Increased Expression of Endothelial and Neuronal Nitric Oxide Synthase In Dura and Pia Mater After Air Stress

Stress is the leading precipitating factor for migraine attacks but the underlying mechanism is currently unknown. Nitric oxide (NO) has been implicated in migraine pathogenesis based on the ability of NO donors to induce migraine attacks. In the present study, we investigated in Wistar rats the effect of air stress on nitric oxide synthase (NOS) mRNA and protein expression in dura and pia mater using real-time polymerase chain reaction and Western blotting, respectively. Endothelial (e)NOS protein expression was significantly increased in dura and pia mater after air stress. Significantly augmented neuronal (n)NOS protein expression was detected in pia mater after air stress but not in dura mater. Inducible NOS mRNA and protein expression levels in dura and pia mater were unaffected by stress. The increased expression of eNOS in dura mater and eNOS and nNOS in pia mater seen after stress could not be antagonized by treatment with the migraine drug sumatriptan. These findings point towards the involvement of increased NO concentrations in dura and pia mater in response to air stress. However, the role of these findings in relation to migraine pathophysiology remains unclear.

Inhibition of NADPH oxidase improves impaired reactivity of pial arterioles during chronic exposure to nicotine

Our goals were to determine whether chronic exposure to nicotine alters nitric oxide synthase (NOS)-dependent reactivity of cerebral (pial) arterioles and to identify a potential role for NADPH oxidase in impaired NOS-dependent responses during chronic exposure to nicotine. We measured in vivo diameter of pial arterioles to NOS-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in saline-treated rats and rats chronically treated with nicotine (2 mg.kg(-1).day(-1) for 2 wk via an osmotic minipump). We found that NOS-dependent, but not -independent, vasodilatation was impaired in nicotine-treated compared with saline-treated rats. In addition, the production of superoxide anion (lucigenin chemiluminescence) was increased in rats treated with nicotine compared with saline-treated rats. Furthermore, using Western blot analysis, we found that chronic exposure to nicotine increased p47phox protein in the parietal cortex. Finally, we found that apocynin (40 mg.kg(-1).day(-1)) in the drinking water to inhibit NADPH oxidase alleviated impaired NOS-dependent cerebral vasodilatation in nicotine treated rats but did not alter NOS-dependent responses in saline treated rats and did not alter NOS-independent reactivity in saline- or nicotine-treated rats. These findings suggest that chronic exposure to nicotine impairs NOS-dependent dilatation of pial arterioles by a mechanism that appears to be related to the formation of superoxide anion via activation of NADPH oxidase.

PTK, ERK and p38 MAPK contribute to impaired NMDA-induced vasodilation after brain injury

N-Methyl-D-aspartate (NMDA)-induced pial artery dilation is reversed to vasoconstriction following fluid percussion brain injury (FPI). This study investigated the contribution of activation of protein tyrosine kinase (PTK) and the extracellular signal-regulated kinase (ERK) and p38 isoforms of mitogen-activated protein kinase (MAPK) in impaired vasodilation to NMDA after fluid percussion brain injury in pigs equipped with a closed cranial window. NMDA (10(-8), 10(-6) M)-induced vasodilation was reversed to vasoconstriction following fluid percussion brain injury, but such responses were partially restored by genistein (4',5,7-trihydroxy isoflavone), U0126 [1,4-diamino-2,3-dicyano-1,4-bis (0-aminophenylmercapto)butadiene] and SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole], PTK, ERK and p38 MAPK inhibitors (9+/-1% and 16+/-1%, sham control; -6+/-2% and -11+/-3%, fluid percussion brain injury; and 3+/-1% and 6+/-1%, fluid percussion brain injury-genistein, respectively). However, the robustness of the protection to NMDA dilation was significantly greater for U0126 vs. SB203580 (4+/-1% and 7+/-1% vs. 1+/-1% and 1+/-2%). Similar results were observed for glutamate. These data show that PTK, ERK and p38 MAPK activation contribute to impaired NMDA cerebrovasodilation after fluid percussion brain injury. These data suggest that activation of the ERK isoform of MAPK contributes to such impairment more than the p38 MAPK isoform.

