Showing papers by "Collège de France published in 1980"

The ontogeny of the neural crest in avian embryo chimaeras.

Abstract: The migration and subsequent development of autonomic ganglion cell precursors can be followed in suitably constructed chimaeric quail-chick embryos, thanks to the distinctive structures of quail and chick interphase nuclei. The decisive role of environmental factors arising from non-neuronal tissues on the chemical differentiation of neurones was demonstrated together with the lability of their phenotype during ontogeny.

Response to stress of mesocortico-frontal dopaminergic neurones in rats after long-term isolation

Abstract: Recent studies suggest that the mesocortico-frontal dopaminergic neurones which originate in the ventral tegmental area (VTA) have an inhibitory role in locomotor activity1,2. They are also markedly activated under stress3–5. This effect was shown in rats and mice subjected to electric foot-shocks by measuring either the rate of decline of dopamine (DA) after α-methylparatyrosine treatment3 or the changes in dihydroxyphenylacetic acid (dopac) levels and the dopac/DA ratio4–6. In rats, stress-induced activation of the dopaminergic neurones was prevented by benzodiazepines4,5, and studies in BALB/c mice introduced for 2 min into an open field further established the role of dopaminergic neurones in emotional responses7. These observations led us to examine the effects of long-term isolation on the activity of the mesocortico-frontal dopaminergic neurones in rats, some of which were subjected to a stressful situation. Indeed, several groups have reported that long-term isolation in rodents induced behavioural disturbances such as increased motor activity8,9 and aggression9,10 and hyper-reactivity to a new environment or stressful stimuli10,11. As measured by the changes in dopac levels or the dopac/DA ratio, we report here that the activity of the mesocortico-frontal dopaminergic neurones was reduced after isolation. This was not the case for the dopaminergic neurones projecting to the nucleus accumbens or the striatum, the rate of DA utilisation in these structures was even enhanced in isolated rats in which the activity of the mesocortico-frontal dopaminergic neurones was markedly reduced. Finally, we will show that a 3-min electric foot-shock session is more effective in enhancing dopac levels or the dopac/DA ratio in the frontal cortex of isolated than grouped rats.

Effect of striatal cells on in vitro maturation of mesencephalic dopaminergic neurones grown in serum-free conditions

Abstract: It is well documented that target cells can regulate the morphological and biochemical development of peripheral afferent neurones1,2, but little is known about the existence of such regulatory mechanisms in the central nervous system. We therefore investigated previously the influence of striatal target cells on the maturation in vitro of nigrostriatal dopaminergic neurones, which survive in culture for more than 5 weeks, develop dense arborizations and both take up 3H-dopamine(DA) by a high-affinity specific process and synthesize 3H-DA from 3H-tyrosine3. Furthermore, depolarization by potassium or veratridine stimulates the release of DA through a calcium-dependent mechanism and tetrodotoxin prevents the veratridine-evoked release of the transmitter4. Both the number of 3H-DA uptake sites and the capacity for 3H-DA synthesis were at least doubled when the neurones were cultured with target cells from the striatum3. To determine whether glial cells which proliferate in serum-complemented medium are partly responsible for the maturation of dopaminergic neurones and/or for the effect of striatal cells, we have now repeated the experiment using serum-free medium in which virtually pure neuronal populations can be obtained5–7. The reduction in the number of glia did not affect either the maturation of dopaminergic cells alone, or the effect of striatal cells. Autoradiographic analysis of the number of dopaminergic cells strongly suggests that the stimulatory effect is related to increased capacities of 3H-DA uptake and synthesis per dopaminergic neurone.

Scaling Description of Two-Dimensional Chain Conformations in Polymer Monolayers

Abstract: It is shown how the molecular weight dependence of the radius of gyration ${R}_{F2}$ of two-dimensional polymeric chains can be derived from surface-pressure isotherms in Langmuir monolayers. ${R}_{F2}$ scales as ${N}^{\ensuremath{ u}}$ with $\ensuremath{ u}=0.56$ for polymethylmethacrylate and 0.79 for polyvinylacetate. These values are in agreement with the scaling predictions for tricritical and excluded-volume behaviors, respectively. The crossover between the dilute and the intermediate regimes is also clearly observed in one case.

