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

Increased expression of the mRNA for brain- and skin-type but not heart-type fatty acid binding proteins following kainic acid systemic administration in the hippocampal glia of adult rats

Increased gene expression for two species of cytosolic fatty acid binding proteins (FABPs) after systemic administration of kainic acid in the rat brain was demonstrated by Northern blotting and in situ hybridization histochemical analyses. The expression of brain (B)- and skin (S)- but not heart (H)-FABP mRNAs were markedly elevated in the hippocampus at 48 h after systemic kainate treatment. The elevated expression patterns of B- and S-FABP mRNAs were quite similar to that for glial fibrillary acidic protein in the normal brain, suggesting strongly that the increased expression for B- and S-FABPs occurs in dedifferentiated and proliferated astrocytes in response to kainic acid-induced seizure.

Brain temperature modulations during global ischemia fail to influence extracellular lactate levels in rats

BACKGROUND AND PURPOSE

While brain tissue lactate increases during cerebral ischemia and is known to be important in the pathogenesis of ischemic brain injury, patterns of extracellular lactate accumulation have been less well characterized, and the influence of brain temperature has not been previously investigated. Mild brain temperature modulations are known to affect the outcome of ischemia dramatically. This study examined changes of extracellular lactate during and after global cerebral ischemia, in which intraischemic brain temperature was held at either 30 degrees C, 37 degrees C, or 39 degrees C.

METHODS

Halothane-anesthetized fasted male Wistar rats underwent 20 minutes of global cerebral ischemia produced by bilateral carotid artery occlusions plus systemic hypotension (40 to 50 mm Hg). Rectal temperature was maintained at 37 degrees C throughout, and intraischemic brain temperature was held at either 30 degrees C (n = 6), 37 degrees C (n = 5), or 39 degrees C (n = 5). Before and after the ischemic insult, brain temperature was maintained at 37 degrees C in all groups. A microdialysis cannula was implanted in the right dorsolateral striatum and perfused with Ringer's solution. Dialysate samples were collected at 10-minute intervals before, during, and after ischemia and were analyzed for lactate by enzymatic-fluorometric techniques.

RESULTS

In all groups, extracellular lactate rose during ischemia and peaked at 10 to 30 minutes of recirculation. Maximal extracellular lactate elevations were sevenfold, eightfold, and eightfold above control in the 30 degrees C, 37 degrees C, 39 degrees C groups, respectively. Significant elevations with respect to control were observed in all groups at 10 to 30 minutes of recirculation. In the 30 degrees C group, these elevations above control were also significant at the 10- and 20-minute ischemic time points (P = .001). At 30 minutes of recirculation, however, lactate levels were lower in the 30 degrees C rats than in the other groups.

CONCLUSIONS

These data provide evidence that extracellular lactate accumulation is not a crucial determinant of ischemic brain injury. Our results suggest that the increased lactate release during ischemia and the accelerated clearance of lactate during recirculation might contribute in part to the neuroprotection of intraischemic hypothermia.

Arachidonic acid as a neurotoxic and neurotrophic substance

In this article we summarize a wide variety of properties of arachidonic acid (AA) in the mammalian nervous system especially in the brain. AA serves as a biologically-active signaling molecule as well as an important component of membrane lipids. Esterified AA is liberated from the membrane by phospholipase activity which is stimulated by various signals such as neurotransmitter-mediated rise in intracellular Ca2+. AA exerts many biological actions which include modulation of the activities of protein kinases and ion channels, inhibition of neurotransmitter uptake, and enhancement of synaptic transmission. AA serves also as a precursor of a variety of eicosanoids, which are formed by oxidative metabolism of AA. AA cascade is activated under several pathological conditions in the brain such as ischemia and seizures, and may be involved in irreversible tissue damage. On the other hand, AA can show beneficial influences on brain tissues and cells in several situations. In a recent study using cultured brain neurons, we have found that AA shows quite distinct actions at a narrow concentration range, such as induction of cell death, promotion of cell survival and enhancement of neurite extension. The neurotoxic action is mediated by free radicals generated by AA metabolism, whereas the neurotrophic actions are exerted by AA itself. The observed in vitro actions of AA might be related to important roles of AA in brain pathogenesis and neural development.

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)

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.

Free fatty acid and diacylglycerol accumulation in the rat brain during recurrent seizures is related to cortical oxygenation

Cerebral blood flow and oxygenation increase during the early seizures of a series, but the increase in cerebral blood flow attenuates during late seizures, sometimes resulting in decreased cortical oxygenation. Cortical free fatty acids (FFA) and diacylglycerols also increase during early seizures and the increase attenuates during late seizures. We analyzed the correlation between lipid accumulation and cortical O2 during periodic pentylenetetrazol-induced seizures. During early seizures, both FFA and diacylglycerols increased in the cerebral cortex, particularly arachidonate (20:4) and stearate (18:0). Changes in lipids were different during late seizures, depending on cortical O2 levels. An increase in cortical O2 during late seizures was associated with lower FFA levels compared with early seizures, and FFA levels recovered to basal levels during interictal periods. A decline in cortical O2 was associated with a further increase in FFA, which remained elevated during interictal periods. Our results indicate that periseizure lipid accumulation is related to cortical oxygenation.

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.

