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K Löffelholz

Publications and source records attributed to K Löffelholz.

At least 19 recordsLinked to original sources
PubMed2001

Glucose plus choline improve passive avoidance behaviour and increase hippocampal acetylcholine release in mice.

The present study tests the effects of glucose and choline, the biosynthetic precursors of acetylcholine, on passive avoidance behaviour and hippocampal acetylcholine release measured by microdialysis in awake mice. Glucose (10 and 30mg/kg) or choline chloride (6-60mg/kg), given by i.p. injection immediately after training, dose-dependently enhanced retention in an inhibitory avoidance task. Combinations of low doses of glucose (10mg/kg) and choline chloride (20mg/kg) which alone were submaximally effective significantly increased retention latencies in a synergistic manner, an effect which was sensitive to atropine (0.5mg/kg). This beneficial effect vanished when higher doses of glucose or choline were combined. Basal hippocampal acetylcholine release in mice habituated to their environment was not affected by administration of glucose and choline. However, when hippocampal acetylcholine release was stimulated either by infusion of scopolamine (0.3microM) or by transferring the mice into a novel environment, the combination of glucose plus choline further increased acetylcholine release to a significant extent. We conclude that low doses of glucose and choline act synergistically to improve memory storage, an effect which is due to facilitation of acetylcholine release. This finding reinforces the view that central cholinergic functions are influenced under certain conditions by dietary intake of precursors.

Acetylcholine↗
PubMed2001

Compensatory mechanisms enhance hippocampal acetylcholine release in transgenic mice expressing human acetylcholinesterase.

Central cholinergic neurotransmission was studied in learning-impaired transgenic mice expressing human acetylcholinesterase (hAChE-Tg). Total catalytic activity of AChE was approximately twofold higher in synaptosomes from hippocampus, striatum and cortex of hAChE-Tg mice as compared with controls (FVB/N mice). Extracellular acetylcholine (ACh) levels in the hippocampus, monitored by microdialysis in the absence or presence of 10(-8)-10(-3) M neostigmine in the perfusion fluid, were indistinguishable in freely moving control and hAChE-Tg mice. Muscarinic receptor functions were unchanged as indicated by similar effects of scopolamine on ACh release and of carbachol on inositol phosphate formation. However, when the mice were anaesthetized with halothane (0.8 vol. %), hippocampal ACh reached significantly lower levels in AChE-Tg mice as compared with controls. Also, the high-affinity choline uptake (HACU) in hippocampal synaptosomes from awake hAChE-Tg mice was accelerated but was reduced by halothane anaesthesia. Moreover, hAChE-Tg mice displayed increased motor activity in novel but not in familiar environment and presented reduced anxiety in the elevated plus-maze test. Systemic application of a low dose of physostigmine (100 microgram/kg i.p.) normalized all of the enhanced parameters in hAChE-Tg mice: spontaneous motor activity, hippocampal ACh efflux and hippocampal HACU, attributing these parameters to the hypocholinergic state due to excessive AChE activity. We conclude that, in hAChE-Tg mice, hippocampal ACh release is up-regulated in response to external stimuli thereby facilitating cholinergic neurotransmission. Such compensatory phenomena most likely play important roles in counteracting functional deficits in mammals with central cholinergic dysfunctions.

Acetylcholine↗
PubMed1998

Phospholipase D in rat myocardium: formation of lipid messengers and synergistic activation by G-protein and protein kinase C.