Pain modulating and reward systems: A single brain mechanism?

Abstract: The hypothesis that brain rewarding and pain modulating systems could involve a common opiate system, identically blocked by naloxone, has been tested in three experiments. The preferences or aversions for sapid solutions in rats have been employed as reliable measures of responses to rewarding or nociceptive stimulations. In the first experiment, it was shown that the spontaneous aversion to a quinine HCl solution was enhanced when rats were offered the solution 30 min after naloxone at a dose of 1 mg/kg. The same enhanced aversion was observed in the second experiment towards a sweet solution previously made aversive through a conditioned taste aversion paradigm. In the third experiment, by using two different procedures and saccharin or glucose solutions, it was found that naloxone acutely abolished the preference for sweet solutions versus water in rats. It is concluded that: (1) the enhancement by naloxone of the aversion to a sapid solution, similar to the naloxone induced hyperalgesia, allows to assimilate this aversion to other responses to nociceptive stimulations; (2) this suggests that, like other responses to nociceptive stimulations, this aversion is normally attenuated through the release of brain or pituitary opiates; (3) the suppressant effect of naloxone upon both this attenuation of aversion and a preference for a sapid solution supports the notion of a biochemical and functional community between rewarding and pain modulating systems.

(3H)-Vasopressin Binding to Isolated Rat Hepatocytes and Liver Membranes: Regulation by GTP and Relation to Glycogen Phosphorylase Activation

Abstract: Specific vasopressin binding to rat hepatocytes and rat liver membranes was measured using biologically active (3H)-Tyr2-Lys8-vaso-pressin (8.5 Ci/mM). In both systems, vasopressin binding was found to be time-dependent, reversible, and saturable. The kinetic parameters for vasopressin binding were: apparent dissociation constants (Kd): 4.9 nM and 15 nM; maximal binding capacities: 0.83 pmoles/mg protein and 2.105 sites/Cell for purified membranes and intact cells respectively. The relative affinities of 19 vasopressin structural analogues were deduced from competition experiments and compared to the previously determined glycogenolytic (or anti-glycogenolytic) potencies of these analogues. For both agonists and antagonists, a highly significant correlation was demonstrated between pKd and pKa (or pKi) values, suggesting that the detected binding sites are the physiological receptors involved in the glycogenolytic action of vasopressin on the rat liver. The affinity of antagonists for binding to t...

In vivo release of acetylcholinesterase in cat substantia nigra and caudate nucleus

Abstract: Acetylcholinesterase (AChE), which is known to inactivate acetylcholine (ACh), is present in great abundance in the substantia nigra, although ACh levels and choline acetylase activity in this region are relatively low1. Nigral dopaminergic cell bodies and their dendrites also contain AChE2–4. The functional significance of this enzyme in nigro-striatal dopaminergic neurones has been questioned1,4,5. Earlier studies demonstrated an evoked release of AChE from unidentified central neurones into cerebrospinal fluid (CSF) in cats6, rabbits7,8 and dogs9. Later experiments have provided indirect evidence that the substantia nigra may contribute to a substantial amount of AChE detected: a unilateral nigral lesion in rabbits reduced AChE levels in the CSF, whereas electrical stimulation of the substantia nigra induced the opposite effect10. To investigate the possible release of AChE from dopaminergic dendrites and terminals we measured the in vivo release of this enzyme from the substantiae nigrae and caudate nuclei of cats implanted with four push–pull cannulae and compared it with that of dopamine (DA). DA is released from dendrites in the substantia nigra11,12 as well as nerve terminals in the caudate nucleus. Spontaneous AChE release was observed in the substantia nigra and in the caudate nucleus. Moreover, the application of potassium (30 mM) in one substantia nigra increased the local release of AChE. This was accompanied by remote changes in the enzyme release from the other three structures which differed from that seen for DA. The different patterns of responses observed for AChE and DA suggest that AChE may also originate from other neurones in both the substantia nigra and the caudate nucleus.

