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PubMed1986

Retention interval and intertrial interval in a serial learning or delayed discrimination task.

In each of four experiments, rats were provided with the same three-event decreasing series (18-1-0) of 0.045-g food pellets in a runway. Tracking, running fast to 18 pellets and running slow to 1 and 0 pellets, was investigated as a function of the temporal interval elapsing between the events of the series (the retention interval), shifts in retention interval, and number of trials each day (or the intertrial interval), a trial being defined as presentation of each of the three events of the series. Neither retention interval, which varied from 15 s to 30 min in various investigations, nor shifts in retention interval affected tracking when only one trial was given each day. But when more than one daily trial was given, tracking was acquired more slowly and was disrupted by a shift in retention interval from 15 s to 5 min. Tracking was also disrupted by a shift from one to two trials each day. These results indicate that when given one 18-1-0 trial each day, the rat partitions events on a first-event/subsequent-event basis; that little forgetting occurs even at long retention intervals; that somewhat different memories signal events when one or more than one 18-1-0 trial occurs each day; and that retention interval deficits can arise owing to the same or similar memories' signaling different events. The results described limit the generality of three hypotheses suggested in two recent investigations: that as retention interval increases, rats find it increasingly difficult to remember and utilize serial position cues; that tracking in serial tasks is not influenced by number of trials each day; and that there are specific stimuli associated with each retention interval which, when changed, necessarily disrupt performance.

Animals↗

PubMed1988

Postoperative urinary retention in general surgical patients.

A prospective study has been performed to measure the incidence of postoperative urinary retention in 280 general surgical patients. Eighteen patients (6 per cent) were catheterized after a range of operations under general anaesthesia. There was no statistical difference in the retention rate between men and women. Increasing age did not predispose to retention of urine. Of 72 patients who had either herniorrhaphy, haemorrhoidectomy or testicular operations, only 1 was catheterized, whereas 16 (23 per cent) of 70 patients undergoing laparotomy were catheterized. Most of these laparotomy patients had upper abdominal procedures carried out. Those having lower abdominal operations were usually catheterized pre-operatively and were excluded from the study. There was a significantly higher incidence of retention among patients who had long anaesthetics (greater than 60 min). There was also a significantly higher incidence of retention among those who were ventilated, relaxed and reversed by atropine and neostigmine. Of those 193 patients who had opiate analgesia, 15 (8 per cent) developed retention of urine, compared with 3 (3 per cent) of the 87 patients who had non-opiate analgesia. There was a significantly higher retention rate among the patients who had opiate analgesia by intravenous infusion compared with those who had opiates by intramuscular bolus injection; 7 patients had painful and 11 had painless retention. This study suggests that postoperative retention of urine is a result more commonly of diminished awareness of bladder sensation, than of factors such as anxiety or local pain.

Adult↗

PubMed2004

Assessment by monte carlo simulation of thermodynamic correlation of retention times in dual-column temperature programmed comprehensive two-dimensional gas chromatography.

The correlation of retention times in comprehensive two-dimensional gas chromatography caused by correlation of enthalpy and entropy changes between two stationary phases, methylsilicone and poly(ethylene glycol), was examined using commercial GC software and in-house Monte Carlo simulation. The enthalpy change, deltaH0, and entropy change, deltaS0, of 93 compounds were predicted from isothermal one-dimensional gas chromatograms predicted by the software. These values then were mimicked by Monte Carlo simulation, which removed the strong correlation of deltaH0 and modest correlation of deltaS0 between the two phases. Retention times in a comprehensive two-dimensional gas chromatogram (GC x GC) and in simulations of it were predicted for typical dual-capillary temperature-programmed conditions using the actual, correlated values of deltaH0 and deltaS0 and their uncorrelated Monte Carlo counterparts, respectively. The uncorrelated deltaH0 and deltaS0 values caused the retention-time range of the simulations' second dimension to expand substantially beyond that in the GC x GC. Other simulations were developed using a restricted range of uncorrelated deltaH0 and deltaS0 values to mimic more closely the retention-time range of the GC x GC's second dimension. The intervals between nearest neighbor retention-time coordinates were calculated in both the latter simulations and the GC x GC. The intervals were larger in the simulations than in the GC x GC because the former contained uncorrelated coordinates and the latter contained correlated ones, which clustered along or near the diagonal. The retention times in the first dimension of the GC x GC were Poisson distributed, as assessed by statistical-overlap theory. In contrast, the two-dimensional reduced retention-time coordinates in the GC x GC were not Poisson distributed, because retention times were correlated. However, the reduced retention-time coordinates in the simulations were Poisson distributed.

