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PubMed1993

Strain-dependent effects of gamma-L-glutamyl-L-aspartate, a NMDA antagonist, on retention of a Y-maze avoidance learning task in mice.

The NMDA receptor antagonist, gamma-L-glutamyl-L-aspartate (gamma-LGLA), suppressed spontaneous improvement in posttraining performance in Swiss mice during the hours following acquisition of a Y-maze avoidance learning task. Since variability in posttraining performance is at least partially due to genetic factors, we compared the effects of gamma-LGLA on retention of Y-maze learning in C57BL/6J, DBA/2J and BALB/c mice. Mice had to leave the start alley of the maze within the first 5 s (temporal component) and to choose the left alley (spatial component). C57BL mice significantly improved their performance from 1 h to 24 h posttraining, whereas DBA/2J and BALB/c mice did not. However, only retention of the temporal component improved over time in C57BL. gamma-LGLA administered immediately posttraining (0.025-25 mumol/kg, i.p.) dose-dependently impaired retention of the temporal component in C57BL mice 48 h later, but had no significant effect on retention of the spatial component. gamma-LGLA administered 24 h posttraining induced a similar but weaker deficit. In contrast, gamma-LGLA did not significantly affect retention of DBA/2J and BALB/c mice, regardless of the component analyzed or the time of administration. It had no effect on locomotor activity or emotional reactivity of animals of any strain. These results support the hypothesis of a specific action of gamma-LGLA on mechanisms involved in the treatment of information during the hours following acquisition, and suggest that NMDA receptors are involved in this action.

Animals↗
PubMed1987

The effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on the acquisition and retention of a conditional visual discrimination: implications for cholinergic hypotheses of learning and memory.

The effects of ibotenic acid-induced lesions of the ventral pallidum/substantia innominata region, the dorsal pallidum or both on the acquisition and retention of a conditional visual discrimination have been studied in the rat. Lesions of the ventral pallidum and large lesions of the dorsal and ventral pallidum severely impaired both the acquisition and retention of the conditional discrimination. Dorsal pallidal lesions had similar, but less marked effects. The same lesions also impaired the retention of a passive avoidance task, but had no effect on a conditioned taste aversion. Neurobiological investigations revealed that the lesions destroyed cholinergic neurons in the magnocellular nucleus basalis and caused reductions in cortical choline acetyltransferase activity of about 30-40%. Tract-tracing experiments indicated that the lesions destroyed, in particular, cholinergic neurons projecting to the frontal dorsolateral cortex and also those projecting to more posterior cortex, but not the occipital lobes. Contingency analysis of the behavioural, neurochemical and neuroanatomical data indicated that those animals with the largest decreases in choline acetyltransferase activity, or the largest areas of neuronal loss in the ventral and dorsal globus pallidus, were most impaired in the retention of the conditional discrimination. The results do not, therefore, indicate a simple relationship between cholinergic neuronal loss and the retention of response rules essential for performance of the task ("reference memory"). The relevance of the results to cholinergic hypotheses of learning and memory is discussed.

Animals↗
PubMed1990

The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets.

The effects of N-methyl-D-aspartate-induced lesions of the basal forebrain (which included the cholinergic cells of the nucleus basalis of Meynert) were studied on three aspects of visual discrimination; learning, retention and reversal performance, in the marmoset. Neurobiological investigations revealed that the lesion produced large reductions in choline acetyltransferase activity within anterior regions of cortex, particularly prefrontal. In Experiment 1 lesioned animals showed impaired retention, one week after surgery, of a visual discrimination learned immediately prior to surgery and subsequently showed impaired performance over a series of reversals. The reversal deficit could be characterized as a tendency to perseverate on the previously correct stimulus on the first reversal and as a failure to show serial reversal learning on subsequent reversals. Acquisition of a novel discrimination was not impaired five weeks after surgery. As time of testing may have been a confounding factor, in Experiment 2 the effects of the same lesion on new learning were examined immediately following surgery and the effects on retention a month later. The lesion was found to disrupt new learning but did not affect retention. From the two experiments it is clear that, whereas disruption of retention and new learning was relatively transient, the impairments in reversal performance were more long lasting. In addition, lesioned animals exhibited behavioural hyperactivity and elevations in consummatory and schedule-controlled licking. The disinhibitory and preservative effects observed following lesions of the basal forebrain in this study are similar to those following lesions of the orbitofrontal cortex while the disruption of serial reversal learning is commonly seen following damage to the amygdala. Therefore, these results are consistent with the hypothesis that the range of behavioural effects of the lesion result from damage to the cholinergic afferents to orbitofrontal cortex and to the amygdala, two structures intimately connected to one another.

