Purinergic receptor blockade in the retrotrapezoid nucleus attenuates the respiratory chemoreflexes in awake rats.

AIM: Recent evidence suggests that adenosine triphosfate (ATP)-mediated purinergic signalling at the level of the rostral ventrolateral medulla contributes to both central and peripheral chemoreceptor control of breathing and blood pressure: neurones in the retrotrapezoid nucleus (RTN) function as central chemoreceptors in part by responding to CO2 -evoked ATP release by activation of yet unknown P2 receptors, and nearby catecholaminergic C1 neurones regulate blood pressure responses to peripheral chemoreceptor activation by a P2Y1 receptor-dependent mechanism. However, potential contributions of purinergic signalling in the RTN to cardiorespiratory function in conscious animals have not been tested. METHODS: Cardiorespiratory activity of unrestrained awake rats was measured in response to RTN injections of ATP, and during exposure to hypercapnia (7% CO2 ) or hypoxia (8% O2 ) under control conditions and after bilateral RTN injections of P2 receptor blockers (PPADS or MRS2179). RESULTS: Unilateral injection of ATP into the RTN increased cardiorespiratory output by a P2-receptor-dependent mechanism. We also show that bilateral RTN injections of a non-specific P2 receptor blocker (pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS) reduced the ventilatory response to hypercapnia (7% CO2 ) and hypoxia (8% O2 ) in unanesthetized rats. Conversely, bilateral injections of a specific P2Y1 receptor blocker (MRS2179) into the RTN had no measurable effect on ventilatory responses elicited by hypercapnia or hypoxia. CONCLUSION: These data exclude P2Y1 receptor involvement in the chemosensory control of breathing at the level of the RTN and show that ATP-mediated purinergic signalling contributes to central and peripheral chemoreflex control of breathing and blood pressure in awake rats.

Brainstem areas activated by intermittent apnea in awake unrestrained rats.

We investigated the role of the autonomic nervous system to cardiovascular responses to obstructive apnea in awake, unrestrained rats, and measured expression of Fos induced by apnea in the brainstem. We implanted a tracheal balloon contained in a rigid tube to allow the induction of apnea without inducing pain in the trachea. During bouts of 15s of apnea, heart rate fell from 371±8 to 161±11bpm (mean±SEM, n=15, p<0.01) and arterial pressure increased from 115±2 to 131±4mmHg (p<0.01). Bradycardia was due to parasympathetic activity because it was blocked by the muscarinic antagonist, methylatropine. The pressor response was due to vasoconstriction caused by sympathetic activation because it was blocked by the α1 antagonist, prazosin. Apnea induced Fos expression in several brainstem areas involved in cardiorespiratory control such as the nucleus of the solitary tract (NTS), ventrolateral medulla (VLM), and pons. Ligation of the carotid body artery reduced apnea-induced bradycardia, blocked heart rate responses to i.v. injection of cyanide, reduced Fos expression in the caudal NTS, and increased Fos expression in the rostral VLM. In conclusion, apnea activates neurons in regions that process signals from baroreceptors, chemoreceptors, pulmonary receptors, and regions responsible for autonomic and respiratory activity both in the presence and absence of carotid chemoreceptors.

Respiratory deficits in a rat model of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of the dopaminergic nigrostriatal pathway. In addition to deficits in voluntary movement, PD involves a disturbance of breathing regulation. However, the cause and nature of this disturbance are not well understood. Here, we investigated breathing at rest and in response to hypercapnia (7% CO2) or hypoxia (8% O2), as well as neuroanatomical changes in brainstem regions essential for breathing, in a 6-hydroxydopamine (6-OHDA) rat model of PD. Bilateral injections of 6-OHDA (24µg/µl) into the striatum decreased tyrosine hydroxylase (TH(+))-neurons in the substantia nigra pars compacta (SNpc), transcription factor phox2b-expressing neurons in the retrotrapezoid nucleus and neurokinin-1 receptors in the ventral respiratory column. In 6-OHDA-lesioned rats, respiratory rate was reduced at rest, leading to a reduction in minute ventilation. These animals also showed a reduction in the tachypneic response to hypercapnia, but not to hypoxia challenge. These results suggest that the degeneration of TH(+) neurons in the SNpc leads to impairment of breathing at rest and in hypercapnic conditions. Our data indicate that respiratory deficits in a 6-OHDA rat model of PD are related to downregulation of neural systems involved in respiratory rhythm generation. The present study suggests a new avenue to better understand the respiratory deficits observed in chronic stages of PD.