Journal Article↗

PubMedDate not supplied

Retention in publicly funded methadone maintenance treatment in two Western States.

This study examined individual and system characteristics associated with retention in methadone maintenance treatment among Medicaid-eligible adults in treatment for opiate use in Oregon and Washington. Logistic regression was used to examine the contributions of predisposing, need, and enabling characteristics on 365 day retention in methadone maintenance treatment. Older patients, patients with a history of methadone maintenance treatment, and persons with stable Medicaid eligibility had higher rates of retention than did patients with disabilities, polysubstance users, and those with an arrest record. In Oregon, which delivers methadone maintenance treatment through managed care, retention rose sharply from 28% to 51% between 1994 and 1998 and then leveled off. During the same time period, retention in Washington State grew from 28% to 34%. The higher rates of retention in Oregon, in part, can be explained by differences in service delivery influenced by financing. Faced with long waiting lists, Washington providers were more than twice as likely to administratively discharge patients for rule violations as their Oregon counterparts. Given the importance of retention, policies and practices that influence retention should be carefully considered. Because Medicaid eligibility has a dramatic impact on retention, policies that help extend eligibility or stabilize eligibility among individuals actively engaged in treatment should be carefully considered.

Adult↗

PubMedDate not supplied

Iodized-oil retention within hepatic hemangioma: characteristics on iodized-oil CT.

OBJECTIVE: The purpose of this study was to describe the characteristic computed tomographic (CT) appearance of iodized-oil retention in hepatic hemangioma and to evaluate the duration of the retention of iodized oil on follow-up CT. METHODS: Seventeen hepatic hemangiomas of 14 patients were studied with CT performed 1-3 weeks after injection of 2-9 ml of iodized oil (iodized-oil CT) for the characterization of focal hepatic lesions, which needed differential diagnosis with hepatocellular carcinoma in 10 patients, for therapy in two patients, and for chemoembolization therapy of accompanying hepatocellular carcinomas in two. Twelve patients had 1-7 follow-up CT scans within an interval of 1-38 months. RESULTS: In all cases, iodized-oil CT showed iodized-oil retention within the tumor, regardless of tumor size, shape, location, and amount of injected iodized oil. The distribution was incomplete and predominantly peripheral in all cases. Central retention was also seen in seven cases, in which a relatively large amount of iodized oil was injected, but retention of iodized oil in the tumor was incomplete even in two cases in which a large amount of iodized oil was injected to relieve symptoms and in three cases in which prominent uptake of surrounding liver parenchyma was seen. Patterns of retention were predominantly spotty in five, predominantly nodular in four, and mixed in eight patients. Retention materials slowly washed out but persisted for at least 3 months and up to 38 months (mean = 18.1 months), and complete washout was not seen in any cases at follow-up CT. CONCLUSION: In all cases of hepatic hemangiomas, iodized oil was retained, and retention persisted over several months. Distribution and patterns of retention were characteristically peripheral, spotty, and nodular at iodized-oil CT. Knowledge of the iodized-oil CT appearance of hepatic hemangioma would be helpful to interpret follow-up CT studies of patients who have undergone iodized-oil chemoembolization procedures.

Adult↗

PubMed1992

Effects of intra-amygdala injections of NMDA receptor antagonists on acquisition and retention of inhibitory avoidance.

