SEARCH · PubMed Health

Results for “synaptosomes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources

PubMed1989

Evidence for the coupling of muscarinic M1 receptors to polyphosphoinositide turnover in rat cortical synaptosomes.

The linking event between the activation of muscarinic M1 receptors and the stimulation of polyphosphoinositide (PPI) turnover was studied in rat brain synaptosomes from the muscarinic M1 enriched cerebrum and M2 enriched cerebellum. The muscarinic M1 selective antagonists, pirenzepine and trihexyphenidyl, and M2 selective antagonist AF-DX-116 were chosen to displace the non-selective labeled cholinergic ligand, 3H-QNB, binding to these two regions of the brain synaptosomes. The IC50 values obtained for these agents revealed a typical characterization of the receptor subtypes of these two regions as they are. Carbachol-induced a stimulation of the PPI turnover cycle: namely, a decrease in 32Pi incorporation into phosphatidylinositol-4,5-bisphosphate (TPI) and phosphatidylinositol-4-phosphate (DPI), and an increase in this incorporation into phosphatidylinositol (PI) and phosphatidic acid (PA) in rat brain synaptosomes from the cerebrum. However, this event was only barely detectable in the synaptosomes from the cerebellum. The IC50 values obtained for these antagonists to block the carbachol-induced PPI turnover cycle in the synaptosomes from the cerebrum were close to the values obtained for the displacement of 3H-QNB binding to the same preparation, and were far away from those values obtained in the synaptosomes from the cerebellum. Our results suggest that there is evidence to support the view that muscarinic M1 receptors are coupled to the PPI turnover event in rat cortical synaptosomes.

Animals↗

PubMed1989

Effect of linoleic acid-rich infant formula feeding on brain synaptosomal lipid accretion and enzyme thermotropic behavior in the piglet.

The effects of a vegetable oil-based infant formula, virtually devoid of n-6 and n-3 long chain polyenoid fatty acids (LCP) and high in 18:2(n-6) and 18:2(n-6)/18:3(n-3) ratio, on brain synaptosome lipid composition and enzyme thermotropic behavior were studied in neonatal piglets. Term gestation piglets were fed either sow milk (SMF) or formula (FF) from birth for 5, 10, 15, or 25 days. Synaptosomal cholesterol, total lipid phosphorus, and phospholipid class composition did not differ between SMF and FF piglets. Synaptosomal fatty acid composition, however, was influenced by diet. The proportion of n-3 LCP, especially 22:6(n-3), was decreased, while the n-6 LCP, especially 22:4(n-6) and 22:5(n-6), were increased in FF compared to SMF piglets. These diet-related changes were most pronounced in the ethanolamine glycerophospholipid fraction and increased with the duration of feeding. FF thus reversed an apparent developmental increase in the synaptosomal n-3/n-6 LCP ratio. The monoene content, especially 18:1, was also reduced in the synaptosomes of FF compared to SMF pigs. FF had no effect on the activity of synaptosomal acetylcholinesterase. However, higher transition temperatures for this enzyme, indicating decreased membrane fluidity, were found in the FF compared to SMF piglets. The data suggest that exclusive feeding of proprietary formulae, devoid of LCP and high in 18:2(n-6) and/or the 18:2 (n-6)/18:3(n-3) ratio, may compromise normal fatty acid accretion and physical properties of brain synaptosomal membranes.

Acetylcholinesterase↗

PubMed1985

Reorganization of actin in depolarized synaptosomes.

Depolarization of whole brain synaptosomes, which stimulates transmitter release, also affects regulation of the assembly of actin microfilaments. Lysates of depolarized synaptosomes contain 20% less cytoskeletal actin than lysates of unstimulated synaptosomes. Parameters affecting the assembly of actin are modified before lysis, but release of actin from the Triton-insoluble cytoskeleton does not occur until after lysis. Actin released from the cytoskeleton is not precipitated with myosin, indicating that it consists of monomers and/or short oligomers. Synaptosomes were incubated for 12 sec in one of three solutions of identical ionic strength but of different salt mixtures: 75 mM KCl-2 mM CaCl2, 5 mM KCl-2mM CaCl2, or 75 mM KCl-0.1 mM EGTA. Synaptosomes were then lysed in an F-actin stabilizing buffer containing 1% Triton X-100. Control synaptosomes (no incubation) were lysed directly into the same lysis buffer containing one of the three different salt mixtures. The cytoskeletal and noncytoskeletal actin pools were separated 25 sec after lysis by centrifugation at 10(4) X g for 1 min, and the actin in each pool was quantitated by the DNase I inhibition assay. The drop in cytoskeletal actin induced by depolarization is maximized by including Ca2+ in the depolarizing buffer, and it is blocked completely by adding a neutral thiol protease inhibitor, leupeptin, to either the pre- or post-lysis buffer. The drop is also completely reversed by repolarizing the synaptosomes.

