Effect of MK-801 on focal brain infarction in normotensive and hypertensive rats.

The effects of the noncompetitive N-methyl-D-aspartate antagonist MK-801 on infarct size and systemic variables after middle cerebral artery occlusion in spontaneously hypertensive and Fischer-344 rats were investigated. Two doses (0.5 and 5 mg/kg) administered before the induction of ischemia were studied. MK-801 significantly reduced the neocortical volume of infarction (by about 32% at both doses) in Fischer-344 rats and had no neuroprotective effects in the striatum. In contrast, MK-801 had no significant influence on either cortical or striatal infarcted volume in spontaneously hypertensive rats. The reduction or lack of MK-801-induced neuroprotection in spontaneously hypertensive rats, as compared with Fischer-344 rats, could be attributed to a reduced collateral supply in the marginal area due to difference in the morphology of the pial anastomoses and/or in the effects of ischemia and treatment on arterial pressure. The results may have major clinical implications since a great proportion of human strokes are associated with hypertension.

Dynamic cerebral microcirculatory changes in transient forebrain ischemia in rats: involvement of type I nitric oxide synthase.

The diameter of surface microvessels and the erythrocyte velocity and flux through intraparenchymal capillaries in the parietal cortex were measured during transient global cerebral ischemia and reperfusion using laser-scanning confocal fluorescence microscopy in anesthetized rats. The role of nitric oxide (NO) from neurons in the microcirculatory changes was also investigated using 7-nitro-indazole (7-NI, 25 mg/kg, i.p.). Wistar rats (4 per group) equipped with a closed cranial window were given fluorescein isothiocyanate (FITC)-Dextran and FITC-labeled erythrocytes intravenously to respectively visualize the microvessels and the erythrocytes in the capillaries. Experiments were videorecorded on-line. Forebrains were made ischemic for 15 minutes and then reperfused for 120 minutes under the microscope. Ischemia was associated with a flattened EEG, a low persistent blood flow, and a transient leakage of fluorescein across the arteriole wall. Unclamping the carotid arteries led to immediate high blood flow in the arterioles, but it was not until 5 minutes later that the arterioles dilated significantly (181% +/- 27%) and erythrocyte velocity in the capillaries increased significantly (460% +/- 263%). Neither nonperfused capillaries nor erythrocyte capillary recruitment occurred. 7-Nitro-indazole significantly reduced the arteriole dilatation and prevented the increase in erythrocyte velocity and flux through capillaries in early reperfusion. 7-Nitroindazole had no influence on the fluorescein leakage. The current study suggests a partial role for NO released from neurons in the postischemic microcirculatory changes and provides new findings on the timing of arteriole dilatation and blood-brain barrier opening, and on erythrocyte capillary circulation in global ischemia.

Reduction of infarct volume by magnesium after middle cerebral artery occlusion in rats.

The effects of magnesium, an endogenous inhibitor of calcium entry into neurons, upon ischemic brain damage were investigated using a well-characterized model of focal cerebral ischemia in rats. Infarct volumes were determined by 2,3,5-triphenyltetrazolium chloride transcardiac perfusion 48 h after middle cerebral artery (MCA) occlusion. The area of ischemic damage was quantified by image analysis in coronal sections taken every 0.5 mm. MgCl2 (1 mmol/kg) was injected intraperitoneally just after MCA occlusion and again 1 h later. Posttreatment with MgCl2 (16 control and 16 treated rats) significantly reduced the cortical infarct volume. Compensation for the hyperglycemic effect of MgCl2 with insulin (17 rats) further reduced the infarct volume in the neocortex. No systemic effects of either treatment could account for the observed neuroprotection.

Nitric oxide of neuronal origin is involved in cerebral blood flow increase during seizures induced by kainate.

