Stimulation of free fatty acid and diacylglycerol accumulation in cerebrum and cerebellum during bicuculline-induced status epilepticus. Effect of pretreatment with alpha-methyl-p-tyrosine and p-chlorophenylalamine

Effects of ischemia on free fatty acids and diacylglycerols in developing rat brain

Post-decapitative ischemic treatment imposed on the developing rat brain elicited a marked increase in its susceptibility to free fatty acid (FFA) release between 14 and 17 days, an observation similar to that reported by Bazan (Acta Physiol. Lat. Am.21, 15, 1971). Although the level of diacylglycerols (DG) also increased during this period, the extent of the increase was not as obvious as the FFA. Ischemic treatment to rats after 17 days of age elicited increases in DG and FFA enriched in stearic and arachidonic acids. The delayed response in susceptibility of brain tissue to ischemia-induced changes seems to suggest that the biochemical mechanism(s) responsible for the FFA and DG release is better correlated to events commensurating with synaptogenesis than with myelination.

Cortical impact injury in rats promotes a rapid and sustained increase in polyunsaturated free fatty acids and diacylglycerols

Neurotrauma activates the release of membrane phospholipid-derived second messengers, such as free arachidonic acid (20:4n-6, AA) and diacylglycerols (DAGs). In the present study, we analyze the effect of cortical impact injury of low-grade severity applied to the rat frontal right sensory-motor cortex (FRC) on the accumulation of free fatty acids (FFAs) and DAGs in eight brain areas 30 min and 24 hours after the insult. At these times, accumulation of FFAs and DAGs occurred mainly in the damaged FRC. The cerebellum was the only other brain area that displayed a significant accumulation of DAGs by day one post-injury. By 30 min, accumulation of free AA in the FRC displayed the greatest relative increase (300% over sham value), followed by free docosahexaenoic acid (22:6n-3, DHA, 150%), while both 20:4-DAGs and 22:6-DAGs were increased 100% over sham values. At day one, free 22:6 and 22:6-DAGs showed the greatest increase (590% and 230%, respectively). These results suggest that TBI elicits the hydrolysis of phospholipids enriched in excitable membranes, targeting early on 20:4-phospholipids (by 30 min post- trauma) and followed 24 hours later by preferential hydrolysis of DHA-phospholipids. These lipid metabolic changes may contribute to the initiation and maturation of neuronal and fiber track degeneration observed following cortical impact injury.

Kindled amygdaloid seizures in rats cause immediate and transient increase in protein kinase C activity followed by transient suppression of the activity

Protein kinase C (PKC) activity in hippocampus and amygdala was measured during kindled seizures and 30 min, 3, 24, and 48 h, and 2 weeks after seizures in amygdaloid-kindled rats. Sham-operated rats not subjected to kindling were used as controls. During kindled seizures, membrane-bound PKC activity in bilateral hippocampi was significantly increased, with a slight reduction in cytosolic PKC activity, but there was no change in either membrane-bound or cytosolic PKC activity in bilateral amygdala. Thirty minutes after seizures, PKC activity in both fractions was significantly increased in bilateral hippocampi and amygdala. Three hours after seizures, PKC activity in both fractions was markedly decreased in bilateral hippocampi. In bilateral amygdala, a similar and significant decrease in membrane-bound PKC activity was noted, with no marked change in the cytosolic fraction. Twenty-four hours after seizures, a significant decrease in membrane-bound PKC activity in bilateral hippocampi and amygdala was again noted, although cytosolic PKC activity was unchanged. Forty-eight hours after the seizures, PKC activity in both fractions had returned to control levels. Two weeks after the last seizure, there was no significant change in PKC activity in either fraction in any region, except for a slight increase in membrane-bound PKC activity in unilateral hippocampus contralateral to the kindled amygdala. These results suggest that kindled amygdaloid seizures cause an immediate and transient increase in PKC activity in limbic structures, followed by suppression of enzyme activity, and that PKC in hippocampus responds to kindled seizures more readily and preferentially than it does in amygdala.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentylenetetrazole-induced chemoshock affects protein kinase C and substrate proteins in mouse brain

Protein kinase C (PKC) activity, western blot analysis of PKC alpha, beta, gamma, epsilon, and zeta by isozyme-specific antibodies, and in vitro phosphorylation of endogenous substrate proteins were studied in the mice brain after pentylenetetrazole-induced chemoshock. The PKC isozymes and endogenous substrates in the crude cytosolic and membrane fractions were partially purified by DE-52 columns eluted with buffer A containing 100 or 200 mM KCl. This method consistently separates cytosolic and membrane proteins and various PKC isoforms. The 100 mM KCl eluates from DE-52 columns contain more PKC alpha and beta in both cytosol and membrane than the 200 mM KCl eluates, whereas PKC gamma, epsilon, and zeta appear in equal amounts in these two eluates. The kinase activity assayed by phosphorylation of exogenous histone was increased in the chemoshocked mice in both the cytosol and membrane of 200 mM KCl eluates. In further analysis by immunoblotting, this increased activity was found to be due to the increase in content of PKC gamma isozyme. As for novel-type epsilon and zeta isozymes, they were not altered in the chemoshocked mice. From autoradiography, the endogenous substrate 17-kDa neurogranin, which was shown below 21 kDa, was mostly eluted by 100 mM KCl from the DE-52 column, whereas 43-kDa neuromodulin, which was also demonstrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, only appeared in the 200 mM KCl eluates. The in vitro phosphorylation of neuromodulin was found to be increased in the chemoshocked mice. Therefore, the increased phosphorylation of neuromodulin and increased content of the PKC gamma isoform were involved in the pentylenetetrazole-induced chemoshock.

Membrane lipid degradation is related to interictal cortical activity in a series of seizures

Brain levels of free fatty acids (FFA) and diacylglycerols (DAG) rise rapidly with the onset of seizures, reflecting activation of phospholipases A2 (PLA2) and C (PLC), respectively. However, the ictal/interictal accumulation of FFA attenuates as recurrent seizures continue. To assess the role of neuronal activity in stimulating PLA2 and C, we compared FFA and DAG in rat cerebral cortex during recurrent ictal periods as a function of associated levels of interictal activity. Pentobarbital-anesthetized rats were paralyzed, ventilated with 30% O2 and subjected to periodic pentylenetetrazol seizures at intervals of 5 min. Animals were killed with focused-microwave irradiation during either the 3rd or 15th seizure. The rise in cortical FFA levels during early seizures for 20:4, 22:6, and 18:0 was 3.6-, 2.5-, and 2.2-fold greater, respectively, when adjacent interictal activity was intense as compared to weak activity. During late seizures, this difference dropped to 2.2-fold for 20:4, the only FFA that showed a significantly higher value between robust versus weak interictal activity. In contrast, accumulation of DAG during early and late seizures was observed only when adjacent interictal activity was high. These results indicate that the cortical accumulation of FFA and DAG during ictal periods of similar intensity and duration depends upon the electrocortical activity during adjacent interictal periods.