Acute exercise-induced activation of Phox2b-expressing neurons of the retrotrapezoid nucleus in rats may involve the hypothalamus.

The rat retrotrapezoid nucleus (RTN) contains neurons that have a well-defined phenotype characterized by the presence of vesicular glutamate transporter 2 (VGLUT2) mRNA and a paired-like homeobox 2b (Phox2b)-immunoreactive (ir) nucleus and the absence of tyrosine hydroxylase (TH). These neurons are important to chemoreception. In the present study, we tested the hypothesis that the chemically-coded RTN neurons (ccRTN) (Phox2b(+)/TH(-)) are activated during an acute episode of running exercise. Since most RTN neurons are excited by the activation of perifornical and lateral hypothalamus (PeF/LH), a region that regulates breathing during exercise, we also tested the hypothesis that PeF/LH projections to RTN neurons contribute to their activation during acute exercise. In adult male Wistar rats that underwent an acute episode of treadmill exercise, there was a significant increase in c-Fos immunoreactive (c-Fos-ir) in PeF/LH neurons and RTN neurons that were Phox2b(+)TH(-) (p<0.05) compared to rats that did not exercise. Also the retrograde tracer Fluoro-Gold that was injected into RTN was detected in c-Fos-ir PeF/LH (p<0.05). In summary, the ccRTN neurons (Phox2b(+)TH(-)) are excited by running exercise. Thus, ccRTN neurons may contribute to both the chemical drive to breath and the feed-forward control of breathing associated with exercise.

An epiphyseal osteochondroma causing mechanical symptoms in the knee.

A case of an epiphyseal osteochondroma in the anteromedial aspect of left tibia in a 4 year old girl, who was presented with knocking between knees and limping. Surgical excision of this bony growth was curative and resolved the mechanical symptoms completely. Interesting clinical and imaging features are presented. The possibility of solitary epiphyseal osteochondroma should be kept in mind for any bony lesion close to the joint, especially in a young child. Early excision of the lesion is recommended to avoid intra-articular development and mechanical block to joint motion.

Pontomedullary and hypothalamic distribution of Fos-like immunoreactive neurons after acute exercise in rats.

During exercise, intense brain activity orchestrates an increase in muscle tension. Additionally, there is an increase in cardiac output and ventilation to compensate the increased metabolic demand of muscle activity and to facilitate the removal of CO(2) from and the delivery of O(2) to tissues. Here we tested the hypothesis that a subset of pontomedullary and hypothalamic neurons could be activated during dynamic acute exercise. Male Wistar rats (250-350 g) were divided into an exercise group (n=12) that ran on a treadmill and a no-exercise group (n=7). Immunohistochemistry of pontomedullary and hypothalamic sections to identify activation (c-Fos expression) of cardiorespiratory areas showed that the no-exercise rats exhibited minimal Fos expression. In contrast, there was intense activation of the nucleus of the solitary tract, the ventrolateral medulla (including the presumed central chemoreceptor neurons in the retrotrapezoid/parafacial region), the lateral parabrachial nucleus, the Kölliker-Fuse region, the perifornical region, which includes the perifornical area and the lateral hypothalamus, the dorsal medial hypothalamus, and the paraventricular nucleus of the hypothalamus after running exercise. Additionally, we observed Fos immunoreactivity in catecholaminergic neurons within the ventrolateral medulla (C1 region) without Fos expression in the A2, A5 and A7 neurons. In summary, we show for the first time that after acute exercise there is an intense activation of brain areas crucial for cardiorespiratory control. Possible involvement of the central command mechanism should be considered. Our results suggest whole brain-specific mobilization to correct and compensate the homeostatic changes produced by acute exercise.

Electron diffraction based analysis of phase fractions and texture in nanocrystalline thin films, part III: application examples.

In this series of articles, a method is presented that performs (semi)quantitative phase analysis for nanocrystalline transmission electron microscope samples from selected area electron diffraction (SAED) patterns. Volume fractions and degree of fiber texture are determined for the nanocrystalline components. The effect of the amorphous component is minimized by empirical background interpolation. First, the two-dimensional SAED pattern is converted into a one-dimensional distribution similar to X-ray diffraction. Volume fractions of the nanocrystalline components are determined by fitting the spectral components, calculated for the previously identified phases with a priori known structures. These Markers are calculated not only for kinematic conditions, but the Blackwell correction is also applied to take into account dynamic effects for medium thicknesses. Peak shapes and experimental parameters (camera length, etc.) are refined during the fitting iterations. Parameter space is explored with the help of the Downhill-SIMPLEX. The method is implemented in a computer program that runs under the Windows operating system. Part I presented the principles, while part II elaborated current implementation. The present part III demonstrates the usage and efficiency of the computer program by numerous examples. The suggested experimental protocol should be of benefit in experiments aimed at phase analysis using electron diffraction methods.

