Eicosanoid formation in the rat cerebral cortex. Contribution of neurons and glia

Involvement of presynaptic TRPV1 channels in prostaglandin E2-induced facilitation of spontaneous synaptic transmission in the rat spinal trigeminal subnucleus caudalis

Prostaglandin E₂ (PGE₂) synthesized in the central nervous system influences various physiological functions including nociception. Recently, we have demonstrated that PGE₂ facilitates spontaneous synaptic transmission through presynaptic EP1 receptors in the spinal trigeminal subnucleus caudalis (Vc) neurons that receive nociceptive signals from the orofacial area. Increasing evidence suggests that the action of PGE₂ is related to activation of transient receptor potential vanilloid 1 (TRPV1) channels. The present study investigated whether TRPV1 channels contribute to the facilitatory effect of PGE₂ on synaptic transmission in the Vc neurons. Spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs) were recorded from Vc neurons in the rat brainstem slice by whole-cell patch-clamp mode. Superfusion of capsaicin (0.3, 1.0 μM) concentration-dependently increased the frequency of both sEPSCs and sIPSCs without any significant effect on their amplitude. The effect of capsaicin was completely abolished by a TRPV1 channel blocker AMG9810 (0.1 μM). PGE₂ (5.0 μM) increased the frequency of sEPSCs and sIPSCs. This facilitatory effect of PGE₂ was attenuated by AMG9810 and in neurons desensitized by repeated application of capsaicin. While a low concentration of either PGE₂ (1.0 μM) or capsaicin (0.1 μM) had an insignificant effect on the sEPSCs and sIPSCs, co-application of these drugs increased their frequency. The present study demonstrated involvement of the presynaptic TRPV1 channels in PGE₂-induced facilitation of spontaneous synaptic transmissions and suggests interaction of PGE₂ with TRPV1 channels in modification of nociceptive signals from the orofacial area to the Vc neurons.

A molecular pathway analysis stresses the role of inflammation and oxidative stress towards cognition in schizophrenia

Cognitive processes have a genetic component and are impaired in Schizophrenia (SKZ). The exact nature of such impairment escapes definition. The aim of the present contribution was the identification of the molecular pathways enriched with mutations (SNPs) associated with cognitive performance during antipsychotic treatment. 765 individuals from the CATIE study, males = 559, mean age 40.93 ± 11.03 were included. Working memory and the verbal memory were the evaluated outcomes. A mixed regression model for repeated measures served in R for clinical and molecular pathway analysis. The analysis of quality was conducted under the following criteria: minor allele frequency >0.01, genotype call rate >95%, missing data frequency <5%, Hardy-Weimberg equilibrium threshold >0.0001. The inflation factor was controlled by lambda values. Input for the pathway analysis was SNPs at a p level <0.05 of association genome-wide. Gender, age, education and the duration of the disease were the clinical and socio-demographic variables associated with the cognitive performance. 4268977 SNPs were available after imputation and quality analysis. Pathways related to inflammation and oxidation were the most strongly associated with verbal memory and working memory at a conservative adjusted p value < 0.01. We report that inflammation and in particular the pathway associated with arachidonic acid was enriched in mutations associated with poorer performance at the verbal memory and working memory tasks in SKZ patients.

Effects of prostaglandin E2 on synaptic transmission in the rat spinal trigeminal subnucleus caudalis

