bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the autoradiographic binding distribution of [3H]‐gabapentin with excitatory amino acid receptor and amino acid uptake site distributions in rat brain
Authors: Thurlow Richard J. , Hill David R. , Woodruff G.N. 
Published: July 2012

Gabapentin is a novel anticonvulsant with an unknown mechanism of action. Recent homogenate binding studies with [3H]‐gabapentin have suggested a structure‐activity relationship similar to that shown for the amino acid transport system responsible for the uptake of large neutral amino acids (LNAA).
The autoradiographic binding distribution of [3H]‐gabapentin in rat brain was compared with the distributions for excitatory amino acid receptor subtypes and the uptake sites for excitatory and large neutral amino acids in consecutive rat brain sections.
Densitometric measurement of the autoradiographic images followed by normalisation with respect to the hippocampus CA1 stratum radiatum, was carried out before comparison of each binding distribution with that of [3H]‐gabapentin by linear regression analysis. The correlation coefficients observed showed no absolute correlation was observed between the binding distributions of [3H]‐gabapentin and those of the excitatory amino acid receptor subtypes. The acidic and large neutral amino acid uptake site distributions demonstrated a much closer correlation to the [3H]‐gabapentin binding site distribution. The correlation coefficients for D‐[3H]‐aspartate, L‐[3H]‐leucine and L‐[3H]‐isoleucine binding site distributions were 0.76, 0.90 and 0.88 respectively.
Concentration‐dependent inhibition by unlabelled gabapentin of autoradiographic binding of L‐[3H]‐leucine and L‐[3H]‐isoleucine was observed, with non‐specific binding levels being reached at concentrations between 10 and 100 μm.
Excitotoxic quinolinic acid lesion studies in rat brain caudate putamen and autoradiography were carried out for the amino acid uptake sites mentioned above. The resulting glial infiltration of the lesioned areas was visualized by autoradiography using the peripheral benzodiazepine receptor specific ligand [3H]‐PK11195. A significant decrease in binding density in the lesioned area compared with sham‐operated animals was observed for D‐[3H]‐aspartate, L‐[3H]‐leucine, L‐[3H]‐isoleucine and [3H]‐gabapentin, whilst [3H]‐PK11195 showed a significant increase in binding density indicative of glial infiltration into the lesioned area. These results suggest that the gabapentin binding site and the acidic and LNAA uptake site may be present on cell bodies of a neuronal population of cells.
From these studies it appears that [3H]‐gabapentin, L‐[3H]‐leucine and L‐[3H]‐isoleucine bind to the same site in rat brain. The inhibition of [3H]‐gabapentin binding by the LNAA uptake system‐specific ligand, BCH, suggests that [3H]‐gabapentin may label this uptake site, termed system‐L. Conversely these ligands could be labelling a novel site that coincidentally has a similar structure‐activity relationship to this uptake site. These results suggest a novel mechanistically relevant site of action for gabapentin and may enable further anti‐epileptic agents of this type to be developed.
VIP‐induced relaxation of guinea‐pig intestinal smooth muscle cells: sequential involvement of cyclic AMP and nitric oxide
Authors: Rekik Moez , Delvaux Michel , Tack Ivan , Frexinos Jacques , Bueno Lionel 
Published: July 2012

A possible interaction between cyclic AMP and nitric oxide (NO) in mediating the relaxant effect of vasoactive intestinal polypeptide (VIP) on intestinal smooth muscle cells has been investigated. The effects of the inhibitor of NO synthesis, NG‐nitro‐L‐arginine methyl ester (L‐NAME), have been studied on VIP‐, forskolin‐, and 8 bromo‐cyclic AMP‐ induced relaxation of cells, dispersed by enzymatic digestion of muscle strips from the circular layer of guinea‐pig ileum.
VIP alone did not modify the length of isolated muscle cells. By contrast, when the cells were contracted by cholecystokinin octapeptide, CCK8 (10 nM), VIP inhibited this contraction, inducing a concentration‐dependent relaxation of the cells. Maximal relaxation was induced by 1 μm VIP (EC50 = 408.2 ± 16.7 pM).