The Janus face of reactive oxygen species in resistance and susceptibility of plants to necrotrophic and biotrophic pathogens.

Plant pathogens can be divided into biotrophs and necrotrophs according to their different life styles; biotrophs prefer living, while necrotrophs prefer dead cells for nutritional purposes. Therefore tissue necrosis caused by reactive oxygen species (ROS) during pathogen infection increases host susceptibility to necrotrophic, but resistance to biotrophic pathogen. Consequently, elevation of antioxidant capacity of plants enhances their tolerance to development of necroses caused by necrotrophic pathogens. Plant hormones can strongly influence induction of ROS and antioxidants, thereby influencing susceptibility or resistance of plants to pathogens. Pathogen-induced ROS themselves are considered as signaling molecules. Generally, salicylic acid (SA) signaling induces defense against biotrophic pathogens, whereas jasmonic acid (JA) against necrotrophic pathogens. Furthermore pathogens can modify plant's defense signaling network for their own benefit by changing phytohormone homeostasis. On the other hand, ROS are harmful also to the pathogens, consequently they try to defend themselves by elevating antioxidant activity and secreting ROS scavengers in the infected tissue. The Janus face nature of ROS and plant cell death on biotrophic and on necrotrophic pathogens is also supported by the experiments with BAX inhibitor-1 and the mlo mutation of Mlo gene in barley. It was found that ROS and elevated plant antioxidant activity play an important role in systemic acquired resistance (SAR) and induced systemic resistance (ISR), as well as in mycorrhiza induced abiotic and biotic stress tolerance of plants.

An open-label trial of rituximab therapy in pulmonary alveolar proteinosis.

Rituximab, a monoclonal antibody directed against the B-lymphocyte antigen CD20, has shown promise in several autoimmune disorders. Pulmonary alveolar proteinosis (PAP) is an autoimmune disorder characterised by autoantibodies to granulocyte-macrophage colony-stimulating factor (GM-CSF). An open-label, proof-of-concept phase II clinical trial was conducted in 10 PAP patients. The intervention consisted of two intravenous infusions of rituximab (1,000 mg) 15 days apart. Bronchoalveolar lavage (BAL) fluid and peripheral blood samples were collected. The primary outcome was improvement in arterial blood oxygenation. Both arterial oxygen tension and alveolar-arterial oxygen tension difference in room air improved in seven out of the nine patients completing the study. Lung function and high-resolution computed tomography scans, which were secondary outcomes, also improved. Peripheral blood CD19+ B-lymphocytes decreased from mean ± sem 15 ± 2% to <0.05% (n = 10) 15 days post-therapy. This decrease persisted for 3 months in all patients; at 6 months, CD19+ B-cells were detected in four out of seven patients (5 ± 2%). Total anti-GM-CSF immunoglobulin (Ig)G levels from baseline to 6 months were decreased in BAL fluids (n = 8) but unchanged in sera (n = 9). In this PAP cohort: 1) rituximab was well-tolerated and effectively ameliorated lung disease; and 2) reduction in anti-GM-CSF IgG levels in the lung correlated with disease changes, suggesting that disease pathogenesis is related to autoantibody levels in the target organ.

Transgenic production of cytokinin suppresses bacterially induced hypersensitive response symptoms and increases antioxidative enzyme levels in Nicotiana spp.

