Choline release and inhibition of phosphatidylcholine synthesis precede excitotoxic neuronal death but not neurotoxicity induced by serum deprivation

MST1 mediates the N-methyl-D-aspartate-induced excitotoxicity in mouse cortical neurons

Excessive activation of the ionotropic N-methyl-D-aspartate (NMDA) receptor has been shown to cause abnormally high levels of Ca2+ influx, thereby leading to excitotoxic neuronal death. In this study, exposure of mouse primary cortical neurons to NMDA resulted in the cleavage and activation of mammalian sterile 20-like kinase-1 (MST1), both of which were mediated by calpain 1. In vitro cleavage assay data indicated that calpain 1 cleaves out the autoinhibitory domain of MST1 to generate an active form of the kinase. Furthermore, calpain 1 mediated the cleavage and activation of wild-type MST1, but not of MST1 (G339A). Intriguingly, NMDA/calpain-induced MST1 activation promoted the nuclear translocation of the kinase and the phosphorylation of histone H2B in mouse cortical neurons, leading to excitotoxicity. Thus, we propose a previously unrecognized mechanism of MST1 activation associated with NMDA-induced excitotoxic neuronal death.

Antiphospholipid syndrome: the need for new international classification criteria

Introduction: As soon as the association of lupus anticoagulant (LAC) and anticardiolipin antibodies (aCL) with thrombosis and miscarriages was described in the 1980s, the definition of the antiphospholipid syndrome (APS) became a need. Early descriptions of the disease by members of the Graham Hughes team included broad categories and unexplained laboratory inclusions. Over time, new clinical and experimental data refined the criteria, especially the obstetric manifestations, as well as the laboratory criteria.Areas covered: The authors performed a review of the literature using the PubMed database, and the following keywords were used: 'antiphospholipid antibody', 'antiphospholipid syndrome', and 'criteria of antiphospholipid'. The history of antiphospholipid criteria, clinical and experimental advancements, and other expert opinions were included in this paper.Expert opinion: It has been 14 years since an international congress on antiphospholipid antibodies has generated new classification based on the recent extensive research performed in the field. Currently, there is a need to update the international APS classification taking into consideration the inclusion of new clinical criteria such as aPL-related nephropathy as well as new standardized antibody specificities (e.g., anti-phosphatidylserine/prothrombin antibodies) with the adoption of a standardized scoring system that can stratify APS patients.

Neurochemical effects of oxytocin in people at clinical high risk for psychosis

Alterations in neurochemical metabolites are thought to play a role in the pathophysiology of psychosis onset. Oxytocin, a neuropeptide with prosocial and anxiolytic properties, modulates glutamate neurotransmission in preclinical models but its neurochemical effects in people at high risk for psychosis are unknown. We used proton magnetic resonance spectroscopy (¹H-MRS) to examine the effects of intranasal oxytocin on glutamate and other metabolites in people at Clinical High Risk for Psychosis (CHR-P) in a double-blind, placebo-controlled, crossover design. 30 CHR-P males were studied on two occasions, once after 40IU intranasal oxytocin and once after placebo. The effects of oxytocin on the concentration of glutamate, glutamate+glutamine and other metabolites (choline, N-acetylaspartate, myo-inositol) scaled to creatine were examined in the left thalamus, anterior cingulate cortex (ACC) and left hippocampus, starting approximately 75, 84 and 93 min post-dosing, respectively. Relative to placebo, administration of oxytocin was associated with an increase in choline levels in the ACC (p=.008, Cohen's d = 0.54). There were no other significant effects on metabolite concentrations (all p>.05). Our findings suggest that, at ∼75-99 min post-dosing, a single dose of intranasal oxytocin does not alter levels of neurochemical metabolites in the thalamus, ACC, or hippocampus in those at CHR-P, aside from potential effects on choline in the ACC.

