Cerebral ischemia: changes in brain choline, acetylcholine, and other monoamines as related to energy metabolism

Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia

Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.

Emerging Treatment Strategies for Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury (CI/RI) injury is a common feature of ischemic stroke which occurs when the blood supply is restored after a period of ischemia in the brain. Reduced blood-flow to the brain during CI/RI compromises neuronal cell health as a result of mitochondrial dysfunction, oxidative stress, cytokine production, inflammation and tissue damage. Reperfusion therapy during CI/RI can restore the blood flow to ischemic regions of brain which are not yet infarcted. The long-term goal of CI/RI therapy is to reduce stroke-related neuronal cell death, disability and mortality. A range of drug and interventional therapies have emerged that can alleviate CI/RI mediated oxidative stress, inflammation and apoptosis in the brain. Herein, we review recent studies on CI/RI interventions for which a mechanism of action has been described and the potential of these therapeutic modalities for future use in the clinic.

Effect of Air Exposure-Induced Hypoxia on Neurotransmitters and Neurotransmission Enzymes in Ganglia of the Scallop Azumapecten farreri

The nervous system expresses neuromolecules that play a crucial role in regulating physiological processes. Neuromolecule synthesis can be regulated by oxygen-dependent enzymes. Bivalves are a convenient model for studying air exposure-induced hypoxia. Here, we studied the effects of hypoxia on the expression and dynamics of neurotransmitters, and on neurotransmitter enzyme distribution, in the central nervous system (CNS) of the scallop Azumapecten farreri. We analyzed the expression of the neurotransmitters FMRFamide and serotonin (5-HT) and the choline acetyltransferase (CHAT) and universal NO-synthase (uNOS) enzymes during air exposure-induced hypoxia. We found that, in early-stage hypoxia, total serotonin content decreased in some CNS regions but increased in others. CHAT-lir cell numbers increased in all ganglia after hypoxia; CHAT probably appears de novo in accessory ganglia. Short-term hypoxia caused increased uNOS-lir cell numbers, while long-term exposure led to a reduction in their number. Thus, hypoxia weakly influences the number of FMRFamide-lir neurons in the visceral ganglion and does not affect peptide expression in the pedal ganglion. Ultimately, we found that the localization and level of synthesis of neuromolecules, and the numbers of cells expressing these molecules, vary in the scallop CNS during hypoxia exposure. This indicates their possible involvement in hypoxia resistance mechanisms.

Prophylaxis with a multicomponent nutraceutical abates transient cerebral ischemia/reperfusion injury

The effect of a multicomponent nutraceutical on cerebral ischemia/reperfusion injury in male Wistar rats was investigated. Animals were administered with the nutraceutical, Trévo™, for 7 days before 30 min of bilateral common carotid artery occlusion-induced cerebral ischemia and 24 hr of reperfusion. Behavioral assessment, biochemical estimations in the brain cortex, striatum, and hippocampus, and hippocampal histopathological evaluation were carried out after treatments. Results showed that ischemia/reperfusion-induced motor and cognitive deficits were abated in rats pretreated with Trévo™. Additionally, prophylaxis with Trévo™ blunted ischemia/reperfusion-induced redox stress, proinflammatory events, disturbances in neurotransmitter metabolism, mitochondrial dysfunction, and histoarchitectural aberrations in the discreet brain regions. In summary, supplementation with Trévo™ provided neuroprotection to rats against transient cerebral ischemia/reperfusion injury and could be explored as a promising approach in stroke prevention. PRACTICAL APPLICATIONS: There is a worldwide increase in the incidence of cerebral ischemia or stroke. Although an advanced health care system and effective control of risk factors have led to the declining incidence in developed nations, a definitive cure for stroke remains elusive and the situation is growing worse in developing nations. The results of the present study revealed that supplementation with Trévo™ ameliorated neurobehavioral, neurochemical, and histopathological consequences of brain ischemia/reperfusion injury and could, therefore, be beneficial in stroke prevention and management.

Values of vanillylmandelic acid and homovanillic acid in the urine as potential prognostic biomarkers in ischaemic stroke patients

BACKGROUND

Suitable biomarkers that have prognostic values are one of the key points of interest in ischaemic stroke. Increased sympathetic nervous system activity in ischaemic stroke causes multiple local and systemic effects that can be detrimental to the outcome. The mechanism of action is increased secretion and activity of catecholamines, whose end metabolic products are vanillylmandelic acid and homovanilic acid. Aim of our study was to determine whether these compounds can be used as potential prognostic biomarkers in ischaemic stroke, as a unique insight into the activity of the sympathetic nervous system.

