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Biomedical subjects

J Seylaz

Publications and source records attributed to J Seylaz.

At least 55 records · Page 3Linked to original sources
PubMed1995

Autoradiographic distribution of cerebral blood flow increases elicited by stimulation of the nucleus basalis magnocellularis in the unanesthetized rat.

The nucleus basalis magnocellularis (NBM) of the rat, equivalent of Meynert's nucleus in the primate, is the origin of the main cholinergic innervation of the cerebral cortex. Stimulation of this area has been previously shown to induced marked, cholinergically mediated, blood flow increases in the frontal and parietal cortices. However, the complete distribution of the cerebrovascular effects of NBM stimulation within the whole brain has not been determined. In the present study, we used the [14C]iodoantipyrine autoradiographic method to measure local cerebral blood flow (CBF) in the unanesthetized rat, chronically implanted with a stimulation electrode. We performed unilateral electrical stimulation of the NBM in order to compare both the interhemispheric differences in blood flow and the differences with a group of sham-stimulated rats. Considerable blood flow increases were found in most neocortical areas, exceeding 400% in the frontal area, compared to the control group. Marked responses also appeared in discrete subcortical regions such as the zona incerta, some thalamic nuclei and structures of the extrapyramidal system. These responses were mostly ipsilateral to the stimulation. The significance and the distribution of these blood flow increases are related first, to anatomical and functional data on mainly the cholinergic projections from the NBM, but also non-cholinergic pathways connected with the NBM, second, to biochemical data on the basalocortical system, and third, to the limited ultrastructural data on the innervation of microvascular elements. This cerebrovascular study represents a step in the elucidation of the function of the basalocortical system and provides data which may be related to certain deficits of degenerative disorders such as Alzheimer's disease in which this system is consistently affected.

Analysis of Variance↗
PubMed1995

A new synthetic flavonoid protects endothelium-derived relaxing factor-induced relaxation in rabbit arteries in vitro: evidence for superoxide scavenging.

A new synthetic flavone derivative, 6,7-dimethoxy-8-methyl-3',4',5-trihydroxyflavone, was studied for its capacity to protect the acetylcholine-induced relaxation of rabbit ear and cerebral arteries from inhibition by superoxide anion. This property was evaluated via two types of in vitro experiments, using rabbit ear or basilar arteries mounted in organ baths equipped for isometric tension measurement. When a high level of superoxide anion was generated by adding 3 x 10(-4) M pyrogallol to the bath, the relaxation to acetylcholine was substantially inhibited. This inhibition was significantly reversed by both superoxide dismutase (25 and/or 50 U/mL) and the flavonoid (3 x 10(-6) M and/or 10(-5) M) in both types of arteries. In the presence of the basal level of superoxide anion, the responses to acetylcholine were significantly potentiated by the flavonoid (10(-5) M) in the ear but not the basilar artery. Thus this flavonoid protects endothelium-dependent relaxation from high levels of superoxide anion possibly by scavenging superoxide anion and may have a certain therapeutic value as an agent capable of promoting natural vasodilatation.

Animals↗
PubMed1995

Chemical sympathectomy favours vimentin expression in arterial smooth muscle cells of young rats.

The aim of the present study was to determine whether sympathectomy could influence the relative expression of two intermediate filament proteins, desmin and vimentin, two markers of differentiation, in arterial smooth muscle cells of the young rat. Newborn rats were treated with either repeated guanethidine or saline injections. Sections of the abdominal aorta, the femoral artery, the basilar and the middle cerebral arteries were processed simultaneously for immunofluorescence with monoclonal antibodies against desmin and vimentin and were then examined under either a conventional or a confocal laser-scanning microscope. In both cases, the mean optical density of the muscle layer staining was estimated by computerized image analysis. All artery sections from guanethidine-treated animals showed a significantly higher vimentin expression (108-119% of control values). Desmin expression was not significantly different except in the femoral artery after sympathectomy, where it was decreased by 6%. The relative increase of vimentin expression in sympathectomized blood vessels observed in the present study directly confirms previous morphometric and ultrastructural studies indicating that the sympathetic innervation of cerebral and peripheral blood vessels influences the phenotypic features of smooth muscle cells during post-natal development.