Activation of phospholipase D (PLD) and phosphoinositide-specific phospholipase C (PI-PLC) by fluoride, to stimulate heterotrimeric G-proteins, and by phorbol esters, to stimulate protein kinase C (PKC), was studied in rat atria. Fluoride and 4beta-phorbol-12beta,13alpha-dibutyrate (PDB), in contrast to 4beta-phorbol-13alpha-acetate (PAc), activated PLD, catalyzing the formation of [3H]-phosphatidylethanol ([3H]-PETH), [3H]-phosphatidic acid ([3H]-PA), choline and sn-1,2-diacylglycerol (DAG). Basal PLD activity was resistant to drastic changes in Ca2+ and to Ro 31-8220, a PKC inhibitor, but was decreased by genistein, an inhibitor of tyrosine kinase, and increased by vanadate, a tyrosine phosphatase inhibitor; both effects were, however, very small. Fluoride-evoked PLD activity was resistant to Ro 31-8220 and to genistein, but was Ca2+-dependent. The rate of fluoride-induced PLD activation was maintained for at least 60 min. In contrast, PDB-mediated PLD activity was blocked by Ro 31-8220 and was resistant to extracellular Ca2+-depletion and desensitized within ca. 15 min. PDB markedly potentiated the fluoride-evoked generation of [3H]-phosphatidylethanol and of choline, but inhibited the formation of [3H]-inositol phosphates ([3H]-IP(1-3)). Ethanol (2%) blocked the PDB-evoked generation of both [3H]-phosphatidic acid and of sn-1,2-diacylglycerol, whereas fluoride-evoked responses were reduced only to approximately 50%. In conclusion, the trimeric G-protein-PLD pathway in heart tissue did not enclose PKC activation and was long-lasting and Ca2+-dependent; there was no evidence for an involvement of tyrosine phosphorylation. However, PKC activation modulated G-protein-coupled PLD and PI-PLC activities in opposite directions. PLD activity significantly contributed to the mass production of sn-1,2-diacylglycerol in the heart. The evidence for a pathophysiological role of PLD activation in cardiac hypertrophy and in ischemic preconditioning is discussed.

Animals↗
PubMed1998

Stimulatory and inhibitory effects of ethanol on hippocampal acetylcholine release.

Using the microdialysis technique and sensitive HPLC procedures for the determination of acetylcholine (ACh) and ethanol, we investigated the release of ACh in rat hippocampus after acute ethanol administration. Systemic administration of ethanol (0.8 and 2.4 g/kg i.p.) led to peak ethanol concentrations of 21 and 42 mM in the hippocampus, respectively. The high dose caused a long-lasting inhibition of basal ACh release by up to 33%. Local infusion of scopolamine (1 microM) enhanced hippocampal ACh release up to eightfold in the presence of neostigmine (10 microM), and this stimulated release was also inhibited after systemic ethanol administration (by up to 45%). The low dose of ethanol (0.8 g/kg) led to a delayed stimulation of hippocampal ACh release. A stimulatory effect on ACh release was also observed when ethanol (50-100 mM) was infused directly into the hippocampus or into the septal area, i.e. to the origin of the cholinergic septohippocampal pathway; thus, the stimulatory effect may be mediated by a direct effect on cholinergic fibres. We conclude that ethanol exerts dual modulatory effects on the activity of the septohippocampal cholinergic fibres, depending on the dose and the site of administration. It is suggested that the inhibition of hippocampal ACh release by intoxicating doses of ethanol may contribute to the well-known cognitive and amnesic effects of ethanol intake.

Acetylcholine↗
PubMed1998

Glutamatergic activation of hippocampal phospholipase D: postnatal fading and receptor desensitization.