METHODS

Urine samples of 96 patients with ischaemic stroke and transitory ischaemic attacks were analysed. Values of vanillylmandelic and homovanillic acids in urine were tested using liquid chromatography on the first and third day post-stroke. Severity of stroke was determined using the NIHSS scale, while functional outcome was determined using the Modified Rankin Scale.

RESULTS

Values of vanillylmandelic and homovanillic acids positively correlated with functional outcome of ischaemic stroke. Favorable outcomes correlated with decreased values, on contrary to increased values, which were associated with unfavourable outcomes.

CONCLUSION

Determining the values of these compounds in the urine is an easily available prognostic tool for the ischaemic stroke outcome, while also influencing potential therapeutic changes.

Early postnatal exposure to intermittent hypoxia in rodents is proinflammatory, impairs white matter integrity, and alters brain metabolism

BackgroundPreterm infants are frequently exposed to intermittent hypoxia (IH) associated with apnea and periodic breathing that may result in inflammation and brain injury that later manifests as cognitive and executive function deficits. We used a rodent model to determine whether early postnatal exposure to IH would result in inflammation and brain injury.MethodsRat pups were exposed to IH from P2 to P12. Control animals were exposed to room air. Cytokines were analyzed in plasma and brain tissue at P13 and P18. At P20-P22, diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) were performed.ResultsPups exposed to IH had increased plasma Gro/CXCL1 and cerebellar IFN-γ and IL-1β at P13, and brainstem enolase at P18. DTI showed a decrease in FA and AD in the corpus callosum (CC) and cingulate gyrus, and an increase in RD in the CC. MRS revealed decreases in NAA/Cho, Cr, Tau/Cr, and Gly/Cr; increases in TCho and GPC in the brainstem; and decreases in NAA/Cho in the hippocampus.ConclusionsWe conclude that early postnatal exposure to IH, similar in magnitude to that experienced in human preterm infants, is associated with evidence for proinflammatory changes, decreases in white matter integrity, and metabolic changes consistent with hypoxia.

Acetylcholine precursor choline evokes NMDA-dependent epileptoid activity in rat hippocampal CA1 area

Application of choline (5 and 10 mM) to electrically stimulated (1 Hz) rat hippocampal slices evoked epileptoid activity manifested by generation of extra population spikes. Application of methyllycaconitine (10 nM), a specific agonist for α7-subunit of nicotinic acetylcholine receptors, did not prevent generation of extra population spikes. In contrast, pretreatment of slices with Mg(2+) (5 mM) or blockade of NMDA-type glutamate receptors with MK-801 (100 μM) prevented generation of the extra population spikes. It was hypothesized that elevation of choline concentration during cerebral pathology can promote activation of NMDA-receptors and provoke epileptoid activity not related to activation of α7-subunit of nicotinic acetylcholine receptor.

Acetylcholine esterase activity and behavioral response in hypoxia induced neonatal rats: effect of glucose, oxygen and epinephrine supplementation

Brain damage due to an episode of hypoxia remains a major problem in infants causing deficit in motor and sensory function. Hypoxia leads to neuronal functional failure, cerebral palsy and neuro-developmental delay with characteristic biochemical and molecular alterations resulting in permanent or transitory neurological sequelae or even death. During neonatal hypoxia, traditional resuscitation practices include the routine administration of 100% oxygen, epinephrine and glucose. In the present study, we assessed the changes in the cholinergic system by measuring the acetylcholinesterase (AChE) activity and the behavioral responses shown by hypoxia induced neonatal rats and hypoxic rats supplemented with glucose, oxygen and epinephrine using elevated plus-maze and open-field test. The acetylcholine esterase enzyme activity showed a significant decrease in cerebral cortex, whereas it increased significantly in the muscle of experimental rats when compared to control. Hypoxic rats supplemented with glucose, glucose and oxygen showed a reversal to the control status. Behavioral studies were carried out in experimental rats with elevated plus-maze test and open-field test. Hypolocomotion and anxiogenic behavioral responses were observed in all experimental rats when compared to control, hypoxic rats supplemented with glucose, glucose and oxygen. Thus, our results suggest that brain damage due to hypoxia, oxygen and epinephrine supplementation in the neonatal rats cause acetylcholine-neuromuscular-defect leading to hypolocomotion and anxiogenic behavioral response. Glucose and glucose with oxygen supplementation to hypoxic neonates protect the brain damage for a better functional status in the later life.

