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PubMed2001

Fluctuating asymmetry is nongenetically related to mating success in Drosophila buzzatii.

To date, there is still no consensus on the real significance of fluctuating asymmetry (FA) in evolutionary biology. Some studies have established links between FA and Darwinian fitness, and in a number of cases intermediate heritabilities for FA have been reported. However, many claims have been raised against the generality of these findings. I therefore tested if FA of a sexually selected trait (wing length) is indeed related to male mating success in Drosophila buzzatii from field and laboratory samples and whether FA has detectable heritability. Single, unsuccessful males had greater asymmetry for wing length than their mating counterparts both in nature and under nonoptimal rearing environments, but the higher FA in single males is most likely due to a poorer average phenotypic condition because there was no evidence of a genetic basis for this trait. Further evidence of an increase in FA under larval food stress is suggested when comparing the magnitude of the FA levels between stressful and optimal environments. On methodological grounds, a linear model is suggested that allows directional asymmetry (DA) and any genetic variation of DA that may be present to be statistically eliminated from estimates of FA.

Analysis of Variance↗
PubMed1992

Purification of Aeromonas hydrophila major outer-membrane proteins: N-terminal sequence analysis and channel-forming properties.

Four outer-membrane proteins of Aeromonas hydrophila were purified and their N-terminal sequences and channel-forming properties were determined. Three could be matched with proteins from other species. One was a maltoporin, as its level increased when cells were grown in maltose-containing media, and the channel it formed was blocked by maltose. Another was like OmpF and OmpC of Escherichia coli, except that its channel fluctuated much more rapidly. The third protein, which was produced in low-phosphate medium, exhibited several properties of the general anion porin PhoE. The fourth showed no similarity to any known proteins. It had a unique N-terminus and it formed small sharply-defined cation-selective channels. Two other proteins which corresponded to OmpW of Vibrio cholerae and E. coli OmpA were partly characterized.

Aeromonas hydrophila↗
PubMed2005

Imaging alpha-hemolysin with molecular dynamics: ionic conductance, osmotic permeability, and the electrostatic potential map.

alpha-Hemolysin of Staphylococcus aureus is a self-assembling toxin that forms a water-filled transmembrane channel upon oligomerization in a lipid membrane. Apart from being one of the best-studied toxins of bacterial origin, alpha-hemolysin is the principal component in several biotechnological applications, including systems for controlled delivery of small solutes across lipid membranes, stochastic sensors for small solutes, and an alternative to conventional technology for DNA sequencing. Through large-scale molecular dynamics simulations, we studied the permeability of the alpha-hemolysin/lipid bilayer complex for water and ions. The studied system, composed of approximately 300,000 atoms, included one copy of the protein, a patch of a DPPC lipid bilayer, and a 1 M water solution of KCl. Monitoring the fluctuations of the pore structure revealed an asymmetric, on average, cross section of the alpha-hemolysin stem. Applying external electrostatic fields produced a transmembrane ionic current; repeating simulations at several voltage biases yielded a current/voltage curve of alpha-hemolysin and a set of electrostatic potential maps. The selectivity of alpha-hemolysin to Cl(-) was found to depend on the direction and the magnitude of the applied voltage bias. The results of our simulations are in excellent quantitative agreement with available experimental data. Analyzing trajectories of all water molecule, we computed the alpha-hemolysin's osmotic permeability for water as well as its electroosmotic effect, and characterized the permeability of its seven side channels. The side channels were found to connect seven His-144 residues surrounding the stem of the protein to the bulk solution; the protonation of these residues was observed to affect the ion conductance, suggesting the seven His-144 to comprise the pH sensor that gates conductance of the alpha-hemolysin channel.

Bacterial Toxins↗
PubMed2006

Selective cerebral hypothermia for post-hypoxic neuroprotection in neonates using a solid ice cap.

