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Etude du comportement du moment magnetique (module et direction) d'un systeme a anisotropie aleatoire en rotation dans un champ statique, a l'aide de deux detecteurs SQUID perpendiculaires. Interpretation des experiences a l'aide d'un modele d'amas

[ 3 H]5-HT specific binding sites have been characterized in the rat spinal cord. Experimental conditions allowed us to study a single class of sites possibly related to the postsynaptic receptor for 5-HT. Binding constants ( K D and B max ) are described for adult and developing animals. No substantial changes in affinity were observed but the number of receptors increased from birth up to day 20 postnatally, stabilizing thereafter. The developmental pattern of a presynaptic marker, tryptophan-5-hydroxylase, was similar to that of binding sites.

The postnatal development of 3H-5-HT specific binding sites has been studied in rat brain. Experimental conditions allowed the characterization of the class of sites corresponding to the synaptosomal receptor for 5-HT. The related affinity constant and maximal binding were measured at various ages after birth. During the second week after birth, the serotonin receptor system developed explosively, the maximal number of sites increasing from a nonsignificant value to that observed in adult rats. Lesion of the presynaptic neurons using 5,6-DHT led to a significant increase of the number of sites.

Reserpine administration in mice causes, among other effects an akinesia which can be reversed by the serotonin agonist-antagonist methysergide. The effect of methysergide is potentiated by clenbuterol, a beta-adrenergic agonist, which itself causes hypomotility. Potentiation is weak after a single injection of clenbuterol, but becomes much stronger after repeated administration for 12 days. This treatment also causes a 50% increase in the number of high affinity 5-HT-1 binding sites in the brain. This increase would explain the increased potency of methysergide against reserpine-induced akinesia. These results show that: a beta-adrenergic drug, clenbuterol modulates the serotoninergic system; this modulation takes its importance after chronic treatment only; this interrelation may be important in depressive illness since it is observed on a test used in the screening of antidepressant drugs.

Magnetic properties of orthoferrosilite FeSiO3 have been examined using susceptibility, magnetization measurements and Mossbauer spectroscopy. From magnetic and Mossbauer measurements, one obtains close values of the magnetic ordering temperature, TN=39±1 K and TN=41±1 K, respectively. The magnetic order is characterized by strong ferromagnetic coupling of Fe2+ moments within the ribbons and a weak antiferromagnetic coupling of the moments between adjacent ribbons. The 4.2 K Mossbauer spectra can be fitted with two different hyperfine magnetic fields Hhf=68 kOe and Hhf=314 kOe which can be assigned to Fe2+ in the octahedrally coordinated M1 and M2 sites, respectively, of the FeSiO3 structure.

A hollow cylinder of a hysteretic type-II superconductor allows applied axial flux to enter the hole smoothly while sustaining trapped azimuthal flux until H/sub c/2 is attained, showing clearly that flux cutting occurs. A comparison of the evolution of the axial flux, with and without trapped azimuthal flux in the wall, yields data on the energy associated with flux-cutting events. Our technique lends itself to a study of the role of many pertinent parameters in this phenomenon.

(1979). Group Counseling for the Elderly. The Journal for Specialists in Group Work: Vol. 4, No. 3, pp. 148-154.

Magnetic properties and hyperfine parameters of the cummingtonites (FexMg1-x)7Si8O22(OH)2 have been examined using susceptibility, magnetisation measurements and Mossbauer spectroscopy. The magnetic ordering temperatures of three cummingtonite samples with x=0.95 (grunerite sample), x=0.49 and x=0.36 have been measured by Mossbauer spectroscopy to be 47+or-1 K, 6.5+or-1 K and 3.5+or-0.5 K, respectively. The magnetic measurements performed on the grunerite sample indicate a magnetic ordering temperature of 44+or-0.5 K, a positive value of the paramagnetic Curie temperature theta p=+47 K and a metamagnetic transition at a critical magnetic field Hc of about 1.4 T accompanied by a small hysteresis. From the analysis of these data, one can deduce the values of the effective magnetic coupling, between the Fe2+ moments on adjacent ribbons z'J' and of the Fe2+ moments inside one ribbon zJ; the ratio z'J'/zJ is about 0.04 which reflects the strong ferromagnetic coupling of moments within each ribbon, and a weaker antiferromagnetic coupling between adjacent ribbons is characteristic of low-dimensional (here 1D) magnetic systems. The Mossbauer spectrum of the grunerite sample recorded at 14 K can be fitted with four different hyperfine magnetic fields Hhf equal to 63, 114, 153 and 245 kOe (with positive values of Vzz) which can be assigned to Fe2+ in the four non-equivalent M1, M2, M3 and M4 sites, respectively. The substantial difference between the Hhf values can be related to the symmetry of the local crystal field connected with the more or less pronounced distortion of the octahedral sites and also to a lower extent to covalency effects.