Methylprednisolone and membrane properties of primary cultures of mouse spinal cord

The present study attempts to define the capacity of methylprednisolone sodium succinate (MP) to protect neuronal membranes against a free radical challenge in primary cultures of fetal mouse spinal cord. Incubation of these cultures with MP significantly increased the Na+,K(+)-ATPase activity, an effect that was blocked by the RNA synthesis inhibitor, actinomysin D and the protein synthesis inhibitor, cycloheximide, suggesting an induction of protein synthesis by MP. In contrast, incubation with FeCl2 for 1 or 2 h significantly inhibited Na+,K(+)-ATPase activity and elevated the levels of thiobarbituric acid-reactive substances (TBARS). Pretreatment with MP prevented the rise in TBARS and partially prevented the decrease in Na+,K(+)-ATPase activity for the first hour of FeCl2 incubation, an effect that was lost during the second hour. A second dose of MP after the first hour of incubation with FeCl2 partially restored Na+,K(+)-ATPase activity and reduced TBARS levels after the second hour of exposure to FeCl2. Co-incubation of MP with cycloheximide completely prevented the decrease in Na+,K(+)-ATPase activity seen after a 2-h incubation with FeCl2 and eliminated the need for a second dose of MP after the first hour of incubation with FeCl2. These findings suggest a capacity for rapid protein induction and antioxidant activity for MP in vitro.

Decreased electroconvulsive shock-induced diacylglycerols and free fatty acid accumulation in the rat brain by Ginkgo biloba extract (EGb 761): selective effect in hippocampus as compared with cerebral cortex

The effect of Ginkgo biloba extract (EGb 761) treatment (100 mg/kg/day, per os, for 14 days) on electroconvulsive shock (ECS)-induced accumulation of free fatty acids (FFA) and diacylglycerols (DAG) was analyzed in rat cerebral cortex and hippocampus. EGb 761 reduced the FFA pool size by 33% and increased the DAG pool by 36% in the hippocampus. These endogenous lipids were unaffected in cerebral cortex. During the tonic seizure (10 s after ECS) the fast accumulation of FFA, mainly 20:4, was similar in sham- and EGb 761-treated rats, in both the cerebral cortex and hippocampus. However, further accumulation of free 18:0 and 20:4, observed in the hippocampus of sham-treated rats during clonic seizures (30 s to 2 min after ECS), did not occur in EGb 761-treated animals. The rise in DAG content triggered in the cortex and hippocampus by ECS was delayed by EGb 761 treatment from 10 s to 1 min, when values similar to those in sham animals were attained. Moreover, in the hippocampus the size of the total DAG pool was decreased by 19% during the tonic seizure. At later times, DAG content showed a faster decrease in EGb 761-treated rats. By 2 min levels of all DAG acyl groups decreased to values significantly lower than in sham animals in both cortex and hippocampus. This study shows that EGb 761 treatment affects, with high selectivity, lipid metabolism and lipid-derived second messenger release and removal in the hippocampus, while affecting to a lesser extent the cerebral cortex.

Regional and temporal variations in the accumulation of unesterified fatty acids and diacylglycerols in the rat brain during kainic acid induced limbic seizures

These experiments tested the hypothesis that limbic seizures induced by kainic acid (KA) activate mechanisms (e.g. phospholipase) that degrade the cell membrane, causing a release and accumulation of free fatty acids (FFAs) and diacylglycerols (DGs) in brain areas susceptible to seizure-related damage. The possible link between these effects on lipids and the subsequent development of seizure-related brain damage was investigated by studying the temporal and regional relationship between alterations in lipids in the hippocampus, frontal cerebral cortex, amygdala, striatum and cerebellum, and the development and severity of seizures. Rats were treated with 10 mg/kg KA (s.c.) and sacrificed by head focused microwave irradiation at 1 h, 2 h, 24 h, or 7 days. Levels of FFAs and DGs were determined by gas liquid chromatography (GLC). Brain regions from control rats differed markedly in the content and composition of both FFA and DG pools. Changes in FFAs and DGs during KA-induced limbic seizures also varied from region to region and over time after drug treatment. The largest increases in FFAs in amygdala, striatum, cortex and hippocampus occurred during the peak of seizure activity. Although DG levels were altered in some areas at some time points, there was no apparent correlation between changes in DGs and seizure severity. However, increases in DGs occurred at later time points, coincident with the occurrence of neuronal cell loss in amygdala, cortex, hippocampus and striatum. These data indicate that limbic seizures activate the accumulation of FFAs through increased neuronal activity, while accumulation of DGs may be related to the development of seizure-related brain damage.

Reciprocal regulation of fatty acid release in the brain by GABA and glutamate

Several model systems have been used to test the hypothesis that the release of FFA in the brain is regulated by depolarization of neurons. This FFA release is likely the result of the activation of phospholipase A2. The increased neuronal activity that occurs due to synchronous depolarization during seizures causes activation of phospholipase A2. Decreasing neuronal activity by administering the anxiolytic, diazepam, appears to decrease the activity of phospholipase A2. The GABA antagonist, bicuculline, which causes depolarization by negating the hyperpolarizing tone imposed on neurons by GABA, causes FFA release in synaptosomes and in neurons in tissue culture. Likewise, the glutamate agonist, kainic acid, which depolarizes neurons by opening sodium channels, increases the activity of phospholipase A2. PC-specific phospholipase C, another enzyme important in the generation of the second messenger, DG, is also activated by depolarization. Several important questions remain to be answered. The site of FFA release, in terms of the pre-vs. postsynaptic membrane, is not clear, although the experiments with synaptosomes support the hypothesis that activation of phospholipase A2 may be an important regulator of presynaptic events. This idea has also been suggested by studies on the phenomenon of long-term potentiation, where free 20:4 or its metabolites may be involved in presynaptic facilitation of neurotransmitter release (Freeman et al., 1990; Massicotte et al., 1990; Williams et al., 1989; also see Dorman, this volume). The activation of the PI cycle and subsequent stimulation of protein kinase C may be a postsynaptic event important in the integration of inputs at the dendrite and soma or a presynaptic event involved in the modulation of neurotransmitter release (Taniyama et al., 1990; El-Fakahany et al., 1990; also see Nishizuka, this volume). Therefore the stimulation of a PC-specific phospholipase C, which is capable of generating large amounts of DG over a prolonged period of time (Exton, 1990; Martinson et al., 1990; Diaz-Laviada et al., 1990), could occur at either site. Another important question is the role of FFA and DG in affecting cell-cell signaling events, particularly with regard to ion fluxes. Modulation of an acetylcholine-linked K+ channel in the heart by FFA and their oxygenation products has been reported (Kim and Clapham, 1989). The cardiac muscarinic receptor is linked to a hyperpolarizing K+ channel via a G protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of GABA-gated chloride channel function by arachidonic acid

