bluuebunny/crossref_metadata_2025 huggingface dataset:
Facilitation of amphetamine‐induced hypothermia in mice by GABA agonists and CCK‐8
Authors: Boschi Gabrielle , Launay Nicole , Rips Richard
Published: July 2012

Amphetamine‐induced hypothermia in mice is facilitated by dopaminergic stimulation and 5‐hydroxytryptaminergic inhibition. The present study was designed to investigate: (a) the involvement of other neuronal systems, such as the γ‐aminobutyric acid (GABA), the opioid and the cholecystokinin (CCK‐8) systems; (b) the possible contribution of hydroxylated metabolites of amphetamine to the hypothermia; (c) the capacity of dopamine itself to induce hypothermia and its mechanisms, in order to clarify the resistance of amphetamine‐induced hypothermia to certain neuroleptics.

Pretreatment with the GABA antagonists, bicuculline and picrotoxin, did not inhibit amphetamine‐induced hypothermia. The GABAB agonist, baclofen (2.5 mg kg−1, i.p.) potentiated this hypothermia, whereas the GABAA agonist, muscimol, did not. γ‐Butyrolactone (GBL) (40 mg kg−1, i.p.) and the neuropeptide CCK‐8 (0.04 mg kg−1, i.p.) also induced potentiation. The opioid antagonist, naloxone, was without effect.

Dopamine itself (3, 9, 16 and 27 μg, i.c.v.) induced less hypothermia than the same doses of amphetamine. Sulpiride did not block dopamine‐induced hypothermia, but pimozide (4 mg kg−1, i.p.), cis(z)flupentixol (0.25 mg kg−1, i.p.) and haloperidol (5 μg, i.c.v.) did. The direct dopamine receptor agonist, apomorphine, did not alter the hypothermia. Neither the 5‐hydroxytryptamine (5‐HT) receptor blocker, cyproheptadine, nor the inhibitor of 5‐HT synthesis, p‐chlorophenylalanine (PCPA), modified dopamine‐induced hypothermia. Fluoxetine, an inhibitor of 5‐HT. reuptake, had no effect, whereas quipazine (6 mg kg−1, i.p.), a 5‐HT agonist, totally prevented the hypothermia. Hypothermia was unaffected by pretreatment with CCK‐8.

These data indicate that the hypothermia induced by amphetamine involves not only dopaminergic and 5‐hydroxytryptaminergic systems which are functionally antagonistic, but is also facilitated by direct or indirect GABA and CCK‐8 receptor stimulation. This facilitation could result, in part, from modulation of dopaminergic neurotransmission. This may explain the apparent resistance of amphetamine‐induced hypothermia to some neuroleptics, while dopamine‐induced hypothermia is not resistant. The possible action of hydroxylated metabolites of amphetamine may also help to explain these differences.
Involvement of capsaicin‐sensitive nerves in the bronchomotor effects of arachidonic acid and melittin: a possible role for lipoxin A4
Authors: Manzini Stefano , Meini Stefania
Published: July 2012

Functional studies have been performed to evaluate the potential involvement of capsaicin‐sensitive nerves in the bronchomotor responses evoked by lipid mediators produced from the metabolic breakdown of arachidonic acid (AA) in the guinea‐pig bronchus.

In the presence of indomethacin, the exogenous administration of AA (0.01–1 mm) produced a concentration‐dependent contractile response in guinea‐pig isolated bronchial rings. AA‐induced contractions were augmented by epithelium‐removal and by thiorphan (10 μm) an inhibitor of tachykinin breakdown. A sustained downward and rightward displacement of the complete concentration‐response curve to AA was observed after in vitro capsaicin desensitization.

BWA4C (1 μm), a selective inhibitor of 5‐lipoxygenase, shifted the AA concentration‐response curve to the right. In the presence of this inhibitor, capsaicin desensitization did not have any further inhibitory action.

A potent, concentration‐dependent and capsaicin‐sensitive bronchoconstrictor effect was also observed with the polypeptide, melittin (10 nm–1 μm), an activator of phospholipase A2, which therefore should generate endogenous AA.

In vitro capsaicin‐desensitization produced a significant reduction of the bronchomotor responses evoked by lipoxin A4 (1–6 μm), but not of those elicited by other lipoxygenases products such as leukotriene D4 (1–100 nm) or by 15‐hydroxyeicosatetraenoic acid (15‐HETE, 1–6 μm).

These findings indicate that lipoxin A4 but not leukotriene D4 or 15‐HETE, might be one of the lipoxygenase mediators of excitatory effects of AA on capsaicin‐sensitive sensory nerves.
Investigation into the 5‐hydroxytryptamine receptor mediating smooth muscle relaxation in the rat oesophagus
Authors: Reeves J.J. , Bunce K.T. , Humphrey P.P.A.
Published: July 2012

An investigation has been made into the 5‐hydroxytryptamine (5‐HT) receptor mediating relaxation of rat oesophagus in preparations precontracted with carbachol.

In tissues treated with pargyline (100 μm) and in the presence of corticosterone (30 μm) and cocaine (30 μm) the potency of 5‐HT and 5‐methoxytyramine (5‐MeOT) was not changed but the maximum response to these agonists was reduced. Thus there was no evidence of metabolism and/or uptake through an amine depleting mechanism.

The relaxant concentration‐effect curves to 5‐HT were shifted to the left in a concentration‐related manner by isobutylmethylxanthine (1 and 10 μm), suggesting the involvement of adenosine 3′:5′‐cyclic monophosphate in these responses.

5‐HT produced concentration‐related relaxations of rat oesophagus with an EC50 value of 0.24 μm. Several indole agonists were tested and the following rank order of potency of key agonists obtained: 5‐HT > α‐methyl‐5‐hydroxytryptamine = 5‐carboxamidotryptamine (5‐CT) > 5‐MeOT. In contrast, 2‐methyl‐5‐hydroxytryptamine, sumatriptan and 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin were weak or inactive.

The substituted benzamides, metoclopramide, cisapride, renzapride and R,S‐zacopride acted as partial agonists, producing 60–70% of the 5‐HT maximum.