These experiments examined the effects of intra-amygdala injections of NMDA receptor antagonists on the acquisition and retention of inhibitory avoidance. In Expt. I, rats received bilateral intra-amygdala injections of the NMDA antagonists D,L-AP5 (1-10 micrograms), D-AP5 (0.03-1 micrograms), CPP (0.125 or 0.375 microgram), or MK-801 (0.2 or 0.5 microgram) prior to training in a continuous multiple-trial inhibitory avoidance (CMIA) task. Acquisition of the task was not significantly affected by any of the drug injections. In contrast, all three competitive antagonists, D,L-AP5, D-AP5 and CPP, produced dose-dependent impairment of 48 h retention performance. Although the MK-801 injections did not significantly impair retention performance, the retention scores of the 0.5 microgram MK-801 group were bimodally distributed, indicating retention impairment in a subgroup of the animals given that dose. Intra-amygdala injections of 3 or 10 micrograms D,L-AP5 did not affect footshock sensitivity (Expt. II) or locomotor activity (Expt. III) and their retention-impairing effects were not due to induction of state dependency (Expt. IV). The retention-impairing effects of intra-amygdala injections of NMDA antagonists were not due to diffusion of the drugs dorsally: injections of 1 microgram D-AP5 into the striatal area directly above the amygdala impaired acquisition but not retention performance (Expt. V). The retention-impairing effects of 1 microgram D-AP5 or 0.5 microgram MK-801 were attenuated by giving additional training to the animals shortly after receiving intra-amygdala injections (Expt. VI). The implications of these findings for hypotheses concerning amygdala function in learning and memory are discussed.

Amygdala↗

PubMed1994

Mechanical retention versus bonding of amalgam and gallium alloy restorations.

The retention of amalgam and gallium alloy restorations in proximal box forms was measured in vitro, and three different adhesives to conventional undercuts were compared. For control, restorations were placed without undercuts or adhesives. No significant difference was found between amalgam and gallium alloys with each of the five methods of retention used. Alloys placed without retention or adhesives were significantly less retentive than all other groups. When Tytin alloy was used, no difference was found in retention among the restorations retained with Panavia or All-Bond adhesive or an occlusal dovetail and retention grooves, but Amalgambond adhesive was less retentive than all three of these methods. When gallium alloy was used, both Panavia and All-Bond adhesive were more retentive than undercuts, but the effect of Amalgambond adhesive was more retentive than undercuts, but the effect of Amalgambond adhesive was comparable to that of undercuts. The results of this study indicate that adhesives could be used in place of traditional undercuts to retain amalgam and gallium alloys, thus saving a considerable amount of tooth structure.

Acid Etching, Dental↗

PubMed1991

Effects of THA on passive avoidance retention performance of intact, nucleus basalis, frontal cortex and nucleus basalis + frontal cortex-lesioned rats.

Unilateral quisqualic acid lesions of the nucleus basalis magnocellularis (NBM) produced marked choline acetyltransferase depletion (-67% ipsilateral to lesion) and impaired passive avoidance (PA) retention at 24 hours. Pretraining injections of tacrine (THA: 1, 3 and 5 mg/kg), an anticholinesterase, failed to facilitate PA retention in intact rats. However, the retention performance of NBM-lesioned rats was improved by pretraining administration of THA at 3 mg/kg but not at either 1 or 5 mg/kg. Frontal cortex lesioning did not impair PA retention, and THA at 3 mg/kg had no effect on the PA retention of frontal cortex-lesioned rats. THA at 3 mg/kg failed to improve retention performance of NBM + frontal cortex-lesioned rats. After 10 days of chronic treatment with THA, NBM lesion-induced PA retention deficits were partially restored at both 3- and 5-mg/kg doses. The results suggest that 1) the insult to cholinergic neurons in the NBM may be involved in the PA memory consolidation deficit induced by nonselective quisqualic acid lesioning; 2) the beneficial effects of THA on NBM lesion-induced PA retention deficit occur in a narrow dose range; 3) the alleviating effects of THA on NBM lesion-induced PA memory deficits are blocked by frontal cortex lesions; and 4) the dose-response window for THA-induced PA retention performance improvement is broadened by repeated treatment.

Animals↗

PubMed1984

Role of ouabain and diuretics on sodium, potassium and chloride retention in perfused rat kidney.

