Serotonin 5-HT1A Receptor Activation Increases Cyclic AMP Formation in the Rat Hippocampus In Vivo

Abstract: In vivo microdialysis was used to examine the efflux of cyclic AMP (cAMP) into the extracellular fluid of the ventral hippocampus in the freely moving rat. The changes in extracellular cAMP concentration were monitored in response to forskolin and the serotonin 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). The basal level of hippocampal extracellular cAMP was 2.3 ± 0.2 pmol/ml (n = 6), after a 3-h postsur- gery stabilisation period. Perfusion of forskolin (100 μM) through the probe for 30 min significantly increased the efflux of cAMP, which returned to baseline levels within 90 min. 8-OH-DPAT (0.3 mg/kg s.c.) also significantly increased cAMP efflux, whereas a similar volume of saline had no effect. Desensitisation of the 8-OH-DPAT-induced increase in cAMP efflux was observed following a second administration of 8-OH-DPAT after a 4-h interval. Administration of 8-OH-DPAT did not alter the efflux of cAMP when forskolin was perfused through the probe. Pretreatment with WAY 100135 [N-tert-butyl 3–4-(2-methoxyphenyl)piperazine-1 -yl-2-phenylpropanamide dihydrochloride] (5 mg/kg s.c.), a specific 5-HT_1A receptor antagonist, prevented the 8-OH-DPAT-induced increase in cAMP efflux. The data indicate that the 8-OH-DPAT-induced increase in cAMP efflux in vivo is mediated by a 5-HT_1A receptor.     

Prevention of kainic acid-induced changes in nitric oxide level and neuronal cell damage in the rat hippocampus by manganese complexes of curcumin and diacetylcurcumin

Curcumin is a natural antioxidant isolated from the medicinal plant Curcuma longa Linn. We previously reported that manganese complexes of curcumin (Cp-Mn) and diacetylcurcumin (DiAc-Cp-Mn) exhibited potent superoxide dismutase (SOD)-like activity in an in vitro assay. Nitric oxide (NO) is a free radial playing a multifaceted role in the brain and its excessive production is known to induce neurotoxicity. Here, we examined the in vivo effect of Cp-Mn and DiAc-Cp-Mn on NO levels enhanced by kainic acid (KA) and L-arginine (L-Arg) in the hippocampi of awake rats using a microdialysis technique. Injection of KA (10 mg/kg, i.p.) and L-Arg (1000 mg/kg, i.p.) significantly increased the concentration of NO and Cp-Mn and DiAc-Cp-Mn (50 mg/kg, i.p.) significantly reversed the effects of KA and L-Arg without affecting the basal NO concentration. Following KA-induced seizures, severe neuronal cell damage was observed in the CA1 and CA3 subfields of hippocampal 3 days after KA administration. Pretreatment with Cp-Mn and DiAc-Cp-Mn (50 mg/kg, i.p.) significantly attenuated KA-induced neuronal cell death in both CA1 and CA3 regions of rat hippocampus compared with vehicle control, and Cp-Mn and DiAc-Cp-Mn showed more potent neuroprotective effect than their parent compounds, curcumin and diacetylcurcumin. These results suggest that Cp-Mn and DiAc-Cp-Mn protect against KA-induced neuronal cell death by suppression of KA-induced increase in NO levels probably by their NO scavenging activity and antioxidative activity. Cp-Mn and DiAc-Cp-Mn have an advantage to be neuroprotective agents in the treatment of acute brain pathologies associated with NO-induced neurotoxicity and oxidative stress-induced neuronal damage such as epilepsy, stroke and traumatic brain injury.     