The relaxation responses to 5‐HT were neither inhibited by antagonists selective for 5‐HT1 or 5‐HT2 receptors nor by the 5‐HT3 receptor antagonists, ondansetron, granisetron or MDL 72222.

The relaxation responses induced by 5‐HT, 5‐CT, 5‐MeOT and renzapride were selectively inhibited by high concentrations of ICS 205–930 with pKB values of approximately 6.

The 5‐HT receptor mediating relaxation in rat oesophagus cannot be designated 5‐HT1, 5‐HT2 or 5‐HT3 under the current 5‐HT classification, but the observed effects are consistent with stimulation of the putative 5‐HT4 receptor.
The role of endogenous thromboxane in contractions to U46619, oxygen, 5‐HT and 5‐CT in the human isolated umbilical artery
Authors: Templeton A.G.B. , McGrath J.C. , Whittle M.J.
Published: July 2012

The effects of selective thromboxane antagonists and a thromboxane synthase inhibitor on the contraction to 9,11‐dideoxy‐11α,9α‐epoxymethano‐prostaglandin F2α (U46619) and oxygen in the human umbilical artery (HUA) were examined. The effect of the antagonists on contractions to both 5‐hydroxytryptamine (5‐HT) and 5‐carboxamidotryptamine (5‐CT) were also examined.

U46619 (0.3 nm–10 μm) contracted the HUA. This contraction was antagonized by two selective thromboxane receptor antagonists EP092 (10 nm–1 μm) and GR32191B (10 nm–1 μm). The contraction was not affected by the selective thromboxane synthase inhibitor, dazoxiben (10 nm–1 μm).

When the oxygen tension was increased from 16 mmHg to 120 mmHg, the HUA transiently contracted. Both thromboxane antagonists inhibited this contraction in a concentration‐dependent manner with 1 μm almost completely abolishing the response (the oxygen‐induced contraction of the control preparation normally increases with a second exposure to 120 mmHg oxygen).

In low (16 mmHg) oxygen, responses to both 5‐HT and 5‐CT were unaffected by both thromboxane receptor antagonists at concentrations up to 1 μm. In high oxygen (120 mmHg) responses to both 5‐HT and 5‐CT were biphasic in nature, with an additional initial high sensitivity phase, which was abolished by a cyclo‐oxygenase inhibitor. In high oxygen, EP092 and GR32191B blocked this initial phase in a concentration‐dependent manner, returning sensitivity to 5‐HT and 5‐CT to that seen in low oxygen.

The thromboxane synthase inhibitor, dazoxiben, at concentrations greater than 10 nm inhibited the contraction to 120 mmHg oxygen and at 1 μm, dazoxiben almost abolished the response. In low oxygen, the response to 5‐HT was unaffected by dazoxiben at concentrations up to 10 μm. In high oxygen, the initial phase of the contraction to 5‐HT was inhibited by concentrations greater than 10 nm, with no effect on the maximum response.

The results show that thromboxane receptor antagonism or blockade of thromboxane synthesis selectively attenuates oxygen‐induced contractions and those responses to 5‐HT and 5‐CT which are dependent on high oxygen for their expression. This suggests that the contractions caused by high oxygen tension, and the enhancement of the contractile effects of low concentrations of 5‐HT and 5‐CT in the presence of high oxygen tension are mediated by endogenously released thromboxane A2.
Mechanisms of the coronary vascular effects of platelet‐activating factor in the rat perfused heart
Authors: Hu Weimin , Kinnaird Anne A. A. , Man Ricky Y.K.
Published: July 2012

In a previous study it was demonstrated that bolus injections of platelet‐activating factor (PAF) in the rat perfused heart resulted in coronary vasodilatation, vasoconstriction or the combination of both, depending on the amount of PAF that was injected. In the present study, the mechanisms of these coronary vascular effects of PAF in the rat perfused heart were investigated.

Pretreatment of the rat perfused heart with the PAF antagonists FR‐900452 or BN‐52021 did not affect the vasodilator effect of PAF but eliminated the vasoconstrictor effect of PAF. FR‐900452 had no effect on the vasoconstrictor response to leukotriene C4 (LTC4) or LTD4.

The cyclo‐oxygenase inhibitor, indomethacin, did not modify the coronary vascular effects of PAF. However L‐649,923 (a leukotriene antagonist) and MK‐886 (a leukotriene synthesis inhibitor) eliminated both the vasodilator and vasoconstrictor effects of PAF.

When leukotrienes were administered by bolus injection in the rat perfused heart, LTB4 produced vasodilatation while LTC4 and LTD4 produced vasoconstriction. L‐649,923 blocked both the vasodilator and vasoconstrictor effects of the leukotrienes tested.

The results suggest that lipoxygenase products are responsible for both the vasodilator and vasoconstrictor actions of PAF in the coronary vasculature of the rat perfused heart while the cyclo‐oxygenase products do not play a significant role. The ineffectiveness of PAF antagonists in blocking the vasodilatation produced by PAF is compatible with the concept that there may be multiple PAF receptors.
Termination of digitalis‐induced ventricular tachycardias by clonidine involves central α2‐adrenoceptors in cats
Authors: Chen Shih‐Ann , Liu Ren‐Hon , Ting Tso‐Hui , Chang Mau‐Song , Chiang B. N. , Kuo Jon‐Son
Published: July 2012

Effects of intravenous (i.v.) and intravertebral arterial (i.a.) administration of the α2‐adrenoceptor agonist, clonidine (Clon) and its antagonist, yohimbine (Yoh, 0.5 mg kg−1, i.v.; 0.05 mg kg−1, i.a.), on ventricular tachycardia (VT) induced by intravenous acetylstrophanthidin (AS) were studied in cats anaesthetized with intraperitoneal chloralose.

AS dose‐dependently produced cardiac arrhythmias including complete atrioventricular conduction block (118 ± 14 μg kg−1, i.v.), junctional tachycardia (128 ± 20 μg kg−1, i.v.), multiform ventricular premature beats (157 ± 21 μg kg−1, i.v.) and sustained VT (220 ± 23 μg kg−1, i.v.).

