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Biomedical subjects

J Adam

Publications and source records attributed to J Adam.

At least 19 recordsLinked to original sources
PubMed1999

The Gap effect for spatially oriented responses.

The gap effect refers to the finding that a temporal gap between fixation point offset and target onset typically results in shorter saccadic latencies than if the fixation point remains on. Recently, this gap effect was found for aimed hand movements as well as saccadic eye movements, but not for simple keypress responses. In order to examine the hypothesis that the hand gap effect occurs for different types of spatially oriented movements, two experiments were conducted. In the first experiment, subjects produced spatially oriented responses to a peripheral target and the target location was known in advance of the targets presentation. This spatially oriented detection task yielded gap effects for both eye and hand responses. In the second experiment, the duration of the temporal gap was varied between 0-400 ms. The duration of the temporal gap had similar effects on the magnitudes of both the eye and hand gap effects, suggesting that a common mechanism may underlie the gap effect for saccadic and manual pointing movements. Overall, the results of the present experiments confirm the finding of a gap effect for spatially oriented hand movements and suggest that this effect may be related to the functioning of the superior colliculus.

Fixation, Ocular↗
PubMed1999

Energy restriction modulates the development of advanced preneoplastic lesions depending on the level of fat in the diet.

Our objective was to investigate the ability of preneoplastic colonic lesions at different stages of development to respond to the growth-retarding effects of energy restriction (ER). Male Fischer 344 rats were given three injections of azoxymethane (15 mg/kg s.c.) and fed a high-fat corn oil diet for 16 weeks. This duration allowed aberrant crypt foci (ACF) to develop and acquire different growth states. ACF growth was assessed by enumerating the number of crypts per focus. At Week 16, 10 animals were killed and their colons were enumerated for ACF (baseline). The remaining animals were then allocated to four dietary groups: high-fat (23% wt/wt), low-fat (5% wt/wt), high-fat energy-restricted (HFER), or low-fat energy-restricted (LFER). After the animals were fed the experimental diets for six weeks, ER decreased the total number of ACF regardless of the level of fat. At Week 12, the LFER diet retarded the appearance of advanced ACF, but this was not the case for the HFER diet. Consequently, the level of fat was identified as the significant variable in affecting the number of ACF with different crypt multiplicity. The animals fed the LFER diet had the fewest tumors and microadenomas per rat. The HFER diet was ineffective in modulating tumor outcome. To our knowledge, these findings are the first to suggest that ER modulated the development of advanced ACF and colonic tumors depending on the level of fat in the diet.

Analysis of Variance↗
PubMed1998

Galactosphingolipids and axono-glial interaction in myelin of the central nervous system.

The myelin of central and peripheral nervous system of UDP-galactose-ceramide galactosyltransferase deficient mice (cgt-/-) is completely depleted of its major lipid constituents, galactocerebrosides and sulfatides. The deficiency of these glycolipids affects the biophysical properties of the myelin sheath and causes the loss of the rapid saltatory conduction velocity of myelinated axons. With the onset of myelination, null mutant cgt-/- mice develop fatal neurological defects. CNS and PNS analysis of cgt-/- mice revealed (1) hypomyelination of axons of the spinal cord and optic nerves, but no apoptosis of oligodendrocytes, (2) redundant myelin in younger mice leading to vacuolated nerve fibers in cgt-/- mice, (3) the occurrence of multiple myelinated CNS axons, and (4) severely distorted lateral loops in CNS paranodes. The loss of saltatory conduction is not associated with a randomization of voltage-gated sodium channels in the axolemma of PNS fibers. We conclude that cerebrosides (GalC) and sulfatides (sGalC) play a major role in CNS axono-glial interaction. A close axono-glial contact is not a prerequisite for the spiraling and compaction process of myelin. Axonal sodium channels remain clustered at the nodes of Ranvier independent of the change in the physical properties of myelin membrane devoid of galactosphingolipids. Increased intracellular concentrations of free ceramides do not trigger apoptosis of oligodendrocytes.

Animals↗
PubMed1998

Diverse effect of fish oil on the growth of aberrant crypt foci and tumor multiplicity in F344 rats.