A novel in situ kidney perfusion technique is described in Sprague-Dawley rats. The procedure involves retrograde perfusion from the renal veins via the kidneys, and then through the renal arteries and dorsal aorta. Ouabain (15 mM) in perfusate increased Na retention by 92%, decreased K retention by 53% and produced no effect on Cl retention. Ethacrynic acid (1 mM) in perfusate decreased Na retention by 52%, increased K retention by 105% and decreased Cl retention by 27%. Furosemide (1.5 mM) in perfusate decreased Na retention by 52%, increased K retention by 47% and decreased Cl retention by 56%. The Na-K-ATPase pump localized at the peritubular side of the proximal tubule cell is ouabain sensitive and Mg dependent. An Na-K pump responsible for Na influx and K effux exists at the luminal side of the proximal tubule cell and is ethacrynic acid and furosemide sensitive.

Animals↗

PubMed2003

Methods for generating second dimension retention index data in comprehensive two-dimensional gas chromatography.

Two methods of generating transportable second dimension retention data are outlined for comprehensive two-dimensional gas chromatography (GC x GC). They are both refinements of a previously outlined procedure, which adapted 'isovolatile' curves to retention prediction maps developed in our laboratory, extended to a more polar homologous series, the linear primary alcohols. The earlier work investigated maps based on alkanes and methyl ketones and methyl esters; here the method of data collection to generate the retention map has also changed, extending the retention base range. The resulting retention map permits a retention basis to be used for GC x GC data, however, a more polar retention set than alkanes is required. The calculation of 'retention indices' is aided by the generation of 'fractional reference compound' curves, by either direct manipulation of data local to the solute, or generation of a discrete curve coincident with the retention co-ordinates of the target compound.

Alcohols↗

PubMed2004

Reliability of the retention factor estimations in liquid chromatography.

The retention factor is one of the most universally used parameters in chromatography. However, large differences in the experimental retention factor values are observed when the same compound is injected in a given stationary/mobile phase system under intermediate precision conditions. Conventional protocols for estimating retention factors have problems that mainly arise from difficulties in the hold-up time measurements and the omission of the existence of extra-column times by practicing chromatographers. In the present paper, three different approaches for estimating retention factors are tested: (i) classical retention factor estimations based on the gross hold-up time, (ii) based on the real hold-up time (taking into account the extra-column time), and (iii) a new approach that uses 'relative' retention factors based on the use of an external standard. Assays are performed in micellar liquid chromatography (MLC) under intermediate precision conditions (different days, equipments, columns lengths, and mobile phase flow rates). The reliability of the three approaches tested is evaluated by means of precision studies, analysis of factors affecting retention factors, and uncertainty calculations. The approach based on 'relative' retention factors was found to be the most precise, reliable, and robust strategy for estimating retention factors.

Chromatography, Liquid↗

PubMed2004

Sensitivity of the methylbenzenes and chlorobenzenes retention index to column temperature, stationary phase polarity, and-number and chemical nature of substituents.

Retention indices of methylbenzenes and chlorobenzenes on two fused silica capillary columns, HP-5 (diphenylsiloxane 5% diphenyldimethylsiloxane) and ZB-WAX (polyethylene glycol), have been calculated at various isothermal temperatures and compared with literature data. The retention index temperature effect was studied for each solute, finding greater retention index the higher the column temperature. A comparison between the straight line fit and the fit to the recently proposed equation I = A + B/T +C ln T was carried out. The effect of the stationary phase polarity on the retention index was checked. In general, a greater retention index was found for the more polar stationary phase. The retention indices of the chlorobenzenes are greater than the retention indices of the methylbenzenes, irrespective of the stationary phase and the column temperature. In addition, the influence of the methyl/chlorine substitution on the benzene molecule was investigated at each temperature. The retention indices increased as the number of substituents (methyl/chlorine) increased. The retention index increments of methyl and chloro derivatives are also discussed, which permits to compare the effect of both, methyl or chlorine, chemical functions, for a fixed substituent number in the benzene molecule.

Benzene Derivatives↗

PubMed2004

An experimental investigation of retention of liquids in corners of a square capillary.