The spinal trigeminal subnucleus caudalis (Vc) receives preferentially nociceptive afferent signals from the orofacial area. Nociceptive stimuli to the orofacial area induce cyclooxygenase both peripherally and centrally, which can synthesize a major prostanoid prostaglandin E2 (PGE2) that implicates in diverse physiological functions. To clarify the roles of centrally-synthesized PGE2 in nociception, effects of exogenous PGE2 on synaptic transmission in the Vc neurons were investigated in the rat brainstem slice. Spontaneously occurring excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs) were recorded, respectively, under pharmacological blockade of inhibitory and excitatory transmission by whole-cell patch-clamp mode. Perfusion of PGE2 (1-5 μM) increased the frequency of sIPSCs in a concentration-dependent manner but had no significant effect on the amplitude. Similarly to the effects on sIPSCs, PGE2 increased the sEPSC frequency without any effect on the amplitude. These facilitatory effects of PGE2 on spontaneous synaptic transmissions were blocked by an EP1 antagonist SC19220 but not by an EP4 antagonist AH23848. Electrical stimulation of the trigeminal tract evoked short latency EPSCs (eEPSCs) in the Vc neurons. PGE2 (5 μM) was ineffective on the eEPSCs. The present study demonstrated that PGE2 facilitated spontaneous synaptic transmissions in the Vc neurons through activating the presynaptic EP1 receptors but had no effect on the trigeminal tract-mediated excitatory transmission. These results suggest that centrally-synthesized PGE2 modifies the synaptic transmission in the Vc region, thereby contributing to the processing of nociceptive signals originated from the orofacial area.

Prostaglandin E2 depresses solitary tract-mediated synaptic transmission in the nucleus tractus solitarius

Prostaglandin E(2) (PGE(2)) is a prototypical inflammatory mediator that excites and sensitizes cell bodies [Kwong K, Lee LY (2002) PGE(2) sensitizes cultured pulmonary vagal sensory neurons to chemical and electrical stimuli. J Appl Physiol 93:1419-1428; Kwong K, Lee LY (2005) Prostaglandin E(2) potentiates a tetrodotoxin (TTX)-resistant sodium current in rat capsaicin-sensitive vagal pulmonary sensory neurons. J Physiol 56:437-450] and peripheral nerve terminals [Ho CY, Gu Q, Hong JL, Lee LY (2000) Prostaglandin E (2) enhances chemical and mechanical sensitivities of pulmonary C fibers in the rat. Am J Respir Crit Care Med 162:528-533] of primary vagal sensory neurons. Nearly all central nerve terminals of vagal afferents are in the nucleus tractus solitarius (NTS), where they operate with a high probability of release [Doyle MW, Andresen MC (2001) Reliability of monosynaptic sensory transmission in brain stem neurons in vitro. J Neurophysiol 85:2213-2223]. We studied the effect of PGE(2) on synaptic transmission between tractus solitarius afferent nerve terminals and the second-order NTS neurons in brain stem slices of Sprague-Dawley rats. Whole-cell patch recording in voltage clamp mode was used to study evoked excitatory postsynaptic glutamatergic currents (evEPSCs) from NTS neurons elicited by electrical stimulation of the solitary tract (ST). In 34 neurons, bath-applied PGE(2) (200 nM) decreased the evEPSC amplitude by 49+/-5%. In 22 neurons, however, PGE(2) had no effect. We also tested 15 NTS neurons for capsaicin sensitivity. Seven neurons generated evEPSCs that were equally unaffected by PGE(2) and capsaicin. Conversely, evEPSCs of the other eight neurons, which were PGE(2)-responsive, were abolished by 200 nM capsaicin. Furthermore, the PGE(2-)induced depression of evEPSCs was associated with an increase in the paired pulse ratio and a decrease in both the frequency and amplitude of the spontaneous excitatory postsynaptic currents (sEPSCs) and TTX-independent spontaneous miniature excitatory postsynaptic currents (mEPSCs). These results suggest that PGE(2) acts both presynaptically on nerve terminals and postsynaptically on NTS neurons to reduce glutamatergic responses.