Correlations and dynamics of polyelectrolyte solutions

Abstract: The dynamics of polyelectrolyte solutions have been studied using a neutron spin echo spectrometer for wave vectors q around the maximum of the static structure factor (qm). The q dependent diffusion coefficient D(q) decreases sharply below q = qm, and is nearly constant above qm. All these features can be understood in terms of a new picture for the correlations, based on : i) the notion of a correlation hole, of diameter ξ = aO-1/2 ; ii) locally rigid chains with a persistence length b = aO-1 (where O is the polymer volume fraction and a the monomer size).

Modulation of the distribution of acetylcholinesterase molecular forms in a murine neuroblastoma x sympathetic ganglion cell hybrid cell line.

Abstract: Studies were carried out on the polymorphism of acetylcholinesterase (AChE, EC 3.1.1.7) in a neuroblastoma x sympathetic ganglion cell hybrid cell line (T28) and its parental clone (N18TG2). These cells contain the tetrameric (G4, 10S), dimeric (G2, 6.5S) and monomeric (G1, 4S) forms of AchE, but not the collagen-tailed A12(16S) form of the sympathetic ganglion. Three variants of these forms could be distinguished on the basis of their solubility properties: (i) secreted forms which do not interact with the detergent Triton X-100; (ii) cellular forms which may be solubilized in detergent-free buffer and which interact reversibly with Triton X-100; (iii) cellular forms which require detergent for solubility, and aggregate in its absence. By using a nonpenetrating inhibitor, we demonstrated that, in T28 stationary cells, the cellular G4 form is associated with the plasma membrane, whereas the G1 form is intracellular. During induction of AChE activity in T28 cells, the relative proportion of the G4 form increases, suggesting, in agreement with previous observations, that G1 is a metabolic precursor of G4. The evolution of AChE molecular forms released into the culture medium closely resembles that of the cellular forms. The preferential accumulation of the G4 molecules does not simply depend on the cellular level of G1. It is favoured by culture conditions which promote morphological differentiation, but does not require the actual extension of neurites. T28 cells as well as other neuroblastoma-derived cells appear to be useful experimental materials to investigate the regulatory mechanisms underlying the maturation of AChE globular forms.

The ipsilateral optic pathway to the dorsal lateral geniculate nucleus and superior colliculus in mice with prenatal or postnatal loss of one eye

Abstract: The projections, and more particularly the ipsilateral projections, from the retina to the dorsal lateral geniculate nucleus (dlGn) and the superior colliculus have been investigated in adult mice of the C57BL/6J strain after rearing in one of four different conditions: 1) after normal visual experience; 2) after unilateral enucleation at birth; 3) in mice with congenital unilateral anophthalmia (in which only one eye develops) 4) in mice with congenital unilateral microphthalmia (in which only one eye is of reduced size while the other is normal). In neonatally enucleated and congenitally monocular mice there is an aberrant uncrossed pathway to regions of the dlGn and the superior colliculus which do not normally receive such a projection. This projection is limited in its distribution; in both the neonatally enucaleated and the congenitally monocular animals the uncrossed projection does not reach the lateral and dorsal parts of the dlGn and it only innervates the rostral half of the superior colliculus. The density of the uncrossed pathway in these animals is highest in those regions in which the normal uncrossed pathway terminates. In microphthalmic mice the expansion of the uncrossed pathway is less marked than in monocular mice. In the superior colliculus the aberrant uncrossed projections innervate the stratum griseum superficiale where they are often found distributed in small patches. An intertectal crossing of retinal fibers is described from the contralateral superior colliculus to the deprived ipsilateral superior colliculus.

Lymphoid stem cell homing to the early thymic primordium of the avian embryo.

Abstract: The quail-chick marker system was used to investigate the mechanism of lymphoid precursor cells (LPC) homing to the early thymic rudiment during development of the avian embryo. Migration of LPC was demonstrated in vivo and in vitro from the yolk sac, spleen and bone marrow to the thymus rudiment at a definite period of the latter's ontogeny. Before and after this period, the thymic rudiment is nonreceptive for LPC. The onset of stem cell seeding depends on a stage-dependent maturation of the thymic primordium while its arrest is regulated by the number of cells which have invaded the organ. An in vitro transfilter culture technique is described which permits LPC to be attracted to a thymic rudiment. The thymus at its physiological receptive period and several other organs were associated with LPC donors. The capacity of these various organs to induce LPC traffic was compared. It appeared that the “receptive” thymus is a much better “attractant” than the liver, the mesonephros or the already colonized thymic rudiment. The hypothesis of the production of a chemotactic factor responsible for LPC attraction by the thymus rudiment is proposed which accounts for experimental data reported in this article, as well as for the events of thymus ontogeny previously established.