Responses of cytokinin overproducing transgenic Nicotiana plants to infections with compatible and incompatible Pseudomonas syringae pathovars were compared. Plants used were transformed with the ipt(isopentenyl transferase) gene that catalyzes the synthesis of cytokinin. In cytokinin overproducing lines that carry the ipt gene fused to the CaMV 35S (Nt+ipt), the wound-inducible proteinase inhibitor II (Ntx+ipt), or the light-inducible Rubisco small subunit protein (Npl+ipt) promoter, development of the hypersensitive response (HR) after infection with incompatible bacteria (P. syringae pv. tomato) was significantly inhibited as compared to the untransformed (Nt) controls. Over a 12 h period following inoculation, P. syrinage pv. tomato populations were slightly reduced in leaves of the cytokinin-overproducing Nt-ipt line compared with the Nt control. When the compatible P. syringae. pv. tabaci was used to infect the ipt transformed lines, slight or no significant differences in necrosis development were observed. Following infection, the titer of P. syringae pv. tabaci increased rapidly in both the transgenic and control lines but was higher in Nt+ipt plants. Leaf superoxide dismutase and catalase enzyme activities were about 60% higher in ipt leaf extracts than in the controls. This augmented antioxidant capacity likely decreased the amount of H(2)O(2) that may be associated with the higher tolerance of plants to pathogen-induced necrosis. In addition, the Nt+ipt lines had a significantly lower molar ratio of free sterols to phospholipids. The more stable membrane lipid composition and the higher antioxidant capacity likely contributed to the suppressed HR symptoms in the cytokinin overproducing Nt+ipt plants. In conclusion, the overproduction of cytokinins in tobacco appears to suppress the HR symptoms induced by incompatible bacteria.

Treatment of malignant glioma cells with the transfer of constitutively active caspase-6 using the human telomerase catalytic subunit (human telomerase reverse transcriptase) gene promoter.

Because the apoptotic pathway is often disrupted in tumor cells, its genetic restoration is a very attractive approach for the treatment of tumors. To treat malignant gliomas with this approach, it would be preferred to restrict induction of apoptosis to tumor cells by establishing a tumor-specific expression system. Telomerase is an attractive target because the vast majority of malignant gliomas have telomerase activity whereas normal brain cells do not. Activation of telomerase is tightly regulated at the transcriptional level of the telomerase catalytic subunit [human telomerase reverse transcriptase, (hTERT)]. Therefore, we hypothesized that using a hTERT promoter-driven vector system, an apoptosis-inducible gene may be preferentially restricted to telomerase- or hTERT-positive tumor cells. In this study, we constructed an expression vector consisting of the constitutively active caspase-6 (rev-caspase-6) under the hTERT promoter (hTERT/rev-caspase-6) and then investigated its antitumor effect on malignant glioma cells. The rationale for using the rev-caspase-6 gene is because it induces apoptosis independent of the initiator caspases. We demonstrated that the hTERT/rev-caspase-6 construct induced apoptosis in hTERT-positive malignant glioma cells, but not in hTERT-negative astrocytes, fibroblasts, and alternative lengthening of telomeres cells. In addition, the growth of s.c. tumors in nude mice was significantly suppressed by the treatment with hTERT/rev-caspase-6 construct. The present results strongly suggest that the telomerase-specific transfer of the rev-caspase-6 gene under the hTERT promoter is a novel targeting approach for the treatment of malignant gliomas.

Chloride distribution in the CA1 region of newborn and adult hippocampus by light microscopic histochemistry.

GABA, the main inhibitory neurotransmitter in the central nervous system, exerts its effect by rendering the postsynaptic GABAA receptors permeable to chloride ions. Thus, depolarizing or excitatory effects of GABA, experienced in early postnatal life or in certain regions and/or conditions of the adult brain, is thought to be associated with a reversed transmembrane chloride gradient. However, there is only limited direct information about the correlation of the actual excitatory versus inhibitory effects of GABA and the local chloride distribution. Precipitation of chloride with silver is a potential way to immobilize and visualize chloride ions in biological tissue. We examined the applicability of light microscopic histochemistry, based on trapping tissue chloride with silver ions during freeze-substitution or aldehyde fixation, to visualize the chloride distribution in hippocampal slices. The freeze-substitution procedure yielded better chloride retention while with aldehyde fixation tissue preservation was more appropriate. Both methods were qualitative only, had limited applicability to the superficial 20-30 microns of slices, but were able to demonstrate a reduced extracellular-to-intracellular chloride gradient in the CA1 pyramidal neurons of the newborn hippocampus as compared to adult animals. In the 4-aminopyridine model of epilepsy, redistribution of chloride from extracellular to intracellular space could also be demonstrated.

Epidermal growth factor regulates astrocyte expression of the interleukin-4 receptor via a MAPK-independent pathway.