Doses of Clon (i.v.) required for termination of VT following i.v. Yoh (62.9 ± 5.2 μg kg−1) or i.a. Yoh (88.5 ± 16.3 μg kg−1) were higher than those for termination of VT without Yoh administration (28.3 ± 6.2 μg kg−1). Doses of Clon (i.a.) required for termination of VT without or with i.a. Yoh administration were 5.8 ± 1.0 or 14.8 ± 3.7 μg kg−1, respectively, and they were significantly different.

These experiments demonstrate that either i.v. or i.a. Yoh antagonizes the antiarrhythmic effect of Clon on AS‐induced VT. Since small doses of Clon administered i.a. act predominantly on the central nervous system, we suggest that its antiarrhythmic effect is likely to be on central α2‐adrenoceptors in the central nervous system.
Lack of effect of zaprinast on methacholine‐induced contraction and inositol 1,4,5‐trisphosphate accumulation in bovine tracheal smooth muscle
Authors: Chilvers Edwin R. , Giembycz Mark A. , Challiss R.A. John , Barnes Peter J. , Nahorski Stefan R.
Published: July 2012

The effects of zaprinast (M&B 22948), a selective guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) phosphodiesterase inhibitor, and sodium nitroprusside on cyclic GMP content, phosphoinositide hydrolysis and airway smooth muscle tone were examined in flurbiprofen pretreated bovine tracheal smooth muscle (BTSM).

Anion‐exchange chromatography of the soluble fraction of BTSM homogenates resolved three peaks of Ca2+/calmodulin‐independent phosphodiesterase (PDE) activity that corresponded to type la (cyclic GMP‐specific, zaprinast‐inhibitable), type II (cyclic GMP‐stimulated) and type IV (Ro 20 1724‐inhibitable) PDE isoenzymes. Zaprinast caused a selective inhibition of the type Ia PDE isoenzyme (IC50 0.94 μm) with respect to the type II and IV (IC50 s 93 μm and 197 μm respectively) isoenzymes.

Pretreatment of BTSM strips with zaprinast (10 μm) for 20min affected neither the initial rate of force development, nor the resultant magnitude of contraction induced by methacholine (10 μm). In addition, zaprinast (10 μm; 20 min) did not affect the cumulative concentration‐response relationship induced by methacholine. In contrast, sodium nitroprusside (300 μm) either alone, or in combination with zaprinast (10 μm), significantly attenuated tone induced by low, but not high concentrations of methacholine. This resulted in a non‐parallel, rightwards shift of the methacholine concentration‐response curves (nitroprusside: 4.0 fold; nitroprusside/zaprinast: 4.8 fold at the EC50 values), without a reduction in the maximum tone generated.

In BTSM slices, zaprinast (10 or 100 μm) did not influence basal or methacholine (10 μm)‐stimulated cyclic GMP accumulation or inositol 1,4,5‐trisphosphate (Ins(1,4,5)P3) mass accumulation over a 60s incubation period, although it did significantly increase cyclic GMP content over longer (30 min) stimulation periods.

In [3H]‐inositol prelabelled BTSM slices, stimulated in the presence of 5 mm LiCl, methacholine (10 μm) caused a marked increase in total [3H]‐inositol phosphate accumulation. This effect was not inhibited by zaprinast (10 μm), sodium nitroprusside (300 μm) or a combination of these drugs despite these agents markedly increasing tissue cyclic GMP content.

These findings demonstrate that despite zaprinast being a potent and selective inhibitor of the type Ia PDE isoenzyme in a cell‐free system, this drug only increases cyclic GMP content in BTSM following prolonged agonist‐stimulation. This may explain its lack of inhibitory effect on methacholine‐induced tone. The inability of drugs which increase tissue cyclic GMP content and exhibit anti‐spasmogenic activity to inhibit methacholine‐stimulated Ins(1,4,5)P3 formation suggests that, unlike vascular smooth muscle, cyclic GMP‐dependent mechanisms do not regulate receptor‐mediated phosphoinositide hydrolysis in BTSM.
Subclassification of the presynaptic α2‐autoreceptors in rabbit brain cortex
Authors: Limberger Norbert , Späth Leni , Starke Klaus
Published: July 2012

α2‐Adrenoceptor binding sites have been subclassified into α2A sites of which a main characteristic is very low affinity for prazosin, and α2B sites with relatively high affinity for prazosin. The presynaptic α2‐autoreceptors in rabbit brain cortex were studied in order to classify them in terms of α2A and α2B. Release of [3H]‐noradrenaline in cortical slices was elicited by trains of 4 pulses delivered at 100 Hz.

Clonidine caused concentration‐dependent inhibition of the stimulation‐evoked overflow of tritium, with an EC50 of 7.5 nm and a maximal inhibition by 96%.

The following α‐adrenoceptor antagonists shifted the concentration‐response curve of clonidine to the right (antagonist‐receptor dissociation constants KD in brackets): yohimbine (14 nm), 2‐[2H‐(1‐methyl‐1,3‐dihydroisoindole)methyl]‐4,5‐dihydroimidazole (BRL 44408; 15 nm) and 1,2‐dimethyl‐2,3,9,13b‐tetrahydro‐1H‐dibenzo[c,f]imidazo[1,5‐a]azepine (BRL 41992; 630 nm). Prazosin 1 μm and 2‐[2‐[4‐(o‐methoxyphenyl)piperazine‐1‐yl]‐ethyl]‐4,4‐dimethyl‐1,3(2H,4H)‐isoquinolinedione (AR‐C 239) μm failed to antagonize the effect of clonidine. Higher concentrations of prazosin and AR‐C 239 greatly accelerated the basal efflux of tritium.