Relationship between cyclooxygenase-2 and nitric oxide synthase-2 in rat cortex after stress

Many studies have focused on the relationships between distinct enzymatic sources of oxidative mediators. Recently, we have shown that cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (NOS-2) isoforms are up-regulated and account for oxidative damage in brain after stress. To assess the time course of these events, we have used adult male Wistar rats, some of which were immobilized for 6 h. Whereas pretreatment with the specific COX-2 inhibitor NS-398 (5 mg/kg i.p.) decreased Ca2+-independent NOS activity after 6 h of stress, pretreatment with the specific NOS-2 inhibitor 1400 W (4 mg/kg i.p.) did not decrease prostaglandin E2 (PGE2) accumulation induced by stress after 6 h. The observed effects of NS-398 and 1400 W were independent of the general response to stress--neither drug modified stress-induced corticosterone response--which might indicate a possible adaptive role for COX-2 and NOS-2 pathways in this situation. These findings are discussed as possible therapeutic targets in the context of neuropsychiatric disorders related to stress.

Induction of cyclooxygenase-2 accounts for restraint stress-induced oxidative status in rat brain

Cyclooxygenase (COX) is the rate-limiting enzyme in the metabolism of arachidonic acid into prostanoids. Although it is constitutively expressed in brain neurons, the inducible isoform (COX-2) is also upregulated in pathological conditions such as seizures, ischemia or some degenerative diseases. To assess whether COX-2 is regulated after stress, we have used adult male Wistar rats, some of which were immobilized during 6 h. An increase in PGE2 concentration occurs in brain cortex after 2-6 h of the onset of stress as well as an enhancement of COX-2 protein. Immunohistochemical studies indicate that COX-2 is expressed in the cortex and hippocampus after stress in cells with morphology of neurons. Administration of PDTC (150 mg/kg), an inhibitor of the transcription factor NF-kappaB or MK-801 (0.2 mg/kg), an N-methyl-D-aspartate receptor blocker, prevents both stress-induced increase in COX-2 activity and protein levels, suggesting an implication of these factors in the mechanism by which stress induces COX-2 in brain. To assess if COX-2 accounts for the oxidative status seen in brain after stress, a group of animals were i.p. injected with NS-398, a specific COX-2 inhibitor 1 h prior to the onset of stress. NS-398 (5 mg/kg) decreases stress-induced malondialdehyde accumulation in cortex as well as prevents the stress-induced oxidation of glutathione. Finally, NS-398 reduced Ca2+-independent inducible nitric oxide synthase (iNOS, NOS-2) activity and lowered the stress-induced accumulation of NO metabolite levels in cortex. These effects of NS-398 seem to be due to the specific inhibition of COX-2, since it has no effect on stress-induced corticosterone release, glutamate release, and NF-kappaB activation. These findings are discussed as possible damaging and/or adaptive roles for stress-induced COX-2 in the brain.

Oncostatin M enhances the expression of prostaglandin E2 and cyclooxygenase-2 in astrocytes: synergy with interleukin-1beta, tumor necrosis factor-alpha, and bacterial lipopolysaccharide

Oncostatin M (OSM), a cytokine of the interleukin-6 family, is expressed in rheumatoid arthritis, multiple sclerosis, multiple myeloma, and other inflammatory and neoplastic conditions. Prostaglandin E(2) (PGE(2)), an eicosanoid also associated with inflammation and cancer, has recently been shown to induce OSM expression. We report here that OSM in turn induces PGE(2) production by astrocytes and astroglioma cells. More importantly, in combination with the inflammatory mediators IL-1beta, tumor necrosis factor-alpha, and lipopolysaccharide, OSM exhibits a striking synergy, resulting in up to 50-fold higher PGE(2) production by astrocytes, astroglioma, and neuroblastoma cell lines. Enhanced PGE(2) production by OSM and IL-1beta treatment is explained by their effect on cyclooxygenase-2 (COX-2), an enzyme that catalyzes the committed step in PGE(2) synthesis. Of the enzymes involved in PGE(2) biosynthesis, only COX-2 mRNA and protein levels are synergistically amplified by OSM and IL-1beta. Nuclear run-on assays demonstrate that OSM and IL-1beta synergistically upregulate transcription of the COX-2 gene, and the mRNA stability assay indicates that COX-2 mRNA is posttranscriptionally stabilized by OSM and IL-1beta. To effect synergy on the PGE(2) level, OSM signals in part through its gp130/OSMRbeta receptor, since neutralizing antibodies against gp130 and OSMRbeta, but not LIFRbeta, decrease PGE(2) production in response to OSM plus IL-1beta. SB202190 and U0126, inhibitors of p38 MAPK and ERK1/2 activation, respectively, inhibit IL-1beta and OSM upregulation of COX-2 and PGE(2), indicating that these MAPK cascades are utilized by both stimuli. This mechanism of PGE(2) amplification may be active in brain pathologies where both OSM and IL-1beta are present, such as glioblastomas and multiple sclerosis.

