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At least 55 records · Page 3Linked to original sources

PubMed1987

The carry-over effect on the bowel habit in elderly long-term patients of long-term bulk-forming products containing stimulant laxative.

This study was undertaken to investigate the possible carry-over effect on elderly long-term patients of bulk-forming products containing stimulant type laxatives. Thirty-six patients received magnesium hydroxide daily for a mean period of 10 months prior to the study, and 23 patients received bulk laxatives containing cassiae senna daily for a mean period of 13 months prior to the study. The pre-study laxatives were randomly changed either to magnesium hydroxide or to bulk laxatives. In the patient group receiving a bulk-forming product containing stimulant type laxative long-term prior to the study, the need for additional stimulant laxatives during the pure bulk laxative (3.0 vs. 3.8/4 weeks, NS) or magnesium hydroxide treatment (2.6 vs. 2.7/4 weeks, NS) was not more frequent and the frequency of defaecation was not lower than in the patients (during bulk laxative 11.2 vs. 9.3/4 weeks, NS and during magnesium hydroxide 12.0 vs. 13.7/4 weeks, NS) who received long-term magnesium hydroxide treatment prior to the study. Thus, our data indicated no carry-over effect after the use of bulk-forming laxatives containing senna for 13 months in elderly long-term patients.

Aged↗

PubMed2004

Nerve growth factor favours long-term depression over long-term potentiation in layer II-III neurones of rat visual cortex.

Nerve growth factor (NGF) has been shown to regulate plasticity in the visual cortex of monocularly deprived animals. However, to date, few attempts have been made to investigate the role of NGF in synaptic plasticity at the cellular level. In the study reported here we looked at the effects of exogenously applied NGF on synaptic plasticity of layer II-III regular spiking (RS) neurones in visual cortex of 16- to 18-day-old rats. We found that local application of NGF converted high frequency stimulation (HFS)-induced long-term potentiation (LTP) into long-term depression (LTD). We showed that this shift of synaptic plasticity was also obtained with bath application of NGF during HFS. Application of NGF subsequent to HFS left LTP unaffected, conferring temporal constraints on NGF efficacy. NGF effects on LTP were mediated by TrkA receptors. Indeed, blockade of TrkA by monoclonal antibody prevented NGF from inducing LTD following HFS. Low frequency stimulation (LFS) elicited LTD in RS cells. We found that NGF or blockade of NGF signalling by anti-TrkA antibody did not change the amplitude of the LTD induced by LFS. Thus, the NGF effect is selective for synaptic modifications induced by HFS in RS cells. The present results indicate that NGF may modulate the sign of long-term changes of synaptic efficacy in response to high frequency inputs.

Animals↗

PubMed1978

[Effect of long-term suppression and long-term stimulation of ACTH secretion on the ultrastructure of tanycytes[].

The ultrastructure of the tanycyte ependyma in males of Wistar albino rats (160--180 g of weight) was studied under experimental long-term suppression of ACTH secretion and its long-term stimulation. The former effect was accomplished by daily (for 8 days) intraperitoneal administration of dexamethasone phsophate; the stimulation of ACTH secretion was achieved by bilateral adrenalectomy. The long-term suppression of the hypophyseal adrenocorticotrophic function was followed by the ultrastructural markers of an increased transport and secretory activity in the tanycytes (mainly in beta-tanycytes, i. e. the ependyma lining floor of the third ventricle): the increased amount of microvesicles in the Golgi area and in the vicinity of the particular membranous cavity system (MCS, according to the authors' definition), the appearance of some figures of exocytosis, the elevated amount of lipid inclusions. On the contrary, the long-term stimulation of ACTH secretion was followed by the ultrastructural changes of the opposite character. The data obtained are in agreement with the previously established fact that there is a negative correlation between the tanycyte activity and the hypophyseal adrenocorticotrophic activity. It is supposed that this correlation is regulated by a feedback mechanism and attest to the involvement of tanycytes in the inhibitory control of ACTH secretion. A possible substrate inhibiting ACTH secretion by the tanycytes is discussed.