In a previous study, we reported that the sustained increase in CBF concomitant with seizures induced by kainate is mainly due to the potent vasodilator nitric oxide (NO). However, the production site of NO acting at cerebral vessels was undetermined. In the present study, we investigated whether NO responsible for the cerebral vasodilation is of either neuronal or endothelial origin. We used a putative selective inhibitor of neuronal NO synthase, 7-nitro indazole (7-NI). CBF was measured continuously in parietal cortex by means of laser Doppler flowmetry in awake rats. Systemic variables and electroencephalograms were monitored. Kainate (10 mg/kg i.p.) was given to rats previously treated with saline (n = 8) or 7-NI (25 mg/kg i.p., n = 8) or L-arginine (300 mg/kg i.p., n = 8) followed 30 min later by 7-NI (25 mg/kg i.p.). Under basal conditions, 7-NI decreased CBF by 27% without modifying the mean arterial blood pressure. Under kainate, 7-NI prevented significant increases in CBF throughout the seizures despite sustained paroxysmal electrical activity. L-arginine, the substrate in the production of NO, prevented any decrease in CBF under 7-NI in basal conditions and partially, but nonsignificantly, reversed the cerebrovascular influence of 7-NI during seizures. In a separate group of rats (n = 6), inhibition of cortical NO synthase activity by 7-NI was assayed at 73%. The present results show that neurons are the source of NO responsible for the cerebrovascular response to seizure activity after kainate systemic injection.

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.

Effect of stimulation of the sphenopalatine ganglion on cortical blood flow in the rat.

The effects of electrical stimulation of the sphenopalatine ganglion on cortical blood flow and gas partial pressures (PO2 and PCO2) were studied in the anesthetized rat. Tissue PO2, PCO2, and local CBF were measured simultaneously in both parietal cortices by means of mass spectrometry. Stimulation of the sphenopalatine ganglion increased CBF and tissue PO2 by approximately 50 and 20%, respectively, in the ipsilateral parietal cortex. Smaller but significant increases in CBF and tissue PO2 were simultaneously seen in the contralateral parietal cortex. These variations were also accompanied by small decreases in PCO2 in both parietal cortices and a 5% increase in mean arterial pressure, whereas cortical electrical activity did not change. We conclude that the cholinergic (and vasoactive intestinal polypeptidergic) innervation of the cerebral blood vessels, arising from the sphenopalatine ganglion has significant vasomotor potential and that this system may be of functional importance.

Dynamic in vivo measurement of erythrocyte velocity and flow in capillaries and of microvessel diameter in the rat brain by confocal laser microscopy.

A new method for studying brain microcirculation is described. Both fluorescently labeled erythrocytes and plasma were visualized on-line through a closed cranial window in anesthetized rats, using laser-scanning two-dimension confocal microscopy. Video images of capillaries, arterioles, and venules were digitized off-line to measure microvessel diameter and labeled erythrocyte flow and velocity in parenchymal capillaries up to 200 microm beneath the brain surface. The method was used to analyze the rapid adaptation of microcirculation to a brief decrease in perfusion pressure. Twenty-second periods of forebrain ischemia were induced using the tour-vessel occlusion model in eight rats. EEG, arterial blood pressure, and body temperature were continuously controlled. In all conditions, labeled erythrocyte flow and velocity were both very heterogeneous in capillaries. During ischemia, capillary perfusion was close to 0, but a low blood flow persisted in arterioles and venules, while EEG was flattening. The arteriole and venule diameter did not significantly change. At the unclamping of carotid arteries, there was an instantaneous increase (by about 150%) of arteriole diameter. Capillary erythrocyte flow and velocity increased within 5 seconds, up to, respectively, 346 +/- 229% and 233 +/- 156% of their basal value. No capillary recruitment of erythrocytes was detected. All variables returned to their basal levels within less than 100 seconds after declamping. The data are discussed in terms of a possible involvement of shear stress in the reperfusion period.

Neurogenic influence on local cerebral blood flow. Effect of catecholamines or sympathetic stimulation as correlated with the sympathetic innervation.

Local cerebral flow was measured continuously in conscious rabbits (thermoclearance technique), and PaO2 and PaCO2 were recorded by mass spectrometry. Though inhalation of CO2 increased flow in caudate nucleus and lateral geniculate body, catecholamines only had effect on caudate nucleus where isoproterenol enhanced and epinephrine and norepinephrine reduced flow. Reduction by electrical stimulation of the neck sympathetic trunk was particularly evident in the caudate. Blood flow increased markedly in both regions after preganglionic conduction blockade. The effects were correlated with a significantly lower degree of sympathetic arteriolar innervation (fluorescence histochemistry) in the lateral geniculate body compared with the caudate nucleus.

