bluuebunny/crossref_metadata_2025 huggingface dataset:
Coexistence of carriers for dopamine and GABA uptake on a same nerve terminal in the rat brain
Authors: Bonanno Giambattista , Raiteri Maurizio
Published: July 2012

The ability of γ‐aminobutyric acid (GABA) to affect the release of [3H]‐dopamine in rat brain synaptosomes prepared from corpus striatum, frontal cortex and hypothalamus and prelabelled with the radioactive catecholamine in the presence of desipramine was examined.

GABA (10–300 μm) increased in a concentration‐dependent way the basal release of [3H]‐dopamine from striatum and cortical synaptosomes; however, its effect was much less pronounced in hypothalamic nerve terminals. 2,4‐Diaminobutyric acid (DABA) mimicked GABA although less potently.

Neutral amino acids such as leucine, valine or α‐aminoisobutyric acid (100–300 μm) did not affect or increased minimally the release of [3H]‐dopamine.

The GABA‐induced [3H]‐dopamine release was not prevented by the GABAA‐receptor antagonists, bicuculline or picrotoxin. The GABAA‐receptor agonist, muscimol (10–300 μm), displayed only a very weak, not significant, enhancing effect on [3H]‐dopamine release. The GABAB‐receptor agonist (—)‐ baclofen (100 or 300 μm) had no effect.

Three novel and selective inhibitors of GABA uptake, N‐(4,4‐diphenyl‐3‐butenyl)‐nipecotic acid (SK&F 89976A), N‐(4,4‐diphenyl‐3‐butenyl)‐guvacine (SK&F 100330A) and N‐(4,4‐diphenyl‐3‐butenyl)‐homo‐β‐proline (SK&F 100561) potently counteracted the enhancing effect of GABA on [3H]‐dopamine release. Nipecotic acid also reduced the effect of GABA.

It is concluded that carriers for the uptake of dopamine and GABA may coexist on the same nerve terminal in the rat brain.
A facilitatory effect of bicuculline on the enteric neurones in the guinea‐pig isolated colon
Authors: Frigo G.M. , Galli A. , Lecchini S. , Marcoli M.
Published: July 2012

Changes in the efficiency of the peristaltic reflex, acetylcholine (ACh) output and motor responses to transmural and periarterial nerve stimulation produced by bicuculline and y‐aminobutyric acid (GABA) receptor desensitization were investigated in the guinea‐pig isolated colon.

Bicuculline, at concentrations unable to affect spontaneous colonic motility and lacking anticholinesterase activity, produced a dose‐dependent increase of both the efficiency of the peristaltic reflex and the stimulated ACh output. Such effects could not be observed in GABA‐desensitized preparations.

A frequency‐dependent potentiation of the cholinergic excitatory and non‐adrenergic non‐cholinergic (NANC) inhibitory responses to transmural stimulation was also observed in the presence of bicuculline. Conversely bicuculline exhibited an inhibitory effect on the relaxation induced by periarterial nerve stimulation.

Acute GABA‐desensitization was unable to affect the contractile responses to transmural stimulation, the ACh output and the efficiency of the peristaltic reflex. On the contrary, desensitization was able to mimic the effects of bicuculline on the inhibitory responses to both transmural and periarterial nerve stimulation.

Our results are consistent with a significant role played by an intrinsic GABAergic pathway in the modulation of both cholinergic excitatory and NANC inhibitory neurones. The hypothesis is advanced that a feed‐back modulation carried out through bicuculline‐sensitive GABAergic synapses could operate during the propagation of peristaltic motor activity.
Muscarinic receptors mediate negative and positive inotropic effects in mammalian ventricular myocardium: differentiation by agonists
Authors: Korth Michael , Kühlkamp Volker
Published: July 2012

The concentration‐dependence of the negative and positive inotropic effect of choline esters and of oxotremorine was studied in isometrically contracting papillary muscles of the guinea‐pig. The preparations were obtained from reserpine‐pretreated animals and were electrically driven at a frequency of 0.2 Hz.

In the presence of the phosphodiesterase inhibitor 3‐isobutyl‐1‐methyl xanthine (IBMX, 100 μmol I−1), choline esters and oxotremorine produced concentration‐dependent negative inotropic effects. Oxotremorine exhibited the highest negative inotropic potency (with a half‐maximal effective concentration, EC50, of 20 nmol l−1) followed by carbachol (139 nmol l−1), methacholine (490 nmol l−1), acetylcholine in the presence of lO μmol l−1 physostigmine (1.36 μmol l−1 and bethanechol (10 μmol l−1)). Atropine was a competitive antagonist of the negative inotropic effects. Carbachol and oxotremorine decreased Vmax, overshoot and duration of slow Ca2+‐dependent action potentials which had been elicited in the presence of 100 μmol l−1 IBMX.