OBJECTIVE: The main objective of this study was to study the safety and efficacy of a simple, cost-effective method of selective head cooling with mild systemic hypothermia in newborn infants with hypoxic ischaemic encephalopathy. DESIGN: Ethical approval was obtained for a randomized controlled study in which 20 asphyxiated neonates with clinical signs of hypoxic ischaemic encephalopathy would be randomised into cooled and non-cooled groups. However, after cooling the first 4 babies, it was clear that repeated revisions to the cooling technique had to be made which was inappropriate in the context of a randomised controlled trial. The study was therefore stopped and the data for the 4 cooled infants are presented here in the form of a technical report. Hypothermia was achieved by applying an insulated ice cap to the heads of the infants and replacing it at 2-3-hourly intervals, aiming to achieve a target rectal temperature of 35-35.5 degrees C and a target scalp temperature of 10-28 degrees C. SETTING: This study was carried out between July 2000 and September 2001 in the neonatal units of Groote Schuur Hospital and Mowbray Maternity Hospital, Cape Town. SUBJECTS: Term infants with signs of encephalopathy were recruited within the first 8 hours of life if they had required resuscitation at birth and had significant acidosis within the first hour of life. RESULTS: Target rectal temperature was achieved in all infants, but large variations in incubator and scalp temperatures occurred in 3 of the 4 infants. Reducing the target core temperature in a stepwise manner did not prevent excessive temperature variation and resulted in a longer time to reach target temperature. There was least variation in scalp temperature when the ice pack was covered in two layers of mutton cloth before application, but the resulting scalp temperatures were above the target temperature. The maximum scalp temperature variation was reduced from 22 degrees C to 12 degrees C using this method. Nasopharyngeal temperatures varied excessively within less than a minute, suggesting that air cooling via mouth breathing was occurring. The surface site that correlated best with deep rectal temperature was the back, with the infant supine. During cooling, the respiratory rate and heart rate dropped while the mean arterial blood pressure was elevated. There were no irreversible adverse events due to cooling, but infants did become agitated and exhibited shivering which required sedation and analgesia. CONCLUSIONS: Nasopharyngeal temperature monitoring was not reliable as an acute clinical indicator of brain temperature in these spontaneously breathing infants, and the back temperature in supine infants correlated better with deep rectal temperature than did exposed skin temperature. This method of cooling achieved systemic cooling but there were large variations in regional temperatures in 3 of the 4 infants. The variations in temperature were probably due to the excessive cooling effect of the ice cap, coupled with the use of external heating to maintain systemic temperature at 35-35.5 degrees C. Variation in temperature was reduced when additional insulation was provided. However, the additional insulation resulted in the loss of the selective cerebral cooling effect. This cooling technique was therefore not an appropriate method of selective head cooling, but did successfully induce systemic hypothermia. This method of insulating an ice cap could therefore be used to induce whole-body cooling but the use of lower core temperatures of 33-34 degrees C is recommended as this will probably result in fewer regional temperature fluctuations. Ideally a more uniform method of cooling should be used.

Body Temperature↗
PubMedDate not supplied

[The alteration of the motility rate of human spermatozoa and relationship to morphological quality].

On the ejaculate of 715 patients with fertility disorders (one spermatogram) as well as on 90 patients (two spermatograms) the alteration of the motility rate comparing the morphological quality of the spermatozoa has been carried out. In some norm orientated subgroups a statistical evaluation (correlation analysis, covariance selection) were determined. We found a positive correlation between increased percentage of pathological spermatozoa and increased motility rate. A special graphic allows more information about the correlative structure of the correlation matrix: this confirms the results of the correlation analysis. On the different malformations of the spermatozoa the intraindividual fluctuation was in the least, but very high on the sperm density. The fluctuation of the fructose content (detailed observed) was very little.

Humans↗
PubMed1994

Pharmacokinetic profile of a new fluoride preparation: sustained-release monofluorophosphate.

The pharmacokinetic profiles of a sustained-release monofluorophosphate (MFP-SR) preparation (76 mg) and of plain MFP (76 mg) were compared in six osteoporotic females. These studies were performed in a randomized, crossover, double-blind design to select a preparation that would result in therapeutic serum levels while avoiding high serum peak values. Following a single dose of 76 mg MFP-SR, the serum fluoride levels remained within the accepted therapeutic range (5-10 microM/liter) for 24 hours. In contrast, following a single dose of 76 mg plain MFP, serum fluoride levels exhibited a wide circadian fluctuation and serum levels approximately threefold higher than those of the MFP-SR preparation (9.5 +/- 1.6 vs 3.5 +/- 0.8 microM/liter, P < 0.005). Compared with plain MFP, the sustained-release MFP had a significantly lower peak concentration (Cmax MFP-SR: 10.6 +/- 3 vs CmaxMFP: 18.9 +/- 5 microM/liter, P < 0.005) and a significantly longer absorption lag time (TmaxMFP-SR 7.3 +/- 1.6 vs TmaxMFP: 3.0 +/- 0.6 h, P < 0.05). Twenty-four-hour urinary fluoride excretion after ingestion of plain or SR fluoride was significantly increased from pretreatment values documenting absorption with either MFP formulation. Our results show that the use of sustained-release MFP preparation that we tested prevents the development of high peak levels associated with the use of plain MFP preparations. Furthermore, a single dose of MFP-SR resulted in serum fluoride levels within the accepted range of 5-10 microM/liter for 24 hours.