Actins↗

PubMed1985

[Membrane potential and transport of neuromediators in synaptosomes of the brain of rats with spontaneous hypertension].

The transport of 3H-GABA, 14C-choline, 14C-noradrenaline and 3H-serotonin in brain synaptosomes of spontaneously-hypertensive rats (SHR) which is controlled by the carrier whose activity is dependent on the sodium gradient and electric potential of the plasma membrane was studied. The initial rate of GABA uptake by SHR synaptosomes was reduced by 25%. The steady state of the content of GABA, noradrenaline and serotonin in SHR synaptosomes was reduced by 15-20%, whereas the steady state of choline content by 35%. The differences are levelled when synaptosomes are depolarized, both due to the elimination of K+-diffusion potential, and the opening of Na channels. An increase in the extracellular calcium concentration up to 1 mmol results in a 20% synaptosomal GABA rise that is unrelated to membrane hyperpolarization. In the presence of the Ca-ionophore A-23187, a similar effect is observed with a 1-2 mmol Ca2+ concentration. The electric potential of SHR synaptosomes which is studied by means of the fluorescent dye dis-C3-(5) was shown to be reduced by 5-10 mV. Partial depolarization of SHR synaptosomes is supposed to be the principal cause of the decrease in both the initial rate of uptake and the steady state of the content of neuromediators.

Acetylcholine↗

PubMed1989

Aplysia synaptosomes. I. Preparation and biochemical and morphological characterization of subcellular membrane fractions.

We prepared and characterized subcellular membrane fractions from the CNS of Aplysia californica that are enriched in isolated nerve terminals (synaptosomes). Ganglia were homogenized in 1.1 M sucrose and fractionated on a 2-step sucrose gradient, yielding 50 micrograms protein/animal in the synaptosomal fraction (P3), which was enriched 3-fold in plasma membrane as compared with the initial homogenate. Quantitative morphometry of electron micrographs revealed that P3 contained 25% intact synaptosomes, a 5-fold enrichment over the homogenate. Although fractionation on a 5-step sucrose gradient reduced the yield of protein in the synaptosomal fraction to 40 micrograms/animal, this fraction (the 0.35 M/0.75 M interface) was more enriched in plasma membrane than P3 and was less contaminated by lysosomes and free mitochondria. By electron microscopy, the 0.35 M/0.75 M interface contained up to 50% synaptosomes. Synaptosomal fractions contained cAMP-, Ca2+/calmodulin-, and Ca2+/phospholipid-dependent protein kinase activities and were enriched in a Mr 40,000 pertussis toxin substrate, Gi/o. In the accompanying paper, we show that these synaptosomes retain the ability to release transmitters.

Animals↗

PubMed1986

Effect of early and late postnatal hypoxia on subcellular synaptosomal fractions from cerebral cortex of rats. II. A quantitative ultrastructural study.

Synaptosomal subfractions were isolated by discontinuous sucrose gradient centrifugation from the P2-fraction of cerebral cortices of juvenile rats exposed to moderate intermittent hypobaric hypoxia from day 2-11 (early postnatal period) or from day 12-21 (late postnatal period) after birth. Ultrastructural investigations were carried out on fractions A and E of the preparation. Quantitative parameters of synaptosomes and mitochondria (volume density, numerical density, profile size frequency distribution) were estimated in a stereological analysis. Early postnatal hypoxia exposition strengthened the irreversible swelling of mitochondria. The effect on synaptosomes was less pronounced, very large synaptosomes showed significant condensation. Late postnatal hypoxia exposition resulted in strong condensation of synaptosomes in all size classes and similar reaction in mitochondria. Both hypoxia experiments produced an enhanced vulnerability of the synaptosomal membranes against the fractionation procedure and the appearance of monstrous large condensed synaptosomes. The results are discussed in view of hypothetical biochemical mechanisms underlying these changes.

