bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the phencyclidine‐induced increase in prefrontal cortical dopamine metabolism in the rat
Authors: Umino Asami , Takahashi Kiyohisa , Nishikawa Toru 
Published: January 2005

We have investigated the effects of a schizophrenomimetic drug phencyclidine (PCP) and N‐methyl‐D‐aspartate (NMDA)‐related agents alone or in combination on dopamine metabolism in the medial prefrontal cortex and striatum of the rats by measuring the tissue concentrations of dopamine and its metabolite, 3,4‐dihyroxyphenylacetic acid (DOPAC), and the rate of dopamine disappearance (dopamine utilization) after its synthesis inhibition.
Systemic injection of PCP and selective, non‐competitive, NMDA antagonists caused an increase of both tissue concentrations of DOPAC and dopamine utilization in the prefrontal cortex but not in the striatum. The PCP‐induced augmentation of cortical dopamine metabolism was not influenced by selective lesion of ascending noradrenergic neurones.
Intra‐prefrontal cortical infusion of PCP or selective competitive or non‐competitive antagonists of the NMDA receptor mimicked the ability of systemic PCP injection to enhance DOPAC levels and dopamine utilization in the prefrontal cortex. However, an NMDA antagonist injected into the cell body area of the mesocortical dopaminergic neurones failed to affect dopamine metabolism in the prefrontal cortex.
The increasing effects of PCP and selective NMDA antagonists on cortical dopamine utilization were not additive, although a dopamine receptor antagonist, haloperidol, still accelerated the disappearance of dopamine, even in the presence of PCP.
Intra‐cortical or intra‐ventricular infusion of NMDA or D‐alanine but not L‐alanine, attenuated the ability of systemic PCP administration to facilitate prefrontal dopamine utilization.
These data suggest that PCP might activate prefrontal cortical dopaminergic neurones, at least in part, by blocking the NMDA receptor in the prefrontal cortex which participates in a tonic inhibitory control of the mesoprefrontal dopaminergic projections.
Effects of pravastatin on cholesterol metabolism of cholesterol‐fed heterozygous WHHL rabbits
Authors: Harsch Michael , Gebhardt Angelika , Reymann Andreas , Lang Gerhard , Schliack Michael , Löser Roland , Hinrich Braesen Jan , Niendorf Axel 
Published: January 2005

We administered the 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitor pravastatin at a daily dose of 1 mg kg−1 body weight to cholesterol‐fed (0.03%) heterozygous Watanabe heritable hyperlipidaemic rabbits, an animal model for heterozygous familial hypercholesterolaemia.
After 12 months of cholesterol treatment, immunohistochemistry with the monoclonal antibody 9D9 was used to detect hepatic low density lipoprotein (LDL) receptors, which were quantified by densitometry. In addition we determined LDL receptor mRNA by competitive reverse transcriptase polymerase chain reaction. The cholesterol precursor lathosterol and the plant sterol campesterol were analysed by gas‐liquid chromatography.
The drug reduced total plasma cholesterol levels by 51% (P=0.04), when compared to the control group. Unexpectedly, hepatic LDL receptor density and mRNA showed no significant differences between the groups. Total plasma levels of lathosterol and campesterol also revealed no significant differences between the groups, if expressed relative to plasma cholesterol.
The findings suggest that mechanisms other than induced hepatic LDL receptors are responsible for the cholesterol‐lowering effect of pravastatin in this animal model. We propose a reduced cholesterol absorption efficiency compatible with similar campesterol levels between both groups observed in our study.
Modulation of extracellular GABA levels in the retina by activation of glial P2X‐purinoceptors
Authors: Neal M J , Cunningham J R , Dent Z 
Published: January 2005