Animals↗
PubMed2004

Effects of electrical stimulation of the nucleus basalis on two-way active avoidance acquisition, retention, and retrieval.

This study assessed the role of the nucleus basalis magnocellularis (NBM) in specific memory phases of two-way active avoidance conditioning. We evaluated the effects of NBM electrical stimulation applied during different phases of the avoidance task. Rats were trained in a 30-trial acquisition session, and were tested again 24 and 48 h later. NBM stimulation was applied at different stages of memory formation of the conditioning: (1) immediately before the first training session to determine the effects on acquisition of the two-way avoidance task; (2) immediately after the first training session to evaluate effects on memory consolidation; and (3) immediately before the 24-h retention session to analyze the effects on the retrieval process. NBM stimulation before training significantly improved the acquisition of the task, without affecting subsequent retention at either 24 or 48 h. Stimulation of the NBM immediately after the first training session slightly impaired performance in the 24-h retention session. Stimulation of the NBM immediately before the 24-h retention session did not affect performance in either the 24 or 48-h retention sessions. Therefore, the NBM may play a more important role in acquisition of memory in aversively motivated conditioning tasks than in consolidation or retrieval of such memories. These results are discussed in the context of attention enhancement and cortical and amygdala activation.

Animals↗
PubMed2006

Patient-controlled epidural analgesia: the role of epidural fentanyl in peripartum urinary retention.

BACKGROUND: Urinary bladder function is impaired during labor and delivery, predisposing to urinary retention. The effect of low-dose epidural opioid on bladder function remains unclear. We tested the hypothesis that adding low-dose fentanyl to epidural ropivacaine for patient-controlled labor analgesia does not promote urinary retention. METHODS: Laboring women who requested patient-controlled epidural analgesia were randomly assigned in a double blind study to 0.2% ropivacaine (R-group, n=100) or 0.2% ropivacaine with fentanyl 2 microg/mL (RF-group, n=98). Urinary bladder distension was assessed clinically every hour. The post-void residual urine volume was measured by ultrasonography. Urine volume exceeding 100 mL was drained by catheterization. Bladder volume of > or =300 mL, as determined by catheterization was considered as evidence of urinary retention. RESULTS: Thirty percent of the patients in each group developed urinary retention during labor. There was no statistically significant difference between the groups. There was an excellent correlation between bladder volume as estimated by ultrasonography and that by catheterization: catheterization volume=0.93 x ultrasound volume + 25; r(2)=0.83. The bias (mean error) was -1+/-99 mL and the precision (average absolute error) between the ultrasound estimate and actual bladder volume determined by catheterization was 58+/-79 mL. CONCLUSION: Addition of fentanyl to patient-controlled epidural analgesia did not increase the risk of urinary retention. Ultrasound measurements were effective and reliable in assessing urinary bladder volumes during labor.

Adult↗
PubMed1997

Tradeoff of semantic relatedness and degree of overlearning: differential effects on metamemory and on long-term retention.

We investigated people's recall and recognition of, and Judgments of Learning (JOLs) and Feelings of Knowing (FOKs) about: (a) pairs of related words that were learned to a criterion of two correct recalls (criterion-learned/related) versus (b) pairs of unrelated words that were learned to a criterion of eight correct recalls (overlearned/unrelated). Recall, FOK on unrecalled targets, and recognition were tested at either (between-subjects variable) two or six weeks after learning. In Experiment 1, subjects JOLs were greater in magnitude for criterion-learned/related items than for overlearned/unrelated items, and they predicted that recall would be the same after a 2-week retention interval as after a 6-week retention interval (between-subjects prediction). In contrast, however, subsequent recall was greater on the 2-week retention test than on the 6-week retention test and was greater for the overlearned/unrelated items than for the criterion-learned/related items; also, subjects' FOKs (and recognition performance) were greater in magnitude for the overlearned/unrelated items than for the criterion-learned/related items. Experiment 2 revealed that the overweighting of the importance of relatedness disappears from JOLs when those JOLs occur one day after the acquisition session. These findings imply that the information tracked by metacognitive monitoring judgments is different for JOLs than for FOKs, with the JOLs (relative to FOKs) based more on semantic relatedness and less on the degree of learning during acquisition. Also, subjects' JOLs are not particularly good at accurately forecasting their eventual level of recall on long-term retention tests that occur several weeks after acquisition.

