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Biomedical subjects

E Nevo

Publications and source records attributed to E Nevo.

At least 109 records · Page 6Linked to original sources
PubMed1997

Brain structure volumes in the mole rat, Spalax ehrenbergi (Spalacidae, Rodentia) in comparison to the rat and subterrestrial insectivores.

Natural blindness and a subterranean, digging mode of life demand peculiar adaptations of the central nervous system in the mole rat Spalax ehrenbergi, which are the focus of this quantitative investigation. Volumes of 25 brain structures in Spalax were evaluated allometrically, using the least encephalized mammalian species, the Madagassian hedgehog-like tenrecs (Tenrecinae) as a reference base, and their sizes compared with those of the rat (as a more generalized representative of rodents) and of some subterranean Insectivora. The allometric approach reveals that Spalax has a larger brain than tenrecs and the rat. Within the brain, the neocortex and diencephalon are well developed, an observation also made in other mammalian species with a relatively high encephalization. An unique feature in Spalax is the enlargement of motor structures of the brain, such as the cerebellum (and cerebellar nuclei), and the striatum. Most conspicuous is the large size of the nucleus motorius nervi trigemini, reflecting the importance of masticatory muscles for the special digging technique, which demand an intense use of the teeth for loosening the soil.

Animals↗
PubMed1997

Cobalt 60 radiation and growth of eleven species of micro-fungi from Evolution Canyon, Lower Nahal Oren, Israel.

Eleven micro-fungal species isolated from both the north facing slope (NFS) and the south facing slope (SFS) of Evolution Canyon, Lower Nahal Oren, Israel, were examined for growth rates before and after exposure to 60Co irradiation. Species of Alternaria, Aspergillus, Humicola, Oidiodendron, and Staphylotrichum from SFS grew faster than the NFS isolates while Fusarium, Sordaria, and Stachybotrys grew at greater rates from the NFS than from the SFS. Mucor and Ulocladium isolates grew at the same rate from both SFS and NFS. The eleven isolates from each slope were next subjected to 60Co irradiation. At 40,000 rads exposure, Alternaria, Fusarium, and Stachybotrys grew more rapidly when isolated from the NFS, while Humicola and Staphylotrichum grew at a faster rate when isolated from the SFS. Aspergillus, Mucor, Sordaria, and Ulocladium from both the NFS and the SFS had relatively the same growth rate at 40,000 rads exposure. At 400,000 rads exposure, growth rates remained much the same for both the N and S exposed isolates as they were at 40,000 rads. Above 10(6) rads, growth ceased but recovery occurred at various times for individual isolates of the same species from opposing canyon slopes.

Alternaria↗
PubMed1996

Complex dynamics of multilocus systems subjected to cyclical selection.

Earlier we have shown that oscillations with a long period ("supercycles") may arise in two-locus systems experiencing cyclical selection with a short period. However, this mode of complex limiting behavior appeared to be possible for narrow ranges of parameters. Here we demonstrate that a multilocus system subjected to stabilizing selection with cyclically moving optimum can generate ubiquitous complex limiting behavior including supercycles, T-cycles, and chaotic-like phenomena. This mode of multilocus dynamics far exceeds the potential attainable under ordinary selection models resulting in simple behavior. It may represent a novel evolutionary mechanism increasing genetic diversity over long-term time periods.

Biological Evolution↗
PubMed1996

Circadian rhythm and the per ACNGGN repeat in the mole rat, Spalax ehrenbergi.

Individual variability in circadian locomotor activity has recently discovered in the blind mole rat, Spalax ehrenbergi. An interesting association was found between different circadian types and two DNA fragments, 5.6 and 5.9 kb long, that contain the ACNGGN repeat sequence, homologous to a part of the period gene of Drosophila. Nine of 12 arrythmic animals showed the 5.6-kb band, while 13 of 17 circadian rhythmic animals had the 5.9-kb band. This repeat exists also in the brain RNA of the mole rat, apparently in higher quantities during the sleeping phase, suggesting that an unusual protein(s), composed of a poly-Thr-Gly segment, affects in circadian rhythm.

Animals↗
PubMed1996

Tethering affects the mechanics of coronary capillaries.

Coronary capillaries are extensively tethered to adjacent myocytes by collagen fibers. The influence of this tethering in the beating heart is studied by structural mechanics as applied to the specific morphology of the capillary-myocyte system. The results show considerable effects of the tethering collagen fibers on the capillary deformation, especially during systole and in the deeper myocardial layers. The tethering fibers prevent total systolic collapse, being taut during systole but partially slack during diastole, in agreement with reported observations. At the deeper wall layers, the systolic/diastolic differences in capillary cross-sectional area are predicted to be more pronounced: about 30 and 50% area reduction in arterial and venous ends, respectively, compared with 10 and 20% increase of area in the subepicardial vessels. These predictions comply well with published, experimental data. A parametric investigation shows a variable effect of the capillary-myocyte distance on the dynamics of the capillary area, while the stiffnesses of both the fibers and wall membrane, and the extent of transmural transmission of intramyocardial pressure, have both considerable quantitative effects. These effects are found to be region dependent and vary along the capillary length and from diastole to systole. The results indicate that capillary tethering to the myocardial tissue has significant effect on its mechanics. Tethering should, therefore, be considered in analyzing the dynamics of coronary flow.