In the rat retina, γ‐aminobutyric acid (GABA) released as a transmitter is inactivated by uptake mainly into glial cells (Müller cells). Activation of P2‐purinoceptors in Müller cells increases [Ca2+]i and the present study was undertaken to see whether this action affected the glial release of [3H]‐GABA from the superfused rat isolated retina.
Adenosine 5′‐triphosphate (ATP) and the P2X‐purinoceptor agonists, α,β‐methylene‐ATP (α,β‐meATP) and β,γ‐methyleneATP (β,γ‐meATP) significantly increased the KCl‐evoked release of [3H]‐GABA from the retina.
Adenosine and the P2Y‐purinoceptor agonist, 2‐chloroATP, had no effect on the KCl‐evoked release of [3H]‐GABA from the retina. However, 2‐methylthioATP (2‐Me‐S‐ATP) significantly enhanced the evoked release of [3H]‐GABA.
The effect of ATP on the glial release of [3H]‐GABA was abolished by the P2‐antagonist, pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS).
When the superfused retina was exposed to the GABA uptake inhibitor, SKF89976A, the enhancing effect of α,β‐meATP on the KCl‐evoked release of GABA was abolished.
The KCl‐evoked release of [3H]‐GABA from the frog retina and rat cerebrocortical slices, which take up GABA mainly into neurones, was not affected by ATP or α,β‐meATP.
We concluded that the glial Müller cells in the rat retina possess P2‐receptors, activation of which increases the ‘release’ of preloaded [3H]‐GABA apparently by reducing uptake. On balance, the results suggest the involvement of P2X‐purinoceptors, although we cannot exclude the possibility that P2Y‐purinoceptors may be involved. Our results suggest that ATP, as well as being a conventional transmitter in the retina, may be involved in neuronal‐glial signalling and modulate the extracellular concentration of GABA.
Differential effects of somatostatin and angiopeptin on cell proliferation
Authors: Alderton Forbes , Lauder Heather , Feniuk Wasyl , Fan Tai‐Ping D , Humphrey Patrick P A 
Published: January 2005

Somatostatin (SRIF) exerts antiproliferative effects, and angiopeptin (an sst2/sst5 receptor‐selective analogue) has recently been evaluated in clinical trials for the prophylaxis of restenosis following coronary angioplasty. Using an in vitro model of cell growth we have examined the effects of SRIF and angiopeptin on cell proliferation in CHO‐K1 cells stably transfected with the human or rat recombinant sst2 or sst5 receptor and compared these with their effects on rat aortic vascular smooth muscle cells (VSMC) expressing endogenous somatostatin receptors.
In CHO‐K1 cells, expressing either human or rat recombinant sst2 or sst5 receptors, or in rat aortic VSMC, SRIF and angiopeptin (0.1–1000 nM) had no effect on basal re‐growth of cells into a denuded area of a previously confluent monolayer. In contrast, basic fibroblast growth factor (bFGF, 10 ng ml−1) stimulated re‐growth of these cells.
SRIF (0.1–1000 nM) caused a concentration‐dependent inhibition of the bFGF‐stimulated re‐growth in CHO‐K1 cells expressing human sst2 (h sst2) or sst5 (h sst5) receptors (pIC50=8.05±0.03 and 8.56±0.12, respectively). In contrast, angiopeptin (0.1–1000 nM) acted as a partial agonist at the h sst2 receptor (44.6±2.7% inhibition of the bFGF‐stimulated re‐growth at 100 nM; pIC50=8.69±0.25) but was devoid of any agonist activity at the h sst5 receptor.
In CHO‐K1 cells stably expressing rat recombinant sst2 (r sst2) or sst5 (r sst5) receptors, SRIF (0.1–1000 nM) was able to inhibit the bFGF‐stimulated re‐growth (pIC50=7.98±24 and 8.50±0.12, respectively). Angiopeptin (0.1–1000 nM) caused a concentration‐dependent inhibition of bFGF‐stimulated re‐growth at the r sst2 receptor (pIC50=8.08±0.24) but acted as a partial agonist at the r sst5 receptor (maximum response=57.7±3.6% inhibition of bFGF‐stimulated re‐growth at 100 nM; pIC50=8.60±0.16).
Although angiopeptin was inactive as an agonist at the h sst5 receptor, 100 nM angiopeptin potently antagonized the SRIF‐induced inhibition of proliferation in CHO h sst5 (estimated pKB=10.4±0.3). 5‐Hydroxytryptamine (0.1 nM–10 μM) also inhibited bFGF‐stimulated re‐growth (pIC50=8.36±0.11) and angiopeptin had no effect on this response (pKB<7).
SRIF (0.1–1000 nM) caused a concentration‐dependent (pIC50=8.04±0.08) inhibition of bFGF‐stimulated re‐growth in VSMC, whereas angiopeptin displayed weak agonist activity, only inhibiting bFGF‐stimulated re‐growth at concentrations greater than 100 nM. Angiopeptin (100 nM) caused a rightward displacement of the concentration‐effect curve to SRIF with an estimated pKB value of 7.70±0.12.
These findings suggest that the low intrinsic activity of angiopeptin at the h sst2 receptor, combined with its lack of agonist activity at the h sst5 receptor, may explain the poor clinical efficacy of angiopeptin in trials for coronary artery restenosis, which contrasts with encouraging data found in equivalent in vivo animal studies.
Hepatobiliary and intestinal clearance of amphiphilic cationic drugs in mice in which both mdr1a and mdr1b genes have been disrupted
Authors: Smit Johan W , Schinkel Alfred H , Weert Betty , Meijer Dirk K F 
Published: January 2005