Choline esters produced a concentration‐dependent positive inotropic effect. With an EC50 of 32 μmol l−1, carbachol was the most potent compound, followed by methacholine (35 μmol l−1), acetylcholine in the presence of 10 μmol l−1 physostigmine (46 μmol l−1) and bethanechol (142 μmol l−1). Compared to carbachol and methacholine which increased force by 100% of control, the increase induced by acetylcholine and bethanechol was only 64 and 58%, respectively. Atropine shifted the concentration‐effect curves of all choline esters to higher concentrations. Choline esters caused intracellular Na+ activity to increase in the quiescent papillary muscle. This effect was reversed by atropine.

Oxotremorine produced a small concentration‐dependent positive inotropic effect (about 30% of the maximal effect of carbachol) which was resistant to atropine. Oxotremorine was a potent inhibitor of the positive inotropic effect of choline esters, and did not cause an increase in intracellular Na+ activity in the quiescent papillary muscle.

The results show that muscarinic receptors of the ventricular myocardium mediate two inotropic effects, which are opposite in direction and differ in their concentration‐dependence by a factor of 100. Although agonists differentiate between both inotropic effects, it is unknown whether the receptors involved represent receptor states or separate receptor subpopulations. The negative inotropic effect of choline esters and of oxotremorine can be best explained by adenylate cyclase inhibition. While stimulation of phosphoinositide hydrolysis might have been responsible for the positive inotropic effect of choline esters via modulation of cation‐fluxes across the cell membrane, such a mechanism was not involved in the positive inotropic effect of oxotremorine.
The effect of nicotine on motoneurones of the immature rat spinal cord in vitro
Authors: Blake J.F. , Evans R.H. , Smith D.A.S.
Published: July 2012

Nicotine [(–)‐nicotine di(+)‐tartrate 1–50 μm] produced depolarization of motoneurones as recorded from ventral roots of immature (1–5 day old) rat hemisected spinal cord preparations. This action of nicotine was accompanied by marked desensitization which persisted for at least 2 h following a 2 min application.

Ventral roots sectioned from the spinal cord, which were sensitive to glycine, failed to respond to nicotine.

Blockade of regenerative electrical activity with tetrodotoxin produced a mean reduction of 39% in the response to 10 μm nicotine.

In order to avoid desensitization, blocking agents were tested for their ability to suppress the initial response to a 2 min application of 10 μm nicotine (0.58 mV ± 0.07 s.e.mean, 21 preparations) in 4 or more naive preparations. Responses to nicotine (10 μm) were significantly reduced by 10 μm hexamethonium and were abolished by 250 μm hexamethonium but were resistant to the following antagonists:‐ atropine (1 μm), phentolamine (2 μm), strychnine (10 μm), kynurenic acid (2mm) and a mixture of bicuculline (50 μm) and picrotoxin (50 μm).

It is concluded that the depolarizing responses to nicotine may be due to the presence of nicotinic receptors either on the motoneurone membrane or on nerve terminals adjacent to motoneurones which release an unidentified neurotransmitter.
A 7‐phenyl substituted triazolopyridazine has inverse agonist activity at the benzodiazepine receptor site
Authors: Biziere K. , Bourguignon J.J. , Chambon J.P. , Heaulme M. , Perio A. , Tebib S. , Wermuth C.G.
Published: July 2012

To investigate further the structural requirements for benzodiazepine (BZD) receptor ligands, we synthesized SR95195, [7‐phenyl‐3‐methyl‐1,2,4‐triazolo‐(4,3‐b) pyridazine], a positional isomer of the 6‐phenyl‐triazolo‐pyridazines, which were the first non‐BZD derivatives to exhibit high affinity for the BZD receptor and BZD‐like activity in vivo.

In vitro, SR95195 displaced specifically bound [3H]‐flunitrazepam from rat cerebellar and hippocampal membranes with respective IC50 values of 4 and 8 μm.

In vivo, SR95195 lacked BZD‐like activity. At high doses SR95195 induced clonic seizures in mice (threshold convulsant dose: 150 mg kg−1; CD50: 160 mg kg−1 i.p.) which were antagonized by Ro 15–1788. At non‐convulsant doses (25 mg kg−1 i.p. and 100 mg kg−1 i.p.). SR95195 significantly decreased punished responding in an operant conflict procedure in the rat, suggesting SR95195 has intrinsic anxiogenic activity.