Choline induces opposite changes in pyramidal neuron excitability and synaptic transmission through a nicotinic receptor-independent process in hippocampal slices

Choline is present at cholinergic synapses as a product of acetylcholine degradation. In addition, it is considered a selective agonist for α5 and α7 nicotinic acetylcholine receptors (nAChRs). In this study, we determined how choline affects action potentials and excitatory synaptic transmission using extracellular and intracellular recording techniques in CA1 area of hippocampal slices obtained from both mice and rats. Choline caused a reversible depression of evoked field excitatory postsynaptic potentials (fEPSPs) in a concentration-dependent manner that was not affected by α7 nAChR antagonists. Moreover, this choline-induced effect was not mimicked by either selective agonists or allosteric modulators of α7 nAChRs. Additionally, this choline-mediated effect was not prevented by either selective antagonists of GABA receptors or hemicholinium, a choline uptake inhibitor. The paired pulse facilitation paradigm, which detects whether a substance affects presynaptic release of glutamate, was not modified by choline. On the other hand, choline induced a robust increase of population spike evoked by orthodromic stimulation but did not modify that evoked by antidromic stimulation. We also found that choline impaired recurrent inhibition recorded in the pyramidal cell layer through a mechanism independent of α7 nAChR activation. These choline-mediated effects on fEPSP and population spike observed in rat slices were completely reproduced in slices obtained from α7 nAChR knockout mice, which reinforces our conclusion that choline modulates synaptic transmission and neuronal excitability by a mechanism independent of nicotinic receptor activation.

Role of Choline in the Modulation of Degenerative Processes: In Vivo and In Vitro Studies

The purpose of the present study was to examine the nutraceutical potential of choline as an added value to its well-known brain nutrient role. Several toxicity, antitoxicity, genotoxicity, antigenotoxicity, and longevity endpoints were checked in the somatic mutation and recombination test in in vivo Drosophila animal model. Cytotoxicity in human leukemia-60 cell line (HL-60) promyelocytic and NIH3T3 mouse fibroblast cells, proapoptotic DNA fragmentation, comet assay, methylation status, and macroautophagy (MA) activity were tested in in vitro assays. Choline is not only safe but it is also able to protect against the DNA damage caused by an oxidative genotoxin. Moreover, it improves the life extension in the animal model. The in vitro results show that it is able to exhibit genetic damage against leukemia HL-60 cells. Single-strand breaks in DNA are observed at the molecular level in treatments with choline, although only a significant hypermethylation on the long interspersed elements-1 and a hypomethylation on the satellite-alpha DNA repetitive DNA sequences of HL-60 cells at the lowest concentration (0.447 mM) were observed. Besides, choline decreased MA at the lower assayed concentration and the MA response to topoisomerase inhibitor (etoposide) is maintained in the presence of treatment with 0.22 mM choline. Taking into account the hopeful results obtained in the in vivo and in vitro assays, choline could be proposed as a substance with an important nutraceutical value for different purposes.

Boosting Endogenous Resistance of Brain to Ischemia

Most survivors of ischemic stroke remain physically disabled and require prolonged rehabilitation. However, some stroke victims achieve a full neurological recovery suggesting that the human brain can defend itself against ischemic injury, but the protective mechanisms are unknown. This study used selective pharmacological agents and a rat model of cerebral ischemic stroke to detect endogenous brain protective mechanisms that require activation of α7 nicotinic acetylcholine receptors (nAChRs). This endogenous protection was found to be (1) limited to less severe injuries; (2) significantly augmented by intranasal administration of a positive allosteric modulator of α7 nAChRs, significantly reducing brain injury and neurological deficits after more severe ischemic injuries; and (3) reduced by inhibition of calcium/calmodulin-dependent kinase-II. The physiological role of α7 nAChRs remains largely unknown. The therapeutic activation of α7 nAChRs after cerebral ischemia may serve as an important physiological responsibility of these ubiquitous receptors and holds a significant translational potential.