Impairment of neuronal nitric oxide synthase-dependent dilation of cerebral arterioles during chronic alcohol consumption

BACKGROUND

Although chronic alcohol consumption impairs endothelial nitric oxide synthase-dependent reactivity of cerebral arterioles, the effect of alcohol consumption on vasodilation in response to activation of neuronal nitric oxide synthase (nNOS) has not been examined. Thus, our first goal was to determine whether chronic alcohol consumption impairs nNOS-dependent reactivity of pial arterioles. Our second goal was to examine potential mechanisms for impaired responses of pial arterioles during chronic alcohol consumption.

METHODS

Sprague Dawley rats were fed liquid diets with or without alcohol for 8 to 12 weeks. By using intravital microscopy, we measured the diameter of pial arterioles in response to nNOS-dependent agonists--NMDA and kainate (KA)--in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) or 7-nitroindazole (7-NI). We also measured responses of pial arterioles to nitroglycerin. Next, using Western blot analysis, we measured protein levels of the NMDA receptor subunit, KA receptor subunit, and nNOS protein in cerebral microvessels, parietal cortex, cerebellum, and brainstem of non-alcohol-fed and alcohol-fed rats.

RESULTS

Topical application of NMDA (100 and 300 microM) and KA (100 and 300 microM) produced dose-related dilation of pial arterioles in non-alcohol-fed and alcohol-fed rats. However, the magnitude of vasodilation in response to NMDA and KA, but not nitroglycerin, was significantly less in alcohol-fed compared with non-alcohol-fed rats. Topical application of L-NMMA (10 microM) or 7-NI (10 microM) significantly inhibited dilation of pial arterioles in response to NMDA and KA in non-alcohol-fed rats. In alcohol-fed rats, only NMDA-induced vasodilation was inhibited by L-NMMA. In addition, we found that NMDA receptor subunit and KA receptor subunit protein levels increased in the parietal cortex and cerebellum of alcohol-fed compared with non-alcohol-fed rats. However, no significant difference in protein level of nNOS was observed between non-alcohol-fed and alcohol-fed rats.

CONCLUSIONS

Our findings suggest that chronic alcohol consumption impairs nNOS-dependent dilation of pial arterioles via a mechanism that appears to be unrelated to quantitative changes in NMDA receptors, KA receptors, or nNOS. Because the regulation of cerebral blood flow is influenced by neuronal activation, impaired reactivity of cerebral blood vessels to neuronal activation may contribute to the pathogenesis of cerebrovascular disorders observed during chronic alcohol consumption.

Role of altered cyclooxygenase metabolism in impaired cerebrovasodilation to nociceptin/orphanin FQ following brain injury

This study was designed to determine the role of altered cyclooxygenase metabolism in impaired pial artery dilation to the newly described opioid, nociceptin orphanin FQ (NOC/oFQ), following fluid percussion brain injury (FPI) in newborn pigs equipped with a closed cranial window. Recent studies show that NOC/oFQ contributes to oxygen free radical generation observed post FPI in a cyclooxygenase dependent manner. FPI was produced by using a pendulum to strike a piston on a saline filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium. NOC/oFQ (10(-8), 10(-6) M) modestly increased cerebrospinal fluid (CSF) 6-keto-PGF(1alpha), and thromboxane B(2) (TXB(2)), the stable breakdown products of PGI(2) and TXA(2), in sham animals (1148 +/- 83 to 1681 +/- 114 and 308 +/- 16 to 424 +/- 21 pg/ml for control and 10(-6) M NOC/oFQ 6-keto-PGF(1alpha), and TXB(2), respectively). In 1-h post FPI animals, basal levels of 6-keto-PGF(1alpha), and TXB(2) were elevated. NOC/oFQ stimulated release of 6-keto-PGF(1alpha), was blocked while such release of TXB(2) was enhanced (720 +/- 63 to 1446 +/- 117 pg/ml for control and 10(-6) M NOC/oFQ CSF TXB(2)). NOC/oFQ (10(-8), 10(-6) M) induced pial artery dilation that was reversed to vasoconstriction by FPI while the cyclooxygenase inhibitor indomethacin (5 mg/kg, intravenous) partially restored such vascular responses (8 +/- 1 and 15 +/- 1 vs. -7 +/- 1 and -12 +/- 1 vs. 7 +/- 1 and 12 +/- 1% for 10(-8), 10(-6) M NOC/oFQ in sham, FPI and FPI-Indo pretreated animals). Similar observations were made in FPI animals pretreated with the thromboxane receptor antagonist SQ 29,548 or the free radical scavenger polyethylene glycol superoxide dismutase and catalase. These data indicate that altered NOC/oFQ induced cyclooxygenase metabolism contributes to impairment of dilation to this opioid following FPI.