SR95195, in mice, reversed the anticonvulsant and myorelaxant actions of diazepam 3 mg kg−1, orally (respective ED50 values: 45 mg kg−1 i.p. and 44 mg kg−1 i.p.). In an operant‐conflict test in rats, SR95195 at non‐anxiogenic doses, antagonized the disinhibitory action of diazepam 4 mg kg−1, i.p. (ED50: 8.6 mg kg−1, i.p.), but not that of pentobarbitone 15 mg kg−1, i.p.

It is concluded that SR95195 has the pharmacological profile of an inverse BZD agonist and that displacing the phenyl from the 6‐ to the 7‐position in the triazolopyridazine series causes a shift from agonist to inverse agonist type activity at the BZD receptor site.
Differential effects of Ca antagonists on the noradrenaline release and contraction evoked by nerve stimulation in the presence of 4‐aminopyridine
Authors: Kato Hitoshi , Takata Yoshinobu
Published: July 2012

We previously reported that verapamil, nicardipine and diltiazem inhibited both neurotransmitter release and contraction evoked by transmural nerve stimulation (TNS) in the canine saphenous vein.

To evaluate whether the three Ca antagonists act on the nerve endings by inhibiting Ca2+ influx, the effects of the three antagonists were studied in the presence of 4‐aminopyridine (4‐AP) 3 × 10–4 m on the TNS‐evoked tritium overflow and contraction of canine saphenous veins preloaded with [3H]‐noradrenaline.

4‐AP increased both tritium overflow and contraction evoked by TNS, but did not enhance the contraction induced by exogenous noradrenaline (10 nmol). In the veins pretreated with 4‐AP, verapamil (3 × 10–5 m) and nicardipine (10–5 m and 3 × 10–5 M) caused no significant effects on the TNS‐evoked tritium overflow, but they still inhibited the contraction. Diltiazem (10–5 m and 3 × 10–5 m) significantly inhibited both responses to TNS in the veins pretreated with 4‐AP, the effects being nearly equipotent to those in the absence of 4‐AP. The (–)‐cis isomer of diltiazem (10−5 m and 3 × 10−5 M), which is about 100 times less potent than diltiazem in inhibiting Ca2+ influx, inhibited both responses to TNS in the presence of 4‐AP to almost the same degree as diltiazem.

When 4‐AP was added after the Ca antagonists, it reversed the TNS‐evoked tritium overflow inhibiting actions of verapamil (3 × 10−5 m) and nicardipine (3 × 10−5 m) much more effectively than that of diltiazem (3 × 10−5 m).

Tetracaine (4 × 10−6 M) significantly inhibited the TNS‐evoked tritium overflow and contraction, which were unaffected by 4‐AP.

Sodium salicylate (10−2 M) failed to modify the inhibition of TNS‐evoked tritium overflow following diltiazem (3 × 10−5 M), but it enhanced that of tetracaine (4 × 10−6 M).

Verapamil but not diltiazem and nicardipine significantly increased the spontaneous tritium overflow from veins pretreated with 4‐AP.

The present study together with previous results suggests that diltiazem but not verapamil and nicardipine may inhibit the TNS‐evoked neurotransmitter release through an action other than inhibition of Ca2+ influx into the adrenergic nerve endings, allowing an inhibition of the resulting contraction.
Nicotine cue in rats: effects of central administration of ganglion‐blocking drugs
Authors: Kumar R. , Reavill C. , Stolerman I.P.
Published: July 2012

In rats trained to discriminate nicotine from saline, a single intraventricular injection of a small dose of the quaternary ganglion‐blocking drug chlorisondamine blocked the response to nicotine for four weeks.

Pentolinium was only weakly active and hexamethonium was inactive as a nicotine antagonist under the conditions used, even in doses that were just below those producing myoclonic jerks.

Chlorisondamine had no blocking effect in rats trained to discriminate the non‐nicotinic drugs midazolam or morphine from saline.

Intraventricular injections of chlorisondamine have a specific and unusually persistent nicotine‐blocking action, the mechanism of which requires further investigation.
1,4‐Dithiothreitol‐induced changes in histamine H1‐agonist efficacy and affinity in the longitudinal smooth muscle of guinea‐pig ileum
Authors: Donaldson J. , Hill S.J.
Published: July 2012

The effect of 1,4‐dithiothreitol (DTT) on histamine H1‐receptor agonist affinity and efficacy has been investigated in longitudinal muscle strips of guinea‐pig ileum.