The method used permits the functional determination of antagonist affinities undistorted by endogenous α2‐autoinhibition. A comparison with affinities derived from radioligand binding experiments indicates that the presynaptic α2‐autoreceptors in rabbit brain cortex are markedly different from the α2B‐subtype and probably belong to the prazosin‐insensitive α2A‐subtype.
Stereoselective effects of the enantiomers of bupivacaine on the electrophysiological properties of the guinea‐pig papillary muscle
Authors: Vanhoutte Filip , Vereecke Johan , Verbeke Norbert , Carmeliet Edward
Published: July 2012

Direct myocardial effects of the S(−)‐ and R(+)‐enantiomers of bupivacaine were compared in the guinea‐pig isolated papillary muscle by recording transmembrane action potentials with the standard microelectrode technique.

In 5.4 mm K+, at a stimulation rate of 1 Hz, the maximal rate of depolarization () was reduced to 59.9 ± 1.4% (n = 10) of control (mean ± s.e.mean) in the presence of 10 μm R(+)‐bupivacaine, and to 76.7 ± 1.2% (n = 14) in the presence of the same concentration of S(−)‐bupivacaine. This was mainly due to a difference in time constant at which block dissipated during the diastolic period. Recovery was slower in the presence of R(+)‐bupivacaine. The slower recovery in the presence of R(+)‐bupivacaine resulted also in a more pronounced frequency‐dependent block of .

Time constants for recovery from use‐dependent block became significantly faster for both enantiomers on hyperpolarization, while no significant change was observed at depolarization. At all membrane potentials recovery was slower in the presence of R(+)‐bupivacaine.

The action potential duration (APD) was shortened to a greater extent in the presence of R(+)‐bupivacaine over a large range of stimulation frequencies.

We conclude that S(−)‐bupivacaine affects and APD in the guinea‐pig papillary muscle less than the R(+)‐enantiomer at different rates of stimulation and resting membrane potentials.
GABAA receptors are differentially sensitive to zinc: dependence on subunit composition
Authors: Smart T.G. , Moss S.J. , Xie X. , Huganir R.L.
Published: July 2012

GABAA receptors with different subunit composition, were expressed in kidney cells and studied by whole cell recording. Expressed GABAA receptors were differentially sensitive to inhibition by zinc; receptors which lacked the γ subunit were inhibited by zinc. Embryonic neurones also exhibited zinc‐sensitive GABA responses, in contrast to adult neurones. This developmentally‐sensitive aspect of GABAA receptor pharmacology may be partly dependent on expression of the γ subunit.
Human, pig and guinea‐pig bladder smooth muscle cells generate similar inward currents in response to purinoceptor activation
Authors: Inoue Ryuji , Brading Alison F.
Published: July 2012

The contribution of purinergic neurotransmission to bladder excitation in pigs and man is small. Exogenously‐applied adenosine‐trisphosphate (ATP) however, elicits large inward currents in dispersed bladder smooth muscle cells in both species. The essential properties of the ATP‐induced current in human and pig detrusor are similar and the current intensity is comparable to those in the guinea‐pig, which has a powerful purinergic excitatory innervation. This suggests that other features of the tissue such as the closeness of the innervation and the degree of cell‐to‐cell coupling may be important in determining the effectiveness of purinergic transmission.
Determination of the role of noradrenergic and 5‐hydroxytryptaminergic neurones in postsynaptic α2‐adrenoceptor desensitization by desipramine and ECS
Authors: Heal D.J. , Prow M.R. , Buckett W.R.
Published: July 2012

Experiments were conducted to determine the respective roles which noradrenergic and 5‐hydroxytryptaminergic neurones play in the down‐regulation of postsynaptic α2‐adrenoceptors by desipramine and electroconvulsive shock (ECS). The functional status of these receptors was monitored by use of clonidine‐induced mydriasis in conscious mice.

Mydriasis to clonidine (0.1 mg kg−1, i.p.) was markedly attenuated by administration of either desipramine (10 mg kg−1, i.p.) for 14 days or ECS (200 V, 2 s) given five times over ten days confirming our previous observations.

The neurotoxin, DSP‐4 (100 mg kg−1, i.p. × 2), reduced brain noradrenaline levels by 64% and abolished the mydriasis induced by the noradrenaline releasing agent and reuptake inhibitor, methamphetamine, without significantly altering the response to clonidine, confirming our earlier results. This lesion prevented the attenuation of clonidine mydriasis by repeated administration of desipramine, but not ECS.

Lesioning of central 5‐hydroxytryptaminergic neurones with 5,7‐dihydroxytryptamine (75 μg, i.c.v.) had no influence on the reduction in clonidine mydriasis produced by repeated administration of either desipramine or ECS.

Since noradrenergic neurones are essential for the desensitization of postsynaptic α2‐adrenoceptors by desipramine, it indicates that this effect is probably the result of increased synaptic noradrenaline levels. This mechanism is not responsible for the change induced by ECS because this adaptation is independent of an intact noradrenergic input. 5‐HT‐containing neurones do not play a permissive role in the down‐regulation of postsynaptic α2‐adrenoceptors by either antidepressant treatment.
Analgesic doses of morphine do not reduce noxious stimulus‐evoked release of immunoreactive neurokinins in the dorsal horn of the spinal cat
Authors: Lang C.W. , Duggan A.W. , Hope P.J.
Published: July 2012

Antibody microprobes were used to detect immunoreactive neurokinin A release in the dorsal spinal cord of barbiturate‐anaesthetized spinal cats.

Noxious mechanical stimulation of the ipsilateral hind paw and electrical stimulation (suprathreshold for unmyelinated primary afferent fibres) of the ipsilateral tibial nerve evoked immunoreactive neurokinin A release.

Systemic morphine, 5 mg kg−1, i.v., did not block immunoreactive neurokinin A release in response to these stimuli.

Subsequent naloxone administration, 0.5 mg kg−1, i.v., did not alter this stimulus‐evoked release.

Basal levels of immunoreactive neurokinin A were unaltered by morphine or naloxone.