Glutathione pathways in the brain

The antioxidant glutathione (GSH) is essential for the cellular detoxification of reactive oxygen species in brain cells. A compromised GSH system in the brain has been connected with the oxidative stress occuring in neurological diseases. Recent data demonstrate that besides intracellular functions GSH has also important extracellular functions in brain. In this respect astrocytes appear to play a key role in the GSH metabolism of the brain, since astroglial GSH export is essential for providing GSH precursors to neurons. Of the different brain cell types studied in vitro only astrocytes release substantial amounts of GSH. In addition, during oxidative stress astrocytes efficiently export glutathione disulfide (GSSG). The multidrug resistance protein 1 participates in both the export of GSH and GSSG from astrocytes. This review focuses on recent results on the export of GSH and GSSG from brain cells as well as on the functions of extracellular GSH in the brain. In addition, implications of disturbed GSH pathways in brain for neurodegenerative diseases will be discussed.

Pathogenesis of hypoxic-ischemic cerebral injury in the term infant: current concepts

Multiple, biochemical cascades contribute to the pathogenesis of neonatal hypoxic-ischemic brain injury. This article summarizes experimental evidence that supports the role of excitatory amino acids, calcium, free radicals, nitric oxide, proinflammatory cytokines, and bioactive lipids. Specific vulnerabilities that distinguish the response of the immature brain from that of the mature brain are highlighted. These include increased susceptibility to excitotoxicity and free radical injury, greater tendency to apoptotic death, and heightened vulnerability of developing oligodendrocytes. Available supportive evidence from human studies is also included. Implications for clinical neuroprotective strategies are discussed.

Differential modulation of nicotinic acetylcholine receptor subtypes and synaptic transmission in chick sympathetic ganglia by PGE(2)

The diversity of neuronal nicotinic acetylcholine receptors (nAChRs) is likely an important factor in the modulation of synaptic transmission by acetylcholine and nicotine. We have tested whether postsynaptic nAChRs are modulated in a subtype-specific manner by prostaglandin E(2) (PGE(2)), a regulator of neuronal excitability in both the central and peripheral nervous systems, and examined the effects of PGE(2) on nicotinic transmission. Somatodendritic nAChRs in chick lumbar sympathetic ganglia include four nAChR subtypes distinguished on the basis of conductance and kinetic profile. Nanomolar PGE(2) applied to the extrapatch membrane differentially regulates opening probability (Po), frequency and the opening duration of each nAChR channel subtype in cell-attached patches. PGE(2) decreases the Po of the predominant nAChR subtype (36 pS) and significantly increases Po and open duration of the 23 pS subtype. The 23 pS subtype is gated by the alpha 7-selective agonist choline, and choline-gated currents are inhibited by alpha-bungarotoxin. To examine whether PGE(2) modulates nAChRs at synaptic sites, we studied the effects of PGE(2) on amplitude and decay of synaptic currents in visceral motoneuron-sympathetic neuron co-cultures. PGE(2) significantly decreases the amplitude of miniature excitatory postsynaptic currents (mEPSCs), consistent with the predominant inhibition by PGE(2) of all but the 23 pS subtype. The time constant of mEPSCs at PGE(2)-treated synapses is prolonged, which is also consistent with an increased contribution of the longer open duration of the 23 pS nAChR subtype with PGE(2) treatment. To examine the presynaptic effect of PGE(2), nanomolar nicotine was used. Nicotine induces facilitation of synaptic transmission by increasing mEPSC frequency, an action thought to involve presynaptic, alpha 7-containing nAChRs. In the presence of PGE(2), nicotine-induced synaptic facilitation persists. Thus the net effect of PGE(2) is to alter the profile of nAChRs contributing to synaptic transmission from larger conductance, briefer opening channels to smaller conductance, longer opening events. This subtype-specific modulation of nAChRs by PGE(2) may provide a mechanism for selective activation and suppression of synaptic pathways mediated by different nAChR subtype(s) at both pre- and postsynaptic sites.

