Showing papers by "Collège de France published in 1973"

Dopaminergic Terminals in the Rat Cortex

Abstract: The destruction of ascending noradreniergic pathways by bilateral microinjections of 6-hydroxydopamnine made laterally to the pedunculus cerebellaris superior completely abolished the in vitro synthesis of [(3)H]norepinephrine from L-[(3)H]tyrosine in slices and in synaptosomes of the rat cortex. However, normal [(3)H]dopamine synthesis could still be observed in both cortical preparations from animals with lesions. These results provide the first biochemical support for the existence of dopaminergic terminals independent of noradrenergic terminals in the rat cortex.

Hyperactivity of remaining dopaminergic neurones after partial destruction of the nigro-striatal dopaminergic system in the rat.

Abstract: INJECTION of 6-hydroxydopamine (6-OHDA) in the cell bodies of the substantia nigra of the rat has been found to produce a selective degeneration of the nigro-striatal dopaminergic pathway1. Electron microscopic2 and biochemical3 investigations have determined the specificity and extent of the nigral 6-OHDA induced damage. This model has been used in the present work to study the metabolism of dopamine (DA) in striatal nerve terminals of still undamaged neurones after different partial destructions of the nigro-striatal dopaminergic system.

Inhibition by hemicholinium-3 of (14C)acetylcholine synthesis and (3H)choline high-affinity uptake in rat striatal synaptosomes.

Abstract: Hemicholinium (HC-3), a neuromuscular blocking agent which inhibits the synthesis and the release of acetylcholine (ACh) was investigated for its effects both on [14C]ACh synthesis from [2-14C]pyruvate or [6-14C]glucose and on [3H]choline uptake in purified rat striatal synaptosomes. The synthesis of the transmitter was reduced to 15% of control by 1 µM HC-3 in the presence of eserine (170 µM). The drug produced half-maximal inhibition at 0.06 µM; this effect was totally reversed by 30 µM choline. Choline concentrations as low as 10 µM stimulated significantly the synthesis of [14C]ACh in a diluted suspension of synaptosomes. The existence of a high-affinity uptake system for choline, recently observed by Yamamura and Snyder, was confirmed in our preparation: its Km was found to be 3.5 µM. Eserine (170 µM) produced only 10% inhibition of the uptake process in the presence of 1 µM choline. HC-3 was found to be a purely competitive inhibitor of the choline high-affinity uptake (Ki = 25 nM). A very good correlation was found between the inhibitory effects of HC-3 on [14C]ACh synthesis and on [3H]choline high-affinity uptake. The results suggest that the high-affinity system for the transport of choline is present in cholinergic synaptosomes and plays an important role in sustaining and perhaps regulating the synthesis of the transmitter.

Dimensions of a Flexible Polymer Chain in the Bulk and in Solution

Abstract: POLYMER molecules dispersed in a good solvent expand1 significantly beyond the size expected from purely random orientation of the segments. In the bulk, however, there are theoretical reasons2 which indicate that the molecule should recover its “Gaussian” size. For a long time experimental evidence for this assertion was missing. Several people (G. Allen and S. F. Edwards, personal communication and refs. 3 and 4) have recently recognized that such evidence may be obtained from a small angle neutron scattering experiment. One of them4 has already published results on polymethyl methacrylate. We discuss here some results for atactic polystyrene.

Feedback regulation of 5-HT synthesis in rat striatal slices.

Abstract: The effects of changes in intraneuronal levels of 5-HT induced by monoamine oxidase inhibitors (MAOI) given in vivo or exogenous 5-HT added in vitro on 5-HT synthesis in striatal slices of the rat have been examined. The synthesis of 5-HT was estimated by the measurement of the total formation of [3H]5-HT and [3H]5-hydroxyindole acetic acid from [3H]tryptophan and by calculation of the conversion index (CI) of tryptophan into 5-HT. The small formation of [3H]tryptamine and [3H]indole acetic acid from [3H]tryptophan was taken into account in the estimation of 5-HT synthesis. Both MAOI pretreament (180 min) and 5-HT (2·8 μM) inhibited synthesis. The latter effect persisted in catecholamine depleted tissues and was related to intraneuronal changes in 5-HT levels, since it could be prevented by chlorimipramine. The inhibition of 5-HT synthesis was related to the decreased conversion of tryptophan into 5-hydroxytryptophan and could not be prevented by p-chloro-phenylalanine pretreatment which depleted 5-HT levels or by dibutyryl cyclic AMP which normally stimulated 5-HT synthesis. Tryptophan uptake in slices was not affected by exogenous 5-HT. The various mechanisms possibly involved in the end product regulation process of 5-HT synthesis are discussed.