N‐ethylmaleimide, inhibitors of adenylate cyclase or somatostatin, abolished the relaxing effect of VIP. (R)‐p‐cAMPs, an antagonist of cyclic AMP on protein kinase A also inhibited the VIP‐induced relaxation by 92.1 ± 6.3%. Inhibitors of nitric oxide synthase (NOS), L‐NAME and L‐NMMA, partially inhibited VIP‐induced relaxation. The effect of L‐NAME was reversed by L‐arginine but not by D‐arginine.
(R)‐p‐cAMPS and L‐NAME also inhibited the cell relaxation induced either by forskolin which directly stimulates adenylate cyclase activity or 8‐bromo‐cyclic AMP, an analogue of cyclic AMP.
When cells were incubated for 30 min with dexamethasone 10 μm, a glucocorticoid known to decrease the synthesis of iNOS, the relaxing effect of a maximal concentration of VIP was decreased by 52 ± 4% and L‐NMMA had no further effect on this residual VIP‐induced relaxation. Milrinone, a phosphodiesterase type III inhibitor, potentiated the relaxant effect of VIP.
These data demonstrate that the intracellular pathway mediating the relaxant effect of VIP in intestinal smooth muscle cells includes the sequential activation of adenylate cyclase, protein kinase A, activation of NOS and finally production of NO and cyclic GMP. NO could in turn regulate the cyclic AMP‐dependent pathway of cell relaxation.
Effects of inhalational general anaesthetics on native glycine receptors in rat medullary neurones and recombinant glycine receptors in Xenopus oocytes
Authors: Downie D.L. , Hall A.C. , Lieb W.R. , Franks N.P. 
Published: July 2012

Glycine responses were studied under voltage clamp in Xenopus oocytes injected with cDNA encoding mammalian glycine receptor subunits and in rat medullary neurones. Bath application of glycine gave strychnine‐sensitive currents which reversed close to the expected equilibrium potentials for chloride ions. The peak currents for the receptors expressed in oocytes fitted a Hill equation with EC50 = 215 ± 5 μm and Hill coefficient nH = 1.70 ± 0.05 (means ± s.e.means). The peak currents from the receptors in medullary neurones fitted a Hill equation with EC50 = 30 ± 1 μm and Hill coefficient nH = 1.76 ± 0.08. The current‐voltage relationship for the receptors expressed in oocytes showed strong outward rectification (with Vrev = −21 ± 2 mV), while that for the glycine responses from the medullary neurones in symmetrical Cl− was linear (with Vrev = 3.2 ± 0.6 mV).
Inhalational general anaesthetics, at concentrations close to their human minimum alveolar concentrations (MACs), potentiated responses to low concentrations of glycine. The potentiation observed with the recombinant receptors (between 60–220%) was approximately twice that found with the medullary neurones (between 40–80%). For both the recombinant receptors and the receptors in medullary neurones, the degree of potentiation increased in the order of methoxyflurane ≅ sevoflurane < halothane ≅ isoflurane ≅ enflurane. There was no significant difference between the potentiations observed for the two optical isomers of isoflurane.
For both the recombinant and native receptors, isoflurane potentiated the currents in a dose‐dependent manner at low concentrations of glycine, although at high glycine concentrations the anaesthetic had no significant effect on the glycine‐activated responses. The major effect of isoflurane was to cause a parallel leftward shift in the glycine concentration‐response curves. The glycine EC50 concentration for the recombinant receptors decreased from a control value of 215 ± 5 μm to 84 ± 7 μm glycine at 610 μm isoflurane, while that for the medullary neurones decreased from a control value of 30 ± 1 μm to 18 ± 2 μm glycine at the same concentration of isoflurane. The potentiation was independent of membrane potential.