The acute effects of MK-801 on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide in conscious and alpha-chloralose anaesthetized rats.

The dynamic effects of the non-competitive N-methyl-D-aspartate receptor antagonist, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine] , on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide were investigated in the striatal and occipital regions of conscious and anaesthetized rats by mass spectrometry. MK-801 (0.5 and 5 mg/kg, i.p.) induced a large increase in the blood flow of both cerebral regions of conscious rats, without significant changes in local tissue partial pressures of oxygen and carbon dioxide. The increase in cerebral blood flow was maximal within 30 min after injection. Its amplitude was independent of the dose of MK-801, but cerebral blood flow remained elevated for up to 4 h after 5 mg/kg MK-801, while it progressively decreased towards its basal level in rats given 0.5 mg/kg MK-801. The amplitude and time-course of the vascular changes were similar in the two cerebral regions studied. The difference in the changes in tissue partial pressure of oxygen induced by MK-801 and by a 6% CO2 inhalation suggests that the MK-801-induced rise in cerebral blood flow in conscious rats is, at least partly, due to an increase in oxidative metabolism. In contrast, MK-801 induced either no changes or decreases in cerebral blood flow in alpha-chloralose-anaesthetized rats. The present results should be taken into account not only to determine the mechanisms by which N-methyl-D-aspartate receptor antagonists may exert their neuroprotective effects but also to further elucidate the sites of action of MK-801 in the central nervous system.

Differential cerebrovascular and metabolic responses in specific neural systems elicited from the centromedian-parafascicular complex.

The effect of electrical stimulation of the centromedian-parafascicular complex on local cerebral blood flow and local cerebral glucose utilization was investigated in anesthetized, paralysed and ventilated rats. Local cerebral blood flow and local cerebral glucose utilization were measured in separate groups of animals using the autoradiographic (14C)iodoantipyrine and (14C)2-deoxyglucose methods, respectively. Because of the well-established centromedian-parafascicular complex neuroanatomical connections, three functional neuronal systems were analysed and compared: the extrapyramidal motor system the limbic system and the reticular formation, also known as the ascending activating system. Cortical regions not included in the limbic system were considered separately. The validity of comparisons between changes in local cerebral blood flow and local cerebral glucose utilization across the brain was verified by assessing the reactivity and stability of the cortical blood flow during long-term centromedian-parafascicular complex stimulation. Centromedian-parafascicular complex stimulation elicited a marked but heterogeneous increase in local cerebral blood flow in 50 of the 52 cerebral structures measured. The most pronounced increases were seen in the lateral habenular nucleus (331 +/- 30% of control), the zona incerta (400 +/- 55%), the mesencephalic reticular formation (415 +/- 122%) and the parietal cortex (211 +/- 35%). In contrast, local cerebral glucose utilization remained statistically unchanged (P greater than 0.05) in 28 of these 50 individual brain regions during centromedian-parafascicular complex stimulation. The most pronounced increases in local cerebral glucose utilization were seen in the zona incerta (123 +/- 28%) and the mesencephalic reticular formation (193 +/- 26%). Local cerebral blood flow and local cerebral glucose utilization were linearly related in unstimulated controls, considering either all brain regions taken as a whole or the three systems separately. The significant increase in the slopes of the regression line between local cerebral blood flow and local cerebral glucose utilization for the reticular formation and the limbic system during centromedian-parafascicular complex stimulation indicates, however, that the coupling mechanisms for these systems, but not for the extrapyramidal motor system, were reset. The local cerebral blood flow to local cerebral glucose utilization ratio was heterogeneous in controls and differentially increased during centromedian-parafascicular complex stimulation, being markedly pronounced in the parietal cortex and in the reticular formation. We conclude that these results, for the first time, provide evidence that, the functionally well-defined neural networks may have different mechanisms whereby changes in vascular and metabolic demands are regulated.

Continuous determination of the cerebrovascular changes induced by bicuculline and kainic acid in unanaesthetized spontaneously breathing rats.

