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Biomedical subjects

L Wecker

Publications and source records attributed to L Wecker.

At least 37 records · Page 2Linked to original sources
PubMed1991

Modulation of acetylcholine release from rat striatal slices: interaction between 4-aminopyridine and atropine.

The objective of these studies was to determine whether the muscarinic receptor-mediated autoregulation of the basal release of acetylcholine (ACh), like the modulation of evoked release, involves 4-aminopyridine (4-AP)-sensitive potassium channels. To accomplish this, striatal and hippocampal slices were incubated with 4-AP in the absence or presence of atropine, and the release of ACh was measured. 4-AP increased the release of ACh in a concentration-dependent manner; a maximal effect (280% of control release) was achieved in the presence of 100 microM. The maximal release of ACh from hippocampal slices was approximately 150% of control release and was achieved in the presence of a broad range of concentrations (33-333 microM 4-AP). Tetrodotoxin (1 microM) totally abolished the 4-AP-induced release of ACh from hippocampal slices, but only attenuated the 4-AP-induced release from striatal slices, i.e., in the presence of tetrodotoxin, the 4-AP-induced release of ACh from the latter was significantly greater than control release by 54%. Atropine (0.1 microM) increased significantly the basal release of ACh from striatal slices by 61%. When striatal slices were incubated with 4-AP in the presence of this maximally effective concentration of atropine, ACh release was significantly greater than release from slices incubated with either atropine or 4-AP alone, suggesting that atropine and 4-AP increase neurotransmitter release by independent mechanisms. Although oxotremorine did not alter either the 4-AP- or atropine-induced release of ACh, it prevented the potentiated response exhibited by slices incubated with both atropine and 4-AP.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗
PubMed1990

Muscarinic receptor blockade increases basal acetylcholine release from striatal slices.

The main objective of these studies was to determine whether the basal release of acetylcholine (ACh) from brain slices was subject to modulation by muscarinic receptor blockade. Incubation of striatal slices with the muscarinic antagonist atropine increased ACh release in a concentration-dependent manner with a maximal effect (1.4-1.8 times control release) achieved with 0.1 to 1.0 microM. In contrast, ACh release from hippocampal slices was unaltered by any concentration of atropine tested, indicating that the basal release of neurotransmitter from striatum, but not hippocampus, was subject to modulation by muscarinic receptor blockade. Incubation of striatal slices with 1 microM tetrodotoxin or removal of Ca++ from the medium decreased the basal release of ACh by 20% and abolished the atropine-induced release of ACh; neurotransmitter release from hippocampal slices was unaltered by tetrodotoxin. Thus, part of the basal release of ACh from striatal slices is a consequence of the intrinsic impulse activity of cholinergic neurons and it is this component of release that is atropine-sensitive. Oxotremorine was unable to antagonize the atropine-induced release of ACh, even with concentrations 100 times that of atropine, whereas pirenzepine increased ACh release and, like that of atropine, the effect of pirenzepine was sensitive to tetrodotoxin and resistant to oxotremorine. These results indicate that a component of basal ACh release from striatal slices is subject to modulation by a receptor that is sensitive to atropine and pirenzepine, but not to oxotremorine, suggesting that this site differs from the nerve terminal muscarinic autoreceptor.

Acetylcholine↗
PubMed1989

Acute choline supplementation in vivo enhances acetylcholine synthesis in vitro when neurotransmitter release is increased by potassium.

The main objective of these studies was to determine whether the acute administration of choline to rats provides supplemental precursor that can be used to support acetylcholine synthesis when the demand for choline is increased by increasing neurotransmitter release. For these experiments, hippocampal and striatal slices were prepared form rats that had received saline or an acute injection of choline. Slices were incubated in a choline-free buffer containing 4.74-35 mM KCl, and acetylcholine synthesis and release and choline production were measured. The initial tissue contents of acetylcholine and choline did not differ between experimental groups for either brain region. When hippocampal slices from the controls were incubated for 10 min with depolarizing concentrations of KCl, acetylcholine release increased and the tissue content decreased in a concentration-dependent fashion; no net synthesis of acetylcholine occurred. In contrast, hippocampal slices from the choline-injected animals maintained their tissue content in the presence of high concentrations of KCl, despite an increase in acetylcholine release that was similar in magnitude to that of the controls; positive net synthesis of acetylcholine resulted. Although the molar concentration of choline achieved in the incubation media at the end of the 10-min period did not differ between groups, the mobilization of free choline from bound stores was significantly greater in hippocampal slices from the choline-injected group than the controls. In addition, the synthesis of acetylcholine by hippocampal slices from the choline-injected group was prevented by the presence of hemicholinium-3 (1 microM) in the media.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1989