Age Factors↗

PubMed1985

[Action of neurotropic substances on gamma-aminobutyric acid release from brain synaptosomes during K+ depolarization].

The effects of aminazine (0.25 mM), phthoracyzine (0.5 mM), trifluperidole (0.5 mM) and imipramine (0.5 mM) on GABA release from rat brain synaptosomes depolarized with K+ (50 mM) were investigated. Incubation of synaptosomes with aminazine led to a 2-fold and that with phthoracyzine, trifluperidole and imipramine to a 1.5-fold increase in GABA release from synaptosomes as compared with its basic level. The raising of K+ in the incubation medium to 50 mM brought about a 2-fold augmentation of GABA release. Exposure of synaptosomes to drugs and a higher K+ concentration at a time did not change GABA release as compared to its basic level. Introduction into the incubation medium of the Ga-ionophore A23187 together with 50 mM K+ and trifluperidole or with K+ and imipramine led to the same increase in GABA release from synaptosomes as that produced by the psychotropic drugs as regards native synaptosomes. It is assumed that the lack of the influence of the psychotropic drugs under study of GABA release from synaptosomes depolarized with K+ is caused by blockade of synaptic membrane conductibility for Ca2+.

Animals↗

PubMed1984

[Correlation between the property changes of opiate receptors and the structural integrity of synaptosomes].

The effect of incubation of rat brain synaptosomes at 37 degrees C isolated by the Hajos method, on parameters of high affinity opiate receptor binding of [3H]naloxone and the structural integrity of synaptosomes was studied. The structural integrity of synaptosomes was controlled by electron microscopy, by changes in lactate dehydrogenase activity as well as by the ability of synaptosomes to maintain the transmembrane potential, using the fluorescent probe 1-anilino-8-naphthalenesulfonate. It was found that during 60 min incubation, the structure of synaptosomes is considerably impaired. The dynamics of changes in the structural integrity of synaptosomes is correlated with the changes of parameters of naloxone binding to opiate receptors, which points to the dependence of synaptosomal receptors' properties on preparation nativity degree.

Anilino Naphthalenesulfonates↗

PubMed1982

[Tetanus toxin disturbance of 3H-GABA transport in the synaptosomes].

Synaptosomes isolated from the rat brain cortex were made use of to study the effect of tetanus toxin (TT) in doses of 1000-1200 MTD/ml (for rats) on 3H-GABA uptake and GABA and 3H-GABA release. After 15 minutes of incubating synaptosomes with TT, partial suppression of 3H-GABA release induced by K+-depolarization (30 and 40 mMK+) was discovered. TT did not suppress GABA release from synaptosomes (35-minute incubation), induced by ouabain (0.5 mM). Incubation of synaptosomes with TT in a Ca2+-containing medium for 2.5 h led to a noticeable (40%) suppression of their ability to accumulate 3H-GABA. Tetrodotoxin (10(-6)-10(-7)lg/1) increased 3H-GABA uptake but did not eliminate differences in the mediator uptake by poisoned and control synaptosomes. Incubation of synaptosomes with TT in media containing no Ca2+ was not followed by suppression of 3H-GABA uptake. The amount of 3H-GABA released during K+-depolarization by synaptosomes incubated with TT for 2.5 h was found to be less (with regard to the absolute magnitudes and proportion of 3H-GABA taken up) than in control.

Animals↗

PubMed1995

Effect of succinyl cholecystokinin heptapeptide on synaptosomal 45Ca uptake of mouse hippocampus.