We have used mice with homozygously disrupted mdr1a and mdr1b genes (mdr1a/1b (−/−) mice) to study the role of the mdr1‐type P‐glycoprotein (P‐gp) in the elimination of cationic amphiphilic compounds from the body. These mice lack drug‐transporting P‐gps, but show no physiological abnormalities under laboratory conditions and have normal bile flow.
3H‐labelled cationic drugs were administered intravenously (i.v.) to mice as a single bolus dose and the disposition of the studied cationic drugs was investigated by focusing on drug secretion into bile, intestinal lumen and urine.
Hepatobiliary secretion of the investigated cationic drugs was profoundly reduced in mice devoid of the mdr1‐type P‐gps. In fact, the cumulative biliary output, measured during 1 h, of the small type 1 compounds tri‐butylmethyl ammonium (TBuMA) and azidoprocainamide methoiodide (APM), as well as of the more bulky type 2 cationic drug vecuronium, was reduced by at least 70% in the mdr1a/1b (−/−) mice compared to wild‐type.
The intestinal secretion of TBuMA, APM and vecuronium was also profoundly reduced in mdr1a/1b (−/−) mice compared to wild‐type mice. The absence of the mdr1‐type P‐gp resulted in virtual elimination of intestinal secretion of TBuMA and APM (>90% reduced as compared to wild‐type (P=0.0001 and 0.0022, respectively)). The intestinal secretion of the type 2 cation drug vecuronium was reduced by 58% (P=0.0004) compared to the wild‐type mice.
Increased renal clearances of both the type 1 compounds TBuMA and APM and also of the type 2 cationic compound vecuronium in the mdr1a/1b (−/−) mice were observed. Furthermore, the balance between hepatic, intestinal and renal clearances of small type 1 organic cations clearly shifted towards a predominant role for renal clearance. Increased renal clearance may be explained by (over)expresion of additional mechanisms for renal organic cation secretion, alternatively they may also point to an as yet undefined role of P‐glycoprotein in kidney physiology and renal secretory function.
We conclude that the elimination from the body of a broad spectrum of cationic amphiphilic drugs via liver and intestine, is largely dictated by the activity of mdr1‐type P‐glycoproteins.
Role of reactive oxygen species in the signalling cascade of cyclosporine A‐mediated up‐regulation of eNOS in vascular endothelial cells
Authors: López‐Ongil S , Hernández‐Perera O , Navarro‐Antolín J , Pérez de Lema G , Rodríguez‐Puyol M , Lamas S , Rodríguez‐Puyol D 
Published: January 2005

