Phylactic role of anti-lipoarabinomannan IgM directed against mannan core during mycobacterial infection in macrophages

Mycobacteria enter host phagocytes, such as macrophages by binding to several receptors on phagocytes. Several mycobacterial species, including Mycobacterium tuberculosis have evolved systems to evade host bactericidal pathways. Lipoarabinomannan (LAM) is an essential mycobacterial molecule for both binding to phagocytes and escaping from bactericidal pathways. Integrin CD11b plays critical roles as a phagocytic receptor and contributes to host defense by mediating both nonopsonic and opsonic phagocytosis. However, the mechanisms by which CD11b-mediated phagocytosis associates with LAM and drives the phagocytic process of mycobacteria remain to be fully elucidated. We recently identified TMDU3 as anti-LAM IgM antibody against the mannan core of LAM. The present study investigated the roles of CD11b and TMDU3 in macrophage phagocytosis of mycobacteria and subsequent bactericidal lysosomal fusion to phagosomes. CD11b knockout cells generated by a CRISPR/Cas9 system showed significant attenuation of the ability to phagocytose non-opsonized mycobacteria and LAM-conjugated beads. Moreover, recombinant human CD11b protein was found to bind to LAM. TMDU3 markedly inhibited macrophage phagocytosis of non-opsonized mycobacteria. This antibody slightly increased the phagocytosis of mycobacteria under opsonized conditions, whereas it significantly enhanced CD11b-mediated bactericidal functions. Taken together, these results show a novel phylactic role of anti-LAM IgM during mycobacterial infection in macrophages.

Lysophosphatidylglucoside/GPR55 signaling promotes foam cell formation in human M2c macrophages

Atherosclerosis is a major cause of cerebral and cardiovascular diseases. Intravascular plaques, a well-known pathological finding of atherosclerosis, have a necrotic core composed of macrophages and dead cells. Intraplaque macrophages, which are classified into various subtypes, play key roles in maintenance of normal cellular microenvironment. Excessive uptake of oxidized low-density lipoprotein causes conversion of macrophages to foam cells, and consequent progression/exacerbation of atherosclerosis. G-protein-coupled receptor 55 (GPR55) signaling has been reported to associate with atherosclerosis progression. We demonstrated recently that lysophosphatidylglucoside (lysoPtdGlc) is a specific ligand of GPR55, although in general physiological ligands of GPR55 are poorly understood. Phosphatidylglucoside is expressed on human monocytes and can be converted to lysoPtdGlc. In the present study, we examined possible involvement of lysoPtdGlc/GPR55 signaling in foam cell formation. In monocyte-derived M2c macrophages, lysoPtdGlc/GPR55 signaling inhibited translocation of ATP binding cassette subfamily A member 1 to plasma membrane, and cholesterol efflux. Such inhibitory effect was reversed by GPR55 antagonist ML193. LysoPtdGlc/GPR55 signaling in M2c macrophages was involved in excessive lipid accumulation, thereby promoting foam cell formation. Our findings suggest that lysoPtdGlc/GPR55 signaling is a potential therapeutic target for inhibition of atherosclerosis progression.

Identification of anti-lipoarabinomannan antibodies against mannan core and their effects on phagocytosis of mycobacteria by human neutrophils

Mycobacterium tuberculosis (MTB) and M. avium-intracellulare complex (MAC) enter host phagocytes, such as neutrophils through lipoarabinomannan (LAM) binding to pattern-recognition receptors, inducing innate immune responses including phagocytosis. Phagocytosis of mycobacteria by human neutrophils depends on the binding of α(1 → 2)-monomannose branching α(1 → 6)-mannan core of LAM/lipomannan (LM), a common component among mycobacterial species, to lactosylceramide (LacCer)-enriched lipid microdomains. We investigated the binding specificities of several anti-LAM antibodies (Abs) to LAMs/LM and found anti-LAM monoclonal IgMs TMDU3 and LA066 were directed against mannan core. Each IgM showed different binding specificity to mannan core. Confocal and stimulated emission depletion microscopy revealed TMDU3 and LA066 strongly bind to MTB and MAC, respectively. Flow cytometric analysis revealed human neutrophils do not express Dectin-2, DC-SIGN or mannose receptor. Furthermore, neutrophil phagocytosis of mycobacteria was markedly inhibited by TMDU3 and LA066, respectively. Similarly, treatment of each mAb with neutrophils reduced the numbers of intracellular MAC. Together, our results suggest that the interaction of LacCer-enriched lipid microdomains with mannan core and its blocking are therapeutic or diagnostic targets for both TB and non-tuberculous mycobacteria infection.