Exposure of ileal smooth muscle to DTT significantly increased the maximal responses to the partial agonists SKF 71473 and DE‐2PEA, indicative of an increase in agonist efficacy. This effect was paralleled by a small decrease in EC50 values. In contrast, DTT produced a parallel displacement of the concentration‐response curve to the full agonist histamine in the same muscle strips.

Studies in which phenoxybenzamine and benzilylcholine mustard were used to reduce the maximum response to histamine suggested that DTT altered both agonist affinity and efficacy. The affinity constant for histamine, calculated by the method of Furchgott & Bursztyn (1967), increased by 2.7 fold in the presence of DTT. Furthermore, agonist efficacy also appeared to increase in the presence of DTT since the maximum response to histamine following phenoxybenzamine treatment increased on application of DTT.

[3H]‐mepyramine binding studies confirmed that DTT increased agonist affinity. DTT produced a significant parallel shift to the left of the displacement curves for histamine, 2‐methylhistamine, 2‐pyridylethylamine and 2‐thiazolylethylamine.

The results of this study therefore suggest that DTT potentiates H1‐receptor‐mediated contractile activity in guinea‐pig ileum by increasing both agonist efficacy and affinity.
Effects of oxytocin‐antagonist injections on luteal regression in the goat
Authors: Homeida A.M. , Khalafalla Amna Eisa
Published: July 2012

Intra‐arterial administration of 0.25 ml physiological saline to the non‐pregnant goat between days 12 and 20 of the oestrous cycle did not affect luteal regression, which was characterized by decreasing peripheral plasma progesterone concentration, beginning on day 13 of the oestrous cycle, and an increase in the plasma concentration of 13,14‐dihydro‐15‐keto‐prostaglandin F2α (PGFM) as oestrus approached on about day 20.

Intra‐arterial administration of oxytocin antagonist (OA) in saline at a dose of 0.2 μg kg−1 body weight to goats between days 12 and 20 of the cycle significantly (P < 0.001) delayed luteal regression beyond day 20 (to day 26).

Injection of OA maintained plasma progesterone secretion at 4–5 ng ml−1 till day 23 of the cycle and suppressed the increase in PGFM concentration.

Corpus luteum extract (100 μ1) of OA‐treated animals released a significant (P < 0.001) amount of PGF2α from rat uterus in vitro as did authentic oxytocin. This oxytocic material failed to release PGF2α during luteolysis in the goat, suggesting that oxytocin receptors for PGF2α release may be occupied by OA.

It is concluded that oxytocin‐receptor interaction in the uterus may be the stimulus for PGF2α release which triggers luteal regression in the goat.
Sulphasalazine and PhCL28A inhibit the formation of ethanol‐ and phenylbutazone‐induced rat gastric ulcers: lack of involvement of endogenous prostaglandins?
Authors: Berry C.N. , Prouteau M. , Lloyd K.G.
Published: July 2012

The effects of sulphasalazine (SZP) and PhCL28A on macroscopic lesion formation and ex vivo prostaglandin inactivation were studied in the ethanol (ETOH) and phenylbutazone (PBT) models of gastric ulcers in the rat. Prostaglandin ‘synthesis’ during homogenisation of the stomachs was also studied in the latter model.

Both PhCL28A and SZP when injected i.p. prevented the formation of ETOH‐ and PBT‐induced gastric ulcers with ED50 values of 13 and 41 mg kg−1 (vs ETOH) and 3 and 32 mg kg−1 (vs PBT) for PhCL28A and SZP respectively. However, neither compound was active orally in the dose ranges used (up to 30 mg kg−1 for PhCL28A and 100 mg kg−1 for SZP).

Irrespective of the route of administration, SZP (100 mg kg−1) and PhCL28A (30 mg kg−1) produced slight but statistically significant decreases in ex vivo prostaglandin inactivation by 100,000 g cytosolic supernatants prepared from stomachs not receiving ulcerogen. When tested in vitro, PhCL28A (IC50 = 230 nM) was approximatively 480 times more potent than SZP (IC50 = 110 μM) against rat stomach cytosolic prostaglandin inactivation.

Both ETOH (50%, 5 ml kg‐1, orally) and PBT (200 mg kg−1 orally) significantly decreased ex vivo gastric cytosolic prostaglandin inactivation. PhCL28A (30 mg kg−1, orally or i.p.) decreased prostaglandin inactivation still further after ulcerogen treatment except when given i.p. before ETOH treatment. SZP (100 mg kg−1) had a similar effect when given orally before PBT treatment.