Cyclosporine A (CsA) increases eNOS mRNA expression in bovine cultured aortic endothelial cells (BAEC). As some effects of CsA may be mediated by reactive oxygen species (ROS), present experiments were devoted to test the hypothesis that the CsA‐induced eNOS up‐regulation could be dependent on an increased synthesis of ROS.
CsA induced a dose‐dependent increase of ROS synthesis, with the two fluorescent probes used, DHR123 (CsA 1 μM: 305±7% over control) and H2DCFDA (CsA 1 μM: 178±6% over control).
Two ROS generating systems, xanthine plus xanthine oxidase (XXO) and glucose oxidase (GO), increased the expression of eNOS mRNA in BAEC, an effect which was maximal after 8 h of incubation (XXO: 168±21% of control values. GO: 208±18% of control values). The ROS‐dependent increased eNOS mRNA expression was followed by an increase in eNOS activity.
The effect of CsA on eNOS mRNA expression was abrogated by catalase, and superoxide dismutase (SOD). In contrast, the antioxidant PDTC augmented eNOS mRNA expression, both in basal conditions and in the presence of CsA.
The potential participation of the transcription factor AP‐1 was explored. Electrophoretic mobility shift assays were consistent with an increase in AP‐1 DNA‐binding activity in BAEC treated with CsA or glucose oxidase.
The present results support a role for ROS, particularly superoxide anion and hydrogen peroxide, as mediators of the CsA‐induced eNOS mRNA up‐regulation. Furthermore, they situate ROS as potential regulators of gene expression in endothelial cells, both in physiological and pathophysiological situations.
P2X receptors in cochlear Deiters' cells
Authors: Chen Chu , Bobbin Richard P 
Published: January 2005

The ionotropic purinoceptors in isolated Deiters' cells of guinea‐pig cochlea were characterized by use of the whole‐cell variant of the patch‐clamp technique.
Extracellular application of adenosine 5′‐triphosphate (ATP) induced a dose‐dependent inward current when the cells were voltage‐clamped at −80 mV. The ATP‐induced current showed desensitization and had a reversal potential around −4 mV.
Increasing intracellular free Ca2+ by decreasing the concentration of EGTA in the pipette solution reduced the amplitude of the ATP‐gated current.
The order of agonist potency was: 2‐methylthioATP (2‐meSATP)>ATP>benzoylbenzoyl‐ATP (BzATP)>α,β‐methyleneATP (α,β,meATP>adenosine 5′‐diphosphate (ADP)>uridine 5′‐triphosphate (UTP)>adenosine 5′‐monophosphate (AMP)=adenosine (Ad).
Pretreatment with forskolin (10 μM), 8‐bromoadenosine‐3′,5′‐cyclophosphate (8‐Br‐cyclic AMP, 1 mM), 3‐isobutyl‐1‐methylxanthine (IBMX, 1 mM) or phorbol‐12‐myristate‐13‐acetate (PMA, 1 μM) reversibly reduced the ATP‐induced peak current.
The results are consistent with molecular biological data which indicate that P2X2 purinoceptors are present in Deiters' cells. In addition, the reduction of the ATP‐gated current by activators of protein kinase A and protein kinase C indicates that these P2X2 purinoceptors can be functionally modulated by receptor phosphorylation.
Activation of midbrain presumed dopaminergic neurones by muscarinic cholinergic receptors: an in vivo electrophysiological study in the rat
Authors: Gronier B , Rasmussen K 
Published: January 2005