Isoflurane also potentiated responses to taurine, a partial agonist at the glycine receptor. This was observed for receptors expressed in oocytes at both low and saturating concentrations of taurine. The EC50 concentration decreased from a control value of 1.6 ± 0.2 to 0.9 ± 0.1 mM taurine in the presence of 305 μm isoflurane, while the maximum response to taurine increased from 47 ± 2 to 59 ± 2% of the maximum response to glycine.
Glycine receptors, like other members of the fast ligand‐gated receptor superfamily, are sensitive to clinically relevant concentrations of inhalational general anaesthetics. Effects at these receptors may, therefore, play some role in the maintenance of the anaesthetic state.
Frequency‐dependent inhibition of neuronal activity by lappaconitine in normal and epileptic hippocampal slices
Authors: Ameri Angela , Metzmeier Petra , Peters Thies 
Published: July 2012

Extracellular recording of the stimulus‐evoked population spike in the CA1 region of rat hippocampal slices in vitro was performed in order to investigate whether lappaconitine affects neuronal excitability. Lappaconitine is a diterpene alkaloid of plants of the Aconitum genus and has analgesic properties.
The results reveal an inhibitory action of lappaconitine (10 μm) manifested in a slow attenuation of the orthodromic and antidromic population spike.
The lappaconitine‐induced inhibitory action was activity‐dependent, that is, it was potentiated when frequency of electrical stimulation was increased. In contrast, washout of the neurotoxin was accelerated when stimulation frequency was decreased.
The activity‐dependent action of lappaconitine raised the question of whether the drug is effective in suppressing the aberrant neuronal activity that occurs during an epileptic seizure. The results obtained from experiments on epileptic hippocampal slices demonstrated a selective reduction of the later spikes in the bursts with less effect on normal neuronal activity.
These data support the conclusion that lappaconitine, in addition to its antinociceptive effect, also has antiepileptic potency due to its highly activity‐dependent mode of action.
Activation by levcromakalim and metabolic inhibition of glibenclamide‐sensitive K channels in smooth muscle cells of pig proximal urethra
Authors: Teramoto Noriyoshi , Brading Alison F. 
Published: July 2012

The effects of levcromakalim (BRL 38227) on ionic currents recorded from pig proximal urethra were investigated by use of tension measurement and patch clamp techniques (conventional whole‐cell configuration, nystatin perforated patch, and cell‐attached configuration).
Levcromakalim (1 μm) caused a relaxation in the resting tone. This levcromakalim‐induced relaxation was inhibited by the pretreatment with 1 μm glibenclamide.
The resting membrane potential recorded from single cells in current‐clamp mode was −36.1 ± 4.4 mV (n = 5).
Levcromakalim induced a concentration‐dependent hyperpolarization with a maximum (at ≥ 10 μm) close to the theoretical equilibrium potential of potassium (EK). The membrane hyperpolarization caused by 1 μm levcromakalim (24.7 ± 5.8 mV, n = 4) was abolished by 1 μm glibenclamide.
Levcromakalim (100 μm) caused an outward K current in whole‐cell recordings which was unaffected by iberiotoxin (300 nM) but abolished by glibenclamide (10 μm).
In cell‐attached patches, levcromakalim activated a 43 pS K channel which was inhibited by the application of glibenclamide.
The metabolic poison, cyanide (CN), also activated a 43 pS K channel which was suppressed by the application of 10 μm glibenclamide.
These results indicate that levcromakalim and metabolic inhibition activate the same 43 pS K channel in pig proximal urethra. The resultant urethral hyperpolarization might reduce the usefulness of K channel openers in the treatment of detrusor instability, but be of value in treating outflow obstruction.