The effects of arachidonic acid and its metabolites on gamma-aminobutyric acid (GABAA) receptor function were determined in rat cerebral cortical synaptoneurosomes. Incubation of synaptoneurosomes with phospholipase A2 decreased muscimol-induced 36Cl- uptake. Arachidonic acid, the major unsaturated fatty acid released by phospholipase A2, also inhibited muscimol-induced 36Cl uptake. Similar inhibition was obtained with other unsaturated fatty acids (docosahexaenoic, oleic) but not with saturated fatty acids (stearic, palmitic). The effect of arachidonic acid on muscimol responses was inhibited by bovine serum albumin (BSA), and BSA enhanced muscimol responses directly, indicating the generation of endogenous arachidonic acid in the synaptoneurosome preparation. The generation of endogenous arachidonic acid was also indicated by the ability of 2 inhibitors of arachidonic acid metabolism, indomethacin and nordihydroguaiaretic acid (NDGA), to inhibit muscimol-induced 36Cl uptake. We conclude that arachidonic acid probably has both direct and indirect actions on muscimol responses since both enzyme inhibitors inhibited muscimol responses but did not prevent the effect of exogenously added arachidonic acid. In additional experiments, arachidonic acid metabolites generated by cyclooxygenase, prostaglandins D2, E2 and F2 alpha, each decreased muscimol responses; prostaglandins F2 alpha was the most potent inhibitor. Since the unsaturated fatty acids and their metabolites are most susceptible to peroxidation, a generating system of superoxide radicals was tested on muscimol responses. A combination of xanthine and xanthine oxidase inhibited muscimol-induced 36Cl uptake in a concentration-dependent manner. We propose that the inhibition of GABAA neurotransmission by arachidonic acid and its metabolites can lead to increased neuronal excitability. This mechanism may play an important role in the development of neuronal damage following seizures or cerebral ischemia.

Vasogenic brain edema induced by arachidonic acid: role of extracellular arachidonic acid in blood-brain barrier dysfunction

The effects of free arachidonic acid on the capillary permeability of normal rat brains were studied by measuring the regional uptake of [14C]aminoisobutyric acid by a quantitative autoradiographic technique. Intracerebral infusion of sodium arachidonate increased capillary permeability in a dose-dependent manner up to a concentration of 2 mmol/L. A high dose of arachidonic acid (more than 5 mmol/L) produced marked tissue destruction around the injection site (needle track) and increased capillary permeability less than 2 mmol/L arachidonic acid did. A time-course study demonstrated that about 80% of the maximum increase in capillary permeability produced by arachidonic acid was observed within 2 hours after the infusion was initiated. In addition, capillary permeability gradually increased with time up to 24 hours, after which it declined to about half of the maximum increase 48 hours after infusion. These effects of arachidonic acid on capillary permeability were localized within about 1.6 mm around the injection site. Pretreatment with dexamethasone did not completely, but did significantly, inhibit the arachidonic acid-induced increase in capillary permeability. The inhibitory effect of dexamethasone was completely suppressed by the administration of actinomycin D, which inhibits de novo protein synthesis, 1 hour before the treatment with dexamethasone. These results suggest that arachidonic acid, which is released and accumulated in the extracellular space, increases the capillary permeability of the brain in at least two different ways. One is the direct action of the arachidonic acid itself, which can stimulate perturbation of the membrane of the capillary endothelial cells, thus promoting an increase in capillary permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemic brain damage: focus on lipids and lipid mediators

The last two decades of research have produced detailed information not only on how ischemia causes degradation of phospholipids and accumulation of potentially cytotoxic breakdown products of such lipids, but also on reactions elicited by the subsequent conversion of these products into a series of lipids, mediating an array of cellular and intercellular reactions. It now seems clear that PAF, as well as several of the cyclooxygenase and lipoxygenase products of arachidonic acid, can induce changes, particularly in the microvasculature, which jeopardize cell survival in reperfused tissue. It is equally clear that, at least following long periods of ischemia, free radicals generated in reactions that are interacting with those producing eicosanoids and PAF play a similar role. A somewhat more speculative mechanism links sustained activation and membrane translocation of PKC to delayed neuronal death following transient ischemia. All of these interactions underscore the importance of lipolytic events for cell damage in ischemia and other conditions with a compromised cellular energy metabolism.

Bicuculline induces free fatty acid release from phospholipids in neuro-2A cells in culture

This study characterizes free fatty acid release in a neuroblastoma cell line (Neuro-2A), a potential model system for the study of factors that control phospholipase A2 in neurons. Two compounds, bicuculline (an antagonist at gamma-aminobutyric acid receptors), and A23187 (a Ca2+ ionophore), were examined. The release of endogenous fatty acids and the turnover of radiolabeled arachidonic and docosahexaenoic acids were measured. The cells actively incorporated radiolabeled fatty acids into various glycerolipid pools. Both endogenous fatty acids and radiolabeled fatty acids were released from glycerolipids in a time-dependent manner. Phosphatidylcholine was a major source of released fatty acids. Release of free fatty acids was markedly stimulated by both bicuculline and A23187. We conclude that the Neuro-2A cells contain phospholipase activity that is sensitive to Ca2+ ionophore and bicuculline, and may provide a good system for further studies on the regulation of phospholipase A2 in neurons.

In vivo 1H spectroscopy of the human brain following electroconvulsive therapy

Recent advances in the methodology of magnetic resonance spectroscopy now permit localized proton (1H) spectroscopy of the human brain in clinical magnetic resonance systems. In this study, localized 1H spectroscopy was used to observe directly the stimulation of brain metabolic activity in patients undergoing electroconvulsive therapy (ECT) and to compare results obtained before and after treatments. Persistent increases in lactate were expected on the basis of animal data but these increases were small and equivocal 1 hour after ECT. In contrast, a large increase in a lipid signal from before to after ECT was observed in 5 patients when short echo times were used. We postulate that a significant portion of this lipid signal is related to maximal activation of the phosphatidylinositol system (increased levels of diacylglycerol and free fatty acids) have generalized inhibitory effects potentially relevant to both the clinical pathophysiology of seizures and the efficacy of ECT in major affective disorders.

A study of 5'-nucleotidase activity in subcellular fractions of rat cerebellum after the administration of the convulsant 3-mercaptopropionic acid

The activity of 5'-nucleotidase in cerebellum subcellular fractions after the administration of the convulsant 3-mercaptopropionic acid was studied. This membrane enzyme presented an increase in its activity in certain fractions containing nerve endings and microsomes (Mic20, Mic100) in seizure and postseizure periods. 5'-nucleotidase activity in nuclear and myelin fractions did not show differences between the control and treated fractions. On the other hand, a decreased activity in the crude mitochondrial fraction and in a nuclear subfraction was found. It is suggested that the changes in the enzyme activity in some cerebellum fractions might be related to structural alterations previously observed in this laboratory and with the anticonvulsant actions of adenosine.

