Age-related changes in the antioxidative potential of cerebral microvessels

To determine if aging in rats is associated with increased susceptibility of cerebral microvessels to oxidative damage microvessels from the cerebrum of 4-, 12-, 18- and 26-month-old male Fischer 344 rats were studied. The malondialdehyde (MDA) (μg/mg protein) content of cerebral microvessels from 12-month-old rats (0.032 ± 0.002) was significantly higher than that in 4-month-old rats (0.020 ± 0.015) P < 0.01. The difference between 26-month-old (0.025 ± 0.002) and 4-month-old rats did not reach statistical significance. The antioxidative potential was measured in the presence of a peroxy radical generator 2,2′-azobis(2-amidionopropane)hydrochloride (AAPH) with monitoring of the fluorescence of phycoerythrin at 37°C. The free radical quenching activity of cerebral microvessels expressed as % inhibition of phycoerythrin oxidation by AAPH was significantly reduced in 12-month-old (33.6 ± 4.6%) and 18-month-old rats (26.9 ± 1.4%) compared with 4-month-old rats (54.3 ± 4.9%) (P < 0.01). The 26-month-old rats (46.4 ± 4.6%) were not significantly different from 4-month-old rats. It is concluded that aging is associated with increased lipid peroxidation byproducts in cerebral microvessels along with a transient decrease in their antioxidative capacity.     

Shortening of poly (A) tail of glucose transporter — one mRNA in experimental diabetes mellitus

To determine the molecular mechanisms of diabetes-related changes in the expression of GLUT-1 in cerebral tissue, streptozotocin-induced diabetic rats and vehicle injected controls were studied after 4 weeks of diabetes. The GLUT-1 mass in cerebral microvessels was reduced in diabetic rats by approximately 38% (P<0.01). The GLUT-1 concentration in insulin-treated diabetic group was not significantly different from controls. The GLUT-1 mRNA content of cerebral tissue in diabetic rats (0.064±0.007) was significantly reduced compared to control rats (0.122±0.011) or insulin-treated diabetic rats (0.122±0.015) P<0.01. The in vitro translation of GLUT-1 mRNA of diabetic rats (0.793±0.047 arbitrary units) was also significantly lower than that in control rats (1.403±0.153) P<0.0l or insulin-treated diabetic rats. (1.124±0.083) P<0.01. These changes occurred in asssociation with a reduction in poly (A) tail length of GLUT-1 mRNA which decreased from a control value of 200–350 nt to only 50–100 nt in diabetic rats. Shortening of poly (A) tail of mRNAs is a novel mechanism of diabetes-related changes in the expression of specific genes which are regulated at a translational level. © 1997 Elsevier Science B.V. All rights reserved.     

In situ quantitative estimates of the age-related and diabetes-related changes in cerebral endothelial barrier antigen

To determine whether aging or diabetes, conditions known to alter the blood-brain barrier (BBB) is associated with changes in endothelial barrier antigen (EBA), a rat BBB-specific protein, in situ quantitation of forty vibrotome sections of cerebral tissue of 5 young (4 months old), 5 aged (26 months old) and 5 streptozotocin-induced diabetic rats after 4 weeks of diabetes were studied using immunohistologic techniques. The anti-EBA-stained microvessels were normalized against the total microvessels identified with either anti-EBA binding or anti-Glut-1 binding. The results indicate that the EBA-stained microvessels of the hippocampus, but not of other cerebral cortical areas or white matter, are reduced in aged rats(88.02±2.19%vs.80.65±2.44%, P < 0.01). There were no significant changes in the diabetic rats. These results support the notion that changes in the BBB correlate with the aging of the central nervous system.     

Blood–brain barrier mechanisms involved in brain calcium and potassium homeostasis

This study examined the potential roles of the plasma membrane Ca²⁺-ATPase (PMCA) at the blood–CSF and blood–brain barriers in brain Ca²⁺ homeostasis and blood–brain barrier Na⁺/K⁺-ATPase subunits in brain K⁺ homeostasis. During dietary-induced hypo- and hypercalcemia (0.59±0.06 and 1.58±0.12 mM [Ca²⁺]) there was no significant change in choroid plexus PMCA (Western Blots) compared to normocalcemic rats (plasma [Ca²⁺]: 1.06±0.11 mM). In contrast, PMCA in cerebral microvessels isolated from hypocalcemic rats was 150% greater than that in controls (p<0.001). Comparison of the α3 subunit of Na⁺/K⁺-ATPase from cerebral microvessels isolated from hypo-, normo- and hyperkalemic rats (2.3±0.1, 3.9±0.1 and 7.2±0.6 mM [K⁺]) showed a 75% reduction in the amount of this isoform during hyperkalemia. None of the other Na⁺/K⁺-ATPase isoforms varied with plasma [K⁺]. These results suggest that both PMCA and the α3 subunit of Na⁺/K⁺-ATPase at the blood–brain barrier play a role in maintaining a constant brain microenvironment during fluctuations in plasma composition.     