Animals↗
PubMed1995

Effect of inhibiting NO synthesis on hippocampal extracellular glutamate concentration in seizures induced by kainic acid.

It has been suggested that nitric oxide (NO) interferes with both glutamatergic neurotransmission and the regulation of cerebral blood flow in epileptic seizures. This study examines the effect of an inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg), on the extracellular concentration of glutamate during seizures induced by kainic acid (KA; 10 mg/kg), both drugs being administered systemically. L-NAME was injected 40 min before KA. The extracellular glutamate concentration was measured in the hippocampus of awake, spontaneously breathing rats using microdialysis combined with HPLC. The arterial blood gases and glycemia were periodically checked. The arterial blood pressure, the electrocorticogram and the body temperature were continuously monitored. In basal conditions, the systemic injection of L-NAME increased arterial blood pressure but did not significantly change the hippocampal glutamate level. In seizure conditions, the hippocampal glutamate concentration was either slightly increased or not significantly changed in saline-treated rats (n = 6) but it was decreased in L-NAME-treated rats (n = 6). At all times after KA injection, the hippocampal glutamate concentration was significantly lower in L-NAME-treated rats than in saline-treated rats. Unlike saline-treated rats, L-NAME-treated rats died during status epilepticus. This study shows that acute systemic injection of L-NAME reduces the extracellular concentration of glutamate in the rat hippocampus during seizures induced by KA.

Animals↗
PubMed1995

Effects of a glutamate uptake inhibitor on glutamate release induced by veratridine and ischemia.

It has been postulated that a reversal of glutamate reuptake ("uptake reverse") may contribute to glutamate release during cerebral ischemia. We tested this hypothesis by studying the effect of threo-3-hydroxy-DL-aspartic acid (THA), a glutamate uptake inhibitor, on extracellular glutamate accumulation measured by microdialysis during 4-vessel ischemia (20 min). The inhibitory effect of THA on sodium-dependent glutamate uptake was measured in vitro on rat hippocampal slices (Ki = 45 +/- 11 microM). We examined in vivo the effect of THA (400 microM in the dialysis solution) on the extracellular glutamate release from the rat hippocampus, during veratridine depolarization and ischemia. THA decreased the amount of glutamate appearing in the extracellular space during veratridine depolarization (61%). In contrast, the glutamate release induced by ischemia was not affected by THA. We conclude that a reversal of the sodium-dependent uptake contributes to an increase in extracellular glutamate during veratridine depolarization. In contrast, glutamate release occurring during ischemia is not mediated by uptake reverse.

Animals↗
PubMed1995

Regional study of the co-localization of neuronal nitric oxide synthase with muscarinic receptors in the rat cerebral cortex.

There is increasing evidence that nitric oxide is an important molecular messenger involved in a wide variety of biological processes including the regulation of the cerebral circulation. For instance, it has been implicated in the vascular response to nucleus basalis magnocellularis stimulation, a structure which is widely recognized as the predominant source of cholinergic fibres projecting to the neocortex. The present investigation was carried out to determine if muscarinic receptors are present on cortical neurons expressing neuronal nitric oxide synthase (nitric oxide-producing enzyme). To this aim, double labelling of both neuronal nitric oxide synthase/vessels and neuronal nitric oxide synthase/muscarinic receptors was performed on free-floating cryosections obtained from rat brain. The observations were made by confocal laser scanning microscopy. The double labelling of neuronal nitric oxide synthase with the arterioles demonstrated the presence of nitroxidergic fibres in the wall of intraparenchymal vessels. A rich network of nitroxidergic fibres independent of the vessels was also seen in the parenchyma. Since the maximal surface of a square of tissue without any nitroxidergic fibres corresponded to 1400 +/- 105 microns2, the distance separating any cortical point from its closest neuronal nitric oxide synthase-positive fibre was never higher than 25 microns (half diagonal of square). According to models of the diffusional spread of nitric oxide, it is likely that nitric oxide can reach the whole cortical volume. Our results on the regional study of neuronal nitric oxide synthase/muscarinic receptors showed a high density of neuronal nitric oxide synthase-positive neurons principally in the frontal and perirhinal cortices and a low density in the occipital cortex. These data fit well with the known pattern of cortical projections from the nucleus basalis magnocellularis as revealed by anterogradely transported markers. The double labelling showed that about 10% of neuronal nitric oxide synthase-positive neurons were co-localized with muscarinic receptors in the frontoparietal cortex. In agreement with previous papers, the vascular innervation by nitroxidergic neuronal processes was often found to lie near the branching points of arterioles. Such localization allows neuronal nitric oxide synthase-positive neurons an extensive control of the vascular tree without requiring a large number of neuronal commands. Therefore, despite the low level of neuronal nitric oxide synthase/muscarinic receptor co-localization, this neuronal subpopulation could represent a possible relay implicated in the vascular effects of the nucleus basalis magnocellularis.