Human astrocytes express the interleukin (IL)-4 receptor alpha chain (IL-4R alpha) in vitro and in vivo but mechanisms governing astrocyte IL-4R alpha expression have not been established. We hypothesized that epidermal growth factor (EGF) and IL-4, agents that profoundly affect astrocyte proliferation, might also alter IL-4R alpha expression. Exposure to EGF for 24 h enhanced IL-4R alpha mRNA levels; in contrast, IL-4 yielded no increase. Immunoblotting demonstrated that EGF but not IL-4 increased astrocyte IL-4R alpha protein after 2--4 days of exposure. Similarly, EGF but not IL-4 strongly activated phosphorylation of p42/p44 extracellular regulated kinase isoforms, a reaction blocked by the mitogen-activated protein kinase (MAPK) inhibitor, PD98059. PD98059 also blocked EGF-stimulated DNA synthesis but not IL-4R alpha mRNA levels, while antibody to the EGF receptor (erbB1) blocked both EGF effects. Data suggest that astrocyte IL-4R alpha expression is upregulated by EGF but not by IL-4 in an EGF-receptor-dependent manner and that mechanisms are independent of MAPK activation.

In vivo expression of the interleukin 4 receptor alpha by astrocytes in epilepsy cerebral cortex.

We reported previously that non-neoplastic astrocytes (derived from brain tissues of patients with epilepsy) expressed interleukin 4 receptor alpha (IL-4Ralpha) and responded to interleukin 4 (IL-4) in culture. To determine whether reactivity of cultured astrocytes was relevant to primary tissue, we investigated IL-4Ralpha expression in specimens of non-neoplastic cerebral cortex removed for surgical treatment of intractable epilepsy compared to specimens of glial tumours, which have been reported to contain IL-4Ralpha. Freshly frozen tissues from eight cases (four epilepsy, four malignant astrocytoma) were evaluated for IL-4Ralpha expression by reverse-transcriptase polymerase chain reaction (RT-PCR), Southern blotting, and double-labelled immunohistochemistry with antibodies to IL-4Ralpha and glial fibrillary acidic protein (GFAP). IL-4Ralpha mRNA was detectable in both non-neoplastic and neoplastic tissues, whereas interleukin 2 receptor gamma chain (IL-2Rgammac) mRNA was not found. By immunohistochemistry, IL-4Ralpha protein co-localized to cells displaying GFAP and astrocytic morphology in epilepsy tissues. As anticipated, IL-4Ralpha was detectable in astrocytoma, but, surprisingly, was also observed in GFAP-positive, non-neoplastic "reactive" astrocytes adjacent to tumour. Results are consistent with the concept that non-neoplastic epilepsy astrocytes express IL-4Ralpha in situ, thus confirming in vitro studies and implying IL-4 sensitivity in vivo.

2-5A antisense telomerase RNA therapy for intracranial malignant gliomas.

Malignant gliomas are the most common intracranial tumors and are considered incurable. Therefore, exploration of novel therapeutic modalities is essential. Telomerase is a ribonucleoprotein enzyme that is detected in the vast majority of malignant gliomas but not in normal brain tissues. We, therefore, hypothesized that telomerase inhibition could be a very promising approach for the targeted therapy of malignant gliomas. Thus, 2-5A (5'-phosphorylated 2'-5'-linked oligoadenylate)-linked antisense against human telomerase RNA component (2-5A-anti-hTER) was investigated for its antitumor effect on an intracranial malignant glioma model. 2-5A is a mediator of one pathway of IFN actions by activating RNase L, resulting in RNA degradation. By linking 2-5A to antisense, RNase L degrades the targeted RNA specifically and effectively. Prior to the experiments using intracranial tumor models in nude mice, we modified the in vitro and in vivo treatment modality of 2-5A-anti-hTER using a cationic liposome to enhance the effect of 2-5A-anti-hTER. Here we demonstrate that 2-5A-anti-hTER complexed with a cationic liposome reduced the viability of five malignant glioma cell lines to 20-43% within 4 days but did not influence the viability of cultured astrocytes lacking telomerase. Furthermore, treatment of intracranial malignant gliomas in nude mice with 2-5A-anti-hTER was therapeutically effective compared with the control (P < 0.01). These findings clearly suggest the therapeutic potentiality of 2-5A-anti-hTER as a novel approach for the treatment of intracranial malignant gliomas.

Interleukin-13 sensitivity and receptor phenotypes of human glial cell lines: non-neoplastic glia and low-grade astrocytoma differ from malignant glioma.

