Effet des androgènes sur l’activité sportive

Androgenic hormones seem to be of beneficial effects on sports performance:

- they increase motivation, will, aggressiveness, resistance to the stress and to the fatigue, leading to an increase of the training quantity,

- they increase bone mineralization and probably mechanical resistance,

- they stimulate the bone marrow and so, with the erythropoietin, the erythropoiesis,

- they increase the tendancy to hyperglycemia, but with a decrease of the tolerance to the glucose,

- they stimulate the fatty acids mobilization from the adipose tissue, for their utilization in the muscle during the exercise,

- they participate, for the trained sportmen, to a better gestion of the muscle glycogen storage: their utilization during exercise is decreased,

- they increase the lean body mass, with an increase of the protein synthesis and a decrease of the protein catabolism, leading also to an increase of the muscle force under training. There is no beneficial effect upon the tendons,

- they have an immunomodulation action.

     

Studies on the origin of the tip potential of glass microelectrode

1. Tip potential (TP) of glass microelectrodes filled with 3 M KCl increased remarkably with the increase in the storage period in 3 M KCl solution at 37? C, while the electrode resistances decreased gradually.
2. The electrical conductivity through the thin glass wall near the tip was found to increase in parallel with the TP increase.
3. The e.m.f. across the thin glass wall in the tip region was directly measured. This seems to contribute to the TP generation of the microelectrode when the conductivity of the glass wall is significantly high in the tip region.
4. Effects of the acid treatment of glass employed and the acidification of fillant electrolyte solution suggested that fixed negative charges on the glass wall play a fundamental role in the TP formation.
5. Based on these experimental results, it was concluded that not only the diffusion potential through the tip pore but also the interfacial potential through the thin glass wall near the tip contributes to the TP generation, and the contribution of the latter increases with a long exposure period of the electrodes to electrolyte solution.
6. In this connection, technical problems related to reduction of the tip potential were also discussed.

     

Phase shifts in heterochromatic flicker photometry and Bidwell's ghost: A model

A simple model of brightness encoding in the retina is proposed that explains:

1. the differential phase shift needed to minimize brightness flicker in a homogeneous red-green counterphase flickering field.
2. the modulation transfer function at low temporal frequencies for flickering lights of one dominant wavelength against the background of light with another dominant wavelength.
3. the occurrence of the Hering, the Purkinje and the Hess afterimages.
4. the ability of monochromatic light to provoke the Purkinje afterimage (Bidwell's ghost).

It is shown that these effects can be treated as pure brightness effects; or that the signal processing of the opponent system is irrelevant to the results. A physiological substrate for the model is tentatively indicated. Some suggestions are made concerning possible experimental checks of the model.     

Temporal discharge patterns of tectal and medullary neurons chronically recorded during snapping toward prey in toads Bufo bufo spinosus

In freely moving toads, the temporal discharge patterns of tectal and medullary neurons were observed during prey-catching.

1. Tectal T5.2 and T8.1 neurons displayed a premotor warming up firing that in the former was addressed specifically to prey orienting or snapping and in the latter generally to almost any kind of body movement.
2. The temporal discharge patterns of T5.2 neurons during snapping were different from those during orienting toward prey. Snapping started in the peak phase of warming up; firing was immediately terminated during the snap; thereafter some rebound activity was observed. Orienting started after the premotor warming up in the declining phase whilst the neuron kept on firing during orienting and then settled when the orienting movement was completed.
3. In toads which were not motivated to catch prey — comparabl to immobilized ones — the discharge frequency of T5.2 neurons toward a prey stimulus revealed no such warming up.
4. Because it is known that prey-selective T5.2 neurons are controlled by pretectal inhibitory influences, the following experiment was conducted: during recording a T5.2 neuron a pretectal lesion was applied ipsilaterally to the recording site. After a few seconds, the neuron showed a strong premotor wanning up in response to any kind of moving object, followed by prey-catching.
5. In the medulla oblongata, different H-type neurons of the hypoglossal nucleus displayed specific discharge patterns which resembled the tongue protractor and retractor muscle activities; a third type resembled the activity of the genio/sterno-hyoid muscle, which are suggested to stabilize the hyoid bone during snapping.
6. There were medullary M8-type neurons with properties similar to T8.1.
7. Snapping could be triggered by electrical stimulation of the optic tectum in the representation of the frontal visual field, but not by stimulation in the hypoglossal nucleus or the adjacent medial reticular formation.
8. A concept of a neuronal circuit for the coordination of tongue muscle contractions in response to prey is proposed.