Piroxicam and NS-398 rescue neurones from hypoxia/reoxygenation damage by a mechanism independent of cyclo-oxygenase inhibition

We studied whether NS-398, a selective cyclo-oxygenase-2 (COX-2) enzyme inhibitor, and piroxicam, an inhibitor of COX-2 and the constitutively expressed COX-1, protect neurones against hypoxia/reoxygenation injury. Rat spinal cord cultures were exposed to hypoxia for 20 h followed by reoxygenation. Hypoxia/reoxygenation increased lactate dehydrogenase (LDH) release, which was inhibited by piroxicam (180-270 microM) and NS-398 (30 microM). Cell counts confirmed the neuroprotection. Western blotting revealed no COX-1 or COX-2 proteins even after hypoxia/reoxygenation. Production of prostaglandin E2 (PGE2), a marker of COX activity, was barely measurable and piroxicam and NS-398 had no effect on the negligible PGE2 production. Hypoxia/reoxygenation increased nuclear factor-kappa B (NF-kappaB) binding activity, which was inhibited by piroxicam but not by NS-398. AP-1 binding activity after hypoxia/reoxygenation was inhibited by piroxicam but strongly enhanced by NS-398. However, both COX inhibitors induced activation of extracellular signal-regulated kinase (ERK) in neurones and phosphorylation of heavy molecular weight neurofilaments, cytoskeletal substrates of ERK. It is concluded that piroxicam and NS-398 protect neurones against hypoxia/reperfusion. The protection is independent of COX activity and not solely explained by modulation of NF-kappaB and AP-1 binding activity. Instead, piroxicam and NS-398-induced phosphorylation through ERK pathway may contribute to the increased neuronal survival.

The detoxification of cumene hydroperoxide by the glutathione system of cultured astroglial cells hinges on hexose availability for the regeneration of NADPH

The ability of astroglia-rich primary cultures derived from the brains of newborn rats to detoxify exogenously applied cumene hydroperoxide (CHP) was analyzed as a model to study glutathione-mediated peroxide detoxification by astrocytes. Under the conditions used, 200 microM CHP disappeared from the incubation buffer with a half-time of approximately 10 min. The half-time of CHP in the incubation buffer was found strongly elevated (a) in cultures depleted of glutathione by a preincubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, (b) in the presence of mercaptosuccinate, an inhibitor of glutathione peroxidase, and (c) in the absence of glucose, a precursor for the regeneration of NADPH. The involvement of glutathione peroxidase in the clearance of CHP was confirmed by the rapid increase in the level of GSSG after application of CHP. The restoration of the initial high ratio of GSH to GSSG depended on the presence of glucose during the incubation. The high capacity of astroglial cells to clear CHP and to restore the initial ratio of GSH to GSSG was fully maintained when glucose was replaced by mannose. In addition, fructose and galactose at least partially substituted for glucose, whereas exogenous isocitrate and malate were at best marginally able to replace glucose during peroxide detoxification and regeneration of GSH. These results demonstrate that CHP is detoxified rapidly by astroglial cells via the glutathione system. This metabolic process strongly depends on the availability of glucose or mannose as hydride donors for the regeneration of the NADPH that is required for the reduction of GSSG by glutathione reductase.