Extracellular single‐unit recording and iontophoresis were used to examine the effects of different cholinoceptor agonists and antagonists on the firing rate and firing pattern of A9 and A10 presumed dopaminergic neurones in the anaesthetized rat.
Administration of low currents (1–5 nA) of the selective muscarinic agonists oxotremorine M (Oxo M) and muscarine and of the non‐selective muscarinic/nicotinic agonist carbamylcholine (CCh) produced a dose‐dependent increase in firing rate in most of the A9 and A10 presumed dopaminergic neurones tested. Oxo M‐induced activation could be completely blocked by iontophoretic application of the muscarinic antagonist butyl‐scopolamine or systemic administration of the muscarinic antagonist scopolamine (300 μg kg−1, i.v.).
Iontophoretic application of the selective nicotinic agonist methylcarbamylcholine (MCCh), but not nicotine, induced a consistent increase in firing rate. Surprisingly, the excitatory effect of MCCh was significantly reduced by the selective muscarinic antagonist scopolamine (300 μg kg−1, i.v.), but not by the selective nicotinic antagonist mecamylamine (2.2 mg kg−1, i.v.). Mecamylamine (3 mg kg−1, i.v.) was also ineffective in reducing the CCh‐induced activation of presumed dopamine neurones, suggesting that both CCh and MCCh increased the activity of dopamine neurones via an interaction with muscarinic receptors.
Iontophoretic application of the endogenous agonist acetylcholine (ACh) had no or little effect on the firing activity of A10 presumed dopaminergic neurones. However, concomitant application of neostigmine, a potent cholinesterase inhibitor, with acetylcholine induced a substantial activation of these neurones. This activation consisted of two components; one, which was prevalent, was scopolamine (300 μg kg−1, i.v.)‐sensitive, and the other was mecamylamine (2 mg kg−1, i.v.)‐sensitive.
In addition to their effect on firing activity, Oxo M, muscarine and concomitant neostigmine/ACh caused a significant increase in burst firing of A10 neurones, but not of A9 neurones.
These data suggest that dopamine cells, both in the A9 and A10 regions, possess functional muscarinic receptors, the activation of which can increase their firing rate and, for A10 neurones, their amount of burst activity. These cholinoceptors would be able to influence the activity of the midbrain dopamine system greatly and may play a role in, and/or be a therapeutic target for, brain disorders in which dopamine is involved (e.g., Parkinson's disease, drug addiction and schizophrenia).
Characterization of prostanoid receptor‐evoked responses in rat sensory neurones
Authors: Smith Jacqueline A M , Amagasu Shanti M , Eglen Richard M , Hunter John C , Bley Keith R 
Published: January 2005

Prostanoid receptor‐mediated sensitization, or excitation, of sensory nerve fibres contributes to the generation of hyperalgesia. To characterize the prostanoid receptors present on sensory neurones, biochemical assays were performed on primary cultures of adult rat dorsal root ganglia (DRG) and the F‐11 (embryonic rat DRG×neuroblastoma hybrid) cell line.In DRG cultures, the IP receptor agonists, cicaprost and carbaprostacyclin (cPGI2) stimulated cyclic AMP accumulation. Prostaglandin E2(PGE2) also increased cyclic AMP levels, but to a lesser extent, while carbocyclic thromboxane A2(cTxA2), PGD2and PGF2αhad negligible effects. The rank order of agonist potency was cicaprost >PGE2=BMY45778=cPGI2=PGI2. In the F‐11 cells, the rank order of agonist potency for the stimulation of cyclic AMP accumulation was: cicaprost>iloprost=cPGI2=PGI2=BMY45778>PGE2=cTXA2. In DRG cultures, cicaprost induced significantly more accumulation of inositol phosphates than PGE2.To examine the effects of prostanoids on C‐fibre activity, extracellular recordings of d.c. potentials from the rat isolated vagus nerve were made with the ‘grease‐gap’ technique. PGI2(0.1 nM–10 μM) produced the largest depolarizations of the nerve. The rank order of agonist potency was: PGI2=cPGI2=PGE1>cTXA2>PGE2=PGD2=TXB2>PGF2α.Prior depolarization of nerves with either forskolin (10 μM) or phorbol dibutyrate (1 μM) alone significantly reduced the response to PGI2(10 μM), while simultaneous application of both forskolin and phorbol dibutyrate attenuated PGI2responses almost completely.Putative EP1and/or TP receptor‐selective antagonists had no effect on the responses to PGI2, cPGI2or PGE2in the three preparations studied.Collectively, these data are consistent with a positive coupling of IP receptors to both adenylyl cyclase and phospholipase C in sensory neurones. These findings suggest that IP receptors play a major role in the sensitization of rat sensory neurones.
Ruthenium red as an effective blocker of calcium and sodium currents in guinea‐pig isolated ventricular heart cells
Authors: Malécot Claire O , Bito Virginie , Argibay Jorge A 
Published: January 2005