     

The role of touch,pressure and nociceptive mechanoreceptors of the leech in unrestrained behaviour

1. The maximum force exerted against an isometric force transducer by 6 leeches weighing 2.6–3.7 g, as they squeezed through apertures of different widths varied inversely with aperture width.
2. T cells in the leech skin code for velocity of indentation, not pressure or displacement. The frequency with which T cells fire is best described by two log functions, one for low, another for fast indentations. T cells responded to indentation velocities down to 10 μms^?1.
3. The average threshold pressure for 5 P cells was 150 kPa and for 5 N cells was 521 kPa.
4. We conclude from these data that when leeches explore their mechanical environment and initiate contact with external objects, the threshold pressure for N cells is rarely crossed. Of the three classes of mechanoreceptor, T cells are the main modality through which leeches obtain contact information, though P cells may occasionally be recruited for local pressure peaks.

     

Survival,osmoregulatory ability,and respiration of idotea chelipes (Crustacea,Isopoda) from lake veere in different salinities and temperatures

1. An ecological and physiological study ofI. chelipes from Lake Veere, The Netherlands, was made.
2. Both osmoregulatory capacity and survival decrease with increasing temperature as well as with decreasing salinity.
3. Respiration experiments suggest that the need of energy by osmoregulatory activity may be supplied at the cost of other physiological processes, at any rate at temperatures of 10°C and higher.
4. It may be expected that, if temperatures higher than 15°C and salinities lower than 8‰ coincide, the population ofI. chelipes will be affected negatively.

     

Cytomechanics of axonal development

Mechanical tension is a robust regulator of axonal development of cultured neurons. We review work from our laboratory, using calibrated glass needles to measure or apply tension to chick sensory neurons, chick forebrain neurons, and rat PC12 cells. We survey direct evidence for two different regimes of tension effects on neurons, a fluid-like growth regime, and a nongrowth, elastic regime. Above a minimum tension threshold, we observe growth effects of tension regulating four phases of axonal development:

1. Initiation of process outgrowth from the cell body;
2. Growth cone-mediated elongation of the axon;
3. Elongation of the axon after synaptogenesis, which normally accommodates the skeletal growth of vertebrates; and
4. Axonal elimination by retraction.

Significantly, the quantitative relationship between the force and the growth response is suprisingly similar to the simple relationship characteristic of Newtonian fluid mechanical elements: elongation rate is directly proportional to tension (above the threshold), and this robust linear relationship extends from physiological growth rates to far-above-physiological rates. Thus, tension apparently integrates the complex biochemistry of axonal elongation, including cytoskeletal and membrane dynamics, to produce a simple “force input/growth output” relationship. In addition to this fluid-like growth response, peripheral neurons show elastic behaviors at low tensions (below the threshold tension for growth), as do most cell types. Thus, neurites could exert small static forces without diminution for long periods. In addition, axons of peripheral neurons can actively generate modest tensions, presumably similar to muscle contraction, at tensions near zero. The elastic and force-generating capability of neural axons has recently been proposed to play a major role in the morphogenesis of the brain.     

Organogenesis at the shoot apex: An attempt at modelization

A geometrical model of the emergence of a primordium at the shoot apex in dicotyledons is proposed. It is based on recent fundamental results on plant morphogenesis, i.e.:

1. the emergence is preceded by the reorganization of the microtubules of the cortical cytoskeleton, leading to a new orientation of the synthesis of the cell wall microfibrils;
2. the resulting global stress is related to the general orientation of the cell growth.

So the model sums up the continuous interactions linking the microtubules, the microfibrils and the cell growth axis. This paper tries to answer three questions which are essential from a botanical point of view:

1. Why does the principal stem shift its growth direction after each lateral emergence?
2. Why do the three axes involved in any ramification (namely the old and the new principal stems and the lateral emergence) exhibit a plane configuration whereas this is an essentially three dimensional phenomenon?
3. Does phyllotaxis exclusively depend upon the local emergence of a primordium?

A come and go between the botanical knowledge and the mathematical model leads to an integrated view of the compatibility mechanisms linking the different microtubules and microfibrils networks, without forgetting the apical dome restoration. A geometrical formalism allows a modern redefinition of both the “generating centre” and the “organizing centre” and their field effects.     