Kainic acid-induced seizures: potentiation by alpha-methyl-p-tyrosine

We have investigated the influence of central noradrenergic and dopaminergic systems on the susceptibility of rats to seizures in the kainic acid (KA)-model of epilepsy. In the dose range of 0.75 to 10 mg/kg s.c., KA dose-dependently induced characteristic behavioural changes. Partial depletion of noradrenaline (NA) and dopamine (DA) in the brain by pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT; 250 mg/kg, i.p.) markedly potentiated KA-induced epileptic symptoms. A low dose of KA (1.5 mg/kg s.c.), which was ineffective in normal rats, triggered in AMPT-pretreated rats a high incidence of wet dog shakes (WDS) and a seizure activity (seizure rating: 3.17 +/- 0.31) which was comparable in degree to that resulting from 10 mg/kg KA in rats with normal catecholamine synthesis (seizure rating: 3.33 +/- 0.28). In AMPT-pretreated rats a higher dose of KA (10 mg/kg) further enhanced seizure activity and was associated with a mortality rate of up to 80%. Within 6.5 h after AMPT-pretreatment the levels of NA and DA in amygdala/pyriform cortex declined from 0.56 +/- 0.02 (control) to 0.23 +/- 0.01 ng/mg tissue and from 0.21 +/- 0.03 to 0.05 +/- 0.01 ng/mg tissue, respectively. At a dose of 1.5 mg/kg KA was ineffective on the levels of NA and DA in normal rats, but further reduced these levels in AMPT-pretreated rats to 0.08 +/- 0.02 and 0.020 +/- 0.004 ng/mg tissue, respectively. Induction of seizure activity and decline in NA and DA levels in amygdala/pyriform cortex after AMPT/KA (1.5 mg/kg) treatment was antagonized by the alpha-adrenoceptor agonist clonidine (0.1 mg/kg, i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of subconvulsive doses of bicuculline on the incorporation of radioactive precursors into glycerolipids in rat brain areas

Bicuculline (either 25 mumol or 12.5 mumol/kg body wt) was administered to rats by intraperitoneal route. Animals treated with 25 mumol/kg experienced convulsions, whereas those receiving 12.5 mumol/kg did not. Controls received saline instead of the drug. Radioactive precursors [2-3H] glycerol and/or [1,2 14C] ethanolamine were injected into cerebral ventriculi simultaneously with bicuculline and the rats were killed 12 min afterwards. Their brains were dissected by hand into four parts (cerebellum, brain stem, hippocampus, cerebral cortex) and the labeling of lipid classes determined after extraction and separation. Although glycerol was incorporated into lipid better than ethanolamine in all areas, the fate of the injected radioactive precursors varied according both to area and treatment. The lowest uptake of radioactivity was in the cerebral cortex and the highest in the brain stem and hippocampus. Moreover, the administration of bicuculline influenced the distribution of radioactivity among lipid classes; these variations, however, were not dependent on the administered doses of bicuculline. We conclude that the effects on glycerolipid metabolism observed in convulsing animals are due to several causes including alterations of systemic parameters (hypertension, hypoxia, etc.). The distribution of glycerol label between phospholipid and neutral lipid is proposed as a biochemical model for the study of convulsive and subconvulsive states.

The effect of oxiracetam treatment on alterations of lipid metabolism in brain areas from spontaneously hypertensive rats

It has been previously demonstrated that spontaneously hypertensive adult rats (SHR) develop severe hypertension and cerebrovascular lesions on drinking 1% NaCl from weaning and that the phospholipid metabolism in the whole brain is actively altered in these lesioned animals (SHR-NaCl) as compared to SHRs which drink only water and show only sporadic cerebrovascular lesions. We have now assayed the incorporation of labelled choline, ethanolamine, glycerol and arachidonic acid into the phospholipids from the cortex and hippocampus of SHR-water and SHR-NaCl at different time intervals from injection into the lateral ventricle of the brain. A noticeable decrease of both choline and arachidonate specific activity (SA) in the phospholipids was found in the cortex and hippocampus (where the effect is most evident) from SHR-NaCl. Based on the literature and the data obtained, we suggest that in SHR-NaCl brain areas a release of choline and fatty acid also occurs from choline glycerophospholipids as a consequence of the cerebrovascular lesions caused by NaCl treatment. Even if a relatively minor loss of the amount of the lipids studied is evident from our results as compared to their entire pool, this change may be quite important if it causes a modification of the lipidic bilayer in excitable membranes. In a parallel group of SHR-NaCl animals, treated with the nootropic drug oxiracetam, we observed that the metabolic utilization of the precursors was completely restored. These experimental data favour the hypothesis that oxiracetam is effective in stimulating the phospholipid metabolism rate at levels even higher than those of the SHR-water animals.

Release of glutamate and of free fatty acids in vasogenic brain edema

The pathophysiological potential of mediator substances in manifestations of secondary brain damage is attracting increased attention. This is particularly true of the excitatory transmitters glutamate and arachidonic acid. Noxious properties of these compounds in central nervous tissue have been demonstrated. The current study was performed to determine whether glutamate and arachidonate are released in brain tissue secondary to focal trauma. For this purpose, a cold injury of exposed cerebral cortex was induced in cats. Marked accumulation of glutamate was observed in interstitially drained edema fluid, reaching 10 to 15 times the level that was assessed in normal cerebrospinal fluid (CSF) prior to trauma. The extracellular release of glutamate was further dramatically enhanced by a critical decrease of the cerebral perfusion pressure due to a malignant increase of intracranial pressure. Under these conditions, glutamate concentrations 1000 to 1500 times normal levels accumulated in vasogenic edema fluid, demonstrating a relationship between the extent of the release of glutamate in damaged brain and the severity of the insult. Although under normal conditions glutamate concentrations in plasma were considerably higher than in the interstitial fluid, the pronounced increase of glutamate in this compartment due to trauma cannot be explained by transport of the compound together with the plasma-like edema from the intravascular space. Corresponding findings were obtained for free fatty acid concentrations in edema fluid. Almost all fatty acids that were studied had a significantly higher concentration in edema fluid than in normal CSF obtained as a control prior to trauma. However, contrary to the findings for glutamate, fatty acid concentrations in edema fluid were lower than in plasma. Accumulation of fatty acids in vasogenic edema fluid might, therefore, have resulted from uptake of the material together with edema fluid through the breached blood-brain barrier. Arachidonic acid was an exception. Its concentrations were significantly higher in edema fluid than in plasma, suggesting that it was released from cerebral parenchyma as the underlying mechanism of its extracellular accumulation. The current observations provide further support for a mediator function of glutamate and arachidonic acid in acute traumatic lesions of the brain. Quantitative assessment of the release of highly active mediator substances in brain tissue may facilitate analysis of the therapeutic efficiency of specific treatment aimed at interfering with the release or pathological function of mediators of secondary brain damage.

The effect of acute and chronic electroconvulsive shock on [3H]phorbol-dibutyrate binding to rat brain membranes

The present study investigated the effect of single and repeated electroconvulsive shock (ECS) on proteinkinase C in rat cerebral cortex, cerebellum, hippocampus and striatum using [3H]Phorbol-12,13-butyrate binding. In the postictal period and 24 hr after a single ECS there was no alteration in any brain region. Twenty four hr after 10 once-daily ECS there was a significant decrease the number of binding sites in cerebral cortex (30%) and in cerebellum (20%) without a change in the affinity constant. These findings are discussed with regard to earlier reports on phosphoinositide turnover following chemically and electrically induced seizures.