Arterioles↗
PubMed1996

Seasonal changes in urinary odors and in responses to them by blind subterranean mole rats.

Breeding and nonbreeding season male and female mole rats from two chromosomal species of the Spalax ehrenbergi superspecies were tested in a tunnel T-maze to assess their responses to urine collected from breeding- and nonbreeding season male and female conspecific and heterospecific donors. The results indicate that S. ehrenbergi mole rat urine contains species-, sex-, and season-specific chemosensory cues and that male and female mole rats change their responses to these chemosensory cue depending upon the season. During the nonbreeding season, mole rats avoid conspecific and heterospecific urine of both sexes. In contrast, during the breeding season, mole rats do not avoid conspecific urine and males do not avoid heterospecific urine. These changes in responses to the chemosensory cues in urine are adaptive to their seasonal life underground because they could help the animals avoid aggressive encounters during the nonbreeding season and facilitate their approaching potential mates and competitors during the breeding season. The results suggest that chemical communication could play a role in social encounters, reproduction, and species isolation in the S. ehrenbergi superspecies.

Animals↗
PubMed1996

Variations in ribosomal DNA and mitochondrial DNA among chromosomal species of subterranean mole rats.

Restriction site variations in nuclear ribosomal DNA (rDNA) spacers and mitochondrial DNA (mtDNA) were examined in several populations of mole rats with variable numbers of chromosomes, which represented the two superspecies Spalax leucodon (2n = 38, 54, or 62) and Spalax ehrenbergi (2n = 52, 54, 58, or 60). Sequence divergence of rDNA spacers between the members of the superspecies was approximately 8%, while the variation within each superspecies was 4% on average. The intrasuperspecies differentiation of rDNA spacers was generally associated with changes in the diploid number of chromosomes. However, substantial divergence (approximately 1.5%) was also detected among populations with the same diploid number of chromosomes. The sequence divergence of mtDNA among haplotypes of S. ehrenbergi was 10% or higher and among haplotypes of S. leucodon it was approximately 12%. By contrast, the range of sequence divergence between superspecies was 7.4%-12%. The large divergence of mtDNAs within each superspecies of mole rats may be explained by the preservation of ancient mtDNA polymorphisms.

Animals↗
PubMed1996

6-Sulphatoxymelatonin secretion in different locomotor activity types of the blind mole rat Spalax ehrenbergi.

6-Sulphatoxymelatonin (aMT6S) excretion was examined in the urine of rhythmic and arrhythmic blind subterranean mole rats (Spalax ehrenbergi) to test the correlation between melatonin secretion (as represented by aMT6S) and variability in circadian locomotor activity. Activity pattern was tested in four males, first for a week under short photoperiod [light:dark (LD) 10:14], followed by 10 days in constant darkness (DD). After several months the experiment was repeated under long photoperiod (LD 14:10), followed by DD conditions. Under LD conditions all animals exhibited aMT6S excretion during the dark phase, with a decline just before the onset of light. No correlation was found between activity pattern and melatonin secretion. The animal with the highest melatonin secretion both under LD and DD had an arrhythmic locomotor pattern. The results suggest that in mole rats melatonin secretion and circadian locomotor activity are controlled by two different mechanisms. There were large differences in the aMT6S levels among individuals, suggesting the importance of duration of melatonin secretion over amplitude for gonadal development and thermoregulatory changes. During summer, i.e., before the breeding season, the animals keep a more stable aMT6S secretion than in winter, and the amplitude of secretion is higher under DD vs. LD conditions.

Activity Cycles↗
PubMed1996

Effect of myocardial swelling on residual strain in the left ventricle of the rat.

Left ventricular (LV) residual strain in the unloaded state was shown previously to affect LV performance. The interrelationship between myocardial swelling and LV residual strain was studied, both experimentally and theoretically. Myocardial swelling was induced by retrograde perfusion of beating, nonworking, isolated rat hearts with perfusate of graded osmolarities (200-420 mosM). The opening angle (an index of residual strain), in radially cut equatorial cross-sectional slices, and their water content were measured in 40 arrested rat LV. Both water content and opening angle decreased significantly with osmolarity from 84.2 +/- 0.45% and 77.2 +/- 9.2 degrees at 200 mosM to 76.5 +/- 1.05% and 36.3 +/- 9.8 degrees at 420 mosM (P < 0.001, respectively). A morphologically based theoretical model was developed and yielded as swelling residual strain relationship, which agrees well with the data. Our results indicate that myocardial swelling is strongly related to LV residual strain, suggesting that swelling, through its effect on residual strain, can affect both LV function and its adaptation to varying loading conditions.