Subtype-Specific Inhibition of Nicotinic Acetylcholine Receptors by Choline: A Regulatory Pathway

Choline is an essential nutrient and a precursor of neurotransmitter acetylcholine (ACh) and is produced at synapses during depolarization, upon hydrolysis of ACh via acetylcholinesterase, and under conditions of injury and trauma. Animal studies have shown that supplementation with choline during early development results in long-lasting improvement in memory in adults; however, the mechanisms underlying this effect are poorly defined. Previous studies revealed that choline interacts with type IA (alpha7*) nicotinic acetylcholine receptors (nAChRs) as a full agonist and as a desensitizing agent and is a weak agonist of type III (alpha3beta4*) nAChRs. Because nAChRs play a role in learning and memory and are generally inhibited by agonists at low concentrations, we investigated in this study the inhibitory effects of choline on non-alpha7 nAChRs such as type II (alpha4beta2*) and type III nAChRs. Using whole-cell patch-clamp recordings from neurons of rat hippocampal and dorsal striatal slices, we demonstrate that choline inhibited type III nAChR-mediated glutamate excitatory postsynaptic currents (EPSCs). Choline inhibited ACh-induced N-methyl-D-aspartate (NMDA) EPSCs in CA1 stratum radiatum (SR) interneurons of rat hippocampal slices with an IC50 of approximately 15 microM. Choline did not inhibit NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in CA1 SR interneurons. Choline inhibited type II nAChRs in CA1 SR interneurons with an IC50 of approximately 370 microM. The present results reveal an order of inhibitory potency for choline type III>type IA>type II nAChRs. It is concluded that brain nAChRs, but not glutamate receptors, are the primary targets for the regulatory actions of choline.

The role of taurine in cerebral ischemia: studies in transient forebrain ischemia and embolic focal ischemia in rodents

Sudden cessation of blood flow to the brain results in a series of events that either result in rapid loss of brain cells or delayed neuronal injury in certain vulnerable regions of the brain. Research over the last three decades has allowed for a better understanding of how neurons and other brain cells die from the effects of ischemia and hypoxia in the central nervous system. Excitatory and inhibitory neurotransmitters exist in a very precise balance for normal function of the brain. Ischemia very rapidly disrupts this balance resulting in a rapid build-up of excitatory neurotransmitters, especially glutamate in the extracellular space. The increased glutamate together with energy loss opens a number of different types of calcium and sodium channels resulting in the build-up of these ions in neurons, leading to cellular dysfunction and death. While most ischemia research has focused on antagonism of excitatory amino acids, there are some reports on enhancement and amplification of inhibitory responses in focal and global ischemia. The majority of work relates to potentiation of GABA, either endogenous or through GABA potentiating medications. Taurine has neuroinhibitory properties and may also have potential for neuroprotection in cerebral ischemia. This present review focuses on the role of taurine as a neuroprotective agent, possibly acting through several different inhibitory mechanisms. Taurine may inhibit neurotransmitter release and may result in normal intracellular osmolality. In transient global ischemia in gerbils, we studied in vivo microdialysis of amino acids before, during and after ischemia. We were able to show that taurine resulted in attenuation of glutamate during ischemia (however did not reach significance). In similar experiments, neuronal damage was assessed in the hippocampus. Our results show 48% damage in taurine treated animals, 60% in alanine treated animals and 69% in control groups (trend towards protection but again did not reach significance) Focal ischemia was induced by embolizing a thrombus into the distal internal carotid artery and origin of the middle cerebral artery. Again, in studies where we compared taurine to a placebo treated animal, there was no significant decrease in the amount of damage with taurine. There are reports in the literature that taurine may attenuate neuronal injury during ischemia. Our studies in two models of cerebral ischemia in rodents did not reveal neuronal protection. It is possible that higher doses or possibly prolonged use of taurine may show better results. Taurine may also potentially offer additive protective effects when used in combination with thrombolysis or other neuroprotective agents. Further studies are necessary to better understand the potential for taurine as a neuroprotective agent in cerebral ischemia.

