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PubMed1976

Platelet retention in glass bead columns: adhesion to glass and subsequent platelet-platelet interactions.

In normal heparinized blood, the retention of platelets in glass bead columns was low in the first 1 or 2 ml, increasing to more than 80% by the 4th or 5th ml. Prior flushing of the columns with platelet-poor plasma or saline lowered retention in all 5 ml. Additional studies were carried out with a two-stage procedure in which a sample of blood (A) was pumped through a column, immediately flushed out with saline or plasma, and followed by a second blood sample (B). When as little as 1 ml of blood A preceded the flushing solution, retention was very high in all 5 ml of the subsequent blood B. This enhancement of retention in B occurred, providing blood A contained platelets (other than thrombasthenic), fibrinogen, and adequate divalent cations. Enhancement did not require von Willebrand factor (vWF) in A, nor was ADP necessary, since enhancement occurred even when heparinized blood as A contained prostaglendin E1 (PGE1) or creatine phosphokinase with creatine phosphate (CPK-CP). However, the presence of PGE1 or CPK-CP in the plasma used to flush the columns prevented the enhancement of retention in the first milliliter of B. Retention in the first milliliter of B (following normal blood as A and saline or normal plasma for flushing) was high when B was afibrinogenemic, moderately high when B contained PGE1 or CPK-CP, and low in thrombasthenic, EDTA, or vWF-deficient blood. Retention declined in subsequent milliliters of PGE1 or CPK-CP blood and remained low in thrombasthenic, vWF-deficient, or EDTA blood. Our findings suggest that (1) the platelets in A adhere to glass; this adhesion requires fibrinogen but not vWF or ADP; (2) the adherent platelets release ADP and become sticky; (3) adhesion of platelets in the first milliliter of B to the sticky platelets from A requires vWF and divalent cations but not ADP; (4) retention is maintained thereafter by repetitive platelet-platelet interactions involving ADP release, alteration of adherent platelets by released ADP, and adhesion of further platelets to these ADP-altered platelets which requires vWF.

Adenosine Diphosphate↗

PubMed1993

Apolipoprotein E modulates low density lipoprotein retention by lipoprotein lipase anchored to the subendothelial matrix.

Lipoprotein lipase (lipase), a key enzyme in lipoprotein triglyceride metabolism, has been shown to markedly increase low density lipoprotein (LDL) retention by subendothelial matrix. In the present study we assessed the role that lipoprotein and matrix components play in retention of LDL by lipase anchored to the subendothelial matrix. Lipase addition to subendothelial matrix increased LDL retention by 66-fold. Scatchard analysis of LDL binding to lipase-containing matrix yielded an association constant of 12 nM. Exogenous addition of the matrix components, heparan sulfate and dermatan sulfate (i.e. chondroitin sulfate B), reduced LDL retention by greater than 90%. These glycosaminoglycans (GAGs) also reduced lipolytic activity associated with the matrix, suggesting that lipase was released from its binding sites on the matrix. In contrast, other matrix components (collagen, fibronectin, vitronectin, and chondroitin sulfate A) neither affected LDL release nor matrix lipolytic activity. Thus, heparan sulfate and dermatan sulfate function to anchor lipase to the subendothelial cell matrix. The effects of apolipoprotein E (apoE) and apoA-I were also examined. Preincubation of the subendothelial matrix with apoE, followed by washing, did not affect subsequent lipase binding to the matrix nor its ability to retain LDL. However, the direct addition of apoE alone or in combination with phospholipid liposomes decreased lipase-mediated LDL retention in a concentration-dependent fashion. Addition of apoA-I had no effect. Thus, in these studies apoE functions to displace LDL bound to lipase, but not lipase anchored to the matrix. To further examine the physiologic implications of this process, we assessed the ability of human apoE-rich and apoE-poor high density lipoproteins (HDL) to displace LDL from matrix-anchored lipase. ApoE-rich HDL reduced LDL retention dramatically (86% at 2.5 micrograms/ml). In contrast, apoE-poor HDL, at the highest concentration evaluated (400 micrograms/ml), decreased LDL retention by only 32%. Overall, these data suggest apoE and specifically apoE-containing HDL reduce the lipase-mediated retention of LDL by subendothelial matrix. This observation, in part could explain the protective effects of apoE and apoE-containing HDL against atherosclerosis.

