Minimising stimulator artefacts in electromagnetic flow signals

Simultaneous electrical stimulation of tissue with the measurement of blood flow using an electromagnetic flowmeter system almost invariably results in large flow measurement inaccuracies. These inaccuracies are because the electrical energy from stimulating artefacts is amplified along with the flow signals. The paper describes the building and use of an inexpensive circuit to remove stimulation artefacts from electromagnetic flow measurements.     

Evolution of neurotransmitter receptor systems

The presence of hormones, neurotransmitters, their receptors and biosynthetic and degradative enzymes is clearly not only associated with the present and the recent past but with the past several hundred million years. Evidence is mounting which indicates substantial conservation of protein structure and function of these receptors and enzymes over these tremendous periods of time. These findings indicate that the evolution and development of the nervous system was not dependent upon the formation of new or better transmitter substances, receptor proteins, transducers and effector proteins but involved better utilization of these highly developed elements in creating advanced and refined circuitry. This is not a new concept; it is one that is now substantiated by increasingly sophisticated studies. In a 1953 article discussing chemical aspects of evolution (Danielli, 1953) Danielli quotes Medawar, "... endocrine evolution is not an evolution of hormones but an evolution of the uses to which they are put; an evolution not, to put it crudely, of chemical formulae but of reactivities, reaction patterns and tissue competences." To also quote Danielli, "In terms of comparative biochemistry, one must ask to what extent the evolution of these reactivities, reaction patterns and competences is conditional upon the evolution of methods of synthesis of new proteins, etc., and to what extent the proteins, etc., are always within the synthetic competence of an organism. In the latter case evolution is the history of changing uses of molecules, and not of changing synthetic abilities." (Danielli, 1953). Figure 4 outlines a phylogenetic tree together with an indication of where evidence exists for both the enzymes that determine the biosynthesis and metabolism of the cholinergic and adrenergic transmitters and their specific cholinergic and adrenergic receptors. This figure illustrates a number of important points. For example, the evidence appears to show that the transmitters and their associated enzymes existed for a substantial period before their respective receptor proteins. While the transmitters and enzymes appear to exist in single cellular organisms, there is no solid evidence for the presence of adrenergic or cholinergic receptors until multicellular organisms where the receptors appear to be clearly associated with specific cellular and neuronal communication (Fig. 4). One can only speculate as to the possible role for acetylcholine and the catecholamine in single cell organisms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Loss of image quality in photobleaching during microscopic imaging of fluorescent probes bound to chromatin

Prolonged excitation of fluorescent probes leads eventually to loss of their capacity to emit light. A decrease in the number of detected photons reduces subsequently the resolving power of a fluorescence microscope. Adverse effects of fluorescence intensity loss on the quality of microscopic images of biological specimens have been recognized, but not determined quantitatively. We propose three human-independent methods of quality determination. These techniques require no reference images and are based on calculation of the actual resolution distance, information entropy, and signal-to-noise ratio (SNR). We apply the three measures to study the effect of photobleaching in cell nuclei stained with propidium iodide (PI) and chromomycin A3 (CA3) and imaged with fluorescence confocal microscopy. We conclude that the relative loss of image quality is smaller than the corresponding decrease in fluorescence intensity. Furthermore, the extent of quality loss is related to the optical properties of the imaging system and the noise characteristics of the detector. We discuss the importance of these findings for optimal registration and compression of biological images.     

Autosome and Sex Chromosome Diversity Among the African Pygmy Mice, Subgenus Nannomys (Murinae; Mus)

The African pygmy mice, subgenus Nannomys, constitute the most speciose lineage of the genus Mus with 19 recognized species. Although morphologically very similar, they exhibit considerable chromosomal diversity which is here confirmed and extended by the G-banding analysis of 65 mice from West and South Africa. On the basis of their karyotype and distribution area, the specimens were assigned to at least five species. Extensive differentiation both within and between species was observed that involved almost exclusively Robertsonian translocations, 23 of which are newly described. Two of the rearrangements were sex chromosome-autosome translocations, associated in some cases with partial deletions of the X or Y chromosomes. Several authors have predicted that the highly deleterious effect of this rearrangement would be reduced if the sex and autosomal segments were insulated by a block of centromeric heterochromatin. The C-banding analyses performed showed that among the species carrying X-autosome translocations, one followed the expected pattern, while the other did not. In this case, functional isolation of the sex and autosome compartments must involve other repetitive sequences or genomic traits that require further molecular characterization. Such studies will provide insight into the causes and consequences of the high diversity of sex chromosome rearrangements in this subgenus.     

Examination of the Short-Term Efficacy of a Parent-Based Intervention to Prevent Skin Cancer

The research evaluated an intervention strategy designed to prevent skin cancer in young adolescents. The intervention used parents as change agents to effectively communicate the risks of skin cancer and encourage their children to avoid high-risk sun-related behaviors while increasing positive sun-safe behaviors. Three hundred and forty parents in two regions of the United States were educated about the dangers of risky sun behaviors and how to convey information about skin cancer prevention to their children. Parents were then encouraged to talk with their children about these issues over a 1-month period prior to the onset of summer. Following this time period, children whose parents received and implemented the intervention materials were compared with a control sample of 129 children. These two groups were matched on age, gender, and school on number of sunburns and sunburn severity, attitudes and beliefs, and sunbathing behavior. Children in the treatment condition differed significantly from controls in the predicted directions on all outcome variables. The findings are discussed in terms of reducing skin cancer risk behaviors of children via parent-based intervention approaches.     

Familial pericentric inversion of chromosome 8

Eight children from seven presumably unrelated families were identified independently as having an unbalanced recombinant chromosome resulting in the presence of extra material on the short arm of a chromosome 8. Parental chromosomes were analyzed, and one member of each couple (four fathers and three mothers) was found to carry a pericentric inversion of a chromosome 8 [inv(8)(p23q22)]. The propositi had an unbalanced recombinant chromosome [rec(8),dup q,inv(8)(p23q22)]. The affected infants all had developmental delay, congenital heart disease, and unusual appearance. A common origin of the pericentric inversion was suggested because of geographic location and Mexican--American ancestry of the seven families.