Hyperglycemic ischemia of rat brain: the effect of post-ischemic insulin on metabolic rate

To identify the mechanism by which hyperglycemia impairs recovery after cerebral ischemia, cortical blood flow (CBF), cortical metabolic rate for oxygen (CMRO₂), and the cortical phosphorylation rate for glucose (CPR_glc) were measured in rats 1 h after a global ischemic insult of the brain. A control group remained hyperglycemic after ischemia. The experimental group received insulin which reduced plasma glucose during the period of recirculation after ischemia. Thus, the brains of both groups were hyperglycemic before and during ischemia. The CMRO₂ after ischemia was higher in insulin-treated rats than in hyperglycemic rats (250 vs 168 μmol·100 g⁻¹·min⁻¹) while the CPR_glc was lower (22 vs 58 μmol·100 g⁻¹·min⁻¹). We conclude that glucose-induced inhibition of oxygen consumption in brain contributes to the impaired recovery after ischemia.     

Localization of immunoreactive glutamyl aminopeptidase in rat brain. I. Association with cerebral microvessels

Glutamyl aminopeptidase (aminopeptidase-A, EC 3.4.11.7) is an ectoenzyme that selectively hydrolyses N-terminal glutamyl and aspartyl residues from oligopeptides, including (Asp¹)angiotensin II. Here we sought to determine the distribution of glutamyl aminopeptidase (EAP) in rat brain. EAP was purified to homogeneity from rat kidney and polyclonal antiserum raised in rabbits. Immune serum inhibited EAP enzyme activity in kidney homogenates and labeled two major protein bands of M_r ≈ 136,000 and M_r = 101,000 in immunoblots of kidney protein. EAP-like immunoreactivity was concentrated on kidney proximal tubule brush borders. Immunocytochemical staining of rat brain indicated that EAP-like immunoreactivity was primarily associated with cerebral microvessels. Positive staining was detected in microvessels ranging in size from capillaries up to vessels approximately 50 μm in diameter. Isolated cerebral microvessels had a 23-fold enrichment in EAP enzyme activity (193.1 ± 40.4 nmol/mg protein/h) compared to brain homogenate. Finally, immunoblots of isolated cerebral microvessels resulted in a pattern of labeling similar to that seen with kidney homogenates. These results indicate that EAP activity in brain is primarily associated with cerebral microvessels, and suggest that EAP may be involved in the metabolism of circulating or locally formed peptides.     

Effect of nitroprusside on regional cerebral cyclic GMP, blood flow and O2 consumption in rat

This investigation was conducted to test whether topical nitroprusside (NP), a cytosolic guanylate cyclase activator, would increase the level of cyclic GMP and alter O₂ consumption or blood flow in the cerebral cortex of rats. Male Long-Evans rats were used in a control (n = 9), low dose NP (n = 13, 10⁻³ M) or high dose NP (n = 12, 10⁻² M) group. Nitroprusside or saline was topically applied to the right side of the cerebral cortex and the left side was used as a control. The cyclic GMP level was determined in five rats in each group using a radioimmunoassay. In the o ther rats in each group, regional cerebral blood flow was measured by [¹⁴C]iodoantipyrine and regional arterial and venous O₂ saturations were determined microspectrophotometrically. Nitroprusside significantly increased the cyclic GMP level from 21.4 ± 12.0 pmol/g (contralateral cortex) to 52.2 ± 36.7 pmol/g (NP treated cortex) in low dose nitroprusside group and from 19.9 ± 22.6 pmol/g (contralateral cortex) to 58.5 ± 15.1 pmol/g (NP treated cortex) in high dose nitroprusside group. High dose nitroprusside significantly increased cerebral blood flow from 80 ± 11 ml · min⁻¹ · 100 g (contralateral cortex) to 114 ± 11 ml · min⁻¹ · 100 g (NP treated cortex). However, there was no significant difference in O₂ extraction and O₂ consumption between the NP treated cortex and contralateral cortex in either the low or the high dose NP groups. In the high dose NP group, the O₂ extraction was 8.0 ± 1.3 ml O₂ · 100 ml⁻¹ in the treated cortex and 8.8 ± 1.5 ml O₂ · 100 ml⁻¹ in the contralateral cortex, while the O₂ consumptions in the NP treated cortex and contralateral cortex were 8.1 ± 1.3 ml O₂ · min⁻¹ · 100 g⁻¹ and 7.3 ± 1.2, respectively. Thus, NP increased the cyclic GMP level without a significant change in O₂ consumption in the cerebral cortex. Our data suggested that O₂ consumption in the cerebral cortex was not affected by the increased level of cyclic GMP.     