Adult↗
PubMed1998

The effects of neurosteroids on acquisition and retention of a modified passive-avoidance learning task in mice.

This study examined the effects of neurosteroids, pregnenolone sulfate (PS) and dehydroepiandrosterone sulfate (DHEAS), on learning and memory processes in a modified passive-avoidance task in mice. The two parameters measured are number of passive-avoidance step-down descents and the active escape latency to reach shock-free zone. Each neurosteroid was administered 60 min before or immediately after the training session, or 60 min before the retention test given 24 h after acquisition. Pretraining injection of PS (0.125-10 mg/kg, s.c.) and DHEAS (0.125-10 mg/kg, s.c.) decreased the number of mistakes committed on training day but had no effect on the latency measure. Both PS (0.125-10 mg/kg, s.c.) and DHEAS (0.125-10 mg/kg, s.c.) decreased the number of mistakes and latency to reach shock-free zone, in a dose-dependent and bell-shaped manner, following pretraining and posttraining administration schedules. Neurosteroids failed to improve memory performance when administered 60 min before retention testing. Injection of PS (0.5 and 1 mg/kg) or DHEAS (1 and 5 mg/kg) before both the training and test sessions, however, also significantly facilitated memory retention. In addition, the memory-facilitating effects of PS (0.5 mg/kg, s.c.) or DHEAS (1 mg/kg) when administered posttraining are blocked by concurrent administration of haloperidol (0.25 mg/kg, i.p.), a prototype sigma receptor antagonist. These results confirm that both PS and DHEAS facilitate retention of a modified learning task when given either pretraining or posttraining, but not prior to retention test. The pretraining neurosteroid-induced memory modulation do not involve state-dependent effects. These results suggest a role for central sigma receptor in the memory-modulating effects of neurosteroids.

Animals↗
PubMed2003

Effects of histamine and cholinergic systems on memory retention of passive avoidance learning in rats.

In the present study, the effects of the histamine and cholinergic systems on memory retention in adult male rats were investigated. Post-training intracerebroventricular injections were carried out in all the experiments. Cholinoceptor agonist, acetylcholine (1-10 microg/rat) or nicotine (1-10 microg/rat), increased, while a cholinoceptor antagonist, scopolamine (5-20 microg/rat), decreased memory retention. The response to acetylcholine was attenuated by scopolamine. Administration of histamine (5-20 microg/rat) reduced, but the histamine H(1) receptor antagonist, pyrilamine (10-50 microg/rat), and the histamine H(2) receptor antagonist, cimetidine (1-50 microg/rat), increased memory retention in rats. The histamine receptor antagonists attenuated the response to histamine. Histamine reduced the acetylcholine- or nicotine-induced enhancement. The histamine receptor antagonists enhanced the nicotine- or acetylcholine-induced response. Histamine potentiated the inhibitory effect induced by scopolamine. It is concluded that histaminergic and cholinergic systems have opposing effects on memory retention. Also, the histaminergic system elicits an interaction with the cholinergic system in memory retention.

Acetylcholine↗
PubMed2000

Proximal plate in conventional circumferential cast clasp retention.

Improper guiding planes are commonly used with conventional removable partial denture cast clasps. Short guiding planes with improper proximal plates decrease retention and cause repetitive traumatic movement of abutments. This article discusses the importance of guiding planes and proximal plates for conventional tooth-supported removable partial dentures with circumferential clasp. The retention force of the clasps was analyzed geometrically. If the guiding plane is short or the prepared surface is oblique, the contact between the proximal plate and the guiding plane or oblique plane diminishes at an early stage, which results in reduction of retention. The guiding plane should be parallel to the path of insertion and must be of a certain length for adequate retention. An elongated proximal plate that is parallel to the path of insertion may compensate for retention deficiency when an adequate guiding plane cannot be prepared.

Dental Abutments↗
PubMed1996

Retention and failure mode after cyclic loading in two post and core systems.