Animals↗
PubMed1995

Leukocyte-induced endothelial dysfunction in the rabbit basilar artery: modulation by platelet-activating factor.

We studied the effects of polymorphonuclear leukocytes (PMNLs) activated by N-formyl-methionyl-leucyl-phenylalanine on the endothelium-dependent relaxation of the rabbit basilar artery (BA). In the presence of activated PMNLs the maximal vessel relaxation to acetylcholine (ACh) and bradykinin (endothelium-dependent dilators) was decreased from 62 +/- 7 and 48 +/- 6% to 23 +/- 9 and 19 +/- 7, respectively, (p < 0.05). The endothelium-independent relaxation to nitroprusside was not affected by PMNLs. When PMNLs were activated in the organ chamber in the presence of a low concentration of platelet-activating factor (PAF, 10(-10) mol/l), the depression of ACh- and bradykinin-induced relaxation increased by 27 +/- 9 and 23 +/- 7%, respectively (p < 0.05), though at this concentration PAF alone did not cause PMNLs to induce endothelial dysfunction. In addition, in the presence of PAF, activated PMNLs inhibited endothelium-dependent relaxation at lower cell concentrations and shorter periods of contact with the endothelium. PMNL effects on the endothelium were correlated with the level of cell exocytosis as tested by accumulation of beta-glucuronidase activity. In the presence of PAF, accumulation of this activity increased from 46 +/- 6 to 79 +/- 8 U/ml (p < 0.05). Examination of BA segments by scanning electron microscopy revealed that, after the treatment with activated PMNLs, the endothelium was morphologically preserved, but in the presence of PAF PMNLs caused more apparent microlesions in the endothelial layer. We conclude that small quantities of PAF potentiate the activation of marginated PMNLs. These cells then become more aggressive towards the endothelium, producing significant depression of the endothelium-dependent relaxation.

Acetylcholine↗
PubMed1995

Microvessels isolated from brain: localization of muscarinic sites by radioligand binding and immunofluorescent techniques.

The present investigation was carried out to determine the extent to which muscarinic acetylcholine receptors (mAChRs) in vascular and perivascular structures were colocalized with glial fibrillary acidic protein (GFAP)-positive structures. To this aim, an immunocytochemical approach on free-floating cryosections and isolated microvessels obtained from rat brain was performed to study the possible colocalization of immunostaining with the anti-mAChR protein antibody (M35) and an anti-GFAP antibody. Double-labeling experiments were carried out by fluorescent techniques. Confocal microscopic observations of GFAP and M35 immunoreactivities on free-floating sections showed a high degree of colocalization on astrocyte processes associated with large vessels or capillaries. This pattern suggests that muscarinic receptors are associated with astrocytic endfeet. Confocal microscopic observations of immunoreactivity from isolated cerebral microvessels strengthen this conclusion since double-labeling of M35 and GFAP showed that perivascular astrocytic structures remained attached to the isolated microvessels and were present on vascular segments showing M35 immunoreactivity. In another set of experiments, the specific binding of [3H]quinuclidinylbenzylate ([3H]QNB) to isolated microvessel membrane preparations from cerebral cortex, caudate nucleus, thalamus, and cerebellum showed that a constant binding yield (20% in bovine and 40% in rat) was observed for microvessels compared with the corresponding brain region. According to our immunocytochemical results, the astrocytic membrane remaining attached to microvessels may account for the majority of the muscarinic binding to isolated microvessels. [3H]QNB binding values found in isolated microvessels cannot therefore be considered as artifacts without any link with vascular function. Taken together, the present study strengthens the idea that the muscarinic receptors may be implicated in the functional relationship between glial and vascular structures.

