Nipping the Cambrian "explosion" in the bud?

In recent years, two schools of thought have emerged with regard to the Cambrian "explosion". One argues that it was very quick, with phyla tumbling into existence in a virtual geological instant. The other view has a more relaxed temporal perspective. It looks to slow aeons of cryptic metazoan history, which led to a final breakthrough in the Cambrian, not in evolution but of fossilization potential. Yet both views have serious difficulties. Now, in a recent issue of Biological Reviews, Graham Budd and S?ren Jensen(1) argue for a third way. In an intriguing blend of functional morphology, the fossil record and cladistic thinking, they suggest that the assembly of metazoan bodyplans took place in a surprisingly straightforward manner.     

"Resonances" in the dielectric absorption of DNA?

An attempt was made to confirm previous reports of resonant-like dielectric absorption of plasmid DNA in aqueous solutions at 1-10 GHz. The dielectric properties of the sample were measured using an automatic network analyzer with two different techniques. One technique used an open-ended coaxial probe immersed in the sample; the other employed a coaxial transmission line. No resonances were observed that could be attributed to the sample; however, resonance-type artifacts were prominent in the probe measurements. The coaxial line technique appears to be less susceptible to such artifacts. We note two important sources of error in the calibration of the automatic network analyzer using the probe technique.     

Is there anything "autonomous" in the nervous system?

The terms "autonomous" or "vegetative" are currently used to identify one part of the nervous system composed of sympathetic, parasympathetic, and gastrointestinal divisions. However, the concepts that are under the literal meaning of these words can lead to misconceptions about the actual nervous organization. Some clear-cut examples indicate that no element shows "autonomy" in an integrated body. Nor are they solely "passive" or generated "without mental elaboration." In addition, to be "not consciously controlled" is not a unique attribute of these components. Another term that could be proposed is "homeostatic nervous system" for providing conditions to the execution of behaviors and maintenance of the internal milieu within normal ranges. But, not all homeostatic conditions are under the direct influence of these groups of neurons, and some situations clearly impose different ranges for some variables that are adaptative (or hazardous) in the tentative of successfully coping with challenging situations. Finally, the name "nervous system for visceral control" emerges as another possibility. Unfortunately, it is not only "viscera" that represent end targets for this specific innervation. Therefore, it is commented that no quite adequate term for the sympathetic, parasympathetic, and gastrointestinal divisions has already been coined. The basic condition for a new term is that it should clearly imply the whole integrated and collaborative functions that the components have in an indivisible organism, including the neuroendocrine, immunological, and respiratory systems. Until that, we can call these parts simply by their own names and avoid terms that are more "convenient" than appropriate.     

Disease associated cellular machinery in anaphylaxis – And the de novo paradigm shift

Anaphylaxis is a sudden immune reaction against an allergen that can potentially lead to Anaphylactic Shock (AS). This immune reaction is characterized by an increase in Immunoglobulin-E (IgE) type of antibodies that bind with FcεRI receptors on mast cells to release inflammatory mediators. Various intracellular signaling molecules downstream of IgE/ FcεRI axis play a potential role in cytokine, chemokine and eicosanoid secretion as well as degranulation of immune cells causing vasodilation, vascular permeability, and reduction of intravascular volume leading to cardiovascular collapse. Here, we discuss the cellular machinery of anaphylaxis and the de novo paradigm shift in the cellular aspects of AS.     

Fifty years of entomological publications in the Revista de Biología Tropical

Over its fifty year history nearly twenty percent of the papers published in the Revista de Biología Tropical have been about insects and arachnids. In the 1950's papers on arthropods of medical importance were dominant, in the 1960's there was a poliferation of papers on bees, and in more recent years the subjects have become increasingly diverse. In terms of nationality of contributing authors, the journal appears to have become increasingly international in later years.     

Caspase-8 in apoptosis: the beginning of "the end"?

Caspase-8 is a member of the cysteine proteases, which are implicated in apoptosis and cytokine processing. Like all caspases, caspase-8 is synthesized as an inactive single polypeptide chain zymogen procaspase and is activated by proteolytic cleavage, through either autoactivation after recruitment into a multimeric complex or trans-cleavage by other caspases. Thus, ligand binding-induced trimerization of death receptors results in recruitment of the receptor-specific adapter protein Fas-associated death domain (FADD), which then recruits caspase-8. Activated caspase-8 is known to propagate the apoptotic signal either by directly cleaving and activating downstream caspases or by cleaving the BH3 Bcl2-interacting protein, which leads to the release of cytochrome c from mitochondria, triggering activation of caspase-9 in a complex with dATP and Apaf-1. Activated caspase-9 then activates further "downstream caspases," including caspase-8. Knockout data indicate that caspase-8 is required for killing induced by the death receptors Fas, tumor necrosis factor receptor 1, and death receptor 3. Moreover, caspase-8-/- mice die in utero as a result of defective development of heart muscle and display fewer hematopoietic progenitor cells, suggesting that the FADD/caspase-8 pathway is absolutely required for growth and development of specific cell types.     

Thirty years of the "Asociación Española de Micología"

Since the foundation of the "Asociación Espa?ola de Micología" thirty years ago, we have consolidated the Spanish mycological community and also witnessed remarkable changes, not only in the Spanish society but in the scientific community as a whole. As it usually happens to human beings, during this time the "Asociación Espa?ola de Micología" has matured transforming itself into a solid scientific society. However, the "Asociación Espa?ola de Micología" will have to continue its transformation to adapt to new changes. This article shows the most relevant aspects in the history of the "Asociación Espa?ola de Micología" as well as new challenges that the society might face in the future.     

