Evaporation retardation by monolayers: another mechanism

The effects on evaporation rates of the suppression of small waves by monolayers, which heretofore have been neglected, are considered to be a major mechanism for retarding evaporation under wind.     

Regeneration of the amputated amphibian limb: retardation by hemicholinium-3

Doses of hemicholinium-3 which partially paralyze the larval salamander profoundly retarded regeneration of the amputated hind limb. The drug also reduced the vascularity and mitotic index of the regenerating tissue. After withdrawal of the drug the rate of regeneration returned to normal. Atropine, in a daily dose of 40 milligrams per kilogram of body weight, did not retard growth. These findings suggest that in the salamander acetylcholine may mediate neurotrophic activity.     

Brain catechol synthesis: control by train tyrosine concentration

Brain catechol synthesis was estimated by measuring the rate at which brain dopa levels rose following decarboxylase inhibition. Dopa accumulation was accelerated by tyrosine administration, and decreased by treatments that lowered brain tyrosine concentrations (for example, intraperitoneal tryptophan, leucine, or parachlorophenylalanine). A low dose of phenylalanine elevated brain tyrosine without accelerating dopa synthesis. Our findings raise the possibility that nutritional and endocrine factors might influence brain catecholamine synthesis by controlling the availability of tyrosine.     

Familial mental retardation: a continuing dilemma

The heterogeneous nature of mental retardation, as well as certain common practices of workers in the area, has resulted in a variety of conceptual am biguities. Considerable order could be brought to the area if, instead of viewing all retardates as a homogeneous group arbitrarily defined by some I.Q. score, workers would clearly distinguish between the group of retardates known to suffer from some organic defect and the larger group of retardates referred to as familial retardates. It is the etiology of familial retardation that currently constitutes the greatest mystery. A number of authorities have emphasized the need for employing recent polygenic models of inheritance in an effort to understand the familial retardate. While appreciating the importance of environment in affecting the distribution determined by genetic inheritance, these workers have argued that familial retardates are not essentially different from individuals of greater intellect, but represent, rather, the lower portion of the intellectual curve which reflects normal intellectual variability. As emphasized by the two-group approach, retardates with known physiological or organic defect are viewed as presenting a quite different etiological problem. The familial retardate, on the other hand, is seen as a perfectly normal expression of the population gene pool, of slower and more limited intellectual development than the individual of average intellect. This view generates the proposition that retardates and normals at the same general cognitive level-that is, of the same mental age-are similar in respect to their cognitive functioning. However, such a proposition runs headlong into findings that retardates and normals of the same mental age often differ in performance. Such findings have bolstered what is currently the most popular theoretical approach to retarded functioning-namely, the view that all retardates suffer from some specific defect which inheres in mental retardation and thus makes the retardate immutably "different" from normals, even when the general level of intellectual development is controlled. While these defect or difference approaches, as exemplified in the work of Luria, Spitz, Ellis, and Lewin and Kounin, dominate the area of mental retardation, the indirect, and therefore equivocal, nature of the evidence of these workers has generated considerable controversy. In contrast to this approach, the general developmental position has emphasized systematic evaluation of the role of experiential, motivational, and personality factors. As a central thesis, this position asserts that performance on experimental and real-life tasks is never the single inexorable product of the retardate's cognitive structure but, rather, reflects a wide variety of relatively nonintellective factors which greatly influence the general adequacy of performance. Thus, many of the reported behavioral differences between normals and retardates of the same mental age are seen as products of motivational and experiential differences between these groups, rather than as the result of any inherent cognitive deficiency in the retardates. Factors thought to be of particular importance in the behavior of the retardate are social deprivation and the positive- and negative-reaction tendencies to which such deprivation gives rise; the high number of failure experiences and the particular approach to problem-solving which they generate; and atypical reinforcer hierarchies. There is little question that we are witnessing a productive, exciting, and perhaps inevitably chaotic period in the history of man's concern with the problem of mental retardation. Even the disagreements that presently exist must be considered rather healthy phenomena. These disagreements will unquestionably generate new knowledge which, in the hands of practitioners, may become the vehicle through which the performance of children, regardless of intellectual level, may be improved.     