Presentation a partir d'experiences et de simulations numeriques, de differents aspects des proprietes d'irreversibilite apparaissant dans les systemes a anisotropie aleatoire a basse temperature. Etude des phenomenes d'hysteresis directionnelle et rotationnelle

Le compose CrUS3 possede une temperature d'ordre magnetique Tc = 110 K. La structure magnetique est determinee par diffraction des neutrons. Les atomes de chrome et d'uranium sont tous deux porteurs de moments magnetiques. Une forte delocalisation uniaxiale du moment de l'uranium, qui est decrite par un modele simple, est mise en evidence. Les proprietes magnetiques observees sous champs intenses revelent une forte anisotropie magnetocristalline qui peut etre associee au type de structure trouvee.

Neutron topographic experiments show that the simultaneous application of an uniaxial stress and a magnetic field when cooling a MnF2 crystal through TN favours one type of 180° antiferromagnetic domain. This appears to be related to the piezomagnetism of MnF2, in spite of the weakness of this effect, which was measured in our case by a SQUID.

The expulsion of flux from flat samples (ribbons and discs) of Nb, NbTa, V and PbIn cooling, from Tc to 4.2 K, in static magnetic fields, H o , has been investigated. A dramatic increase in expulsion of the component of the magnetic flux threading the specimen parallel to its flat faces is observed when H o is tilted to pierce these broad surfaces. We attribute this phenomenon to the extinction of a surface barrier against flux exit by H⊥, the transverse component of H o . The effect of B⊥ = μoH⊥ on the flux profiles is also examined. The concept of equilibrium diamagnetism is applied to this novel situation. A simple picture, incorporating prevailing views, is developed. With this picture, although crude approximations are used in the computations, we reproduce several families of data curves quite well. The barrier against flux exit is seen to be an appreciable fraction of Hc1 and information on its variation with the tilt angle of H o is obtained.

The magnetic properties of two orthopyroxenes FexMg1-xSiO3 with x=1.0 (synthetic sample) and x=0.87 (natural compound XYZ) have been investigated by means of susceptibility and magnetisation measurements, neutron diffraction and Mossbauer spectroscopy. A collinear antiferromagnetic ordering is observed below TN(x=1.0)=45K and TN(x=0.87)=26K characterised by a wave-vector k=(010) and by an alignment of the moments along the b axis. Inside one ribbon formed by two non-equivalent M1 and M2 sites the moments are parallel to each other resulting from a preponderant ferromagnetic nearest-neighbour coupling. The Fe2+ ions on M1 and M2 sites are quite distinct: large orbital contributions were found in FeSiO3 for the moments on the M1 site leading to m0(M1)=4.1 mu B (neutron result) and to low values of the hyperfine field Hhf(M1)=70 kOe (Mossbauer data), compared with m0(M2)=3.3 mu B and Hhf(M2)=315 kOe on the M2 site. For x=0.87 a distribution of Hhf around these mean values is present. The strongly anisotropic character of these systems is reflected by the large difference observed between the susceptibilities along the orthorhombic axes even at T=300K, and by the metamagnetic transition that occurs at Hc(x=1)=50 kOe and Hc(x=0.87)=35 kOe.

Hysteresis losses and the behavior of the magnetic flux threading superconducting disks of Nb oscillating slowly over various angular displacements in static magnetic fields H0 directed perpendicular to the axis of rotation have been investigated by continuously monitoring 〈Bz〉 and 〈By〉, the average components of the magnetic induction, in the plane of the disk, parallel and perpendicular to H0. A simple model proposed previously satisfactorily accounts for the initial changes, starting from various initial flux configurations, the subsequent cyclical behavior, and the hysteresis losses. Expulsion of flux from the disk occurs during part of the first oscillation, then the amount of flux threading the disk remains constant during the subsequent oscillations, although the orientation distribution of the flux profile undergoes spectacular periodic variations. The analysis shows that dψ/dx = ±k dB/dx describes the orientation of the sheets of flux lines with respect to H0 with distance from the flat surfaces....