Intrastriatal Infusion of (±)-S-Nitroso-N-Acetylpenicillamine Releases Vesicular Dopamine via an Ionotropic Glutamate Receptor-Mediated Mechanism: An In Vivo Microdialysis Study in Chloral Hydrate-Anesthetized Rats

Abstract: The existence of both nitric oxide synthase (NOS) immunoreactive interneurons and amino acid neurotransmitter-mediated nitric oxide (NO) release in the striatum suggests a role for NO in modulating striatal function. To explore the potential interaction between NO and dopaminergic neurotransmission, the NO-releasing agent (±)-S-nitroso-N-acetylpenicillamine (SNAP) was administered locally into the anterior medial striatum of chloral hydrate-anesthetized rats. SNAP, at 0.5, 1, and 2 mM concentrations, elevated striatal extracellular (EC) dopamine (DA) to 200 ± 42, 472 ± 120, and 2,084 ± 496%, respectively, above baseline levels. Perfusion with (±)-penicillamine (PEN, 1 mM), the non-NO-containing carrier component of SNAP, was ineffective, indicating that PEN is not responsible for SNAP-mediated DA release. Additional microdialysis experiments suggest SNAP-mediated DA release is not due to NO-induced neurotoxicity or blockade of the DA transporter. The DA-releasing effect of SNAP was attenuated under calcium-free conditions and abolished in rats pretreated with reserpine (5 mg/kg), implicating a calcium-sensitive vesicular-dependent release process. To determine the mechanism of SNAP-mediated DA release, the guanylyl cyclase (GC) inhibitor LY 83583 (100 µM) was administered 100 min before and during the SNAP pulse. LY 83583 elevated EC DA levels approximately fivefold and potentiated the DA-releasing effect of SNAP to 2,598 ± 551% above basal DA levels. Similar pretreatments with both the noncompetitive N-methyl-d -aspartate (NMDA) antagonist MK-801 (10 µM) and the competitive NMDA-receptor antagonist (±)-3-(carboxypiperazin-4-yl)propyl-1-phosphonic acid [(±)-CPP, 100 µM] blocked SNAP-mediated DA release. SNAP-mediated DA release was also significantly blunted by pretreatment and coperfusion with MgSO₄ (10 mM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 µM) but not (+)-2-amino-3-phosphonopropionic acid (AP-3, 10 µM). These results suggest that NO releases DA via a calcium-sensitive vesicular-dependent process that is independent of GC activation. In addition, NMDA and kainate/(±)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated mechanisms are implicated in NO-induced DA release.     

Effect of Pentylenetetrazole-Induced Kindling on Acetylcholine Release in the Hippocampus of Freely Moving Rats

Abstract: The role of γ-aminobutyric acid (GABA) modulation of septohippocampal cholinergic neurons in kindling was investigated. Hippocampal acetylcholine release was evaluated with the microdialysis technique in freely moving rats either after acute administration of isoniazid (an inhibitor of GABA synthesis) or pentylenetetrazole (PTZ)(a blocker of the GABA_A receptor-associated Cl⁻ channel) or after chronic administration of PTZ. Short-term treatment with PTZ (5–50 mg/kg, i.p.) or isoniazid (150–250 mg/kg, s.c.) increased hippocampal acetylcholine release in a dose-dependent manner. In contrast, the basal concentration of acetylcholine in the dialysate from the hippocampus of rats chronically treated with PTZ (kindled animals) was significantly reduced relative to that of vehicle-treated rats (2.39 ± 0.21 vs. 4.2 ± 0.31 pmol per 20-min sample; p < 0.01). Moreover, the release of acetylcholine was markedly more sensitive to the effect of a challenge injection of PTZ (10 or 20 mg/kg, i.p.) in kindled rats than in naive rats or rats chronically treated with vehicle. Abecarnil, a selective benzodiazepine receptor agonist with marked anticonvulsant activity, was administered together with chronic PTZ to evaluate whether persistent activation of GABA_A receptors and suppression of seizures during kindling might affect the sensitivity of septohippocampal cholinergic neurons to a challenge dose of PTZ. Abecarnil (1 mg/kg, i.p.) administered 40 min before each PTZ injection neither antagonized the decrease in basal acetylcholine release (2.26 ± 0.19 pmol per 20-min sample) nor prevented the development of kindling. In contrast, abecarnil prevented the chronic PTZ-induced increase in the sensitivity of acetylcholine release to a challenge dose of PTZ. These results provide novel in vivo data concerning the role of hippocampal acetylcholine function in the development of kindling and potentially in the learning and memory deficits associated with this phenomenon.     