Action of the calcium channel blocker lacidipine on cardiac hypertrophy and endothelin‐1 gene expression in stroke‐prone hypertensive rats
Authors: Feron Olivier , Salomone Salvatore , Godfraind Théophile 
Published: July 2012

The tissue‐protective effects of calcium channel blockers in hypertension are not well dissociated from their effect on systolic blood pressure (SBP). We have previously shown that lacidipine, a dihydropyridine‐type calcium antagonist, reduced the cardiac hypertrophy and the cardiac endothelin‐1 (ET‐1) gene overexpression occurring in salt‐loaded stroke‐prone spontaneously hypertensive rats (SL‐SHRSP), an effect occurring without systolic blood pressure (SBP) change. In the present study, we have examined whether this action was dose‐related and if it could be associated with ET receptor changes. The action of lacidipine was also examined in control SHRSP and in Wistar Kyoto rats (WKY).
The daily dose of 0.3 mg kg−1 lacidipine which did not lower SBP but significantly prevented ventricle hypertrophy and cardiac preproET‐1‐mRNA expression in SL‐SHRSP was inactive in control SHRSP. With the higher dose of lacidipine (1 mg kg−1 day−1), we observed a further reduction of cardiac hypertrophy and of ET‐1 gene expression in SL‐SHRSP and a significant effect on those parameters in control SHRSP but only a small reduction of SBP in both groups.
In WKY, salt loading did not induce change in SBP or increase of cardiac ET‐1 gene expression and ventricle mass. In these normotensive rats, lacidipine (1 mg kg−1 day−1) did not modulate the basal preproET‐1‐mRNA expression and did not affect SBP or heart weight.
The maximum binding capacity (Bmax) and the dissociation constant (KD) of [125I]‐ET‐1 binding and the relative proportion of low‐ and high‐affinity binding sites for ET‐3 were not significantly affected by salt loading or lacidipine treatment in SHRSP.
These results show that lacidipine exerted a dose‐related inhibition of ventricle hypertrophy and preproET‐1‐mRNA expression in SHRSP and indicate that this effect was unrelated to SBP changes. The dose‐dependency of this inhibition suggests that salt‐induced cardiac hypertrophy could be related to ET‐1 gene overexpression. The results further show that ET receptor changes are not involved in the pathophysiological process studied here.
Further investigations into the mechanism of the antihypertensive activity of the angiotensin AT1 receptor antagonist, GR138950
Authors: Hilditch A. , Prior Helen M. , Drew G.M. 
Published: July 2012

The angiotensin AT1 receptor antagonist, GR138950, produces a long‐lasting antihypertensive effect in conscious renal artery ligated hypertensive (RALH) rats but this effect does not correlate temporally with its antagonist profile against angiotensin II (AII). In the present experiments we have compared the inhibitory profiles of GR138950 and enalapril, against angiotensin I (AI), with their respective antihypertensive activities.
GR138950 (1 mg kg−1, i.a.) and enalapril (3 mg kg−1, i.a.) reduced blood pressure in RALH rats to a similar degree. Maximum reductions in blood pressure occurred approximately 5–24 h and 3–5 h after administration, respectively. The antihypertensive effect of GR138950 lasted for 24–48 h. However, the effect of enalapril lasted for only 5–24 h.
In conscious normotensive rats, inhibition of AI‐induced pressor responses was maximal 1 h after systemic administration of GR138950 and enalapril. Dose‐response curves to AI were displaced to the right, in a parallel manner, 1406 and 102 fold by GR138950 (1 mg kg−1, i.a.) and enalapril (3 mg kg−1 i.a.), respectively. The inhibitory effect of enalapril lasted for < 24 h whereas that of GR138950 lasted for up to 48 h.
Contractile responses to AI were extensively inhibited in aortae removed from either RALH rats or normotensive rats, 1 and 5 h after administration of GR138950 (1 mg kg−1, i.a.). Responses were still significantly reduced 24 h after administration but had returned to control levels after 48 h. Enalapril pretreatment (3 mg kg−1, i.a.) did not inhibit contractile responses to AI in aortae isolated from normotensive rats at any time point.
These experiments confirm that GR138950 is an effective and long‐lasting antihypertensive agent. GR138950 was a more potent and longer lasting antagonist against AI than has previously been found against AII, and the duration of its antihypertensive activity coincides better with its blockade of responses to AI. Blockade of the effects of AII generated locally within the vascular wall might play an important role in the antihypertensive profile of GR138950.