The transport of choline

Choline has many physiological functions throughout the body that are dependent on its available local supply. However, since choline is a charged hydrophilic cation, transport mechanisms are required for it to cross biological membranes. Choline transport is required for cellular membrane construction and is the rate-limiting step for acetylcholine production. Transport mechanisms include: (1) sodium-dependent high-affinity uptake mechanism in synaptosomes, (2) sodium-independent low-affinity mechanism on cellular membranes, and (3) unique choline uptake mechanisms (e.g., blood-brain barrier choline transport). A comprehensive overview of choline transport studies is provided. This review article examines landmark and current choline transport studies, molecular mapping, and molecular identification of these carriers. Information regarding the choline-binding site is presented by reviewing choline structural analog (hemicholinium-3 and 15, and other nitrogen/methyl-hydroxyl compounds) inhibition studies. Choline transport in Alzheimer's disease, brain ischemic events, and aging is also discussed. Emphasis throughout the article is placed on targeting the choline transporter in disease and use of this carrier as a drug delivery vector.

Microsphere embolism-induced changes in noradrenaline uptake of the cerebral cortex in rats

The present study was undertaken to elucidate pathophysiological changes in noradrenaline (NA) transporter and Na+/K+-ATPase, key regulators of cation gradient across the plasma membrane, in nerve terminals of the cerebral cortex after microsphere-induced cerebral embolism in rats. The Vmax value of NA uptake, when analyzed by the Eadie-Hofstee plot, tended to decrease on the 1st day and decreased on the 3rd and 7th days after the embolism without any change in the Km value. The NA content in cerebrocortical synaptosomes did not alter on the 1st day, but decreased on the 3rd and 7th days after the embolism. Ouabain (1 mM) inhibited NA uptake on the 1st day, but did not alter the uptake on the 3rd and 7th days after the embolism. The activity of Na+/K+-ATPase of cerebrocortical synaptosomes increased on the 1st day and gradually decreased up to the 7th day after the embolim. These results suggest that NA uptake in nerve terminals of the cerebral cortex decreased after microsphere embolism, which may be due to a reduction in function of NA transporters. The changes in Na+/K+-ATPase following microsphere embolism may represent a compensatory action to maintain ion homeostasis in nerve terminals at an early stage of ischemic injury.

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.

Phospholipid biosynthetic enzymes in human brain

Growing evidence suggests an involvement of brain membrane phospholipid metabolism in a variety of neurodegenerative and psychiatric conditions. This has prompted the use of drugs (e.g., CDPcholine) aimed at elevating the rate of neural membrane synthesis. However, no information is available regarding the human brain enzymes of phospholipid synthesis which these drugs affect. Thus, the objective of our study was to characterize the enzymes involved, in particular, whether differences existed in the relative affinity of substrates for the enzymes of phosphatidylethanolamine (PE) compared to those of phosphatidylcholine (PC) synthesis. The concentration of choline in rapidly frozen human brain biopsies ranged from 32-186 nmol/g tissue, a concentration similar to that determined previously for ethanolamine. Since human brain ethanolamine kinase possessed a much lower affinity for ethanolamine (Km = 460 microM) than choline kinase did for choline (Km = 17 microM), the activity of ethanolamine kinase in vivo may be more dependent on substrate availability than that of choline kinase. In addition, whereas ethanolamine kinase was inhibited by choline, and to a lesser extent by phosphocholine, choline kinase activity was unaffected by the presence of ethanolamine, or phosphoethanolamine, and only weakly inhibited by phosphocholine. Phosphoethanolamine cytidylyltransferase (PECT) and phosphocholine cytidylyltransferase (PCCT) also displayed dissimilar characteristics, with PECT and PCCT being located predominantly in the cytosolic and particulate fractions, respectively. Both PECT and PCCT exhibited a low affinity for CTP (Km approximately 1.2 mM), suggesting that the activities of these enzymes, and by implication, the rate of phospholipid synthesis, are highly dependent upon the cellular concentration of CTP. In conclusion our data indicate different regulatory properties of PE and PC synthesis in human brain, and suggest that the rate of PE synthesis may be more dependent upon substrate (ethanolamine) availability than that of PC synthesis.