Long-term effects of intracerebroventricular insulin microinjection on renal sodium handling and arterial blood pressure in rats

The role of the central nervous system (CNS) in the control of hydrosaline homeostasis has been strikingly demonstrated by several studies. Our laboratory recently showed that centrally administered insulin produced a dose-related increase in the urinary output of sodium, which was abolished by bilateral renal denervation, nitric oxide synthase inhibition and cerebroventricular streptozotocin administration in rats. Recent studies have shown that hyperinsulinemia induces subtle derangements of intracellular insulin–insulin receptor trafficking and insulin metabolism, which are associated with an impairment of insulin signaling. The long-term effect of high insulin levels on the periventricular region could alter insulin signaling, which in turn, may modify the central natriuretic and cardiovascular effects of this peptide. In order to evaluate this hypothesis, we investigated the effects of 7-day i.c.v. insulin administration on tubular handling and blood pressure in conscious, unrestrained rats and their controls, randomly assigned to one of two separate groups: (a) i.c.v. 0.15 M NaCl-injected (n = 7) and (b) i.c.v. 126.0 ng insulin-injected rats (n = 7). In the current study, there were no significant differences between the blood pressure, daily tap water intake and serum sodium, potassium, lithium and creatinine levels in control i.c.v. 0.15 M NaCl-injected rats, compared with the insulin-treated group. Conversely, there was a significant decrease in the daily solid rat chow intake (Co: 16.4 ± 3.5 g vs. Ins: 10.3 ± 2.6 g, P = 0.003) in 7-day long-term insulin-treated rats, compared with the control group. We confirmed that centrally administered insulin produced a substantial increase in the urinary output of Na⁺, Li⁺ and K⁺, and that the response was significantly enhanced in long-term i.c.v. insulin pre-treated animals, when compared with controls (fractional sodium excretion (FE_Na) from basal: 0.047 ± 0.18% to Ins-treated: 0.111 ± 0.035%, P = 0.001). Additionally, we demonstrated that insulin-induced natriuresis occurred by increasing fractional proximal (FEP_Na) from basal (16.8 ± 2.6% to Ins-treated: 26.7 ± 2.8%, P = 0.001) and post-proximal sodium excretion (FEPP_Na) from basal (0.37 ± 0.03% to Ins-treated: 0.42 ± 0.05%, P = 0.043), despite a decreased Na⁺ filtered load and rat food intake. The current data suggest that centrally injected insulin maintain its CNS ability to amplify neuronal hypotensive and natriuretic pathways that counteract the known peripheral antinatriuretic effects of insulin.     

Role of nitric oxide in regulation of cerebral microvascular tone and autoregulation of cerebral blood flow in cats

