Binding of a tritiated enkephalinergic analog (FK 33-824) to a mitochondrial fraction of rat brain

FK-33-824 (Try-D-Ala-Gly-MePhe-Met(O)ol) is a potent enkephalin analog which has been tritium labelled with a high specific radioactivity (41 Ci/mmole). The labelled drug exhibits specific and saturable binding to rat brain crude mitochondrial fraction. Specific binding is inhibited by low concentrations of morphine, levallorphan and beta-endorphin, suggesting that FK 33-824 [3H] binds preferentially to mu opiate sites. Binding studies at equilibrium and kinetics of formation and dissociation of the labelled ligand-receptor complex indicate that FK 33-824 [3H] binds to two classes of specific sites. Their affinities are distinguishable at 0 degree (KD = 1.3 and 5.8 nM) and very close to each other at 37 degree (KD = 1.9 nM).     

An anatomofunctional brain database

This study proposes a closer look at the neuropsychological method defined as the study of the neural bases of the behavioural and cognitive functions using an organisation-representation model for current data and knowledge of the brain, and the application of an anatomofunctional database. A Centre of Cognitive Anatomy (CAC) was set up for the collection and processing of neuronatomical, neuropsychological, and psycho-behavioural data for patients presenting sequels of focal brain damage. Such a system would allow concurrent treatment of anatomical and functional data. We would expect the results from such a model to produce stable 'anatomofunctional laws' that would be independent of all inter-individual variations in the functioning of the brain and could be checked against the entire database of information. A direct application would be the improvement of cognitive and/or behavioural rehabilitation of patients with brain damage.     

Purification and properties of aromatic L-amino acid decarboxylase (4.1.1.28) of rat brain]

L-aromatic aminoacid decarboxylase has been purified more than thousand times from homogenates of rat brain, in several steps : centrifugation, DEAE-cellulose, CM cellulose, hydroxylapatite, DEAE sephadex. Its properties have been studied, most of them on an intermediate fraction of the purification, because of the instability of the purified enzyme in spite of the addition of different stabilizing agents : the enzyme decarboxylates 5-hydroxytryptophan (5 HTP) and DOPA in a ratio constant throughout the purification but does not decarboxylate tryptophan, tyrosine, histidine at a measurable rate. Optimum pH, Km, Vm, have been measured with 5 HTP and DOPA as substrates. The enzyme has a molecular weight of 115.000, an apparent isoelectric point of 6,4-6,5. It is inhibited by serotonin, dopamine, some cations : Cu++, Fe++, Ni++ by N-ethylmaleimide, sodium dodecylsulfate. Some pyridoxal-5 phosphate (PLP) remains strongly bound to the enzyme. For relatively weak concentrations of substrate, the enzyme is inhibited by an excess of PLP ; for weak concentrations of PLP, the enzyme in inhibited by an excess of substrate, particularly of DOPA. We also observe a spontaneous decarboxylation of the substrates that reaches a plateau and is enhanced by high concentrations of PLP, by serotonin, dopamine, Cu++ and reduced by mercaptoethanol and the presence of crude or boiled homogenates. Several possible explanations of the spontaneous decarboxylation and of the enzymic inhibitions by an excess of PLP and by the substrates are given.     

Calcium as an extracellular signalling molecule: perspectives on the Calcium Sensing Receptor in the brain

Calcium acts as a universal signal that is responsible for controlling a spectrum of cellular processes ranging from fertilization to apoptosis. For a long time, calcium was regarded solely as an intracellular second messenger. However, the discovery that calcium can also act as an external ligand together with the molecular cloning of its cell surface receptor, the Calcium Sensing Receptor (CaSR), demonstrated that calcium also acts as an important extracellular or first messenger. Here, we give an overview of the main structural, pharmacological and physiological features of the CaSR and provide an assessment of its functions and cellular and molecular mechanisms of action. In addition, we propose possible avenues for future research into the trafficking of CaSR and the role(s) of this receptor in the central nervous system.     

Substrates and products of fatty acid elongation in mouse brain microsomes]

In brain microsomes, palmitate and stearate elongation involve a membrane lipid-bound substrate. After elongation by malonyl-CoA, acyl-products are partially bound to proteins. Acyl-proteins are not found when endogenous fatty acid elongation takes place. In the dysmyelinating Quaking mouse mutants, "stearyl-membrane" substrate formation is normal; thus, the deficiency observed in very long chain fatty acid formation is not due to a lack in substrate formation.     