Presynaptic modulation by L‐glutamate and GABA of sympathetic co‐transmission in rat isolated vas deferens
Authors: Kwan Yiu Wa , Ngan Man‐Piu , Tsang Kay‐Yan , Lee Ha‐Man , Chu Lai‐Ah 
Published: July 2012

The modulatory effects of L‐glutamate and its structural analogues, and of γ‐aminobutyric acid (GABA), on sympathetic co‐transmission were studied in the rat isolated vas deferens exposed to electrical field stimulation (EFS).
Application of exogenous L‐glutamate caused a concentration‐dependent (1 μm‐3 mM) inhibition of the rapid twitch component of the biphasic EFS contraction. However, L‐glutamate (1 μm‐3 mM) had a minimal effect on the phasic contraction induced by exogenous adenosine 5′‐triphosphate (ATP, 150 μm) and noradrenaline (50 μm). Unlike L‐glutamate, D‐glutamate had no effect on the EFS contraction.
The L‐glutamate‐induced inhibition of the EFS contractions was significantly attenuated by the glutamate decarboxylase (GAD) inhibitor 3‐mercapto‐propionic acid (150 μm) and was abolished in the presence of the GABA transaminase (GABA‐T) inhibitor, 2‐aminoethyl hydrogen sulphate (500 μm).
The L‐glutamate‐induced inhibition of the electrically evoked contraction was not affected by the adenosine A1‐receptor antagonist, 8‐cyclopentyl‐1, 3‐dipropylxanthine (DPCPX)(30 nM), reactive blue 2 (30 μm) or the GABAA receptor antagonist bicuculline (50 μm). However, the GABAB receptor antagonist 2‐hydroxysaclofen (50 μm) significantly inhibited the L‐glutamate effect.
Similar to L‐glutamate, GABA also caused a concentration‐dependent (0.1 – 100 μm) inhibition of the EFS contractions. This GABA‐induced inhibition was not affected by either the GABAA receptor antagonist bicuculline (50 μm) or reactive blue 2 (30 μm). However, a significant attenuation of the GABA‐mediated effect was recorded with the GABAB receptor antagonist 2‐hydroxysaclofen (50 μm). Contractions of the vas deferens induced by exogenous ATP and noradrenaline were not affected by GABA (0.1 – 100 μm).
The L‐glutamate analogues, N‐methyl‐D‐aspartate (NMDA) (1 μm‐1 mM) and quisqualate (Quis 0.1 μm‐0.3 mM) had no effect, whilst kainate (Kain, 1 μm‐1 mM) caused an inhibition of the EFS‐induced contractions. Effects of Kain could be abolished by the non‐NMDA receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2, 3‐dioxine (CNQX, 10 μm). NMDA, Quis and Kain had no effect on the exogenous ATP‐ or noradrenaline‐induced contractions.
It is concluded that the excitatory amino acid L‐glutamate modulates the electrically evoked vas deferens contraction through conversion to the inhibitory amino acid GABA by a specific GABA transaminase. The GABA formed may then act on GABAB receptors and cause inhibition of the contraction through a presynaptic mechanism.
Study of the mechanisms involved in adenosine‐5′‐O‐(2‐thiodiphosphate) induced relaxation of rat thoracic aorta and pancreatic vascular bed
Authors: Saïag B. , Hillaire‐Buys D. , Chapal J. , Petit P. , Pape D. , Rault B. , Allain H. , Loubatières‐Mariani M.M. 
Published: July 2012

The endothelium‐dependent relaxation of blood vessels induced by P2Y‐purinoceptor activation has often been shown to involve prostacyclin and/or nitric oxide (NO) release. In this work, we have investigated the mechanisms involved in the relaxant effect of the P2Y agonist, adenosine −5′‐O‐(2‐thiodiphosphate) (ADPβS) using two complementary preparations: rat pancreatic vascular bed and aortic ring.
