PubMed · 5763490
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J R Gentile. 1969-01-03. Learning environment.. https://doi.org/10.1126/science.163.3862.18
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Obesity has increased at an alarming rate in recent years and is now a worldwide public health problem. In addition to suffering poor health and an increased risk of illnesses such as hypertension and heart disease, obese people are often stigmatized socially. But major advances have now been made in identifying the components of the homeostatic system that regulates body weight, including several of the genes responsible for animal and human obesity. A key element of the physiological system is the hormone leptin, which acts on nerve cells in the brain (and elsewhere) to regulate food intake and body weight. The identification of additional molecules that comprise this homeostatic system will provide further insights into the molecular basis of obesity, and possibilities for new treatments.
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In plantlets of Bidens pilosa L., under severely limiting environmental conditions the growth of the buds at the axil of the cotyledons (cotyledonary buds) is asymmetric (i.e. one of the buds starts growing before the other one), this asymmetry being oriented by the pricking of one of the cotyledons (i.e. pricking one cotyledon increases the probability that the bud at the axil of the other cotyledon be the first to start to grow). As long as the plant apex (i.e. the terminal bud) is present, the growth of the cotyledonary buds is inhibited (apical dominance), but the souvenir of the asymmetric message caused by sub-optimal environmental conditions and the orientation given by the cotyledon pricking is always present in the plant and can be revealed by removing the apex. Depending on the conditions for removing the plant apex and/or on the application of a variety of symmetrical treatments (e.g. thermal treatment, symmetrical pricking treatments, etc.) the stored asymmetry will either take effect (the bud at the axil of the non-pricked cotyledon will be the first to start to grow more often than the other one) or not (both buds will have equal chance to be the first to start to grow). This has been termed 'recalling' the stored asymmetry. By combining several successive symmetrical treatments, it is possible to reversibly switch on and off the recall function several times. This recall of the stored plant-asymmetry is analogous to the evocation function of a memory system. In this paper, we will present first a discrete logical version of the observed interaction structure between the main components of the bud growth system, then a continuous differential version, taking into account the main features of the observed experimental reality and trying to explain this phenomenology. The interaction structure of both the discrete and the continuous models presents similar positive and negative feedback circuits, necessary condition for observing multistationarity and stability.