Acetylcholine synthesis from [2‐14c]pyruvate in rat striatal slices

Abstract: — Rat striatal slices were incubated with [2-14C]pyruvate or [6-14C]glucose as sole carbon source. The method devised to study the accumulation of labelled ACh in tissues and incubating medium in the presence or absence of eserine 200 μM derived from the previous studies of FONNUM (1969) and Hemsworth and Morris (1964). Total ACh was estimated by biological assay. The specific activity of newly synthesized ACh was found to be equal to that of the precursors, even for short incubation times and low substrates concentrations. When slices were incubated with [2-14C]pyruvate and eserine, the spontaneous release of ACh occurred at a constant rate, was not modified by the addition of 2 mM-choline in the medium, and consisted only of newly synthesized transmitter. The initial rate of ACh synthesis was found to be independent of choline concentration, but dependent on the [2-14C]pyruvate concentration, and reached a maximal value corresponding to about 5 per cent of the measured striatal choline acetyltransferase activity. The appearance of the so called ‘surplus ACh’ pool, obtained in the presence of eserine, could be detected only after 30 min and represented 26 per cent of the total tissue ACh content after 180 min of incubation. In the absence of eserine, tissue ACh levels increased six-fold in 80 min and then remained stable until the end of the incubation period (180 min), if sufficient substrate was provided. The maximal ACh accumulation in slices was independent of both excess of choline and [2-14C]pyruvate. The ‘ACh plateau’ represented the attainment of a new dynamic equilibrium, since ACh synthesis could still be stimulated by 30 mM-K+. From these results, it was concluded that ACh synthesis is controlled by a negative feed-back regulation.

The fine structure of the cerebellar central nuclei in the cat. II. Synaptic organization.

Abstract: The synaptic organization of the cerebellar deep nuclei in the cat has been analysed with the Golgi technique and the electron microscope. The Golgi picture is qualitatively very similar in the four nuclei. Both thick and thin fibers, with the latter being more numerous, contribute to the formation of pericellular nests around large neurons, where a large amount of boutons “en passant” can be observed. The electron microscopic study corroborates these observations since the cell surface of large neurons is mostly covered by axon terminals, while smaller neurons receive very few axo-somatic synapses. According to their size and shape three types of axon terminals have been encountered synapsing on large neurons: medium-sized, large slender and climbing-like boutons. The two last types only represent less than 13% of the total amount of axon terminals, and they are considered as synaptic boutons arising from different sources. The medium-sized boutons must represent a mixed population. A majority of these boutons contain rounded vesicles, while some, in a variable proportion from one animal to another, contain flattened or pleomorphic vesicles. The morphological features of “active” zones present in medium-sized boutons are not related to the shape of the vesicular population. This lack of association between vesicular shape and a specific pattern of “active” zones has been discussed.

The fine structure of the cerebellar central nuclei in the cat. I. Neurons and neuroglial cells.

Abstract: The four deep cerebellar nuclei exhibit a similar pattern of organization. They consist of isodendritic neurons of different sizes. The dendritic fields of the neurons display the characteristics of “noyaux fermes”. The medium sized neurons contain small Nissl bodies anastomosed by threads of the same material giving rise to a tridimensional network; the large majority of the polyribosomes are free and suspended among the cisterns of the Nissl substance. Peculiar inclusions, resembling laminated inclusion bodies, are occasionally present in the perikarya. The origin of such inclusions from the endoplasmic reticulum has been proved, since intermediary steps in the transformation of endoplasmic reticular cisterns into laminated bodies have been disclosed. Rarely, annulate lamellae occur in the perinuclear region. The smaller neurons contain a large nucleus, almost 2/3 of the somatal volume, and in their cytoplasm Nissl bodies are practically absent. The Golgi impregnation and the electron microscopic observations have revealed the existence of large dendritic varicosities, giving rise to long slender filopodia localized in distal segments of some dendrites. The varicosities are filled with mitochondria and some glycogen particles. These features are characteristics of growing tips of dendrites (Sotelo and Palay, 1968). The immediate environment of medium sized neurons consists of axon terminals and astrocytic processes, in a near similar proportion. On the other hand, smaller neurons are in intimate contact with satellite oligodendrocytes, astrocytic processes, myelinated fibers and very few axon terminals. Close appositions, resembling “gap” junctions have been disclosed between perikarya of interfascicular oligodendrocytes.

Monoamine oxidase and aldehyde dehydrogenase activity in the striatum of rats after 6-hydroxydopamine lesion of the nigrostriatal pathway.

