Étude de l'effet de la température sur la division des cellules séparées de feuilles deCalystegia sepium (L.) R.Br.

Cells mechanically isolated from homogenized leaves ofC. sepium dividein vitro. The rate of cell division is strongly influenced by temperature with the optimum between 31 and 34 °C. The rate of cell division increases proportionally with a rise in temperature up to 31 °C and is accompanied by a reduction in the length of the preparatory phase of the division. A supraoptimal temperature (40 °C) inhibits or stops the cell division which can be restored provided that the cells are transferred to 31 °C. If the preparatory phase to the commencement of cell division is accomplished at 17 °C the cells then exposed to 31 °C divide more rapidly than if they are exposed directly to 31 °C.     

Recherches écologiques sur les faunes des plages arbitées de la région d'Arcachon

Resume 1. Le présent travail est consacré à l'étude écologique des plages abritées de la baie d'Arcachon (France). L'auteur tout d'abord, reconnaît et localise dans la région étudiée les quatres zones classiques qui partagent les estrans meubles abrités: slikke, haute slikke, schorre et zone parhalienne. Chacune d'entre elles est ensuite étudiée de manière plus détaillée, quant aux peuplements qui les occupent et aux structures édaphiques qui leur correspondent.2. Dans la slikke, l'auteur, reconnaît et décrit quatre faciès fondamentaux: les herbiers deZostera nana, les sables nus, type sables à arénicoles, les vases àNereis diversicolor et les vases à scrobiculaires. Chacun de ces faciès est analysé quant à sa teneur en eau, porosité, salinité, pH et oxygène dissous, répartition hypsométrique. En ce qui concerne la faune de ces slikkes sablo-vaseuses, l'auteur souligne l'importance de la macrofaune endogée, son caractère infralittoral, la faible mobilité de ses représentants.3. Dans la haute slikke, l'auteur reconnaît et décrit cinq faciès: les sables argileux àBledius spectabilis, les sables vaseux àCorophium volutator, les sables poreux àBledius arenarius, les aires àSpartina maritima et les microfalaises. De nouveau, sont étudiés successivement les caractéristiques abiotiques, puis les peuplements de chaque faciès; l'auteur souligne l'action réciproque des structures édaphiques sur la répartition des peuplements, mais aussi des peuplements sur les structures édaphiques. Par exempleCorophium volutator etBledius spectabilis édifient des galeries à parois stables, permanentes, qui ne peuvent être aménagées que dans certains types de sédiments; mais tandis que les galeries deB. spectabilis sont denses et étanches à la marée, celles deC. volutator sont plus dispersées et inondables; aussi la présence de l'insecte permet l'installation d'une faune d'accompagnement supralittorale, qui s'enterre au moment de la haute mer, celle de l'amphipode s'accompagne au contraire, d'une faune médiolittorale inondable.4. Enfin, dans le schorre et la zone parhalienne, l'auteur souligne l'absence de macrofaune endogée, la mobilité des peuplements vagiles épigés, leur balancement saisonnier lié au régime des marées. Il montre notamment qu'en été, le schorre abrite à la fois des espèces supralittorales marines ou halobies, et des espèces adlittorales haloxènes qui, venant de la zone parhalienne, sont attirées par la richesse trophique du Puccinellietum. En hiver, au contraire, la fréquence des immersions dans le schorre oblige la faune à refluer dans la zone parhalienne, où elle trouve son abri.5. Une classification des faciès étudiés en fonction de leur teneur en eau écologiquement utilisable par la macrofaune, un tableau de correspondance entre slikke, haute slikke, schorre et zone parhalienne d'une part, et étages intertidaux d'autre part, enfin une comparaison entre les peuplements des plages abritées et plages semi-abritées, complètent l'ensemble du travail.

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Ecological research on the faunas of the sheltered beaches of the region of Arcachon

