Ketamine protects cultured astrocytes from glutamate-induced swelling

Narrative Review: Low-Dose Ketamine for Pain Management

Pain is the leading cause of medical consultations and occurs in 50-70% of emergency department visits. To date, several drugs have been used to manage pain. The clinical use of ketamine began in the 1960s and it immediately emerged as a manageable and safe drug for sedation and anesthesia. The analgesic properties of this drug were first reported shortly after its use; however, its psychomimetic effects have limited its use in emergency departments. Owing to the misuse and abuse of opioids in some countries worldwide, ketamine has become a versatile tool for sedation and analgesia. In this narrative review, ketamine's role as an analgesic is discussed, with both known and new applications in various contexts (acute, chronic, and neuropathic pain), along with its strengths and weaknesses, especially in terms of psychomimetic, cardiovascular, and hepatic effects. Moreover, new scientific evidence has been reviewed on the use of additional drugs with ketamine, such as magnesium infusion for improving analgesia and clonidine for treating psychomimetic symptoms. Finally, this narrative review was refined by the experience of the Pain Group of the Italian Society of Emergency Medicine (SIMEU) in treating acute and chronic pain with acute manifestations in Italian Emergency Departments.

NMDA receptor-mediated modulation on glutamine synthetase and glial glutamate transporter GLT-1 is involved in the antidepressant-like and neuroprotective effects of guanosine

Guanosine has been reported to elicit antidepressant-like responses in rodents, but if these actions are associated with its ability to afford neuroprotection against glutamate-induced toxicity still needs to be fully understood. Therefore, this study investigated the antidepressant-like and neuroprotective effects elicited by guanosine in mice and evaluated the possible involvement of NMDA receptors, glutamine synthetase, and GLT-1 in these responses. We found that guanosine (0.05 mg/kg, but not 0.01 mg/kg, p. o.) was effective in producing an antidepressant-like effect and protecting hippocampal and prefrontocortical slices against glutamate-induced damage. Our results also unveiled that ketamine (1 mg/kg, but not 0.1 mg/kg, i. p, an NMDA receptor antagonist) effectively elicited antidepressant-like actions and protected hippocampal and prefrontocortical slices against glutamatergic toxicity. Furthermore, the combined administration of sub-effective doses of guanosine (0.01 mg/kg, p. o.) with ketamine (0.1 mg/kg, i. p.) promoted an antidepressant-like effect and augmented glutamine synthetase activity and GLT-1 immunocontent in the hippocampus, but not in the prefrontal cortex. Our results also showed that the combination of sub-effective doses of ketamine and guanosine, at the same protocol schedule that exhibited an antidepressant-like effect, effectively abolished glutamate-induced damage in hippocampal and prefrontocortical slices. Our in vitro results reinforce that guanosine, ketamine, or sub-effective concentrations of guanosine plus ketamine protect against glutamate exposure by modulating glutamine synthetase activity and GLT-1 levels. Finally, molecular docking analysis suggests that guanosine might interact with NMDA receptors at the ketamine or glycine/d-serine co-agonist binding sites. These findings provide support for the premise that guanosine has antidepressant-like effects and should be further investigated for depression management.

Glutamate-induced c-Jun expression in neuronal PC12 cells: the effects of ketamine and propofol

Transcription factor c-Jun affects neuronal cell death and survival in mammalian brain. As general anesthetics, such as ketamine and propofol, are thought to provide some degree of neuroprotection, this study was intended to test whether the protection of injured neuronal PC12 cells by ketamine and propofol is related to the inhibition of phospho-c-Jun. Using neuronal PC12 cells from rat pheochromocytoma cells differentiated with nerve growth factor, we found that 24 hours of exposure to glutamate (1 to 100 mM) induced concentration-dependent cell death as determined by an ability to reduce the tetrazolium derivative, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) into a blue formazan salt. Neuronal PC12 cells were exposed to ketamine (0.1, 1.0 mM) or propofol (0.5, 5.0 microM) and glutamate (0, 20 mM) for 24 hours. Cell injury was assessed using MTT, in situ terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling, and c-Jun activity assay. Glutamate, 20 mM, induced about 70% of cell death as determined by MTT and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling staining. Glutamate-induced cell death was related to an increase in expression of phospho-c-Jun. Glutamate-induced cell death was reduced by ketamine (0.1, 1.0 mM) in a dose-dependent manner and also by propofol (0.5, 5.0 microM). In addition, the expression of phospho-c-Jun was substantially reduced by ketamine (0.1, 1.0 mM) and propofol (0.5, 5.0 microM), respectively, as determined by Western blot assay. These results suggest that inhibition of c-Jun activity is involved in the neuroprotective effects of ketamine and propofol on glutamate-induced injury in neuronal PC12 cells.

Effect of ketamine on apoptosis by energy deprivation in astroglioma cells using flow cytometry system

Apoptosis is a programmed, physiologic mode of cell death that plays an important role in tissue homeostasis. As for the central nervous system, ischemic insults can induce pathophysiologic cascade of apoptosis in neurophils. Impairment of astrocyte functions during brain ischemia can critically influence neuron survival by neuronglia interactions. We aimed to elucidate the protective effect of ketamine on apoptosis by energy deprivation in astrocytes. Ischemic insults was induced with iodoacetate/ carbonylcyanide m-chlorophenylhydrazone (IAA/CCCP) 1.5 mM/20 microm or 150 microm/2 microm for 1 hr in the HTB-15 and CRL-1690 astrocytoma cells. Then these cells were reperfused with normal media or ketamine (0.1 mM) containing media for 1 hr or 24 hr. FITC-annexin-V staining and propidium iodide binding were determined by using flow cytometry. Cell size and granularity were measured by forward and side light scattering properties of flow cytometry system, respectively. An addition of ketamine during reperfusion increased the proportion of viable cells. Ketamine alleviated cell shrinkage and increased granularity during the early period, and ameliorated cell swelling during the late reperfusion period. Ketamine may have a valuable effect on amelioration of early and late apoptosis in the astrocytoma cells, even though the exact mechanism remains to be verified.