Animals↗
PubMed1996

Validation of carotid artery tonometry as a means of estimating augmentation index of ascending aortic pressure.

Our objective was to validate a carotid artery tonometry-derived augmentation index as a means to estimate augmentation index (AI) of ascending aortic pressure under various physiological conditions. A total of 66 patients (50 men, 16 women; mean age, 55 years; range, 21 to 78 years; 44 in Taiwan and 22 in the United States) undergoing diagnostic catheterization were studied. Arterial pressure contours were obtained simultaneously from the right common carotid artery by applanation tonometry with an external micromanometer-tipped probe and from the ascending aorta by a micromanometer-tipped catheter at baseline (n = 62), after handgrip (n = 36), or after sublingual nitroglycerin administration (n = 17). The AI (expressed as percentage values) was calculated as the ratio of amplitude of the pressure wave above its systolic shoulder to the total pulse pressure. The carotid AI was consistently lower than the aortic AI, but the two were highly correlated at baseline and after both handgrip and nitroglycerin. Mean +/- SD and correlation coefficients were baseline (14 +/- 16, 28(+) +/- 17, .77), handgrip (18 +/- 19, 32(+) +/- 15, .86), and nitroglycerin (7 +/- 12, 18(+) +/- 13, .52). In addition, after adjusting for age, sex, height, blood pressure, heart rate, and study site, the changes of both AIs from baseline values with handgrip or nitroglycerin were highly associated such that the aortic AI could be approximated from the carotid AI with appropriate regression equations. The high correlations and predictable changes after interventions between the central AI and those estimated from noninvasive carotid tonometry suggest that this technique may have wide applicability for many cardiovascular studies.

Adolescent↗
PubMed1996

Sequential estimation of linkage between PCR-generated markers and a target gene employing stepwise bulked analysis.

PCR-based markers are used for targeting plant genes. However, mapping these markers requires laborious and expensive analysis of individual genotypes. We propose here a sequential procedure for fine mapping of PCR markers relative to a target gene. Stepwise bulked analysis is employed to get a censored estimation of the recombination rate. The sequential estimation is compared to fixed sample size design. In both cases, the proposed procedure can achieve a substantial reduction in the number of PCR runs (up to 90-97% for close linkage) as compared to the standard individual-by-individual analysis.

Biometry↗
PubMed1995

Genetic supercycles caused by cyclical selection.

Typical behavior of a two-locus genetic system experiencing cyclical selection, includes fixation (in one or both loci) or a stable polymorphic cycle with a period equal to that of environmental changes. By considering the time scale in terms of environmental periods, the last case could be trivially classified as a polymorphic stable point. Here we report on some results showing the complex limiting behavior of diploid population trajectories resulting from selection in a cyclically changing environment. We found that simple cyclical selection could produce genetic supercycles composed of many hundreds of environmental periods.

Alleles↗
PubMed1995

Convergent evolution of the vestibular organ in the subterranean mole-rats, Cryptomys and Spalax, as compared with the aboveground rat, Rattus.

The membranous labyrinth of the vestibular organ (examined in toto) in two unrelated species of subterranean rodents, Cryptomys sp. from Zambia and Spalax ehrenbergi from Israel, was in many parameters (streamline length, curvature radius, and cross-sectional area of the lumen) relatively or even absolutely (especially the cross-sectional area) larger than in the laboratory Norway rat. The mechanical sensitivity of the vestibular organ (estimated according to the mathematical model of Oman et al., [1987] Acta. Otolaryngol (Stockh.) 103:1-13) was similar in both subterranean rodent species and significantly higher than that in the laboratory rat. The most pronounced differences in morphometry and the resulting mechanical sensitivity between the subterranean forms and the rat occurred in the lateral (i.e., phylogenetically and ontogenetically most recent and presumably most plastic) semicircular duct. The area of the sensory epithelia, and density and total numbers of vestibular receptors, were estimated on surface specimens for both maculae and for all three cristae for all three species. While the density of hair cells in comparable sensory epithelia was similar in all three species, the sensory area and thus, also, the total receptor counts were significantly larger in both subterranean forms. The peripheral vestibular organ in subterranean rodents is, in comparison to a generalized aboveground dwelling form, i.e., the rat, progressively specialized, and in any case cannot be denoted as degenerate.

Animals↗
PubMed1995

A new methodology for non-invasive clinical assessment of cardiovascular system performance and of ventricular-arterial coupling during stress.