When the prostaglandin content of the stomach homogenates was used as a measure of ex vivo prostaglandin synthesis in the PBT experiments, PhCL28A 30 mg kg−1 orally (but not i.p.) produced an 88% increase in prostaglandin E2 (PGE2) levels, but had no effect on 6‐keto‐PGF1α or thromboxane B2 formation during homogenization. SZP (100 mg kg−1 i.p. or orally) was without effect.

We conclude from these results that the anti gastric ulcer activity of SZP and PhCL28A is independent of prostaglandin inactivation and endogenous prostaglandin formation is probably not involved.
Changes in central GABAergic function following acute and repeated stress
Authors: Losada Matilde E. Otero
Published: July 2012

The function of γ‐aminobutyric acid (GABA)ergic systems in response to acute and repeated stressful manipulations was evaluated in both the corpus striatum and frontal cerebral cortex of the rat.

In the corpus striatum the activity of the synthetic enzyme for GABA (glutamic acid decarboxylase, GAD) and the levels of GABA were reduced by acute immobilization stress (1 h). GABA turnover was reduced only by acute cold stress (3 h, 4°C).

In the frontal cerebral cortex no changes were observed after acute stressful manipulations, but repeated stress (0.5 h immobilization per day for 14 days) enhanced both GAD activity and GABA turnover, and reduced GABA levels.

In conclusion, it would appear that the GABAergic system in the corpus striatum of the rat is most sensitive to acute stress and that the system in the frontal cerebral cortex area is preferentially responsive to chronic stress. It is speculated that the cortical GABAergic system is responsible for adaptive responses to the adverse conditions prevailing during chronic stress.
Stereoselective effects of lysophosphatidylserine in rodents
Authors: Chang Hyeun Wook , Inoue Keizo , Brupi Alessandro , Boarato Elena , Toffano Gino
Published: July 2012

The pharmacological action of the l‐ and d‐enantiomers of lysophosphatidylserine has been studied in vivo by following the increase in blood and brain glucose content caused by this phospholipid in mice. Preliminary experiments have confirmed that these effects are the consequence of lysophosphatidylserine‐induced mast cell activation since they are not observed in mast cell‐deficient mice bearing the W/Wv genotype.

Maximal hyperglycaemic response and brain glucose accumulation occur at 10 mg kg−1 lysophosphatidyl‐l‐serine (i.v.). Half‐maximal effect is at 3.5 mg kg−1. Lysophosphatidyl‐d‐serine at doses of up to 25 mg kg−1 i.v. elicits 40% (blood glucose) and 60% (brain glucose) of the maximal effect. The difference in activity between the two enantiomers is also observed in the desensitization to lysophosphatidylserine occurring when this phospholipid is administered by the oral route.

Lysophosphatidyl‐l‐serine is more active than the d‐enantiomer in mouse isolated peritoneal mast cells. Activity ratios of 10 are observed between 20 and 50% histamine release. Similar results are obtained with rat isolated peritoneal mast cells.

It is concluded that the configuration of the alpha carbon atom of serine influences the activity of lysophosphatidylserine in vivo and in vitro. Thus, the appropriate position of the serine amino group is required for optimal interaction of the phospholipid head group and a receptor in the mast cell membrane.
Effects of diuretics on GABA‐gated chloride current in frog isolated sensory neurones
Authors: Inomata N. , Ishihara T. , Akaike N.
Published: July 2012

Effects of three diuretics (furosemide, amiloride and α‐human atrial natriuretic polypeptide (α‐hANP)) on GABA‐activated chloride current (ICl) were investigated in frog isolated sensory neurones, following suppression of Na+, K+ and Ca2+ currents, by use of a ‘concentration‐clamp’ technique.

Furosemide inhibited the GABA‐activated ICl in a non‐competitive manner and facilitated the inactivation phase, while amiloride inhibited the GABA response in a competitive manner, both inhibitions being concentration‐dependent. α‐hANP had no effects on the GABA‐induced ICl.

The reversal potential of GABA‐activated ICl (EGABA) was not shifted in the presence of amiloride or furosemide.