Aged↗
PubMed1994

Behavioral significance of phasic changes in mesolimbic dopamine-dependent electrochemical signal associated with heroin self-injections.

High-speed chronoamperometry with monoamine-selective carbon fiber electrodes was used in rats to monitor, during 5-6 consecutive daily sessions, changes in DA-dependent electrochemical signal in the nucleus accumbens (NAcc) during intravenous heroin (0.1 mg/kg) self-administration (SA) behavior and passive repeated drug injections performed with a temporal scheme similar to that in the SA experiment. In trained animals, biphasic signal fluctuations time-locked to the individual lever-presses were found to accompany all but the first daily SAs. The signal gradually increased by 30-40 nM for the 10 minutes preceding the SA, reached a peak at the moment of lever-press and decreased abruptly by approximately 40 nM for 3-4 min after heroin SA. The cycle then repeated, reaching a new peak at the moment of the next lever-press. Rapid bi-directional fluctuations in signal associated with individual heroin SAs were superimposed on substantial tonic increase in signal baseline (400-500 nM). This increase quickly developed after presentation of heroin-related light cue and the first SA, was relatively stable during all subsequent SAs and decreased towards the baseline after the last SA of a session. Changes in signal baseline induced by repeated heroin SAs depended strongly upon the signal's basal level (r = -0.787); that signal preferentially increased when its basal values were low (0-300 nM), and decreased when signal was tonically elevated (> 600 nM). Repeated passive heroin injections also induced biphasic signal fluctuations and a similar tonic increase in signal baseline. Although a transient signal decrease (25 nM for 2-4 minutes) followed by a prolonged signal increase occurred after each but not the first passive injection, the gradual pre-injection signal acceleration was absent. Although DOPAC, a principal DA metabolite, may significantly contribute to the tonic increase in electrochemical signal seen during SA session, the changes in extracellular DA may be the main contributor to both the rapid signal increases preceding drug-taking and the transient signal decreases following heroin SA. If so, the present findings suggest that activation of mesolimbic DA cells and increase in DA transmission may be involved in the mediation of motivational and/or activational components of drug-seeking and drug-taking behavior. An acute termination of previous drug- and behavior-associated DA activation with a transient inhibition of DA release, immediately following heroin SA may correlate with the drug's rewarding action, representing a part of a mechanism regulating drug-taking behavior.

Animals↗
PubMed1999

Modes selection in polymer mixtures undergoing phase separation by photochemical reactions.

Phase separation kinetics and morphology of binary polymer mixtures (A/B) in the presence of photochemical reactions were investigated by using phase-contrast optical microscopy combined with digital image analysis. The polymers were chemically designed in such a way that two types of chemical reactions, intermolecular photodimerization and intramolecular photoisomerization, of polymer segments can be induced and controled by irradiation with ultraviolet light. Unlike the conventional case, the phase separation in the presence of these reactions is spontaneously frozen due to the suppression of the long-wavelength instabilities, resulting in stationary spatial structures with intrinsic periodicities. These characteristic length scales are determined by the competition between the two antagonistic interactions: phase separation as a relatively short-range activation and the photochemical reaction as a long-range inhibition. Furthermore, it was found that the spatial symmetry breaking of concentration fluctuations can emerge from the elastic stress associated with the nonhomogeneous kinetics of the reactions. Experimental data obtained with three types of reactions: A-A only cross-link, A-A and B-B simultaneous cross-links and the reversible A<-->B photoisomerization are described. These results do not only indicate that combination of chemical reactions and phase separation could provide a novel method to control the morphology of multiphase polymer materials, but also suggest that photoreactive polymers can be used as a chemical system to study the mode-selection process in polymers far from thermodynamic equilibrium. (c) 1999 American Institute of Physics.

