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R Malinow

Publications and source records attributed to R Malinow.

52 records · Page 3Linked to original sources
PubMed1990

Presynaptic enhancement shown by whole-cell recordings of long-term potentiation in hippocampal slices.

Long-term potentiation (LTP) of synaptic transmission in the hippocampus is a widely studied model system for understanding the cellular mechanisms of memory. In region CA1, LTP is triggered postsynaptically by Ca2(+)-dependent activation of protein kinases, but the locus of persistent modification remains controversial. Statistical analysis of synaptic variability has been proposed as a means of settling this debate, although a major obstacle has been the poor signal-to-noise ratio of conventional intracellular recordings. We have applied the whole-cell voltage clamp technique to study synaptic transmission in conventional hippocampal slices (compare refs 28-30). Here we report that robust LTP can be recorded with much improved signal resolution and biochemical access to the postsynaptic cell. Prolonged dialysis of the postsynaptic cell blocks the triggering of LTP, with no effect on expression of LTP. The improved signal resolution unmasks a large trial-to-trial variability, reflecting the probabilistic nature of transmitter release. Changes in the synaptic variability, and a decrease in the proportion of synaptic failures during LTP, suggest that transmitter release is significantly enhanced.

Animals↗
PubMed1989

Inhibition of postsynaptic PKC or CaMKII blocks induction but not expression of LTP.

Long-term potentiation (LTP) of synaptic transmission is a widely studied cellular example of synaptic plasticity. However, the identity, localization, and interplay among the biochemical signals underlying LTP remain unclear. Intracellular microelectrodes have been used to record synaptic potentials and deliver protein kinase inhibitors to postsynaptic CA1 pyramidal cells. Induction of LTP is blocked by intracellular delivery of H-7, a general protein kinase inhibitor, or PKC(19-31), a selective protein kinase C (PKC) inhibitor, or CaMKII(273-302), a selective inhibitor of the multifunctional Ca2+-calmodulin-dependent protein kinase (CaMKII). After its establishment, LTP appears unresponsive to postsynaptic H-7, although it remains sensitive to externally applied H-7. Thus both postsynaptic PKC and CaMKII are required for the induction of LTP and a presynaptic protein kinase appears to be necessary for the expression of LTP.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1988

Persistent protein kinase activity underlying long-term potentiation.

Long-term potentiation (LTP) of synaptic transmission in the hippocampus is a much-studied example of synaptic plasticity. Although the role of N-methyl-D-aspartate (NMDA) receptors in the induction of LTP is well established, the nature of the persistent signal underlying this synaptic enhancement is unclear. Involvement of protein phosphorylation in LTP has been widely proposed, with protein kinase C (PKC) and calcium-calmodulin kinase type II (CaMKII) as leading candidates. Here we test whether the persistent signal in LTP is an enduring phosphoester bond, a long-lived kinase activator, or a constitutively active protein kinase by using H-7, which inhibits activated protein kinases and sphingosine, which competes with activators of PKC (ref. 17) and CaMKII (ref. 18). H-7 suppressed established LTP, indicating that the synaptic potentiation is sustained by persistent protein kinase activity rather than a stably phosphorylated substrate. In contrast, sphingosine did not inhibit established LTP, although it was effective when applied before tetanic stimulation. This suggests that persistent kinase activity is not maintained by a long-lived activator, but is effectively constitutive. Surprisingly, the H-7 block of LTP was reversible; evidently, the kinase directly underlying LTP remains activated even though its catalytic activity is interrupted indicating that such kinase activity does not sustain itself simply through continual autophosphorylation (see refs 9, 13, 15).

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1981

Maculopathy in cynomolgus monkeys. A correlated fluorescein angiographic and ultrastructural study.

Maculae of seven cynomolgus macaque monkeys (Macaca fascicularis) showing abnormalities in color fundus photographs and fluorescein angiograms were studied in serial sections by light and electron microscopy and compared with three eyes without clinically visible defects in the macula. Maculae that showed hyperfluorescent nonleaking window defects showed no drusen or interruptions in the retinal pigment epithelium (RPE). Six of these monkeys had mis-shapen foveal depressions, all showed some degree of photoreceptor degeneration, and one had cells in Bruch's membrane. Bright yellow spots correlated with scattered RPE filled with lipid vacuoles. Shallow RPE elevations correlated with diffuse nonleaking window defects. Patches of RPE deficient in melanin occurred at sites of hyperfluorescence. Quantitative studies showed that maculae with window defects had more lipofuscin and less melanin per RPE cell. Maculae deemed normal by photography showed degenerating photoreceptors.