AIM: To study the effect of a new peptide, succinyl cholecystokinin heptapeptide (SCH), on the uptake of 45Ca by synaptosomes from mouse hippocampus, and compare it with that of sincalide. METHODS: Protein concentration was determined by the dye method. 45Ca uptake was determined by adding 45CaCl2 into synaptosome suspending solution. Samples were incubated and terminated by filtration through glass microfiber filters and finally counted in a Beckman LS 9800 liquid scintillation spectrometer. RESULTS: SCH 0.125 - 2 mumol.L(-1) dose-dependently depressed synaptosomal 45Ca uptake, and the depressive extent was similar to that of sincalide. The suppressive effect induced by either SCH or sincalide on synaptosomal 45Ca uptake was antagonized by proglumide, which itself did not affect 45Ca uptake of synaptosomes. The inhibition of synaptosomal 45Ca uptake induced by SCH or sincalide was blocked by beta-endorphin. CONCLUSION: The replacement of the N-terminal aspartic acid residue of sincalide does not influence its effect on 45Ca uptake of hippocampal synaptosomes.

Animals↗

PubMed1997

Active polysomes are present in the large presynaptic endings of the synaptosomal fraction from squid brain.

Previous data have suggested that the large nerve terminals present in the synaptosomal fraction from squid optic lobe are capable of protein synthesis (Crispino et al., 1993a,b). We have further examined this issue by comparing the translation products of synaptosomal and microsomal polysomes. Both preparations programmed an active process of translation, which was completely abolished by their previous treatment with EDTA. After immunoabsorption of the newly synthesized neurofilament (NF) proteins, the labeling ratio of the 60 and 70 kDa NF proteins was found to differ, in agreement with comparable differences obtained with intact synaptosomes. These observations indicate that the set of mRNAs translated by synaptosomes differs from that translated by nerve cell bodies. Hence, because NF proteins are neuron-specific, they support the view that the active synaptosomal polysomes are mostly localized in the large nerve terminals that represent the most abundant neuronal component of the fraction. This hypothesis was confirmed (1) by electron spectroscopic data demonstrating the presence of ribosomes and polysomes within the large nerve endings of the synaptosomal fraction, as well as in the carrot-like nerve endings of the retinal photoreceptors that constitute the only large terminals in the optic lobe, and (2) by light and high resolution autoradiography of synaptosomal samples incubated with [3H]leucine, showing that most labeled proteins are associated with the large nerve endings. This response was abolished by cycloheximide. Taken together, the data provide the first unequivocal demonstration that presynaptic nerve terminals are capable of protein synthesis.

Animals↗

PubMed1985

Substrate oxidation by isolated rat brain mitochondria and synaptosomes.

The rates of [6-14C]-glucose oxidation by reconstituted systems of cytosol and mitochondria or cytosol and synaptosomes were essentially the same as the rate of oxidation of [3-14C]-3-hydroxybutyrate. However, the rate of [U-14C]-glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The addition of glutamine (5 mM) caused a reduction in the rates of oxidation [6-14C]-glucose of 20% and 40% by mitochondria and synaptosomes, respectively. Conversely, the addition of glucose (5 mM) had little or no effect on the rate of [U-14C]-glutamine oxidation by either organelle. Amino-oxyacetate decreased [U-14C]-glutamine oxidation by mitochondria more than 35% but had little or no effect on the rate of glutamine oxidation by synaptosomes. When glucose (5 mM) was added to [3-14C]-3-hydroxybutyrate, the rates of oxidation by the mitochondria and synaptosomes were increased by 65% and 77%, respectively. However, in the reverse situation the addition of 3-hydroxybutyrate decreased [6-14C]-glucose oxidation by synaptosomes (35%) but did not decrease the rate by mitochondria. These results suggest that differences in the rates of substrate utilization by mitochondria and synaptosomes and differences in substrate interactions in these two subcellular organelles may contribute to metabolic compartmentation in the brain.

Animals↗

PubMed1984

Protein-mediated exchange of synthetic phosphatidylcholines into synaptosomal membranes.