The role of nitric oxide in the regulation of cerebrocortical microvascular tone and autoregulation of cerebral blood flow (CBF) was examined in 24 anesthetized cats. The local cerebral blood volume (CBV), mean transit time of blood (MTT), and CBF in the cortex were measured by our photoelectric method. CBV represents the cumulative dimensions of the cerebral microvessels. Intravenous injection of 0.35–0.7 mg/kg/minN^G-monomethyl-l-arginine (l-NMMA), an inhibitor of nitric oxide synthesis, significantly increased mean arterial blood pressure (MABP; 8.4–14.1%,P < 0.01), decreased CBV (15.2–28.7%,P < 0.01), and decreased CBF (20.0–29.8%,P < 0.01) in a dose-related manner. The changes in MABP, CBV, and CBF elicited byl-NMMA were inhibited (P < 0.05) by simultaneous infusion of 35 mg/kg/minl-arginine. Autoregulation of CBF was examined during controlled hypotension of −30 to −40 mmHg (artificial bleeding) and recovery of blood pressure (reinfusion of blood). Although CBF remained constant with blood pressure changes in the control state (ΔCBF/ΔMABP of 0.037±0.155 with hypotension), CBF became dependent on blood pressure changes (ΔCBF/ΔMABP of 0.478±0.135, P < 0.05) during infusion of 0.35 mg/kg/minl-NMMA. It is concluded that nitric oxide participates in both the regulation of basal tone of cerebral microvessels and the autoregulation of CBF.     

Effect of up-regulation of NMDA receptors on cerebral O2 consumption and blood flow in rat

We tested the hypothesis that cerebrocortical blood flow and O₂ consumption would be proportional to an up-regulated number of functional N-methyl- -aspartate (NMDA) receptors. Previous work had shown a relationship between cerebral metabolism and NMDA receptor activity. We increased the specific binding to NMDA receptors in the cerebral cortex, from 2.2 ± 0.9 to 4.5 ± 0.8 (density units) in male Long-Evans rats by daily giving two intraperitoneal injections (30 mg/kg) of CGS-19755, an NMDA receptor inhibitor, for 7 consecutive days (discontinued for 20 h before experiment). Twelve up-regulated (CGS treated) and 12 control rats were used in this study. Under isoflurane anesthesia and after topical stimulation of the right cerebral cortex with 10⁻² M NMDA, the blood flow (¹⁴C-iodoantipyrine method) increased from 98 ± 11 ml/min/100 g in the unstimulated cortex of the control rats to 161 ± 37 ml/min/100 g in the stimulated cortex. The unstimulated value for blood flow (95 ± 7 ml/min/100 g) did not change in the upregulated group but it doubled (194 ± 69 ml/min/100 g) in the stimulated, upregulated cortex. Similarly, O₂ consumption (cryomicrospectrophotometrically determined) in normal rats increased 46%, from 9.3 ± 1 ml/min/100 g to 13.6 ± 4 after NMDA stimulation. While in the upregulated animals, O₂ consumption increased 103% from 7.9 ± 0.6 to 16 ± 6.5 after NMDA stimulation. In conclusion, NMDA receptor upregulation does not alter basal cerebrocortical blood flow or O₂ consumption but in the NMDA-stimulated cortex, the blood flow and O₂ consumption increase is dependent on the number of NMDA receptors present.     

Cerebral extracellular lactate concentration and blood flow during chemical stimulation of the nucleus tractus solitarii in anesthetized rats

The extracellular lactate concentration and blood flow in the cerebral cortex of urethane-anesthetized, paralyzed and artificially ventilated rats were monitored continuously and simultaneously using an enzyme electrode and a laser Doppler flowmeter (LDF), respectively, during chemical stimulation of the nucleus tractus solitarii (NTS) by microinjection of -glutamate (1.7 nmol 50 nl). Chemical stimulation of the NTS significantly decreased the arterial blood pressure (ABP) from 85 ± 17 to 68 ± 14 mmHg, heart rate from 418 ± 13 to 402 ± 19 beats · min⁻¹ and cerebral blood flow (CBF) by 17.9 ± 6.2% (P < 0.001). However, chemical stimulation of the NTS significantly increased the lactate concentration by 58.9 ± 17.3 μM (P < 0.001). Barostat maneuver, which held systemic ABP constant during chemical stimulation of the NTS attenuated the responses in CBF and lactate concentration by 30 and 27%, respectively. The onset of the increase in lactate concentration was delayed about 19 s after that of the CBF decrease. Circulatory lactate produced no significant change in the cerebral extracellular lactate concentration. These results indicate that chemical stimulation of the NTS induces an increase in extracellular lactate concentration in the cerebral cortex through a decrease in CBF via cerebral vasoconstriction.     