Cerebral ischemia in young and adult gerbils: effects on cholinergic metabolism

The effect of transient cerebral ischemia on cholinergic metabolism was investigated in adult and young gerbils subjected to bilateral carotid artery occlusion (15 min) alone or with release. Ischemia decreased brain acetylcholine (ACh) and increased choline (Ch) levels, affecting the young to a lesser degree than the adult gerbils. Blood recirculation induced a rapid early restoration of brain ACh levels in young animals, whereas a tremendous rebound of ACh was observed in the adults. After 2 h of reflow, Ch levels normalized in the adult brain, whereas a decreased choline level was seen in the young brain. This is the first study demonstrating an age-dependent susceptibility of cholinergic neurotransmission to cerebral ischemia.

In utero hypoxic ischemia decreases the cholinergic agonist-stimulated poly-phosphoinositide turnover in the developing rat brain

Perinatal hypoxic-ischemic (HI) insult is known to cause cellular and molecular disturbances leading to functional and behavioral abnormalities during brain development. In this study, we examined the effects of an in utero HI insult on poly-phosphoinositide turnover in vivo in the cerebrum and cerebellum as well as cholinergic-stimulated turnover in cortical slices from developing rat brain. In utero HI treatment was carried out by clamping the uterine blood vessels of near-term fetuses for 5, 10 and 15 min followed by resuscitation of the newborn pups. The in vivo protocol for examining poly-PI signaling activity in 2 week-old pup brain involved intracerebral injection of [3H]inositol for 16 hr and subsequent intraperitoneal injection with lithium (8 meq/kg) for 4 hr prior to decapitation. In the control pups, lithium elicited a 2.6 fold increase in labeled inositol phosphate (IP) in the cerebrum as compared to a 1.3 fold increase in the cerebellum. In utero HI insult (5 to 15 min) resulted in a small increase in labeled IP in the cerebrum but not in the cerebellum. Carbachol stimulation of poly-PI turnover was examined in brain slices prelabeled with [3H]inositol in vivo. Incubation of the prelabeled slices with carbachol in the presence of LiCl (10 mM) resulted in a time-, dose- and age-dependent increase in labeled IP. Brain slices from 2 week-old pups that experienced in utero HI-treatment for 10 and 15 min (but not 5 min) showed a significant decrease in carbachol-stimulation of labeled IP as compared with control pups. These results indicate the effects of in utero HI on the choninergic-stimulated poly-PI signaling pathway and its implication on related functional deficits in the developing brain.

Changes in brain energy metabolism, neurotransmitters, and choline during and after incomplete cerebral ischemia in spontaneously hypertensive rats

In order to investigate changes in energy metabolism, neurotransmitters, and membrane disorder accompanying incomplete cerebral ischemia, a bilateral common carotid artery occlusion model of spontaneously hypertensive rats was utilized. We measured concentrations of ATP, phosphocreatine (PCr), lactate (Lac), glucose (Glu), acetylcholine (ACh), choline (Ch), and gamma-aminobutyric acid (GABA) in both the cerebral cortex and the subcortical regions after 1 h ischemia, 2 h ischemia, and 2 h reflow following 2 h ischemia, and then examined changes in concentrations of these substances during and after incomplete cerebral ischemia. Also, examined were interrelations of changes in these substance levels during ischemia. In the cerebral cortex, levels of ATP, PCr, Glu, and ACh decreased, and levels of Lac, Ch, and GABA increased during ischemia. After recirculation, levels of ATP, PCr, Ch, and GABA tended to return to the normal range. On the other hand, the Lac level remained in the ischemic range and the Glu level rose and greatly exceeded the normal range. With regard to ACh, most animals showed normal levels but some exceeded the normal range. Changes in the subcortical regions were qualitatively the same as those in the cerebral cortex during and after ischemia (except with Glu), but only smaller in degrees. Glu levels remained unchanged during ischemia. Correlation of the levels of these substances in the cerebral cortex was examined using normal and ischemic values. A high correlation was generally observed between ATP and other substance levels. The relations between ATP and either PCr or Glu levels were linear. The relation between ATP and ACh levels was logarithmic.(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease in brain choline-containing compounds following a short period of global ischemia in gerbils as detected by 1H NMR spectroscopy in vivo