The therapeutic promise of positive allosteric modulation of nicotinic receptors

In the central nervous system, deficits in cholinergic neurotransmission correlate with decreased attention and cognitive impairment, while stimulation of neuronal nicotinic acetylcholine receptors improves attention, cognitive performance and neuronal resistance to injury as well as produces robust analgesic and anti-inflammatory effects. The rational basis for the therapeutic use of orthosteric agonists and positive allosteric modulators (PAMs) of nicotinic receptors arises from the finding that functional nicotinic receptors are ubiquitously expressed in neuronal and non-neuronal tissues including brain regions highly vulnerable to traumatic and ischemic types of injury (e.g., cortex and hippocampus). Moreover, functional nicotinic receptors do not vanish in age-, disease- and trauma-related neuropathologies, but their expression and/or activation levels decline in a subunit- and brain region-specific manner. Therefore, augmenting the endogenous cholinergic tone by nicotinic agents is possible and may offset neurological impairments associated with cholinergic hypofunction. Importantly, because neuronal damage elevates extracellular levels of choline (a selective agonist of α7 nicotinic acetylcholine receptors) near the site of injury, α7-PAM-based treatments may augment pathology-activated α7-dependent auto-therapies where and when they are most needed (i.e., in the penumbra, post-injury). Thus, nicotinic-PAM-based treatments are expected to augment the endogenous cholinergic tone in a spatially and temporally restricted manner creating the potential for differential efficacy and improved safety as compared to exogenous orthosteric nicotinic agonists that activate nicotinic receptors indiscriminately. In this review, I will summarize the existing trends in therapeutic applications of nicotinic PAMs.

A type-II positive allosteric modulator of α7 nAChRs reduces brain injury and improves neurological function after focal cerebral ischemia in rats

In the absence of clinically-efficacious therapies for ischemic stroke there is a critical need for development of new therapeutic concepts and approaches for prevention of brain injury secondary to cerebral ischemia. This study tests the hypothesis that administration of PNU-120596, a type-II positive allosteric modulator (PAM-II) of α7 nicotinic acetylcholine receptors (nAChRs), as long as 6 hours after the onset of focal cerebral ischemia significantly reduces brain injury and neurological deficits in an animal model of ischemic stroke. Focal cerebral ischemia was induced by a transient (90 min) middle cerebral artery occlusion (MCAO). Animals were then subdivided into two groups and injected intravenously (i.v.) 6 hours post-MCAO with either 1 mg/kg PNU-120596 (treated group) or vehicle only (untreated group). Measurements of cerebral infarct volumes and neurological behavioral tests were performed 24 hrs post-MCAO. PNU-120596 significantly reduced cerebral infarct volume and improved neurological function as evidenced by the results of Bederson, rolling cylinder and ladder rung walking tests. These results forecast a high therapeutic potential for PAMs-II as effective recruiters and activators of endogenous α7 nAChR-dependent cholinergic pathways to reduce brain injury and improve neurological function after cerebral ischemic stroke.

Changes in phospholipid composition of synaptic membranes in frontal lobes of cerebral hemispheres in cats at various stages of hemorrhagic shock

Phospholipid composition of synaptic membranes in the frontal lobes of cerebral hemispheres was studied in cats with hemorrhagic shock. The compensatory and adaptive mechanisms of regulation of neurotransmission in this region of the brain at the initial stage of hemorrhagic shock are associated with increased degradation of phosphatidylinositol. Accumulation of this phospholipid in synaptic membranes during severe hemorrhagic shock reflects instability of the key neuroregulatory pathway, which is mediated by phosphatidylinositol metabolites. Dysregulation of transmembrane signaling in hemorrhagic shock is related to depletion of phosphatidylcholine and phosphatidylserine in synaptic membranes and accumulation of phosphatidylethanolamine.