Dietary choline intake modulates benzodiazepine receptor binding and gamma-aminobutyric acidA receptor function in mouse brain.

Several lines of evidence suggest that dietary choline intake influences the metabolism of membrane phospholipids with possible effects on GABAergic neurotransmission. Based on these findings, the present experiments determined whether chronic choline supplementation or deficiency alters GABAergic function at the level of the gamma-aminobutyric acid (GABA)/benzodiazepine-chloride channel complex. To accomplish this, mice were fed diets containing 0% (deficient), 0.2% (basal) or 2.0% (supplemented) choline chloride for 28 days, and behavior, ligand binding at several sites in the complex and chloride uptake were determined in various brain regions. For both rotarod ataxia and open-field activity, mice receiving choline supplementation had a decreased response to clonazepam compared to those receiving basal and deficient diets. Choline supplementation significantly increased the in vivo binding of [3H]Ro15-1788 to cortex and cerebellum by 19% and 24%, respectively, and in vitro studies in cortical membranes indicated a significant 36% increase in the maximal number of [3H]flunitrazepam binding sites without a change in affinity, as compared to basal controls. In contrast, [3H]Ro15-1788 binding in vivo in all brain regions from mice fed the deficient diet decreased significantly to 20 to 58% of control values. Dietary choline intake did not alter GABA levels in brain, the binding of [35S]t-butylbicyclophosphorothionate to the chloride channel or the coupling between GABA and either the t-butylbicyclophosphorothionate site or the benzodiazepine site. However, the function of the GABAA receptor, determined by muscimol-stimulated chloride uptake into cortical synaptoneurosomes, was increased significantly in tissue from the supplemented group as compared to both control and deficient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Influence of dietary choline availability and neuronal demand on acetylcholine synthesis by rat brain.

The main objective of this study was to test the hypothesis that the chronic administration of choline supplements a bound pool of choline from which free choline can be mobilized and used to support acetylcholine synthesis when the demand for precursor is increased. For these experiments, brain slices from rats fed diets containing different amounts of choline were incubated in a choline-free buffer and acetylcholine synthesis was measured under resting conditions and in the presence of K+-induced increases in acetylcholine synthesis and release. Rats fed the choline-supplemented diet had circulating choline levels that were 52% greater than the controls, and striatal and cerebral cortical slices from this group produced significantly more free choline during the incubation than slices from the controls. However, the synthesis and release of acetylcholine by these tissues did not differ from those by controls, during either resting or K+-evoked conditions. In contrast, acetylcholine synthesis and release by striatal and hippocampal slices from choline-deficient rats, animals that had circulating choline levels that were 80% of control values, decreased significantly; the production of free choline by these tissues was also depressed. Results indicate that, despite an increased production of free choline by brain slices from choline-supplemented rats, the synthesis of acetylcholine was unaltered, even in the presence of an increased neuronal demand. In contrast, the choline-deficient diet led to a decreased release of free choline from bound stores and an impaired ability of brain to synthesize acetylcholine.

Acetylcholine↗
PubMed1988

Adenosine inhibits choline kinase activity and decreases the phosphorylation of choline in striatal synaptosomes.