In these ecological studies of the sheltered beaches of the bay of Arcachon (France), the author distinguishes and locates four traditional zones: slikke, upper slikke, schorre and parhalian zone. Animal communities and edaphic structures of each zone are treated in detail. In the slikke, four fundamental facies are distinguished:Zostera nana zones, bare sands (such asArenicola sands),Nereis diversicolor slime andScrobicularia slime. Each facies is analyzed with regard to its amount of water, porosity, salinity, pH and dissolved oxygen content, as well as its hypsometric distribution. With respect to the fauna of sand and slime slikkes, the importance of the endogeous macrofauna, its infralittoral characteristics and the low degree of mobility of its species are emphasized. In the upper slikke five facies are described:Bledius spectabilis clay sands,Corophium volutator slimy sands,Bledius arenarius porous sands,Spartina maritima areas and micro cliffs. Again, abiotic characteristics and animal communities of each facies are studied successively. The importance of edaphic structures for the distribution of animal communities, and vice versa, is stressed. For instance, the amphipodCorophium volutator and the coleopteranBledius spectabilis build tubes with firm and permanent inner surfaces only in certain types of sediment: yet, while theBledius spectabilis tubes are dense and watertight, those ofCorophium volutator are less tight and often flooded. Thus, the presence of the insect allows a supralittoral fauna to establish itself, whereas that of the amphipod is, in contrast, accompanied by a mediolittoral fauna resistant to flooding. In the schorre and parhalian zone, endogeous macrofauna elements are entirely absent; the vagrant epigeous species exhibit considerable degrees of mobility, migrating according to tidal rhythms. In summer, the schorre zone shelters both marine supralittoral or halobiotic species as well as adlittoral haloxene species which, coming from the parhalian zone, are attracted by the trophically rich Puccinellietum. In winter, however, frequent floodings of the schorre force the fauna to retreat to the parhalian zone for shelter. A classification is presented of the facies studied, based on the amount of water ecologically usable by their respective macrofaunas. The relationships between slikke, upper slikke, schorre and parhalian zone on the one hand, and the intertidal zones on the other are illustrated in the form of a synopsis. Finally, a comparison is made between animal communities of sheltered and of partly sheltered beaches.

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Ce travail constitue la 2ème partie d'une thèse de Doctorat ès Sciences naturelles soutenue à la Faculté des sciences de l'Université de Bordeaux (n^o d'ordre 197) et intitulée «Recherches écologiques sur les faunes des plages arbitées et des étangs saumatres de la region d'Arcachon». L'exemplaire dactylographié de la thèse in extenso a été déposé au C.N.R.S. et enregistré sous le n^o A.O. 1612.     

Le nouveau paysage du cannabis I. Données récentes sur la neurobiologie des endocannabinoïdes et du cannabis

Among all the drugs of abuse cannabis is the only one containing an active principle that can be stored in the body for several weeks, delta-9-Tetrahydrocannabinol (Δ9-THC). It induces both psychic and physical dependency, which are masked because the disappearance of Δ9-THC from plasma corresponds to its storage in lipids, especially in cerebral lipids. In the brain Δ9-THC mimics, in a non regulated, diffuse and intense manner, the neuromodulation which endocannabinoids (anandamide, 2-arachidonyl-glycerol, etc.) physiologically und subtly exert through the stimulation of specific receptors, the so-called CBl receptors. These receptors have an influence on a great variety of psychological functions. For instance, at the hippocampal level receptor reserve is high, and it allows the development of a maximal response even though only a low proportion of these receptors are stimulated. This occurs even for low doses of Δ9-THC. The desensitization / down regulation of these receptors has no functional consequences since they always remain numerous enough to ensure the function. Thus the Δ9-THC-induced cognitive disturbances persist as long as cannabis use persists. On other systems, without CBl receptor reserve, the long lasting use of Δ9-THC induces a desensitisation / down regulation of CBl receptors, leading to a tolerance to its effects.     

Le nouveau paysage du cannabis II. Données récentes sur la psychotoxicité du cannabis

After delta-9-tetrahydrocannabinol (Δ9-THC) has supported the anandamidergic tone, thereby increasing its anxiolytic and antidepressant effects, it loses its efficacy in this respect. Anxious and/or depressive troubles which could have prompted the abuse of cannabis then reappear more intensely. They peak when consumption is completely stopped. Cannabis consumption may contribute to polydrug abuse. Its association with tobacco makes it more difficult to give up both substances of abuse. Cannabis use encourages the consumption of alcohol and this association is especially deleterious as regards car accidents. Δ9-THC sensitises cannabis abusers to perceive the appetitive effects of heroin in a more acute manner. Cannabis consumption also makes withdrawal symptoms associated with heroin abuse more severe. Cannabis appears to be able to reveal schizophrenia in patients bearing a neurobiological vulnerability substratum to this disease. It seems especially appreciated by people suffering of negative symptoms of schizophrenia, which could prompt them to abuse cannabis, and then triggering the positive symptoms of the disease. These positive symptoms are particularly resistant to treatment with antipsychotic medication when cannabis abuse is continued. All this recent data necessitates extreme care with this drug of abuse, whose dangerous effects are becoming more and more known.