Adrenalectomy↗

PubMed2000

Characterization of three nef-defective human immunodeficiency virus type 1 strains associated with long-term nonprogression. Australian Long-Term Nonprogressor Study Group.

Long-term survivors (LTS) of human immunodeficiency virus type 1 (HIV-1) infection provide an opportunity to investigate both viral and host factors that influence the rate of disease progression. We have identified three HIV-1-infected individuals in Australia who have been infected for over 11 years with viruses that contain deletions in the nef and nef-long terminal repeat (nef/LTR) overlap regions. These viruses differ from each other and from other nef-defective strains of HIV-1 previously identified in Australia. One individual, LTS 3, is infected with a virus containing a nef gene with a deletion of 29 bp from the nef/LTR overlap region, resulting in a truncated Nef open reading frame. In addition to the Nef defect, only viruses containing truncated Vif open reading frames of 37 or 69 amino acids could be detected in peripheral blood mononuclear cells isolated from this patient. LTS 3 had a viral load of less than 20 copies of RNA/ml of plasma. The other two long-term survivors, LTS 9 and LTS 11, had loads of less than 200 copies of RNA/ml of plasma and are infected with viruses with larger deletions in both the nef alone and nef/LTR overlap regions. These viruses contain wild-type vif, vpu, and vpr accessory genes. All three strains of virus had envelope sequences characteristic of macrophagetropic viruses. These findings further indicate the reduced pathogenic potential of nef-defective viruses.

Amino Acid Sequence↗

PubMed1999

Controversial indications for long-term respiratory care: long-term oxygen therapy.

Long-term oxygen therapy is the only therapy proven to alter the late course of chronic obstructive pulmonary disease, but it should be reserved for selected patients. Only patients with chronic, stable hypoxaemia and with associated organ system dysfunction should have long-term oxygen therapy prescribed. It is highly likely that the delivery of oxygen via ambulatory systems is superior to oxygen available solely from a stationary source. Transtracheal oxygen appears to be an advance in selected patients. Newer oxygen technologies will continue to provide improved methods of care for patients with advanced hypoxaemic states.

Humans↗

PubMed2006

Active involvement and long-term goals influence long-term adherence to behavioural graded activity in patients with osteoarthritis: a qualitative study.

QUESTION: Why do some patients who have received a behavioural graded activity program successfully integrate the activities into their daily lives and others do not? DESIGN: Qualitative study. PARTICIPANTS: 12 patients were selected according to the model of deliberate sampling for heterogeneity, based on their success with the intervention as assessed on the Patient Global Assessment. INTERVENTION: Behavioural graded activity. OUTCOME MEASURES: Data from 12 interviews were coded and analysed using the methods developed in grounded theory. The interviews covered three main themes: aspects related to the content of behavioural graded activity, aspects related to experience with the physiotherapist, and aspects related to characteristics of the participant. RESULTS: Interview responses suggest that two factors influence long-term adherence to exercise and activity.First, initial long-term goals rather than short-term goals seem to relate to greater adherence to performing activities in the long term. Second, active involvement by participants in the intervention process seems to relate to greater adherence to performing activities in the long term. CONCLUSION: Although involvement of patients in the intervention process is already part of behavioural graded activity, it would be beneficial to emphasise the importance of active involvement by patients right from the start of the intervention. Furthermore, to increase the success of behavioural graded activity, physiotherapists should gain a clear understanding of the patient's initial motives in undergoing intervention.

Activities of Daily Living↗

PubMed2006

Distinct roles for Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) and Ras-GRF2 in the induction of long-term potentiation and long-term depression.