Retention of a prefabricated post and composite resin core system was compared with that of a cast post and core restoration in anterior maxillary teeth on which root canal preparations, enlarged in the coronal part, were performed. The effect of cyclic loading on restoration retention was also investigated. Retention of restorations not subjected to cyclic loading was not influenced by post type, but loaded prefabricated post restorations showed lower retention than both loaded cast post and core restorations and nonloaded prefabricated post restorations. After dislodgement, the failure mode was also determined. The results of this study suggest that if a canal requires extensive preparation, a well-adapted cast post and core restoration may be more retentive than a prefabricated post restoration that does not match the canal shape.

Composite Resins↗
PubMed1996

The effect of simulated function on the retention of bar-clip retained removable prostheses.

Patients wearing bar-clip retained removable prostheses may have loss of retention because of changes within the bar-clip assembly. This in vitro study recorded and compared the retention of one- and two-clip retained simulated mandibular complete denture prostheses before and after simulated function. Cast metal Hader bars and clip holders were used to make 10 one-clip and 10 two-clip specimen pairs. Tensile removal values before and after simulated function were recorded and compared by repeated-measures analysis of variance and Student tau tests (significance level 0.05). The results revealed that the use of two clips instead of one significantly increased retention of the simulated prosthesis. It was also found that there was a significant loss of retention after the specimens were placed on the bars and then removed once for both the one- and two-clip groups. Simulated function did not cause a significant change in retention for either group.

Analysis of Variance↗
PubMed1997

Effect of convergence angle on retention of resin-bonded retainers cemented with resinous cements.

STATEMENT OF PROBLEM: Poor retention is a common cause of failure for resin-bonded restorations. PURPOSE: This study evaluated the effect of the convergence angle of tooth preparations on retention of resin-bonded restorations, luted with adhesive and conventional resinous cements. MATERIAL AND METHODS: A total of 80 posterior retainers with four different tooth preparation angles were cemented with two different resinous cements, and retentive strength was measured. RESULTS: The results indicated that (1) increased tapering of tooth preparations resulted in loss of retention and this variable was statistically significant for both cements used when convergence angles exceeded 10 degrees and (2) sandblasted nickel-chromium retainers, combined with adhesive resins, should provide sufficient retention for posterior resin-bonded fixed partial dentures.

Adhesives↗
PubMed1998

Retention of prefabricated attachments for implant stabilized overdentures in the edentulous mandible: an in vitro study.

STATEMENT OF PROBLEM: Bar and stud attachments are widely used to stabilize overdentures on implants in the mandible. There is strong evidence that retention of the attachment is an important factor for a patient's satisfaction. PURPOSE: This study describes retentive forces and wear of commercially available attachments of 4 implant systems (31, IMZ, Nobel Biocare, ITI Straumann) and 2 magnets (Steco). METHODS: Forces while removing the keyway portion of an attachment in its path of insertion were measured with a platform load cell. A total of 15,000 removals were performed to simulate fatigue. RESULTS: Retentive forces ranged between 3 and 85 N. The fatigue test revealed an initial increase of forces with some attachments. After 15,000 cycles, most of the attachments showed little loss of retention compared with the initial retentive forces. It is suggested that conventional fatigue tests with application of axial loads do no simulate clinical fatigue adequately.

Dental Abutments↗
PubMed1998

Prostatic infarction/infection in acute urinary retention secondary to benign prostatic hyperplasia.

PURPOSE: We assess the role of acute prostatic infarction and prostatic inflammation in causing acute urinary retention in patients with benign prostatic hyperplasia (BPH). MATERIALS AND METHODS: A prospective controlled clinicopathological study was undertaken comparing 35 patients who presented with acute urinary retention secondary to BPH with another 35 patients with symptomatic BPH. All 70 patients were treated with transurethral resection. The prostatic chips in each group were examined by 1 histopathologist, who was unaware of the clinical presentation of the patient, for changes of infarction, acute and chronic inflammation, and predominant histological pattern. RESULTS: There was a higher incidence of glandular pattern in the retention group compared to a stromal pattern in the control group, which was statistically significantly different (p < 0.001). A 5-fold higher incidence of prostatic carcinoma was noted in the acute retention group, which was also statistically significant (p < 0.05). CONCLUSIONS: Prostatic infarction and inflammation had no role in the etiology of acute urinary retention due to BPH.

Acute Disease↗
PubMed2004

The effect of a resin-based sealer on crown retention for three types of cement.