The effect of ruthenium red on calcium and sodium currents was studied in guinea‐pig isolated ventricular heart cells with the whole cell patch‐clamp technique.
Ruthenium red very efficiently blocked the L‐type calcium current in a dose‐dependent manner. A significant block was observed for concentrations as low as 0.3 μM. Analysis of the dose‐response curve with the logistic equation indicated an EC50 of 0.8 μM, a maximum inhibition of 85% reached at 5 μM, and a coefficient of 2.37.
There was no shift in the voltage‐dependence of the Ca current activation, nor in that of its steady‐state inactivation determined with a 1 s prepulse. However, removal of Ca current inactivation at positive voltage was considerably reduced in the presence of concentrations of ruthenium red above 1 μM. A slowing of the time‐course of inactivation of the Ca current was also observed.
At 10 μM, a concentration generally used to block the sarcoplasmic Ca release channels or the mitochondrial Ca uptake, ruthenium red blocked 26.7±4.3% (n=8) of the sodium current, and slowed its inactivation time‐course. No effect was observed on the voltage‐dependence of the current activation or inactivation. The peak sodium current was also decreased at a 10 times lower concentration by 7.6±2.7% (n=3).
Thus, at concentrations used to assess intracellular Ca movements, ruthenium red induced in heart cells a significant block of both Ca and Na channels.
Effect of clenbuterol on non‐endothelial nitric oxide release in rat mesenteric arteries and the involvement of β‐adrenoceptors
Authors: Marín Jesús , Balfagón Gloria 
Published: January 2005

The aim of the present study was to explore the contribution of adrenergic, sensory and nitrergic innervations to the inhibitory effects of the β2‐adrenoceptor agonist clenbuterol on responses to electrical field stimulation (EFS, 200 mA, 0.3 ms, 1–16 Hz, for 30 s, at 1 min interval) in rat mesenteric artery segments without endothelium and the possible involvement of adrenergic, sensory and nitrergic innervations.
Clenbuterol (1 μM) reduced EFS‐induced contractile responses, and this effect was reversed by the β‐antagonist propranolol (1 μM) (contraction at 16 Hz expressed as % of 75 mM K+‐induced contraction was: control, 69±9, clenbuterol, 31±6, n=13, P<0.001; control, 83±5, clenbuterol+propranolol 70±7, n=11, P>0.05).
In arteries preincubated with [3H]‐noradrenaline (NA), clenbuterol did not modify the tritium overflow evoked by EFS (200 mA, 0.3 ms, 4 Hz, for 60 s; ratio between tritium release in the second and first stimuli was: control, 0.80±0.05 and clenbuterol added before second stimulus, 0.91±0.11, n=5, P>0.05).
The nitric oxide (NO) synthase inhibitors NG‐monomethyl‐L‐arginine (L‐NMMA) and NG‐nitro‐L‐arginine methyl ester (L‐NAME) (10 and 100 μM), and the guanylate cyclase inhibitor methylene blue (10 μM) increased the contractions caused by EFS (% contraction at 16 Hz, control, 81±7, n=26; 10 μM L‐NMMA, 109±12, n=8, P<0.05; methylene blue, 119±6, n=6, P<0.05). However, these contractions were decreased by the NO synthase substrate L‐arginine 10 μM (14±6%, n=6, P<0.001), but not modified by either the sensory neurones toxin capsaicin (0.5 μM, 75±6%, n=6, P>0.05) or the protein synthesis inhibitor cycloheximide (10 μM, 83±6%, n=8, P>0.05). None of these drugs altered the concentration‐response curves to exogenous NA (n=7).
Pretreatment with capsaicin or cycloheximide did not modify the reduction of the EFS‐evoked contraction provoked by clenbuterol. However the presence of L‐NMMA (or L‐NAME) or methylene blue did decrease the effect of clenbuterol (% contraction at 16 Hz, clenbuterol, 31±6, n=13; clenbuterol+10 μM L‐NMMA, 93±11, n=8, P<0.05; clenbuterol+methylene blue, 90±7, n=6, P<0.05).
These results suggest that the reduction caused by clenbuterol in the contraction induced by EFS in rat mesenteric arteries seems to be mediated by NO release, through the activation of β2‐adrenoceptors probably present on nitrergic nerves.