NMDA-type glutamate receptors (NMDARs) contribute to many forms of long-term potentiation (LTP) and long-term depression (LTD). NMDARs are heteromers containing calcium-permeating neuronal receptor 1 (NR1) subunits and a variety of NR2 subunits. Evidence suggests that, in the CA1 region of the hippocampus, NR2A-containing NMDARs promote LTP whereas NR2B-containing receptors promote LTD. However, the calcium sensors that distinguish between these signals to promote the appropriate form of synaptic plasticity are not known. Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) and Ras-GRF2 are highly similar calcium-stimulated exchange factors that activate Ras and Rac GTPases. Here, using a set of Ras-GRF knock-out mice, we show that Ras-GRF2 contributes predominantly to the induction of NMDAR-dependent LTP, whereas Ras-GRF1 contributes predominantly to the induction of NMDAR-dependent LTD in the CA1 region of the hippocampus of postpubescent mice (postnatal days 25-36). In contrast, neither Ras-GRF protein influences synaptic plasticity in prepubescent mice (postnatal days 14-18). Ras-GRF2 mediates signaling from (R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl-phosphonic acid-sensitive (NVP-AAM077-sensitive) (NR2A-containing) NMDARs to the Ras effector extracellular signal-related protein kinase 1/2 (Erk1/2) mitogen-activated protein (MAP) kinase, a promoter of NMDAR-induced LTP at this site. In contrast, Ras-GRF1 mediates signaling from ifenprodil-sensitive (NR2B-containing) NMDARs to the Rac effector p38 MAP kinase, a promoter of LTD. These findings show that, despite their similar functional domain organization, Ras-GRF1 and Ras-GRF2 mediate opposing forms of synaptic plasticity by coupling different classes of NMDARs to distinct MAP kinase pathways. Moreover, the postnatal appearance of Ras-GRF-dependent LTP and LTD coincides with the emergence of hippocampal-dependent behavior, implying that Ras-GRF proteins contribute to forms of synaptic plasticity that are required specifically for mature hippocampal function.

Animals↗

PubMed1996

Increased susceptibility to induction of long-term depression and long-term potentiation reversal during aging.

Homosynaptic long-term depression (LTD) and reversal of long-term potentiation (LTP) were examined extracellularly at CA3-CA1 synapses in stratum radiatum of slices from adult (6-9 months) and aged (20-24 months) Fischer 344 rats. Prolonged low-frequency stimulation (LFS) (900 pulses/1 Hz) of the Schaffer collaterals depressed the initial slope of the excitatory postsynaptic potential (EPSP) in aged but not adult rats. LTD at aged synapses was pathway-specific, persistent, and sensitive to the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5). Adult slices exhibited AP5-sensitive LTD in high [Ca2+] medium, whereas LTD in aged slices was blocked by high [Mg2+], suggesting that differences in Ca2+ regulation may underlie susceptibility to LTD. Despite age-related differences in LTD induction, no age difference in LTP magnitude was revealed. Additionally, LFS delivered 60 min after LTP induction resulted in similar LTP reversal for both age groups. Susceptibility differences to LTP reversal were indicated after multiple short-duration LFS bursts (30 pulses/1 Hz), with each burst separated by 10 min. Aged synapses exhibited significant reversal after a single burst and complete reversal after three LFS episodes. In adult slices, LTP reversal appeared after the fourth burst, and at no time was LTP depressed to initial baseline levels. This study provides the first characterization of homosynaptic LTD/LTP reversal in the aged animal and demonstrates that one form of plasticity, depression attributable to LFS, is increased during aging.

2-Amino-5-phosphonovalerate↗

PubMed2002

A study of the long-term effect of malar fat repositioning in face lift surgery: short-term success but long-term failure.

In 1990, the author reported on a series of 403 cases of deep plane face lifts, the first published technique describing the repositioning of the cheek fat, known as malar fat, in face lift surgery. This study examines the long-term results of 20 of the original series in an attempt to determine what areas of the rejuvenated face (specifically, the malar fat) showed long-term improvement. The results were judged by comparing the preoperative and long-term postoperative views in a half-and-half same-side hemiface photograph. The anatomy of the jawline (superficial musculoaponeurotic system [SMAS]), the nasolabial fold (malar fat), and the periorbital diameter were evaluated. The results confirmed that repositioning of the SMAS remained for longer than improvement in the nasolabial fold and that the vertical diameter of the periorbit did not change at all. The early results of malar fat repositioning shown at 1 to 2 years were successful, but the long-term results showed failure of the early improvement, manifested by recurrence of the nasolabial folds. There was, however, continuation of the improved results of the forehead lift and SMAS maneuvers of the original procedure. The conclusion is that only a direct excision will produce a permanent correction of the aging nasolabial fold.