Journal Article↗
PubMed1998

Src protein and tyrosine-phosphorylated protein profiles in marrow stroma during osteogenic stimulation.

Src protein is essential for the regulation of bone turnover primarily via bone resorption because it is required in osteoclast differentiation and function. We followed temporal changes of Src protein abundance in marrow stromal cells induced to mineralize by dexamethasone (DEX), growth in cold temperature, or both. Given the tyrosine kinase function of Src and its numerous substrates, profiles of phosphotyrosine-containing proteins were followed as well. On day 11 of stimulation, specific alkaline phosphatase (ALP) activity at 30 degrees C decreased under DEX relative to 37 degrees C cultures, in accord with increased cell counts. Mineralization per well under DEX increased by 25% at 37 degrees C, whereas at 30 degrees C it increased by more than threefold regardless of the DEX stimulation. At 30 degrees C, on a per cell basis mineralization increased 2.5 and 3 times with and without DEX, respectively. Cultures at 37 degrees C showed a general drop per cell of many phosphotyrosine-containing proteins on day 3 relative to days 1 and 2 in both DEX-stimulated and nonstimulated cultures; several proteins did recover (recuperate) thereafter. On days 1 and 2, the phosphotyrosine signal was higher in several proteins under DEX stimulation; this trend became inverted after day 3. The changes in abundance per cell of Src protein (pp60src) followed a similar trend, and in addition a truncated Src molecule, p54/52src, was detected as a putative cleavage product presumably representing its carboxy terminus. The pp60src was most abundant, relative to its truncated product, in day 7 nonstimulated cultures, whereas under DEX stimulation the truncated species pp54/52src showed the highest relative abundance on days 7. At 30 degrees C, DEX stimulation accentuated the increase in Src protein on day 3, showed no change on day 7, and returned to increase Src protein on day 10. Potassium ionophorvalinomycin, considered to select against mineralizing osteoprogenitors at 30 degrees C, showed on day 10 in the absence of DEX a relative increase in truncated Src protein compared to both DEX-stimulated and nonstimulated cultures in the absence of valinomycin. On day 7 of DEX stimulation, the presence of valinomycin resulted in low p54/52src. Among phosphotyrosine-containing proteins, a 32-34 kDa band, as yet unidentified, showed the most concordant changes with mineralization induction. P32-34 decreased by DEX on days 2 and 8 and increased by low temperature alone or combined with DEX on day 3. On day 7, p32-34 did not change under DEX, but valinomycin selected cells with less phoshpotyrosine-containing p32-34. Taken together, high Src abundance at the start of osteogenic induction followed by a decrease 1 week later is probably related to energy metabolism-dependent induction of mineralization. This is in temporal accord with the increase in Src truncation and fluctuation in mitochondrial membrane potential (which affects mineralization). The reported binding of amino-terminal Src oligopeptide to p32 ADP/ATP carrier in the mitochondrial inner membrane raises the question of its possible involvement in mitochondria-regulated mineralization.

Animals↗
PubMed2005

Structural and conformational changes in myocardial and erythrocyte actin during cardiac ischemia.

Structural and conformational changes in myocardial and erythrocyte actin during cardiac ischemia were studied by the method of fluorescence resonance energy transfer with highly selective fluorescent probes. In contrast to 15-min coronary artery occlusion, 120-min ischemia was accompanied by irreversible structural and conformational changes in the small domain of erythrocyte actin. Posttranslational changes during myocardial ischemia concerned the N- and C-terminal regions of actin and went beyond the allowed conformational fluctuations in the actin molecule without breaking the energy barrier. Our results suggest that under conditions of ischemia, actin of the myocardium and erythrocyte cytoskeleton loses its ability to acquire conformation required for force generation by cardiomyocyte myofibrils and maintenance of elasticity and integrity of the erythrocyte membrane.

Actins↗
PubMed1987

Fractal analysis of a voltage-dependent potassium channel from cultured mouse hippocampal neurons.