On the pancreatic vascular bed, ADPβS (1.5 and 15 μm) infused for 30 min induced a concentration‐dependent vasodilatation; it was progressive during the first 10 min (first period) and sustained from 10 to 30 min (second period). Indomethacin (10 μm) delayed ADPβS‐induced vasodilatation (1.5 and 15 μm) by about 6 min. Nω‐nitro‐L‐arginine methyl ester (L‐NAME) (200 μm) suppressed the relaxation for about 5 min but thereafter ADPβS at the two concentrations progressively induced an increase in the flow rate. Even the co‐administration of L‐NAME and indomethacin did not abolish the ADPβS‐induced vasorelaxation.
On 5‐hydroxy tryptamine (5‐HT) precontracted rings mounted in isometric conditions in organ baths, we observed that ADPβS induced a concentration‐dependent relaxation of rings with a functional endothelium; this effect was stable for 25 min. The ADPβS relaxant effect was strongly inhibited by Reactive Blue 2 (30 μm) and was suppressed by pretreatment of rings with saponin (0.05 mg ml−1 for 30 min), which also abolished the acetylcholine‐induced relaxation.
ADPβS‐induced relaxation of 5‐HT precontracted rings is largely inhibited by indomethacin (100 or 10 μm) or L‐NAME (100 μm).
We conclude that: the ADPβS‐induced relaxation is endothelium‐dependent, mediated by P2Y‐purinoceptors, and at least in part linked to NO and prostacyclin release, depending on the preparation used. Furthermore, on the pancreatic vascular bed, (an)other mechanism(s) than prostacyclin and NO releases may be involved in ADPβS‐induced vasodilatation.
Modulation by nitric oxide of spontaneous motility of the rat isolated duodenum: role of tachykinins
Authors: Martinez‐Cuesta M.A. , Esplugues J.V. , Whittle B.J.R. 
Published: July 2012

Incubation of proximal segments of the rat isolated duodenum with NG‐nitro‐L‐arginine (L‐NOARG; 3–100 μm) produced a concentration‐dependent increase in both resting tone and the amplitude of the spontaneous contractions. These effects were attenuated by concurrent incubation with L‐arginine (1 mM) but not D‐arginine (1 mM).
These changes in resting tone and motility induced by L‐NOARG (30 μm) were substantially reduced by concurrent incubation with tetrodotoxin (1 μm) or hexamethonium (10 μm), implicating the involvement of a local neuronal response.
The L‐NOARG‐induced increase in duodenal motility was not, however, inhibited by atropine (1 μm), guanethidine (6.4 μm) phentolamine (1 μm), or indomethacin (10 μm), indicating a non‐cholinergic, non‐adrenergic and non‐prostanoid‐mediated contractile response.
The NK1/NK2 tachykinin receptor antagonist, (D‐Pro2, D‐Trp7,9 substance P, 1–10 μm), and the NK2‐receptor antagonists, MEN 10,207 and MEN 10,376 (1–5 μm), concentration‐dependently reduced the effect of L‐NOARG (30 μm) on spontaneous duodenal motility.
The resting tone and amplitude of the spontaneous contractions was likewise increased by incubation with NG‐monomethyl‐L‐arginine (L‐NMMA; 100–1000 μm). However, incubation with L‐NMMA (100 μm) attenuated the actions of more potent L‐NOARG (30 μm) on resting motility.
Administration of E.coli endotoxin (3 mg kg−1, i.v.) to the rat 5 h prior to tissue removal, at a time of known induction of NO synthase, reduced the amplitude of spontaneous contractions of the isolated duodenum, an effect inhibited by pretreatment of the rats with dexamethasone (1 mg kg−1) 2 h prior to endotoxin challenge.
These findings indicate a role of endogenous NO in the modulation of spontaneous tone and motility in the rat duodenum. Induction of NO synthase may result in a reduction in spontaneous motility of the tissue. By contrast, inhibition of constitutive NO biosynthesis unmasks a contractile response that is neuronally mediated and involves tachykinin NK2 receptors.