Animals↗

PubMed2003

Effects of prenatal cocaine exposure and maternal separation on heart rate, orienting response habituation, and retention.

Effects of the presence or absence of the dam during testing and the retention interval on pretone heart rate (HR) and habituation and retention of an HR orienting response to tone were examined in prenatally cocaine-exposed and nontreated Sprague Dawley rat pups in two experiments. On postnatal day 16, each pup received two test sessions, separated by a 4-hr retention interval during which pups were either isolated or placed with their dam and siblings. For testing, each pup was placed in the test apparatus in the presence or absence of an anesthetized dam where, after a 15-min adaptation period, 10 tone presentations were given, each separated by a 65-s intertrial interval, with HR measured during a 5-s pretone period and throughout the 10-s tone for each trial. Experiment 1 used offspring from the regular breeding colony and observed the typical HR lowering effect of maternal presence during testing, an effect that was surprisingly potentiated, however, following the retention interval in animals that were isolated during this interval. This apparent potentiation by prior isolation of the HR lowering effect of the dam was confirmed in Experiment 2 in nontreated offspring, but did not emerge convincingly in offspring of either dams subcutaneously injected with 40 mg/kg of cocaine HCl daily from gestational days 8 to 20 (C40) or dams injected with saline and pair-fed 4 days (PF4) to mimic the acute anorexic effects of cocaine administration. Consistent with prior work, C40 offspring also were found to exhibit better retention of the habituated orienting response than offspring of NT dams and to some extent PF4 dams as well, a retention effect that was not significantly influenced, however, by social context during the retention interval.

Acoustic Stimulation↗

PubMed1997

Insular cortex and amygdala lesions induced after aversive training impair retention: effects of degree of training.

These experiments examined the effects of N-methyl-D-aspartate (NMDA)-induced lesions of the amygdala and insular cortex induced 1 week after rats were trained on a footshock motivated escape task in a two-compartment runway. In the first experiment, male rats were given 10 training trials and, 1 week later, received microinjections of a buffer solution or NMDA into either the insular cortex (IC) or the amygdala (AM). In an inhibitory avoidance retention test 1 week after the microinjections, the retention latencies (i.e., latencies to enter the compartment where shock had been delivered) of both the AM- and "IC-lesioned" groups were significantly lower than those of the buffer-injected groups. Additionally, in comparison with the buffer controls, rats in the two lesioned groups made significantly more crossings between the two compartments during the retention test. In a second experiment, male rats were given 1, 10, or 20 escape training trials 1 week before receiving either sham or NMDA lesions in the IC. The retention test was given 1 week after microinjection. Those sham or lesioned animals that were given only one training trial did not demonstrate retention. Both lesioned groups given 10 or 20 training trials were significantly disrupted on both the step-through latencies, and the number of crossings between the two compartments. The retention-impairing effects of NMDA-induced lesions were slightly attenuated in the group given 20 escape training trials. The findings provide additional evidence that the AM and the IC are involved in regulating the long-term retention of aversively motivated training.

Amygdala↗

PubMed1998

Temporal determinants of olfactory long-term retention in honeybee classical conditioning: nonmonotonous effects of the training trial interval.