The main objective of the present study was to investigate the amenability of preneoplastic lesions at different developmental stages to the growth-regulatory effects of two types of dietary lipids. F344 male rats were given three injections of azoxymethane (15 mg/kg) and fed a low-fat corn oil diet for 12 weeks to allow preneoplastic lesions or aberrant crypt foci (ACF) to develop. At this time, the colons of rats had a large number of ACF exhibiting various crypt multiplicities (number of crypts/focus). These rats were then randomly allocated to three dietary groups: high-fat corn oil (HFC), high-fat fish oil (HFF), and low-fat corn oil (LFC). The number and crypt multiplicity of ACF and adenomatous lesions were determined after 6 and 12 weeks of dietary intervention. After six weeks, the HFF group had the highest number of ACF of all crypt multiplicities and microadenomas among the dietary groups. After 12 weeks of feeding, the HFC diet increased the number of tumors without significantly changing the number of ACF. In contrast, the HFF diet increased significantly (p < 0.05) the number of ACF with higher crypt multiplicity without affecting the number of tumors. Consequently, the total number of tumors per group in decreasing order was as follows: HFC > LFC > HFF. These findings suggest that dietary lipids varying in fatty acid composition, namely corn oil and fish oil, exerted a growth-enhancing and -inhibiting effect, respectively, on different preneoplastic stages in a selective and differential manner. Most notably, transition of microscopic preneoplastic lesions to macroscopic lesions (microadenomas or adenomas) appears to be retarded by an HFF diet.

Animals↗
PubMed1998

Sun-protective clothing.

BACKGROUND: Topical sunscreens have been used for many years on exposed areas (i.e., hands, face) to protect the skin from the damaging effects of ultraviolet radiation. Most people do not use sunscreens on their bodies when they are wearing clothes. An average weight cotton T shirt gives only a sun protection factor (SPF) of 7. This is inadequate protection when out of doors. Therefore, clothing with adequate sunscreening properties should be worn. OBJECTIVE: The purpose of this study is to identify the factors in clothing fabrics that contribute to or detract from blocking ultraviolet radiation and to recommend criteria for establishing a standard for sunprotective clothing. METHOD: The study involves a review of the dermatologic and textile literature to identify various factors in fabrics that contribute to blocking ultraviolet radiation through textiles. CONCLUSION: For fabrics, the term ultraviolet protection factor (UPF) is used as the measure of ultraviolet radiation penetration through the fabric. The UPF of a fabric depends upon fiber content and weave, fabric colour, finishing processes, and the presence of additives. The performance of a fabric depends upon stretching, shrinkage, hydration, laundering, and wear of the fabric over time. Based upon these criteria the minimum CDA standard UPF for clothing should be 40 to 50+.

Clothing↗
PubMed1998

Cell fate choices and the expression of Notch, Delta and Serrate homologues in the chick inner ear: parallels with Drosophila sense-organ development.

The sensory patches in the vertebrate inner ear are similar in function to the mechanosensory bristles of a fly, and consist of a similar set of cell types. If they are truly homologous structures, they should also develop by similar mechanisms. We examine the genesis of the neurons, hair cells and supporting cells that form the sensory patches in the inner ear of the chick. These all arise from the otic epithelium, and are produced normally even in otic epithelium cultured in isolation, confirming that their production is governed by mechanisms intrinsic to the epithelium. First, the neuronal sublineage becomes separate from the epithelial: between E2 and E3.5, neuroblasts delaminate from the otocyst. The neuroblasts then give rise to a mixture of neurons and neuroblasts, while the sensory epithelial cells diversify to form a mixture of hair cells and supporting cells. The epithelial patches where this occurs are marked from an early stage by uniform and maintained expression of the Notch ligand Serrate1. The Notch ligand Delta1 is also expressed, but transiently and in scattered cells: it is seen both early, during neuroblast segregation, where it appears to be in the nascent neuroblasts, and again later, in the ganglion and in differentiating sensory patches, where it appears to be in the nascent hair cells, disappearing as they mature. Delta-Notch-mediated lateral inhibition may thus act at each developmental branchpoint to drive neighbouring cells along different developmental pathways. Our findings indicate that the sensory patches of the vertebrate inner ear and the sensory bristles of a fly are generated by minor variations of the same basic developmental program, in which cell diversification driven by Delta-Notch and/or Serrate-Notch signalling plays a central part.

Animals↗
PubMed1997

Maintenance of neuroepithelial progenitor cells by Delta-Notch signalling in the embryonic chick retina.