Cerebral and pial microvessels: differential expression of gamma-glutamyl transpeptidase and alkaline phosphatase

Pial microvessels have several important blood-brain barrier (BBB) characteristics in common with cerebral microvessels, despite lacking their astrocytic ensheathment. We have therefore determined whether they have the same distribution of two enzymes, gamma-glutamyl transpeptidase (GGTP) and alkaline phosphatase, both of which are known to be astrocyte-dependent. GGTP was absent from all rat pial microvessels but strongly present in brain cortical capillaries. Alkaline phosphatase was heterogeneously expressed in pial microvessels, including capillaries, but strongly positive in brain cortical capillaries. Diffusible, inductive factors produced by astrocytes could account for these differences in enzyme distribution between the two vessel types. Furthermore, differences in expression between the two markers may reflect their differing sensitivities to the astrocytic factors. Caution is urged in the common usage of the pial microvessel as a model system in BBB studies.

Cytosolic phospholipase A2 (cPLA2) distribution in murine brain and functional studies indicate that cPLA2 does not participate in muscarinic receptor-mediated signaling in neurons

Cytosolic phospholipase A2 (cPLA2) catalyzes the selective release of arachidonic acid from the sn-2 position of membrane phospholipids and has been suggested as an effector in the receptor-mediated release of arachidonic acid in signal transduction. The potential role of cPLA2 as an effector in muscarinic acetylcholine receptor signaling was investigated through ectopic expression of either the m1 or m5 receptor in combination with cPLA2 in COS-1, CHO and U-373 MG cell lines. U-373 MG and COS-1 cells express undetectable or very low levels of cPLA2. CHO cell extracts are characterized by a significant endogenous PLA2 activity that was increased over 20-fold following transient expression with cPLA2 cDNA. However, in none of the cells lines did the co-expression of muscarinic receptor and cPLA2 result in a significant increase in muscarinic receptor-mediated arachidonic acid release over cells expressing muscarinic receptor alone. The distribution of cPLA2 mRNA and cPLA2 immunoreactivity in murine brain were determined in order to investigate a potential role for cPLA2 in neurotransmission. cPLA2 mRNA was expressed in white matter, including cells contained within linear arrays characteristic of interfascicular oligodendrocytes. cPLA2 immunoreactivity in white matter was evident throughout the processes of fibrous astrocytes. cPLA2 expression in gray matter was confined to astrocytes at the pial surface of the brain. cPLA2 mRNA was detected in pia mater, both at the brain surface and inner core of the choroid plexus. cPLA2 may not be directly linked to neurotransmission since enzyme expression, mRNA, and cPLA2 immunoreactivity were undetectable in neurons of murine brain. Support or regulation of neurotransmission may be provided through the activity of cPLA2 in glial cells.

Effect of lipopolysaccharide on the permeability and reactivity of the cerebral microcirculation: role of inducible nitric oxide synthase

The goal of this study was to examine the effect of lipopoly saccharide on the permeability of the blood-brain barrier and reactivity of cerebral arterioles. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood-brain barrier (clearance of fluorescent-labeled dextran; molecular weight 10,000 Da; FITC-dextran-10K) and diameter of pial arterioles were measured in the absence and presence of topical application of vehicle (saline) or lipopolysaccharide (200 ng/ml). During superfusion with vehicle, clearance of FITC-dextran-10K from pial vessels was minimal, and diameter of pial arterioles remained constant. Topical application of lipopolysaccharide (200 ng/ml) produced an increase in clearance of FITC-dextran-10K and dilated pial arterioles. To determine whether lipopolysaccharide-induced changes in permeability of the blood-brain barrier and dilatation of cerebral arterioles was related to the synthesis/release of inducible nitric oxide, we examined the effects of aminoguanidine (0.5 mM). Aminoguanidine inhibited lipopolysaccharide-induced increases in permeability of the blood-brain barrier and dilatation of cerebral arterioles. The findings of the present study suggest that lipopolysaccharide increases permeability of the blood-brain barrier and diameter of pial arterioles via the activation of inducible nitric oxide synthase.