These results suggest that the analgesic effects of morphine at the spinal cord level are not brought about by activation of presynaptic opiate receptors on neurokinin A containing afferent terminals.
Role of the σ receptor in the inhibition of [3H]‐noradrenaline uptake in brain synaptosomes and adrenal chromaffin cells
Authors: Rogers Cheryl , Lemaire Simon
Published: July 2012

Rat brain synaptosomes and cultured bovine adrenal chromaffin cells were used to monitor the inhibitory effects of phencyclidine (PCP) and sigma (σ)‐receptor ligands on the uptake of [3H]‐noradrenaline ([3H]‐NA).

A Na+‐dependent high affinity uptake was observed in synaptosomes (30°C) and chromaffin cells (37°C) with Km of 0.22 and 0.56 μm and Vmax of 2.5 pmol min−1 mg−1 protein and 0.7 pmol min−1 per 106 cells, respectively.

PCP and haloperidol inhibited the high affinity uptake with IC50 of 0.17 and 0.42 μm, respectively in synaptosomes and 0.24 and 0.47 μm, respectively in adrenal chromaffin cells.

A close correlation (r = 0.96) was established between the ability of various PCP and σ‐receptor ligands to inhibit [3H]‐NA uptake in both systems: PCP > TCP > haloperidol > 3‐(+)‐PPP > MK‐801 ≥ (−)‐butaclamol > (+)‐SKF‐10047 > DTG. Spiperone and opioid receptor ligands were ineffective at 20 μm.

These results indicate that the central and peripheral inhibitory effects of PCP and σ‐receptor ligands on [3H]‐NA uptake involves a receptor (σ1‐like) which is distinct from that (PCP2) recognized for the inhibition of [3H]‐dopamine uptake by PCP.
Identification of a D1 dopamine receptor, not linked to adenylate cyclase, on lactotroph cells
Authors: Schoors Danny F. , Vauquelin Georges P. , De Vos Hilde , Smets Gerda , Velkeniers Brigitte , Vanhaelst Luc , Dupont Alain G.
Published: July 2012

We studied the lactotroph cells of the rat by both in vivo and in vitro pharmacological techniques for the presence of D1‐receptors. Both approaches revealed the presence of a D2‐receptor, stimulated by quinpirole (resulting in an inhibition of prolactin secretion) and blocked by domperidone.

Administration of fenoldopam, the most selective D1‐receptor agonist currently available, resulted in a dose‐dependent decrease of prolactin secretion in vivo (after pretreatment with α‐methyl‐p‐tyrosine) and in vitro (cultured pituitary cells). This increase was dose‐dependently blocked by the selective D1‐receptor antagonist, SCH 23390, and although the effect of fenoldopam was less than that obtained by D2‐receptor stimulation, these data suggest that a D1‐receptor also controls prolactin secretion.

In order to detect the location of these dopamine receptors, autoradiographic studies were performed by use of [3H]‐SCH 23390 and [3H]‐spiperone as markers for D1 and D2‐receptors, respectively. Specific binding sites for [3H]‐SCH 23390 were demonstrated. Fenoldopam dose‐dependently reduced [3H]‐SCH 23390 binding, but had no effect on [3H]‐spiperone binding. Immunocytochemical labelling of prolactin cells after incubation with [3H]‐SCH 23390 revealed that the granulae and hence, D1 binding sites were present on the lactotroph cells.

Radioligand binding studies performed on membranes from anterior pituitary cells revealed the presence of the D2‐receptor (54 fmol mg−1 protein) with a Kd of 0.58 nm for [3H]‐spiperone, but failed to detect D1 ‐receptors.

Finally, we studied the effect of dopamine and of fenoldopam on the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) content of anterior pituitary cells. Although cyclic AMP increased upon prostacyclin administration, indicating an intact adenylate cyclase system, fenoldopam failed to increase the cyclic AMP production.

It is tempting to speculate that fenoldopam reduces prolactin secretion through interaction with a non‐cyclase‐linked D1‐receptor on the lactotroph cells.
Measurements of tacrine and monoamines in brain by in vivo microdialysis argue against release of monoamines by tacrine at therapeutic doses
Authors: Baldwin H.A. , De Souza R.J. , Sarna G.S. , Murray T.K. , Green A.R. , Cross A.J.
Published: July 2012

The concentration of tacrine (tetrahydroaminoacridine or THA) in plasma, regions of brain and cerebral extracellular fluid has been studied in the rat at various times following injection of a dose of 5 mg kg−1, i.p.

The peak plasma THA concentration was 2.46 nmol ml−1, and occurred 30 min post injection and clearance was first order (t1/2 = 90min). The concentration in the brain peaked between 30–60 min, and was around 30 times plasma concentration (striatum peak concentration = 65 ± 3 nmol g−1). Extracellular cerebral concentration measured by in vivo microdialysis was similar to plasma concentration with the peak occurring 100 min post‐injection.

No evidence was obtained by in vivo dialysis for THA inducing dopamine release from striatum or 5‐hydroxytryptamine (5‐HT) release from the frontal cortex. Enhanced release of dopamine did occur after (+)‐amphetamine (5 mg kg−1, i.p.) injection, while KCl (100 mm) in the probe released both dopamine and 5‐HT.

Since the minimum plasma THA concentration achieved in this study was at least twice that found in the plasma of patients given THA for the treatment of dementia, these results suggest that monoamine release in the brain does not occur during therapy.
Effect of NG‐monomethyl l‐arginine (l‐NMMA) and NG‐nitro l‐arginine (l‐NOARG) on non‐adrenergic non‐cholinergic relaxation in the circular muscle of the human ileum
Authors: Maggi Carlo Alberto , Barbanti Gabriele , Turini Damiano , Giuliani Sandro
Published: July 2012

We have investigated the effect of the NO synthesis inhibitors, NG‐monomethyl l‐arginine (l‐NMMA) and NG‐nitro l‐arginine (l‐NOARG) on the non‐adrenergic non‐cholinergic (NANC) relaxation produced by electrical field stimulation in the circular muscle of the human ileum.

In the presence of atropine and guanethidine (1 and 3 μm, respectively), electrical field stimulation produced tetrodotoxin‐sensitive relaxation of the strips. l‐NMMA, starting from 100 μm, produced a concentration‐dependent inhibition of the evoked relaxations (2 Hz); maximal inhibition at 1 mm averaged about 35%.