The main objective of these studies was to determine whether adenosine inhibits choline kinase in rat striata, leading to a decreased incorporation of choline into phosphorylcholine, a mechanism that may mediate seizure-induced increases in the levels of free choline in brain. Incubation of particulate and soluble fractions of striatal synaptosomes with adenosine or its metabolically stable analogues significantly inhibited enzyme activity. The inhibition was noncompetitive versus choline and competitive versus MgATP. Inhibitor constants for adenosine, 2-chloroadenosine, and 2',5'-dideoxyadenosine at the MgATP site were 94, 49, and 207 microM, respectively; these values were less than the Michaelis constant for MgATP (340 microM). To determine whether adenosine altered the phosphorylation of choline in an intact preparation, synaptosomes were incubated with [3H]choline in the presence or absence of adenosine or its analogues and the amount of [3H]-phosphorylcholine formed from the [3H]choline taken up was measured. All compounds tested significantly reduced the synthesis of [3H]phosphorylcholine. Results suggest that following seizures or hypoxia, when levels of adenosine increase and the concentration of ATP decreases, inhibition of choline phosphorylation may be manifest, resulting in increased levels of free choline in brain.

2-Chloroadenosine↗
PubMed1987

Chronic choline supplementation attenuates the behavioral effects of pentobarbital.

The behavioral and neurochemical effects of pentobarbital were investigated in rats maintained for 28-35 days on a standard choline-containing diet or on a diet containing 10 times the concentration of choline present in standard rodent chow. The supplemented dietary regimen increased the concentration of free choline in serum by 52%, but did not alter the steady-state concentrations of either choline or acetylcholine in brain. Choline supplementation attenuated both the sedative/hypnotic and hypothermic effects of pentobarbital through an action that could not be attributed to either an enhanced peripheral metabolism of pentobarbital or to an attenuation of the cholinergic effects of pentobarbital. Rather, results indicate that chronic supplementation with choline increases cerebral glucose metabolism and causes a behavioral hyperactivity, effects that may mediate the attenuation of the behavioral response of pentobarbital.

Acetylcholine↗
PubMed1987

Concomitant increases in the levels of choline and free fatty acids in rat brain: evidence supporting the seizure-induced hydrolysis of phosphatidylcholine.

The main objective of this study was to determine whether the excitotoxic cholinesterase inhibitor soman increases the catabolism of phospholipids in rat brain. Injections of soman (70 micrograms/kg, s.c.), at a dose that produced toxic effects, increased the levels of both free fatty acids (175-250% of control) and free choline (250% of control) in rat cerebrum 1 h after administration. All fatty acids contained in brain phosphatidylcholine were elevated significantly including palmitic (16:0), stearic (18:0), oleic (18:1), arachidonic (20:4), and docosahexaenoic (22:6) acids. The changes observed were consistent with those reported to occur following ischemia and the administration of other convulsants. Pretreatment of rats with the anticonvulsant diazepam (4 mg/kg, i.p.) prevented both the signs of soman toxicity and the soman-induced increase of choline and free fatty acids. Diazepam alone did not affect the levels of choline or free fatty acids, cholinesterase activity, or soman-induced cholinesterase inhibition, suggesting that soman toxicity involves a convulsant-mediated increase in phosphatidylcholine catabolism. In addition, administration of the convulsant bicuculline, at a dose that produces seizures and increases the levels of free fatty acids in brain, significantly increased the levels of choline. Results suggest that excitotoxic events enhance the hydrolysis of phosphatidylcholine in brain as evidenced by a concomitant increase in the levels of choline and free fatty acids.

Animals↗
PubMed1986

Elevated choline levels in brain. A non-cholinergic component of organophosphate toxicity.

The role of cholinergic and non-cholinergic mechanisms in mediating organophosphate cholinesterase (ChE) inhibitor-induced elevations in choline levels in brain was investigated. The nerve agents soman and sarin, when administered to rats at doses greater than the IC50 for acetylChE inhibition, significantly increased the levels of choline and acetylcholine in both the striatum and hippocampus. The elevation in choline levels was evident 1 hr after injection with a maximal increase at 2 hr. Levels of choline returned to control by 4 hr. In contrast, the administration of diisopropyl phosphorofluoridate at doses greater than the IC50 for acetylChE inhibition increased the levels of acetylcholine, but did not alter the concentration of choline during the first 3 hr. Between 4 and 24 hr after injection, however, a significant decrease in choline levels was apparent. This effect persisted for 48 hr. When rats were pretreated with the anticonvulsant diazepam, the sarin- and soman-induced increases in choline levels were attenuated significantly. Results indicate that the organophosphates differentially alter the levels of choline in brain and suggest that the effect of soman and sarin to elevate choline levels is not a reflection of excessive cholinergic activity, but rather may be a consequence of the excitotoxic actions of these compounds.