Phospholipase D (PLD) activity was determined in rat hippocampal slices between postnatal days 3 and 35. After birth, basal PLD activity was low and, within 2 weeks, increased to reach a plateau that was maintained up to the adult age. Likewise the response to glutamate developed postnatally to reach a maximum at day 8, but then faded rapidly and was almost absent at day 35. Activation of PLD by 4beta-phorbol 12beta,13alpha-dibutyrate (PDB) was independent of age, whereas the effect of aluminum fluoride (AlF4-) increased to a plateau within the first week. At day 8, PLD stimulation by glutamate via metabotropic receptors involved protein kinase C activation, but was independent of Ca2+ influx; the time course of PLD activation by PDB or AlF4- was linear throughout the experiment, whereas the response to glutamate or 1-aminocyclopentane-1,3-dicarboxylic acid followed a biphasic pattern: the rapid "first phase activation" desensitized within a few minutes and disclosed a small, but maintained "second phase." Pretreatment experiments confirmed desensitization of PLD activation by glutamate, but not by AlF4- or PDB. The biphasic pattern of glutamatergic PLD activation changed during development, i.e., the first phase activation faded and the second phase remained. These results were fully confirmed by the time courses of the PLD-mediated efflux of choline evoked by glutamate. In conclusion, postnatal glutamatergic activation of hippocampal PLD is composed of a pronounced and desensitizing first phase activation and a small, but nondesensitizing second phase. The first, but not the second, phase activation fades rapidly during development. The hypothesis is discussed that the glutamatergic activation of PLD occurs along different pathways in neonate and adult tissue.

Aging↗
PubMed1997

Modulation of hippocampal acetylcholine release after fimbria-fornix lesions and septal transplantation in rats.

Female Long-Evans rats sustained electrolytic lesions of the fimbria and the dorsal fornix causing a partial lesion of the septohippocampal pathway. Two weeks later, the rats received intra-hippocampal grafts of fetal septal cell suspensions. Nine to twelve months later, the release of acetylcholine (ACh) in the hippocampus of sham-operated, lesion-only and grafted rats was measured by microdialysis. The extent of cholinergic (re)innervation was determined by acetylcholinesterase (AChE) staining and densitometry. In both lesion-only and grafted rats, the ratio of ACh release to AChE staining intensity was increased as compared to sham-operated rats, indicating a loss of endogenous inhibitory mechanisms. Scopolamine (0.5 mg/kg i.p.), a muscarinic antagonist, increased ACh release in all treatment groups. 8-OH-DPAT (0.5 mg/kg s.c.), an agonist at serotonergic 5HT1A-receptors, induced an increase of hippocampal ACh release in sham-operated rats. This effect was lost in lesion-only rats, but was fully restored by neuronal grafting. As 8-OH-DPAT influences hippocampal ACh release by a postsynaptic action, this finding indicates that the host brain exerts a serotonergic influence on the grafted cholinergic neurons.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1997

Phospholipid breakdown and choline release under hypoxic conditions: inhibition by bilobalide, a constituent of Ginkgo biloba.

A marked increase of choline release from rat hippocampal slices was observed when the slices were superfused with oxygen-free buffer, indicating hypoxia-induced hydrolysis of choline-containing phospholipids. This increase of choline release was suppressed by bilobalide, an ingredient of Ginkgo biloba, but not by a mixture of ginkgolides. The EC50 value for bilobalide was 0.38 microM. In ex vivo experiments, bilobalide also inhibited hypoxia-induced choline release when given p.o. in doses of 2-20 mg/kg 1 h prior to slice preparation. The half-maximum effect was observed with 6 mg/kg bilobalide. A similar effect was noted after p.o. administration of 200 mg/kg EGb 761, a ginkgo extract containing approximately 3% of bilobalide. We conclude that ginkgo extracts can suppress hypoxia-induced membrane breakdown in the brain, and that bilobalide is the active constituent for this effect.

Animals↗
PubMed1997

Ontogenetic and pharmacological studies on metabotropic glutamate receptors coupled to phospholipase D activation.