Adipose Tissue↗

PubMed1998

Computerised evaluation of fetal heart rate in post-term fetuses: long term variation.

Computerised fetal heart rate records were obtained between 1987 and 1993 using the Sonicaid System 8000 for a cross-sectional study of postdates fetal heart rate variation; 567 singleton pregnancies at 41 and 43 weeks provided 1502 records. In all cases gestational age had been verified by ultrasound examination in early pregnancy. The mean minute range of the long term pulse interval variation, which is known to be correlated with fetal oxygenation was found to decrease progressively from an average value of 48.5 ms at 41 weeks to 46.4 ms and 42.4 ms at 42 and 43 or more weeks, respectively. When conservative management of postdate pregnancies is chosen, accurate measurements are needed to follow the evolution of fetal condition. Reference values for calculated pulse interval variation at later gestational ages are now provided.

Cardiotocography↗

PubMed1993

[Tenosynovectomy of the flexors in rheumatoid polyarthritis. Analytic study of short term and long term mobility of the fingers].

Between 1970 and 1988, 115 patients with rheumatoid arthritis underwent flexor tenosynovectomy. Fifty patients were reviewed (64 hands). The diagnosis of flexor tenosynovitis remains a clinical diagnosis. Three main groups can be distinguished: isolated carpal tenosynovitis (20%), palmodigital tenosynovitis (50%), diffuse tenosynovitis (30%). Standard surgical techniques were used, particularly in terms of the incisions. All patients underwent rehabilitation in the same rehabilitation centre. The authors analyse their results by comparing overall preoperative and postoperative mobility of the fingers (TAM: Total Active Motion, TPM: Total Passive Motion) and the angular gain in each joint (MCP, PIP, DIP). They report the results obtained at 4 months to eliminate the bias related to progression of the disease. The long-term results (8 years of follow-up) are also analysed. Statistical analysis compares two groups depending on whether flexor tenosynovectomy was isolated (44%) or combined with a dorsal surgical procedure at the same operation (extensor synovectomy, articular synovectomy, stabilisation-realignment of the dorsal aspect of the wrist, resection of the ulnar head) (56%). Ninety percent of patients declared themselves to be subjectively improved. Objectively, mobility was always improved at 4 months then deteriorated to return to its preoperative level at 8 years. Only three patients were reoperated for recurrence. Flexor tenosynovectomy in rheumatoid arthritis is an excellent operation. Its analgesic effect is maintained in time and, when performed early, it appears to protect the patient from the risk of subsequent tendon rupture.

Adult↗

PubMed2004

The kinetic profile of intracellular calcium predicts long-term potentiation and long-term depression.

Efficiency of synaptic transmission within the neocortex is regulated throughout life by experience and activity. Periods of correlated or uncorrelated presynaptic and postsynaptic activity lead to enduring changes in synaptic efficiency [long-term potentiation (LTP) and long-term depression (LTD), respectively]. The initial plasticity triggering event is thought to be a precipitous rise in postsynaptic intracellular calcium, with higher levels inducing LTP and more moderate levels inducing LTD. We used a pairing protocol in visual cortical brain slices from young guinea pigs with whole-cell recording and calcium imaging to compare the kinetic profiles of calcium signals generated in response to individual pairings along with the cumulative calcium wave and plasticity outcome. The identical pairing protocol applied to layer 2/3 pyramidal neurons results in different plasticity outcomes between cells. These differences are not attributable to variations in the conditioning protocol, cellular properties, inter-animal variability, animal age, differences in spike timing between the synaptic response and spikes, washout of plasticity factors, recruitment of inhibition, or activation of different afferents. The different plasticity outcomes are reliably predicted by individual intracellular calcium transients in the dendrites after the first few pairings. In addition to the differences in the individual calcium transients, the cumulative calcium wave that spreads to the soma also has a different profile for cells that undergo LTP versus LTD. We conclude that there are biological differences between like-type cells in the dendritic calcium signals generated by coincident synaptic input and spiking that determine the sign of the plasticity response after brief associations.

Aniline Compounds↗

PubMed2004

Multiple forms of long-term potentiation and long-term depression converge on a single interneuron in the leech CNS.