The inhibitory effect of l‐NMMA was unchanged by previous incubation with d‐arginine while it was prevented by l‐arginine (l‐Arg). l‐NMMA did not affect isoprenaline‐induced relaxation.

l‐NOARG (1–30 μm) concentration‐dependently inhibited the evoked relaxations at 2 Hz, up to a maximum of 65% inhibition, although in some strips complete inhibition of the response was observed. The effect of l‐NOARG was reversed by l‐Arg. l‐NOARG did not affect isoprenaline‐induced relaxation.

These results suggest that NO may be involved in inhibitory NANC transmission in the circular muscle of the human ileum.
Capsaicin‐sensitive vagal stimulation‐induced gastric acid secretion in the rat: evidence for cholinergic vagal afferents
Authors: Sharkey Keith A. , Oland Lorraine D. , Kirk David R. , Davison Joseph S.
Published: July 2012

The effects of electrical vagal stimulation on frequency‐dependent gastric acid secretion were investigated in urethane‐anaesthetized rats in vivo.

Stimulation at 4, 16 or 32 Hz was performed in rats treated with atropine (1mg kg−1, i.v.), hexamethonium (10 mg kg−1, i.v. bolus and 1 mg kg−1 min−1, i.v. infusion) or atropine and hexamethonium (doses as above); in some experiments pentagastrin (1.2 μg kg−1 h−1, i.v. infusion) was infused prior to stimulation.

Maximal acid secretion occurred at 16 Hz. This was significantly reduced but not abolished by atropine or hexamethonium and completely abolished after atropine and hexamethonium. In the presence of pentagastrin, the acid secretory response to 16 Hz stimulation was augmented, atropine or hexamethonium reduced stimulated secretion by about 70%, whereas atropine and hexamethonium completely abolished stimulated secretion.

In rats in which the vagus nerve was pretreated with capsaicin 10–14 days before experimentation there was a significant reduction (by about 40%) in stimulated acid secretion at 16 Hz, which was virtually abolished by atropine treatment. After acute treatment of the vagus nerve with capsaicin (at the time of experimentation) maximally stimulated acid secretion was significantly reduced by about 50%.

Taken together, these results indicate that capsaicin‐sensitive afferent fibres contribute to the acid secretory response induced by electrical vagal stimulation in the rat. Based on pharmacological evidence, the capsaicin‐sensitive afferent fibres may be cholinergic, since atropine and hexamethonium totally abolish vagal stimulation‐induced acid secretion.
R‐(+)‐HA‐966, a glycine/NMDA receptor antagonist, selectively blocks the activation of the mesolimbic dopamine system by amphetamine
Authors: Hutson P.H. , Bristow L.J. , Thorn L. , Tricklebank M.D.
Published: July 2012

The effects of the glycine/NMDA receptor antagonist, (+)‐HA‐966 on the neurochemical and behavioural responses to amphetamine have been determined in the mouse and rat.

In vehicle‐treated control mice, (+)‐HA‐966 (30–100 mg kg−1) did not affect dopamine synthesis in either the nucleus accumbens or striatum and was without marked effect on spontaneous locomotor activity.

In the mouse, (+)‐HA‐966 (30 and 100 mg kg−1) dose‐dependently blocked the enhancement of dopamine synthesis induced in the nucleus accumbens by amphetamine, but was without effect on the increase in dopamine synthesis in the striatum.

Intracerebroventricular administration of the glycine/NMDA receptor antagonist, 5,7‐dichlorokynurenic acid, in the mouse (10 μg) also significantly attenuated amphetamine‐enhanced DOPA accumulation in the nucleus accumbens, but not in the striatum.

The decrease of dopamine synthesis in striatum and nucleus accumbens induced by the dopamine receptor agonist, apomorphine, was unaffected by (+)‐HA‐966 (100 mg kg−1).

(+)‐HA‐966 (30 mg kg−1) failed to attenuate the hyperactivity induced by the systemic administration of amphetamine in the mouse, but totally prevented the hyperlocomotion following infusion of amphetamine into the rat nucleus accumbens. In contrast, stereotyped behaviour induced by infusion of amphetamine into the rat striatum was not altered following pretreatment with (+)‐HA‐966 (30 mg kg−1).

The results are consistent with a selective facilitatory role of glycine/NMDA receptors on mesolimbic dopaminergic neurones.
Electrophysiological studies of the GABAA receptor ligand, 4‐PIOL, on cultured hippocampal neurones
Authors: Kristiansen U. , Lambert J.D.C. , Falch E. , Krogsgaard‐Larsen P.
Published: July 2012

Whole‐cell, patch‐clamp recordings from cultured hippocampal neurones have been used to characterize the action of the GABAA ligand, 5‐(4‐piperidyl)isoxazol‐3‐ol (4‐PIOL). The action of 4‐PIOL was compared with that of the established GABAA agonist, isoguvacine.

With a symmetrical Cl−gradient across the membrane and a holding potential of −60 mV, both isoguvacine and 4‐PIOL evoked an inward current. The reversal potentials of the responses to both agents were identical (+8.8 mV, n = 4) and the current/voltage relationships showed outward‐going rectification.

The response to 300 μm 4‐PIOL was completely blocked by the GABAA antagonist, bicuculline methobromide (BMB, 10 μm). The pA2 of BMB was >6.46. With 2 mm 4‐PIOL about 15% of the response remained in the presence of 100 μm BMB. This may represent a non‐specific component of the response to large concentrations of 4‐PIOL.

4‐PIOL was about 200 times less potent as an agonist than isoguvacine. Because of the rapid fade (desensitization) of isoguvacine‐induced currents, the maximum response to this agonist was not determined. However, the response to 2 mm 4‐PIOL was only a small fraction of that evoked by submaximal concentrations of isoguvacine.

Setting the response to 1 mm 4‐PIOL as maximum, the EC50 for 4‐PIOL was 91 μm (95% confidence limits: 73–114 μm).