IRFI 042 reduces oxidative stress against kainic acid toxicity in the rat brain

We investigated if IRFI 042, an analog of vitamin E, protects the brain against oxidative stress induced by intraperitoneal administration of Kainic acid (KA) (10 mg/kg); sham brain injury rats were used as controls. Animals received either IRFI 042 (20 mg/kg) or its vehicle 30 min before KA injection and after 6 h were sacrificed to measure malonildyaldheide (MDA) and glutathione levels (GSH) in the diencephalon. Behavioral changes were also monitored. Intraperitoneal administration of IRFI decreased MDA (micromol/g wet tissue: KA + vehicle = 22.5 ± 4.2; KA + IRFI = 17.1 ± 1; P < 0.005) and prevented GSH loss (nmol/g wet tissue: KA + vehicle = 0.41 ± 0.1; KA + IRFI = 1.86 ± 0.2; P < 0.005) in the diencephalon. The latency of occurrence of behavioral signs increased from 39 ± 1 to 62 ± 6 min in IRFI 042 group. The data suggest that IRFI 042 might protect against KA‐induced oxidative stress.     

Basal Endothelial Nitric Oxide Release Is Preserved in Overweight and Obese Adults

Objective: Impaired basal nitric oxide release is associated with a number of cardiovascular disorders including hypertension, arterial spasm, and myocardial infarction. We determined whether basal endothelial nitric oxide release is reduced in otherwise healthy overweight and obese adult humans. Research Methods and Procedures: Seventy sedentary adults were studied: 32 normal weight (BMI <25 kg/m²), 24 overweight (BMI ≥ 25 < 30 kg/m²), and 14 obese (BMI ≥ 30 kg/m²). Forearm blood flow (FBF) responses to intra‐arterial infusions of N^g‐monomethyl‐l ‐arginine (5 mg/min), a nitric oxide synthase inhibitor, were used as an index of basal nitric oxide release. Results: N^g‐monomethyl‐l ‐arginine elicited significant reductions in FBF in the normal weight (from 4.1 ± 0.2 to 2.7 ± 0.2 mL/100 mL tissue/min), overweight (4.1 ± 0.1 to 2.8 ± 0.2 mL/100 mL tissue/min), and obese (3.9 ± 0.3 to 2.7 ± 0.2 mL/100 mL tissue/min) subjects. Importantly, the magnitude of reduction in FBF (～30%) was similar among the groups. Discussion: These results indicate that the capacity of the endothelium to release nitric oxide under basal conditions is not compromised in overweight and obese adults.     

Use of a Hemoglobin-Trapping Approach in the Determination of Nitric Oxide in In Vitro and In Vivo Systems

We describe methods for measuring the release of nitric oxide (NO) derived from organic nitrates in vitro, using triple wavelength and difference spectrophotometry in the presence and absence of concentric microdialysis probes. These methods are based on the ability of NO to oxidize oxyhemoglobin (OxyHb) to methemoglobin (MetHb) quantitatively in aqueous solution. Isosorbide dinitrate (ISDN), a thiol-dependent organic nitrate, increased MetHb concentration in 45 min from 2.47 ± 0.47 to 4.15 ± 0.12 M (p < 0.05) and decreased OxyHb concentration from 2.13 ± 0.35 to 0.33 ± 0.26 M (p < 0.05) at 37°C. At 27°C, the OxyHb concentration was not significantly altered (2.04 ± 0.23 to 1.60 ± 0.04 M) by ISDN, nor was the MetHb concentration (from 2.68 ± 0.50 to 2.59 ± 0.25 M). Sodium nitroprusside (SNP), a thiol-independent organic nitrate, increased MetHb concentrations in 30 min from 4.21 ± 0.26 to 6.00 ± 0.56 M (p < 0.05) at 37°C, and from 4.23 ± 0.39 to 5.90 ± 0.43 M (p < 0.01) at 27°C. SNP also decreased OxyHb concentrations in 30 min from 1.99 ± 0.32 to 0.13 ± 0.12 M (p < 0.01) at 37°C, and from 2.25 ± 0.31 to 0.13 ± 0.09 M (p < 0.01) at 27°C. Difference spectrophometry indicated that 0.25-5 mM SNP significantly increased NO production in a dose-dependent fashion. This hemoglobin-trapping technique was also useful in quantifying the concentrations of NO released from SNP in aqueous solution in vitro, using concentric microdialysis probes. The NO concentration following exposure to SNP was 530 ± 50 nM, as determined using the difference spectrophotometric technique. To demonstrate the applicability of this technique to in vivo microdialysis, we implanted concentric microdialysis probes into hippocampus and cerebellum of conscious and anesthetized rats. Baseline NO concentrations in hippocampus of conscious and anesthetized rats were 11 ± 2 nM and 23 ± 9 nM, respectively, while in the cerebellum NO concentrations were 28 ± 9 nM and 41 ± 20 nM, respectively. These results demonstrate that microdialysis using a novel hemoglobin-trapping technique possesses adequate sensitivity to measure the NO levels produced from organic nitrates in aqueous solutions, and further document the applicability of this approach to in vivo systems.     