Is there "Metabolic" DNA in the Mouse Seminal Vesicle?

This study was designed to answer the question: Is H³-thymidine uptake by nuclei of the mouse seminal vesicle evidence for DNA synthesis and mitosis, or does it signify some "metabolic" function of DNA unrelated to chromosome duplication? Mice were given an intraperitoneal injection of H³-thymidine. Six hours later Feulgen squashes of the seminal vesicle epithelium were made and covered with autoradiographic stripping film. The silver grains above labeled nuclei were counted, and the Feulgen dye contents of these same nuclei were determined photometrically after removal of the grains from the emulsion. Unlabeled nuclei were also measured. The dye contents of non-radioactive nuclei form a unimodal distribution, indicating that polyploidy is absent from this tissue. The radioactive nuclei fall into two groups. In the first, the average dye content is the same as that of the cold nuclei (2C). In the second, the values range from 2C to 4C. In the 2C to 4C group the grain count is proportional to the dye content, showing that incorporation is correlated with synthesis. The radioactive 2C nuclei arose by mitosis during the course of the experiment. This is shown by the following facts: (1) They frequently occur in pairs. (2) They average smaller than unlabeled 2C nuclei. (3) Their average grain count is approximately half that of the 4C nuclei. (4) Labeled division figures are found. (5) A mitotic rate estimated from the number of labeled 2C nuclei accords reasonably well with one based on the number of observed mitoses. Since the incorporation of thymidine accompanies DNA synthesis and precedes mitosis, there is no reason to postulate a special "metabolic" DNA in this tissue.     

Role of de Vries in the rediscovery of Mendel's paper. II. Did de Vries really understand Mendel's paper?

In this paper, we discuss briefly three of the several lines of evidence that we believe demonstrate de Vries's lack of understanding of Mendel's paper. In our view, at least part of de Vries's failure of understanding derives from the fact that he appears to have viewed Mendel's paper as being mainly about the inheritance of characters that was his own interest. Therefore, he looked at it to see whether Mendel had found any laws of inheritance. Mendel had done his research for another purpose, to find the laws describing the formation of hybrids and the development of their offspring. Thus, de Vries started his examination of Mendel's paper with a very fundamental misunderstanding of what it was about.     

Has the "Equal Environments" assumption been tested in twin studies?

A recurring criticism of the twin method for quantifying genetic and environmental components of human differences is the necessity of the so-called "equal environments assumption" (EEA) (i.e., that monozygotic and dizygotic twins experience equally correlated environments). It has been proposed to test the EEA by stratifying twin correlations by indices of the amount of shared environment. However, relevant environments may also be influenced by genetic differences. We present a model for the role of genetic factors in niche selection by twins that may account for variation in indices of the shared twin environment (e.g., contact between members of twin pairs). Simulations reveal that stratification of twin correlations by amount of contact can yield spurious evidence of large shared environmental effects in some strata and even give false indications of genotype x environment interaction. The stratification approach to testing the equal environments assumption may be misleading and the results of such tests may actually be consistent with a simpler theory of the role of genetic factors in niche selection.     

Is "scopolamine-induced amnesia" in rats the result of state-dependent learning?

The effects of a single and repetitive administration of m-cholinoblocker scopolamine (Sc) to male rats on retention of step-through passive avoidance (PA) or active avoidance (AA) in a shuttle-box were compared. In case of PA Sc (1 mg/kg) was injected i.p. only 30 min before training, only 30 min before testing, or both before training and before testing. In case of AA Sc (0.5 mg/kg/day) was injected i.p. only 15 min before each training session or both before training and before testing (44 days after achievement of learning criterion). The PA and AA retention were impaired only in the experiments, where the drug was administered before training, but did not differ from control, when Sc was injected twice. The Sc-induced amnesia (like many other cases of memory deficits) is suggested to be a manifestation of state-dependent learning. Similarity between the brain state during memory consolidation and during the retention test is necessary for recollection.     

Can the Golgi form de novo?

Does the Golgi apparatus proliferate by adding new material to a permanent template, or do Golgi structures form de novo by a process of self-organization? Recent work suggests that the Golgi is capable of forming de novo.     

Koffka, Köhler, and the "crisis" in psychology

This paper examines the claims of the Gestalt psychologists that there was a crisis in experimental psychology ca. 1900, which arose because the prevailing sensory atomism excluded meaning from among psychological phenomena. The Gestaltists claim that a primary motivation of their movement was to show, against the speculative psychologists and philosophers and Verstehen historians, that natural scientific psychology can handle meaning. Purportedly, they revealed this motivation in their initial German-language presentations but in English emphasized their scientific accomplishments for an American audience. The paper finds that: there was a recognized crisis in the new experimental psychology ca. 1900 pertaining especially to sensory atomism; that the Gestaltists responded to the crisis with new experimental findings and theoretical concepts (Gestalten) that challenged atomism; in both languages, they raised problems of meaning and discussed the contest with speculative psychology and philosophy only after presenting their scientific case; that they introduced phenomenological observations on meaning and perceptual organization into their psychology but did not develop a theory of meaning or solve philosophical problems; that they argued "philosophically," that is, using abstract, conceptual arguments; and that this aspect of their cognitive style was not received well by some prominent members of their American audience.