Glial activation and TNFR-I upregulation precedes motor dysfunction in the spinal cord of mnd mice

Mice homozygous for the spontaneous motor neuron degeneration mutation (mnd) show at the age of 8 months a marked impairment of the motor function and accumulation of lipofuscin granules in the cytoplasm of almost all neurons of the central nervous system. We previously reported a significant increase in GFAP protein levels in the lumbar spinal cord homogenates by western blot analysis and upregulation of TNF, a proinflammatory cytokine, in the motor neurons of lumbar spinal cord of mnd mice, already in a presymptomatic stage (4 months of age). In the present study, using immunohistochemical analysis, we performed a time course in mnd mice (1, 4 and 9 months of age) evaluating the expression and the distribution of astroglial and microglial cells and the expression of both TNF receptors, TNFR-I and TNFR-II. We observed a marked increase in astroglial and microglial cells and in TNFR-I immunoreactivity already at the 4th month. Since motor neuron dysfunction occurs in mnd mice in the absence of evident loss of spinal motor neurons, the present results indicate that the activation of microglial cells and astrocytes is independent from neuronal degeneration. The role of TNF and TNFR-I on motor neurons is still to be demonstrated.

Effect of ketamine on hypoxic-ischemic brain damage in newborn rats

The present study tests the hypothesis that ketamine, a dissociative anesthetic known to be a non-competitive antagonist of the NMDA receptor, will attenuate hypoxic-ischemic damage in neonatal rat brain. Studies were performed in 7-day-old rat pups which were divided into four groups. Animals of the first group, neither ligated nor exposed to hypoxia, served as controls. The second group was exposed to hypoxic-ischemic conditions and sacrificed immediately afterwards. Animals of the third and fourth groups were treated either with saline or ketamine (20 mg/kg, i.p.) in four doses following hypoxia. Hypoxic-ischemic injury to the left cerebral hemisphere was induced by ligation of the left common carotid artery followed by 1 h of hypoxia with 8% oxygen. Measurements of high energy phosphates (ATP and phosphocreatine) and amino acids (glutamate and glutamine) and neuropathological evaluation of the hippocampal formation were used to assess the effects of hypoxia-ischemia. The combination of common carotid artery ligation and exposure to an hypoxic environment caused major alterations in the ipsilateral hemisphere. In contrast, minor alterations in amino acid concentrations were observed after the end of hypoxia in the contralateral hemisphere. These alterations were restored during the early recovery period. Post-treatment with ketamine was associated with partial restoration of energy stores and amino acid content of the left cerebral hemisphere. Limited attenuation of the damage to the hippocampal formation as demonstrated by a reduction in the number of damaged neurons was also observed. These findings demonstrate that systemically administered ketamine after hypoxia offers partial protection to the newborn rat brain against hypoxic-ischemic injury.

Neuroprotective concentrations of the N-methyl-D-aspartate open-channel blocker memantine are effective without cytoplasmic vacuolation following post-ischemic administration and do not block maze learning or long-term potentiation

The potential of most N-methyl-D-aspartate antagonists as neuroprotectants is limited by side effects. We previously reported that memantine is an open-channel N-methyl-D-aspartate blocker with a faster off-rate than many uncompetitive N-methyl-D-aspartate antagonists such as dizocilpine maleate. This parameter correlated with memantine's known clinical tolerability in humans with Parkinson's disease. Memantine is the only N-methyl-D-aspartate antagonist that has been used clinically for excitotoxic disorders at neuroprotective doses. Therefore, we wanted to investigate further the basis of its clinical efficacy, safety, and tolerability. Here we show for the first time for any clinically-tolerated N-methyl-D-aspartate antagonist that memantine significantly reduces infarct size when administered up to 2 h after induction of hypoxia/ischemia in immature and adult rats. We found that at neuroprotective concentrations memantine results in few adverse side effects. Compared to dizocilpine maleate, memantine displayed virtually no effects on Morris water maze performance or on neuronal vacuolation. At concentrations similar to those in brain following clinical administration, memantine (6-10 microM) did not attenuate long-term potentiation in hippocampal slices and substantially spared the N-methyl-D-aspartate component of excitatory postsynaptic currents, while dizocilpine maleate (6-10 microM) or D-2-amino-5-phosphovalerate (50 microM) completely blocked these phenomena. We suggest that the favorable kinetics of memantine interaction with N-methyl-D-aspartate channels may be partly responsible for its high index of therapeutic safety, and make memantine a candidate drug for use in many N-methyl-D-aspartate receptor-mediated human CNS disorders.