Effect of the Non-NMDA Receptor Antagonist GYKI 52466 on the Microdialysate and Tissue Concentrations of Amino Acids Following Transient Forebrain Ischaemia

Abstract: The effect of the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466) on ischaemia-induced changes in the microdialysate and tissue concentrations of glutamate, aspartate, and γ-aminobutyric acid (GABA) was studied in rats. Twenty minutes of four-vessel occlusion resulted in a transient increase in microdialysate levels of glutamate, aspartate, and GABA in striatum, cortex, and hippocampus. Administration of GYKI 52466 (10 mg/kg bolus + 10 mg/kg/60 min intravenously starting 20 min before onset of ischaemia) inhibited ischaemia-induced increases in microdialysate glutamate and GABA in striatum without affecting the increases in hippocampus or cortex. Twenty minutes of four-vessel occlusion resulted in immediate small decreases and larger delayed (72 h) decreases in tissue levels of glutamate and aspartate. Transient increases in tissue levels of GABA were shown in all three structures at the end of the ischaemic period. At 72 h, after the ischaemic period, significantly reduced GABA levels were observed in striatum and hippocampus. GYKI 52466, given under identical conditions as above, augmented the ischaemia-induced decrease in striatal tissue levels of glutamate and aspartate, without significantly affecting the decreases in hippocampus and cortex. Twenty minutes of ischaemia resulted in a large increase in microdialysate dopamine in striatum. GYKI 52466 failed to inhibit this increase. Kainic acid (500 μM infused through the probe for 20 min) caused increases in microdialysate glutamate and aspartate in the striatum. GYKI 52466 (10 mg/ kg bolus + 10 mg/kg/60 min) completely inhibited the kainic acid-induced glutamate release. In conclusion, the action of the non-NMDA antagonist, GYKI 52466, in the striatum is different from that in the cortex and hippocampus. The inhibition by GYKI 52466 of ischaemia-induced and kainate-induced increases in microdialysate glutamate concentration in the striatum may be related to the neuroprotection provided by GYKI 52466 in this region.     

Extracellular Glutamate During Focal Cerebral Ischaemia in Rats: Time Course and Calcium Dependency

Abstract: The time course of changes in extracellular glutamic acid levels and their Ca²⁺ dependency were studied in the rat striatum during focal cerebral ischaemia, using microdialysis. Ischaemia-induced changes were compared with those produced by high K⁺-evoked local depolarization. To optimize time resolution, glutamate was analysed continuously as the dialysate emerged from the microdialysis probe by either enzyme fluorimetry or biosensor. The Ca²⁺ dependency of glutamate changes was examined by perfusing the probe with Ca²⁺-free medium. With normal artificial CSF, ischaemia produced a biphasic increase in extracellular glutamate, which started from the onset of ischaemia. During the first phase lasting ～10 min, dialysate glutamate level increased from 5.8 ± 0.9 µM· min^?1 to 35.8 ± 6.2 µM where it stabilized for ～3 min. During the second phase dialysate glutamate increased progressively to its maximum (82 ± 8 µM), reached after 55 min of ischaemia, where it remained for as long as it was recorded (3 h). The overall changes in extracellular glutamate were similar when Ca²⁺ was omitted from the perfusion medium, except that the first phase was no longer detectable and, early in ischaemia, extracellular glutamate increased at a significantly slower rate than in the control group (2.2 ± 1 µM· min^?1; p < 0.05). On the basis of these data, we propose that most of the glutamate released in the extracellular space in severe ischaemia is of metabolic origin, probably originating from both neurons and glia, and caused by altered glutamate uptake mechanisms. Comparison with high K⁺-induced glutamate release did not suggest that glutamate “exocytosis,” early after middle cerebral artery occlusion, was markedly limited by deficient ATP levels.     