Acetylcholinesterase↗
PubMed1986

Evidence of necrosis in human intercostal muscle following inhalation of an organophosphate insecticide.

Intercostal muscle samples obtained from autopsy of a 51-year-old male exposed to an organophosphate insecticide were analyzed for cholinesterase activity and muscle fiber integrity. Muscle cholinesterase activity, 5 days after exposure, was reduced to 53% of control values. Histological analysis indicated the presence of muscle fibers with subsarcolemmal grouped granular basophilic inclusions and scattered necrotic fibers. Results indicate that acute organophosphate exposure through inhalation can lead to skeletal muscle fiber damage in humans, similar to results obtained by ingestion. Furthermore, the pathology is comparable to the histological alterations observed in rats following acute injection of organophosphates.

Aerosols↗
PubMed1986

Neurochemical effects of choline supplementation.

Whether or not the brain can use supplemental choline to enhance the synthesis of acetylcholine (ACh) is an important consideration for assessing the merits of using choline or phosphatidylcholine (lecithin) for the treatment of neuropsychiatric disorders postulated to involve hypocholinergic activity. While it is well documented that administered choline is incorporated into ACh, the ability of supplemental choline to increase the synthesis and release of ACh has been questionable. Studies in my laboratory have demonstrated that acute or chronic choline supplementation does not, by itself, enhance the levels of ACh in brain under normal biochemical and physiological conditions. However, supplemental choline prevents the depletion of ACh in brain induced by numerous pharmacological agents that increase the firing of cholinergic neurons. Since the levels of free choline in brains from supplemented rats were not different from controls prior to drug challenge, evidence suggested that the observed effects of choline were mediated by alterations in the mobilization of choline from choline-containing compounds. Studies investigating the release of choline from brain indicated that more choline was released per unit time in tissues from choline-supplemented rats than from controls. In addition, brain tissue from choline-supplemented rats had increased concentrations of total lipid phosphorus as compared with controls. Hence, although choline supplementation does not alter the levels of ACh in brain under normal conditions, it does appear to support ACh synthesis during drug-induced increases in neuronal activity, an effect most likely mediated by alterations in the metabolism of choline-containing phospholipids.

Acetylcholine↗
PubMed1985

Trace element concentrations in hair from autistic children.

The concentrations of 14 elements were determined in scalp hair samples from control, autistic and autistic-like children. Significant differences were noted between normal males and females for calcium, magnesium and mercury. The autistic population had significantly lower levels of calcium, magnesium, copper, manganese and chromium and higher levels of lithium as compared to sex- and age-matched controls. Children with autistic features (autistic-like), classified as having childhood-onset pervasive disorder, had lower levels of magnesium, cadmium, cobalt and manganese as compared to controls. Discriminant function analysis using the 14 trace elements correctly classified 90.5% of the normal and 100% of the autistic population. Using a stepwise procedure, the five elements with the greatest discriminatory power were calcium, copper, zinc, chromium and lithium. Analysis based on these five trace elements led to the correct classification of 85.7% of the normal and 91.7% of the autistic group. Results indicate that the concentrations of trace elements in hair from normal children differ from patterns observed in both autistic and autistic-like children. Furthermore, evidence suggests that hair analysis may have potential use as a diagnostic tool for autism.

Autistic Disorder↗
PubMed1985

Effects of chronic paraoxon administration on skeletal muscle fiber integrity.