4‐PIOL antagonized the response to isoguvacine with a parallel shift to the right of the dose‐response curve. The antagonist action of 4‐PIOL was about 30 times weaker than that of BMB. When allowance was made for the intrinsic agonist action of 4‐PIOL, the Ki was 116 μm (95% confidence limits: 102–130 μm). This was not significantly different from EC50 (P = 0.86; non‐parametric Mann‐Whitney test).

It is concluded that 4‐PIOL is a partial agonist at the GABAA receptor on cultured hippocampal neurones.
Pharmacological analysis of agonist‐antagonist interactions at acetylcholine muscarinic receptors in a new urinary bladder assay
Authors: Durant P.A.C. , Shankley N.P. , Welsh N.J. , Black J.W.
Published: July 2012

Agonist‐antagonist interactions at acetylcholine (ACh) muscarinic receptors have been analysed by use of an improved urinary bladder assay, isolated and intact, from the mouse. With 5‐methylfurmethide as agonist, validated cumulative concentration‐effect curves were obtained in less than 7 min by re‐dosing before the response plateaux began to fade.

The pKB value estimated for pirenzepine was 6.76. The pKB values estimated for atropine and N‐methylatropine from data obtained at concentrations which produced dose‐ratios greater than 20 and 60 were 8.90 and 9.58, respectively.

The deviation from simple competitive behaviour at low dose‐ratios with atropine and N‐methylatropine was consistent with the operation of saturable antagonist removal processes. The deviation observed with atropine was corrected by pre‐incubation with methylbutyrate, an alternative substrate for ‘atropine esterase’.

The simple competitive behaviour of N‐methylatropine was restored following pre‐incubation with the neuronal choline uptake blocker hemicholinium‐3 (HC‐3). However, the pKB estimated for N‐methylatropine under these conditions was low. This latter result could be accounted for by the observed behaviour of HC‐3 as a competitive antagonist of ACh muscarinic receptors (pKB = 4.01).

We conclude that the modified mouse urinary bladder assay is suitable for the quantitative analysis of muscarinic receptor interactions. In addition, we postulate the existence of a previously undescribed uptake mechanism for quaternary muscarinic receptor antagonists.
Factors affecting the regional haemodynamic responses to glyceryl trinitrate and molsidomine in conscious rats
Authors: Phillips K. , Gardiner S.M. , Kemp P.A. , Bennett T.
Published: July 2012

A series of experiments was performed in conscious, unrestrained, male, Long Evans rats, chronically instrumented for the measurement of regional haemodynamics.

Infusion of glyceryl trinitrate (GTN, 0.1 mg kg−1 min−1, i.v.) for 10 min elicited tachycardia, but no sustained change in mean arterial blood pressure. Renal haemodynamics were unaffected, but there were reductions in hindquarters flow and vascular conductance together with substantial increases in flow and conductance in the mesenteric vascular bed.

In the presence of captopril (2 mg kg−1 bolus, and 1 mg kg−1 h−1 infusion, i.v.) GTN elicited significant hypotension and increases in renal blood flow and vascular conductance, indicating that activation of the renin‐angiotension system opposed the dilator effects of GTN in this vascular bed. However, the mesenteric and hindquarters haemodynamic effects of GTN were not affected by captopril. In contrast, in the presence of enalaprilat (2 mg kg−1 bolus, and 1 mg kg−1 h−1 infusion, i.v.) there was significant enhancement of the mesenteric, as well as renal, haemodynamic effects of GTN. Hence, these results provide no evidence for the sulphydryl groups in captopril exerting a specific effect to enhance the haemodynamic actions of GTN in our experimental protocols.

Administration of molsidomine alone (1 mg kg−1, i.v. bolus) elicited tachycardia and hypotension; there were no changes in mesenteric or hindquarters haemodynamics, but renal flow and vascular conductance fell. Thus, the hypotensive effect of molsidomine was probably due to a reduction in cardiac output, consequent upon venodilatation.

In the presence of captopril or enalaprilat, molsidomine evoked renal and mesenteric vasodilatations in association with hypotension, indicating that activation of the renin‐angiotensin system contributed to the lack of vasodilator responses to administration of molsidomine alone. However, since the effects of enalaprilat were more marked than those of captopril (in spite of the dose of both drugs being supramaximal for inhibition of angiotensin‐converting enzyme), other factors must have been involved.

In a separate experiment, pretreatment with the nitric oxide synthesis inhibitor, NG‐nitro‐l‐arginine methyl ester (1 mg kg−1 h−1, i.v.), enhanced the mesenteric vasodilator effect of molsidomine. Collectively, these results are consistent with in vitro data showing that endogenous nitric oxide can inhibit the vasodilator effects of nitric oxide derived from molsidomine, and that the sulphydryl groups of captopril can protect endogenous nitric oxide from inactivation by oxygen‐derived free radicals, thereby enhancing the inhibitory effect of endogenous nitric oxide on the vasodilator responses to exogenous nitric oxide derived from molsidomine (or GTN).
The effects of sham and full spinalization on the systemic potency of μ‐ and κ‐opioids on spinal nociceptive reflexes in rats
Authors: Herrero Juan F. , Headley P. Max
Published: July 2012

Flexor withdrawal reflexes to noxious mechanical pinch stimuli were recorded as single motor unit activity in α‐chloralose anaesthetized rats, by means of tungsten bipolar electrodes inserted per‐cutaneously into hindlimb flexor muscles. The relative spinal and supraspinal contributions to μ‐ and κ‐opioid agonists in inhibiting these spinal reflexes, together with possible potency changes elicited by surgical trauma, were examined by comparing their relative potencies in spinally unoperated, sham spinalized and spinalized rats.

The noxious stimuli, which were of comparable intensity in the three groups, elicited similar mean firing rates of the motor units in all groups. This indicates that the excitability levels in the reflex pathway were not greatly affected by either sham or actual spinalization.

The μ‐agonists morphine and fentanyl, and the κ‐agonist U‐50,488H, inhibited the reflexes in a dose‐dependent manner, when administered intravenously in a log2 cumulative dose regime.