Anoxic and ischemic injury of myelinated axons in CNS white matter: from mechanistic concepts to therapeutics

White matter of the brain and spinal cord is susceptible to anoxia and ischemia. Irreversible injury to this tissue can have serious consequences for the overall function of the CNS through disruption of signal transmission. Myelinated axons of the CNS are critically dependent on a continuous supply of energy largely generated through oxidative phosphorylation. Anoxia and ischemia cause rapid energy depletion, failure of the Na(+)-K(+)-ATPase, and accumulation of axoplasmic Na+ through noninactivating Na+ channels, with concentrations approaching 100 mmol/L after 60 minutes of anoxia. Coupled with severe K+ depletion that results in large membrane depolarization, high [Na+]i stimulates reverse Na(+)-Ca2+ exchange and axonal Ca2+ overload. A component of Ca2+ entry occurs directly through Na+ channels. The excessive accumulation of Ca2+ in turn activates various Ca(2+)-dependent enzymes, such as calpain, phospholipases, and protein kinase C, resulting in irreversible injury. The latter enzyme may be involved in "autoprotection," triggered by release of endogenous gamma-aminobutyric acid and adenosine, by modulation of certain elements responsible for deregulation of ion homeostasis. Glycolytic block, in contrast to anoxia alone, appears to preferentially mobilize internal Ca2+ stores; as control of internal Ca2+ pools is lost, excessive release from this compartment may itself contribute to axonal damage. Reoxygenation paradoxically accelerates injury in many axons, possibly as a result of severe mitochondrial Ca2+ overload leading to a secondary failure of respiration. Although glia are relatively resistant to anoxia, oligodendrocytes and the myelin sheath may be damaged by glutamate released by reverse Na(+)-glutamate transport. Use-dependent Na+ channel blockers, particularly charged compounds such as QX-314, are highly neuroprotective in vitro, but only agents that exist partially in a neutral form, such as mexiletine and tocainide, are effective after systemic administration, because charged species cannot penetrate the blood-brain barrier easily. These concepts may also apply to other white matter disorders, such as spinal cord injury or diffuse axonal injury in brain trauma. Moreover, whereas many events are unique to white matter injury, a number of steps are common to both gray and white matter anoxia and ischemia. Optimal protection of the CNS as a whole will therefore require combination therapy aimed at unique steps in gray and white matter regions, or intervention at common points in the injury cascades.

Polyamines and NMDA receptors modulate pericapillary astrocyte swelling following cerebral cryo-injury in the rat

Four hours following cryo-injury rat cerebral pericapillary astrocytes from the perilesional area were markedly swollen occupying 17% of the pericapillary space as compared to 11% in sham operated controls. Ornithine decarboxylase activity and polyamine levels were increased over sham controls. The astrocytic swelling, the percentage of the pericapillary space occupied by astrocytic processes, and polyamine levels were reduced to near control levels by the following: (1) alpha-difluoromethylornithine; (2) Ifenprodil; and (3) MK-801. alpha-Difluoromethylornithine is a specific inhibitor of ornithine decarboxylase, Ifenprodil is an inhibitor of the polyamine binding site on the n-methyl-d-aspartate receptor, and MK-801 is an antagonist to n-methyl-d-aspartate binding to the n-methyl-d-aspartate receptor. Addition of putrescine, the product of ornithine decarboxylase activity, reversed the effect of alpha-difluoromethylornithine and restored the pericapillary swelling. Putrescine did not affect the MK-801-induced reduction in pericapillary astrocytic swelling. Therefore, polyamines and the n-methyl-d-aspartate receptor modulate excitotoxic responses to cryo-injury in pericapillary cerebral astrocytes.

Therapeutic time window and dose response of the beneficial effects of ketamine in experimental head injury

BACKGROUND AND PURPOSE

The aim of this study was to determine the time and dose response of the therapeutic effects of the N-methyl-D-aspartate receptor antagonist ketamine in experimental head injury.

METHODS

Sixty-six male Sprague-Dawley rats were divided into eight groups. Groups A, B, and C were surgically prepared but received no trauma. Groups D through H received a nonpenetrating impact to the left cranium. Group A (n = 7) received no treatment. Groups B (n = 4) and C (n = 5) received 60 and 120 mg/kg IP ketamine, respectively. Group D (n = 8) received no treatment. Groups E (n = 8) and F (n = 7) received 120 and 180 mg/kg IP ketamine, respectively, 1 hour after head trauma. Groups G (n = 7) and H (n = 9) were treated with 180 mg/kg IP ketamine 2 and 4 hours after head trauma, respectively. Neurological severity score (NSS, 0 through 25 from no injury to severe injury) was determined at 1, 24, and 48 hours after head trauma. After death at 48 hours, cortical slices were taken adjacent to the lesion on the traumatized hemisphere and from comparable sites in the contralateral hemisphere for determination of tissue specific gravity and water content. Brains were then placed in 4% formaldehyde, and the volume of hemorrhagic necrosis was measured 4 days later. NSS was compared within and between groups using the Kruskal-Wallis test for repeated measurements and Mann-Whitney U test for post hoc testing. Water content, specific gravity, and hemorrhagic necrosis were compared within and between groups using two-way ANOVA followed by Fisher's protected least significant difference procedure. A value of P < .05 was considered statistically significant.

RESULTS

Head trauma alone increased NSS, decreased specific gravity, increased water content, and caused cerebral infarction in the injured hemisphere. Ketamine given in two time-dose regimens, 180 mg/kg IP at 2 hours (group G) and 120 mg/kg IP at 1 hour (group F) after trauma, improved NSS from 11.6 +/- 1.7 and 14.4 +/- 0.8 at 1 hour to 4.4 +/- 1.3 and 8.0 +/- 1.4 (mean +/- SEM) at 48 hours, respectively (P < .03). Compared with the untreated group (group D), 180 mg/kg IP ketamine given at 2 and 4 hours after head trauma decreased the volume of hemorrhagic necrosis from 37.1 +/- 9.5 mm3 to 10.1 +/- 3.8 and 15.3 +/- 3.6 mm3, respectively (P < .05). Brain tissue specific gravity and water content at 48 hours were not significantly different between treated and untreated groups. There was no difference in rectal and temporalis muscle temperature between groups.

CONCLUSIONS

We conclude that 180 mg/kg IP ketamine was effective in ameliorating neurological dysfunction after head trauma in rats when the administration time was delayed for 1 hour to 2 hours but not after 4 hours. When given at 1 hour after head trauma, ketamine at 120 mg/kg but not 60 mg/kg is effective in reducing neurological damage after head trauma.