Multiplicity of Glycosphingolipid-Enriched Microdomain-Driven Immune Signaling

Glycosphingolipids (GSLs), together with cholesterol, sphingomyelin (SM), and glycosylphosphatidylinositol (GPI)-anchored and membrane-associated signal transduction molecules, form GSL-enriched microdomains. These specialized microdomains interact in a cis manner with various immune receptors, affecting immune receptor-mediated signaling. This, in turn, results in the regulation of a broad range of immunological functions, including phagocytosis, cytokine production, antigen presentation and apoptosis. In addition, GSLs alone can regulate immunological functions by acting as ligands for immune receptors, and exogenous GSLs can alter the organization of microdomains and microdomain-associated signaling. Many pathogens, including viruses, bacteria and fungi, enter host cells by binding to GSL-enriched microdomains. Intracellular pathogens survive inside phagocytes by manipulating intracellular microdomain-driven signaling and/or sphingolipid metabolism pathways. This review describes the mechanisms by which GSL-enriched microdomains regulate immune signaling.

Lysophosphatidylglucoside is a GPR55 -mediated chemotactic molecule for human monocytes and macrophages

Neutrophils undergo spontaneous apoptosis within 24-48 h after leaving bone marrow. Apoptotic neutrophils are subsequently phagocytosed and cleared by macrophages, thereby maintaining neutrophil homeostasis. Previous studies have demonstrated involvement of lysophosphatidylglucoside (lysoPtdGlc), a degradation product of PtdGlc, in modality-specific repulsive guidance of spinal sensory axons, via its specific receptor GPR55. In the present study, using human monocytic cell line THP-1 as a model, we demonstrated that lysoPtdGlc induces monocyte/macrophage migration with typical bell-haped curve and a peak at concentration 10^-9 M. Lysophosphatidylinositol (lysoPtdIns), a known GPR55 ligand, induced migration at higher concentration (10^-7 M). LysoPtdGlc-treated cells had a polarized shape, whereas lysoPtdIns-treated cells had a spherical shape. In EZ-TAXIScan (chemotaxis) assay, lysoPtdGlc induced chemotactic migration activity of THP-1 cells, while lysoPtdIns induced random migration activity. GPR55 antagonist ML193 inhibited lysoPtdGlc-induced THP-1 cell migration, whereas lysoPtdIns-induced migration was inhibited by CB₂-receptor inverse agonist. SiRNA experiments showed that GPR55 mediated lysoPtdGlc-induced migration, while lysoPtdIns-induced migration was mediated by CB₂ receptor. Our findings, taken together, suggest that lysoPtdGlc functions as a chemotactic molecule for human monocytes/macrophages via GPR55 receptor, while lysoPtdIns induces random migration activity via CB₂ receptor.

Glycosphingolipid synthesis in cerebellar Purkinje neurons: roles in myelin formation and axonal homeostasis

Glycosphingolipids (GSLs) occur in all mammalian plasma membranes. They are most abundant in neuronal cells and have essential roles in brain development. Glucosylceramide (GlcCer) synthase, which is encoded by the Ugcg gene, is the key enzyme driving the synthesis of most neuronal GSLs. Experiments using conditional Nestin-Cre Ugcg knockout mice have shown that GSL synthesis in vivo is essential, especially for brain maturation. However, the roles of GSL synthesis in mature neurons remain elusive, since Nestin-Cre is expressed in neural precursors as well as in postmitotic neurons. To address this problem, we generated Purkinje cell-specific Ugcg knockout mice using mice that express Cre under the control of the L7 promoter. In these mice, Purkinje cells survived for at least 10-18 weeks after Ugcg deletion. We observed apparent axonal degeneration characterized by the accumulation of axonal transport cargos and aberrant membrane structures. Dendrites, however, were not affected. In addition, loss of GSLs disrupted myelin sheaths, which were characterized by detached paranodal loops. Notably, we observed doubly myelinated axons enveloped by an additional concentric myelin sheath around the original sheath. Our data show that axonal GlcCer-based GSLs are essential for axonal homeostasis and correct myelin sheath formation.