Cerebral blood flow was sequentially determined (every 2-3 min) with helium clearance in two "vulnerable" structures: the hippocampus and the frontoparietal cortex during bicuculline (n = 11) and kainic acid (n = 9)-induced seizures in unanaesthetized, spontaneously breathing rats. Tissue partial pressures of oxygen and carbon dioxide were continuously and simultaneously evaluated in the same brain areas. All these variables were measured by mass spectrometry with a single gas sampling cannula previously implanted in each structure. The systemic variables, arterial blood pressure, arterial partial pressures of oxygen and carbon dioxide, pH, and bicarbonate concentration were also determined. Arterial and venous catheters were chronically implanted several days prior to the definitive experiments. Bicuculline induced short (about 15 min), recurrent, generalized seizures, with an abrupt rise in arterial blood pressure, an arterial metabolic acidosis and comparable blood flow increases (4-fold) in the hippocampus and the neocortex. A marked increase in tissue partial pressure of oxygen was always preceded by an increase in tissue partial pressure of carbon dioxide. After the seizures, in the 5 rats that survived, cerebral blood flow was significantly lowered; tissue partial pressure of oxygen and partial pressure of carbon dioxide also decreased, but to a lesser extent. Histological examination revealed two types of lesions: predominantly selective chromatolysis but also ischaemic cell change. Kainic acid first induced a decrease in arterial pressure and then hypertension during status epilepticus, with a return of arterial pressure towards basal levels during the recovery period (4 h after the injection). Respiratory alkalosis occurred throughout the experiment. Cerebral blood flow increased progressively to become maximal during status epilepticus. This vasodilatation was greater in the hippocampus (x 8) than in the neocortex (x 4). During recovery, cerebral blood flow tended to decrease but remained significantly elevated. In both structures, tissue partial pressure of oxygen was first lowered while tissue partial pressure of carbon dioxide was elevated; with the occurrence of the wet dog shakes, tissue partial pressure of O2 increased and tissue partial pressure of CO2 decreased. The changes in tissue gases were maximal during status epilepticus and tended to return to their basal levels thereafter, but no decrease in tissue partial pressure of O2 was observed, even 4 h after kainic acid administration. Histological analysis demonstrated ischaemic cell changes, particularly in the limbic system.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood flow compensates oxygen demand in the vulnerable CA3 region of the hippocampus during kainate-induced seizures.

Local blood flow, and partial pressures of oxygen and carbon dioxide were directly monitored in the vulnerable region of Ammon's horn (e.g. CA3) of unanaesthetized, freely breathing rats in which epileptic seizures of 120 min duration were induced by parenteral kainic acid. Blood flow was periodically determined by helium clearance. Partial pressures of oxygen and carbon dioxide were simultaneously and continuously measured by means of mass spectrometry, in order to determine if the neuronal damage occurring during the seizures were due to local hypoxia or if blood flow compensated the metabolic demand. During the wet shakes period, a decrease of 35% in the partial pressure of oxygen occurred, concomitant with an increase of 33% in the partial pressure of carbon dioxide and of 330% in local blood flow in Ammon's horn. During the limbic motor seizures, the partial pressure of oxygen increased progressively to twice its baseline value, while the partial pressure of carbon dioxide returned to its baseline value and blood flow underwent a six-fold increase. Thus the seizures produced by kainate do not lead to a mismatch between oxygen supply and blood flow. Our results provide direct evidence that hypoxia cannot be considered responsible for the damage produced by the seizures in CA3. It is concluded that brain damage in CA3 is due to an enhanced neuronal activity associated with the release of a toxic endogenous substance and an excessive rise of intracellular concentration of calcium.

Inhibition of neuronal (type 1) nitric oxide synthase prevents hyperaemia and hippocampal lesions resulting from kainate-induced seizures.

