MS 2005 num. 02
http://hdl.handle.net/10608/5384
2024-03-28T11:43:04ZAcides gras ω-3 et troubles psychiatriques
http://hdl.handle.net/10608/5458
Acides gras ω-3 et troubles psychiatriques
Bourre, Jean-Marie
Les acides gras ω-3 ont été parmi les premiers nutriments dont un effet sur la structure et la fonction du cerveau a été démontré. L’exceptionnelle richesse de cet organe en acides gras ω-3 explique, au moins en partie, l’étude de l’influence des apports alimentaires en ces nutriments sur certaines maladies psychiatriques et sur le déclin cognitif lié au vieillissement. Au final, les acides gras ω-3 semblent efficaces dans la prévention du stress, de la dépression et de la démence, notamment au cours de la maladie d’Alzheimer. Si leur rôle comme régulateur de l’humeur demeure hypothétique, ils pourraient être impliqués dans la dépression, notamment celle du post-partum, et dans le trouble bipolaire. Enfin, le rôle des acides gras ω-3 alimentaires dans l’autisme et la schizophrénie doit encore être démontré. Les relations établies entre ces apports alimentaires et certains troubles mentaux justifient que l’on se préoccupe de l’insuffisance en acides gras ω-3 dans le régime de la population française (moins de 50% des apports conseillés pour l’acide α-linolénique), d’autant que ce déficit pourrait être facilement résorbé, notamment par la consommation d’huile de colza.; The brain is one of the organs with the highest level of lipids (fats). Brain lipids, formed of fatty acids, participate in the structure of membranes, for instance 50% fatty acids are polyunsaturated in the gray matter, 1/3 are of the omega-3 family, and are thus of dietary origin. The omega-3 fatty acids (mainly alpha-linolenic acid, ALA) participated in one of the first experimental demonstration of the effect of dietary substances (nutrients) on the structure and function of the brain. Experiments were first of all carried out on ex vivo cultured brain cells, then on in vivo brain cells (neurons, astrocytes and oligodendrocytes) from animals fed ALA deficient diet, finally on physicochemical (membrane fluidity), biochemical, physiological, neurosensory (vision an auditory responses), and behavioural or learning parameters. These findings indicated that the nature of polyunsaturated fatty acids (in particular omega-3) present in formula milks for human infants determines to a certain extend the visual, neurological, and intellectual abilities. Thus, in view of these results and of the high polyunsaturated fatty acid content of the brain, it is normal to consider that they could be involved in psychiatric diseases and in the cognitive decline of ageing. Omega-3 fatty acids appear effective in the prevention of stress, however their role as regulator of mood is a matter for discussion. Indeed, they play a role in the prevention of some disorders including depression (especially post partum), as well as in dementia, particularly Alzheimer’s disease. Their role in major depression and bipolar disorder (manic-depressive disease), only poorly documented, is not clearly demonstrated. The intervention of omega-3 in dyslexia, autism, and schizophrenia has been suggested, but it does not necessarily infer a nutritional problems. The respective importance of the vascular system (where the omega-3 are actually active) and the cerebral parenchyma itself, remain to be resolved. However, the insufficient supply of omega-3 fatty acids in today diet in occidental (less than 50% of the recommended dietary intakes values for ALA) raises the problem of how to correct inadequate dietary habits, by prescribing mainly rapeseed (canola) and walnut oils on the one hand, fatty fish (wild, or farmed, but the nature of fatty acids present in fish flesh is the direct consequence of the nature of fats with which they have been fed), and eggs from laying hens fed omega-3 fatty acids.
2005-01-01T00:00:00ZL’ambroisie : Chronique de l’extension d’un « pollutant biologique » en France
http://hdl.handle.net/10608/5456
L’ambroisie : Chronique de l’extension d’un « pollutant biologique » en France
Dessaint, Fabrice; Chauvel, Bruno; Bretagnolle, Francois
L’ambroisie à feuilles d’armoise (Ambrosia artemisiifolia L.) fait partie des espèces dites « envahissantes » en France. Cette plante, originaire d’Amérique du Nord, est arrivée au cours du XVIIIe siècle en Europe, mais ne s’est réellement installée qu’au milieu du siècle suivant. Aujourd’hui naturalisée, on la trouve sur une grande partie du territoire national. Elle pose d’importants problèmes, à la fois en termes de santé publique (pollen allergisant) et de désherbage, en raison d’un faible nombre de programmes herbicides efficaces.; In France, common ragweed (Ambrosia artemisiifolia L.) is an invasive species, which most probably originates from North America. This plant is responsible for human health problems as the pollen causes allergic rhinitis and seasonal asthma ; in addition, it engenders agronomical problems as the efficient herbicide treatments are few. Consequently, various departments of the Rhône-Alpes region set up eradication programs for common ragweed. The species is distri-buted over a large range of ecological environments (road margins, embankments, river beds) and does not seem to be dependent on soil properties. Its ability to occupy different environments varies with the geographic location. Common ragweed was cultivated in botanical gardens during the XVIIIth century but seems to have arrived in France in seed lots during the XIXth century. It therefore began its « invasion » as a crop weed. Because of its late emergence date (late March), common ragweed is most frequently found in spring crops as well as during the inter-crop season. Its « natural » dispersal mechanisms are rudimentary; its seeds are probably dispersed mostly during the transport of material (soil, gravel, compost…), irrigation and especially via harvest combines. The development history of this species in France is scarcely known. The examination of herbarium collections helped to partially reconstruct the history of the species. According to the first results, the species arrived in several locations and at different dates in France. However, common ragweed spread most successfully in the Lyons region because of reasons still unknown.