Comprehensive analysis of monoclonal antibodies against detergent-insoluble membrane/lipid rafts of HL60 cells

Glycosphingolipids and cholesterol are principal components of plasmamembrane microdomains, i.e. lipid rafts. Recent studies revealed the possible presence of a variety of microdomains that distinctly differ in terms of their molecular composition and functions. To understand their precise structures and functions, we produced monoclonal antibodies (MAbs) by immunizing mice to the microdomains prepared from a fraction of detergent-insoluble membrane (DIM) of HL60 cells. Biochemical characterization of the antigen epitopes led to classification of the MAbs into two groups. One group consists of MAbs that react with lipids such as phosphatidylglucoside, lysophosphatidylinositol, and gangliosides (GM1a and GD1b), and the other consists of MAbs that react with proteins such as annexin I, aminopeptidase N and acrogranin. Immunofluorescence staining of HL60 cells with the MAbs, except for the MAbs that recognize lysophosphatidylinositol or annexin I, resulted in patchy-like images of the cell membranes. Interestingly, MAbs belonging to the former group had the potential to induce cell proliferation/differentiation in vitro. Our MAbs against the DIM fraction of HL60 cells can be valuable tools for the study of membrane microdomains.

Drosophila glucosylceramide synthase: a negative regulator of cell death mediated by proapoptotic factors

Glucosylceramide synthase (GlcT-1) catalyzes the formation of glucosylceramide (GlcCer), the core structure of major glycosphingolipids (GSLs), from ceramide and UDP-glucose. Ceramide and its metabolites, such as sphingosine-1-phosphate, are now known to be important mediators of apoptosis and cell survival. Recently, we have shown that GlcT-1 functions to regulate intracellular ceramide levels via glycosylation of ceramide. In this study, we employ the fruit fly Drosophila melanogaster as a model system for understanding the in vivo roles of GlcT-1. We isolated and characterized a GlcT-1 homologue (DGlcT-1) from Drosophila. When DGlcT-1 was expressed in GM-95 cells deficient in GSLs (because of the absence of GlcT-1 activity), these cells regained the ability to synthesize GSLs. Northern blot and in situ hybridization analyses revealed that the expression of DGlcT-1 mRNA was ubiquitous throughout development, suggesting that DGlcT-1 is important for development and differentiation. Indeed, RNA interference experiments demonstrated that the loss of GlcT-1 function enhances apoptotic cell death. Conversely, targeted expression of GlcT-1 partially rescued cell death caused by the proapoptotic factors Reaper and Grim, suggesting that ceramide generation might be one signal pathway that executes the cell death program. We also found that GlcT-1 localized not only in the Golgi apparatus but also in the perinuclear endoplasmic reticulum, providing the first visual evidence of GlcT-1 in membranes. These results indicate that GlcT-1 might down-regulate ceramide generated in these membranes.

Oxidized low density lipoprotein (Ox-LDL) as a marker of atherosclerosis in hemodialysis (HD) patients

AIM

To characterize the relationship between oxidative stress and atherosclerosis in HD patients.

METHODS

Seventy-five HD patients were entered into the study. Ox-LDL was measured as a probe for peroxidation and compared to clinical atherosclerotic parameters. Prospective studies were also performed to assess the effects of vitamin E-bonded membrane on oxidative stress.

RESULTS

Elderly patients tended to show elevated Ox-LDL (alpha = 0.060+/-0.021 ng/microg LDL protein/year, r = 0.35, p < 0.05). Levels of Ox-LDL in the patients with positive history for atherosclerotic diseases (3.1+/-0.4 ng/microg LDL protein, n = 36) were higher than those with a negative history (1.6+/-0.2, n = 39, p < 0.01). Further-more, ankle/brachial pressure index was negatively correlated to Ox-LDL (alpha = -0.052+/-0.012/ng/microg LDL protein, r = 0.42, p < 0.01). Application of vitamin E-bonded membrane for 10 months (-38+/-11%, n = 14, p < 0.05), but not synthetic membrane, ameliorated Ox-LDL.

CONCLUSIONS

Our results indicate that Ox-LDL is elevated in aged HD patients. In addition, the present data provide evidence that vitamin E-bonded dialyzers attenuate oxidative stress. Finally, our findings suggest that Ox-LDL correlates to the magnitude of peripheral arterial diseases in HD patients.