Plant morphogenesis: A geometrical model for the ramification

A geometrical model is proposed that describes the emergence of a primordium at the shoot apex in Dicotyledons. It is based on recent fundamental results on plant morphogenesis, viz.:

the emergence is preceded by the reorganization of the microtubules of the cortical cytoskeleton, leading to a new orientation of the synthesis of the cell wall microfibrils;

the resulting global stress is related to the general orientation of the cell growth;

The model sums up the continuous interactions that link the microtubules, the microfibrils and the cell growth axis. The paper tries to answer three essential questions:

Why does the principal stem shifts its growth direction after each lateral emergence?

Why do the three axes involved in any ramification (namely the old and the new principal stems and the lateral emergence) exhibit a plane configuration whereas this is an essentially three dimensional phenomenon?

Does phyllotaxis exclusively depend upon the local emergence of a primordium?

An interactive procedure between empirical botanical knowledge and the mathematical model leads to an insight of the compatibility mechanisms that link the various microtubules and microfibrils networks, and the apical dome restoration. A geometrical formalism allows a redefinition of both the “generating centre” and the “organizing centre”, and their field effect.     

Polarization of tryptophan fluorescence measurements in muscle

The degree of polarization of the intrinsic tryptophan fluorescence of glycerinated single muscle fibres or fibre bundles (rabbit psoas or dorsal longitudinal muscle of Lethocerus maximus) was measured:

1. With sufficiently high (15 mM) ATP concentration or when an ATP regenerating system was used no difference in the degree of polarization of a contracting and a relaxed muscle was detected, whereas a distinct difference was detected between the relaxed and the rigor state. In contrast a distinct difference between the relaxed and contracting state was obtained at low ATP concentrations (5 mM). This difference is interpreted to be caused by an ATP-free core (rigor core) in the centre of the fibre.
2. No change in the polarization degree was detected after a rapid release of the contracting muscle.
3. In rigor state no difference in the degree of polarization of the tryptophan fluorescence was observed in the presence or absence of AMPPNP (concentration 0.5 mM).

These findings and the lack of difference between the polarization degree of the contracting and the relaxed muscle is interpreted to indicate that the polarization degree of the tryptophan fluorescence is not sensitive to the orientation of the cross bridges, or that the cross bridges do not rotate.     

A study on the rate of water transport of the clam katelysia opima in relation to environmental conditions

1. The neutral red technique was employed to study the rate of filtration in Katelysia opima.
2. The weight specific water filtration was found to be greater for younger clams compared to the older ones.
3. The rate of water filtration increased with decreasing salinity.
4. Water filtration was found to increase as temperature increased, reaching a maximum at 35°C. but then sharply decreasing at 39°C.
5. Light had no significant effect on the rate of filtration.
6. Suspended matter was found to affect the rate of water filtration.
7. The rate of filtration was low at high pH and high in low pH.
8. The rate of water filtration was found to be faster during high tide than during low tide.
9. The presence of the parasitic crab, Pennotheris sp., in the mantle cavity of clams had a marked effect on the particle filtration.
10. Accidental cut of the siphon tips had no effect on the rate of filtration.

     

Tension field theories for soft tissues

All soft tissues are modeled as either one-dimensionalstrings, two-dimensionalmembranes, or three-dimensionalsolids. Attention is restricted to tissues in which one of the principal stress components is large and positive in comparison with the other negligible components. Results indicate the following:

1. If a deformed string isconstrained to lie on a surface and is free of tangential pressure, the tension is carried by rays which are geodesics of the surface. If a string or membrane isfree to deform in space without normal pressure, the tension rays are straight lines. If a membrane deforms without tangential surface loads, the tension rays are always geodesics on the deformed surface. If a solid deforms without body forces, the tension rays are straight lines.
2. The stress in a string is a constant if the string is free of tangential pressure and has constant cross-sectional area. The stress in flat tension fields free of tangential surface loads decays inversely with distance along a tension ray from the edge of regression. The stress in a spherically symmetric tension field free of body forces decays inversely with the square of the distance from the center of the sphere.
3. Stress singularities can occur in soft tissues, such as at the corners of a closed rectangular hole in a flat membrane strip.
4. The tension rays in the torsion of soft annular membranes are more steeply inclined from the radial direction than the tension rays for hard metals equally displaced.