The question of which acquisition parameters govern long-term retention is important to an understanding of memory function. We investigate the effects of the time interval between learning trials on mediate (1 day)- and long-term (4 days) retention. In classical conditioning of the proboscis extension reflex, we train honeybees to associate an odorant with a sucrose reward using intertrial intervals of either 30 s, 1 min, 3 min, or 20 min. Intervals of 20 and 1 min result in stable retention but 3-min and 30-s intervals result in reduced retention after 4 days compared to that seen after 1 day. Thus, stability of long-term retention depends nonmonotonously on the intertrial interval. Reduced retention with 3-min intervals might be caused by a disruption of memory consolidation which is known to be especially sensitive to interference 3 min after a conditioning trial. Habituation and backward inhibitory learning are discussed as explanations for reduced retention with 30-s intervals.

Animals↗

PubMed2002

Urinary retention following endoscopic totally extraperitoneal inguinal hernioplasty.

BACKGROUND: The impact of preperitoneal mesh after endoscopic totally extraperitoneal inguinal hernioplasty (TEP) on voiding function has not been previously examined. The objectives of the present study were to evaluate the incidence of and risk factors for urinary retention following TEP. METHODS: Three hundred consecutive patients who underwent TEP between June 1999 and September 2001 were recruited. Patient records were reviewed retrospectively to identify those who developed postoperative urinary retention. For each case patient, five age-matched control patients were randomly selected. We then compared the clinical data for the case and control groups. A prospective study of uroflowmetry in patients who underwent bilateral TEP was conducted to evaluate the effect of preperitoneal mesh on voiding function. RESULTS: The overall incidence of urinary retention following TEP was 4% (n = 12). Patients who developed urinary retention stayed in hospital for a significantly longer period than the control group. No significant association was found between the clinical data and postoperative urinary retention. Bilateral TEPs were not associated with significant deterioration in uroflowmetry. CONCLUSIONS: Urinary retention is a frequent morbidity after TEP and significantly prolongs the length of hospital stay. Preperitoneal Prolene mesh did not cause outflow obstruction or alter bladder contractility. No specific clinical factors were identified that might predict postoperative urinary retention, which was probably multifactorial in causation in our patient population.

Adult↗

PubMed1995

The effects of pregnenolone sulfate and ethylestrenol on retention of a passive avoidance task.

Two experiments using male rats evaluated the effects of a range of doses of the neurosteroid, pregnenolone sulfate (PS), or of the synthetic neurosteroid, ethylestrenol (E), on the retention of a passive avoidance task. The steroids either were given immediately after the training trial or 1 h before the first retention test. Retention tests were given both 24 h and 48 h after acquisition. In both experiments, separate groups of animals were trained under low or moderate footshock conditions. At all doses tested both PS and E improved retention under the low footshock conditions. In groups trained with the higher footshock, the steroid-treated groups performed no better than the vehicle controls. Indeed, there were suggestions that some doses impaired retention. These results seem best understood as an induction of bimodality or 'turbulence' in behavior as used in Chaos theory rather than a shift in an inverted U-shaped retention function. In the second experiment in which the steroids were given before retention testing, they were generally without effect.

Animals↗

PubMed1992

Effect of surface roughness and cement space on crown retention.

The effects of varying luting agent space and internal surface roughness with different types of cores and cements were studied. One hundred eighty amalgam and 180 composite cores were cemented into standardized stainless steel retainers. Cores and retainers were divided into 12 groups according to core type, core diameter, and retainer roughness. Each group was further subdivided according to cement, A: zinc phosphate (ZOP); B: resin; and C: glass ionomer cement (GIC). Subgroups were divided into thermal-cycled and nonthermal-cycled groups. Thermal cycling was at 5 degrees to 55 degrees C, repeated 500 times. Cores were separated from their retainers with a compression rod in an Instron testing machine at a crosshead speed of 0.02 cm/minute. Results were as follows: Amalgam cores were most retentive. Resin and ZOP cements were equally retentive with amalgam cores, but GIC was less retentive. Resin cores cemented with resin cement were more than twice as retentive than those cemented with ZOP or GIC cements. Retainers with rough internal surfaces were most retentive. A reduced cement space between core and retainer was most retentive. Thermal cycling reduced retention.