Anoxic injury of rat optic nerve: ultrastructural evidence for coupling between Na+ influx and Ca(2+)-mediated injury in myelinated CNS axons

Physiological studies in the anoxic rat optic nerve indicate that irreversible loss of function, measured by the compound action potential, is due to depolarization and run-down of the transmembrane Na+ gradient which triggers Ca2+ entry through reverse Na(+)-Ca2+ exchange. EM studies in the anoxic optic nerve have demonstrated characteristic changes, including mitochondrial swelling and dissolution of cristae, submyelinic vacuoles, detachment of perinodal oligodendrocyte-axon loops, and severe cytoskeletal damage with loss of microtubules and neurofilaments within the axoplasm. To further examine the coupling between Na+ influx and Ca(2+)-mediated injury in myelinated axons within anoxic white matter, we have examined the ultrastructural effects of tetrodotoxin (TTX), in the anoxic optic nerve. Optic nerves, maintained in an interface brain slice chamber, were exposed to a 60-min period of anoxia. TTX (1 microM) was introduced 10 min before the onset of anoxia. Nerves were examined at the end of the anoxic period, or after 80 min in 1 microM TTX for normoxic controls. Under normoxic conditions, optic nerve axons exposed to TTX exhibited a normal ultrastructure. In optic nerves exposed to TTX studied at the end of a 60-min period of anoxia, mitochondria showed swelling and loss of cristae, and terminal oligodendroglial loops were detached from the nodal axon membrane. Cytoskeletal architecture was preserved in anoxic optic nerve axons treated with TTX, and axonal microtubules and neurofilaments maintained their continuity. Submyelinic empty spaces were not present. Perinodal astrocyte processes often appeared to be replaced by cellular remnants containing multiple membranous profiles; clusters of shrunken astrocytic processes were present between myelinated axons.(ABSTRACT TRUNCATED AT 250 WORDS)

L-glutamate-stimulated taurine release from rat cerebral cultured astrocytes

We characterized L-glutamate-stimulated taurine release from cultured astrocytes prepared from rat cerebrum. L-glutamate (0.5 mM) stimulated release of 3H-labeled and endogenous taurine, where the rate of release reached maximum in 40 min. L-glutamate increased astrocytic volume [3H-O-methyl-D-glucose (3H-OMG) space] with a similar time course to 3H-taurine release. Quisqualate, L-aspartate, DL-homocysteate, and L-cysteate increased both astrocytic 3H-OMG space and 3H-taurine release from cultured astrocytes, while kainate (1 mM) stimulated 3H-taurine release without affecting astrocytic volume. N-methyl-D-aspartate had no effect on 3H-taurine release and astrocytic volume. Treatment of astrocytes with dibutyryl cAMP reduced the effect of kainate on 3H-taurine release. L-glutamate-stimulated 3H-taurine release was attenuated by removal of extracellular Cl- and in hyperosmotic medium, which prevented L-glutamate-induced increase in 3H-OMG space of cultured astrocytes. These results indicate that L-glutamate stimulates taurine release from astrocytes through swelling-triggered mechanisms and that kainate causes the release through volume-independent mechanisms.

Astrocytes: form, functions, and roles in disease

Astrocytes, once relegated to a mere supportive role in the central nervous system, are now recognized as a heterogeneous class of cells with many important and diverse functions. Major astrocyte functions can be grouped into three categories: guidance and support of neuronal migration during development, maintenance of the neural microenvironment, and modulation of immune reactions by serving as antigen-presenting cells. The concept of astrocytic heterogeneity is critical to understanding the functions and reactions of these cells in disease. Astrocytes from different regions of the brain have diverse biochemical characteristics and may respond in different ways to a variety of injuries. Astrocytic swelling and hypertrophy-hyperplasia are two common reactions to injury. This review covers the morphologic and pathophysiologic findings, time course, and determinants of these two responses. In addition to these common reactions, astrocytes may play a primary role in certain diseases, including epilepsy, neurological dysfunction in liver disease, neurodegenerative disorders such as Parkinson's and Huntington's diseases, and demyelination. Evidence supporting primary involvement of astrocytes in these diseases will be considered.

Mechanisms of glutamate induced swelling in astroglial cells

Relative changes in volume were registered in single cells by using a microspectrofluorometric equipment and the fluorescent probe fura-2/AM, excited at its isosbestic point. At this wavelength the probe is ion-insensitive and the fluorescent signals emitted is dependent on variations in the concentration of the dye. Variations in cell volume thus lead to changes in fluorescence intensity as the probe concentration is changed in the lightened delimited zone selected for each cell. When changing the excitation wavelength Ca2+ transients can be recorded. Glutamate (Glu) induced swelling of type I astroglial cells in primary culture and a parallel intracellular Ca2+ increase was obtained. A Glu induced swelling was obtained even after blockade of the Glu ionotropic receptors with NBXQ, suggesting that activation of ionotropic receptors might not be necessary for swelling to occur. On the other hand, blockade of the Glu carrier, or of pertussis toxin sensitive G-proteins reduced the Glu induced swelling. Blockade of Ba2+ or TEA sensitive K+ channels completely blocked the Glu induced swelling as did also blockade with furosemide of the Na+/K+/Cl- co-transporter. Glu induced swelling occurred in parallel with intracellular Ca2+ transients but extracellular Ca2+ did not seem necessary for swelling to occur.