The lithium phthalocyanine π-radical compound is a molecular semiconductor which exhibits exceptional magnetic properties. These latter are interpreted as resulting from two distinct spin species. One species is delocalized and its behaviour may be interpreted in the frame of itinerant magnetism. It is responsible of an extremely narrow ESR line. The other species is due to localization of the PcLi spins interacting with molecular oxygen. At low temperature this magnetic coupling is shown to stabilize a septet spin state which involves indirect ferromagnetic coupling between neighbouring π-spins. The experimental results obtained up to now on this unexpected spin state are presented and discussed.

CoU2S5 exhibits below 270 K a pure colinear antiferromagnetic structure for the Co moments and a canted one for the U moments. These later can be described by two Ising sublattices weakly coupled to the cobalt ones.

We have investigated under high pressure a sintered L~~CU~.~~O~-, sample which exhibits bulk supercon- ductivity below Tc 2( 37 K and antiferromagnetic ordering below TN N 240 K. dTN ldp has been determined using d.c. susceptibility and resistivity measurements under pressure. dTc ldp and dTN ldp are found to have opposit signs. This experimental result is confronted to the theory.

Nous avons etudie dans des champs magnetiques jusqu'a 320 kOe les proprietes des composes TIn3 et TSn3. Ceux-ci presentent des phenomenes de metamagnetisme et de spinflopping. Une etude de diffraction neutronique montre que la structure ordonnee est caracterisee par un vecteur de propagation (1/2, 1/2, 0) dans les composes TIn3 et (1/2, 0, 0) dans les composes TSn3. The magnetic properties of TIn3 and TSn3 compounds have been studied in magnetic fields up to 320 kOe. They present metamagnetism and spin-flopping phenomena. Neutron diffraction studies show that the ordered structure is determined by a propagation vector (1/2, 1/2, 0) in TIn3 compounds and (1/2, 0, 0) in TSn3 compounds.

Specific heat measurements under magnetic field have been performed in order to study the magnetic phases transitions of a single crystal of Ytterbium iron garnet along the |111| direction. The observed specific heat anomalies are characteristic of first order transitions. These transitions arise at the limit of regions in the (H − T) plane where the net Yb and Fe moments are either colinear or canted. We have evaluated the latent heats associated to these transitions. The agreement between experiment and a mean field model with G and g tensors of Wickersheim is quite poor.

Magnetization measurements on a single crystal of the orthorhombic CeNi0.8Pt0.2 dense Kondo ferromagnet (TC = 8.6 K) are presented. Whereas the large observed magnetocrystalline anisotropy which favors the c-axis comes from crystal field effects, the large reduction of the Ce moment (MCe = 0.54μB at 0 K) essentially arises from the Kondo effect.

Antidepressant drugs are generally thought to act by changing aminergic neurotransmission. Thus, according to the indoleamine hypothesis1, antidepressant drugs increase the amount of serotonin (5-HT) available at the receptor level by inhibition either of 5-HT uptake or of its degradative enzyme (monoamine oxidase)2. Various experimental observations have, however, suggested that the effects of antidepressant drugs may be located at the postsynaptic receptor level3–7. We report here that antidepressant drugs alter the structural conformation of the postsynaptic serotoninergic receptor in synaptosomal membranes isolated from rat and horse brains in such a way as to inactivate them.

The magnetic properties of two samples of acmite, one natural and the other synthetic, were determined using magnetization and susceptibility measurements, Mossbauer spectroscopy and neutron diffraction. Exchange interactions are quite strongly antiferromagnetic, the paramagnetic Curie temperature being -46 K for a purely ferric synthetic sample, but its Neel temperature is only 8 K. The principal magnetic mode has the periodicity of the crystallographic structure and is made of ferromagnetic chains, coupled antiferromagnetically. Moments are oriented in a direction close to the chain axis, c. The antiferromagnetic exchange between adjacent Fe3+ ions in the same chain is overcome by their coupling to a common Fe3+ neighbour in the next chain. This indicates that the whole (SiO4) group can act as a superexchange ligand in silicates.