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.

Nonedited 1H NMR lactate/n-acetyl aspartate ratios and the in vivo determination of lactate concentration in brain

The 1H lactate/n-acetyl aspartate ratio is commonly used for the quantitation of brain lactate under pathological conditions. We demonstrate that the intensity of the lactate methyl region in water-suppressed, nonedited 1H spectra increases following mild brain trauma as a result of factors other than lactate accumulation.

Regulation of gamma-aminobutyric acid/barbiturate receptor-gated chloride ion flux in brain vesicles by phospholipase A2: possible role of oxygen radicals

Preincubation of brain membranes with phospholipase A2 (PLA2) has been shown previously to affect the binding characteristics of various recognition sites associated with the gamma-aminobutyric acid (GABA) receptor complex. In the present study, we have investigated the effects of PLA2 (from Naja naja siamensis venom) on the functional activity of the GABA receptor/chloride ion channel. PLA2 (0.001-0.02 U/mg protein) preincubation decreased pentobarbital-induced 36Cl- efflux and muscimol-induced 36Cl- uptake in rat cerebral cortical synaptoneurosomes. The effect of PLA2 was prevented by EGTA and two nonselective PLA2 inhibitors, mepacrine and bromophenacyl bromide. The removal of free fatty acids by addition of bovine serum albumin both prevented and reversed the effect of PLA2. Products of the catalytic activity of PLA2, such as the unsaturated free fatty acids, arachidonic and oleic acids, mimicked the effect of PLA2. However, the saturated fatty acid, palmitic acid, and lysophosphatidyl choline had no effect on pentobarbital-induced 36Cl- efflux. Because unsaturated free fatty acids are highly susceptible to peroxidation by oxygen radicals, the role of oxygen radicals was investigated. Xanthine plus xanthine oxidase, a superoxide radical generating system, mimicked the effect of PLA2, whereas the superoxide radical scavenger, superoxide dismutase, diminished the effects of PLA2 and arachidonic acid on pentobarbital-induced 36Cl- efflux. Similarly, the effect of PLA2 was also inhibited by methanol (1 mM), a scavenger of the hydroxyl radical, and by catalase. These data indicate that exogenously added PLA2 induces alterations in membrane phospholipids, possibly promoting the generation of oxygen radicals and fatty acid peroxides which can ultimately modulate GABA/barbiturate receptor function in brain.

Foreign and endogenous serum protein extravasation during harmaline tremors or kainic acid seizures in the rat: a comparison

Cerebrovascular permeability to protein (CVP-p) was assessed in rats following the systemic injection of either kainic acid (KA) or harmaline. The extravasation of a foreign (horseradish peroxidase, HRP) or an endogenous (rat immunoglobulin G, IgG) tracer protein was determined using immunohistochemical methods. During KA-induced seizures, an extravasation of both HRP and presumed IgG occurred in similar forebrain loci; a lamina-specific extravasation occurred within the dorsal hippocampus. During harmaline-induced tremors protein extravasation also occurred, but was tracer dependent. HRP reaction product was observed within the inferior olive, the cortex of the cerebellar vermis and the neocortex. However, IgG-like immunoreactivity was only detected within the circumventricular organs of harmaline-treated rats. Because KA, but not harmaline, is neurotoxic, the results are consistent with an influence of endogenous serum protein extravasation on seizure-related hippocampal damage. Possible homeostatic properties of altered CVP-p are also considered.

Incorporation of glycerol and ethanolamine into glycerophospholipid in rat brain areas during bicuculline-induced convulsive seizures

The effect of bicuculline-induced convulsive seizures on lipid metabolism has been studied in four brain areas (cerebellum, cerebral cortex, hippocampus, and brainstem) using [2-3H]glycerol and [1,2-14C]ethanolamine as radioactive lipid precursors administered simultaneously with bicuculline. Twelve minutes after the administration, the uptake of radioactivity depended both on brain area and treatment, being generally higher in convulsing rats. The uptake of glycerol was influenced to a larger extent than that of ethanolamine and increased during convulsions, but its incorporation into lipids did not. In contrast, the amount of ethanolamine incorporated into lipids increased during bicuculline-induced seizures. The difference in behavior of glycerol and of ethanolamine is also indicated by the decrease of the 3H/14C ratio of phosphatidyl-ethanolamine in various brain areas during convulsions. It is, therefore, evident that the metabolism of the two precursors is affected differently by seizures.

Effect of bicuculline-induced status epilepticus on prostaglandins and hydroxyeicosatetraenoic acids in rat brain subcellular fractions

Rat cerebrum, prelabeled in vivo by intraventricular injection of [1-14C]arachidonic acid, was used to assess cyclooxygenase and lipoxygenase reaction products in total homogenates, cytosol, synaptosomes, and microsomes. Effects of bicuculline-induced status epilepticus on arachidonic acid metabolism in synaptosomes and microsomes were also measured. Lipoxygenase activity, resulting in the synthesis of hydroxyeicosatetraenoic acids (HETEs), and cyclooxygenase activity, resulting in the synthesis of prostaglandins (PGs), were measured by reverse-phase and normal-phase HPLC with flow scintillation detection. Endogenous lipoxygenase products in synaptosomes were identified by capillary gas chromatography-mass spectrometry. PGs and HETEs were detected in all subcellular fractions. The synaptosomal fraction showed the highest lipoxygenase activity, with 5-HETE, 12-HETE, and leukotriene B4 as the major products. Following bicuculline-induced status epilepticus, endogenous free arachidonic acid and other fatty acids accumulated in synaptosomes, but not in microsomes. Incorporation of [1-14C]arachidonic acid into synaptosomal and microsomal phospholipids was decreased after bicuculline treatment. Bicuculline-induced status epilepticus resulted in increased synthesis of HETEs in synaptosomes. PG synthesis increased in the microsomal fraction. When [1-14C]arachidonic acid-labeled synaptosomes and microsomes were incubated for 1 h at 37 degrees C the synthesis of eicosanoids, particularly PGD2, was increased significantly in bicuculline-treated rats, as compared with untreated rats. Depolarization (45 mM K+) of synaptosomes induced a loss of [1-14C]arachidonic acid from phosphatidylinositol, and increased the synthesis of PGD2 and HETEs, an effect that was enhanced in bicuculline-treated rats. This study localizes changes in arachidonic acid metabolism and lipoxygenase activity resulting from bicuculline-induced status epilepticus in the brain subcellular fraction enriched in nerve endings.