Concentrations of amino acids in extracellular fluid after opening of the blood-brain barrier by intracarotid infusion of protamine sulfate

This article evaluates the influence of an opening of the blood-brain barrier (BBB) on compounds in brain extracellular fluid. The concentrations of amino acids and some other primary amines were determined in dialysates sampled from the right parietal cortex of rats before and after an intracarotid infusion of protamine sulfate. Extravasated plasma proteins were visualized by Evans blue/albumin and immunohistochemistry. CSF albumin--an indicator of blood-CSF barrier opening--was quantified with immunoelectrophoresis. The brains were macroscopically edematous after 10 mg but not after 5 mg of protamine sulfate. The higher dose led to a 50% death rate. The concentrations of amino acids did not change 10 min after the BBB opening. No significant alterations in the amino acid concentrations were observed after the lower dose. The concentrations of glutamate, aspartate, GABA, glycine, taurine, and phosphoethanolamine increased significantly within 50-80 min after the infusion of 10 mg of protamine sulfate. CSF albumin levels were significantly increased 1 h after infusion. We conclude that a dysfunction of the BBB, of a degree known to induce brain edema (10 mg of protamine sulfate), significantly increases the extracellular concentration of excitatory amino acids, GABA, taurine, and phosphoethanolamine in the extracellular space.

Ketamine alters calcium and magnesium in brain tissue following experimental head trauma in rats

We previously reported that the N-methyl-D-aspartate receptor antagonists dizocilpine maleate and ketamine improved the neurological severity score (NSS) after head trauma in rats. Other investigators have reported increased calcium and decreased magnesium following head trauma in untreated rats. The present study was designed to determine whether ketamine influences the concentrations of calcium and magnesium in brain tissue following head trauma. Eighty-six male Sprague-Dawley rats (180 +/- 15 g) were divided into eight groups. Groups A (no head injury) and C (head injury) received no treatment. Groups B (no head injury) and D-H (head injury) received ketamine. In groups D, E, and F, ketamine, 180 mg/kg i.p., was given 1, 2, and 4 h after head trauma, respectively. In groups G and H, ketamine, 120 and 60 mg/kg, respectively, was given 1 h after head trauma. After we killed the rats at 48 h, cortical slices were taken to measure tissue calcium and magnesium content by the inductively coupled plasma atomic emission spectroscopy method. In the contused hemispheres, calcium increased and magnesium decreased (p < 0.0001). Among the head-injured groups, the increase in brain tissue calcium was smaller in groups receiving 60 mg/kg of ketamine at 1 h or 180 mg/kg of ketamine at 1, 2, or 4 h than in the group not receiving ketamine. The decrease in brain tissue magnesium was smaller in the groups receiving 180 mg/kg of ketamine at 1 and 2 h than in the group not receiving ketamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of AMPA receptors reduces brain edema following opening of the blood-brain barrier

The aim of our study was to evaluate whether blockade of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors could reduce brain edema in two experimental models of edema following opening of the blood-brain barrier (BBB). The brain specific gravity was determined 2 h after opening the BBB by a 30-s infusion of protamine sulfate (10 mg in 200 microliters 0.9% NaCl) or arabinose (1.5 or 1.8 mol/L, 0.06 ml.s-1) into the right internal carotid artery. Cisternal CSF was withdrawn for albumin determination before the carotid infusion and before killing 2 h later. After infusion of protamine sulfate or arabinose, CSF albumin increased in all groups. The brain specific gravity was significantly lower in the right than in the left (control) frontal, parietal, and occipital cortex and striatum. NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenxo(F)quinoxaline), an AMPA receptor antagonist, given intravenously 10 min after opening the BBB (5 mg/kg), significantly increased the specific gravity in the treated rats (p < 0.01 for the difference from control rats) without reducing CSF albumin or albumin extravasation in the brain as evaluated with Evans blue. We hypothesize that intracerebral (glial?) AMPA receptors may play a role in brain edema following opening of the BBB.

Intracellular calcium dynamics and cerebral injury: modeling various insults in vitro

The magnitude and time course of intracellular [Ca2+]i alterations were studied after excitatory amino acid challenge (EAA) or chemical energy depletion in mature spinal cultures. While either cytotoxic event led to prompt increases in [Ca2+]i, the pattern of these changes before and after exposure to the toxin was different. EAA [Ca2+]i changes seem primarily dependent on surface membrane alterations from which the cells rapidly recover while energy depletion effects release of [Ca2+]i from intracellular stores and produces a lasting compromise in the ability of these neurons in culture to recover from the initial insult.

Cerebral aspartate utilization: near-equilibrium relationships in aspartate aminotransferase reaction

The pathways of nitrogen transfer from 50 microM [15N]aspartate were studied in rat brain synaptosomes and cultured primary rat astrocytes by using gas chromatography-mass spectrometry technique. Aspartate was taken up rapidly by both preparations, but the rates of transport were faster in astrocytes than in synaptosomes. In synaptosomes, 15N was incorporated predominantly into glutamate, whereas in glial cells, glutamine and other 15N-amino acids were also produced. In both preparations, the initial rate of N transfer from aspartate to glutamate was within a factor of 2-3 of that in the opposite direction. The rates of transamination were greater in synaptosomes than in astrocytes. Omission of glucose increased the formation of [15N]-glutamate in synaptosomes, but not in astrocytes. Rotenone substantially decreased the rate of transamination. There was no detectable incorporation of 15N from labeled aspartate to 6-amino-15N-labeled adenine nucleotides during 60-min incubation of synaptosomes under a variety of conditions; however, such activity could be demonstrated in glial cells. The formation of 15N-labeled adenine nucleotides was marginally increased by the presence of 1 mM aminooxyacetate, but was unaffected by pretreatment with 1 mM 5-amino-4-imidazolecarboxamide ribose. It is concluded that (1) aspartate aminotransferase is near equilibrium in both synaptosomes and astrocytes under cellular conditions, but the rates of transamination are faster in the nerve endings; (2) in the absence of glucose, use of amino acids for the purpose of energy production increases in synaptosomes, but may not do so in glial cells because the latter possess larger glycogen stores; and (3) nerve endings have a very limited capacity for salvage of the adenine nucleotides via the purine nucleotide cycle.