Purified glial membrane preparations have been isolated from horse brain striatum. Tritiated 5-HT bound to these membranes with a high affinity (KD = 10 nM); the corresponding binding is reversible and appears specific of the serotoninergic structure. In parallel, 5-HT activates an adenylate cyclase with a low affinity (KD = 1 microM). The sites involved in this binding and in this adenylate cyclase activation appear different from the serotoninergic sites reported in the neuronal membrane preparations.

The analysis of the magnetization measurements performed on two Co-Cu multilayers confirm the antiferromagnetic coupling already observed with neutron experiments. Both exchange and anisotropy energies are taken into account and estimated. Their competitive role in the individual moment orientation leads to typical moment arrangements and hysteresis loops.

Several neurochemical theories of major affective disorders have been presented during the last decades. Initially, the fact that patients treated with reserpine developed symptoms which resemble certain forms of depression suggested that biogenic amines may play an important role in the disease (Freis, 1954; Achor et al., 1955; Muller et al., 1955; Lemieux et al., 1956). It is known that reserpine depletes brain tissues not only in dopamine and in noradrenaline but also in serotonin (5-hydroxytryptamine, 5-HT) (Pletscher et al., 1956); therefore the hypothesis has been proposed that depression might be related to a deficit in those amines, and, in particular, may involve 5-HT metabolite disturbances (Coppen, 1967; Murphy et al., 1978; van Praag, 1982). However, Crow et al. (1984) did not observe any changes in serotonin metabolites in individuals committing suicide.

5 hydroxytryptamine binds to crude brain membrane preparations with two different affinities (KD = 1 to 2 X 10(-9) M for the highest, 1 to 2 X 10(-8) M for the lowest). LSD also binds with two affinities (KD = 3 to 4 X 10(-9) M and KD = 2 to 3 X 10(-8) M). Subcellular distribution of these sites shows that binding involves the two binding affinities in microsomal membranes but solely the high affinity binding sites are present in purified synaptosomal membranes. High affinity sites for 5 HT and for LSD are different as no direct competitive inhibition is observed in that case. On microsomal membranes, direct relationship occurs between low affinity binding for 5 HT and high affinity binding for LSD.

Ligand-macromolecule interactions are studied by nonlinear regression analysis performed using a microcomputer (SYMAG-Micromachine 3000/Z). The basic phenomenon is described by the Clark equation B = (Formula: see text), where B and F represent bound and free ligand, respectively, Ni the total concentration of binding sites, and Ki their corresponding affinity constant. The programs of calculation have been extended also for Hill and for Adair equations using the Gauss algorithm described by E. E. Beaulieu and J. P. Raynaud [Eur. J. Biochem. 13, 293 (1970)]. A statistical test of F type is introduced to test the quality of the fit and compare the representations of the phenomenon using the different equations.

The solubilization of the serotonergic 5HT1 and 5HT3 sites was performed with digitonin and sodium cholate at 1% (final concentration). Two binding sites for [3H]5HT were observed on rat or horse brain synaptosomal membranes solubilized with these detergents. The corresponding dissociation constants (KD) were 1-3 nM and 13-30 nM respectively. These values were closely similar to those corresponding to 5HT1 and 5HT3 sites located in intact membranes. The solubilized sites specifically bound 5HT. The effect of GTP decreasing the binding to 5HT1 sites was lost on solubilized 5HT1 sites; it was recovered, however, by addition of phospholipids (asolectin 0,2%). The apparent molecular weights of these sites were determined using the gel filtration method (438 and 235 K daltons). The photoactivation of [3H]5HT by U.V. light was used to label 5HT1 and 5HT3 sites irreversively in membranes. The binding of [3H]5HT following U.V. irradiation was not dissociated after dilution; it was saturable and prevented by serotonergic drugs and not by adrenergic or dopaminergic antagonists. Moreover, GTP added prior to the irradiation reduced it markedly thus showing that 5HT1 sites were labelled. Electrophoretic and fluorographic analyses of the labelled material evidenced a 60 K dalton-band specifically labelled with [3H]5HT (5 or 20 nM). These results tend to indicate that the 60 K dalton-proteic band might represent a proteic subunit constituting part of 5HT1 and 5HT3 sites.