The possible roles for nitric oxide produced by neurons in epileptic conditions have been investigated from two different aspects: microcirculation and delayed damage. Our aim was to determine whether the selective inhibition of neuronal (type 1) nitric oxide synthase by 7-nitroindazole, during seizures induced by systemic kainate, modifies hippocampal blood flow and oxygen supply and influences the subsequent hippocampal damage. Experiments were performed in conscious Wistar rats whose electroencephalogram was recorded. 7-Nitroindazole (25 mg/kg, i.p.) or its vehicle was injected 30 min before kainate administration (10 mg/kg, i.p.) and then twice at 1-h intervals. Kainate triggered typical limbic seizures evolving into status epilepticus, identified by uninterrupted electroencephalographic spike activity. The seizures were stopped by diazepam (5 mg/kg, i.p.) after 1 h of status epilepticus. Three types of experiments were performed in vehicle- and 7-nitroindazole-treated rats. (1) Hippocampal nitric oxide synthase activity was measured under basal conditions, at 1 h after the onset of the status epilepticus and at 24 h after its termination (n = 4-6 per group). (2) Hippocampal blood flow and tissue partial pressure of oxygen were measured simultaneously by mass spectrometry for the whole duration of the experiment, while systemic variables and body temperature were monitored (n = 6 per group). (3) Hippocampal damage was revealed by Cresyl Violet staining and evaluated with a lesion score seven days after status epilepticus (n = 12 per group). Hippocampal nitric oxide synthase activity was not significantly modified during status epilepticus or the following day in vehicle-treated rats. In contrast, it was inhibited by 57% in 7-nitroindazole-treated rats, both in basal conditions and after 1 h of status epilepticus, but was not different from its basal level 24 h later. 7-Nitroindazole significantly decreased basal hippocampal blood flow and tissue partial pressure in oxygen by 30% and 35%, respectively without affecting any systemic or thermal variable. During status epilepticus, 7-nitroindazole significantly reduced the increase in hippocampal blood flow by 70% and prevented any increase in the tissue partial pressure of oxygen. Seven days later, the hippocampal damage in the CA1 and CA3 layers was significantly less in 7-nitroindazole-treated rats than in vehicle-treated rats. These results indicate that the inhibition of neuronal nitric oxide synthase by 7-nitroindazole protects neurons from seizure-induced toxicity despite reducing blood flow and oxygen supply to the hippocampus.

Distribution of bone morphogenetic protein and bone morphogenetic protein receptor transcripts in the rodent nervous system and up-regulation of bone morphogenetic protein receptor type II in hippocampal dentate gyrus in a rat model of global cerebral ischemia.

Bone morphogenetic proteins belong to the transforming growth factor-beta superfamily and act through serine/threonine kinase type I and type II receptors such as bone morphogenetic protein receptor type I and type II. In order to further understand the roles that these factors exert in the nervous system, we have examined the expression pattern of seven bone morphogenetic proteins and bone morphogenetic protein receptor type I and II transcripts in the brain and spinal cord of rodent. Whereas bone morphogenetic protein receptor type I expression was low in rat brain, in situ hybridization studies performed with specific digoxigenin-labelled riboprobes revealed the presence of bone morphogenetic protein receptor type II-positive cells throughout the brain, with a notable localization in dopaminergic cells of the substantia nigra. Bone morphogenetic protein receptor type II transcripts were also expressed by large motoneuron-like cells located in the ventral horn of the spinal cord and by sensory neurons of dorsal root ganglia. In addition, we observed a significant up-regulation of bone morphogenetic protein receptor type II in the granule cells of the dentate gyrus 48 h after transient global cerebral ischemia in rat suggesting that modulation of this receptor intervenes during neuronal plasticity or repair that occur upon brain injury. Among the potential ligands for this receptor, bone morphogenetic protein-6 and bone morphogenetic protein-7 were expressed in meninges and the choroid plexus, while bone morphogenetic protein-4-expressing cells were spatially and temporally regulated in myelinated structures during development and in the adult suggesting its expression in oligodendrocytes. These data clearly indicate that besides their roles in bone and embryonic tissues, bone morphogenetic proteins and their receptors may have also important functions in adult neural tissues.

Influence of the antioxidant quercetin in vivo on the level of nitric oxide determined by electron paramagnetic resonance in rat brain during global ischemia and reperfusion.