Animals↗
PubMed1994

Is alpha-chloralose plus halothane induction a suitable anesthetic regimen for cerebrovascular research?

The aim of this study was to determine whether alpha-chloralose, when associated with an initial period of halothane, is a suitable anesthetic regimen for cerebrovascular studies. For this purpose, rats anesthetized with alpha-chloralose plus halothane induction were first subjected to noxious stimuli, and the behavior, EEG and systemic variables were recorded. During a second step, cortical blood flow was measured with laser-Doppler flowmetry and the time-course of the cerebrovascular reactivity to hypercapnia were measured in artificially ventilated rats anesthetized with either alpha-chloralose (40 mg.kg-1, s.c.) plus halothane induction (1.5% given during the first 45-60 min) or halothane alone (1.5%). Finally, an experimental paradigm was developed that allowed the comparison of the hypercapnic reactivity, both in awake and anesthetized conditions in the same animal. Our results show that the association of alpha-chloralose with halothane leads to stable cardiovascular parameters and immobility of ventilated rats, placed in ear bars without curare, for 3 h without any sign of discomfort. Based on EEG criteria, we found that halothane induction lengthens the duration of alpha-chloralose anesthesia (253 +/- 19 vs. 200 +/- 15 min, P < 0.01). Under alpha-chloralose alone or in association with halothane induction, the vascular reactivity to hypercapnia was considerably impaired (-85% compared to the awake state, P < 0.01), but this impairment was transient, since a control reactivity was restored 150-190 min after induction of anesthesia. Under halothane alone, the vascular reactivity remained reduced throughout the experiment. These results provide evidence that alpha-chloralose plus halothane induction is a suitable anesthetic regimen which displays a temporal window of normal cerebrovascular reactivity.

Anesthesia↗
PubMed1994

Basal forebrain control of cortical blood flow and tissue gases in conscious aged rats.

Cholinergic projections from the basal forebrain are capable of influencing local cortical blood flow (CoBF). The effect of age on this influence was investigated by measuring CoBF and tissue gas partial pressures (PtO2, PtCO2) by mass spectrometry in conscious young adult (2-4 months) and aged (22-28 months) Fischer 344 rats. Electrical stimulation (50 microA) of the substantia innominata (SI) increased frontal (+100.9%) and parietal (+28.4%) CoBF in young rats, but the effects were less in aged rats (frontal, +48.6%, P < 0.05; parietal, +18.9%, difference N.S.). Frontal PtO2 was increased in young but not aged rats (P < 0.01.). During standard hypercapnia, changes in CoBF, PtO2 and PtCO2 did not differ between young and aged rats. Under physostigmine infusion (0.15 mg/kg/h, i.v.), the CoBF increases to SI stimulation were approximately doubled in both cortices, in young and aged rats, and PtO2 increases were also significantly greater. However, frontal PtO2 increases were significantly smaller in aged (+7.6%) than in young (32.7%) rats, as were frontal PtCO2 reductions. We conclude: (i) the influence of the SI on frontal CoBF and PtO2 is substantially reduced with age; (ii) although physostigmine treatment potentiates this influence in both groups, the beneficial effects are relatively limited for aged rats.

Aging↗
PubMed1994

Effects of an A1 adenosine receptor agonist on the neurochemical, behavioral and histological consequences of ischemia.

Untreated rats and rats given the A1 receptor adenosine agonist, R-phenylisopropyladenosine (R-PIA), were subjected to four vessel ischemia. The effect of R-PIA on hippocampal amino acid release, hippocampal neuronal damage, exploratory behavior, learning capacity and global neurological score were evaluated. R-PIA decreased by half the glutamate released during ischemia and improved the global neurological scores 3, 24, 48, 78 h and 7 days after ischemia. But R-PIA had no effect on taurine/GABA release (during ischemia), hippocampal neuronal damage (7 days post-ischemia), exploratory behavior (48 h post-ischemia) or learning capacity (7 days post-ischemia). Thus, a decrease in glutamate release by R-PIA is not systematically correlated with an improvement of histological damage or learning capacity. Reduced glutamate release is not therefore a sufficient criterion on which to evaluate the neuroprotective capacity of a drug.