Long-term potentiation (LTP) of synaptic transmission was observed in two types of synapses that converge on the same postsynaptic neuron in the leech CNS. These synapses were made by identifiable sensory neurons, the mechanosensory touch (T-) and pressure (P-) cells, onto the S-cell, an interneuron critical for certain forms of learning. Changes in both the T-S and P-S synapses appear to be activity dependent because LTP was restricted to inputs that had undergone tetanization; however, properties of synaptic plasticity at the T-S and P-S connections differ considerably. At the P-S synapse, LTP was induced in the tetanized synapse but not in the nontetanized synapse tested in parallel. P-S LTP was blocked by the NMDA receptor antagonist dl-2-amino-5-phosphono-valeric acid (AP-5) or by lowering the extracellular concentration of glycine, an NMDA receptor (NMDAR) co-agonist. P-S LTP was strongly affected by the initial amplitude of the synaptic potential at the time LTP was induced. Smaller amplitude synapses (<3.5 mV) underwent robust potentiation, whereas the less common, larger amplitude synapse (>3.5 mV) depressed after tetanization. At the T-S synapse, tetanization simultaneously induced homosynaptic LTP in the tetanized input and heterosynaptic long-term depression (LTD) in the input made by a nontetanized T-cell onto the same S-cell. Interestingly, AP-5 failed to block homosynaptic LTP at the T-S synapse but did prevent heterosynaptic LTD. T-S LTP was not affected by the initial EPSP amplitude. Thus, leech neurons exhibit synaptic plasticity with properties similar to LTP and LTD found in the vertebrate nervous system.

Animals↗

PubMed2004

Influence of visual experience on developmental shift from long-term depression to long-term potentiation in the rat medial vestibular nuclei.

The influence of visual experience deprivation on changes in synaptic plasticity during postnatal development was studied in the ventral part of the rat medial vestibular nuclei (vMVN). We analysed the differences in the occurrence, expressed as a percentage, of long-term depression (LTD) and long-term potentiation (LTP) induced by high frequency stimulation (HFS) of the primary vestibular afferents in rats reared in the light (LR) and those in the dark (DR). In LR rats, HFS only induced LTD in the early stages of development, but the occurrence of LTD progressively decreased to zero before their eyes opened, while that of LTP enhanced from zero to about 50%. Once the rats' eyes had opened, LTD was no longer inducible while LTP occurrence gradually reached the normal adult value (70%). In DR rats, a similar shift from LTD to LTP was observed before their eyes opened, showing only a slightly slower LTD decay and LTP growth, and the LTD annulment was delayed by 1 day. By contrast, the time courses of LTD and LTP development in DR and LR rats showed remarkable differences following eye opening. In fact, LTD occurrence increased to about 50% in a short period of time and remained high until the adult stage. In addition, the occurrence of LTP slowly decreased to less than 20%. The effect of light-deprivation was reversible, since the exposure of DR rats to light, 5 days after eye opening, caused a sudden disappearance of LTD and a partial recover of LTP occurrence. In addition, we observed that a week of light deprivation in LR adult rats did not affect the normal adult LTP occurrence. These results provide evidence that in a critical period of development visual input plays a crucial role in shaping synaptic plasticity of the vMVN, and suggest that the visual guided shift from LTD to LTP during development may be necessary to refine and consolidate vestibular circuitry.

Animals↗

PubMed1991

Refining the temporal definition of an association at the neuronal level using long-term potentiation and long-term depression in the dentate gyrus.

This study sharpens the temporal definition of an association in the context of long-term synaptic modification of the monosynaptic projections from entorhinal cortex to dentate gyrus in the anesthetized rat. The ipsilateral projection produces a powerful postsynaptic excitation and shows synaptic potentiation following 7.5 ms trains. On the other hand, brief, high-frequency contralateral stimulation just after this powerful postsynaptic excitation is followed by long-term depression (LTD) at the synapses of this pathway. Therefore, based on the differential induction of long-term potentiation (LTP) or LTD, a cell can distinguish associated pre- and postsynaptic activation at a temporal resolution at least as small as 7.5 ms.