The present study was aimed at characterizing the metabotropic receptor subtype which is involved in the activation of phospholipase D (PLD) by glutamate in rat hippocampal slices. We first observed that the ontogenetic profile of glutamate-induced hydrolysis of phosphoinositides and of phosphatidylcholine was strikingly similar. Both pathways were significantly activated by glutamate in tissue taken from 3-, 8- and 15-day old rats, but not in adult rats. PLD activation was strongest in slices taken from 8-day old rats. At this age, quisqualate had a higher potency for PLD activation (EC50: 0.6 microM) than 1S,3R-ACPD (EC50: 16 microM) and DHPG, a specific activator of group I mGluR, was a full agonist at PLD activation (EC50: 3.5 microM) indicating an involvement of a group I mGluR (mGluR1 and 5). MCPG and AIDA, two putative antagonists at mGluR1 receptors, caused a small but (in the case of MCPG) significant inhibition. DCG-IV, an activator of group II mGluR, was a weak partial agonist at PLD activation (EC50: 22 nM) while L-AP 4, an activator at group III mGluR, was totally inactive. Likewise, forskolin, a stimulant of cyclic AMP formation, was inactive either alone, or in combination with glutamatergic agonists. Pretreatment of the slices with pertussis toxin did not affect PLD activation. In summary, the glutamate-mediated activation of hippocampal PLD, which occurs transiently during postnatal development, is mediated by a group I mGluR, possibly involving mGluR5.

Animals↗
PubMed1997

Acetylcholine release and choline availability in rat hippocampus: effects of exogenous choline and nicotinamide.

The influence of choline availability on acetylcholine (ACh) release in the hippocampus of the awake rat was investigated using the microdialysis procedure. Three treatments enhancing choline availability for basal and atropine-evoked ACh release were evaluated: acute administration of choline chloride (20 mg/kg i.p.); pretreatment of animals with nicotinamide (10 mmol/kg s.c.) 2 hr before atropine injection and dietary choline supplementation (5-fold increase of choline intake for 15-18 days). Although acute choline administration led to a short-lasting (15 min) increase of basal choline efflux by 25% and nicotinamide caused a long-lasting (5 hr) increase by 105%, neither one affected basal ACh release. However, basal release of choline (1.38 pmol/min) and of ACh (114 fmol/min) in the hippocampus was slightly increased in choline-supplemented animals (choline: 1.92 pmol/min; ACh: 140 fmol/min). In untreated animals, atropine administration caused a 3-fold increase of ACh efflux that lasted approximately 2.5 hr. All treatments, acute or chronic choline and nicotinamide, led to significant increases of the maximum and duration of atropine-evoked ACh release. Total atropine-evoked ACh efflux (area under the curve) was increased 2- to 3-fold, with the largest effect evoked by the combination of nicotinamide and choline. The results clearly demonstrate that, under stimulated conditions, hippocampal ACh release could be facilitated when the availability of choline for ACh synthesis was enhanced by dietary or pharmacological means. Under certain conditions, significant effects of increased choline availability on ACh release can be revealed in the absence of an overall increase of extracellular choline.

Acetylcholine↗
PubMed1996

Adrenergic activation of phospholipase D in primary rat astrocytes.

Phospholipase D (PLD) activity was investigated in astrocytes prepared from newborn rat cerebral cortex using the transphosphatidylation assay. Basal PLD activity was measurable and was found to be enhanced by ATP, carbachol and noradrenaline. The activation by noradrenaline (EC50, 0.68 microM) was mimicked by methoxamine (EC50, 65 microM), an alpha 1-specific adrenergic agonist, and was inhibited by prazosine, an alpha 1-specific adrenergic antagonist. Clonidin, an alpha 2-adrenergic agonist, slightly lowered PLD activity whereas beta-adrenergic drugs were without effect. Experiments with mitogens indicate that PLD activation in astrocytes may be involved in the control of astrocytic cell proliferation.

Animals↗
PubMed1996

Effects of nicotinamide on central cholinergic transmission and on spatial learning in rats.