Macular corneal dystrophy in Saudi Arabia: a study of 56 cases and recognition of a new immunophenotype

PURPOSE

To determine the immunophenotype or immunophenotypes of macular corneal dystrophy in Saudi Arabia.

METHODS

We studied 56 cases of macular corneal dystrophy. Tissue from 60 corneal transplant buttons was stained by the avidin-biotin complex method using an anti-keratan sulfate monoclonal antibody. The serum antigenic keratan sulfate was measured in 23 of the 56 patients, four unaffected relatives, and 13 individuals with chronic actinic keratopathy. Serum and corneal tissue were studied in 17 of the 50 affected individuals with corneal transplant material.

RESULTS

Thirty-five corneas (58.3%) of 29 of 50 patients did not react with anti-keratan sulfate monoclonal antibody. The stroma and abnormal intracellular and extracellular corneal accumulations reacted with anti-keratan sulfate monoclonal antibody in seven corneas (11.7%). The stroma in the other 18 corneas (30.0%) from 15 patients did not react with the anti-keratan sulfate monoclonal antibody, but corneal fibroblasts did. Twenty-one of the 23 patients with macular corneal dystrophy had no detectable serum antigenic keratan sulfate (< 9 ng/ml); two had values of 12 and 51 ng/ml, respectively, and their corneal stroma and abnormal accumulations reacted with anti-keratan sulfate monoclonal antibody.

CONCLUSIONS

We detected macular corneal dystrophy type IA, a new immunophenotype characterized by the lack of detectable antigenic keratan sulfate in the serum (< 9 ng/ml), and a corneal stroma that did not react with the keratan sulfate monoclonal antibody but in which corneal fibroblasts did react with keratan sulfate monoclonal antibody (in 15 of 50 patients).

Macular corneal dystrophy in Iceland. A clinical, genealogic, and immunohistochemical study of 28 patients

BACKGROUND

The frequency of different types of macular corneal dystrophy (MCD) was determined in Iceland where MCD accounts for one third of every penetrating keratoplasty.

METHODS

The authors determined the serum levels of antigenic keratan sulfate (aKS) in 27 patients with MCD and 53 unaffected family members by an enzyme-linked immunosorbent assay that uses an anti-KS monoclonal antibody (5-D-4). The authors also stained sections from 37 corneal buttons (including 2 regrafts) from 23 patients with MCD by the avidin-biotin complex method using the same anti-KS monoclonal antibody.

RESULTS

Based on the serum analyses, 22 patients had MCD type I and 5 had MCD type II. The corneas from patients without detectable KS in the serum lacked immunohistochemical reactivity to the anti-KS antibody. Every MCD cornea examined from individuals with normal serum KS levels showed KS reactivity. All 53 unaffected siblings and parents carrying the recessive gene had normal serum KS levels.

CONCLUSIONS

Macular corneal dystrophy types I (78.6%) and II (21.4%) both occur in Iceland. Members of affected sibships had only one of these types, not both. Nine patients with MCD type I and four persons with MCD type II belonged to a large pedigree in which individuals have been traced as far back as the beginning of the 16th century. The linking of patients with MCD types I and II in an inbred pedigree suggests that both types may be manifestations of the same abnormal gene rather than independent entities. The serum KS levels were not helpful in detecting heterozygous MCD carriers.

Decreased autophosphorylation and kinase activity of insulin receptors in diabetic Chinese hamsters

To clarify the role of the insulin receptor in diabetes, the hepatic insulin receptor was investigated in the spontaneously diabetic Chinese hamsters, which are the animal models for insulin-deficient diabetes. Insulin binding in the diabetic animals increased mainly due to an increase in the number of receptors. It was also observed that both the autophosphorylation and kinase activity of the hepatic insulin receptor were decreased in the diabetic animals compared to the control animals. These changes in the hepatic insulin receptor may be caused by the diabetes itself. As the phosphorylated protein of 95 kDa was immunoprecipitated by the anti-insulin receptor antibody (B-10, human) in both diabetics and controls, it was supposed that the 95 kDa protein would be the beta-subunit of insulin receptors, as in other animals. These animals seem to be useful for examining insulin receptors in diabetes.