We characterized the changes in nitric oxide (NO) levels in the brain during global forebrain ischemia and reperfusion and tested the ability of the natural flavonoid, quercetin, and a synthetic flavonoid, FB277, to increase the amount of available NO by elimination of the superoxide radicals produced during reperfusion. In Sprague-Dawley rats, we used a four-vessel occlusion model of forebrain ischemia (15 min) and reperfusion (30 min). Brain NO was measured on samples of cerebral cortex and cerebellum ex vivo by electron paramagnetic resonance (EPR) spectroscopy. The spin trap used was diethyldithiocarbamate sodium salt (DETC) associated with ferrous citrate. The complex Fe(DETC)2NO was detected at 77 K as a triplet signal at g = 2.035. Groups of animals were treated with quercetin or FB277 (3-morpholinomethyl-3',4',5,7tetramethoxyflavone) or polyethylene glycol-conjugated superoxide dismutase (PEG-SOD). In control (intact anesthetized animals), the signal was about 3 times greater in the cortex than in the cerebellum. During ischemia, the signal rose to 110% in cortex (NS) and 283% in cerebellum (P < 0.05). In reperfusion, it fell again to 91% of control in cerebellum (NS) and 35% in cortex (P < 0.05). Treatment by quercetin (5 mg/kg i.v.) of intact and ischemia-reperfusion groups did not significantly change the signal amplitude in the cerebellum, but did double it in the cortex (to 76% of control) for the ischemia-reperfusion group (P < 0.05). In contrast, FB277 (3.75 mg/kg i.v.) did not increase the signal in the cortex during ischemia-reperfusion, but did do so in the cerebellum (to 152% of control, P < 0.05). The results obtained for PEG-SOD (10,000 U/kg i.v.) were similar to those for FB277. In separate in vitro measurements, we found that quercetin but not FB277 efficiently scavenged superoxide. We hypothesize that quercetin but not FB277 scavenged superoxide anions released in the cortex during reperfusion, thus diminishing the amount of NO removed by the formation of peroxynitrite. The lack of effect of PEG-SOD may be related to the need for chronic treatment to obtain protection.

Carbon monoxide regulates cerebral blood flow in epileptic seizures but not in hypercapnia.

Carbon monoxide (CO) is an endogenously produced gas sharing many properties with nitric oxide (NO), notably activating soluble guanylate cyclase and relaxing blood vessels. The brain can generate high quantities of CO from a constitutive enzyme, haem oxygenase (HO-2). To determine whether CO is involved in the regulatory mechanisms of cerebral blood flow (CBF), two conditions associated with a reproducible CBF increase were studied in rats: epileptic seizures induced by kainate, and hypercapnia. The HO inhibitor tin protoporphyrin (Sn-PP) did not modify the basal level of CBF, significantly reduced the increase in CBF during status epilepticus, and did not affect the cerebrovascular response to hypercapnia. It is concluded that CO participates in the regulation of CBF in specific conditions, notably those associated with glutamate release.

Passage of spermidine across the blood-brain barrier in short recirculation periods following global cerebral ischemia: effects of mild hyperthermia.

Transport of a polyamine (PA), spermidine (SPMD) into rat brain at various early postischemic periods was studied. Rats underwent 20 min of four-vessel occlusion (4VO) followed by 5, 10, 30 and 60 min of recirculation (RC) periods with natural brain temperature. 3H-aminoisobutyricacid (AIB) and 14C-SPMD were utilised to search dual functions of the blood-brain barrier (BBB); barrier and carrier functions, respectively. Unidirectional blood-to-brain transfer constant (Kin) was calculated for AIB and SPMD in four brain regions-parieto-temporal cortex, striatum, hippocampus and cerebellum. Kin for SPMD ranged between 1.2+/-0.3 x 10(3) ml g(-1) min(-1) (for striatum) and 2.2+/-0.4 x 10(3) ml g(-1) min(-1) (for cerebellum) in controls. Kin for AIB showed similar values. At 5 and 10 min RC periods, Kin for both substances increased in a non-specific manner in all brain regions studied. In the cortex, Kin for SPMD at 5 and 10 min RC periods were 3.2+/-0.4 x 10(3) and 2.9+/-0.3 x 10(3) ml g(-1) min(-1), respectively, and found to be maximum with respect to other brain regions studied. 30 and 60 min RC groups showed specific transport for SPMD, whilst there were no changes for Kin for AIB, in all brain regions studied. Hippocampus showed the maximum increase in Kin SPMD at 60 min RC (2.7+/-0.3 x 10(3) ml g(-1) min(-1)), corresponding to a percentage rise of 121%. Intraischemic mild brain hyperthermia (39 degrees C) gave rise to a striking increase in Kin at 60 min postischemia for both substances. These results suggest that there is a specific transport of SPMD into brain at 30 and 60 min RC periods following 20 min of forebrain ischemia. Moreover, dual functions of the BBB were perturbed with intracerebral mild hyperthermia during ischemia.