Chronic hyperammonemia reduces the activity of neuronal nitric oxide synthase in cerebellum by altering its localization and increasing its phosphorylation by calcium-calmodulin kinase II

Impaired function of the glutamate-nitric oxide-cGMP pathway contributes to cognitive impairment in hyperammonemia and hepatic encephalopathy. The mechanisms by which hyperammonemia impairs this pathway remain unclear. Understanding these mechanisms would allow designing clinical treatments for cognitive deficits in hepatic encephalopathy. The aims of this work were: (i) to assess whether chronic hyperammonemia in vivo alters basal activity of neuronal nitric oxide synthase (nNOS) in cerebellum and/or its activation in response to NMDA receptor activation and (ii) to analyse the molecular mechanisms by which hyperammonemia induces these alterations. It is shown that hyperammonemia reduces both basal activity of nNOS and its activation following NMDA receptor activation. Reduced basal activity is because of increased phosphorylation in Ser847 (by 69%) which reduces basal activity of nNOS by about 40%. Increased phosphorylation of nNOS in Ser847 is because of increased activity of calcium-calmodulin-dependent protein kinases (CaMKII) which in turn is because of increased phosphorylation at Thr286. Inhibiting CaMKII with KN-62 normalizes phosphorylation of Ser847 and basal NOS activity in hyperammonemic rats, returning to values similar to controls. Reduced activation of nNOS in response to NMDA receptor activation in hyperammonemia is because of altered subcellular localization of nNOS, with reduced amount in post-synaptic membranes and increased amount in the cytosol.

Full length Bid is sufficient to induce apoptosis of cultured rat hippocampal neurons

Background

Bcl-2 homology domain (BH) 3-only proteins are pro-apoptotic proteins of the Bcl-2 family that couple stress signals to the mitochondrial cell death pathways. The BH3-only protein Bid can be activated in response to death receptor activation via caspase 8-mediated cleavage into a truncated protein (tBid), which subsequently translocates to mitochondria and induces the release of cytochrome-C. Using a single-cell imaging approach of Bid cleavage and translocation during apoptosis, we have recently demonstrated that, in contrast to death receptor-induced apoptosis, caspase-independent excitotoxic apoptosis involves a translocation of full length Bid (FL-Bid) from the cytosol to mitochondria. We induced a delayed excitotoxic cell death in cultured rat hippocampal neurons by a 5-min exposure to the glutamate receptor agonist N-methyl-D-aspartate (NMDA; 300 μM).

Results

Western blot experiments confirmed a translocation of FL-Bid to the mitochondria during excitotoxic apoptosis that was associated with the release of cytochrome-C from mitochondria. These results were confirmed by immunofluorescence analysis of Bid translocation during excitotoxic cell death using an antibody raised against the amino acids 1–58 of mouse Bid that is not able to detect tBid. Finally, inducible overexpression of FL-Bid or a Bid mutant that can not be cleaved by caspase-8 was sufficient to induce apoptosis in the hippocampal neuron cultures.

Conclusion

Our data suggest that translocation of FL-Bid is sufficient for the activation of mitochondrial cell death pathways in response to glutamate receptor overactivation.

Magnetisation transfer ratio of choline is reduced following epileptic seizures

The purpose of this study was to characterise the concentration and magnetisation transfer ratio (MTR) of brain metabolites following epileptic seizures. Magnetic resonance spectroscopy was performed in 10 patients with temporal or extra-temporal lobe epilepsy as soon as possible after a seizure, with a second interictal scan between 1 and 3 days after the postictal scan and 10 healthy controls were scanned twice. Voxels (26 +/- 2 mL) were placed in the frontal lobe in all patients and controls, on the side of seizure focus in the patient group. Spectra were obtained using a modified PRESS sequence (TE 30 ms, TR 3 s, with three hard pulses offset from the water frequency by 2,500 Hz for MT presaturation). Mean metabolite concentrations and median metabolite MTRs of N-acetylaspartate (NAA), creatine, choline (Cho), myo-inositol (Ins) and glutamate plus glutamine were compared between the first and second scans in each group. A significant decrease in the MTR of Cho was seen postictally in the patient group, but the metabolite concentrations showed no significant difference between interictal and postictal scans and in the control group there was no difference between the two scans. Inter-group comparison showed significantly reduced concentrations of NAA and Ins in the patients. Reduced MTR of Cho indicates a shift from a bound to a more mobile fraction. These changes might indicate membrane perturbation in areas of seizure spread.