Measurement of unbound caffeic acid in rat blood by on-line microdialysis coupled with liquid chromatography and its application to pharmacokinetic study

To monitor the levels of caffeic acid in rat blood, an on-line microdialysis system coupled with liquid chromatography was developed. The microdialysis probe was inserted into the jugular vein/right atrium of male Sprague-Dawley rats. Caffeic acid (100 mg/kg, i.v.) was then administered via the femoral vein. Dialysates were automatically injected onto a liquid chromatographic system via an on-line injector. Samples were eluted with a mobile phase containing methanol–100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5). The UV detector wavelength was set at 320 nm. The detection limit of caffeic acid was 20 ng/ml. The in vivo recoveries of the microdialysis probe for caffeic acid at 0.5 and 1 μg/ml were 48.34±2.68 and 47.64±3.43%, respectively (n=6). Intra- and inter-assay accuracy and precision of the analyses were ≤10% in the range of 0.05 to 10 μg/ml. Pharmacokinetics analysis of results obtained using such a microdialysis–chromatographic method indicated that unbound caffeic acid in the rat fitted best to a biexponential decay model.     

Improved method for the measurement of glutamate and aspartate using capillary electrophoresis with laser induced fluorescence detection and its application to brain microdialysis

We have previously published data on the analysis of glutamate in microdialysis samples using a commercially availble CE apparatus. Here we demonstrate further improvements in the analysis of both glutamate and aspartate from very small volume microdialysates. The limit of detection of our system has been increased to 10⁻⁹ M for both glutamate and aspartate. This permits microdialysis sampling time to be reduced to 2 min, thus improving the temporal resolution of microdialysis sampling. Concurrently, migration time has also been reduced such that resolution of both amino acids can be achieved inside 2 min. This new analytical method has been applied to the measurement of the EAA from microdialysis samples from the dentate gyrus of the hippocampus. Extracellular concentrations of both glutamate and aspartate increased to a maximum of 5- and 4.5-fold of preinfusion values, respectively, during infusion of 100 mM K⁺ through the microdialysis probe. This is consistent with the depolarization-evoked release of both amino acids from this brain region.     

Hippocampal Serotonin 5-HT1A Receptor Enhances Acetylcholine Release in Conscious Rats

Abstract: We investigated changes in the extracellular levels of acetylcholine (ACh) following local application of serotonergic agents to the dorsal hippocampus of freely moving rats by means of perfusion using a microdialysis technique. Perfusion of serotonin (5-HT; 10 μM, for 30 min at a rate of 3 μl/min), dissolved in Ringer's solution containing 10 μM eserine, showed no marked effect on the extracellular levels of ACh. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 20 μM), a 5-HT_1A agonist, increased ACh levels, whereas 7-trifluoromethyl-4-(4-methyl-1 -piperazinyl)-pymoto[1,2-a]quinoxaline (CGS-12066B; 100 μM), a 5-HT_1B agonist, decreased it. Clomipramine (2 μM), an uptake inhibitor of 5-HT, had no effect on ACh levels. Following perfusion of 1-(2-methoxyphenyl)-4-[4- (2-phthalimido)butyl]piperazine (NAN-190; 10 μM), which is a selective 5-HT_1A antagonist, the effect of 8-OH-DPAT was totally abolished, whereas CGS-12066B decreased extracellular ACh levels. 5-HT, as well as Clomipramine, had a decreasing effect on ACh levels after pretreatment with NAN-190. These results indicate that the 5-HT_1A receptor, which exists in the dorsal hippocampus, enhances the spontaneous ACh release, and that the mechanism of serotonergic modulation of ACh release partly depends on both the stimulatory control via the 5-HT_1A receptor and the suppressive one via the 5-HT_1B receptor in the dorsal hippocampus of rats.     