Interaction between the glutamine cycle and the uptake of large neutral amino acids in astrocytes

When astrocyte cultures are incubated with glutamate and ammonium, the clearance of these substrates followed by the formation and export of glutamine simulates the action of the "glutamine cycle" that is believed to function in the CNS. In the present study this process was found to increase the uptake of large neutral amino acids (LNAAs), namely, histidine, kynurenine, leucine, phenylalanine, and tryptophan, by two- to threefold in mouse cerebral astrocytes. The enhancement of kynurenine uptake was shown to depend on the formation of glutamine and to saturate at low levels of glutamine. LNAAs transiently lowered the glutamine content of astrocytes that were incubated with glutamate and ammonium, but they did not affect net export of glutamine to the solution at normal physiological pH. However, on adjustment of the pH of the solution to 7.8, which causes a large increase in glutamine content without affecting export, kynurenine now significantly increased net glutamine export. These findings relate to proposed mechanisms of cerebral dysfunction in hyperammonemia.

Extracellular calcium is a mediator of astroglial injury during combined glucose-oxygen deprivation

We tested the hypothesis that extracellular calcium is a mediator of astroglial injury during combined glucose-oxygen deprivation. Both differentiated and undifferentiated astroglial cultures were exposed to combined glucose-oxygen deprivation in the presence and absence of extracellular calcium. Lactate dehydrogenase efflux was used as an index of cellular injury. Both types of cultures exhibited significantly less cellular injury when exposed to combined glucose-oxygen deprivation in the absence of extracellular calcium (e.g. lactate dehydrogenase efflux in undifferentiated cultures after 12 h of exposure: presence of calcium, 65.2 +/- 2.5% vs. absence of calcium, 21.4 +/- 1.3%). To further elucidate the mechanism by which extracellular calcium produces injury, we studied the effect of nimodipine, an L-type calcium channel blocker, on astroglial injury resulting from combined glucose-oxygen deprivation. Nimodipine decreased cellular injury in both types of cultures (e.g. lactate dehydrogenase efflux in undifferentiated cultures after 12 h of exposure: untreated, 65.4 +/- 2.2% vs. 10 nM nimodipine, 44.6 +/- 4.2%). Extracellular calcium appears to be a mediator of astroglial injury during combined glucose-oxygen deprivation. These results suggest that influx of extracellular calcium via L-type voltage-gated calcium channels may contribute to astroglial injury during cerebral ischemia.

Volume regulation of single astroglial cells in primary culture

Relative volume variations in cultured astrocytes were examined by microspectrofluorimetry after loading the cells with the highly fluorescent intracellular probes 2,7-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF/AM) or fura-2/AM. At their isosbestic points, 450 nm and 358 nm, respectively, the probes were ion-insensitive and the fluorescent signals emitted related only to the intracellular dye concentration. By varying the excitation wavelengths, changes in intracellular pH or Ca2+ transients could be recorded simultaneously with the relative volume variations of the individual cells. After exposure to a hypotonic buffer, type 1 astrocytes swelled within 30 s and subsequently underwent regulatory volume decrease (RVD). When exposed to a hypertonic buffer, the astrocytes shrunk and exhibited regulatory volume increase (RVI). One mM glutamate induced an increase in astrocyte volume in 60 sec and evoked cytosolic Ca2+ transients but did not change intracellular pH.

Ultrastructural concomitants of anoxic injury and early post-anoxic recovery in rat optic nerve

To study the effects of anoxia on CNS white matter, we examined the ultrastructure of axons and glial cells in a white matter tract, the rat optic nerve, that was subjected to a standardized anoxic insult in vitro. Previous electrophysiological studies showed that in this model, action potential conduction is rapidly abolished by anoxia, and conduction is restored after reoxygenation in about 30% of axons following a 60-min anoxic period. The present study examined the ultrastructural correlates of anoxic injury and early post-anoxic recovery in this model. Optic nerves examined immediately following 60 min of anoxia displayed numerous large, apparently empty zones located within myelin sheaths adjacent to the axon. The myelin remained compact and retained its periodicity. In some regions, the extracellular space was enlarged. There was mitochondrial swelling with loss of normal cristae. There was also loss of microtubules and, to a smaller degree, of neurofilaments in large-diameter axons. Some nodes of Ranvier in anoxic optic nerves displayed detachment of terminal oligodendroglial loops or retraction of the myelin from the node; the presence of tongue-like processes, extending from nearby cells under the detached myelin loops, suggested a possible role of cell-mediated damage to the paranodal myelin. Bundles of dense astrocyte processes were present, and there was vesicular degeneration of perinodal astrocyte processes. In optic nerves that had been permitted to recover for 60 min in oxygenated Ringers following the anoxic period, empty zones were only rarely observed within myelin sheaths and, when present, were smaller than in optic nerves immediately following 60 min of anoxia. The axoplasm of large fibers continued to show loss of microtubules and neurofilaments, as well as mitochondrial swelling. Myelin appeared normal, and only rare paranodal oligodendroglial processes remained unattached from the axon membrane. These results provide support for the idea that, during anoxia, myelinated axons are damaged with significant injury to cytoskeletal elements, probably due to an influx of calcium. The ultrastructural results, together with our earlier observations on the physiological correlates of anoxia and re-oxygenation, suggest that the development of intramyelinic spaces or damage to paranodes lead to conduction block in the anoxic optic nerve. These results also suggest that repair of these structural abnormalities may provide a morphological basis for the early recovery of conduction that occurs after re-oxygenation.