Inhibition of sodium-potassium-ATPase: a potentially ubiquitous mechanism contributing to central nervous system neuropathology

Direct and indirect evidence suggests that Na+/K(+)-ATPase activity is reduced or insufficient to maintain ionic balances during and immediately after episodes of ischemia, hypoglycemia, epilepsy, and after administration of excitotoxins (glutamate agonists). Recent results show that inhibition of this enzyme results in neuronal death, and thus a hypothesis is proposed that a reduction and/or inhibition of this enzyme contributes to producing the central neuropathy found in the above disorders, and identifies potential mechanisms involved. While the extent of inhibition of Na+/K(+)-ATPase during ischemia, hypoglycemia and epilepsy may be insufficient to cause neuronal death by itself, unless the inhibition is severe and prolonged, there are a number of interactions which can lead to a potentiation of the neurotoxic actions of glutamate, a prime candidate for causing part of the damage following trauma. Presynaptically, inhibition of the Na+/K(+)-ATPase destroys the sodium gradient which drives the uptake of acidic amino acids and a number of other neurotransmitters. This results in both a block of reuptake and a stimulation of the release not only of glutamate but also of other neurotransmitters which modulate the neurotoxicity of glutamate. An exocytotic release of glutamate can also occur as inhibition of the enzyme causes depolarization of the membrane, but exocytosis is only possible when ATP levels are sufficiently high. Postsynaptically, the depolarization could alleviate the magnesium block of NMDA receptors, a major mechanism for glutamate-induced neurotoxicity, while massive depolarization results in seizure activity. With less severe inhibition, the retention of sodium results in osmotic swelling and possible cellular lysis. A build-up of intracellular calcium also occurs via voltage-gated calcium channels following depolarization and as a consequence of a failure of the sodium-calcium exchange system, maintained by the sodium gradient.

Lithium ion does not protect brain against transient ischemia in gerbils

It has been proposed that lithium ion desensitizes neuronal receptors that function via the inositol phospholipid signaling mechanism. We examined the effects of lithium chloride on the morphologic outcome after 5 minutes of cerebral ischemia induced in gerbils by occluding both common carotid arteries under brief halothane anesthesia. In three treated groups of 10 gerbils each, 5 meq/kg i.p. lithium chloride was given 2 days, 1 day, and 2 hours before ischemia; 2 hours before ischemia; or immediately after the end of ischemia. Corresponding control groups of nine or 10 gerbils each received equivalent volumes of saline injected at comparable times. All gerbils were perfusion-fixed 1 week later, and neuronal density of the hippocampal CA1 pyramidal cells was determined. Lithium induced very mild intraischemic systemic hypothermia, but postischemic hyperthermia developed in both treated and control groups. Neuronal densities were equal in corresponding groups. The results indicate that our regimen of lithium administration provides no benefit in survival of hippocampal neurons, and intraischemic hypothermia of less than 0.8 degrees C is not protective. Other strategies to inactivate the signal transduction system that is specific for excitatory neurotransmission should be evaluated.

Protein kinase C activity in the gerbil hippocampus after transient forebrain ischemia: morphological and autoradiographic analysis using [3H]phorbol 12,13-dibutyrate

The influence of transient forebrain ischemia on the temporal alteration of protein kinase C (PKC) activity in the gerbil hippocampus was analyzed by quantitative autoradiography using [3H]phorbol 12,13-dibutyrate (PDBu). The [3H]PDBu binding activity in the stratum oriens of the CA1 subfield increased at 6 h after ischemia, but the binding activity in this subfield decreased at 7 days after ischemia. In contrast, the [3H]PDBu binding activity increased in the molecular layer of the dentate gyrus at 7 days after ischemia. Pre-treatment of pentobarbital prevented an increase in the [3H]PDBu binding activity in the stratum oriens of the CA1 subfield at 7 days after ischemia. These results indicate the possibilities that PKC may play a pivotal role in the post-ischemic neuronal damage in the hippocampal CA1 subfield.

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.

Cerebral phosphoinositide, triacylglycerol and energy metabolism during severe hypoxia and recovery

The cerebral concentrations of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidic acid (PA), triacylglycerol (TAG) and free fatty acids (FFA), as well as cerebral metabolites, were measured in rats subjected to 10 min of hypoxia and subsequent recovery of 7 or 30 min duration. The experiments were carried out with control of physiological variables. Hypoxia (paO2 values of about 15 mm Hg) caused a decrease in PI, whereas PIP and PIP2 did not change significantly. A two-fold increase of total FFA was noted, mainly comprising stearic and arachidonic acids. TAG-arachidonate tended to increase, but the other species in TAG decreased. Adenosine triphosphate (ATP) and energy charge (EC) decreased slightly and there was a marked lactate accumulation. PA did not change throughout the experiment. With recovery of 7 min duration, PI decreased further and total FFA continued to increase. TAG-arachidonate increased significantly. ATP remained depressed but EC recovered to the control range. Both tissue and plasma glucose increased. Tissue lactate remained elevated and systemic acidosis occurred. After a recovery period of 30 min, all lipids normalized and the energy state returned toward control. The data suggest that the phosphoinositide alterations during hypoxia are metabolically linked to changes in FFA and the lipid changes are accompanied by alterations in cerebral energy and carbohydrate metabolism. The selective increase in TAG-arachidonate may represent an incorporation of arachidonic acid into TAG, which may serve to reduce the free arachidonic acid level in the brain.