Analysis of Variance↗

PubMed1993

Comparison of the retention of endodontic posts after preparation with EDTA.

Significant differences in the retention of preformed endodontic posts for endodontically treated teeth were determined with (1) parallel-sided, passively placed Para-Post dowel versus mechanically engaging, threaded Flexi-Post dowel; (2) irrigation of canals with EDTA; (3) cementation with urethane dimethacrylate resinous or zinc phosphate cement. It was hypothesized that EDTA would substantially increase retention by removing the smear layer on the prepared canal wall and create micromechanical retention in the dentin. Extracted teeth were prepared with endodontic posts and divided in groups representing combinations of variables. The forces for post removal and the locations of the retentive bond failures were recorded. The results indicated that EDTA did not significantly affect retention. The Flexi-Post dowel was significantly more retentive than the Para-Post dowel but also exhibited a greater potential for tooth damage compared with the Para-Post dowel during retentive failure loads.

Analysis of Variance↗

PubMed1994

Spatial working memory over long retention intervals: dependence on sustained cholinergic activation in the septohippocampal or nucleus basalis magnocellularis-cortical pathways?

Previous direct neurochemical studies of the temporal dynamics of cholinergic activation in the septohippocampal and nucleus basalis magnocellularis-cortical pathways at various stages during repeated testing of mice with selective spatial reference or working memory protocols [Durkin and Toumane (1992), Behav. Brain Res. 50, 43-52] showed that the post-test durations of cholinergic activation in each pathway varied as a function of the type of memory tested and the level of task mastery. Since (i) the hippocampal formation is considered to constitute a critical component of a temporary memory buffer, and (ii) working memory items are not thought to be submitted to consolidation and permanent storage, we postulated that the duration of testing-induced cholinergic activation in the septohippocampal pathway may govern the maintenance of the working memory trace over the retention interval. In order to test directly this hypothesis C57 B1/6 mice were extensively trained (one trial/day, 25-30 days) on an identical selective working memory task to attain high levels of retention (> 80% correct), but using either 5 min (Group 1), or 60 min (Group 2) retention intervals. At various times (30 s-75 min) following the initial acquisition phase of the test, cholinergic activity in the hippocampus and frontal cortex was quantified using measures of high-affinity choline uptake. Whereas cholinergic activation was observed in both pathways at 30 s post-acquisition and throughout the 5 min retention interval in Group 1, the situation in Group 2 is different, activation of the septohippocampal pathway being maintained for only 15 min, while activation in the nucleus basalis magnocellularis-cortical pathway is maintained for the totality of the 1 h retention interval. The nucleus basalis magnocellularis-cortical cholinergic pathway, in addition to its role in long-term reference memory storage processes may, thus, via an intervention in the temporal encoding of information, also subsume a complementary intermediate-term buffer storage role in working memory situations requiring retention intervals in excess of 15 min in mice. This secondary, "backup", function of the nucleus basalis magnocellularis-cortical pathway would thus liberate the septohippocampal complex from its primary active role in the temporary maintenance and/or accessibility of the working memory trace in these particular cases requiring long retention intervals.

Acetylcholine↗

PubMed2005

Incidence and predictors of prolonged urinary retention after TVT with and without concurrent prolapse surgery.