Differential expression of neuronal and endothelial nitric oxide synthase in blood vessels of the rat brain

Constitutively expressed isoforms of nitric oxide synthase in the brain comprise the neuronal (nNOS) and the endothelial (eNOS) enzyme. However, they show striking differences in terms of their preferred histological compartments: nNOS is found predominantly in neurons, eNOS preferentially in endothelia. Our study demonstrates, by means of in-situ hybridization, that nNOS mRNA also localizes to the endothelia of pial vessels but not to those of capillaries. eNOS, however, is expressed in brain capillaries and, as shown by immunohistochemistry, likewise in larger blood vessels, but never in neurons or glia. The endothelial expression of nNOS and eNOS was also confirmed by RT-PCR. The differential distribution of NOS isoforms in brain vessels might be explained with their different mode of activation by stimuli affecting only one particular NOS isoform.

Differential expression of acetylcholinesterase in the developing barrel cortex of three rodent species

Acetylcholinesterase (AChE) is transiently expressed in several immature axon systems. Its presence in developing thalamocortical afferents has led to the use of enzyme histochemistry to visualize this axon system in rats. Because of the spatiotemporal distribution of the enzyme in the rat neocortex, it has been suggested that AChE plays a role in the establishment of thalamocortical connectivity. We show here that AChE is distributed in a pattern that is markedly different in SI cortex of rats as compared to that of mice and hamsters. In rat pups, AChE-rich patches are distributed in a vibrissa-related array in the SI cortex soon after birth, whereas regions of cortex that lie between individual patches, and between rows of patches, are impoverished in the enzyme. In contrast, sections through flattened cortices from PND3 and older mice and hamsters reveal lightly stained AChE-positive spots in the center of barrel cores, while barrel walls remain devoid of AChE; septae that divide individual barrels are densely enzyme positive. Differences in laminar localization of the enzyme for all three species are also visible. In the thalamus of postnatal rats, both the ventral posterior medial (VPM) and ventral posterior lateral (VPL) nuclei express AChE, correlating with the presence of enzyme-containing patches throughout the barrelfield cortex. In the other two rodents, however, the enzyme is present in VPL but not in VPM, despite the fact that in these species the cortical barrels associated with both thalamic nuclei have very little of the enzyme. Thus, the relationship between the distribution of AChE in nuclei of the thalamic ventrobasal complex and the presence of AChE in the terminals of their cortical axons in the barrelfield is not consistent across different rodent species. Our results call for caution in the use of AChE histochemistry as a universal marker for immature thalamocortical axons, and challenge the generality of currently hypothesized roles for this transiently expressed enzyme during the development of the rodent thalamocortical projection.

Dominant expression of mRNA for prostaglandin D synthase in leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain

Glutathione-independent prostaglandin D synthase [prostaglandin-H2 D-isomerase; (5Z,13E)-(15S)-9 alpha,11 alpha-epidioxy-15-hydroxyprosta-5,13-dienoate D-isomerase, EC 5.3.99.2] is an enzyme responsible for biosynthesis of prostaglandin D2 in the central nervous system. In situ hybridization with antisense RNA for the enzyme indicated that mRNA for the enzyme was predominantly expressed in the leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain. The findings agree with those obtained by immunohistochemical staining with antibodies against the enzyme. It was further revealed that prostaglandin D synthase activity was considerably greater in the isolated leptomeninges (14.2 nmol per min per mg of protein) and choroid plexus (7.0 nmol per min per mg of protein) than the activity in the whole brain (2.0 nmol per min per mg of protein). These results, taken together, indicate that the enzyme is mainly synthesized and located in the leptomeninges, choroid plexus, and oligodendrocytes in the brain.