Simultaneous measurement of blood and brain microdialysates of granisetron in rat by high-performance liquid chromatography with fluorescence detection

Simultaneous microdialysis probes in the blood and brain and sensitive high-performance liquid chromatography with fluorescence detection were used to examine the granisetron concentration in the jugular vein and frontal cortex of rats after drug administration. Two microdialysis probes were inserted into the right jugular vein and frontal cortex of male Sprague–Dawley rats to which granisetron (6 mg/kg, i.v.) had been administered. Dialysates were automatically collected using a microfraction collector. Samples were eluted with a mobile phase containing 25 mM acetate buffer (pH 4.8)–acetonitrile (72:28, v/v). Excitation and emission wavelengths were set at 305 and 360 nm, respectively, on a scanning fluorescence detector. The limit of quantification for granisetron was 0.5 ng/ml. The in vitro recovery of granisetron was 29.7±1.2% (n=6) for the jugular vein microdialysis probe and 6.1±0.5% (n=6) for the frontal cortex microdialysis probe. The increasing brain/blood concentration ratio of granisetron suggests that granisetron penetrates the blood–brain barrier.     

A Previous Potassium Stimulation Enhances the Increases of Striatal Extracellular Dopamine and 5-Hydroxytryptamine During Global Ischaemia Under Simulated Penumbral Conditions

The effect of a previous K^± stimulation on striatal extracellular monoamine levels during global ischaemia, under simulated penumbral conditions, was investigated. Rats were implanted with microdialysis probes in both striata, monoamine release was stimulated unilaterally by adding K^± (100 mM, 20 min) to the artificial CSF perfused through one probe, and bilateral partial ischaemia was imposed after monoamine levels had returned to basal values or below. Resultant increases in dialysate levels of dopamine and 5-hydroxytryptamine were markedly and significantly greater on the side previously exposed to K^±, even though electrophysiological measurements indicated similarly severe ischaemia on both sides. Associated monoamine metabolite changes did not differ significantly between the two sides. There was no evidence of greater neuronal loss in the K^±-stimulated striata 7 days after ischaemia. However, striatal tissue probably exposed to the highest concentrations of K^± could not be examined because of extensive gliosis around the probe.     

NO介质在大鼠红藻氨酸诱导癫痫发作中的作用

目的：进一步探讨脑内一氧化氮(NO)介质(NO或NO衍生物)在复杂部分性及全身强直阵挛性癫痫发作中的作用。方法：采用红藻氨酸(KA)诱导大鼠癫痫发作,以NO合酶抑制剂L-硝基精氨酸(L-NNA)或NO前体L-精氨酸(L-Arg)予以预处理,观察其癫痫发作行为及海马结构内NO含量(NO2^-/NO3^-)的变化。结果：给予大鼠惊厥剂量KA(10mg/kg),15min时出现湿狗样抖动(WDS),1～3h出现全身痉挛;经L-NNA(50mg/kg)或L-Arg(40mg/kg)预处理的大鼠,注射相同剂量的KA后,其癫痫行为发生明显变化,L-NNA预处理的大鼠癫痫发作行为明显加重,表现为全身痉挛的潜伏期缩短、时间延长、死亡率提高;L-Arg预处理的大鼠癫痫发作行为减弱,WDS和全身痉挛的潜伏期均延长,发作程度减轻、时间缩短,观察时间内无一例死亡。KA给药后30min海马结构内的NO2^-/NO3^-含量迅速增多,7d时仍持续增高;与NS预处理组相比,经L-Arg预处理的动物,KA给药后3h及3d,其NO2^-/NO3^-浓度升高明显。结论：兴奋诱导性癫痫发作过程中内源性NO介质的变化可能具有重要的抗发作作用。     

Hepatic-dependent and -independent insulin actions are impaired in the obese Zucker rat model