A phosphatidylcholine (PC) exchange protein from bovine liver was used to exchange endogenous synaptosomal membrane PC's with PC's of defined fatty-acid composition from phospholipid vesicles. Up to 50% of the total synaptosomal PC could be exchanged during a 3 h incubation with PC's which were in the liquid-crystalline state at the temperature of incubation (dimyristoyl-, dioleoyl- and dielaidoyl-PC). The biphasic kinetics of the exchange of 14C-labeled 1-palmitoyl-2-oleoyl-PC into isolated synaptic plasma membrane vesicles indicated that the half-time for transbilayer equilibrium of PC in these membranes was about 10 h. Hence, the observed 50% exchange of total synaptosomal PC probably represented nearly complete exchange of PC in the outer face of the synaptosomal plasma membrane. This extensive exchange was accomplished without apparent loss of synaptosomal function, including membrane potential and high-affinity uptake of choline and gamma-aminobutyric acid. PC's in the gel state (dipalmitoyl- and distearoyl-PC) could not be exchanged extensively into the synaptosomal membranes. However, from within gel-state distearoyl-PC liposomes, a trace amount of fluid 1-palmitoyl-2-oleoyl-PC (Tm less than 10 degrees C) could be preferentially exchanged into the synaptosomes at 32 degrees C with little transfer of the saturated PC.

Androgen-Binding Protein↗

PubMed1971

Neurotransmitter-specific synaptosomes in rat corpus striatum: morphological variations.

This communication describes ultrastructural variations among synaptosomal fractions isolated from the corpus striatum of the rat by incomplete equilibrium sedimentation in sucrose density gradients, and attempts to relate the variations to neurotransmitter-specific synaptosomes. The concentration of synaptosomes in each fraction of the density gradient was found to be correlated with the concentration of potassium, a marker for cytoplasm occluded within synaptosomes. Monoamine oxidase activity was found to be correlated with the incidence of free mitochondria in the gradients. Synaptosomes from denser gradient fractions showed a markedly increased frequency of adherent postsynaptic elements and intraterminal mitochondria. These denser gradient fractions were rich in synaptosomes containing norepinephrine, dopamine, serotonin, and acetylcholine, while synaptosomes in lighter portions of the gradients were rich in gamma-aminobutyric acid and other amino acids. These data suggest that significant morphological variations may exist among different neurotransmitter-specific nerve terminals in the brain.

Aminobutyrates↗

PubMed2004

Enrichment of presynaptic and postsynaptic markers by size-based gating analysis of synaptosome preparations from rat and human cortex.

BACKGROUND: Synapse regions in the brain are difficult to isolate and study; resealed nerve terminals (synaptosomes) are a widely used in vitro system for the study of neurotransmission, but nonsynaptosomal elements in the homogenate complicate data interpretation. With the goal of quantitative analysis of pathways leading to synapse loss in neurodegenerative disease, we have developed a method that allows focus on the intact synaptosomes within a crude synaptosomal preparation by gating the largest particles based on forward angle light scatter (FSC). METHODS: Crude synaptosomal fractions (P-2) were prepared and labeled with a viability dye (calcein AM), a presynaptic marker (SNAP-25), and a postsynaptic marker (PSD-95). Forward scatter gates based on size standards were drawn to identify the large population (1.4-4.5 microm), and the enrichment of each marker was quantified in preparations from fresh rat homogenates and from cryopreserved human cortex. RESULTS: Gating on forward scatter resulted in an increase that was highly significant (P < 0.001) for all three markers examined. The calcein-AM-positive fraction in the large synaptosomes was 98% +/- 0.8, and 75% +/- 9.8 for rat and human, respectively. Of large particles, 90% +/- 2.7 in rat and 82% +/- 2.6 in human were positive for SNAP-25, indicating a relatively pure population of intact synaptosomes. A total of 76% +/- 2.9 of the large particles were positive for PSD-95 in rat. This compared to 36% +/- 3.0 in human tissue, and indicates that both presynaptic and postsynaptic elements may be analyzed with this methodology. CONCLUSIONS: Most nonsynaptosomal elements can be excluded and the intact subpopulation of interest within the P-2 can be identified based on size. Size-based gating analysis provides a simple and cost-effective method to monitor fluorescence changes in synapse regions.

Aged↗

PubMed1993

Glial plasmalemmal vesicles: a subcellular fraction from rat hippocampal homogenate distinct from synaptosomes.