Animals↗
PubMed1977

Effects of estradiol-17beta on cholesterol metabolism in the rat: a study using a deuterium label and mass spectrometry.

The effect of estradiol-17beta (E2) on several important aspects of cholesterol metabolism were examined in the rat. Ovariectomized rats were implanted subcutaneously with 1 or 4 cm. of silastic tubing packed with E2, and were also given 2% D2O in their drinking water. The E2 diffused slowly out of the implants and the two different lengths of tubing resulted in constant E2 blood concentrations of either high (4.0 cm) or physiological (1.0 cm) levels. By measuring the rate of incorporation of deuterium into plasma cholesterol by mass spectrometry over a period of 42 days, we determined the rate constant of cholesterol synthesis and cholesterol turnover time and rate under two E2 dosage conditions. E2 treatment did not affect the rate constant of cholesterol turnover rate (mg synthesized/day) showed a dose dependent reduction with increasing doses of E2. This may be secondarily caused by E2's suppression of both food intake and subsequent weight gain; E2 treated animals are smaller and, therefore, synthesize less cholesterol per day. Additionally, E2 treated animals showed a rise in plasma cholesterol levels and in the fraction of labeled cholesterol appearing in the plasma.

Animals↗
PubMedDate not supplied

No change in NMDA receptor-mediated response rise-time during development: evidence against transmitter spillover.

Glutamatergic transmission was examined in tadpole optic tectum to test the possibility that transmitter concentration reaching N-methyl-D-aspartate (NMDA) receptors increases over development. Pharmacologically isolated NMDA receptor-mediated transmission was monitored with whole-cell recordings. Synaptic responses were recorded from cells at different locations in the optic tectum, corresponding to different stages of development. Rise-times and decay-times of NMDA currents were analyzed. We found no significant correlation between rise-time and developmental stage. As NMDA rise-times can correlate with concentration for glutamate concentrations below 200 microM, these results argue that, if there is developmental variation in transmitter concentration, this occurs for values greater than 200 microM. Furthermore, we found a correlation between rise-times and decay-times, consistent with a model in which transmitter concentration is high and rise-time is controlled by channel closings. These results argue against synaptic models in which low concentrations of transmitter (as by spillover from nearby release sites) selectively activates NMDA receptors.

Animals↗
PubMedDate not supplied

Postsynaptic hyperpolarization during conditioning reversibly blocks induction of long-term potentiation.

Activity-induced changes in the efficacy of synaptic transmission between neurones are central to several prominent theories of learning. In both in vivo and in vitro preparations of the hippocampus, a conditioning high-frequency stimulus delivered to afferent fibres results in a long-term potentiation of synaptic transmission at those inputs. Evidence has been provided supporting both presynaptic and postsynaptic sites as loci where critical events occur in the development of potentiation. In this study we report that long-term potentiation is reversibly blocked by intracellular injection of hyperpolarizing current in the postsynaptic cell during the conditioning high-frequency stimulus, suggesting the involvement of a voltage-dependent postsynaptic mechanism.

Animals↗
PubMedDate not supplied

Examination of the role of cGMP in long-term potentiation in the CA1 region of the hippocampus.

The mechanisms underlying the generation of NMDA receptor-dependent LTP in the CA1 region of the hippocampus continue to receive a great deal of attention because of the postulated importance of LTP as a synaptic mechanism for learning and memory. It is well accepted that the initial induction of LTP occurs in the postsynaptic cell, but the site of expression remains controversial. One prominent hypothesis is that LTP involves the release of one or more retrograde messengers that act on the presynaptic terminal to enhance transmitter release. Recently, evidence has been presented that retrograde messengers function to activate presynaptic guanylyl cyclase and that the resulting rise in presynaptic cGMP levels, when accompanied by presynaptic activity, is responsible for generating an early component of LTP. We have tested this hypothesis by examining whether synaptic strength is increased by coupling tetanic stimulation with application of a membrane-permeable analog of cGMP. The experiments were done in the presence of an NMDA receptor antagonist to block postsynaptic induction mechanisms. Under a variety of experimental conditions, this manipulation failed to generate LTP, suggesting that an increase in cGMP levels accompanied by presynaptic activity is not sufficient to generate LTP in the CA1 region of the hippocampus.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Deficiency in induction but not expression of LTP in hippocampal slices from young rats.