Electron-microscopic cytochemical studies on the secretory process in rat prolactin cells in primary culture.

Abstract: Three aspects of the secretory process in male rat prolactin (PRL) cells grown in primary cultures for 7--14 days have been investigated by cytochemical methods. The subcellular localization of prolactin has been studied using preembedding or postembedding immunocytochemical methods after various fixatives. With the postembedding method, PRL is localized essentially in secretory granules. The maximum intensity of staining is obtained with PAF fixative. With the preembedding method, subcellular localization of the staining varies depending on the fixative. After PAF-fixation, positive staining is observed on secretory granules, ground cytoplasm, the outer face of some RER cisternae and, in a few cells, on the innermost Golgi cisternae, as well as on masses of condensing secretory material. After Ohtsuki's hypotonic fixative followed by saponin permeabilization, PRL is visualized within the totality of RER cisternae, including the perinuclear cisternae and the peripheral saccules on the cis-Golgi face. Secretory granules are unstained. Membrane traffic was investigated using the Con A-HRP indirect method as a tracer of surface saccharides. Plasma membrane, coated with Con A-HRP at 4 degrees C, is slowly internalized at 37 degrees C. This involves both randomly distributed invaginations and capping. The final step of endocytosis (1--2 hours) is located in the Golgi zone, where very few smooth membranes are stained. In contrast, a conspicuous deposit is found around the dense content of secretory granules. This suggests a recycling of internalized membrane and a transfer of Con A-HRP from the inner face of smooth cisternae to the secretory material. The internalization of Con A-HRP-coated membrane leads to an inhibition of PRL release starting after 30 minutes. This is accompanied by a marked increase of acid phosphatase activity, mostly around forming and mature secretory granules.

Weak Nematic Gels

Abstract: We give some theoretical predictions concerning the mechanical, optical and electrical properties of weak networks made with nematic polymers. The network may be permanently crosslinked, or may exist only in transient states, and be due only to physical entanglements. We construct an elastic theory involving both the deformations of the gel and the distortions of the director field. We conclude that weak gels may show some interesting mechanooptic properties.

In vivo insulin resistance during pregnancy in the rat

Abstract: The glucose disappearance rate measured after IV glucose injection (1 g/kg body wt) remained unchanged between 12 and 21 day of gestation in the rat. In contrast, insulin secretion in response to IV glucose was markedly increased on day 19 and 21 of pregnancy, suggesting resistance to endogenous insulin. Glucose kinetics (glucose production, utilization and clearance) in response to various doses of IV insulin have been studied in anaesthetised postabsorbtive 19 day pregnant and virgin rats using 6-3H glucose. With the supramaximal dose of insulin (4 U/kg body wt) no differences in glucose kinetics were found between pregnant and virgin rats. In contrast, with the two lower doses of insulin (0.15 and 0.05 U/kg body wt) glucose production was inhibited by 36±3% and 13±2% (Mean±SEM) respectively in virgin rats, but was not decreased in pregnant rats. When the effect of insulin on glucose clearance was expressed as % of the maximal effect obtained with 4 U/kg body weight, the rise in glucose clearance in response to the two lower doses of insulin (0.15 and 0.05 U/kg body wt) was lower in pregnant (57.5±6 and 27.4±4%) than in virgin rats (73.3±6 and 42.2±7%). These results suggest that a decreased sensitivity to insulin appears in late pregnancy in the rat and could involve both liver and skeletal muscle.

Rotational Diffusion of Sterically Interacting Rodlike Macromolecules

Abstract: The rotational diffusion of rodlike $M\ensuremath{-}13$ viruses in solution has been measured at concentrations intermediate between the dilute and the concentrated regimes. The strong concentration dependence observed is in agreement with the Doi-Edwards model based upon simple steric hindrance arguments between rotating rodlike macromolecules. The dependence of the rotational diffusion coefficient on the virus length has also been investigated.