Many of the actions and receptor components of interleukin-13 (IL-13), a pleiotrophic cytokine with immunotherapeutic potential, are shared with IL-4. Because human low-grade astrocytoma cells express IL-4 receptors and their growth is arrested by IL-4, we speculated that IL-13 sensitivity and receptor expression might also be present. The purpose of the current study was to investigate IL-13 receptor components and sensitivity in a series of glial cell lines derived from adult human non-neoplastic cerebral cortex, low-grade astrocytoma, anaplastic astrocytoma, and glioblastoma multiforme. Unlike peripheral blood lymphocytes (PBL), glial cells did not express IL-2 receptor gamma chain. IL-13 receptor alpha-1 (IL-13Ralpha1), however, was present in 11/13 glial lines and PBL. Deficient cell lines were all glioblastoma-derived. All anaplastic astrocytoma and glioblastoma but not other glial lines or PBL expressed IL-13 receptor alpha-2 (IL-13Ralpha2). In non-neoplastic glia, low-grade, and anaplastic astrocytoma, IL-13 decreased DNA synthesis, an effect reversible with antibody to IL-4Ralpha. Results indicate that low-grade astrocytoma cells resemble non-neoplastic glia in terms of IL-13 sensitivity and IL-4Ralpha/IL-13Ralpha1 receptor profile but alterations occur with malignant progression. Glioblastoma cells were uniformly insensitive to IL-13 and, unlike other glia, failed to phosphorylate STAT6 after IL-13 challenge. Data suggest that IL-13 and analysis of IL-13 receptors may have clinical application in glial tumors.

Anti-sense oligonucleotide of p21(waf1/cip1) prevents interleukin 4-mediated elevation of p27(kip1) in low grade astrocytoma cells.

Elevation of the cyclin-dependent kinase (cdk) inhibitor, p27(kip1) is necessary for Interleukin (IL)-4-mediated growth arrest of human low grade astrocytoma (RTLGA) cells and occurs at 24 h of treatment. Pathways involved in IL4 alteration of p27(kip1) are unknown, however. Here we investigated whether other cdk inhibitors contributed to the actions of IL-4 on RTLGA cells. By 12 h of IL-4 treatment, both cdk4 and cdk2 kinase activities against the retinoblastoma protein (pRb) were reduced and nuclear entry of pRb was prohibited. Twelve-hour cdk complexes contained elevated p21(waf1/cip1) but not p27(kip1), p15(ink4B) or p16(ink4A). IL-4 increased p21(waf1/cip1) but not p27(kip1) mRNA levels, and stimulated luciferase activity of a p21(waf1/cip1) promoter-luciferase reporter. In p53-mutant WITG3 cells, IL-4 did not alter p21(waf1/cip1) mRNA and promoter-luciferase activity or p27(kipl) protein, suggesting a need for functional p53. STAT6 phosphorylation by IL-4, however, occurred in both p53-mutant WITG3 and p53-functional RTLGA cells. Pre-treatment of RTLGA with anti-sense but not missense p21(waf1/cip1) oligonucleotide prior to IL-4: (a) restored cdk activities; (b) reduced cdk4-associated p21(waf1/cip1) levels; (c) prevented p27(kipl) elevation; and (d) reversed growth arrest. These results are the first to suggest that p21(waf1/cip1) is essential for IL-4-mediated elevation of p27(kip) and growth arrest of astrocytoma cells.

Anticonvulsive effect of AMPA receptor antagonist GYKI 52466 on 4-aminopyridine-induced cortical ictal activity in rat.

The effect of GYKI-52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine), a selective antagonist of AMPA receptor was investigated on the generation and manifestation of 4-aminopyridine-induced cortical epileptiform activity. In vivo experiments were carried out on pentobarbital-anaesthetised adult rats. Ictal epileptiform activity was induced by local application of 4-aminopyridine (4-Ap) to the surface of somatosensory cortex. In one group of animals, GYKI 52466 was administered intraperitoneally before 4-Ap application, in another group, the already active primary focus was treated locally by GYKI 52466. Different parameters of epileptic activity were measured and compared in GYKI 52466-treated and control animals. The results demonstrate that GYKI 52466 exerts anticonvulsive effects on both the induction and the expression of epileptiform activity, by delaying the onset of the first ictal event, decreasing the numbers and duration of ictal periods, as well as the amplitudes of epileptiform discharges both in the primary and mirror foci. However, seizure propagation to other cortical areas seemed to be facilitated. The anticonvulsive effect of GYKI 52466 was stronger in pretreatment than in treatment of ongoing epileptiform activity. As a conclusion, it is supposed that AMPA receptors are probably more dominant in the induction of epileptiform activity than in the maintenance of it, mainly through the activation of corticothalamo-cortical networks. It is also supposed that the cortical inhibition which blocks the propagation of epileptiform process might be activated mainly through non-N-methyl-D-aspartate receptors.