OBJECTIVES: The purpose of this study was to describe the time to adequate voiding, incidence of urinary retention, and predictors of voiding efficiency and urinary retention after tension-free vaginal tape (TVT) with and without concurrent prolapse surgery. STUDY DESIGN: Medical records of patients who underwent TVT between August 1999 and July 2003 were reviewed. Urinary retention was defined as the need for urethrolysis, urethral dilation, or postoperative catheterization for >6 weeks. Linear and logistic regression models were used to determine predictors of time to adequate voiding and urinary retention. RESULTS: Two hundred sixty-seven patients were available for analysis; 66% had concurrent prolapse repair, 4% had concurrent laparoscopically assisted vaginal hysterectomy (LAVH), and 30% had an isolated TVT. TVT with and without concurrent prolapse repair or LAVH were statistically similar with respect to median days to voiding (8 vs 5) and the rate of urinary retention (11.2% vs 11.3%). Overall, 4.9% underwent urethrolysis, 1.9% received urethral dilation, and 4.1% required prolonged catheterization. Increasing age, decreasing BMI, and postoperative urinary tract infection were independent predictors of time to adequate voiding. Previous history of incontinence surgery was the only independent predictor of urinary retention (Adjusted odds ratio [AOR] 2.96, 95%CI [1.17-7.06]). CONCLUSION: Concurrent prolapse surgery does not appear to significantly alter postoperative voiding efficiency or increase the risk of prolonged urinary retention compared with TVT alone.

Adult↗

PubMed1995

Retentive characteristics of different dental magnetic systems.

It is necessary to recognize the retentive capabilities of magnetic systems to assess their clinical performance. This study determined the retentive characteristics of one open-field and two closed-field commercial dental magnetic systems. The effect of speed of separation and the space between the magnet and its keeper on the retention force were evaluated. The magnets and their respective keepers, embedded in acrylic resin blocks, were tested with fast and slow speeds of separation. The maximum retention values of the magnetic systems were tested with slow speed of separation. The fast speed of separation was designed to reflect mandibular movement. Various spaces were developed between the magnets and their respective keepers, and magnetic systems were tested only in slow speed of separation. The fast speed of separation dramatically lowered the retention force of each magnetic system. As the space increased between the magnet and keeper, the retention values diminished rapidly. While closed-field systems demonstrated higher retentive forces than the open-field system, the open-field system was less affected by the various spaces.

Denture Retention↗

PubMed1997

Urodynamic assessment of patients with acute urinary retention: is treatment failure after prostatectomy predictable?

PURPOSE: Some patients with acute urinary retention due to benign prostatic hyperplasia do not have successful outcome after prostatectomy and require either a chronic indwelling urethral catheter or clean intermittent catheterization. Urodynamic and clinical parameters were examined preoperatively in 81 men 56 to 93 years old (mean age 72 years) in search of an outcome predictor after prostatectomy. MATERIALS AND METHODS: International Prostate Symptom Score, prostate volume, retention episodes, retention volume and urodynamic parameters from a multichannel pressure-flow study were analyzed preoperatively and postoperatively. All patients underwent transurethral prostatectomy and were reexamined 2, 4, 12 and 24 weeks after surgery. A multichannel pressure-flow study was performed preoperatively and 12 weeks postoperatively. RESULTS: At 24 weeks postoperatively 11 patients (13%) were unable to void and therefore classified as treatment failures while the remaining patients voided spontaneously and were classified as treatment successes. There were statistically significant differences (p < 0.005) between treatment failure and treatment success regarding age (83.5 +/- 7 versus 70.1 +/- 8 years), preoperative volume of retention (1,780 versus 1,080 ml.), and maximal detrusor pressure (24.4 versus 73.5 cm. water), but not to International Prostate Symptom Score, episodes of retention and prostate volume. The ability to void during preoperative pressure flow study and the presence of detrusor instability predicted good outcome. In treatment success patients postoperative urodynamic data showed significant decrease in detrusor pressure at maximum flow rate (from 80.8 +/- 33 to 34.6 +/- 10 cm. water). Those with treatment failure had an increase in maximal detrusor pressure (from 26 +/- 12 to 42.6 +/- 13 cm. water), suggesting detrusor recovery. CONCLUSIONS: Patients with acute urinary retention, age 80 years or older, with retention volume greater than 1,500 ml., no evidence of instability and maximal detrusor pressure less than 28 cm. water are at high risk of treatment failure. However, despite treatment failure the detrusor may recover in patients younger than 80. Therefore, prostatectomy should still be performed in this group (less than 80 years old) even if preoperative urodynamics suggest an unfavorable outcome.