Brain regional alterations in the modulation of the glutamate-nitric oxide-cGMP pathway in liver cirrhosis. Role of hyperammonemia and cell types involved

Hepatic encephalopathy is a complex neuropsychiatric syndrome present in patients with liver disease that includes impaired intellectual function and alterations in personality and neuromuscular coordination. Hyperammonemia and liver failure result in altered glutamatergic neurotransmission, which contributes to hepatic encephalopathy. Alterations in the function of the glutamate-nitric oxide-cGMP pathway may be responsible for some of the neurological alterations found in hepatic encephalopathy. The function of this pathway is altered in brain from patients died with liver cirrhosis and one altered step of the pathway is the activation of soluble guanylate cyclase by nitric oxide, which is increased in cerebral cortex and reduced in cerebellum from these patients. Portacaval anastomosis and bile duct ligation plus hyperammonemia in rats reproduce the alterations in the activation of soluble guanylate cyclase by NO both in cerebellum and cerebral cortex. We assessed whether hyperammonemia is responsible for the region-selective alterations in guanylate cyclase modulation in liver cirrhosis and whether the alteration occurs in neurons or in astrocytes. Activation of guanylate cyclase by nitric oxide is lower in cerebellar neurons exposed to ammonia (1.5-fold) than in control neurons (3.3-fold). The activation of guanylate cyclase by nitric oxide is higher in cortical neurons exposed to ammonia (8.7-fold) than in control neurons (5.5-fold). The activation is not affected in cerebellar or cortical astrocytes. These findings indicate that hyperammonemia is responsible for the differential alterations in the modulation of soluble guanylate cyclase by nitric oxide in cerebellum and cerebral cortex of cirrhotic patients. Moreover, under the conditions used, the alterations occur selectively in neurons and not in astrocytes.

Real time single cell analysis of Bid cleavage and Bid translocation during caspase-dependent and neuronal caspase-independent apoptosis

Bcl-2 homology domain (BH) 3-only proteins couple stress signals to evolutionarily conserved mitochondrial apoptotic pathways. Caspase 8-mediated cleavage of the BH3-only protein Bid into a truncated protein (tBid) and subsequent translocation of tBid to mitochondria has been implicated in death receptor signaling. We utilized a recombinant fluorescence resonance energy transfer (FRET) Bid probe to determine the kinetics of Bid cleavage and tBid translocation during death receptor-induced apoptosis in caspase 3-deficient MCF-7 cells. Cells treated with tumor necrosis factor-alpha (200 ng/ml) showed a rapid cleavage of the Bid-FRET probe occurring 75.4 +/- 12.6 min after onset of the tumor necrosis factor-alpha exposure. Cleavage of the Bid-FRET probe coincided with a translocation of tBid to the mitochondria and a collapse of the mitochondrial membrane potential (DeltaPsim). We next investigated the role of Bid cleavage in a model of caspase-independent, glutamate-induced excitotoxic apoptosis. Rat cerebellar granule neurons were transfected with the Bid-FRET probe and exposed to glutamate for 5 min. In contrast to death receptor-induced apoptosis, neurons showed a translocation of full-length Bid to the mitochondria. This translocation occurred 5.6 +/- 1.7 h after the termination of the glutamate exposure and was also paralleled with a collapse of the DeltaPsim. Proteolytic cleavage of the FRET probe also occurred, however, only 25.2 +/- 3.5 min after its translocation to the mitochondria. Subfractionation experiments confirmed a translocation of full-length Bid from the cytosolic to the mitochondrial fraction during excitotoxic apoptosis. Our data demonstrate that both tBid and full-length Bid have the capacity to translocate to mitochondria during apoptosis.