Amino Acids↗
PubMed1994

Effects of kainate-induced seizures on cerebral metabolism: a combined 1H and 31P NMR study in rat.

The cerebral metabolic changes elicited by kainate-induced seizures in the rat were investigated by in vivo combined NMR spectroscopy of 31P and 1H. Systemic injection of kainate induced no significant changes in cerebral ATP or PCr levels during up to 90 min of continuous, generalised seizures, and the cerebral 31P spectra showed only a transient mild cerebral acidosis 30 min after kainate administration. In parallel with the changes in intracellular cerebral pH, the 1H spectra showed a significant increase in lactate, which remained elevated throughout the seizures. These findings indicate that oxidative metabolism does not completely match the increased glycolysis during seizures though the energy homeostasis is maintained. This suggests that oxidative metabolism has a limited capacity to satisfy the brain's energy needs during the kainate-induced seizures, but that the different pathways of energy production in the brain cells can overcome this limitation. Thus the brain damage associated with this experimental model of epilepsy is not due to extended major failure of the energy supply.

Acidosis↗
PubMed1994

Autoradiographic study of the cerebrovascular effects of stimulation of the substantia innominata: convenient stimulation paradigm.

The aim of this study was to determine the distribution within the whole brain of the vascular effects of stimulation of the substantia innominata. This basal forebrain nucleus is the major cholinergic input in the neocortex in the rodent. The local cerebral blood flow was measured by the autoradiographic [14C]iodoantipyrine technique in a group of control and a group of stimulated unanesthetized rats. The substantia innominata was electrically stimulated through a chronically implanted electrode. The stimulation induced blood flow increases exceeding 200% in the hemisphere ipsilateral to the stimulation and 100% in the contralateral hemisphere compared to the control group. The ipsilateral vasodilations were observed not only in the cortical areas but also in some subcortical structures. Comparison with previous data suggests that part of the effects is due to cholinergic neurons of the substantia innominata and part to non-cholinergic neurons and indirect effects. However, only two out of eight stimulated rats displayed this response. The low reproducibility of the results is discussed, considering the stimulation paradigm which has been developed for future measurements of the cerebral glucose utilization which requires a long duration stimulation period.

Animals↗
PubMed1994

Endothelial dysfunction in cerebral vessels following carotid artery infusion of phorbol ester in rabbits: the role of polymorphonuclear leukocytes.

The effect of 4 beta-phorbol-12 beta-myristate-13 alpha-acetate (PMA) on endothelium-dependent and endothelium-independent vasoconstriction and vasodilation was studied in isolated segments of rabbit middle cerebral artery (MCA). Concentration-dependent responses of the left and right MCA to the constrictors KCl, noradrenaline, uridine 5'-triphosphate, serotonin, and histamine, as well as to the dilators acetylcholine, bradykinin, sodium nitroprusside, and calcium ionophore (A23187), were compared in control animals and after PMA injection into the left common carotid artery. In the control animals there was no significant difference in the responses of the left and right MCA to either the constrictors or the dilators studied. After PMA injection the endothelium-dependent relaxation in response to acetylcholine, bradykinin, and A23187 was reduced in the left MCA (PMA-injected side), whereas the effect of the endothelium-independent dilator sodium nitroprusside remained unchanged. Simultaneously greater contractile responses of the left MCA to serotonin and histamine were obtained. Neither infusion of L-arginine in vivo before the PMA injection nor incubation of the isolated MCA segments with L-arginine affected this difference in MCA reactivity. Platelet depletion did not change the PMA-induced reduction in the endothelium-dependent relaxation, whereas after leukocyte depletion this reduction practically disappeared. These results suggest that the PMA-induced brain microembolia causes acute endothelial dysfunction, which is possibly mediated by intravascular activation of leukocytes and is independent of nitric oxide synthesis from L-arginine. This phenomenon might play an important role in cerebral angiospastic disorders after intravascular activation of leukocytes in cerebral ischemia and reperfusion.