Effects of perfusion flow rate, prostaglandin F2α, phenylephrine, and serotonin on isolated, perfused brains of spontaneously hypertensive rats

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F_2α (PGF_2α) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 ± 3mm Hg(n = 11) in SHR and 32 ± 2mm Hg(n = 12)in WKY(P < 0.005). The perfusion pressures at all flow rates tested (2.5−6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to sertonin compared with phenylephrine and PGF_2α. EC₅₀ values (−logM) for serotonin in the perfused brains of SHR and WKY were 7.0 ± 0.06 (n = 10)and6.5 ± 0.06 (n = 11), respective (P < 0.01). There were no differences in EC₅₀ values for phenylephrine or PGF_2α between SHR and WKY. Exogenous serotonin and phenulephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF_2α was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY, and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.     

Cortical spreading depression-associated hyperemia in rats: involvement of serotonin

We investigated whether the vasoactive neurotransmitter serotonin (5-HT) is involved in cortical spreading depression (CSD)-associated hyperemia in the rat. We focused on the 5-HT₂ receptor, which is engaged in 5-HT induced small arteriolar relaxation in cats, as well as on the 5-HT_1D/1B receptor, the binding site of the potent antimigraine drug sumatriptan. In male barbiturate anaesthetized Wistar rats (n=25) CSDs were elicited by brain topical application of 1 M KCl, and the DC-potential and regional cerebral blood flow (rCBF, by Laser Doppler flowmetry) were measured over the same hemisphere through dura and thinned bone, respectively. Intravenous application of 8 mg/kg of the 5-HT_2A/2C receptor antagonist ritanserin (group I; n=8) significantly reduced the hyperperfusion amplitude during CSD by 44% (p<0.05, from 342±124 to 194±97%, baseline before CSD=100%), and prolonged its duration by approx. 30%. Vehicle alone (group II; n=4) did not affect CSD hyperperfusion. The highly selective 5-HT_1D/1B receptor agonist 311C90 was given in two doses: 100 μg/kg i.v. (n=5) had no effect on CSD hyperperfusion, while 800 μg/kg (n=5) increased hyperperfusion significantly (p<0.05, from 224±86 to 310±148%). We conclude that serotonin is, probably via 5-HT₂ receptors, involved in the modulation of the regional cerebral blood flow increase during CSD. Novel highly selective receptor antagonists may help to discriminate the differential contribution of various 5-HT receptor subspecies.     

Iron intake increases infarct volume after permanent middle cerebral artery occlusion in rats

Experimental and clinical data suggest an important role of iron in cerebral ischaemia. We measured infarct volume and analysed the oxidative stress, and also the excitatory and inflammatory responses to brain injury in a rat stroke model after an increased oral iron intake. Permanent middle cerebral artery occlusion (MCAO) was performed in ten male Wistar rats fed with a diet containing 2.5% carbonyl iron for 9 weeks, and in ten control animals. Glutamate, interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) were determined in blood samples before and at 2, 4, 6, 8, 24 and 48 h after MCAO, and thiobarbituric acid reaction substances (TBARS) were analysed at 48 h. Infarct volume was measured at 48 h by image analysis on brain slices stained with 1% TTC. Tissue iron was measured by atomic absorption spectrophotometry. Infarct volume was 66% greater in the iron fed rats than in the control group (178±49 mm³ versus 107±53 mm³, P<0.01). Significant higher levels of glutamate, IL-6 and TNF-α were observed in the group with iron intake (peak values were obtained at 6, 8 and 4 h, respectively). Iron-fed animals also showed significantly higher levels of TBARS than those receiving a normal diet (6.52±0.59 vs. 5.62±0.86 μmol/l, P=0.033) Liver iron stores (3500±199 vs. 352±28 μg Fe/g, P<0.0001), but not brain iron stores (131 vs. 139 μg Fe/g, P=0.617), were significantly higher in the iron fed rats group. These results suggest that iron intake is associated with larger infarct volumes after MCAO in the rat. This effect seems to be associated with higher oxidative stress, excitotoxicity and inflammatory responses.     