The glutathione system of peroxide detoxification is less efficient in neurons than in astroglial cells

The ability of neurons to detoxify exogenously applied peroxides was analyzed using neuron-rich primary cultures derived from embryonic rat brain. Incubation of neurons with H2O2 at an initial concentration of 100 microM (300 nmol/3 ml) led to a decrease in the concentration of the peroxide, which depended strongly on the seeding density of the neurons. When 3 x 10(6) viable cells were seeded per dish, the half-time for the clearance by neurons of H2O2 from the incubation buffer was 15.1 min. Immediately after application of 100 microM H2O2 to neurons, glutathione was quickly oxidized. After incubation for 2.5 min, GSSG accounted for 48% of the total glutathione. Subsequent removal of H2O2 caused an almost complete regeneration of the original ratio of GSH to GSSG within 2.5 min. Compared with confluent astroglial cultures, neuron-rich cultures cleared H2O2 more slowly from the incubation buffer. However, if the differences in protein content were taken into consideration, the ability of the cells to dispose of H2O2 was identical in the two culture types. The clearance rate by neurons for H2O2 was strongly reduced in the presence of the catalase inhibitor 3-aminotriazol, a situation contrasting with that in astroglial cultures. This indicates that for the rapid clearance of H2O2 by neurons, both glutathione peroxidase and catalase are essential and that the glutathione system cannot functionally compensate for the loss of the catalase reaction. In addition, the protein-normalized ability of neuronal cultures to detoxify exogenous cumene hydroperoxide, an alkyl hydroperoxide that is reduced exclusively via the glutathione system, was lower than that of astroglial cells by a factor of 3. These results demonstrate that the glutathione system of peroxide detoxification in neurons is less efficient than that of astroglial cells.

Modulation of nicotinic AChR channels by prostaglandin E2 in chick sympathetic ganglion neurons

The effects of prostaglandin E2 (PGE2), an important metabolite of arachidonic acid, were studied on the activity of nicotinic AChR channels in cultured chick sympathetic ganglion neurons. In whole cell recordings, PGE2 (25 nM) inhibited significantly the ACh-evoked macroscopic current. In cell-attached patch recordings, PGE2 significantly inhibited single AChR channel currents as a result of a decrease in the frequency of channel opening, with no change in open time and conductance. PGE2 did not alter the extent or rate of agonist-induced desensitization of the AChR channels. These effects are specific since the related compound PGD2 had no effect on AChR channel function. Because there is an abundant endogenous production of PGE2 within sympathetic ganglia in response to certain stimuli, the inhibition of AChR channel function by PGE2 could serve an important role to modulate synaptic transmission in the sympathetic nervous system.

Prostanoids synthesized by cyclo-oxygenase isoforms in rat spinal cord and their contribution to the development of neuronal hyperexcitability

1. The responses of wide dynamic range spinal dorsal horn neurones to noxious mechanical stimulation of the ankle or knee joint were tested before and after spinal administration of the non-selective cyclooxygenase (COX) inhibitors, indomethacin and meclofenamic acid. Neither of these drugs altered the responses of these neurones to noxious mechanical stimulation. 2. Wind-up of a spinal nociceptive reflex evoked by electrical stimulation of the sural nerve at C-fibre strength was dose-dependently inhibited by intravenous administration of indomethacin, a non-selective COX inhibitor, and SC58125, a selective COX-2 inhibitor. Intrathecal administration of indomethacin also reduced the wind-up of this nociceptive reflex. 3. Western blot analysis of proteins extracted from normal rat spinal cord revealed the presence of both cyclo-oxygenase (COX)-1 and COX-2 proteins. 4. Immunocytochemistry of sections of normal rat spinal cord with specific COX-1 antiserum revealed little specific COX-1-like immunoreactivity in the grey matter. With the same antiserum, intense COX-1-like immunoreactivity was observed in the cytoplasm, nuclear membrane and axonal processes of small to medium sized (< 1000 microns2) dorsal root ganglion (DRG) cell bodies. 5. Immunocytochemistry of sections of normal rat spinal cord incubated with specific COX-2 antiserum showed intense COX-2-like immunoreactivity (COX-2-li) in the superficial dorsal horn of the spinal cord (laminae I and II) and around the central canal (lamina X). COX-2-li was also observed in some neurones in deep dorsal horn and in individual motor neurones in ventral horn. COX-2-li was not observed in the cell bodies of DRG. 6. Superfusion of the lumbar spinal cord of normal rats with artificial CSF and subsequent radioimmunoassay revealed the presence of prostaglandin D2 (PGD2) < PGE2, but not PGI2 (determined by measurement of the stable metabolite, 6-keto-PGF1 alpha) or PGF2 alpha. 7. These data suggest that eicosanoids synthesized by an active COX pathway in the spinal cord of normal animals may contribute to nociceptive processing, but only when the spinal cord neurones are rendered hyperexcitable following C-fibre stimulation. Selective inhibition of one or both of the COX isoforms in normal animals may represent a novel target for spinal analgesia.