Cerebral phosphoinositide, triacylglycerol and energy metabolism during sustained seizures induced by bicuculline

In ventilated rats, levels of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DAG), triacylglycerol (TAG), free fatty acids (FFA) and phosphatidic acid, as well as their fatty acid contents, were measured in forebrain tissue after 1, 20 and 60 min of seizures induced by bicuculline. Cerebral energy state was also measured. PI decreased progressively throughout 60 min of seizures, whereas the levels of PIP and PIP2 did not change. DAG increased modestly and persistently. FFA increased markedly during the early seizure period, but decreased later. Following an initial drop, TAG rose above control. Phosphatidic acid did not change. The levels of ATP and energy charge potential decreased slightly and lactate accumulated. Stearic acid (18:0) and arachidonic acid (20:4) primarily accounted for the changes in the levels of the lipids. At the onset of seizures, the decrease of 18.0 and 20:4 in PI occurred in parallel with an enrichment of these fatty acids in FFA and DAG. Despite the fact that the losses of 18:0 and 20:4 from PI were quantitatively similar to each other at all times examined, the increase in free 18:0 was much larger than the increase in free 20:4 at 20 min of seizures. Concurrently there was a rise of 20:4 in TAG. As the FFA levels declined thereafter, 20:4 and docosahexaenoate (22:6) in TAG continued to increase. The results are consistent with the view that seizure activity stimulates the hydrolytic breakdown of brain phosphoinositides--the pathway catalyzed by phosphodiesterase of the phospholipase C type followed by lipases, and probably the pathway catabolized by phospholipases A as well. Preferential incorporation of polyunsaturated fatty acids into TAG-acyl residues may represent a mechanism to reduce the level of their free forms when the latter are produced in large amounts.

Acidic phospholipids, diacylglycerols, and free fatty acids in gerbil brain: a comparison of ischemic changes resulting from carotid ligation and decapitation

The levels of brain acidic phospholipids (poly-PI, PI, PA, and PS), DG, and FFA and their acyl group profiles were determined after induction of ischemia in gerbils by ligation of the common carotid arteries and decapitation. Ischemia induced by both procedures resulted in a significant decrease in poly-PI (20% for 1-min decapitation and 1-min ligation). Except for a 16% increase in PI in the 5-min decapitation group, no apparent change was found in other phospholipids after either ischemic condition. The level of DG was increased one- and three-fold after 1 and 5 min, respectively, of decapitative ischemic treatment. Ligation of the carotid arteries for 1 min resulted also in a one-fold increase in the DG level. The decapitative model resulted in a one- and five-fold increase in FFA level (with respect to 1 and 5 min, respectively), whereas ligation for 1 min resulted in an increase of 42% of the FFA. The acyl groups of poly-PI and PI in the control gerbil brain are enriched in 18:0 and 20:4, but those of DG, FFA, and PA have a higher proportion of 16:0 besides 18:0 and 20:4. However, a preferential increase in the proportion of 18:0 and 20:4 was shown for the DG and FFA in both types of ischemic treatments. It is concluded from the results that both models of ischemic treatment elicit a similar decrease in poly-PI and increase in DG, but differ in the amount of FFA release. The higher level of FFA release in the decapitative model suggests that other biochemical mechanisms may be activated to cause the additional release.

Cerebral phosphoinositide, triacylglycerol, and energy metabolism in reversible ischemia: origin and fate of free fatty acids

Levels of phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), phosphatidic acid, diacylglycerol (DAG), triacylglycerol (TAG), and free fatty acids (FFAs), as well as their fatty acid composition, were determined in rat forebrain during ischemia and postischemic recirculation. Cerebral energy state and electroencephalograms (EEGs) were also studied. Fifteen minutes of ischemia resulted in a decrease in PIP2 and PIP contents but not in PI content, concurrent with an enlargement of the FFA and DAG pools. The latter were enriched in stearate and arachidonate. Prolongation of ischemia did not produce further changes in content of any of the inositol phospholipids, but the increase in levels of FFAs and DAG continued. At the end of 45 min of ischemia, levels of both PIP2 and PIP decreased by 45-50%, and the total phosphoinositide content (PIP2 + PIP + PI) decreased by 21%, whereas levels of FFAs and DAG increased to 14- and 3.6-fold of control levels, respectively. During ischemia, the TAG-palmitate level decreased, but the TAG-arachidonate level increased; the tissue energy state deteriorated severely; and the EEG was suppressed. A 30-min recirculation period after 15 or 45 min of ischemia led to increases in PIP2, PIP, and total phosphoinositide contents, whereas levels of FFAs and DAG promptly decreased toward control values. The TAG-arachidonate level peaked and the TAG-palmitate level returned to a low control value during early recirculation. The ischemic changes in tissue lipids were completely reversed within 3 h of recirculation after both periods of ischemia. Adenylates were fully phosphorylated with as little as 30 min of reflow. The EEG activity partially recovered during reflow after 15 min of ischemia, whereas it remained depressed after prolonged ischemia. Thus, phosphodiesteric cleavage of PIP2 and PIP followed by deacylation of DAG is likely to contribute to the production of FFAs in early ischemia. Deacylation of undetermined lipids plays a role for the increment in levels of FFAs in the later period of ischemia. The rapid postischemic increase in levels of PIP2 and PIP indicates active synthesis not only from existing PI, but probably also by means of accumulated FFAs and DAG. These results indicate that the impaired resynthesis of inositol phospholipids cannot be a cause of the poor EEG activity after prolonged ischemia. Degradation and resynthesis of polyphosphoinositides and formation of TAG-arachidonate may be important for modulation of free arachidonic acid levels in the brain during temporary ischemia.

Polyphosphoinositides as a probable source of brain free fatty acids accumulated at the onset of ischemia

The quantitative relationship between phosphoinositides and free fatty acids (FFAs) in brain ischemia was studied by measuring contents of individual fatty acids in phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), phosphatidic acid (PA), diacylglycerol (DAG), and the FFA pool. Various periods of complete ischemia (1, 3, 10, and 30 min) were produced by decapitation. Ischemia of 1-3 min caused rapid decreases in PIP2 and PIP content together with preferential production of stearic and arachidonic acids in the DAG and FFA pools. The decrement in levels of these fatty acid residues in polyphosphoinositides was sufficient to account for their increment in levels in the enlarged DAG and FFA pools. After 10 min of ischemia, levels of PIP2, PIP, and DAG approached plateau values, but levels of all FFAs continued to increase. The increases in content of DAG and FFAs at later ischemic periods could not be accounted for by the decreases in content of PIP2 and PIP, PI and PA levels showed only transient and subtle changes. These results indicate that, at the onset of ischemia, phosphodiesteric cleavage of PIP2 and PIP and subsequent deacylation by lipases are primarily responsible for the preferential increase in levels of free stearic and arachidonic acids and that, later, hydrolysis of other phospholipids plays a major role in the continuous accumulation of FFAs.