An in vitro investigation of the action of ketamine on excitatory synaptic transmission in the hippocampus of the guinea-pig

The effect of ketamine on excitatory synaptic transmission was examined in vitro in slices of guinea-pig hippocampus. Ketamine (100-500 microM) depressed the amplitude of the field excitatory post-synaptic potential (e.p.s.p.) and the population spike evoked in the dentate gyrus by stimulation of the perforant path. It did not affect the coupling between the e.p.s.p. and the population spike. Ketamine (0.2 mM) had no consistent depolarizing or hyperpolarizing effect on the resting membrane potential of the granule cells nor did it alter their input resistance. It did, however, reduce the amplitude of the intracellularly recorded e.p.s.p. Ketamine (5-200 microM) reduced the sensitivity of the granule cells to 1-glutamate applied iontophoretically but did not significantly depress the potassium-stimulated efflux of [3H]glutamate from synaptosomes. It is concluded that ketamine depresses excitatory synaptic transmission in the dentate gyrus by depressing chemical transmission probably via a post-synaptic mechanism.

Insulin receptors on hepatocytes from spontaneously diabetic Chinese hamsters

Insulin receptors on hepatocytes were studied in spontaneously diabetic Chinese hamsters, which are the animal models for insulin deficient diabetes. Insulin binding in diabetic animals increased mainly due to an increase in the number of receptors. Although binding affinity of diabetic animals was similar to that of control animals, a kinetic study revealed that both the association rate constant and the dissociation rate constant decreased in diabetic animals. Negatively cooperative interactions between receptors were demonstrated in control and diabetic animals, and both the magnitude and sensitivity of this effect was the same in both types of animals. A significant inverse correlation between insulin binding and the plasma insulin concentration was found in these animals. These results therefore suggest that there is an increase in the insulin binding in the insulin deficient diabetic state mainly due to an increase in the number of receptors with a decrease in both the association and dissociation rate constants, and these changes may be important in the altered metabolic state.

Metabolic and morphological changes of the heart in Chinese hamsters (CHAD strain) with spontaneous long-term diabetes

We studied the effect of spontaneous long-term (9-10 months) diabetes on the heart of Chinese hamsters (CHAD strain) to elucidate the relationship between diabetes mellitus and cardiomyopathy. The diabetic hamsters, aged approximately 11 months, showed body weight loss, hyperglycemia (mean fasting plasma glucose 402 mg/dl), hypoinsulinemia, hyperlipidemia and ketonemia. The diabetic hamsters showed reduced activities of cytoplasmic glycolytic key enzymes; hexokinase, pyruvate kinase and phosphofructokinase, increases in cardiac glycogen and glucose-6-phosphate contents and a 40% decrease in cardiac ATP content, indicating decreased energy production. An accumulation of myocardial triglyceride and cholesterol was found in the diabetic hamsters. In addition, the cardiac norepinephrine content was increased in the diabetic hamsters, suggesting the presence of autonomic nervous disorder. Increased heart weight and thickening of the septum and both ventricular walls were found in the diabetic hamsters. Light-microscopic analysis revealed that 42.9% of the diabetic hamsters had myocardial degeneration without any vascular lesion of extramural large and intramural small vessels, whereas the non-diabetic controls had no myocardial or vascular lesions. These data suggest that the diabetic Chinese hamsters had cardiomyopathy, which is possibly caused by extravascular factors such as metabolic or autonomic nervous disorder although conclusive evidence is lacking.

Increased frequency of apolipoprotein epsilon 4 allele in type II diabetes with hypercholesterolemia

The apolipoprotein E (apoE) phenotype and allele frequencies were examined in type II (non-insulin-dependent) diabetic patients with normolipidemia (n = 134) and hypercholesterolemia (type IIa hyperlipoproteinemia, n = 35; type IIb hyperlipoproteinemia, n = 42). The frequencies of apoE4-present phenotypes (apoE4/3, apoE4/4, and apoE4/2) were highest in the type IIa group (51.4%), followed by the type IIb group (38.1%) and the normolipidemic group (16.4%), respectively, whereas the frequency of the most common phenotype, apoE3/3, was lowest in the type IIa group (48.6%), followed by the type IIb group (61.9%) and the normolipidemic group (79.9%), respectively. There were significant differences in the apoE phenotype frequencies between the normolipidemic group and the type IIa and IIb groups. The frequency of the epsilon 4 allele was significantly higher in the type IIa (28.6%) and IIb (20.2%) groups than in the normolipidemic group (8.9%), whereas the frequency of the epsilon 3 allele was significantly lower in the type IIa (71.4%) and IIb (78.6%) groups than in the normolipidemic group (89.2%). The frequency of the epsilon 2 allele tended to be lower in diabetic patients with hypercholesterolemia. In addition, these frequencies were also examined in nondiabetic subjects (n = 59). The frequency of the epsilon 4 allele tended to be higher in hypercholesterolemic diabetic subjects (24.1%) than in hypercholesterolemic nondiabetic subjects (15.3%). These data suggest that diabetic patients with the epsilon 4 allele may be more susceptible to hypercholesterolemia than diabetic patients without the epsilon 4 allele and possibly nondiabetic subjects with the epsilon 4 allele, although the underlying mechanism is unknown.