It is confirmed by new magnetization measurements that a magnetic transition occurs sharply at 30 K in the monoclinic pyrrhotite Fe7S8. Though its nature is not yet fully understood, this transition shows some similarities with the Verwey transition and can provide a powerful tool for the identification of pyrrhotite in rocks.

Previously, a 5-hydroxytryptamine receptor has been described in neuronal membrane preparations. This receptor corresponds to a recognition site for 5-HT, and is seemingly related to an effector which consists of an adenylate cyclase activated by 5-HT and having a high apparent affinity constant (KD close to 1 nM). Moreover, this neuronal receptor is distinct of the glial serotoninergic receptor (Fillion et al., 1980). The method used to measure the binding of 3H-5-HT has been previously reported (FILLION et al., 1978). Adenylate cyclase activity was determined by measurement of cAMP using a radioimmunoassay (FILLION et al., 1979 a, b). Membranes were pretreated as follows: (1) membranes were preexposed to 5-HT (i.e.: incubated in the presence of 5-HT, generally 10 nM) at 37 degrees C, washed by centrifugation and resuspended in a medium free of 5-HT (or diluted in the same medium) or (2) membranes were incubated with a single concentration of 5-HT for a prolonged duration. Results were as follows: 1. The binding of 3H-5-HT, incubated for 10 min at 37 degrees C, corresponds to a KD close to 20 nM whereas a prolongation of the incubation duration to 15-25 induces the binding of 5-HT with a KD close to 2 nM. 2. Preexposure of the membranes to 5-HT leads to the same increase in affinity with, apparently, a reduced number of sites. 3. N-ethylmaleimide pretreatment of the membranes prior to their preexposure to 5-HT inhibits the change in affinity. 4. GTP, but not GDP, reverses the affinity change. 5. The adenylate cyclase activated by 5-HT is desensitized by preexposure of the membranes to 5-HT. 6. GTP reverses the process of desensitization. These results support the hypothesis of the existence of a regulatory mechanism for the 5-HT neuronal receptor. The regulatory mechanism would involve structural conformation changes of the recognition site corresponding to different affinities of the adenylate cyclase. A nucleotide binding protein is presumably involved in the coupling of these two subunits of the receptor.

The biogenic amine, 5-hydroxytryptamine (5-HT), was first described in extracts of natural materials almost 30 years ago (see review by Collier, 1957). Twarog and Page (1953) and Amin et al. (1954) were the first to demonstrate, on pharmacological evidence, the occurence of 5-HT in the central nervous system of the dog which was confirmed by Bogdanski et al. (1956) and Correale (1956) by physicochemical criteria.

The postnatal development of 3H-5-HT specific binding sites has been studied in rat brain. Experimental conditions allowed the characterization of the class of sites corresponding to the synaptosomal receptor for 5-HT. The related affinity constant and maximal binding were measured at various ages after birth. During the second week after birth, the serotonin receptor system developed explosively, the maximal number of sites increasing from a nonsignificant value to that observed in adult rats. Lesion of the presynaptic neurons using 5,6-DHT led to a significant increase of the number of sites.

A serotonine-sensitive adenylate cyclase system has been observed in horse brain membrane preparations. In crude mitochondrial fraction two types of activation sites were characterized, the Ka being = 2 nM and 1 micrometer. In purified synaptosomal membranes, a single adenylate cyclase activation was observed corresponding to the highest apparent affinity (KD = 2nM). This activation site might be related to the high affinity binding site (KD = 2NM) were previously described in the same membrane preparations.

Crude membranal fractions isolated from mammalian brain tissue contain two classes of recognition sites capable of binding [3H]5-HT with high affinity constants. These classes of sits are characteristics of the postsynaptosomal membrane fraction for the higher affinity and of a glial cell membrane fraction for the lowest. They are observed with similar properties in cultured neuronal and glial cell respectively. Two 5-HT stimulated adenylate cyclases are present in crude membrane fraction; they are also separable as neuronal and glial components. These observations correspond likely to the existence of two classes of receptors for 5-HT. Their mechanisms of regulation involve presumably structural conformation changes of the recognition site coupled to various states of the activity of the receptor.