     

Varying amounts of stretch stimulus regulate stretch-induced muscle hypertrophy in the chicken

• 1.1. The effects of different amounts of passive stretch per day and number of days of stretch on muscle hypertrophy in the chicken patagialis (PAT) muscle were determined.
• 2.2. Stretch for 24 hr per day (h/d) resulted in a more rapid hypertrophy both on a wet and dry tissue basis (P < 0.001) than stretch for 4 h/d.
• 3.3. Stretch increased PAT weight 43% and 25% in 24 h/d and 4 h/d treatments, respectively, after 10 days of stretch, but by day 25 of stretch there was no difference between treatments.
• 4.4. In a second experiment, the PAT muscle was hypertrophied and then the effects of intermittent stretch (4 h/d) on regression of hypertrophy (muscle atrophy) were investigated.
• 5.5. Intermittent stretch (4 h/d) for 5 and 10 d significantly (P < 0.001) inhibited regression of hypertrophied muscle.
• 6.6. The results of the present study indicate that stretch-induced hypertrophy can be modulated by varying the amount of stretch applied per day.
• 7.7. Intermittent stretch can be used to inhibit the regression which occurs when a continuous stretch stimulus is removed.
• 8.8. Intermittent stretch is a useful model for investigating mechanisms of muscle hypertrophy and inhibition of muscle atrophy.

     

Neurotransmitters of cephalopods

1. ACh, dopamine, noradrenaline, 5-HT,l-glutamate, and GABA are widely distributed in cephalopods and probably all function as neurotransmitters; octopamine also occurs and at one site is known to act as a neuromodulator.
2. Several peptides are also present, as well as nitric oxide synthase.
3. In the brain and sense organs cholinergic, aminergic, serotonergic and glutamatergic systems seem to be the most important.
4. ACh is also active in the gut, vascular system and some body muscles: it is generally inhibitory. The ACh receptors are similar to the vertebrate nicotinic type.
5. The catecholamines are important in the gut and vascular system: they are generally excitatory. The NA receptors are like the α-adrenergic subtype of vertebrates, but the nature of the DA and OA receptors is less certain.
6. 5-HT is important in the gut but is endogenous in some chromatophore nerves and acts on receptors that seem like the vertebrate 5-HT₁ type.
7. l-glutamate is an excitatory transmitter at the chromatophore (and probably at other) nerve-muscle junctions and is an extremely strong candidate for being the excitatory transmitter at the squid giant synapse. There are NMDA receptors on Schwann-cells but the receptors on neurons and muscles are like the vertebrate kainate type.
8. Little is known about the mode of action of cephalopod peptides; nor has it ever been shown that they co-exist with conventional transmitters in these animals.
9. The structure of one (FMRFamide) receptor has been elucidated, but apart from this nothing is known of the molecular biology of receptors in cephalopods.

     

Two kinds of peripheral afferent neurons in the earthworm reflex arc

• 1.1. Two kinds of neurons were identified in the body-wall longitudinal muscle layer of the earthworm, Amynthas hawayanus, by the simultaneous potential recording and Lucifer Yellow-CH injection method with a single microelectrode.
• 2.2. Both kinds of neurons have their somata, neuntes and longitudinal processes imbedded in the longitudinal muscle layer. Those with two circular processes extending into the third segmental nerve trunk are tentatively named “intra-nerve-trunk” neurons and those with four circular processes extending into four setae shafts are tentatively named “intramural” neurons.
• 3.3. Both kinds of neurons responded to electrical and mechanical stimuli applied in an afferent direction to them.
• 4.4. The “intra-nerve-trunk” neuron decreased its response amplitudes to these stimuli after the third nerve trunk was sectioned in correlation to the response amplitude decrease recorded from the nerve trunk after it was sectioned.
• 5.5. The response amplitude decrease due to denervation implies a nonlinear structure of the earthworm reflex circuits.
• 6.6. The “intramural” neurons are believed to be primary sensory neurons connected to the mechanoreceptors in the setae.

     

Model study of muscle spindles subjected to static fusimotor activation

An earlier proposed mechanical model of the de-efferented muscle spindle endings has been developed further in order to study whether the functional effects of activating the static fusimotor fibres may be accounted for by relatively simple mechanical events in the intrafusal muscle fibres. Particular attention has been paid to important controversial problems related to the processes involved in the fusimotor activation of the mammalian muscle spindles. In order to develop an adequate model, preliminary simulation studies of the functional effects of various reasonable modifications of the original “de-efferented” model were first carried out by means of a convenient direct electronic analogue of the mechanical system. The following results apparently reflect pertinent details about the peripheral receptor mechanisms associated with the activation of the static fusimotor fibres:

1. The γ _s-activation is most adequately accounted for by mechanical events occurring in the nuclear chain fibres.
2. Any uniform chain fibre contraction fails to account for the effects of the γ _s-activation.
3. The simulation of a local chain fibre contraction could apparently account for all significant effects of the γ _s-activation.
4. A reasonable increase of the position sensitivity and the vibration sensitivity of both the primary and the secondary endings could be accounted for by increasing the stiffness of about 1/4–1/2 of the length of the simulated nuclear chain fibre by a factor of about 2–10.
5. The powerful modulation of the background discharge of the receptor endings that is associated with the γ _s-activation could be accounted for by an independent contraction force related to the intensity of the static fusimotor activity.
6. The model predicts a decrease of the rate sensitivity of the primary endings (group Ia) and a slight increase of the (moderate) rate sensitivity of the secondary endings.
7. By an adequate selection of the parameters, the simulated γ _s-activation showed a negligible influence on the absolute level of the dynamic phase of the ramp response of the simulated primary endings, in spite of a considerable increase of the steady state (background) discharge before and after the termination of a simulated stretch.

     

The use of a continuous assay system to show the stimulation of phosphoenolpyruvate production in intact mitochondria by valinomycin and by Mn2+

1. A method for the direct recording of the PEP efflux from isolated mitochondria is described.
2. This method has been used to show the stimulation of PEP efflux by externally added Mn⁺⁺ ions.
3. Valinomycin, uncoupler and oleate were also shown to stimulate PEP efflux.
4. Valinomycin caused an increase in the internal concentration of both PEP and citrate.
5. The results indicate that the major pathway of PEP synthesis in isolated mitochondria is via PEP carboxykinase and the results do not call for an unknown pathway of metabolism.
6. Two interactions between PEP and citrate are described; competition for the mitochondrial interior and the stimulation of PEP production by citrate.

     

The use of toxicokinetics for the safety assessment of drugs acting in the brain

Pharmacological and toxicological studies undertaken on drugs that affect the brain are frequently performed in disparate species under various experimental conditions, at doses often greatly in excess of those expected to be administered to humans, and the findings are extrapolated implicitly or explicitly with scant regard to differences in the biodisposition of the drugs. Such considerations are necessary since:

1. Species;
2. Strain;
3. Gender;
4. Route;
5. Dose;
6. Frequency and time of administration;
7. Temperature;
8. Coadministration of drugs; and
9. Surgical manipulation

are but some of the factors that have been shown to influence the kinetics and metabolism of drugs. This article, using MDMA and other phenylethylamines as examples, provides evidence for the need to measure the exoosure of the drugs and their active metabolites in blood and brain (toxicokinetics) in order that conclusions based only on dynamic, biochemical, or histological evidence are more pertinent. Further, the combined use of toxicokinetic-dynamic modeling can lead to a better appreciation of the mechanisms involved and a more useful approach to the calculation of safety margins.     

Length dependent state of activation — Length change dependent kinetics of cross bridges in skinned insect flight muscle

Stretch induced activation and release induced deactivation of single glycerol-extracted insect flight muscle fibres were investigated. The results are interpreted to indicate that the muscle length controls the number of acting cross bridges, whereas their attachment-detachment kinetics in mainly determined by the state of strain of the cross bridges. It is concluded that the net detachment rate of the cross bridges is enhanced if the muscle is released thereby “unloading” the cross bridges. This behaviour of the unloaded cross bridge is a basic postulation of most of the molecular muscle contraction models.

1. The delayed tension rise induced by stretches of different amplitudes could be restored to the level before the stretch by a release to the initial length.
2. The delayed tension decrease induced by a release of moderate (up to δL=1.5% L _i)amplitude is quantitatively restored within the delayed increase induced by the restretch to the initial length.
3. Stiffness, which decreased during the delayed tension drop after release, is restored during a delayed stiffness increase effected by a restretch to the initial length.
4. The rate and the extent of the stiffness drop after release increased with increasing amplitude of the release and with increasing temperature.
5. After the deactivation, i.e., after tension and stiffness achieved a new steady level after the release, the attached cross bridges are already in the same state of strain as they were before the release. This finding is interpreted to indicate that within the deactivation phase all cross bridges attached prior the release are replaced by cross bridges attached after the release.
6. The rate of tension and stiffness decay after release does not depend on the absolute muscle length but on the amplitude of the release which induced the deactivation.

     

Water balance of small lactating rodents —III. Estimates of milk production and water recycling in lactating Mus musculus under various water regimes

1. The exchanges of water between lactating female and young Mus musculus were modelled on the computer.
2. The model was used to estimate rates of milk production and water recycling in various litter sizes under various water regimes by following the time course of injected tritiated water.
3. The high correlation between estimated rates of milk production and actual growth rates of young was taken to indicate that the method gave if not the actual rates of milk production a very constant proportion of it.
4. Approximately 50% of the water secreted in milk is returned to the mother by recycling.