Abstract: Monoamine oxidase and aldehyde dehydrogenase activity were significantly reduced in the striatum of rats 8 days after lesion of the nigrostriatal nerve pathway caused by 6-hydroxydopamine. Evidence is presented for the existence of an intraneuronal 'dopamine monoamine oxidase' and intraneuronal aldehyde dehydrogenase. Dopamine concentrations were reduced to 10% of their control values.

In vivo continuous estimation of 3 H-dopamine synthesis and release in the cat caudate nucleus. Effects of -methyl-p-tyrosine and of transection of the nigro neostriatal pathway.

Abstract: Synthesis and release of 3H-DA were examined during the continuous superfusion of a limited area of the ventricular surface of the cat caudate nucleus with l-3,5-3H-tyrosine, using a cup technique. 3H−H2O, an index of the conversion of l-3,5-3H-tyrosine into 3H-Dopa, and 2H-DA were estimated in serial superfusate fractions. Alpha-methyl-paratyrosine (α-MpT) (10−4 M) inhibited rapidly and simultaneously both 3H−H2O formation and 3H-DA release. Transection of the nigro-striatal dopaminergic pathway immediately blocked 3H-DA release but 3H−H2O levels were reduced by 30% one hour later.

Statistical properties of focal conic textures in smectic liquid crystals

Abstract: 2014 In a smectic sample, the layers must be equidistant, but they may be curved. When the boundary conditions are not compatible with flat layers, one obtains a focal conic texture. We consider here the most familiar case where each unit in this texture fills a certain cone. The interstices between these cones are filled by smaller cones, etc. We discuss some features of this iterative filling of space, and show that it should persist down to a few molecular lengths. An estimate of the energy associated with the iterated structure indicates, that (in the absence of all external fields) focal conic textures are less expensive than grain boundaries, in agreement with the standard optical aspect of smectic samples. We discuss the scattering of light by an iterated focal conic texture, in terms of a simple scaling law ; the resulting angular dependence of the scattered intensity is anomalous and may allow for a direct determination of the « scaling index » n associated with the iterative process. LE JOURNAL DE PHYSIQUE TOME 34, JUILLET 1973, Classification Physics Abstracts 14.80 14.82

Recherches sur les Substances Mésomorphes III. Tolanes Nématiques

Abstract: New p.p'-disubstituted diphenylacetylenes of the formula RO - C6H4 - C = C - C6H4 - R' have been prepared. Symmetrical and non-symmetrical diethers (R' = OR and R' = OR) and p' alkylated monoethers are described. Most of these compounds are nematic at temperatures lower than 50°. The temperatures and heats of transition and electro-optical characteristics (∊⊥ and ∊∥) of the compounds are given. The preparation of mesomorphic mixtures at room temperature is discussed.

Yeast 3‐Phosphoglycerate Kinase

Abstract: The mechanism of the transphosphorylation reaction catalyzed by yeast 3-phosphoglycerate kinase has been studied by means of spectrophotometric investigations. The binding sites, one for the nucleotide substrates and one for the acceptor, have been characterized. The interaction of nucleotide substrates with the enzyme, which is not metal-dependent, resulted only in a perturbation of the spectrum of the nucleotide chromophore characterized by hypochromic and red shift effects. The hydrophobicity of this site was estimated by using a reporter group reagent, 2-(dansylamino)ethyl monophosphate. The interaction of 3-phosphoglycerate with its corresponding site produced perturbation of a tyrosyl chromophore. Furthermore, spectrophotometric studies evidenced the formation of binary and ternary complexes in accord with a random reaction mechanism proceeding via interconversion of ternary complexes. We also observed partial exchange reaction between ATP and ADP. Properties of this exchange reaction have been investigated. The partial reaction points out the existence of a covalent phosphoryl-enzyme intermediate.

The delayed rejection of tumors formed from the administration of tumor cells mixed with killed Corynebacterium parvum.

Abstract: The effect of killed Corynebacterium parvum was studied on two different tumors; the syngeneic CAD2 mammary adenocarcinoma. transplantable only in DBA/2 mice and the Shay chloroma carried in outbred albino rats. The results show that if killed C. parvum is mixed with the tumor-cell inoculum, the formed solid tumors undergo rapid rejection beginning 2 weeks later in both animal systems. The animals remain tumor-free and are protected against challenges of large doses of the same tumor cells, a protection that can be eventually overwhelmed when the challenge dose is massive. Histological sections of tumors from similarly inoculated animals revealed minimal necrosis and infiltration with macrophages and lymphocytes. Groups of tumor-inoculated animals receiving intraperitoneal injections of killed C. parvum alone or with killed tumor cells demonstrated an inhibition of tumor growth when compared to similar animals receiving saline. An enhancement of tumor growth was observed in animals receiving injections of killed tumor cells alone.