The retention of liquids in the corners of a 0.03-cm square capillary after the passage of a gas slug was studied experimentally as a function of capillary number in the range from 10(-3) to 10(-6). In gas-wetting liquid systems, for capillary number greater than 5 x 10(-4), the retention of a wetting liquid in the corners showed a strong dependence on the capillary number; i.e., the retention of the liquid decreased with decreasing capillary number. For capillary number less than 10(-4), the retention of a wetting liquid was found to be determined by the capillary forces and the rate (or viscous) effect was negligible. In gas-oil-water systems involving double displacements--gas was displacing oil which was in turn displacing water--the total retention of water and oil vs capillary number curve showed the same trend as the retention of a wetting phase in a gas-wetting liquid system. However, because of the viscous effect, the water retention showed a continuous decrease with decreasing capillary number and could be lower than the capillary equilibrium value at very low capillary numbers. As a result of this, the oil retention vs capillary number curve in the double displacement process showed a minimum; i.e., oil retention increased with decreasing capillary number in the range of very low capillary numbers.

Journal Article↗

PubMed2003

Daily use of dentifrice with and without xylitol and fluoride: effect on glucose retention in humans in vivo.

The effect of daily use of three different dentifrices on glucose retention after glucose mouth rinsing was tested in this study regarding xylitol and fluoride. Six experimental groups used three different dentifrices produced by two different companies: xylitol- and fluoride-containing dentifrice (XF), non-xylitol- and fluoride-containing dentifrice (F), and non-xylitol- and non-fluoride-containing dentifrice (NonX-NonF). Subjects were divided at random and rinsed their mouths for 15s with 20ml of 0.5M glucose solution. Glucose and lactate retention were determined by collecting samples of saliva from the approximal areas of the maxillary and mandibular anterior teeth and using the enzyme membrane test. Samples were collected 0, 1 and 2 months after the start of regular dentifrice use. There were significant differences in glucose retention in relation to the dentifrice used, month of sampling, site of sampling, and time since start of rinsing. Their contribution ratios were 2.0, 4.4, 11.7 and 7.4%, respectively (P<0.01). There were significant differences observed between the XF and NonX-NonF groups, with the XF group presenting lower glucose retention than the NonX-NonF group. The XF group presented lower glucose retention than the F group. The F group showed lower glucose retention than the NonX-NonF group. There were significant differences in lactate retention in relation to the month and site of sampling, and their contribution ratios were 3.3 and 2.8%, respectively (P<0.01). There were, however, no significant differences in glucose and lactate retention in relation to the dentifrice manufacturer. It was concluded that the XF dentifrice was the most effective, and the F dentifrice was more effective in reducing glucose retention than the NonX-NonF dentifrice.

Adult↗

PubMed2000

Arterial intimal retention of pro-atherogenic lipoproteins in insulin deficient rabbits and rats.

Recent observations that remnants of triglyceride rich lipoproteins become trapped within the subendothelial of arterial vessels gives rise to the possibility that these particles could initiate the atherogenic cascade. Increased frequency and progression of atherosclerosis in diabetes might in part be a consequence of raised concentrations in plasma of remnant lipoproteins. In addition, diabetes may lead to changes in the arterial vasculature which exacerbate arterial retention of pro-atherogenic lipoproteins. To explore these possibilities, in this study we determined aortic retention of chylomicron remnants, which are of intestinal origin, and of hepatically derived low-density lipoproteins (LDL) in insulin deficient rabbits and rats. The two species were selected because of their disparate susceptibility to develop atherosclerosis in the presence of diabetes induced hyperlipidemia. Chylomicron remnants and LDL were differentially radiolabelled with a residual marker and injected simultaneously into conscious rabbits or rats. Arterial retention was determined 2 h after injection, and relative retention was expressed as a percentage of mean arterial exposure. We found in insulin deficient rabbits and rats that intimal and medial retention of chylomicron remnants was positively related to the degree of hyperglycemia and was significantly greater than in non-diabetic control groups. In contrast, insulin deficiency did not influence arterial retention of LDL. Rabbits which are susceptible to diabetes induced atherogenesis had significantly greater intimal retention of chylomicron remnants compared to rats. Results from this study support the hypothesis that chronic hyperglycemia promotes arterial retention of triglyceride rich remnant lipoproteins and that atherosclerotic susceptibility might be related to degree of remnant entrapment within the subendothelial space. Greater retention of remnant lipoproteins could in part explain the increased prevalence of atherogenesis in diabetes.