High-dose nicotinamide (1000 mg/kg) leads to a minor increase of plasma choline but to a major increase of the choline concentrations in the intra- and extracellular spaces of the brain. In the hippocampus, the nicotinamide-induced increase in choline was associated with an increase in the release of acetylcholine under stimulated conditions. In young rats, nicotinamide in doses between 10 and 1000 mg/kg did not influence spatial learning, as tested in the Morris water maze. In old rats, low doses of nicotinamide were ineffective whereas the high dose of 1000 mg/kg even impaired spatial learning. The combined administration of choline and nicotinamide had a synergistic effect on brain choline levels but had similar effects as nicotinamide given alone in the behavioral experiments. Additional tests for spontaneous behaviour and locomotion revealed procholinergic and sedative effects of the compound. We conclude that the ineffectiveness of the putative cognition enhancer nicotinamide in the learning task may be due to the observed sedative effect. Therefore, the development of nonsedative nicotinamide derivatives is recommended.

Acetylcholine↗
PubMed1994

Phospholipase C and phospholipase D are independently activated in rat hippocampal slices.

In order to investigate a possible G-protein-mediated activation of phospholipase D (PLD) and its relationship to the activation of phosphoinositide-specific phospholipase C (PI-PLC), we measured the effects of aluminium fluoride and carbachol on choline release, the PLD-specific transphosphatidylation reaction (generation of phosphatidylpropanol) and the formation of inositol phosphates in rat hippocampal slices. Aluminium fluoride markedly enhanced the formation of choline and phosphatidylpropanol but failed to increase the formation of inositol phosphates. In contrast, the muscarinic agonist carbachol strongly stimulated PI-PLC but failed to activate PLD. We conclude that PLD in hippocampal slices is activated by a G-protein independently of phosphoinositide hydrolysis.

Aluminum Compounds↗
PubMed1993

Release of choline from rat brain under hypoxia: contribution from phospholipase A2 but not from phospholipase D.

Moderate hypoxia induced in rats by inhalation of 10% oxygen led to an increase of the concentration of free choline in the brain and caused a large net-release of choline from the brain into the venous blood as determined by the measurement of the arterio-venous difference. In hippocampal slices from rat brain, hypoxia increased the release of choline into the superfusion medium. The activity of phospholipase D, as measured by the formation of phosphatidylpropanol in the presence of propanol, was not stimulated under these conditions. However, the mobilization of choline was completely depressed by lowering extracellular calcium and by 0.1 mM mepacrine. We conclude that hypoxia leads to a selective activation of phospholipase A2 in the brain and, consequently, to a net loss of choline-containing phospholipids and membrane structures.

Animals↗
PubMed1993

Free choline and choline metabolites in rat brain and body fluids: sensitive determination and implications for choline supply to the brain.

In the central nervous system, choline is an essential precursor of choline-containing phospholipids in neurons and glial cells and of acetylcholine in cholinergic neurons. In order to study choline transport and metabolism in the brain, we developed a comprehensive methodical procedure for the analysis of choline and its major metabolites which involves a separation step, selective hydrolysis and subsequent determination of free choline by HPLC and electrochemical detection. In the present paper, we report the levels of choline, acetylcholine, phosphocholine, glycerophosphocholine and choline-containing phospholipids in brain tissue, cerebrospinal fluid and blood plasma of the untreated rat. The levels of free choline in blood plasma (11.4 microM), CSF (6.7 microM) and brain intracellular space (64.0 microM) were sufficiently similar to be compatible with an exchange of choline between these compartments. In contrast, the intracellular levels of glycerophosphocholine (1.15 mM) and phosphocholine (0.59 mM) in the brain were considerably higher than their CSF concentrations of 2.83 and 1.70 microM, respectively. In blood plasma, glycerophosphocholine was present in a concentration of 4.58 microM while phosphocholine levels were very low or absent (< 0.1 microM). The levels of phosphatidylcholine and lyso-phosphatidylcholine were high in blood plasma (1267 and 268 microM) but very low in cerebrospinal fluid (< 10 microM). We concluded that the transport of free choline is the only likely mechanism which contributes to the supply of choline to the brain under physiological conditions.

Acetylcholine↗