Rats were injected daily for up to 60 days with low doses of paraoxon to determine the effects of chronic organophosphate cholinesterase (ChE) inhibition on skeletal muscle fiber integrity. Administration of .05 or .10 mg/kg paraoxon for 30 days did not lead to any overt signs of organophosphate toxicity, but did produce lesions in diaphragm muscle. Further injections, for up to 60 days, did not increase the severity of the myopathy. ChE activity in the end plate region of the diaphragm was progressively inhibited by both doses of paraoxon throughout the 60 day period. Enzyme activity in the non-end plate region from rats injected with .05 mg/kg was unaffected until 60 days of injections, while activity in muscle from rats receiving the higher dose was maximally inhibited after 15 days and remained at that level of inhibition for the remaining 45 days. Plasma ChE activity was maximally inhibited by both doses at 15 days of injection. Acetylcholinesterase (AChE) activity in red blood cells from rats injected with the low dose of paraoxon showed a progressive inhibition throughout the treatment schedule, whereas enzyme activity in red blood cells from rats receiving the higher dose was maximally inhibited by 15 days. Results indicate that prolonged exposure to low doses of organophosphate ChE inhibitors leads to necrosis of skeletal muscle fibers and may be observed without other overt signs of organophosphate toxicity.

Animals↗
PubMed1984

Kinetic mechanism of choline kinase from rat striata.

The kinetic mechanism of choline kinase associated with both the cytosolic and membrane fractions of synaptosomes isolated from rat striata was studied. The velocity of choline kinase was measured using various concentrations of MgATP at several concentrations of uncomplexed Mg2+ and a single concentration of choline. This experiment was repeated using different concentrations of choline. Analysis of these data according to a terreactant mechanism indicates that MgATP binds in rapid equilibrium prior to Mg2+, but the binding of MgATP and choline is random. Product inhibition by phosphorylcholine was noncompetitive versus both choline and MgATP. Hemicholinium-3 (HC-3), an analog of choline and competitive inhibitor of the sodium-dependent high affinity choline transport system, was noncompetitive versus choline and uncompetitive versus MgATP at high levels of Mg2+. However, when the concentration of Mg2+ was decreased below the KMg2 +, HC-3 was noncompetitive versus MgATP. Thiocholine, another analog of choline, gave slope-linear intercept hyperbolic inhibition versus choline. Mg-5'-adenylyl imidodiphosphate, an analog of MgATP, was competitive versus MgATP and noncompetitive versus choline. Virtually identical results were obtained using either soluble or particulate forms of choline kinase from rat striata. All data are consistent with the mechanism suggested by initial velocity studies alone and additionally suggest that the release of MgADP is slow, occurs last, and may limit the overall rate of the reaction.

Adenosine Triphosphate↗
PubMed1984

Effects of chronic (dietary) choline availability on the transport of choline across the blood-brain barrier.

The effects of dietary choline availability on the transport of choline across the blood-brain barrier (BBB) were investigated using the intracarotid injection technique. Maintenance of rats on choline-deficient, basal choline, or choline-supplemented diets for 28-32 days led to respective increases in blood levels of choline and correlative increases in the velocity of transport of choline measured using a buffer injectate. When serum from these rats was included in the injectate and transport determined in control animals, there was a marked inhibition of choline transport that was related to the concentration of choline in the diets. Results suggest that the activity of the choline carrier at the BBB is antagonized by an inhibitory substance in serum whose concentration or activity may be modified by chronic alterations in circulating levels of choline and whose presence may normally regulate the velocity of choline transport.

Animals↗
PubMed1983

Evidence for membrane-associated choline kinase activity in rat striatum.

The distribution of choline kinase (EC 2.7.1.32) activity was investigated in subcellular fractions of rat striatum. Enzyme activity in the crude mitochondrial fraction, determined after dissolution in Triton X-100, was 5.90 mumol/g initial wet weight/h. When a crude mitochondrial preparation was hypoosmotically shocked and fractionated, followed by the addition of Triton X-100, choline kinase activity in the soluble and particulate fractions was 4.58 and 1.40 mumol/g initial wet weight/h, respectively. Enzyme activity in the particulate fraction was not detected in the absence of Triton X-100 or in the presence of NaCl (up to 1.5 M). Subcellular enzyme markers indicated that the membrane-associated activity was not attributable to mitochondrial or microsomal contamination. Kinetic analysis of the activity of soluble and membrane-solubilized choline kinase indicated Km values of 0.74 mM and 0.68 mM, respectively. Results indicate that choline kinase activity may be measured in both the soluble and the particulate fractions of rat striatum, the latter most likely involving enzyme associated with membrane through hydrophobic or covalent interactions. The specific function of the membrane-associated enzyme has not yet been determined.

Adenosine Triphosphate↗