Fluorocarbons: a potential treatment of cerebral air embolism in open-heart surgery.

This study was designed to assess whether an oxygenated fluorocarbon solution could reduce ischemic brain damage related to arterial air embolism. Air embolism was produced by injecting air bubbles into the carotid artery of barbiturate-anesthetized rats breathing 100% oxygen. Results were assessed on electrocorticogram. In an additional set of experiments, mass spectrometry was used to provide continuous monitoring of intracerebral tissue oxygen (PO2) and carbon dioxide (PCO2) tensions and intermittent measurement of cerebral blood flow (CBF). Fluorocarbon or saline solution (containing the emulsifying agent of fluorocarbons) was given intravenously after the initial air embolism (0.2 ml), and injections of air (0.1 ml) were repeated thereafter every five minutes. The maximal amount of air required to achieve complete and irreversible flattening of the electrocorticogram was 1.60 +/- 0.06 ml (mean +/- standard error of the mean) in the saline-treated rats and 5.20 +/- 0.44 ml in the fluorocarbon-treated group (p less than 10(-7)). In the second experiment, air embolism caused CBF to rise in both groups, the average percent of increase being higher in treated (41.6%) than in control animals (38.3%) (p less than 0.02). However, in the control group, the increase in CBF did not prevent intracerebral tissue PO2 from decreasing by 7.4 +/- 7.0% over the same period; conversely, in the fluorocarbon group, PO2 levels fell by only 2.5 +/- 3.7% (p less than 0.001 versus controls), but this time-averaged percentage was calculated over a longer period of cumulative ischemia because of the greater number of air emboli tolerated by treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Focal cerebral ischemia in chronic hypertension: no protection by (R)-phenylisopropyladenosine.

The effects of the adenosine agonist, (R)-phenylisopropyladenosine on focal cerebral ischemia induced by middle cerebral artery occlusion were investigated in spontaneously hypertensive rats. The drug was given 30 min before occlusion and each hour thereafter for 6 h. The neurological status of the rats was estimated 2, 24 and 48 h after occlusion. Infarct volumes were measured 48 h after occlusion (Cresyl violet-stained sections). (R)-Phenylisopropyladenosine did not significantly reduce infarct size, nor did it modify the neurological score. As there is considerable evidence of the neuroprotective effects of adenosine in normotensive rats, the present results may be due to a more abrupt reduction in cerebral blood flow in the territory surrounding the ischemic core, where neuroprotection could be expected, in the spontaneously hypertensive rat strain. Consequently, neuroprotection may be more difficult when focal cerebral ischemia is associated with hypertension.

Dynamic cerebral and systemic circulatory effects of adenosine, theophylline and dipyridamole.

The effects of intravenous adenosine, dipyridamole and theophylline on local cerebral blood flow were studied in conscious rabbits. Long-term quantitative blood flow measurements were performed in 5 cerebral structures together with tissue pO2 and pCO2 measurements by a mass spectrometry technique. In an additional study, the time course of the cerebrovascular changes was determined by thermal clearance. It was found that: firstly, adenosine failed to modify local blood flow except in the caudate nucleus; secondly, dipyridamole increased cerebral blood flow in all 5 structures under study, and lastly, theophylline decreased cerebral blood flow in the same 5 structures. The increase in caudate blood flow induced by adenosine was instantaneous and lasted only for the duration of the infusion, whereas the cerebrovascular changes induced by dipyridamole and theophylline were gradual and persisted after their administration. Theophylline blocked the systemic and cerebrovascular changes caused by adenosine alone and by dipyridamole alone. In anesthetized rabbits, the intracarotid infusion of adenosine showed that the caudate reaction only occurred in the ipsilateral hemisphere. Taken together, our findings suggest that the transport system for adenosine in cerebral vessels is not only species-dependent but also structure-dependent. Furthermore, perivascular adenosine helps to maintain resting cerebrovascular tone and finally, cerebral adenosine may be involved in the control of cerebral blood flow via specific adenosine receptors.