STATEMENT OF PROBLEM: In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products. PURPOSE: This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents. MATERIAL AND METHODS: Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5 degrees C and 55 degrees C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with alpha=.05. The nature of failure was also recorded and the data analyzed with a chi-square test. RESULTS: Mean dislodgment stresses for unsealed and sealed conditions were 3.7 +/- 1.0 and 2.2 +/- 0.8 MPa for zinc phosphate; 2.7 +/- 1.2 and 4.2 +/- 0.9 MPa for glass ionomer, respectively (P<.001). Retentive stress of castings cemented with modified-resin cement was 6.4 +/- 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgment in 9 of 11 specimens cemented with modified-resin cement. CONCLUSIONS: Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.

Analysis of Variance↗
PubMed1999

How efficient are central mechanisms for the learning and retention of coincident timing actions?

We compared the adaptive strategy and retention capacity of a deafferented subject and control subjects when intercepting, with a sliding-throw, an apparent movement coming at various speeds. Subjects were submitted to five practice sessions (30 trials per session) and to a retention test. The throwing kinematics was analysed, and spatial and temporal performance errors were measured. With practice, the deafferented subject showed modifications in movement initiation strategies and throwing patterns. With a slow apparent movement, the deafferented subject's initial behavior was characterized by short movement initiation and movement times. With practice, she showed an important increase in movement time in session 5, allowing longer visual control and leading to better temporal and spatial accuracy than that shown in session 1. In the retention session, the deafferented patient showed a late movement initiation strategy, similar to that of the control subjects. This increased movement initiation time was accompanied by an improved temporal accuracy compared to the deafferented subject's early results. However, spatial accuracy improvement was labile and could not be maintained over the retention interval. At the fast speed, all temporal components of the response, namely, movement initiation time (MIT), movement time (MT), and disk travel time (DTT), were similar for the deafferented and control subjects. Overall, the deafferented subject reduced her temporal error through practice, though without attaining the control subjects' accuracy. However, with a fast-moving stimulus, she showed a deteriorated spatial accuracy, even doubling her spatial errors at retention. In brief, the deafferented subject achieved proper temporal (perceptivo-cognitive) lasting control of her interceptive action, whereas spatial (sensorimotor) regulation raised mnemonic problems.

Afferent Pathways↗
PubMed1998

Transition zone index as a risk factor for acute urinary retention in benign prostatic hyperplasia.

OBJECTIVES: To examine the efficacy of various parameters obtained by transrectal ultrasonography (TRUS) as predictors of the onset of acute urinary retention in patients with benign prostatic hyperplasia (BPH). METHODS: From April 1993 to March 1997, 331 men aged 51 to 84 years with symptoms of BPH were enrolled in this study. Among them, 64 patients presented to our clinic because of acute urinary retention. TRUS was used to calculate the transition zone (TZ) volume, the transition zone index (TZ index = TZ volume/total prostate volume), the total prostate volume, and presumed circle area ratio (PCAR). To compare the usefulness of the various indices, the area under the receiver-operator characteristic (ROC) curve was calculated for each index. RESULTS: There were significant differences in the American Urological Association (AUA) symptom score, total prostate volume, TZ volume, TZ index, and PCAR between patients with and without acute urinary retention, but no significant differences in age and quality of life score. In patients with acute urinary retention, the area under the ROC curve was 0.924 for the TZ index, 0.834 for the TZ volume, 0.753 for the PCAR, 0.684 for the total prostate volume, and 0.628 for the AUA symptom score. CONCLUSIONS: The TZ index is an accurate predictor of acute urinary retention in patients with BPH and may be a useful method for deciding between surgical intervention and antiandrogen treatment.

Acute Disease↗
PubMed1998

Effects of eugenol and noneugenol endodontic sealer cements on post retention.

Resin cements are sometimes recommended to enhance the retention of posts in endodontically treated teeth. Many sealer cements used in endodontics contain eugenol, however, which has been shown to inhibit the polymerization of resins. The purpose of this study was to evaluate the effects of a eugenol and a noneugenol sealer cement on the retention of posts. Sixty extracted canines were divided equally into four groups. Each tooth received conventional endodontic therapy and was prepared to receive a post. Two sealer cements were used in obturation: one contained eugenol and one was eugenol-free. The posts were cemented with either zinc phosphate cement or resin cement. Each combination of sealer and post cement was tested for retention on an Instron testing machine. The type of sealer used had no effect on post retention with either cement. Post retention was significantly greater with the zinc phosphate cement than the resin cement.

Analysis of Variance↗