Brain cells in culture: morphological transformation by a protein

One type of elmbryonic rat brain cell having an epithelioid morphology in the monolayer culture can be transformed by brain extract into cells having extensive processes resembling mature astrocytes. The transforming factor is a protein with a molecular weight of 350,000. A partially purified sample showed that it is active at a concentration as low as 1 x 10(-8)M. The transforming actvity is high in adult brains but low in embryonic brains and tumors of the nervous systems.     

Brain edema: induction in cortical slices by polyunsaturated fatty acids

The presence of polyunsaturated and saturated fatty acids in leukocytic membranes prompted study of their possible role in the induction of brain edema. Polyunsaturated fatty acids including sodium arachidonate, sodium linoleate, sodium linolenate, and docasahexaenoic acids induced edma in slices of rat brain cortex. This cellular edema was specific, since neither saturated fatty acids nor a fatty acid containing a single double bond had such effect.     

Brain serotonin content: physiological regulation by plasma neutral amino acids

When plasma tryptophan is elevated by the injection of tryptophan or insulin, or by the consumption of carbohydrates, brain tryptophan and serotonin also rise; however, when even larger elevations of plasma tryptophan are produced by the ingestion of protein-containing diets, brain tryptophan and serotonin do not change. The main determinant of brain tryptophan and serotonin concentrations does not appear to be plasma tryptophan alone, but the ratio of this amino acid to other plasma neutral amino acids (that is, tyrosine, phenylalanine, leucine, isoleucine, and valine) that compete with it for uptake into the brain.     

橄榄苦苷对D-半乳糖致衰老小鼠衰老相关生化指标的影响

为了研究橄榄苦苷对D-半乳糖致衰老小鼠的抗衰老作用及其机制,将40只健康小鼠随机分成正常组、衰老模型组、橄榄苦苷组和维生素E组,采用D-半乳糖建立亚急性衰老小鼠模型,测定每组小鼠的脏器指数,比色法检测心、肝和脑组织中超氧化物歧化酶(SOD)活性、谷胱甘肽过氧化物酶(GSH-Px)活性、及丙二醛(MDA)含量,PCR-ELISA检测心、肝和脑组织端粒酶活性,ELISA检测小鼠血清中Ig G、Ig M和补体C3、C4含量,放射免疫法测定血清中IL-2含量。结果显示,与模型组比较,橄榄苦苷能增加小鼠脏器指数(P0.05);提高SOD、GSH-Px活性,降低MDA含量(P0.05,P0.01);提高心、肝和脑端粒酶活性、血清中Ig G、Ig M和补体C3、C4及IL-2的含量(P0.05,P0.01),上述衰老相关生化指标基本恢复到正常水平,且与维生素E的治疗结果无显著差异(P0.05)。表明橄榄苦苷能通过拮抗自由基损伤,增强衰老小鼠心、肝和脑组织端粒酶活性和机体免疫功能发挥抗衰老作用。     

Brain blood flow: alteration by prior exposure to a learned task

Chicks with the eyelids of one eye sutured were trained to discriminate between grains and pebbles. The learned experience was completely recognizable by the naive eye that had been occluded during training. When both eyes were opened after monocular training, the velocity of blood flow through paired left and right brain regions was identical. However, when chicks were reexposed to the discrimination situation, blood flow through the cerebral hemisphere associated with the naive eye was greater than that through the hemisphere associated with the trained eye.     

Brain histamine: rapid apparent turnover altered by restraint and cold stress

Histamine content of rat brain was lowered quickly by inhibitors of histidine decarboxylase, suggesting that a portion of brain histamine turns over rapidly. Restraint and exposure to cold also reduced brain histamine levels and markedly augmented its formation in the hypothalamus.     

Human aging: usual and successful

Research in aging has emphasized average age-related losses and neglected the substantial heterogeneity of older persons. The effects of the aging process itself have been exaggerated, and the modifying effects of diet, exercise, personal habits, and psychosocial factors underestimated. Within the category of normal aging, a distinction can be made between usual aging, in which extrinsic factors heighten the effects of aging alone, and successful aging, in which extrinsic factors play a neutral or positive role. Research on the risks associated with usual aging and strategies to modify them should help elucidate how a transition from usual to successful aging can be facilitated.