Cyclooxygenase-1 and cyclooxygenase-2 in the human optic nerve head

To investigate the hypothesis that eicosanoids act as cellular mediators in the optic nerve head of normals and of patients with glaucoma, we have determined the presence of the two cyclooxygenase (COX) isoforms in human tissue. Histological sections of optic nerve heads were studied by immunohistochemistry. Age matched normal donors were compared with eyes from glaucoma patients with moderate to severe nerve damage. Polyclonal antibodies to human COX-1 and COX-2 were localized with immunoperoxidase staining. Specific antibodies for vascular endothelia and microglia were also colocalized. In normal and glaucomatous eyes. COX-1 was localized exclusively to the prelaminar and lamina cribrosa regions of the optic nerve head. No staining for COX-1 was observed in the nerve fiber layer or the myelinated optic nerve. COX-1 was associated with the astrocytes of the glial columns and the cribriform plates, but not with the endothelia lining the capillaries. In glaucoma, more astrocytes appeared to be stained with antibody to COX-1 than in normals and staining was intensely perinuclear. There was no staining for COX-2 in normal tissue. A few COX-2 positive cells were found in the prelaminar, lamina cribrosa and postlaminar regions of the glaucomatous optic nerves. Positive staining for COX-2 was not associated with microglia. COX-1 is constitutively present in astrocytes that are localized exclusively to the prelaminar and lamina cribrosa regions of the human optic nerve head. Eicosanoids, synthesized by COX-1 in this tissue, may have a homeostatic and a neuroprotective role related to the axons of the retinal ganglion cells. The sparse presence of COX-2 in glaucomatous tissue probably reflects the lack of inflammation associated with glaucomatous optic neuropathy.

Activated microglia are the principal glial source of thromboxane in the central nervous system

Thromboxane A2(TxA2) is a potent vasoconstrictor associated with cerebrovascular disease and is thought to be synthesized within tissues of the brain. In order to determine the cellular sources of TxA2 in the central nervous system (CNS), we measured the release of the stable metabolite TxB2 in cultures of mixed or highly enriched populations of brain glia. Using techniques which isolated large numbers of highly enriched microglia and astroglia, we found that only microglia release TxB2. Moreover, microglia, not astroglia, contain the requisite synthetic enzyme thromboxane synthase. Phagocytic signals and lipopolysaccharide are potent stimulants of microglial release of thromboxane, with lesser effects shown by platelet activating factor and substance P. We conclude that microglia, when activated, are the principal source of brain-derived thromboxane and may help to control vascular flow at sites of acute CNS injury.