The surgery of sham spinalization had little effect on the potency of morphine and fentanyl, whereas it doubled the potency of U‐50,488.

Spinalization did not affect the potency of morphine. In contrast it decreased the potency of fentanyl 2–4 fold and that of U‐50,488 approximately 6 fold.

The effects of all agonists were antagonized by naloxone. Dose‐dependence studies indicating that antagonism of U‐50,488H required about 5 times the dose of naloxone that antagonized morphine.

The data suggest that surgical trauma to the spinal column and/or dura mater triggers supraspinal mechanisms that significantly enhance the potency of κ‐ but not μ‐agonists.

It is concluded that most of the effects of systemic morphine on spinal reflexes are mediated, under all three conditions tested, by direct effects in the spinal cord. In contrast, the inhibition of reflexes by U‐50,488H is mediated at both spinal and supraspinal levels, the latter being enhanced in the presence of surgical trauma. The differences between morphine and fentanyl remain unexplained.
The effects of idazoxan and other α2‐adrenoceptor antagonists on food and water intake in the rat
Authors: Jackson Helen C. , Griffin I.J. , Nutt D.J.
Published: July 2012

Idazoxan (1, 3, 10 mg kg−1, i.p.) produced a significant increase in food and water intake in freely feeding rats during the daylight phase.

The more selective and specific α2‐adrenoceptor antagonists, RX811059 (0.3, 1, 3 mg kg−1, i.p.) and RX821002 (0.3, 1, 3 mg kg−1, i.p.), did not produce hyperphagia in rats, however, the highest dose produced a significant increase in water intake.

The peripherally acting α2‐adrenoceptor antagonist, L‐659,066 (1, 3, 10 mg kg−1, i.p.), did not affect food intake in the 4 h following injection, but the highest dose (10 mg kg−1), produced a large increase in water intake.

These results indicate that α2‐adrenoceptor antagonists may increase water intake by a peripherally mediated mechanism.

The lack of effect of RX811059 and RX821002 on food intake contrasts with the large dose‐related increases induced by idazoxan and suggests that the hyperphagic effects of idazoxan are not due to α2‐adrenoceptor blockade but may instead reflect its affinity for a non‐adrenoceptor site, a property not shared by the other α2‐antagonists.
Methylxanthine‐induced attenuation of pecking in chickens
Authors: Zarrindast M.R. , Nasir T.
Published: July 2012

Apomorphine induced dose‐dependent pecking in chickens.

The response was decreased by theophylline or caffeine in a dose‐dependent manner.

Administration of theophylline or caffeine alone did not exert any effect on pecking behaviour.

Dipyridamole administration neither induced pecking nor altered the pecking induced by apomorphine.

Administration of 5‐N‐ethylcarboxamide‐adenosine to animals caused variable effects on pecking induced by apomorphine. The drug did not induce pecking by itself.

It is concluded that the inhibitory response to methylxanthines may be mediated through blockade of adenosine receptors. However, to prove this, more experiments are needed.
Effects of calcium modulators on vagally‐mediated constriction in the guinea‐pig isolated trachea
Authors: McCaig Dorothy J. , Aitken Susan
Published: July 2012

The effects of calcium modulators on tracheal constriction evoked by vagal stimulation were examined in the isolated, innervated trachea of the guinea‐pig. Responses were assessed in the Krebs‐filled trachea as changes in intraluminal pressure (ILP), increases and decreases reflecting constriction and dilatation, respectively.

Preparations had a positive resting ILP, indicating significant spontaneous tone. Verapamil and nifedipine reduced baseline ILP, whilst Bay K 8644 had mixed effects.

Verapamil and nifedipine attenuated vagal responses in a concentration‐dependent manner. At lower concentrations attenuation was due entirely to postjunctional effects but at higher concentrations prejunctional effects may have contributed to attenuation.

Verapamil and nifedipine attenuated vagal responses in the absence or presence of flurbiprofen, indicating that their effects are largely independent of the generation of cyclo‐oxygenase products. Nifedipine, however, was less effective in reducing responses to low frequency vagal stimulation (up to 5 Hz) when flurbiprofen was present.

Bay K 8644 augmented vagal responses, the degree varying widely between preparations.

It was concluded that influx of Ca2+through voltage‐operated Ca2+channels contributes significantly to vagally‐mediated tracheal constriction in normal trachea and in trachea where endogenous release of cyclo‐oxygenase products is inhibited.
Clonidine inhibits ATP‐sensitive K+channels in mouse pancreatic β‐cells
Authors: Plant T.D. , Jonas J‐C. , Henquin J.C.
Published: July 2012

The effects of clonidine and adrenaline on adenosine 5′‐triphosphate (ATP)‐sensitive K+channels were studied in pancreatic β‐cells from normal mice.

When perifused with a medium containing 1 mm glucose, many of the ATP‐sensitive K+channels in the β‐cell membrane are open. Under these conditions, clonidine (5–100 μm) reversibly decreased 86Rb efflux from the islets, whereas adrenaline was ineffective at concentrations up to 100 μm.

In 6 mm glucose, most of the ATP‐sensitive K+channels in the β‐cell membrane are closed. Opening these channels by diazoxide (100 μm) caused a marked acceleration of 86Rb efflux from the islets, which was attenuated by 100 μm clonidine.

ATP‐sensitive K+currents were measured in single β‐cells by the whole cell mode of the patch‐clamp technique. At concentrations above 4 μm, clonidine reversibly inhibited the ATP‐sensitive K+current in a dose‐dependent manner.

Voltage‐sensitive K+currents were unaffected by 20 μm but decreased slightly by 100 μm clonidine.

Calcium currents, measured by the whole cell or perforated patch technique, were unaffected by clonidine at concentrations up to 100 μm.

It is concluded that high concentrations of the α2‐adrenoceptor agonist clonidine, but not of adrenaline, can inhibit ATP‐sensitive K+channels in pancreatic β‐cells. Other ionic channels are only slightly affected or unaffected.