic pressure as such--a review.

This review of available literature attempts to interpret net effects of metabolically inert light gases (He, H2, and Ne) as the resultant of hydrostatic pressure and intrinsic pharmacological effects associated with exposure to these gases, and to assess the relative importance of each component with respect to a number of biological responses. A common pattern is recognizable for pressure reversal of anesthesia, high pressure convulsions, high pressure bradycardia, and certain characteristics of liposome model systems. Using the method of analysis proposed, these lightest gases can be shown to conform to the pattern of relation of potency to physical properties characteristic of more potent gaseous anesthetics, including N2, N2O, and Xe. The relations between effect produced and partial pressure of the acting gas are approximately linear to total pressures of 100 ATA for anesthesia or pressure reversal of anesthesia and (or to a much smaller extent) for the liposome model systems, but not for high pressure convulsions. As a result of these general factors no single gas can be expected to neutralize the effects of hydrostatic pressure with regard to all of the biological responses tested over any significant pressure range. A series of experiments with single cells and tissue cultures have revealed interactions between high pressure and inert gas that do not conform to the pattern set by the responses mentioned so far. These responses cannot yet be shown to constitute a homogeneous group and may represent at least two subgroups. Responses falling into this second heterogeneous category include cell motility, development of cell abnormalities and lysis, and cell and perhaps virus replication or multiplication. The implication of these results for the formulation of biophysical hypotheses to explain interactions between inert gas and high pressure, for considerations of high pressure effects as a safety hazard, and for the problem of experimental approaches to the study of pressure acclimation are discussed briefly.

Anesthesia, Inhalation↗
PubMed1979

Compensation of postural reactions to fall in the vestibular neurectomized monkey. Role of the reamining labyrinthine afferences.

The electromyographic (EMG) responses from soleus and tibialis anterior muscles and the monosynaptic H- and T-reflex responses from soleus muscles were recorded bilaterally from conscious baboon while unexpectedly dropping it with unrestricted vision. These responses were recorded either after unilateral vestibular neurectomy (U.N. Baboons) or after bilateral neurectomy performed in one stage (B.N. 1 baboons) and in two stages (B.N. 2 baboons). A positive correlation was found between modifications and development of EMG responses and reflex data. In the U.N. baboons, some differences were observed when comparing data from the H- and T-reflex methods, suggesting that recovery of normal responses to fall is achieved both by means of direct influences on alpha-motoneurons and via the gamma-loop. In the U.N. baboons postural reactions to fall developed in three distinct periods. The first or critical stage showed asymmetrical EMG and reflex responses with increased responses from contralateral soleus muscle and decreased responses from ipsilateral soleus. Opposite effects were recorded from tibialis anterior flexor muscles. The second or acute stage which began around 4 to 7 days after surgery exhibited symmetrical, but very reduced, responses when compared to the control in soleus muscles, and symmetrical, but increased, responses from tibialis anterior muscles. This stage lasted until about the end of the second postoperative week and was followed by the third or compensatory stage during which EMG as well as reflex responses developed towards the control pattern in all tested muscles. Almost normal responses were recorded on both sides 3 weeks after surgery. Only a partial recovery was found in the B.N. 1 baboons, indicating that the contralateral remaining labyrinthine afferences constitute a necessary condition for the full compensation of postural reactions to fall in the case of unilateral vestibular neurectomy. The Bechterew's compensation was obtained in the B.N. 2 baboons. These results are discussed in relation with the general organization of the vestibulospinal pathways and with those concerning development of the postoperative activity at the vestibular nuclei level. A model of vestibular compensation achieved by means of a multisensory substitution process is suggested.

Afferent Pathways↗
PubMed1978

Muscle responses and monosynaptic reflexes in falling monkey. Role of the vestibular system.

The free fall has been used in our laboratory as a way to test vestibular function in baboons in order to quantify vestibular compensation in the hemilabyrinthectomized animal. This study presents only those results that concern the contribution of the vestibular system to muscle responses due to sudden fall. EMG activity was recorded from the fully conscious animal using chronic electrodes implanted in various muscles. Spinal monosynaptic reflexes (Hoffmann's and tendon reflexes) were studied in the soleus muscle. Baboons were seated in a special chair suspended from an electromagnet and unexpectedly dropped 90 cm. Experiments were performed in normal, unilateral and bilateral vestibular neurectomized baboons. 1. In normal baboons, results showed a first short-latency response in all tested muscles, followed by a second peak of EMG activity in these muscles. Comparison with data from bilateral vestibular neurectomized baboons demonstrates that normal vestibular function is essential for the appearance of the first peak; the second peak rapidly disappears in our experimental situation where the animal's fall is mechanically braked and interrupted, so the animal does not have to make the postural adjustments necessary for landing, It is suggested that the first peak is concerned with the automatic and reflex control of landing, the second with the voluntary breaking of landing. 2. The modulation of monosynaptic spinal reflexes is closely related to the EMG response in soleus muscle. Facilitation of the H-reflex begins just prior to the onset of the EMG activity and continues as long as the baboon is falling. The T-reflex modulation presents a similar time course except in its early phase where it is depressed. Decrease in T and increase in H-reflexes suggest that the EMG response is most likely due to direct activation of alpha-motoneurons and not by means of the gamma-loop. 3. In unilateral vestibular neurectomized baboons, EMG and reflexological data show the classical asymmetry characterized by a strong decrease of the responses on the side of the lesion, and by a pronounced increase on the contralateral side. It is concluded that this represents the imbalance between the resting discharge of the vestibular neurons, and discloses the influence of labyrinthine afferences at the spinal level. We suggest consequently the use of EMG responses and modulation of spinal reflexes to fall in order to quantify vestibular compensation.

Animals↗
PubMed1976

Critical flicker frequency (CFF) and subjective fatigue during an oxyhelium saturation dive at 62 ATA.

Two divers spent over 50 hours at 610 msw in a helium-oxygen mixture (PO2:0.38-0.52 ATA). The dive duration was 27 days, including predive stages of confinement, compression, time at maximum pressure, and decompression. The divers were asked to answer 30 questions on their feelings of mental and physical fatigue and to indicate on a nine-point scale their estimation of a general feeling of fatigue. Subjective feelings of fatigue reported in this dive suggested that the divers were in good condition. Hyperbaric arthralgia and physical complaints were reported, especially during decompression, with some postdive persistence, but they should be considered as distinct signs of feelings of fatigue. The critical flicker frequency (CFF), measured throughout the dive for the two divers, showed systematic variations and a relationship between compression and pressure. These variations were grossly parallel to EEG modifications reported in other studies and probably reveal neurophysiological troubles that were not apparent from subjective reports.

Adult↗