The objective of the study was to develop a non-invasive method for the quantitative evaluation of cardiovascular performance and ventricular-arterial (VA) coupling during varying physiological states. VA-coupling was represented by the ratio between the arterial and ventricular elastances-Ea/Ees. Approximate indices of the relative change of Ees and VA-coupling during stress were developed and tested. These indices can be evaluated directly from non-invasive measurements of ejection fraction values (for VA-coupling) and measurements of stroke volumes and systolic and diastolic arterial pressures (for Ees). Additional relative indices can be evaluated from these data (e.g., stroke work, cardiac output) to yield a complete representation of the cardiovascular response to stress. The present methodology was applied to assess the exercise stress response in healthy subjects (H, n = 8) and in patients with left ventricular dysfunction (n = 24). Left ventricular volumes were determined by nuclear angiography and arterial pressures were measured non-invasively by a new, validated method. Using published data obtained invasively, we found that the relative indices of Ees and VA-coupling showed a high correlation with the invasive ones (r > 0.8, P < 0.01). The patients were subgrouped by their maximal exercise capacitance (P2-50W, P3-75W). At rest, the two patient groups had similar ejection fraction values (45 +/- 15% and 48 +/- 16%), which were significantly different from those of the healthy subjects (66 +/- 7%, P < 0.05). During stress, a larger increase in stroke work and cardiac output was found in the healthy subjects. All three groups showed similar relative increases in Ees and heart rate, but relative Ea increased in P2 and decreased in H, while the opposite was found for the end-diastolic volume. The relative VA-coupling index in P2 was significantly larger than that in P3 and H (P < 0.05). The present non-invasively based indices can be used to quantitatively monitor the individual cardiovascular response to stress testing or drug interventions and to evaluate the importance of VA-coupling in the clinical setting.

Arteries↗
PubMed1995

Activity pattern and rhythm in the subterranean mole rat superspecies Spalax ehrenbergi.

Good candidates for naturally occurring variability in circadian rhythms may be subterranean herbivores, since they are not normally subjected to entraining light stimulation. To test this possibility, we selected the blind mole rat Spalax ehrenbergi superspecies in Israel and tested it in short- and long-term experiments. Short-term experiments showed that the animals exhibited three patterns of activity: a regular circadian rhythm (26.6%), an altered circadian rhythm (shorter or longer than normal, 53.1%), and an arrhythmic pattern (20.3%). A long-term experiment showed that the arrhythmic pattern indeed reflected a genuine arrhythmic genotype. The mole rats were found to be active less than 25% of the day and exhibited a multiphasic mode of activity, both diurnally and nocturnally. The number of activity periods and the level of activity were negatively correlated: Animals that exhibited a high level of activity per unit of time showed low numbers of activity periods, while animals that exhibited a lower level of activity showed higher numbers.

Animals↗
PubMed1994

Cyclical behavior of genotype frequencies in a two-locus population under fluctuating haploid selection.

Numerical iterations have shown that periodic haploid two-locus selection with nonoverlapping generations can produce large-scale cyclical behavior with a period differing significantly from the environmental period. Among other types, we observed slowly damping oscillations with very long periods, stable T-cycles with a length containing several environmental periods, and chaotic-like dynamics. Possible biological implications are discussed.

Environment↗
PubMed1994

Functional anatomy of the thalamus in the blind mole rat Spalax ehrenbergi: an architectonic and electrophysiologically controlled tracing study.

The occipital cortex of the naturally blind mole rat, Spalax ehrenbergi, is occupied by an area of somatosensory representation. To date, no visual cortex has been identified electrophysiologically. In order to determine whether there are corresponding modifications in the thalamus, thalamocortical connections were studied with neuroanatomical tracing methods. Three different fluorescent tracers were injected under electrophysiological control into distinct cortical areas. Injections into the somatosensory head/face and hindlimb/trunk areas of representation revealed a posteromedial ventral nucleus and a posterolateral ventral nucleus, respectively. Additional somatotopic labeling was found in an area dorsomedial to the two ventral nuclei. This structure may be equivalent to the posterior nuclear complex in the laboratory rat. Injections into the auditory cortex of the mole rat resulted in labeling of the medial geniculate body. In contrast to the situation in the laboratory rat, in which a prominent dorsolateral geniculate body and a ventrolateral geniculate body assume dorsolateral positions, the somatosensory thalamus of the mole rat almost reaches the dorsolateral surface. This finding is corroborated by the results of the architectonic study, which failed to reveal a differentiated lateral geniculate body. Our observations suggest that the thalamocortical visual system in the mole rat is minute, whereas the somatosensory system is expanded. This situation fits the mode of life of this subterranean animal, for which touch is more important than vision.

Animals↗