Acute Disease↗

PubMed1997

Natural history of prostatism: risk factors for acute urinary retention.

PURPOSE: We determined the occurrence of and risk factors for acute urinary retention in the community setting. MATERIALS AND METHODS: A cohort of 2,115 men 40 to 79 years old was randomly selected from an enumeration of the Olmsted County, Minnesota population (55% response rate). Participants completed a previously validated baseline questionnaire that assessed symptom severity, and voided into a portable urometer to measure peak urinary flow rates. A 25% random subsample underwent transrectal sonographic imaging of the prostate to determine prostate volume. Followup was performed through a retrospective review of community medical records to determine the occurrence of acute urinary retention in the subsequent 4 years. RESULTS: During the 8,344 person-years of followup 57 men had a first episode of acute urinary retention (incidence 6.8/1,000 person-years, 95% confidence interval [CI] 5.2, 8.9). Among men with no to mild symptoms (American Urological Association symptom index score 7 or less) the incidence of acute urinary retention increased from 2.6/1,000 person-years among men 40 to 49 years old to 9.3/1,000 person-years among men 70 to 79 years old. By contrast, rates increased from 3.0/1,000 person-years for men 40 to 49 years old to 34.7/1,000 person-years among men 70 to 79 years old among men with moderate to severe symptoms (American Urological Association symptom index score greater than 7). Men with depressed peak urinary flow rate (less than 12 ml. per second) were at 4 times the risk of acute urinary retention compared with men with urinary flow rates greater than 12 ml. per second (95% CI 2.3, 6.6). Men with an enlarged prostate (greater than 30 ml.) experienced a 3-fold increase in risk (95% CI 1.0, 9.0, p = 0.04). CONCLUSIONS: Lower urinary tract symptoms, depressed peak urinary flow rates, enlarged prostates and older age are associated with an increased risk of acute urinary retention in community dwelling men. These findings may help to identify men at increased risk of acute urinary retention in whom closer evaluation may be warranted.

Acute Disease↗

PubMed2001

Survey of voiding dysfunction and urinary retention after anti-incontinence procedures.

OBJECTIVE: To describe trends in the management of prolonged voiding dysfunction and urinary retention after anti-incontinence procedures. METHODS: Physician members of the American Urogynecologic Society were queried by means of a two-page questionnaire regarding the management of prolonged voiding dysfunction and urinary retention after anti-incontinence procedures. RESULTS: A total of 344 (42%) of 825 questionnaires were completed and returned. Of the 344 respondents, 61% identified themselves as urogynecologists, 50% worked in a university-affiliated practice, and 26% had been in practice for 11-20 years. Respondents rarely encountered prolonged urinary retention after anti-incontinence procedures. Among the respondents, 30% allowed 3-6 months for resumption of spontaneous voiding before performing surgical revision, and 90% performed multichannel urodynamic studies before surgical revision. However, 66% performed surgical revision transabdominally when urinary retention occurred after retropubic urethropexy, and 61-81% of respondents performed surgical revision transvaginally when urinary retention followed needle suspension, pubovaginal sling, or tension-free vaginal tape procedures. A total of 90-96% did not perform an anti-incontinence procedure concomitantly with surgical revision. The majority of respondents reported spontaneous voiding in greater than 80% of patients, and recurrent stress urinary incontinence in less than 10% of patients after surgical revision. CONCLUSION: Although certain trends in the management of prolonged urinary retention after anti-incontinence procedures were identified, there was no clear consensus on the method of surgical revision used, nor the management of recurrent stress urinary incontinence after surgical revision. Randomized clinical trials are required to determine the optimal management of prolonged urinary retention after anti-incontinence procedures.

Female↗

PubMed1997

Retention of context blocking in taste-aversion learning.