Vasodilatory actions of calcitonin gene-related peptide and nitric oxide in parenchymal microvessels of the rat hippocampus

Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are potent dilators in a variety of vascular beds. Recent evidence suggests that NO may serve as an intermediary messenger for CGRP and/or CGRP may serve as an intermediary messenger for NO in the expression of vasodilation. The present study was designed to provide an initial characterization of the responses to NO and CGRP in parenchymal microvessels and to determine whether NO and/or CGRP act as intermediaries for one another. Microvessels in the parenchyma of in vitro hippocampal slices from rat brain were examined using computer-assisted videomicroscopy. The resting diameter of the microvessels ranged from 9 to 26 μm. Treatment with the nitric oxide synthase inhibitor, N^G-nitro-l-arginine ( -NNA; 100 μM) constricted vessels to 64.2% ± 3.0% of resting luminal diameter. Sodium nitroprusside (SNP; 1 μM), a donor of NO, reversed the -NNA-induced vasoconstriction by 77.0% ± 15.0%. CGRP alone (10 nM) elicited a small but significant vasodilatory effect on resting vascular tone (2.3% ± 0.6%). In the presence of -NNA, CGRP elicited a significant dose-dependent vasodilatory response, and 10 nM CGRP elicited a sizeable response, reversing the -NNA-induced constriction by 84.3% ± 15.5%. This CGRP-induced dilation was inhibited by pretreatment with the CGRP receptor antagonist, CGRP fragment (8–37) (1 μM). In contrast, pretreatment with 1 μM CGRP fragment (8–37) did not attenuate the SNP-induced dilation in the presence of -NNA. Taken together, these findings demonstrate that CGRP and NO are potent dilators of parenchymal microvessels, and that NO provides a substantial relaxant effect on resting tone. In addition, the results indicate that CGRP is not a necessary intermediary in NO-induced dilation, and that NO is not a necessary intermediary in CGRP-induced dilation in parenchymal microvessels.     

Differential patterns of local cerebral glucose utilisation associated with rilmenidine- or B-HT 933-induced hypotension

The anti-hypertensive drug, rilmenidine, has activity at both imidazoline-preferring receptors (IPRs) andα₂-adrenoceptors. However, available evidence suggests that its hypotensive effect is mediated via central IPRs. In the present study, the neuroanatomical regions involved in mediating the hypotensive response to rilmenidine were investigated using the [¹⁴C]2-deoxyglucose in vivo autoradiographic technique to map drug-induced changes in glucose utilisation within the CNS of conscious, spontaneously hypertensive rats (SHR). The cerebral metabolic effects of rilmenidine were compared with those of B-HT 933, a selective,α₂-adrenoceptor agonist with no selectivity for the IPR. Rilmenidine (1 mg/kg, s.c.) and B-HT 933 (2 mg/kg, s.c.) both elicited a moderate but significant hypotension (−24±2 and−18±5mmHg, resp.) and bradycardia (−62±19.5 and−69±14 beats/min, resp.). [¹⁴C]2-deoxyglucose autoradiography, initiated after stabilisation of the drug-induced reduction in blood pressure, revealed significant reductions (P < 0.05) in local cerebral glucose utilisation (LCGU) in the intermediolateral cell column of the spinal cord, area postrema, ventrolateral medulla, nucleus tractus solitarius and cuneate nucleus of rilmenidine-treated rats. Rilmenidine did not significantly alter LCGU in a number of structures containing high densities ofα₂-adrenoceptors such as nucleus accumbens, locus coeruleus, frontal cortex. No significant changes in glucose use were evident in any of the 26 CNS regions examined following B-HT 933 administration. These results provide evidence for the functional involvement of brainstem cardiovascular control centres in the central hypotensive effects of rilmenidine. In addition, the neuroanatomical localisation of rilmenidine-induced glucose use changes in relation to the distributions of IPR andα₂-adrenoceptor binding sites, further supports the involvement of IPRs in the hypotensive response to rilmenidine.     

Effect of hypothermia on kainic acid-induced limbic seizures: an electroencephalographic and C-deoxyglucose autoradiographic study

The effect of body temperature on kainic acid (KA)-induced limbic seizures was examined in Wistar rats. In rats undergoing limbic seizure induced by 1 μg intra-amygdaloid injection of KA, the post-injection latency of initial ictal discharges in the left amygdala was significantly longer in rats whose body temperature was lowered to 30°C (2.55±0.94 min at 37°C, 13.19±5.70 min at 30°C; p=0.0017). The post-injection latency of initial ictal discharges in the left hippocampus was also significantly longer under the same conditions (23.68±9.96 min at 37°C, 43.85±17.98 min at 30°C; p=0.0253). The number of limbic seizures occurring in the first 2 h post-injection was significantly lower in hypothermic rats (30.0±10.7 at 37°C, 8.71±2.69 at 30°C; p=0.0017), as was the total duration of limbic seizures over the same period (23.61±8.45 min at 37°C, 10.30±4.48 min at 30°C; p=0.0060). Local cerebral glucose utilization (LCGU), measured 2 h post-injection, was significantly lower in hypothermic rats, mainly in the limbic structures. ¹⁴C-deoxyglucose autoradiograms showed decreased radiation density not only in the left amygdala and bilateral hippocampus, but also in the cerebral cortex of hypothermic rats. The results of the present experiment demonstrate that the use of hypothermia, which has been shown to be effective in the treatment of acute cerebral ischemia and brain injury, may also be effective in the treatment of status epileptics.     