Successive appearance of glutathione S-transferase-positive cells in developing rat brain: choroid plexus, pia mater, ventricular zone and astrocytes

Indirect immunocytochemical staining with antisera raised against purified glutathione S-transferase (GST) was employed to analyse astrogliogenesis in rat brain from embryonic day-16 (E16) rats to birth (which occurs at E20) and in postnatal rats to day 56 (P56). Some GST-positive cells are already recognized at E16 in the choroid plexus and pial surface. At a slightly older age--between E18 and birth--GST-positive cells are located in the ventricular zone. After this age, GST-positive cells are easily recognized in the subventricular zone and in astroglial cells of white and gray matter. On the other hand, neurons and oligodendroglial cells have never been stained all through the ages examined.

Localization of catechol-O-methyltransferase in the leptomeninges, choroid plexus and ciliary epithelium: implications for the separation of central and peripheral catechols

Catechol-O-methyltransferase (COMT) was localized in cells of the pia-arachnoid, and in epithelial cells of the choroid plexus, using an indirect immunofluorescence technique. The specific activity of COMT derived from these tissues was determined by radioenzymatic assay, and in the case of the choroid plexus was found to be 9-fold greater than that measured in whole rat brain. The level of COMT specific activity in pia-arachnoid was twice as high as that in whole brain. Indirect immunofluorescence studies also revealed an intensity of COMT immunofluorescence in the ciliary epithelium at the blood-aqueous barrier in the rat eye, similar to that visualized in the epithelium of the choroid plexus at the blood-cerebrospinal fluid barrier. The localization of COMT in the leptomeninges, choroid plexus, and ciliary epithelium is consistent with a role for this enzyme in the separation of catechol compounds synthesized in the central nervous system, from those of peripheral origin. Thus, catecholamines derived from the peripheral sympathetic system may be prevented from entering the brain parenchyma, which is innervated by the functionally distinct central catecholaminergic systems.

Collagen biosynthesis in healing wounds of the spinal cord and surrounding membranes

Kinetics of collagen synthesis and deposition were studied in the canine spinal cord, pia mater, and dura mater and in wounds of these tissues over the first 8 weeks. Little collagen is present in unwounded spinal cord compared with surrounding mesenchymal membranes. Collagen synthetic potential was found within the spinal cord, a tissue of neurectodermal origin. Rate of collagen synthesis per collagen content in the unwounded spinal cord was high. This synthetic rate was as high as that of wounds at their maximum collagen synthetic rates. Substantial deposition of collagen followed spinal cord wounding. Wounding the spinal cord, pia mater, and dura mater caused substantial elevations in rates of collagen synthesis in each tissue. These synthetic rates remained at maximum levels throughout the 8-week study, a prolonged period when compared with other wounded tissues previously studied. The role of mesenchymal tissue physiology in central nervous system wound healing is discussed. The potential value of these findings for further studies and for experimental manipulation of the healing process in spinal cord and central nervous system wounds is presented. Implications of these findings on the hypothetical relationship of scar to spinal cord and central nervous system regeneration are noted.

The influence of psychotropic drugs on the phosphodiesterase activity in the rat brain meninges

Phosphodiesterase (PDE) is present in brain meninges. Its activity is higher in the pia than in the dura mater. Phenothiazine neuroleptics: fluphenazine, trifluoroperazine, thioproperazine, chloropromazine and thioridazine at concentration 10(-5)--10(-4) M in vitro inhibit the PDE activity in the pia and dura mater. Most potent in this respect were fluphenazine and trifluoroperazine. Much less pronounced inhibition of PDE activity in brain meninges was found after in vitro administration of tricyclic antidepressant: nortriptyline, chlorimipramine, protriptyline, desipramine and imipramine in concentrations 10(-4)--10(-3) M. Administered in vivo in a dose of 0.1 mg or 5 mg/kg ip fluphenazine inhibited the hydrolysis of 32P-cAMP injected into subarachnoid space. The results indicate that PDE present in the rat brain meninges may control the cAMP level in the cerebrospinal fluid. Treatment with phenothiazine neuroleptics which inhibit the PDE activity in meninges may significantly depress the hydrolysis of cAMP in the cerebrospinal fluid.