Asymmetry of diacylglycerol metabolism in rat cerebral hemispheres

Diacylglycerols (DGs) were found to be asymmetrically distributed between the two cerebral hemispheres of rat brain. The left cerebral hemisphere (LCH) contained 100% more DG than the right cerebral hemisphere (RCH). The lateralization was enhanced in animals subjected to depolarization induced by a single electroconvulsive shock (ECS). During the acute phase of the convulsion, the DG pool increased in both hemispheres, with the LCH attaining a concentration 180% higher than the RCH. Stearate and arachidonate were the principal DG-acyl groups accumulated in the RCH, whereas in the LCH stearate and palmitate were mainly involved. After the last of a series of five shocks (one per day) the lateralization of the "DG response" was less accentuated during the acute phase of the ECS. Whereas DG release was drastically reduced in the LCH, in the RCH it was minimally affected. The DG sidedness after five shocks was nevertheless maintained at the level of arachidonate-containing DGs, which showed a higher accumulation in the LCH than in the RCH. The kinetics of DG removal showed a rapid phase during the first minute following a single or five ECSs. Total DG levels returned to basal values in the RCH, whereas in the LCH they remained slightly increased with respect to the initial levels 1 min after the convulsive episode. Minimal changes occurred in the subsequent 4 min. Chronic ECS altered the endogenous DG content and composition. Thus, 24 h after the last of four ECSs, total levels of DGs diminished by 40% in the RCH, whereas they remained unchanged in the LCH.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced labeling of brain phosphatidylinositol, triacylglycerols, and diacylglycerols by [1-14C]arachidonic acid after electroconvulsive shock: potentiation of the effect by adrenergic drugs and comparison with palmitic acid labeling

The effect of electroconvulsive shock on the labeling of phospholipids and neutral lipids in mice brains was examined after intracerebral injection of [1-14C] arachidonic acid or [1-14C]palmitic acid. Electroconvulsive shock reduced greatly the removal of radiolabeled arachidonic acid from the free fatty acid pool. At the same time, the incorporation of arachidonic acid was partially inhibited in triacylglycerol, diacylglycerol, and phosphatidylinositol, whereas the incorporation of [1-14C]palmitic acid was not affected. Pretreatment with desipramine and pargyline potentiated the lipid effect of electroconvulsive shock in neutral glycerides. These electroconvulsive shock-induced changes reflect alterations in the metabolism of intracerebrally injected arachidonic acid, but not of similarly injected palmitic acid. From the available data whether decreased ATP, enzyme inhibition or other factors are involved cannot be ascertained. Moreover, the electroconvulsive shock-enhanced endogenous free arachidonic acid may possibly dilute the injected radiolabeled fatty acid, thus decreasing its availability for arachidonoyl-coenzyme A synthesis. Hence, a partial inhibition of the activation-acylation of these fatty acids, primarily arachidonic acid, also may be involved in the seizure-induced accumulation of free fatty acids in the brain.

Membrane lipid changes in laminectomized and traumatized cat spinal cord

Free fatty acid (FFA), diacylglycerol (acyl2Gro), icosanoid, phospholipid, and cholesterol levels were measured in samples of cat spinal cord (L2) that were frozen in situ with vertebrae intact, at various times after laminectomy, and at various times after laminectomy with compression trauma to the spinal cord. Tissue samples either were grossly dissected into gray and white portions prior to FFA and acyl2Gro analysis or were used whole for the other lipid types. Gray matter total FFA and acyl2Gro values were abnormally high in samples frozen with vertebrae intact and in those frozen 10 min after laminectomy. This indicates that the surgical procedures resulted in some perturbation of spinal cord lipid metabolism. If the experimental animals were allowed to recover for 90 min after laminectomy, the gray matter FFA and acyl2Gro levels were greatly reduced. Compression of the spinal cord with a 170-g weight for 1, 3, or 5 min (following 90 min of recovery after laminectomy) caused significant elevations of total FFA, acyl2Gro, icosanoids, and phosphatidic acid and significant decreases in ethanolamine plasmalogens and cholesterol. Among the total FFA, arachidonic acid was found to have the largest relative increase. Comparisons of gray and white matter demonstrate that, in general, changes in white matter FFA and acyl2Gro were similar to those seen in gray matter. However, the increases in white matter levels of FFA and acyl2Gro were delayed, occurring after the elevations in gray matter. For some FFA (e.g., arachidonate), the rise in white matter occurred as gray matter levels were decreasing. This suggests that the initial alteration in spinal cord lipid metabolism after trauma was in gray matter but, with time, spread radially into white matter.

Circannual rhythm of free fatty acids and diacylglycerols in 5-day-old rat cerebrum during pentylenetetrazol-induced convulsions

Free fatty acids (FFA) and diacylglycerol (DG) content and composition in the cerebrum of 5-day-old rats were studied after pentylenetetrazol (PTZ)-induced convulsions. A threefold increase in brain FFA was observed 30 min after PTZ injection in experiments carried out in spring. In contrast, a 50% decrease in FFA content was observed during summer. These changes were accounted for by saturated and monoenoic fatty acids, whereas arachidonic and docosahexaenoic acids were not affected during the convulsive episode in either season. The effect of PTZ on brain DG was much smaller than it was on FFA, and less sensitive to seasonal influence. However, DG released in the summer was significantly less enriched in arachidonic acid than in the spring. Levels of FFA and DG in untreated animals were found to be subject to a circannual rhythm. Both the levels of FFA and their degree of unsaturation (unsaturated fatty acids/total FFA) were highest in summer and lowest in winter, whereas the opposite was true for DG. Circannual variations in these metabolites may be the manifestation of a programmed biological calendar regulating enzymes of brain lipid metabolism in homeotherms that under natural conditions must adapt to changing environmental temperatures.

Endogenous asymmetry of rat brain lipids and dominance of the right cerebral hemisphere in free fatty acid response to electroconvulsive shock

An asymmetric distribution of free fatty acids (FFA) is shown to occur between right and left cerebral hemispheres (RCH, LCH) of the rat. The RCH contains 35% less FFA than the LCH, the difference being mainly accounted for by saturated and monoenoic fatty acids. Acute and chronic electroconvulsive shock (ECS) affects the distribution and apparent rate of fatty acid production differently in each hemisphere. Taking into consideration the basal content of each hemisphere, RCH produces significantly higher amounts of FFA during the acute tonic phase of the convulsion evoked by a single ECS. The largest increases correspond to arachidonic and stearic acids (1800% and 420% in RCH, 1200% and 330% in LCH, respectively). The hemispheric sidedness is evened out after successive ECSs. The removal of the released fatty acids is also faster in the RCH, as suggested by its lower FFA levels 5 min after a single shock (the acute condition) or after the last of a series of 5 daily shocks (the chronic condition). The endogenous FFA content and composition is altered by chronic ECSs. Thus, 24 h after the last of a series of 4 daily ECSs, total FFAs remain about 40% higher than in the controls for both hemispheres. Arachidonic acid increase amounts to 150%, doubling its percentage contribution to the FFA pool. The lower endogenous FFA content in RCH, its higher responsiveness to ECS, and its ability to more rapidly recover the pre-convulsive levels, suggest that the deacylation and reacylation of complex lipids are more active in this hemisphere.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of free fatty acid and ceramide during brain handling: lability of sphingomyelin

Intact brain and brain homogenates readily form free fatty acids and ceramides, even in the cold during subcellular isolation procedures. The fatty acid formation is slightly stimulated by chelators and might be due to phospholipid hydrolysis by lysosomal phospholipases. The ceramide formation is accompanied by loss of sphingomyelin and is apparently due to the action of neutral, metal ion-activated sphingomyelinase. The latter reaction is inhibited by EDTA whereas both degradative processes are inhibited by mercuriphenylsulfonate, the thiol-reacting inhibitor. Cerebroside does not seem to be a source of accumulated ceramide.