Neurons exposed to ammonia reproduce the differential alteration in nitric oxide modulation of guanylate cyclase in the cerebellum and cortex of patients with liver cirrhosis

The activation of soluble guanylate cyclase by nitric oxide is increased in the frontal cortex but is reduced in the cerebellum of patients who died with liver cirrhosis. The aims of this work were to assess whether hyperammonemia is responsible for the region-selective alterations in guanylate cyclase modulation in liver cirrhosis and to assess whether the alteration occurs in neurons or in astrocytes. The activation of guanylate cyclase by nitric oxide was lower in cerebellar neurons exposed to ammonia (1.5-fold) than in control neurons (3.3-fold). The activation of guanylate cyclase by nitric oxide was higher in cortical neurons exposed to ammonia (8.7-fold) than in control neurons (5.5-fold). The activation was not affected in cerebellar or cortical astrocytes. These findings indicate that hyperammonemia is responsible for the differential alterations in the modulation of soluble guanylate cyclase in cerebellum and cerebral cortex of cirrhotic patients. Moreover, the alterations occur specifically in neurons and not in astrocytes.

Bile duct ligation plus hyperammonemia in rats reproduces the alterations in the modulation of soluble guanylate cyclase by nitric oxide in brain of cirrhotic patients

Modulation of soluble guanylate cyclase (sGC) by nitric oxide (NO) is altered in brain from cirrhotic patients. The aim of this work was to assess whether an animal model of cirrhosis, bile duct ligation, alone or combined with diet-induced hyperammonemia for 7-10 days reproduces the alterations in NO modulation of sGC found in brains from cirrhotic patients. sGC activity was measured under basal conditions and in the presence of NO in cerebellum and cerebral cortex of the following groups of rats: controls, bile duct ligation without or with hyperammonemia and hyperammonemia without bile duct ligation. In cerebellum activation of sGC by NO was significantly lower in bile duct ligated rats with (12 +/- five-fold) or without (14 +/- six-fold) hyperammonemia than in control rats (23 +/- seven-fold). In cerebral cortex activation of sGC by NO was higher in rats with bile duct ligation with hyperammonemia (124 +/- 30-fold) but not without hyperammonemia (59 +/- 15-fold) than in control rats (66 +/- 11-fold). The combination of bile duct ligation and hyperammonemia reproduces the alterations in the modulation of soluble guanylate cyclase by NO found in cerebral cortex and cerebellum of cirrhotic patients while bile duct ligation or hyperammonemia alone reproduces the effects in cerebellum but not in cerebral cortex.

Possible neuroprotective effects of lecithin and alpha-tocopherol alone or in combination against ischemia/reperfusion insult in rat brain

A close correlation exists between ischemia/reperfusion (I/R)-induced insult and the release of free radicals. Lecithin is a polyunsaturated phosphatidylcholine that corresponds to the phosphatidylcholine molecule. Phosphatidylcholines are high-energy functional and structural elements of all biologic membranes. alpha-Tocopherol is the major lipid-soluble chain-breaking antioxidant in the body tissues and effectively protects against neuronal damage. Therefore, we studied the effect of lecithin (300 mg/kg, p.o., 14 days) and alpha-tocopherol (200 mg/kg, p.o., 14 days), alone or in combination, on the brain redox state during I/R. Adult male Wistar rats were subjected to global ischemia by the occlusion of the two carotid arteries 24 h after the last dose of drug administration. Reperfusion was carried out 1 h after induction of ischemia and lasted for another hour. Brain lipid peroxides (MDA) and glutathione (GSH) contents, as well as superoxide dismutase (SOD) and catalase (CAT) activities were assessed. The results showed that I/R elevated brain lipid peroxides content which was accompanied by a reduction in both antioxidant enzyme activities, however, brain GSH level remained unaltered. Lecithin, alpha-tocopherol and their combination restored MDA content, as well as CAT activity with a slight tendency to normalize SOD activity. We conclude that lecithin has a possible neuroprotective effect partly through its antioxidant action which is comparable to that of alpha-tocopherol.