The kinetics of ion channels have been widely modeled as a Markov process. In these models it is assumed that the channel protein has a small number of discrete conformational states and the kinetic rate constants connecting these states are constant. In the alternative fractal model the spontaneous fluctuations of the channel protein at many different time scales are represented by a kinetic rate constant k = At1-D, where A is the kinetic setpoint and D the fractal dimension. Single-channel currents were recorded at 146 mM external K+ from an inwardly rectifying, 120 pS, K+ selective, voltage-sensitive channel in cultured mouse hippocampal neurons. The kinetics of these channels were found to be statistically self-similar at different time scales as predicted by the fractal model. The fractal dimensions were approximately 2 for the closed times and approximately 1 for the open times and did not depend on voltage. For both the open and closed times the logarithm of the kinetic setpoint was found to be proportional to the applied voltage, which indicates that the gating of this channel involves the net inward movement of approximately one negative charge when this channel opens. Thus, the open and closed times and the voltage dependence of the gating of this channel are well described by the fractal model.

Animals↗
PubMed1999

Programming ovulation in the menstrual cycle by a simple innovative approach: back to the future of assisted reproduction.

OBJECTIVE: To synchronize the intercycle FSH elevation with exogenous E2 for programming ovulation in the menstrual cycle. DESIGN: Open single-arm study. SETTING: Teaching hospital. PATIENT(S): Twenty-six patients with infertility whose menstrual cycles normally lasted 25-35 days and who underwent our routine programming method for postcoital tests and ovulation evaluations. INTERVENTION(S): Participants received estradiol valerate (2 mg) twice a day from day 25 of the previous cycle until 1-15 days after the onset of menses. Women had ultrasonography on the last day of E2 treatment or on functional day 0 and 13 days later or on functional day 13. Hormones were determined on functional days 0, 3, 9, and 13. The increase in FSH in response to E2 withdrawal was defined as deltaFSH. MAIN OUTCOME MEASURE(S): LH surge and other ovulatory indices on functional day 13. RESULT(S): On functional day 13, 73% of the women had an LH surge. Fifteen percent had evidence of previous ovulation with low LH and elevated plasma P levels, and the remaining 12% had low LH levels and no evidence of past or imminent ovulation. Women with evidence of early ovulation were older and had higher FSH signal amplitude. CONCLUSION(S): It is feasible and practical to program ovulation in the menstrual cycle with exogenous E2. In 73% of women, the true duration of the follicular phase (intercycle FSH elevation to LH surge interval) remained constant (13 days). Hence, common fluctuations in menstrual cycle length mainly result from variations in the timing of the intercycle FSH elevation. Although rare, truly short follicular phases also exist (15%). This simple and practical system for programming natural ovulation offers new possibilities for using the menstrual cycle in assisted reproductive technology, at least in selected individuals.

Adult↗
PubMed1997

Game-theory models of interactions between tumour cells.

The population of cells that comprises a tumour may consist of genetically different individuals. Often, such polymorphisms result from the expansion of a new, advantageous clone. The hypothesis is presented that sometimes tumour cells may adopt genetically-determined strategies to boost their own replication at the expense of other cells in the tumour. Simple game-theory models have been used to study this hypothesis, taking as an example the hypothetical advantage gained by tumour cells which produce a cytotoxin to harm other tumour cells. The models show that genotypes which cause cells to produce cytotoxic substances can spread through the tumour cell population, as can genotypes for resistance to the cytotoxin; in other circumstances, stable polymorphisms between these strategies can occur. The path of the tumour cell population to internal or external equilibrium is often complex, with large fluctuations in genotype frequencies. Flexible strategies are usually superior to fixed strategies. As in populations of whole organisms, 'social' interactions between tumour cells can act in favour of the individual cell at the expense of the tumour as a whole: strategies that retard the growth of the tumour can be selected and tumour regression is theoretically possible. Many mutations in tumours, especially in large or late-stage lesions, may play a role in relations between tumour cells rather than providing those cells with a simple replicative advantage.

Cell Communication↗
PubMed2005

An improved biclustering algorithm and its application to gene expression spectrum analysis.

Cheng and Church algorithm is an important approach in biclustering algorithms. In this paper, the process of the extended space in the second stage of Cheng and Church algorithm is improved and the selections of two important parameters are discussed. The results of the improved algorithm used in the gene expression spectrum analysis show that, compared with Cheng and Church algorithm, the quality of clustering results is enhanced obviously, the mining expression models are better, and the data possess a strong consistency with fluctuation on the condition while the computational time does not increase significantly.

Algorithms↗
PubMed1998

Variation in cytoplasmic calcium increase in platelets as a normal response in healthy persons.