Identification of rat brain polysomes synthesizing the brain specific enolase (14.3.2 protein), S100 protein and alpha and beta tubulin subunits

Polysomes prepared from frozen rat brain powder were fractionated by centrifugation in a sucrose gradient. Individual fractions were used to program a reticulocyte lysate in a run-off reaction. The products of cell-free synthesis were assayed for the brain-specific enolase (14.3.2 protein) and S100 protein by immunoprecipitation with specific antisera and for tubulin by two-dimensional electrophoresis in polyacrylamide slab gels. The relative synthesis of these proteins by unfractionated free brain polysomes were 0.1 per cent, 0.05 per cent and 0.7 per cent respectively. After centrifugation in a sucrose gradient polysomes synthesizing S100 protein were separated from those synthesizing the other two markers. There was a threefold enrichment in the specific messenger RNA activity for each of the three proteins studied in their respective peak fractions of polysomes.     

Sunflower seed protein: size and charge heterogeneity in subunits of the globulin fraction

The subunit heterogeneity of the globulin fraction of sunflower seeds was investigated by two dimensional electrophoresis, using isoelectric focusing in the first dimension and sodium dodecyl sulphate polyacrylamide gel electrophoresis in the second dimension. Under non reducing conditions, intermediary subunits B, C and D (molecular weight 54 000, 48 000 and 40 000, respectively) were focused within a pI range 5.4-6.0 but intermediary subunits A (molecular weight 60 000) focused within a pI range 6.3-6.8. Under reducing conditions the electrophoretic patterns show that intermediary subunits consist in large "acidic" and small "basic" subunits linked by disulphide bonds. The large subunits of B species are more acidic and less heterogeneous than the corresponding subunits of the A species. These results confirm that helianthinin had a "legumin-type" structure.     

Ecologie des Dermestidae,une famille de Coléoptères nécrophages associée aux cadavres squelettisés

Lorsqu’un animal meurt, son cadavre forme un écosystème local instable et éphémère où différentes communautés d’insectes nécrophages vont se nourrir. Cette étude a pour but de caractériser les relations entre deux familles fréquentes en contextes médico-légal : les Diptères Calliphoridae et les Coléoptères Dermestidae. Des expériences de choix binaire (olfactomètres en T) et de prédation des Dermestes sur les larves de Diptères ont constitué le 1er axe de notre étude. Il en ressort que l’espèce D. maculatus (adultes et larves) n’exerce qu’une très faible prédation sur les larves de L. sericata. En absence de nourriture, les Dermestes sont néanmoins capables de prédater les pupes de L. sericata, et donc de faire disparaitre ces traces particulièrement importantes en entomologie médico-légale et en archéo-entomologie. Le second axe s’est focalisé sur les relations de compétition et d’agrégation entre D. maculatus et D. haemorrhoidalis. Les résultats obtenus n’ont pas mis en évidence de mécanismes de compétition ou d’exclusion entre ces deux espèces pourtant amenées à fréquenter simultanément le même habitat et à exploiter les mêmes ressources. Placées en condition de choix binaire (2 spots identiques), les 2 espèces s’agrègent ensemble. Mais le développement conjoint de ces 2 espèces sur une seule source de nourriture non limitante entraine une baisse significative du taux de survie chez les deux espèces. Au vu de ces résultats, nous avons conclu à la possibilité d’une coexistence de ces différentes espèces (L. sericata, D. maculatus et D. haemorrhoidalis) sur un cadavre.     

Status of the so-called African pygmy elephant (Loxodonta pumilio (NOACK 1906)): phylogeny of cytochrome b and mitochondrial control region sequences

Among the African elephants, it has been unanimously acknowledged that the forest elephants (cyclotis form) are peculiar, so that they have been elevated to the specific rank. The development of molecular analyses of extant Loxodonta has only focused on two forms yet: the savannah form (africana) and the forest form (cyclotis), disregarding the so-called pygmy elephants (pumilio or fransseni) the systematic status of which has been debated since their discovery. Therefore, we have sampled nine dwarfed-labelled specimens in collection and eight specimens of typical forest elephants that we compared to three savannah elephants and two Asian elephants. Because of the degraded nature of the nuclear DNA content in bone samples of old specimens, we assayed mitochondrial markers; 1961 bp of the mitochondrial genome were sequenced (over a continuous range spanning the cytochrome b gene, tRNA Thr, tRNA Pro, hypervariable region 1 and central conserved region of the control region). Pumilio and cyclotis are not sister-taxa: the phylogenetic analyses rather account for the inclusion of the so-called pygmy elephants within a monophyletic group of forest elephants sensu lato. The internal structure of this clade reveals to depend on isolation and remoteness between populations, characteristics that may have been extensively influenced by climatic variations during the Quaternary period. We conclude that the specific taxon Loxodonta pumilio (or Loxodonta fransseni) should be abandoned.