Identification and characterization of adrenergic receptors and catecholamine-stimulated adenylate cyclase in hog pial membranes

In order to define the adrenergic receptors in small pial blood vessels, we studied [3H]dihydroalprenolol (DHA) binding, [3H]dihydroergocryptine (DHE) binding, and catecholamine-stimulated adenylate cyclase in membranes prepared from the hog pia. [3H]dha bound to a saturable number of sites (0.09 pmol/mg protein) with a high affinity to (10 mM). The ability of a small series of adrenergic agents to compete for [3H]DHA binding was as expected for binding to beta-adrenergic membrane receptors. The receptor binding appeared to be composed largely of beta 2-adrenergic sites but some sites with beta 1 properties were detected. The beta-adrenergic agonist, isoproterenol, stimulated adenylate cyclase activity by 20% in pial membranes in the presence of GTP. The potency of catecholamines in stimulating adenylate cyclase correlated well with theif sites (0.39 pmol/mg) on these membranes. alpha-Adrenergic agents were potent competitors for [3H]DHE binding but dopamine, serotonin and histamine had effects only at high concentrations. These data demonstrate the presence of alpha- and beta-adrenergic membrane receptors and beta-adrenergically stimulated adenylate cyclase activity in small pial blood vessels from the hog.

Metabolic profiles of canine cerebrovascular tree: a histochemical study

Intriguing questions have recently been raised regarding the applicability of direct observations of the pial microcirculation to the behavior of the total cerebral microcirculation. Operating under the assumption that arteriolar tone and, thus, cerebrovascular resistance is, to some extent, directly related to the intrinsic energy metabolism of the arteriolar wall, a comparative histochemical analysis of cerebral microvessels, both pial and parenchymal, was undertaken. Reactions were chosen on the bases of representation of substrate and of enzymes of glycolysis, the hexose monophosphate shunt, beta-oxidation of fat, Krebs cycle, cytochrome system and ATP hydrolysis. Three metabolically distinct segments of the cerebral microvasculature were delineated with the pial vessels showing strong capacities for glycolysis, beta-oxidation of fats and utilization of glucose through the hexose monophosphate shunt. Microvessels of the gray matter have a qualitatively similar metabolic profile but the capacities of each pathway are lower when compared to pial arterioles. Arterioles of the white matter demonstrate the weakest energy-yielding capacities.

[Glucose-6-phosphatase activity of the pia mater of several representative vertebrates]

Studies have been made on the glucose-6-phosphatase activity in the pial matter of the lamprey Lampetra fluviatilis, carp Cyprinus carpio, frog Rana temporaria, tortoises Emys orbicularis and Testudo horsfieldi, hen, rabbit and cat. The data obtained not only confirmed earlier observations on extremely high activity of the enzyme in lamprey's brain, but also demonstrated high activity of glucose-6-phosphatase in the pial matter of other vertebrates, especially in tortoises.

Enzyme response of traumatized tissue after intracortical injection into 5 day old rat brain

Penetration of a microneedle and injection of 4 μl. saline into the neocortex of the 5 day old rat brain produced no changes in behaviour of the rats up to 21 days post-injection. Within 24 hours sections indicated that tissue damage was apparent only at the pia-arachnoid membrane and where fluid was released; elsewhere the needle pathway was identified by the enzyme response. The enzyme histochemistry showed a marked increase in glial cell activity of some phosphatases within 24 hours at the site of injury; the pia-arachnoid and outer limiting membrane also showed abnormally high phosphatase reactions. NADH(2)-diaphorase was the only dehydrogenase that was raised in some nerve and glial cells at 24 hours post-injection but other dehydrogenases, mainly LDH and SDH, showed changes at four days post-injection. The phosphatases and 5'-nucleotidase previously showing intense glial cell enzyme reactions appeared to reach peaks of activity at eight days, and at 16 days the onset of scarring was apparent. In the pia-arachnoid enzyme activity increased to 21 days. Some enzymes, particularly AChE and MAO, showed no alterations of note throughout.