Animals↗
PubMed1994

Blockade of nitric oxide synthesis inhibits hippocampal hyperemia in kainic acid-induced seizures.

We investigated whether the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) affects the cerebrovascular changes occurring in seizures induced by kainic acid (KA) in awake, spontaneously breathing rats. Blood flow and tissue PO2 and PCO2 were continuously and simultaneously measured by mass spectrometry from a cannula chronically implanted into the dorsal hippocampus, L-NAME (20 mg/kg; n = 8) or saline (n = 9) was administered i.p. 30 min prior to i.p. KA (10 mg/kg) injection. L-NAME significantly decreased hippocampal blood flow and PO2 and increased mean arterial blood pressure (MABP). In L-NAME-treated rats, seizure activity occurred about 10 min sooner than in control rats, and status epilepticus was inevitably followed by a flat electroencephalogram and sudden death. In contrast, control rats survival KA-induced seizures. Hippocampal blood flow was significantly less elevated during the seizures in L-NAME-treated rats than in control rats (maximal levels, 170 and 450%, respectively, of baseline values), though MABP remained significantly higher. Hippocampal PO2 was significantly decreased at all times after KA injection in L-NAME-treated rats, whereas it remained at or above normoxic levels in control rats. The present results show that L-NAME markedly attenuates the hippocampal blood flow and tissue PO2 changes in response to enhanced metabolic activity due to limbic seizures and suggest that NO is of major importance in cerebral blood flow control during KA-induced seizures.

Animals↗
PubMed1994

Widespread attenuation of the cerebrovascular reactivity to hypercapnia following inhibition of nitric oxide synthase in the conscious rat.

Despite the increasing number of publications devoted to the cerebrovascular role of NO, its precise influence in awake animals is still poorly characterized. The effect of nitric oxide synthase (NOS) inhibition on the cerebrovascular CO2 reactivity was therefore studied in conscious rats. Regional CBF was measured using the [14C]iodoantipyrine technique and brain tissue sampling. The CO2 reactivity was determined 60 min after administration of 30 mg kg-1 N omega-nitro-L-arginine methyl ester (L-NAME). Blockade of NOS by L-NAME significantly decreased CBF in all 11 brain regions studied (-17 to -49%) and increased arterial pressure from 117 +/- 12 to 147 +/- 11 mn Hg. In control conditions, CO2 responsiveness ranged from 1.3 +/- 0.4 in the hypophysis to 6.4 +/- 0.6 ml 100 g-1 min-1 mm Hg-1 in the parietal cortex. Following L-NAME injection, the reactivity to hypercapnia was significantly attenuated in all structures, the magnitude of the reduction ranging from 57% in the medulla to 74% in the cerebellum. This result shows that NO is an important mediator of the hypercapnic vasodilation in the conscious rat.

Amino Acid Oxidoreductases↗
PubMed1994

Digestibility and bulking effect of ispaghula husks in healthy humans.

The digestibility of ispaghula, a mucilage from Plantago ovata composed mainly of arabinoxylans, and its faecal bulking effect were studied in seven healthy volunteers who ingested a low fibre controlled diet plus either placebo or 18 g/day of ispaghula for two 15 day periods. Whole gut transit time and gas excretion in breath and flatus were not different during the periods of ispaghula and placebo ingestion. Faecal wet and dry weights rose significantly, however, during ispaghula ingestion. Faecal short chain fatty acid concentrations and the molar proportions of propionic and acetic acids also increased. Most of the ispaghula had reached the caecum four hours after ingestion in an intact highly polymerised form. During ispaghula ingestion, the increase in the faecal output of neutral sugars was accounted for by the faecal excretion of arabinose and xylose in an intact highly polymerised form; the apparent digestibilities of these sugars were 24 (11) and 53% (6) respectively (mean (SEM)). In conclusion, ispaghula is more resistant to fermentation than previously reported in humans, and its bulking effect largely results from intact material.

Acetates↗