Animals↗

PubMed2002

Improving the accuracy of Kováts' retention indices in isothermal gas chromatography.

Isothermal Kováts' retention indices are currently reported as whole numbers, and are frequently deduced from a linear least mean squares fitting of the logarithms of adjusted retention times of a number of n-alkanes versus carbon number, following an iterative method that minimises errors. The currently accepted accuracy is about one retention index unit for apolar stationary phases, and lower for polar stationary phases. This paper presents results that show how the accuracy of the retention index may be safely reported to one-tenth of a retention index unit by the use of a non-linear equation, with present day gas chromatographs without electronic flow controllers. Results are presented that prove the correctness of the retention indices found for several substances on one particular capillary column. Hints on the minimum retention times needed to achieve the 0.1 retention index accuracy are mentioned, for retention times recorded in minutes and in seconds. According to results of this paper, two chromatograms, run under the appropriate conditions, are sufficient to obtain the desired accuracy. The method proposed in this paper does not require knowledge of the hold-up time of the chromatogram.

Chromatography, Gas↗

PubMed1987

Effects of ion-pairing reagents on the prediction of peptide retention in reversed-phase high-performance liquid chromatography.

We have examined the resolution, on reversed-phase columns, of a series of model synthetic peptides and commercially available synthetic peptide standards under gradient elution conditions, using a water-acetonitrile mobile phase containing hydrophilic (phosphoric acid) or hydrophobic (trifluoroacetic acid, heptafluorobutyric acid) ion-pairing reagents. Increasing hydrophobicity or concentration of the ion-pairing reagents increased peptide retention times. It was clearly shown that these reagents effected changes in peptide retention time solely through interaction with the basic residues in the peptide. In general, each positive charge, whether originating from a lysine, arginine or histidine side-chain, or from an N-terminal alpha-amino group, exerts an equal effect on peptide retention. Different counterions have different effects on the change in peptide retention time per positively charged residue due to their differences in hydrophobicity. However, increasing concentrations of a specific counterion have an essentially equal effect per positively charged residue. These effects are also column dependent (n-alkyl chain length and ligand density). These results, demonstrating a simple relationship between peptide retention in different ion-pairing systems, enabled the determination of rules for prediction of peptide retention times in one ion-pairing system from observed or predicted retention times in another system. The small average deviation of predicted and observed retention times for a series of basic peptides was good evidence for the value of this predictive method. This study provides a clear understanding of the effect of changing counterion hydrophobicity or concentration on peptide retention, and thus can be extremely beneficial in the purification of peptides and for providing proof of peptide homogeneity.

Amino Acid Sequence↗

PubMed2000

Modelling retention in liquid chromatography as a function of solvent composition and pH of the mobile phase.

The aim of this work was to develop a model that accurately describes retention in liquid chromatography (LC) as a function of pH and solvent composition throughout a large parameter space. The variation of retention as a function of the solvent composition, keeping other factors constants, has been extensively studied. The linear relationship established between retention factors of solutes and the polarity parameter of the mobile phase, E(N)T, has proved to predict accurately retention in LC as a function of the organic solvent content. Moreover, correlation between retention and the mobile phase pH, measured in the hydroorganic mixture, can be established allowing prediction of the chromatographic behavior as a function of the eluent pH. The combination of these relationships could be useful for modelling retention in LC as a function of solvent composition and pH. For that purpose, the retention behavior on an octadecyl silica column of a group of diuretic compounds covering a wide range of physico-chemical properties were studied using acetonitrile as organic modifier. The suggested model accurately describes retention of ionizable solutes as concomitant effects of variables included and is applicable to all solutes studied. We also aimed to establish an experimental design that allows to reproduce to a good approximation the real retention surface from a limited number of experiments, that is from a limited number of chromatograms. Ultimately, our intention is to use the model and experimental design for the simultaneous interpretive optimization of pH and proportion of organic solvent of the mobile phase to be used in the proposed separation.

Chromatography, Liquid↗