Objective: Whole‐body insulin sensitivity (IS) depends on a hepatic pathway, involving parasympathetic activation and hepatic nitric oxide (NO) production. Both atropine and N‐monomethyl‐l ‐arginine (l ‐NMMA, NO synthase inhibitor) induce insulin resistance (IR). IR is associated with obesity. Because NO action was shown to be impaired in animal models of obesity, such as the obese Zucker rat (OZR), we tested the hypothesis that the hepatic‐dependent pathway is diminished in OZR, resulting in IR. Research Methods and Procedures: Lean Zucker rats (LZRs) were used as OZR controls. IS was evaluated in terms of glucose disposal [milligrams of glucose per kilogram of body weight (bw)]. Two groups were submitted to two protocols. First, a control clamp was followed by a post‐atropine (3 mg/kg intravenously) clamp. Second, after the control clamp, l ‐NMMA (0.73 mg/kg intraportally) was given, and a second clamp was performed. Hepatic‐dependent IS was assessed by subtracting the response after atropine or l ‐NMMA from the basal response. Results: In the first protocol, basal IS was lower in OZR than in LZR (OZR, 73.7 ± 14.2; LZR, 289.2 ± 24.7 mg glucose/kg bw; p < 0.001), and atropine decreased IS in the same proportion for both groups (OZR, 41.3 ± 8.0%; LZR, 40.1 ± 6.5%). Equally, in the second protocol, OZR presented lower IS (OZR, 79.3 ± 1.6; LZR, 287.4 ± 22.7 mg glucose/kg bw; p < 0.001). l ‐NMMA induced IS inhibition in both groups (OZR, 48.3 ± 6.6%; LZR, 46.4 ± 4.1%), similar to that after atropine. Discussion: We show that the IR in OZR is due to similar impairment of both hepatic‐dependent and ‐independent components of insulin action, suggesting the existence of a defect common to both pathways.     

Endothelium-dependent vasorelaxation is inhibited by in vivo depletion of vascular thiol levels: Role of endothelial nitric oxide synthase

Thiols like glutathione may serve as reducing co-factors in the production of nitric oxide (NO) and protect NO from inactivation by radical oxygen species. Depletion of thiol compounds reduces NO-mediated vascular effects in vitro and in vivo. The mechanisms underlying these actions are not clear, but may involve decreased synthesis of NO and/or increased degradation of NO. This study investigates the effect of glutathione depletion on the response to NO-mediated vasodilation induced by acetylcholine (Ach, 10 μg/kg), endothelial NO synthase (eNOS) activity and potential markers of vascular superoxide anion (O^·-₂) production in conscious chronically catheterized rats. Thiol depletion induced by buthionine sulfoximine (BSO, 1 g ip within 24 h) decreased the hypotensive effect of Ach by 30% (MAP reduction before BSO 27 ± 3 mmHg, 19 ± 3 mmHg after BSO, (mean ± SEM), p < .05n = 8). The impaired effect of Ach was associated with a significant reduction in eNOS activity (control: 7.7 ± 0.8, BSO: 3.9 ± 0.4 pmol/min/mg protein (p < .05), n = 6). In contrast, neither NADH/NADPH driven membrane-associated oxidases nor lucigenin reductase activity were significantly (p < .05) affected by BSO (BSO: 4415 ± 123, control: 4105 ± 455 counts/mg, n = 6) in rat aorta. It is concluded that in vivo thiol depletion results in endothelial dysfunction and a reduced receptor-mediated vascular relaxation. This effect is caused by reduced endothelial NO formation.     

Glutamate measured by 6-s resolution brain microdialysis: capillary electrophoretic and laser-induced fluorescence detection application

In the present experiment the combination of brain microdialysis and CZE–LIFD permitted the measurement of glutamate in 100 nl microdialysis samples collected every 5 or 6 s. Samples were collected every 6 s, in rats anesthetized with two different anesthetic agents (ketamine and sodium thiopental). A microdialysis probe was inserted in the cortex of an anesthetized rat in the territory irrigated by the middle cerebral artery. The artery was clamped for 30 s and then released. The samples were derivatized with fluorescein isothiocyanate I (FITC) by means of a continuous-flow reactor, collected and injected into a home-made CZE–LIFD instrument. Glutamate decreased immediately after clamping the artery in ketamine anesthetized rats and increased 1 min after the onset of the ischemia in sodium thiopental anesthetized rats. In another experiment a 60 mM KCl solution was injected through a microdialysis probe inserted in the hippocampus of an anesthetized rat. In the first 5 s after the KCl solution reached the tissue, glutamate increased but γ-aminobutytic acid and glutamine did not. The experiments show that time resolution of brain microdialysis can be reduced to a few seconds if the analytical technique is the proper one.     