A series of experiments examined recovery from context blocking across a retention interval. In two flavor-aversion studies, rats received 0, 2, or 4 context + US pairings in Phase 1, a flavor + US pairing in Phase 2, and flavor testing after a 3-day or a 14-day retention interval. The procedures in Experimental 1 were performed in a novel context, whereas Experiment 2 was conducted in a moderately familiar context. In Experiment 1, the effects of 2 context + US pairing dissipated over the retention interval (i.e., the taste aversion increased in strength), but the effects of 4 context + US pairings did not change. In Experiment 2, no context blocking was observed after 2 context + US pairings, but the effects of 4 context + US pairings decreased across the retention interval. These studies are the first to show recovery from context blocking across a retention interval following single-element conditioning. Furthermore, Experiment 3 demonstrated that extinction of the context prior to taste conditioning eliminated context blocking, and Experiment 4 showed that weak taste aversions do not increase in strength across a retention interval. It is proposed that forgetting of the context-US association across an extended retention interval is the mechanism underlying recovery from context blocking.

Animals↗

PubMed1997

Neonatal caffeine alters passive avoidance retention in rats in an age- and gender-related manner.

Chronic administration of an adenosine receptor antagonist disturbs spatial learning and memory in adult mice and neonatal caffeine exposure results in long-term behavioral and biochemical sequelae in mice and rats. We thus postulated that early treatment with caffeine would have latent effects on learning and memory as measured in a passive avoidance paradigm. Rats were not handled or received caffeine (15-20 mg/kg/day) by gavage over postnatal days 2-6. At 28 or 70-90 days of age, rats were trained to avoid an electrified grid and tested for retention 24 h, 72 h, and 7 days later. At 28 days, caffeine-exposed rats required more trials to meet criterion than did control rats, regardless of gender. There was minimal effect on retention of either neonatal treatment or gender at this age. At 70-90 days, there was no effect of either gender or treatment on learning; however, there was a significant effect of gender (P < 0.05) on retention at 24 h that was more pronounced in neonatally caffeine-treated rats (P < 0.01). At 72 h, the effect of caffeine on retention differed between male and female rats. Neonatal caffeine exposure significantly improved retention in females (P < 0.01) and significantly decreased retention in males (P < 0.05). Thus, caffeine exposure limited to the first week of life resulted in alterations in passive avoidance retention that became apparent over pubertal development. These changes were a function of the gender of the animal.

Age Factors↗

PubMed2000

A triphasic curve characterizes the retention of lever-pressing behavior rewarded by lateral hypothalamic stimulation during the immediate-post-trial period in rats: implications for a transient-intermediate stage between short- and long-term memory.

We investigated the retention of lever-pressing behavior in rats rewarded by lateral hypothalamic (LHT) stimulation. Rats with electrodes implanted into the lateral hypothalamus were trained to press a lever to receive LHT stimulation. More than 90% of rats which had self-stimulated for longer than 30 min retained this behavior when tested 1 or 7 days later, indicating that intracranial self-stimulation (ICSS) produced a stable long-term memory lasting for at least 7 days. Subsequently, we examined retention at shorter ICSS-test intervals. Retention rates were measured 15, 30, 60, 90, 120, 180 or 360 min after the end of a 90-min period of ICSS, using a different group of 15 rats for each interval. Unexpectedly, retention rates in shorter interval tests were lower than those observed after 1 or 7 days. We observed a characteristic fluctuation in retention rates with lower rates at 30 and 180 min, giving a triphasic form to the retention curve with peaks at 15, 90 and 360 min. When a group of rats that had been previously stimulated and shown to have retained the lever-pressing behavior was allowed to re-stimulate a second time, no fluctuations were observed in short-term interval tests. This indicates that the fluctuations in the retention curve immediately after initial ICSS are closely related to the initial acquisition of the memory. Our results support a three-phase model of memory formation that includes a transient-intermediate stage between short- and long-term memory.

Animals↗