Seasonal changes in cell physiology are well known. Fluctuations of mood in humans are reflected in the serotonin metabolism in platelets. The mechanisms involved remain unknown. Over four years we have studied the increase in levels of platelet calcium caused by minimal doses of the agonists adenosine 5' diphosphate (ADP) and arginine vasopressin (A8VP) using the calcium-selective fluorescent probe fura-2. We found that in blood platelets from healthy people the basal level of calcium, the amount of calcium mobilized to the cytoplasm and, for vasopressin, the rate of calcium rise, varied periodically and sufficiently to be statistically significant.

Adenosine Diphosphate↗
PubMed1991

Single band amplitude envelope cues as an aid to speechreading.

Amplitude envelopes derived from speech have been shown to facilitate speech-reading to varying degrees, depending on how the envelope signals were extracted and presented and on the amount of training given to the subjects. In this study, three parameters related to envelope extraction and presentation were examined using both easy and difficult sentence materials: (1) the bandwidth and centre frequency of the filtered speech signal used to obtain the envelope; (2) the bandwidth of the envelope signal determined by the lowpass filter cutoff frequency used to "smooth" the envelope fluctuations; and (3) the carrier signal used to convey the envelope cues. Results for normal hearing subjects following a brief visual and auditory-visual familiarization/training period showed that (1) the envelope derived from wideband speech does not provide the greatest benefit to speechreading when compared to envelopes derived from selected octave bands of speech; (2) as the bandwidth centred around the carrier frequency increased from 12.5 to 1600 Hz, auditory-visual (AV) performance obtained with difficult sentence materials improved, especially for envelopes derived from high-frequency speech energy; (3) envelope bandwidths below 25 Hz resulted in AV scores that were sometimes equal to or worse than speechreading alone; (4) for each filtering condition tested, there was at least one bandwidth and carrier condition that produced AV scores that were significantly greater than speechreading alone; (5) low-frequency carriers were better than high-frequency or wideband carriers for envelopes derived from an octave band of speech centred at 500 Hz; and (6) low-frequency carriers were worse than high-frequency or wideband carriers for envelopes derived from an octave band centred at 3150 Hz. These results suggest that amplitude envelope cues can provide a substantial benefit to speechreading for both easy and difficult sentence materials, but that frequency transposition of these signals to regions remote from their "natural" spectral locations may result in reduced performance.

Adult↗
PubMed1999

The role of habitat in structuring Halipegus occidualis metapopulations in the green frog.

The transmission dynamics of the trematode Halipegus occidualis in its definitive host, Rana clamitans, have been examined over a 5-yr period in a North Carolina pond. The breeding season of green frogs coincides with the period of worm recruitment, during which time male frogs are territorial and females show strong site fidelity. This site fidelity allows inferences to be made regarding the suitability of a particular habitat for worm transmission based on frog infection intensities within that habitat. Four foci of infection were identified in the pond by plotting worm infrapopulation size against site of host capture. Sites within infection foci are characterized by shallow water and emergent vegetation, factors favorable for overlapping distributions of the 4 hosts in the life cycle of H. occidualis. Consistent year-to-year worm prevalences and intensities, despite fluctuations in frog population size, are thought to be the result of a relatively constant proportion of the frog population being present in infection foci each year. Removal of worms from heavily infected frogs in the fifth year resulted in further heavy worm recruitment by treated frogs suggesting that site selection can predispose a frog to heavy infection. Further, the sum of removed parasites and those recruited after parasite removal by treated frog hosts was higher than worm infrapopulations observed in previous years, indicating that worm density regulates parasite infrapopulation size in heavily infected frogs.

Animals↗
PubMed1981

Measuring interstate migration flows: an origin-destination network based on Internal Revenue Service records.

"This paper examines gross interstate migration flows for five periods for the years between 1969 and 1978. The analysis is based upon a newly available data source--Federal income tax returns. Approximately 90% of the US population is covered by this data series. The matching of Internal Revenue Service (IRS) returns between filing dates enables the determination both of the origin and of the destination of migrants, with few of the risks of geographic miscoding present. "These data illustrate that despite divergent economic fluctuations over the past nine years, the patterns of interstate migration have remained virtually unchanged. With few exceptions, the number of migrants either leaving or entering a particular state comprise identical proportions over time.... In addition, these data offer considerable evidence that current residence has a significant impact on the selection of a destination." Comparisons are made with data from the Current Work History Sample and the 1970 census.

Americas↗