Apolipoprotein E polymorphism and hyperlipemia in type II diabetics

The relationship between apolipoprotein E (apoE) polymorphism and plasma lipids and hyperlipemia was investigated in 105 male type II diabetics and 111 male nondiabetics. ApoE phenotypes were determined by a one-dimensional rapid flat gel isoelectric focusing method as described previously. The apoE phenotype frequency in diabetics was similar to that in nondiabetics. The frequency of hyperlipemia was higher in diabetics (56.2%) than in nondiabetics (32.4%). It was highest in the apoE3/2 group of diabetics and nondiabetics, followed by the apoE4/3 and apoE3/3 groups in the order described, indicating that the susceptibility to hyperlipemia differs among the apoE phenotype groups. ApoE3/2 diabetics had significantly higher levels of apoE and very-low-density lipoprotein (VLDL) cholesterol (chol)/VLDL triglyceride (TG) ratios than apoE3/3 diabetics. The effects of diabetes mellitus on plasma lipid levels differed among the various apoE phenotype groups: i.e., plasma total chol and low-density lipoprotein (LDL) chol increased only in apoE3/2 and apoE4/3 diabetics and plasma high-density lipoprotein chol decreased only in apoE3/3 diabetics, as compared with the corresponding apoE phenotype groups of nondiabetics, whereas plasma TG, VLDL TG, and VLDL chol increased in the three apoE phenotype diabetics. Furthermore, an increase of apoEII:apoEIII ratio was observed in apoE3/3 diabetics, particularly in those with hypertriglyceridemia. This study has also shown that the increased apoEII:apoEIII ratio is due to increased sialation of apoE based on the study of sialidase digestion of apo VLDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein E phenotypes and plasma lipids in young and middle-aged subjects

The relationship between apolipoprotein (apo) E phenotypes and the levels of plasma lipid, lipoprotein and apo E in young (mean, 21 years of age) and middle-aged (mean, 49 years of age) subjects was investigated. Apo E phenotypes were determined by a rapid flat gel isoelectric focusing method that we had developed previously. Young subjects with apo E3/2 and E4/3 had significantly higher levels of plasma triglyceride (TG), very low density lipoprotein (VLDL)-TG and VLDL-cholesterol than those with apo E3/3. Middle-aged subjects with apo E3/2 (54.5%) and E4/3 (39.1%) had higher frequency of hyperlipoproteinemia (mainly type IV) than those with apo E3/3 (25.8%). Furthermore, the middle-aged subjects with apo E3/2 had significantly higher levels of plasma TG, VLDL-TG and apo E, and significantly lower levels of plasma high density lipoprotein-cholesterol than those with apo E3/3. These results indicate that apo E phenotype E3/2 and E4/3 are associated with lipid abnormalities even in young subjects, which may be caused by impaired functions of apo E2 and E4.

Anticonvulsant actions of enflurane on epilepsy models in cats

The effects of enflurane on three epilepsy models were studied in cats. The models used were seizures in amygdaloid kindled cats and those induced by bicuculline and penicillin. The authors found that not only a subconvulsive (1.5%) but a convulsive (3.5%) dose of enflurane suppressed the seizures in all models. There was no sign of activation by enflurane of the epileptic focal activities in the dose range studied: the penicillin-induced cortical seizure was suppressed completely, and the threshold dose of bicuculline required to induce seizure in normal cats and the threshold current required to induce seizure in amygdaloid-kindled cats were both increased by both the subconvulsive and convulsive dose of enflurane. The pattern of suppression was, however, dissimilar in each model. It was dose dependent in the case of penicillin-induced seizure, while it was biphasic in several aspects in the seizures of bicuculline-induced and amygdaloid kindled models. For the subconvulsive dose the degrees of increase in the thresholds required to induce seizure in bicuculline-induced and amygdaloid-kindled models were both greater than those for the convulsive dose of enflurane. In spite of such a definite suppression of the excitability of focus, the propagation of amygdaloid after-discharge was facilitated by the convulsive dose. The intensity of convulsion induced by suprathreshold dose of bicuculline was depressed in a dose-related manner. The intensity of the convulsion in the amygdaloid-kindled model was also suppressed when it was estimated by visual inspection of behavior and the degree of activation of the brain electrical activities. The authors conclude that there is little, if any, exacerbation by enflurane of preexisting epileptic foci, the only exception possibly being the case of certain myoclonic type epilepsies such as progressive myoclonic epilepsy and photosensitive epilepsy. This anesthetic probably can be used with a considerable degree of safety for epileptic patients.