2005-01-01T00:00:00ZÉmergence du système immunitaire adaptatif : Hypothèses en présence
http://hdl.handle.net/10608/5457
Émergence du système immunitaire adaptatif : Hypothèses en présence
Bleyzac, Pierre; Exbrayat, Jean-Marie; Fellah, Julien S.
Le système immunitaire adaptatif se rencontre exclusivement chez les vertébrés à mâchoire (les gnathostomes). Il pourrait trouver son origine dans le système immunitaire inné des invertébrés ou, de façon plus proche, des agnathes (vertébrés sans mâchoire). Cette transition, brutale, reste encore énigmatique et source de nombreuses spéculations. Parallèlement, le tissu lymphoïde associé au tube digestif, ou GALT (gut associated lymphoïd tissu), semble jouer un rôle essentiel dans le développement de cette réponse immune à mémoire. Les gnathostomes arborent ainsi des défenses innées ancestrales et adaptatives dont l’acquisition sera discutée dans cet article. Les conséquences de l’intégration dans le génome des gènes rag1 et rag2 (recombination activating genes) seront également débattues.; The adaptive immune system (AIS) appears exclusively at the vertebrate ones with jaw. In parallel, the lymphoid tissu associated with the digestive tract, or GALT (gut associated lymphoïd tissu), seems to play an essential part in the development of this response immune with memory. That one could find its origin in the innate immune system of the invertebrates and closer the cyclostomes (vertebrates without jaws). But the transition is brutal since the chondrychtyens (lines, sharks) do have the AIS but the cyclostomes not. Moreover, it is still enigmatic and source of speculations. The gnathostomes (vertebrate with jaw) raise ancestral and adaptive innate defences of which acquisition will be discussed here. We will also discuss the consequences of integration in the genome by rag1 and rag2 genes (recombination activating genes).
2005-01-01T00:00:00ZL’affaire Lyssenko, une éclipse de la raison
http://hdl.handle.net/10608/5455
L’affaire Lyssenko, une éclipse de la raison
Gratzer, Walter
L’influence néfaste de Trofim Lyssenko (1898- 1976) domina la biologie dans l’empire soviétique durant le règne de Staline. Lyssenko assura son succès en promettant de sauver l’agriculture soviétique de la catastrophe où elle se trouvait à la suite de la politique désastreuse de collectivisation et d’une succession de mauvaises récoltes. Lyssenko affirmait avoir mis au point des méthodes permettant d’imposer des caractères héréditaires voulus à des plantes, et même de transformer à volonté une espèce en une autre. Il dénonçait la « génétique bourgeoise » comme une imposture et finit par étouffer tout débat scientifique et toute opposition en faisant arrêter ou exécuter nombre de scientifiques éminents. Les théories absurdes de Lyssenko contaminèrent les milieux scientifiques en Europe de l’ouest et furent saluées par beaucoup d’intellectuels communistes, notamment en France. Le phénomène Lyssenko est un exemple extrême de la perversion de la science par l’idéologie, souvent avec l’assentiment de la communauté scientifique. Est-il aussi certain que ce type d’événement ne puisse arriver aujourd’hui ?; Trofim Lysenko was a Ukrainian peasant whose malign influence dominated biology in the Soviet Union and its imperium through most of Stalin’s reign. Lysenko owed his ascendancy to repeated promises that he would rescue Soviet agriculture from the catastrophic state into which it had sunk, following Stalin’s disastrous policy of collectivisation of the farms, and a succession of bad harvests. He claimed to have devised methods of imposing desirable hereditary characteristics on plants, and even of converting one species into another at will. He noisily denounced modern genetics as a bourgeois imposture, a view that resonated well with Marxist doctrine. As Lysenko’s power grew he was able to smother scientific debate, and to crush all opposition through the arrest and often execution of many leading scientists. Lysenko’s preposterous theories became the accepted orthodoxy in the academies and universities of Eastern Europe, and were greeted with enthusiasm by many Communist intellectuals in the West, not least in France. The Lysenko phenomenon is the most extreme, but by no means the only example of the perversion of science by ideology, often with the acquiescence of the scientific community. Nor can we be confident that nothing of the kind could happen today.
2005-01-01T00:00:00Z