NMDA receptor overactivation inhibits phospholipid synthesis by decreasing choline-ethanolamine phosphotransferase activity

Overactivation of NMDA receptors is believed to induce neuronal death by increasing phospholipid hydrolysis and subsequent degradation. We showed previously that NMDA releases choline and inhibits incorporation of [3H]choline into phosphatidylcholine before excitotoxic neuronal death. On the basis of these results, we hypothesized that excitotoxicity results from inhibition of synthesis rather than from increased degradation of phospholipids. We now investigated the effect of NMDA receptor overactivation on synthesis and degradation of major membrane phospholipids in the early stages of the excitotoxic process. Exposure of cortical neurons to neurotoxic concentrations of NMDA increased extracellular choline and activated hydrolysis of phosphatidylcholine and phosphatidylinositol by phospholipase A2 but did not induce significant degradation of phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, or phosphatidylserine. In contrast, NMDA strongly reduced the incorporation of [3H]choline and [3H]ethanolamine into their respective phospholipids. Metabolic labeling experiments in whole cells showed that NMDA receptor overactivation does not modify the activity of phosphocholine or phosphoethanolamine cytidylyltransferases but strongly inhibits choline-ethanolamine phosphotransferase activity. This effect was observed well before any significant membrane damage and cell death. Moreover, cholinephosphotransferase activity was lower in microsomes from NMDA-treated cells. These results show that membrane damage by NMDA is preceded by inhibition of phospholipid synthesis and not by phospholipid degradation in the early stages of the excitotoxic process, and that NMDA receptor overactivation decreases phosphatidylcholine and phosphatidylethanolamine synthesis by inhibiting choline-ethanolaminophosphotransferase activity.

Regulation of neuronal function by choline and 4OH-GTS-21 through alpha 7 nicotinic receptors

A unique feature of alpha7 nicotinic acetylcholine receptor physiology is that, under normal physiological conditions, alpha7 receptors are constantly perfused with their natural selective agonist, choline. Studying neurons of hypothalamic tuberomammillary (TM) nucleus, we show that choline and the selective alpha7 receptor agonist 4OH-GTS-21 can regulate neuronal functions directly, via activation of the native alpha7 receptors, and indirectly, via desensitizing those receptors or transferring them into a state "primed" for desensitization. The direct action produces depolarization and thereby increases the TM neuron spontaneous firing (SF) rate. The regulation of the spontaneous firing rate is robust in a nonphysiological range of choline concentrations >200 microM. However, modest effects persist at concentrations of choline that are likely to be attained perineuronally under some conditions (20-100 microM). At high physiological concentration levels, the indirect choline action reduces or even eliminates the responsiveness of alpha7 receptors and their availability to other strong cholinergic inputs. Similarly to choline, 4OH-GTS-21 increases the TM neuron spontaneous firing rate via activation of alpha7 receptors, and this regulation is robust in the range of clinically relevant concentrations of 4OH-GTS-21. We conclude that factors that regulate choline accumulation in the brain and in experimental slices such as choline uptake, hydrolysis of ACh, membrane phosphatidylcholine catabolism, and solution perfusion rate influence alpha7 nAChR neuronal and synaptic functions, especially under pathological conditions such as stroke, seizures, Alzheimer's disease, and head trauma, when the choline concentration in the CSF is expected to rise.

Cholecystokinin octapeptide CCK-8 and carbachol reduce [(32)P]orthophosphate labeling of phosphatidylcholine without modifying phospholipase D activity in rat pancreatic acini

We have studied phospholipase D activation in [(32)P]orthophosphoric acid-prelabeled rat pancreatic acini by measuring the formation of (32)P-phosphatidylalcohols as stimulated in the presence of ethanol or butanol. A small but significant and time-dependent basal accumulation of [(32)P]phosphatidylethanol and [(32)P]phosphatidylbutanol was detected, which was further stimulated by phorbol myristate acetate, orthovanadate and pervanadate. However, the secretagogues cholecystokinin octapeptide and carbachol did not enhance basal accumulation of (32)P-phosphatidylalcohol, yet they decreased [(32)P]phosphatidylcholine content and stimulated the generation of [(32)P]phosphatidic acid. Our results stress the need to examine the transphosphatidylation reaction as well as agonist effects on the synthesis of phosphatidylcholine in order to assess unambiguously phospholipase D activity.