Histaminergic Modulation of Hippocampal Acetylcholine Release In Vivo

Abstract: In order to elucidate the modulatory role of the histaminergic neural system in the cholinergic neural system, the acetylcholine release from the CA1-CA3 region in the hippocampus of anesthetized rats was studied by an in vivo microdialysis method coupled with HPLC-electrochemical detection. The mean value for the basal acetylcholine release was 0.98 β 0.04 pmol/20 min. The acetylcholine release was increased to 172% of the basal level when an electrical stimulation at 200 μA was applied to the tuberomammillary nucleus. An administration of α-fluoromethylhistidine (100 mg/kg i.p.) blocked the electrically evoked release of histamine both from the septal-diagonal band complex and the hippocampus, and abolished the electrically evoked release of acetylcholine from the hippocampus. Zolantidine (5 mg/kg i.p.) attenuated the increase in the electrically stimulated acetylcholine release, but pyrilamine (5 mg/kg i.p.) did not attenuate the increase in the acetylcholine release. These drugs showed no significant effect on the basal acetylcholine release. An administration of ( R )-α-methylhistamine (5 mg/kg i.p.) caused a decrease in the acetylcholine release to 48.7% of the basal level, whereas thioperamide (5 mg/kg i.p.) caused an increase in the acetylcholine release 60 min after the injection. These results suggest that the histaminergic system may contribute to the modulation of the activity of the septohippocampal cholinergic system, mainly through H₂ receptprs.     

Activity of Ionotropic Glutamate Receptors in Retinal Cells: Effect of Ascorbate/Fe2+-Induced Oxidative Stress

Abstract: The effect of oxidative stress induced by the oxidant pair ascorbate/Fe²⁺ on the activity of ionotropic glutamate receptors was studied in cultured chick retina cells. The release of [³H]GABA and the increase of the intracellular free Na⁺ concentration ([Na⁺]_i), evoked by glutamate receptor agonists, were used as functional assays for the activity of the receptors. The results show that the maximal release of [³H]GABA evoked by kainate (KA; ～20% of the total) or AMPA (～11% of the total) was not different in control and peroxidized cells, whereas the EC₅₀ values determined for peroxidized cells (33.6 ± 1.7 and 8.0 ± 2.0 µM for KA and AMPA, respectively) were significantly lower than those determined under control conditions (54.1 ± 6.6 and 13.0 ± 2.2 µM for KA and AMPA, respectively). The maximal release of [³H]GABA evoked by NMDA under K⁺ depolarization was significantly higher in peroxidized cells (7.5 ± 0.5% of the total) as compared with control cells (4.0 ± 0.2% of the total), and the effect of oxidative stress was significantly reduced by a phospholipase A₂ inhibitor or by fatty acid-free bovine serum albumin. The change in the intracellular [Na⁺]_i evoked by saturating concentrations of NMDA under depolarizing conditions was significantly higher in peroxidized cells (8.9 ± 0.6 mM) than in control cells (5.9 ± 1.0 mM). KA, used at a subsaturating concentration (35 µM), evoked significantly greater increases of the [Na⁺]_i in peroxidized cells (11.8 ± 1.7 mM) than in control cells (7.1 ± 0.8 mM). A saturating concentration (150 µM) of this agonist triggered similar increases of the [Na⁺]_i in control and peroxidized cells. Accordingly, the maximal number of binding sites for (+)-5-[³H]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate ([³H]MK-801) was increased after peroxidation, whereas the maximal number of binding sites for [³H]KA was not affected by oxidative stress. These data suggest that under oxidative stress the activity of the ionotropic glutamate receptors is increased, with the NMDA receptor being the most affected by peroxidation.