BACKGROUND: Neurons of the vertebrate central nervous system (CNS) are generated sequentially over a prolonged period from dividing neuroepithelial progenitor cells. Some cells in the progenitor cell population continue to proliferate while others stop dividing and differentiate as neurons. The mechanism that maintains the balance between these two behaviours is not known, although previous work has implicated Delta-Notch signalling in the process. RESULTS: In normal development, the proliferative layer of the neuroepithelium includes both nascent neurons that transiently express Delta-1 (Dl1), and progenitor cells that do not. Using retrovirus-mediated gene misexpression in the embryonic chick retina, we show that where progenitor cells are exposed to Dl1 signalling, they are prevented from embarking on neuronal differentiation. A converse effect is seen in cells expressing a dominant-negative form of Dl1, Dl1(dn), which we show renders expressing cells deaf to inhibitory signals from their neighbours. In a multicellular patch of neuroepithelium expressing Dl1(dn), essentially all progenitors stop dividing and differentiate prematurely as neurons, which can be of diverse types. Thus, Delta-Notch signalling controls a cell's choice between remaining as a progenitor and differentiating as a neuron. CONCLUSIONS: Nascent retinal neurons, by expressing Dl1, deliver lateral inhibition to neighbouring progenitors; this signal is essential to prevent progenitors from entering the neuronal differentiation pathway. Lateral inhibition serves the key function of maintaining a balanced mixture of dividing progenitors and differentiating progeny. We propose that the same mechanism operates throughout the vertebrate CNS, enabling large numbers of neurons to be produced sequentially and adopt different characters in response to a variety of signals. A similar mechanism of lateral inhibition, mediated by Delta and Notch proteins, may regulate stem-cell function in other tissues.

Animals↗
PubMed1995

Expression of a Delta homologue in prospective neurons in the chick.

The product of the Delta gene, acting as ligand, and that of the Notch gene, acting as receptor, are key components in a lateral-inhibition signalling pathway that regulates the detailed patterning of many different tissues in Drosophila. During neurogenesis in particular, neural precursors, by expressing Delta, inhibit neighbouring Notch-expressing cells from becoming committed to a neural fate. Vertebrates are known to have several Notch genes, but their functions are unclear and their ligands hitherto unidentified. Here we identify and describe a chick Delta homologue, C-Delta-1. We show that C-Delta-1 is expressed in prospective neurons during neurogenesis, as new cells are being born and their fates decided. Our data from the chick, combined with parallel evidence from Xenopus, suggest that both the Delta/Notch signalling mechanism and its role in neurogenesis have been conserved in vertebrates.

Amino Acid Sequence↗
PubMed1993

[The effect of middle-molecular ninhydrin-positive substances isolated from the rat myocardium on rat serum arylamidase activity after administration of ethanol].

Protein-free extract from the myocardium of control rats and the majority of its fractions were found to stimulate arylamidase activity. Ethanol administration to rats for 1, 3 or 7 weeks increased the amount of fractions which displayed an inhibitory effect. The observed changes were probably due to enhanced protein degradation and/or to decreased amino acid incorporation into proteins following ethanol administration. (Tab. 4, Fig. 2, Ref. 19.).

Aminopeptidases↗
PubMed1993

[The effect of ethanol on the occurrence of peptides with antibacterial effects in the rat myocardium]].

The effect of 7% ethanol on the peptide content in the myocardium was studied during prolonged exposition. The protein-free extract from the myocardium of controls as well as experimental groups following 1-8 weeks ethanol administration contained peptides with antibacterial activity. Long-term ethanol administration resulted in changes in physico-chemical properties of peptides both compared with controls and also among the experimental groups mutually. The changes were manifested by differences in the elution profiles following gel chromatography and RF values after electrophoresis or by different amino acid composition. The results are compared with the influence of peptides on the growth of bacterial cultures S. aureus. Ethanol administration induced diminution of the diameter of the inhibitory zones. This effect was most marked in the group fed with ethanol for 3 and 8 weeks. (Fig. 5, Ref. 17.)

Amino Acids↗
PubMed1992

Effects of discrimination training on responding during a compound conditioned stimulus.

Four experiments examined responding in the presence of a triple-element compound ABC after discrimination training in which 2 compounds, AB and BC, signaled the delivery of food and 1 element alone, B, signaled the absence of food. In Experiments 1 and 2, using rats, responding during ABC was more vigorous than in a control group for which A and C but not B had been individually paired with food. This finding was replicated in Experiment 3, which used pigeons, and in Experiment 4, where all 3 stimuli of the control condition were individually paired with food. The results are more consistent with a configural than with an elemental theory of learning.

Animals↗
PubMed1992

The survival game.

This paper describes a flexible and enjoyable learning game and summarizes our experiences of using it (including the medical students' own evaluation of the game). The description is sufficiently detailed to encourage readers to reproduce and adapt the game to fit their own requirements.

England↗