Animals↗

PubMed2001

Olfactory learning modifies predisposition for long-term potentiation and long-term depression induction in the rat piriform (olfactory) cortex.

Learning-related modifications in predisposition for long-term potentiation (LTP) and long-term depression (LTD) were studied in brain slices of the rat piriform cortex following olfactory learning. Rats were trained to discriminate between pairs of odors until they demonstrated rule learning. We have previously shown that such training is accompanied by enhanced neuronal excitability and increased synaptic transmission in the intrinsic synaptic pathway. Here we show that the susceptibility for further enhancing synaptic connectivity by inducing LTP in slices from trained rats is markedly reduced after training, compared with slices from pseudo-trained and naive rats. Accordingly, while 900 stimuli at 1 Hz did not induce LTD in slices from control rats, it induced significant LTD in slices from trained rats. Post-tetanic potentiation (PTP) was also reduced after training, indicating that synaptic release is enhanced after odor learning, as previously suggested. We suggest that learning-related cellular modifications and activity-dependent synaptic plasticity share a common mechanism in the primary olfactory cortex. Our data also support the prediction generated according to the sliding modification threshold theory that learning should be accompanied by reduced capability of inducing LTP and increased susceptibility for LTD induction.

Animals↗

PubMed1999

Calcium signals in long-term potentiation and long-term depression.

We describe postsynaptic Ca2+ signals that subserve induction of two forms of neuronal plasticity, long-term potentiation (LTP) and long-term depression (LTD), in rat hippocampal neurons. The common induction protocol for LTP, a 1-s, 50-Hz tetanus, generates Ca2+ increases of about 50-Hz in dendritic spines of CA1 neurons. These very large increases, measured using a low affinity indicator (Mg fura 5), were found only in the spines and tertiary dendrites, and were dependent upon influx through N-methyl-D-aspartate (NMDA) gated channels. High affinity Ca2+ indicators (e.g., fura 2) are unable to demonstrate these events. In acute slices, neighboring dendritic branches often showed very different responses to a tetanus, and in some instances, neighboring spines on the same dendrite responded differently. LTD in mature CA1 neurons was induced by a low frequency stimulus protocol (2 Hz, 900 pulses), in the presence of GABA- and NMDA-receptor blockers. This LTD protocol produced dendritic Ca2+ increases of <1 microM. Duration of the Ca2+ increase was approximately 30 s and was due to voltage-gated Ca2+ influx. Finally, the ability of synaptically addressed Ca2+ stores to release Ca2+ was studied in CA3 neurons and was found to require immediate preloading and high intensity presynaptic stimulation, conditions unlike normal LTP-LTD protocols.

Animals↗

PubMed2003

In vivo recordings of long-term potentiation and long-term depression in the dentate gyrus of the neonatal rat.

Previous in vitro studies demonstrated that long-term potentiation (LTP) could be elicited at medial perforant path (MPP) synapses onto hippocampal granule cells in slices from 7-day-old rats. In contrast, in vivo studies suggested that LTP at perforant path synapses could not be induced until at least days 9 or 10 and then in only a small percentage of animals. Because several characteristics of the oldest granule cells are adult-like on day 7, we re-examined the possibility of eliciting LTP in 7-day-old rats in vivo. We also recorded from 8- and 9-day-old rats to further elucidate the occurrence and magnitude of LTP in neonates. With halothane anesthesia, all animals in each age group exhibited synaptic plasticity of the excitatory postsynaptic potential following high-frequency stimulation of the MPP. In 7-day-old rats, LTP was elicited in 40% of the animals and had an average magnitude of 143%. Long-term depression (LTD) alone (magnitude of 84%) was induced in 40% of the animals, while short-term potentiation (STP) alone (magnitude of 123%) was induced in 10%. STP followed by LTD was elicited in the remaining 10%. Data were similar for all ages combined. In addition, the N-methyl-d-aspartate (NMDA) antagonist (R,S)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked the occurrence of LTP at each age and doubled the percentage of animals expressing LTD alone for all ages combined. These results demonstrate that tetanic stimulation can elicit LTP or LTD at MPP synapses in 7-day-old rats, supporting our premise that at least a portion of the dentate gyrus is functional at this early age.

Animals↗