The biphasic pattern of the convulsive property of enflurane in cats

The nature of the epileptoid state produced by enflurane was examined in the concentration range 2-5% in cats. A biphasic pattern in the convulsant property was revealed. The ease of induction of seizure by repetitive peripheral stimulation, the duration of seizures, and the activation of reticular neuronal firing during seizure activity showed peak values between 3 and 4%, whereas the values were significantly lower both above and below this range. The amplitudes of the somato-sensory evoked potential also showed a biphasic pattern which correlated well with the severity of the epileptoid state as judged by the aforementioned indices. These findings, when compared with evidence on the actions of other convulsant drugs, and with the known depressant actions of enflurane, suggest a combination of depressant and convulsant properties, the balance of which varies depending on the depth of anaesthesia.

Effects of nitrous oxide on the epileptogenic property of enflurane in cats

A method was developed to standardize the induction of seizure activity during enflurane anaesthesia in cats. The effects of nitrous oxide on the epileptogenic property of enflurane were investigated. A potent anticonvulsant action of nitrous oxide was noted, but partial tolerance to this effect rapidly developed. Some evidence of withdrawal hyperexcitability was also detected. The changes induced by nitrous oxide, despite existing enflurane anaesthesia, suggest that these two anaesthetic agents have different sites or mechanisms of actions.

The tetraphasic action of lidocaine on CNS electrical activity and behavior in cats

Effects of intravenously administered lidocaine on CNS electrical activities were studied in cats with surface and depth electrodes implanted chronically in the brain. Lidocaine was administered using a constant rate infusion pump. The changes induced in CNS electrical activities were correlated with the behavioral changes in the unrestrained freely moving state. During infusion of lidocaine at the rate of 1 mg . kg-1 . min-1, a sequence of changes was observed: the initial stage was represented by diffuse EEG slowing and a decrease of reticular neuronal firing, associated with behavioral depression; the second stage by low-voltage fast-wave EEG and increase of reticular neuronal firing, associated with agitation and/or catatonic behavior; the third stage by reappearance of slow-wave EEG and decrease of reticular neuronal firing, associated with a behavioral depression; and the fourth stage by an epileptiform EEG and increase of reticular neuronal firing associated with generalized tonic or tonic/clonic convulsions. Higher rates of infusion, such as 4, 8, and 15 mg . kg-1 . min-1, diminished the manifestation of the signs of both electrographic and behavioral depression, leaving the signs of excitation unaffected or somewhat enhanced. These findings support the widely prevailing view that recording the surface EEG is not valuable diagnostically in detecting the onset of local anesthetic intoxication, in that the preconvulsive CNS state can be represented by either a high-voltage slow-wave or low-voltage fast-wave pattern in the surface EEG.

E.E.G. activity during halothane anaesthesia in man

The effects of i.v. administration of suxamethonium and noxious stimulation induced by skin incision on the e.e.g. were studied during halothane anaesthesia in man. These stimuli induced activation of the e.e.g. which was represented by either low-voltage fast waves or high-voltage slow waves. The low-voltage fast wave response was observed in adult patients while the high-voltage slow wave response was the predominant response in infants and children aged less than 8 yr. Suxamethonium induced the high-voltage slow wave response in 77% of cases; skin incision in 88%. The e.e.g. of four infants aged less than 60 days did not show activation with either stimulus. Both types of e.e.g. activation were associated with an increase in heart rate, increase in arterial pressure and pupillary dilatation. The possible mechanisms involved in the production of activation of e.e.g. by i.v. administration of suxamethonium are discussed.