In this study we examine developmental changes between postnatal day (PND) 4 and 14 in synaptic transmission and plasticity in the CA1 region of hippocampal slices. We confirm previous results that tetanus-induced long-term potentiation (LTP) in field recordings is diminished in slices from younger animals. LTP in whole-cell current-clamp recordings is also diminished in younger animals. However, robust LTP can be induced in young animals if sufficient postsynaptic depolarization is provided during LTP induction. Furthermore, we find differences in synaptic transmission between PND 4 and 14, suggesting that the depolarization during tetanic stimulation in young tissue is ineffective to produce LTP. These results indicate that the smaller potentiation in field recordings in slices from younger animals is attributable to insufficient postsynaptic depolarization during LTP induction rather than a defect in expression mechanisms.

Aging↗
PubMedDate not supplied

Fluctuations in intracellular calcium responses to action potentials in single en passage presynaptic boutons of layer V neurons in neocortical slices.

The release of neurotransmitter from a nerve terminal on invasion by an action potential shows large trial-to-trial fluctuations. The factors contributing to this variability have not been elucidated clearly. Here, simultaneous patch-clamp and optical measurements from layer V neocortical pyramidal neurons have been used to assess the extent to which the fluctuations in transmitter release may be caused by variability in calcium rise in presynaptic structures. Boutons on axon collaterals were visualized and increases in intracellular calcium, assessed by Fura-2, were observed in response to single action potentials. In some boutons, calcium responses showed trial-to-trial variability and occasional apparent failures despite the faithful conduction of the action potential. These results suggest that a factor contributing to the fluctuation in transmitter release may be the variability with which depolarization of a presynaptic bouton produces an increase in intrabouton calcium.

Action Potentials↗
PubMedDate not supplied

CA1 long-term potentiation is diminished but present in hippocampal slices from alpha-CaMKII mutant mice.

Previous work has shown that mice missing the alpha-isoform of calcium-calmodulin-dependent protein kinase II (alpha-CaMKII) have a deficiency in CA1 hippocampal long-term potentiation (LTP). Follow-up studies on subsequent generations of these mutant mice in a novel inbred background by our laboratories have shown that whereas a deficiency in CA1 LTP is still present in alpha-CaMKII mutant mice, it is different both quantitatively and qualitatively from the deficiency first described. Mice of a mixed 129SvOla/SvJ;BALB/c;C57B1/6 background derived from brother/sister mating of the alpha-CaMKII mutant line through multiple generations (>10) were produced by use of in vitro fertilization. Although LTP at 60 min post-tetanus was clearly deficient in these (-/-) alpha-CaMKII mice (42.6%, n = 33) compared with (+/+) alpha-CaMKII control animals (81.7%, n = 17), alpha-CaMKII mutant mice did show a significant level of LTP. The amount of LTP observed in alpha-CaMKII mutants was normally distributed, blocked by APV (2.7%, n = 8), and did not correlate with age. Although this supports a role for alpha-CaMKII in CA1 LTP, it also suggests that a form of alpha-CaMKII-independent LTP is present in mice that could be dependent on another kinase, such as the beta-isoform of CaMKII. A significant difference in input/output curves was also observed between (-/-) alpha-CaMKII and (+/+) alpha-CaMKII animals, suggesting that differences in synaptic transmission may be contributing to the LTP deficit in mutant mice. However, tetani of increasing frequency (50, 100, and 200 Hz) did not reveal a higher threshold for potentiation in (-/-) alpha-CaMKII mice compared with (+/+) alpha-CaMKII controls.

Animals↗
PubMedDate not supplied

[Lack of correlation between plasma homocysteine levels and cerebral microangiopathy in patients wtih transient ischemic attack].

OBJECTIVE: The aim of this study is to evaluate cerebral MRI findings in patients with atherothrombotic transient ischemic attacks (TIA) and its correlation with plasma homocysteine (Hcy) levels. PATIENTS AND METHODS: A total of 62 consecutive patients with the diagnosis of TIA of atherothrombotic origin were studied. MRI examinations were performed in all patients for the evaluation of the presence of infarct and/or white matter hyperintensities (WMHI). Plasma Hcy levels were determined according to the method described by Smolin and Schneider modified. RESULTS: Plasma Hcy levels were significantly (p < 0.036) higher in patients with MRI-detected infarcts (9.69 +/- 2.06 mumol/l) compared with patients without infarcts (8.65 +/- 1.7 mumol/l. There was no correlation (p < 0.33) between plasma Hcy levels and the presence or absence of WMHI seen on MRI. CONCLUSIONS: In TIA patients, plasma Hcy levels were significantly higher in patients with cerebral infarcts, but did not correlate with the presence of WMHI. Our results suggest that mild hyperhomocysteinemia would be associated with large-medium vessel rather than with small vessel disease.

Adult↗