Morphologic Changes in Cultured Astroeytes After Exposure to Glutamate

Cultured astrocytes, exposed to glutamate at a dose that is generally neurotoxic in vitro (1 mM), exhibit transient swelling in the absence of cell death. In the present study, we further characterize this response by examining the distribution of intermediate filaments and evaluating cellular ultrastructure in primary cultures of astrocytes after exposure to 1 mM glutamate. In addition, cellular swelling was determined using the nonmetabolizable hexose 3-O-methyl [14C]-glucose (3-MG). Glial fibrillary acidic protein (GFAP) was immunolocalized at the light microscopic level to study the distribution of intermediate filaments. GFAP was immunolocalized to a fine cytoskeletal network in control cultures. Four to 24 h after exposure to glutamate, this detailed localization was replaced by a diffuse, uneven pattern of immunoreactivity. The most prominent ultrastructural changes were identified at 4 and 8 h after glutamate exposure. Nucleoli underwent transformation from a normal compact appearance to a markedly dispersed state. The cell body typically exhibited cytoplasmic lucency, swollen mitochondria, and dilated cisterns. Intermediate filaments within cellular processes appeared widely spaced in comparison to the controls. These ultrastructural changes coincided with findings of increased intracellular water space as determined with 3-MG. These findings demonstrate that astrocytes exposed to 1 mM glutamate exhibit transient morphologic changes that not only suggest cellular swelling but also define a more diverse response that is reflected in the altered immunolocalization of GFAP and in unique changes in the nucleolus.

Effects of ketamine on outcome from temporary middle cerebral artery occlusion in the spontaneously hypertensive rat

This experiment evaluated the potential for ketamine HCl, a non-competitive glutamate antagonist, to minimize injury resulting from temporary focal cerebral ischemia. Male spontaneously hypertensive rats were randomly assigned to receive either ketamine (n = 13) or halothane anesthesia (n = 12) during 2 h of reversible middle cerebral artery occlusion (MCAO). Ketamine was administered as a 50 mg/kg i.v. loading dose followed by a continuous 1.25 mg/kg/min i.v. infusion beginning 25 min prior to ischemia and continued until 30 min after reperfusion. An additional group of rats (ketamine-shams, n = 8) underwent craniectomy and ketamine administration (as above) but the middle cerebral artery was not ligated. Physiologic values were similar between groups with the exception of plasma glucose which was elevated in the halothane-MCAO group. After 4 days recovery, rats in all groups were neurologically evaluated. There were no differences between the two groups undergoing MCAO for neurologic grading or open field behavior, although both groups performed worse than did ketamine-shams (P less than 0.05). In contrast, motor performance revealed more severe deficits in the ketamine-MCAO rats vs either the halothane-MCAO or ketamine-sham groups (P less than 0.05). Cerebral infarct volume was then planimetrically measured after triphenyl tetrazolium chloride (TTC) staining of fresh brain sections. Mean +/- S.D. infarct volume was not different between the halothane-MCAO (134 +/- 51 mm3) and ketamine-MCAO (131 +/- 64 mm3) groups. Seven of 8 sham rats were free of TTC demarcated injury and in the remaining rat injury was minimal.(ABSTRACT TRUNCATED AT 250 WORDS)

Staining of glial fibrillary acidic protein (GFAP) in lumbar spinal cord increases following a sciatic nerve constriction injury

The change in staining density of glial fibrillary acidic protein (GFAP) was analyzed in rats that sustained a chronic constriction injury produced by sutures tied loosely around one sciatic nerve. This injury model of peripheral neuropathy resulted in a behavioral hyperalgesia evidenced by a decrease in mean foot withdrawal latency to radiant heat. Increased GFAP immunostaining was observed in the gray matter of the spinal cord ipsilateral to the lesion and specific to spinal segments in which the sciatic nerve is distributed. Elevated GFAP staining density was attributed primarily to hypertrophy of astrocytes rather than their proliferation or migration since counts of astrocyte profiles demonstrated no significant difference when comparing the lesioned to the control side. The magnitude of the increase in GFAP staining correlated with the degree of hyperalgesia. Thus, these data suggest that astrocytes participate in the sequelae occurring in the dorsal horn following constriction injury of a peripheral nerve.

A morphological study on glutamate-induced swelling of cultured astrocytes: involvement of calcium and chloride ion mechanisms

Morphological changes in cultured astrocytes exposed to L-glutamate (Glu) were examined light and electron microscopically. The treatment with 0.1 mM Glu for 60 min caused marked swelling of the cells, which was characterized by reduction in staining of cytoplasm with Toluidine blue, disappearance of the cytoplasmic granular ground substances, swollen mitochondrion and nucleus, and dispersed chromatin. The above changes were prevented by the removal of Na+, Ca2+ or Cl- from the incubation medium for Glu treatment. However, the Glu treatment in a Cl(-)-free medium caused conspicuous aggregation of 10 nm filaments.

Glutamate and GABA receptors in vertebrate glial cells

Glial cells of the central nervous system express receptors for the main inhibitory and excitatory neurotransmitters, GABA and glutamate. The glial GABA and glutamate receptors share many properties with the neuronal GABAA and kainate/quisqualate receptors, but are molecularly and, in some aspects, pharmacologically distinct from their neuronal counterparts. The functional role of these receptors is as yet speculative: They have been proposed to control proliferation of astrocytes, serve to balance ion changes at GABAergic synapses, or they could enable the glial cell to detect neuronal synaptic activity.