Immunofluorescent localization of constitutive and inducible prostaglandin H synthase in ovine astroglia

We have used immunofluorescent techniques to examine the distribution of prostaglandin H synthase (PGHS) in ovine astrocyte-enriched secondary cultures and in mixed cortical cells in primary culture. A battery of monoclonal and polyclonal antibodies specific for the constitutive (PGHS-1) or inducible (PGHS-2) forms of the enzyme were used to examine the cells in culture. Varying levels of PGHS-1 and PGHS-2-specific immunofluorescence were seen in astrocytes as well as in other cells. The fluorescent pattern and localization seen with antisera to both PGHS-1 and PGHS-2 were similar but were not identical. Both immunoreactive species were confined to nuclear and perinuclear regions of the cell, with no immunoreactivity evident in plasmalemma. In addition, PGHS-2-specific fluorescence was concentrated often as a homogeneous ring around the nucleus in heavily stained astrocytes. Mixed cortical glia/fibroblasts in primary culture were double labeled with antibodies to glial fibrillary acidic protein (GFAP) and to PGHS-2. GFAP and PGHS-2 were colocalized in clusters of astrocytes, but PGHS-2 was evident in GFAP- cells as well. Cells treated with the mitogenic agent phorbol dibutyrate displayed more PGHS-2+ immunofluorescence compared to either vehicle control or cells pretreated with dexamethasone. We conclude that astrocytes cultured in serum express both constitutive and inducible forms of PGHS and that PGHS-2 is induced by mitogens in this cell type.

N-methyl-D-aspartate-evoked release of cyclo-oxygenase products in rabbit hippocampus: an in vivo microdialysis study

In vivo microdialysis of the rabbit hippocampus was used to study the effects of N-methyl-D-aspartate (NMDA) receptor stimulation on dialysate concentrations of thromboxane B2 (Tx B2)- and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha)-immunoreactive materials that are stable metabolites of biologically active thromboxane A2 and prostacyclin. All pharmacological substances were applied in the dialysis medium. The application of 1 mM NMDA for 20 min resulted in five- and eightfold increases in Tx B2 and 6-keto PGF1 alpha concentrations, respectively. An increase in NMDA concentration to 2.5 mM did not potentiate a peak eicosanoid release, but significantly prolonged this effect. Either 10 microM MK-801 or the extrusion of Ca2+ from the dialysis medium inhibited the release by about 50%. Quinacrine, a phospholipase A2 inhibitor (250 microM), decreased the NMDA-evoked eicosanoid release by 30%, whereas 10 microM indomethacin, a cyclo-oxygenase inhibitor, completely suppressed the release. One hundred micromolar furegrelate, an inhibitor of thromboxane synthase, reduced by 75% Tx B2 release with concomitant 100% increase in 6-keto PGF1 alpha formation. Thus, stimulation of NMDA receptors induces calcium-dependent formation of thromboxane A2 and prostacyclin in the hippocampus, which may have pathophysiological implications. The neuronal site of their formation seems probable, although a transcellular mechanism of their synthesis should be also considered.

Rapid induction of prostaglandin synthesis in piglet astroglial cells by interleukin 1 alpha

We examined effects of interleukin 1 alpha (IL-1 alpha) on prostaglandin production in piglet cultured astroglia. Immuno- and morphologically identified polymorphic and process-bearing astrocytes were collected from cerebral cortex and white matter from piglets (1-3 days of age). Levels of prostaglandins were determined using enzyme immunoassay. Baseline levels for prostaglandin (PG) F2 alpha were 631 +/- 332 pg/ml and increased to 1417 +/- 353 pg/ml 20 min after addition of 11 micrograms/ml IL-1 alpha (p < 0.05) and to 2280 +/- 391 pg/ml 20 min after addition of 22 micrograms/ml IL-1 alpha (p < 0.05) (n = 7). Only small amounts of 6-keto-PGF 1 alpha or PGE2 were detected in medium under baseline conditions or in the presence of IL-1 alpha. Medium alone did not change PGF2 alpha levels (n = 3). Coapplication of cycloheximide (10(-3) M) blocked the increase in PGF2 alpha (n = 3). We conclude that IL-1 alpha causes a rapid increase in prostaglandin production by astroglia, and this process involves a step requiring continued or increased protein synthesis.