Cerebral metabolism was studied in the postischaemic gerbil brain using surface coil 31P and 1H NMR spectroscopy. The ratio of choline-containing compounds (Cho) to total creatine (Cr) in the brain decreased from 0.46 +/- 0.02 to 0.32 +/- 0.02 by the fifth day following exposure to 5 min of global ischaemia and it remained at this low level for at least 19 days. The amounts of cerebral Cho as quantified by 1H NMR in vivo were 1.70 +/- 0.15 and 1.09 +/- 0.22 mmol/kg in control and postischaemic animals, respectively. The T2 of Cho was longer in the postischaemic cerebral cortex than in the control one. N-acetyl aspartate (NAA) as determined by 1H NMR in vivo did not differ in the two animal groups. High-resolution 1H NMR of acid-extracted brain cortices showed a decrease in total Cho (glycerophosphocholine, phosphocholine and choline) by 31%, but no changes in NAA, total creatine, taurine and myo-inositol, in the brain cortex seven days postischaemia relative to control animals. The decrease in acid extractable Cho was mainly due to the drop in glycerophosphocholine concentration. 31P NMR indicated normal energy state and phosphomonoester/phosphocreatine (PCr) and phosphodiester/PCr ratios in the in vivo brain 7 days postischaemia. Silver impregnation did not reveal neuronal degeneration but immunohistochemical staining showed a number of glial fibrillary acidic protein expressing astrocytes as indicators of reactive gliosis in the postischaemic cerebral cortex. These data show, for the first time, that a 1H NMR decrease in Cho metabolites takes place as a consequence of brief ischaemic episode even in the absence of obvious neuronal degeneration.

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.

Regional and temporal glycerol changes induced by forebrain ischemia in gerbils

Temporal ischemic changes in glycerol and energy metabolites were studied in the striatum, hippocampus and cortex of gerbils subjected to 15 min of bilateral carotid artery occlusion alone or with various periods of recirculation. The same tissue sample served for the determination of glycerol and energy reserve by a simple enzymatic fluoro- and spectrometric assay after perchloric acid extraction. Cerebral ischemia increased the levels of glycerol (8- to 10-fold) and depleted the energy stores. During the first hour of recirculation, the glycerol content decreased and thereafter (at 2 h), normalized in all structures. However, the glycerol content was still twice as high in the striatum and hippocampus as compared to their respective controls. At the same time, an incomplete restoration of energy reserves was observed in these structures. The findings indicate that glycerol is not a stable postischemic indicator of the ischemia-induced membrane damage.

Effects of hypoxia on choline exchange among organs

Cerebral blood flow (CBF) and the arteriovenous (A-V) difference for choline (Ch) across brain, lung, splanchnic territory, liver, kidney, and lower limb were studied in anesthetized, mechanically ventilated rats subjected to 10-20-min periods of hypoxia induced by lowering the inspired O2 concentration to 13%. A large, time-dependent increase in arterial blood Ch concentration occurred during hypoxia. This phenomenon coincided with a net rate of uptake of Ch by the brain during hypoxia (0.81 +/- 0.24 nmol/min, n = 10; p less than 0.05), which contrasted with a net rate of loss of Ch by this organ during the control period that preceded hypoxia (-0.20 +/- 0.08 nmol/min, n = 10; p less than 0.05). During hypoxia, lungs and splanchnic territory showed negative A-V differences for Ch levels (net Ch loss), whereas brain, liver, kidney, and lower limb showed positive A-V differences for Ch levels (net Ch uptake). Ch output from lungs was already detected at 5 min within the period of hypoxia and reversed rapidly after restoration of normal oxygenation. On the other hand, Ch output from the splanchnic territory became evident only 10 min after commencement of hypoxia and outlasted this experimental condition. It is concluded that extracerebral production of Ch during hypocapnic hypoxia raises the arterial concentration of this molecule and, by reversing the gradient across cerebral capillaries, prevents the cerebral loss of Ch in this condition.

Post-ischemic regional changes in acetylcholine synthesis following transient forebrain ischemia in gerbils

The synthesis rate of brain acetylcholine (ACh) was estimated 30 min and 5 days following transient forebrain ischemia performed by 10 min bilateral carotid occlusion in gerbils. ACh synthesis was evaluated from the conversion of radiolabeled choline (Ch) into ACh after an i.v. administration of [methyl-3H]Ch. Endogenous and labeled Ch and ACh were quantified by HPLC. The synthesis rate of Ach was significantly decreased following 30 min of recirculation. The reductions reached 55.4% in the hippocampus, 51.2% in the cerebral cortex and 44.4% in the striatum. Five days after ischemia, the values returned to normal in the cerebral cortex and in the striatum, while ACh synthesis remained selectively lowered (-30.4%, p less than 0.01) in the hippocampus. These cholinergic alterations may account for both early and delayed post-ischemic behavioral and mnesic deficits.