By a Percoll density-gradient centrifugation of rat hippocampal homogenate, we found a novel subcellular fraction (specific gravity approximately 1.046 g/ml), besides synaptosomes (approximately 1.060 g/ml), which showed a high activity of Na(+)-dependent glutamate uptake. The initial rate of the glutamate uptake in this fraction was as high as twice that in synaptosomes. Activities of choline acetyltransferase and high affinity choline uptake were, on the other hand, much lower. gamma-Aminobutyric acid uptake activity was nearly equivalent in both fractions. Electron microscopic observations revealed that the fraction was morphologically different from synaptosomal or myelin fractions, but mainly consisted of two different types of empty membrane vesicles; irregular (0.3-0.8 micron in diameter) and spheroid type (0.2 micron). The immunoreactivity to glial fibrillary acidic protein was appreciably high in this fraction. The marker enzyme analysis showed the fraction was rich in plasma membranes. On the basis of these results, the fraction is termed glial plasmalemmal vesicles (GPV). We analyzed kinetically the reaction of Na(+)-dependent glutamate uptake by GPV comparing with that by synaptosomes. Km values for glutamate in GPV was 4.7 microM and Vmax was 33 nmol/mg/min, while in synaptosomes 11 microM and 17 nmol/mg/min, respectively. Hill coefficients of Na+ activation in GPV and synaptosomes were 1.1 and 2.0, respectively. Thus, the mechanism or transporter molecule in glial cells for Na(+)-dependent glutamate transport is likely to be different from that in neurons.

Animals↗

PubMed1987

The combined effect of Pb2+ and Mn2+ on monoamine uptake and Na+, K+-ATPase in striatal synaptosomes.

Rat striatal synaptosomes (P2-fraction) were subjected to lipoperoxidation by the addition of 120 microM Fe2+ and 200 microM ascorbic acid. This preparation (pretreated synaptosomes) was used to investigate the interaction of Pb2+ and Mn2+ on the uptake of tritiated catecholamines, Na+, K+-ATPase activity and malondialdehyde (MDA) formation in order to understand the mechanism of enhanced neurotoxicity by concurrent exposure to these metals. The combination of Pb2+ and Mn2+ (25 microM + 100 microM, respectively) produced a significant increase in the uptake of 3H-Dopamine only in the untreated synaptosomes. No significant effect was noted on the uptake of 3H-Norepinephrine in either pretreated or untreated synaptosomes. However, the combination of Pb2+ and Mn2+ produced a pronounced decrease in the activity of Na+, K+-ATPase, but the magnitude of the change was the sum of the individual metal effects. Metal interaction did not produce any significant change in the formation of MDA compared to the control (without addition of metals). These results indicate that Pb2+ and Mn2+ interaction may produce inhibition in the activity of transport ATPase in both the preparation of synaptosomes, with more pronounced effect of synaptosomes subjected to lipoperoxidation and these changes may be responsible for the disruption in the physiology of nerve impulse transmission.

Animals↗

PubMed1988

Toluene-induced alterations in rat synaptosomal membrane composition and function.

Toluene is a widely used organic solvent that can produce acute central nervous system (CNS) effects. Since toluene reaches relatively high concentrations in the CNS and is extremely lipophilic, we investigated its effects on rat brain membrane composition and function. Toluene (1 g/kg, lh) did not alter total brain microsomal phospholipid (PL) or cholesterol (CL) content. However, synaptosomal PL was decreased (24%), while synaptosomal CL was unaltered. The PL/CL ratio, an indirect index of membrane fluidity, did not change, suggesting that toluene did not affect membrane fluidity. Fluorescence polarization studies employing 1,6-diphenyl-1,3,5-hexatriene (DPH) showed that toluene did not alter synaptosomal membrane fluidity after administration in vivo (1 g/kg) or in vitro (0.5 to 5.0 mM). Dose-response and time-course studies showed that toluene maximally decreased synaptosomal PL after 1 g/kg, 1 h. The dose-response and time-course studies also showed that the toluene-induced decreases in PL were a result of specific decreases in phosphatidylethanolamine (PE). Since PE was decreased, we assessed whether toluene altered synaptosomal membrane function by investigating phospholipid methylation, a reaction which uses PE as its initial substrate. Toluene decreased the incorporation of methyl groups into lipid when [3H]-methionine was used as the methyl donor, but did not affect methylation when [3H]-adenosylmethionine was the methyl donor. These data suggest that toluene-induced specific decreases in synaptosomal PE and inhibition of phospholipid methylation may alter normal synaptic function and play a critical role in the mechanism(s) of action of toluene's CNS effects.

Animals↗