L-glutamate-induced swelling of cultured astrocytes is dependent on extracellular Ca2+

L-Glutamate (L-Glu)-induced swelling of astrocyte cultures from rat brain was examined by determining [3H]O-methyl-D-glucose ([3H]OMG) uptake. Time-course of the L-Glu (0.5 mM)-induced increase in [3H]OMG space of astrocytes showed two phases; about 30% increase was obtained in 10 min and the increased [3H]OMG space was steady up to 20 min. Then, the [3H]OMG space was further increased during the incubations longer than 30 min. In Ca2(+)-free conditions, while the time-course up to 20 min was similar to that in the normal condition, the increase in [3H]OMG space by further incubations was not shown. The L-Glu-increased [3H]OMG space persisted for 2 h in a L-Glu-free medium and thereafter turned to the normal level in 4 h. In contrast, the incubation in a L-Glu-free medium for 30 min reversed the increased [3H]OMG space in the absence of extracellular Ca2+. These results indicate that swelling of astrocytes induced by L-Glu is characterized by an accompanied influx of Ca2+.

Excitatory amino acid receptors in primary cultures of glial cells from the retina

Binding of 3H-L-aspartate to membranes from retinal glial cells in primary culture was characterized. Binding kinetics showed a saturable, reversible binding to three populations of sites with KB = 40, 200, and 1,300 nM. The first two were present at 1 day in vitro (DIV), whereas the latter two were observed at 12 DIV. The possibility of the 40 nM site being neuronal cannot be discarded, since some neurons are present at 1 DIV. In 12 DIV cultures, the presence or absence of sodium determined two different pharmacological patterns, comparable to those described for electrogenic glutamate transport in Müller cells, and QA metabotropic receptors in astrocytes, respectively. Results suggest that, as has been shown for some receptors in nerve tissue, the properties of glial cell receptors undergo age-dependent changes. In turn, this could be related to changes in the function of neurotransmitter substances during development.

Anoxic injury of mammalian central white matter: decreased susceptibility in myelin-deficient optic nerve

The rat optic nerve, a typical central nervous system white matter tract, rapidly loses excitability when it is exposed to anoxia and is irreversibly damaged by prolonged anoxia. Neonatal optic nerve is extremely resistant to anoxia-induced dysfunction and injury; the adult pattern of response to anoxia appears between 10 and 20 days postnatal, that is, during the period of oligodendroglial proliferation and myelination. To test the hypothesis that myelination, or associated events, confer anoxic susceptibility on developing white matter, we analyzed the effects of anoxia on the myelin-deficient (md) strain of rat. Acutely isolated optic nerves from 19- to 21-day-old md rats and control optic nerves from unaffected male littermates were maintained in vitro at 37 degrees C, and exposed to a standard 60-minute period of anoxia. The supramaximal compound action potential was recorded and amplitude of the compound action potential, expressed as % of amplitude before anoxic exposure, was determined. The compound action potential was nearly abolished within 3 to 6 minutes after onset of anoxia in control optic nerves, while optic nerves from md rats displayed a slower decrease in compound action potential amplitude during anoxia, with a distinct action potential present even after 60 minutes of anoxia. Optic nerves from md rats showed significantly greater recovery of compound action potential (71 +/- 25%) than did control optic nerves (33 +/- 21%; p less than 0.02) after 60 minutes of anoxia. These findings support the hypothesis that myelination, or changes associated with it, may be important in the development of anoxic susceptibility in central white matter.

Mechanisms underlying glutamate-induced swelling of astrocytes in primary culture

The effects of glutamate and its agonists and antagonists on the swelling of primary astrocytes were studied. Glutamate, aspartate, homocysteate, and quisqualate caused a significant increase in astrocytic swelling as measured by 3-0-methyl-[14C]-glucose uptake and by phase-contrast microscopic observations. N-methyl-D-aspartate and kainate were not effective, nor were the competitive NMDA receptor antagonists. Ketamine and MK-801, the non-competitive NMDA receptor antagonists protected the cultured astrocytes against glutamate-induced swelling. Moreover, Glu-induced astrocytic swelling was significantly reduced when sodium-ions were depleted from the culture medium. The sodium ion dependence of Glu-induced astrocytic swelling is rather specific, since depletion of Ca2+ or Mg2+ had no effect. Our data suggest that Na(+)-dependent, Glu-mediated cell swelling occurs in primary cell cultures of astrocytes.

Effects of MK-801 on glutamate-induced swelling of astrocytes in primary cell culture

The effects of glutamate and its agonists and antagonists on the swelling of primary astrocytes were studied. Glutamate (Glu), aspartate (Asp), homocysteate (HCA), and quisqualate (Quis) at 1 mM concentration caused a significant increase in astrocytic swelling as measured by the 3-0-methyl-[14C]-glucose, whereas kainate (KA), N-methyl-D-aspartate (NMDA), and receptor antagonists 2-amino-5-phosphonovaleric acid (APV), 2-amino-7-phosphonohepatanoic acid (APH), and kynurenic acid (Kynu) were not effective. This glial swelling was time-dependent since 1-hr or greater incubations with Glu or its agonists were needed to produce such an effect. Preincubation of glutamate or NMDA receptor anatogonists including Kynu, APH, and APV failed to ameliorate the Glu effects. However, MK-801, a noncompetitive NMDA antagonist, when added to the Glu-incubated astrocytes significantly reduced Glu-induced astrocytic swelling. MK-801 was also effective in reducing the astrocytic swelling induced by agonists including Asp, Quis, and HCA, suggesting that those agonists may share similar mechanisms of Glu in inducing astrocytic swelling. Since the cultured astrocytes lack the NMDA receptors, our data suggest that the observed beneficial effects of MK-801 on excitotoxin-induced swelling of astrocytes may be mediated by mechanisms other than NMDA receptors.