MRZ 2/579, a novel uncompetitive N-methyl- -aspartate antagonist, reduces infarct volume and brain swelling and improves neurological deficit after focal cerebral ischemia in rats

The purpose of this study was to evaluate the effects of MRZ 2/579, an uncompetitive N-methyl- -aspartate antagonist, on infarct size, extent of swelling and neurological deficit in a model of transient middle cerebral artery occlusion in rats. Physiologically controlled Sprague–Dawley rats received 2 h MCAo by retrograde insertion of an intraluminal suture coated with poly- -lysine. The agent (MRZ 2/579) or vehicle (sodium chloride 0.9%) was administered i.v. immediately after suture removal following a 2-h period of MCAo. Two experimental groups were studied: group A was treated by vehicle (bolus infusion:1 ml/kg for 10 min followed by infusion of 6 ml/kg/h over 6 h). Group B was treated by MRZ 2/579 (bolus infusion:10 mg/kg for 10 min followed by infusion of 6 mg/kg/h over 6 h). The neurological status was evaluated during occlusion (at 60 min) and daily for 3 days after MCAo. Brains were then perfusion-fixed, and infarct volumes and brain swelling were determined. MRZ 2/579 significantly improved the neurological score compared to vehicle-treated rats at 48 h (6.2±0.6 and 8.7±0.5, respectively; P<0.004) and 72 h after MCAo (5.2±0.6 and 8.4±0.5, respectively; P<0.001). Treatment with MRZ 2/579 also significantly reduced total infarct volume (29.3±11.1 and 83.2±16.5 mm³, respectively; P<0.01), cortical infarct volume (24.8±11.2 and 70.0±18.0 mm³, respectively; P<0.04) and subcortical infarction (21.2±4.1 and 49.6±4.5 mm³, respectively; P<0.0002). Brain swelling was also markedly reduced compared with vehicle-treated rats (4.7±1.3 and 10.8±2.1%, respectively; P<0.02). These results demonstrate that treatment with MRZ 2/579, when administered promptly after reperfusion, confers neuroprotective effects on infarct volume, brain swelling, and neurological score compared to the vehicle group.     

Cerebrovascular changes elicited by electrical stimulation of the centromedian-parafascicular complex in rat

Electrical stimulation of the centromedian-parafascicular complex (CM-Pf) in anesthetized (chloralose) and paralyzed (tubocurarine) rats elicites a widespread cerebrovascular dilatation. Regional cerebral blood flow (rCBF) was measured in dissected tissue samples of 10 brain regions (medulla, pons, cerebellum, inferior colliculus, superior colliculus, frontal parietal and occipital cortices, caudate-putamen and corpus callosum) by [¹⁴C]iodoantipyrine method. In unstimulated and sham-operated rats rCBF ranged from 40±3 (ml/100g/min) in corpus callosum to 86±6 (ml/100g/min) in inferior colliculus. During CM-Pf stimulation, rCBF increased significantly P < 0.05, analysis of variance and Scheffe's test) in all cerebral regions bilaterally ranging from +118% in parietal cortex to +38% in cerebellum. Although cerebral vasodilation elicited by CM-Pf stimulation persisted after unilateral transection of the cervical sympathetic trunk, the cortical CBF was significantly reduced (P < 0.05) on the denervated side. Acute adrenalectomy significantly (P < 0.05) decreased elevated rCBF during CM-Pf stimulation in all cortical regions (frontal −36%, parietal −34%, and occipital −27%) and in caudate nucleus (−37%). Thus, excitation of neurons originating in, or fibers passing through the CM-Pf can elicit a powerful cerebral vasodilation. The cerebral vasodilation is modulated by cervical sympathectomy and circulating adrenal hormones. We conclude that CM-Pf elicited vasodilation is at least partly mediated by intrinsic neural pathways.