Long-chain acyl CoA synthetase in microsomes from rat brain gray matter and white matter

Long-chain acyl coenzyme A (CoA) synthetase in homogenates and microsomes from rat brain gray and white matter was studied. The formation of the thioesters of CoA was studied upon addition of [1-14C]-labeled fatty acids. The maximal activities were seen with linoleic acid, followed by arachidonic, palmitic, and docosahexaenoic acids in both gray and white matter homogenates and microsomes. The specific activities in microsomes were 3-5 times higher than in homogenates. The presence of Triton X-100 in the assay system enhanced the activity of long-chain acyl CoA synthetase in homogenates. The effect was more pronounced in palmitic and docosahexaenoic acid activation. The apparent Km values and Vmax values for palmitic and docosahexaenoic acids were much lower than for linoleic and arachidonic acids. The presence of Triton X-100 in the medium caused a definite decrease in the apparent Km and Vmax values for all the fatty acids except palmitic acid in which case the reverse was true. There were no significant differences observed in the kinetic measurements between gray and white matter microsomes. These findings are similar to those resulting from the known interference of Triton X-100 in the measurement of kinetic variables of long-chain acyl CoA synthetase of liver microsomes. In this work, no correlation was observed between the fatty acid composition of gray and white matter and the capacity of these tissues for the activation of different fatty acids.

Synthesis of arachidonoyl coenzyme A and docosahexaenoyl coenzyme A in synaptic plasma membranes of cerebrum and microsomes of cerebrum, cerebellum, and brain stem of rat brain

Synthesis of arachidonoyl CoA and docosahexaenoyl CoA in homogenates and microsomes from cerebrum, cerebellum, and brain stem and in synaptic plasma membranes from cerebrum of control rats and rats undergoing bicuculline-induced status epilepticus were studied. Arachidonoyl CoA synthesis was 3-5 times higher than docosahexaenoyl CoA in homogenates and microsomes. The synaptic plasma membranes showed only 1.5- to 2.5-fold higher activity. The presence of Triton X-100 (0.1%) in the incubation medium did not alter the activity of arachidonoyl CoA synthesis but did increase the synthesis of docosahexaenoyl CoA in homogenates, microsomes, and especially in synaptic plasma membranes. The synthesis of these polyenoic fatty acyl CoAs were 4-6 times higher in microsomes than in homogenates. Synaptic plasma membranes exhibited about the same amount of activity as homogenates in the synthesis of docosahexaenoyl CoA, but only half the activity of the latter in arachidonoyl CoA synthesis. The synthesis of arachidonyl CoA and docosahexaenoyl CoA in cerebral homogenates and microsomes was higher than that of cerebellum and brain stem. The apparent Km values for labeled arachidonic acid (17 microM) and docosahexaenoic acid (12 microM) in synaptic plasma membranes were lower than the values for microsomes isolated from different brain regions. The Vmax values were also 4-10 times lower. Microsomes from different regions did not differ in their apparent Km values, but did show variations in apparent Vmax values. Cerebellar microsomes showed lower Vmax values than the other two regions. The presence of Triton X-100 caused a significant decrease in the apparent Km values with little change in the Vmax values. Bicuculline-induced seizures did not alter the kinetic properties of arachidonoyl CoA and docosahexaenoyl CoA synthesis, except there was a significant decrease in the apparent Km and Vmax values for cerebellar microsomal docosahexaenoyl CoA synthesis. In conclusion, there were marked differences in the activation of polyenoic fatty acids in different parts of the brain and in subcellular fractions. Although bicuculline-induced convulsions accumulate free polyenoic fatty acids in the brain, no changes were detected when the fatty activation was assayed with exogenous cofactors, except in cerebellum.

Effect of oleate on neurotransmitter transport and other plasma membrane functions in rat brain synaptosomes

The effects of fatty acids, oleate and palmitate, on gamma-aminobutyric acid (GABA), aspartate, and 3,4- dihydroxyphenylethylamine (dopamine) transport and a variety of other membrane functions were studied in rat brain synaptosomes at a constant lipid-to-protein ratio. Under the conditions utilized oleate, but not palmitate, caused statistically significant changes in synaptosomal functions. Oleic acid inhibited the uptake of the amino acid neurotransmitters and dopamine in a tetrodotoxin-insensitive manner; it also induced the release of neurotransmitters from synaptosomes. The synaptosomal membrane potential decreased and the maximum GABA accumulation ratio [( GABA]i/[GABA]o) declined in parallel. The same depolarizing effect was seen in the presence of 50 microM verapamil or when chloride was replaced by propionate. The rate of respiration was stimulated by the unsaturated fatty acid; neither verapamil (50 microM) nor ouabain (100 microM) was effective in preventing the increase in oxygen consumption. By contrast, ruthenium red substantially decreased the stimulatory effect of oleate. The intrasynaptosomal [Ca2+] was increased by 40%, whereas [Na+]i remained unaltered. It is postulated that under the conditions used the inhibition of neurotransmitter uptake and the decrease in their accumulation caused by oleate result from the depolarization of synaptosomes that arises, at least in part, from increased permeability of the plasma membrane to calcium ions.

Increased cerebrovascular permeability to protein during systemic kainic acid seizures

Cerebrovascular permeability to protein (CVP-p) was assessed during limbic seizures by injecting unrestrained rats intraperitoneally with kainic acid followed by intravenous horseradish peroxidase (HRP); animals survived approximately 1 h after seizure onset. Brains were processed for the blue HRP reaction product followed by light microscopic examination of sequential sagittal sections. In all cases kainate-induced seizures caused increased CVP-p within the thalamus, temporal hippocampal formation, and neocortex. Somewhat less frequently other limbic structures and the striatum were HRP-positive. A lamina-specific extravasation occurred in the dorsal hippocampus; reaction product occupied the mossy fiber zone of field CA3, a likely focus of kainate action. Extravasation of HRP also occurred within, or juxtaposed to, certain myelinated fiber bundles. Brains from animals treated as blanks (kainate but no HRP) were devoid of peroxidase activity, and in nonseizing animals HRP gained access only to circumventricular organs. Although regions of increased CVP-p partially covary with areas of increased electrical activity and glucose metabolism, neuronal activation occurs over a much greater volume of brain tissue than does CVP-p. A close relationship may exist between these circumscribed areas of protein extravasation and seizure foci. Both vasogenic and cytotoxic edema appear to be simultaneously present during kainate seizures.