The results suggest that amiloride may act at the GABA binding site while furosemide may act on the GABA‐gated chloride channel.
A quantitative pharmacological analysis of some excitatory amino acid receptors in the mouse neocortex in vitro
Authors: Burton N.R. , Smith D.A.S. , Stone T.W.
Published: July 2012

The effects of 2‐amino‐5‐phosphonovalerate and kynurenate, either alone or in combination, were tested on responses evoked by the excitatory amino acid agonists quinolinate, ibotenate, N‐methyl‐d‐aspartate and N‐methyl‐dl‐aspartate by use of an in vitro preparation of mouse neocortex and artificial cerebrospinal fluid nominally free of magnesium.

Schild plots for 2‐amino‐5‐phosphonovalerate, using each of the excitatory amino acids, were linear and had a slope not significantly different from one. The apparent pA2 values for 2‐amino‐5‐phosphonovalerate using each of the excitatory amino acids were 4.98 (quinolinate), 5.00 (N‐methyl‐dl‐aspartate), 4.92 (N‐methyl‐d‐aspartate) and 5.05 (ibotenate). The apparent pA2 obtained using ibotenate was distinct from that of N‐methyl‐d‐aspartate but there were no significant differences between pA2 estimates for quinolinate, N‐methyl‐d‐aspartate or N‐methyl‐dl‐aspartate.

Schild plots for kynurenate, using each of the excitatory amino acids, were linear and had a slope of 1.36 ± 0.03, significantly greater than one. The estimated apparent pA2 values for kynurenate were 3.65 (quinolinate), 3.71 (N‐methyl‐dl‐aspartate), 3.65 (N‐methyl‐d‐aspartate) and 3.89 (ibotenate). The apparent pA2 obtained using ibotenate was distinct from that of the other agonists.

Experiments using combinations of 2‐amino‐5‐phosphonovalerate and kynurenate indicated that both antagonists apparently acted competitively at receptors activated by ibotenate or by quinolinate.

These results indicate that ibotenate acts at a site distinct from that of quinolinate, N‐methyl‐d‐aspartate and N‐methyl‐dl‐aspartate.
Enhancement of guinea‐pig intestinal peristalsis by blockade of muscarinic M1‐receptors
Authors: Schwörer H. , Kilbinger H.
Published: July 2012

The effects of pirenzepine and hyoscine on the peristaltic reflex were investigated in the guinea‐pig isolated small intestine. Peristalsis was induced by raising the intraluminal pressure and the volume of fluid propelled was taken as a measure of the efficiency of peristaltic activity.

Low concentrations of pirenzepine (0.1‐1 nm) and of hyoscine (0.01 nm) significantly enhanced peristalsis, whereas larger concentrations of both drugs caused inhibition. Pirenzepine was about 6 times less potent than hyoscine in increasing peristalsis, but was about 100 times less potent in inhibiting it.

Neither tolazoline (1 μm) nor naloxone (0.3 μm) affected the stimulatory action of pirenzepine on peristalsis.

Bicuculline increased the efficiency of peristalsis at concentrations of 1 μm and 10 μm; at 10 nm, bicuculline reduced significantly the increase of peristalsis by pirenzepine. γ‐Aminobutyric acid (GABA) did not affect peristaltic activity, but the stimulatory effect of pirenzepine was abolished in the presence of 100 μm GABA.

The results indicate that activation of neuronal M1‐receptors causes inhibition of small intestinal peristalsis. Bicuculline‐sensitive ‘GABAergic’ synapses are probably involved in this inhibition.
The effect of dantrolene sodium on the discharge of alpha and gamma motoneurones to the soleus muscle in the decerebrate rat
Authors: Farquhar Ruth , Part N.J.
Published: July 2012

The effects of intravenous infusion of the direct acting muscle relaxant, dantrolene sodium (5 mg kg−1), on tension, integrated EMG, soleus muscle motor unit discharge frequency and gamma nerve fibre discharge were measured in the decerebrate rat.

Dantrolene sodium did not have any detectable direct effect upon the discharge of the gamma nerve fibres.

The soleus muscle of the decerebrate preparations exhibited spontaneous tension and reflex responses.

With the muscle held at constant length, dantrolene sodium caused an increase in the integrated EMG in 15 out of 18 experiments and a decrease in muscle tension in 15 out of 17. The results from these experiments showed great variability.

Dantrolene sodium caused a slight reduction in the tension response to tonic stretch; this was accompanied by an increase in the integrated EMG.

Dantrolene sodium also caused a shift in the relationship between tension and integrated EMG during the phasic component of the stretch reflex, with a greater integrated EMG being associated with a reduced tension.

Motor unit discharge frequencies were found to increase but not sufficiently to overcome the action of dantrolene sodium. It is concluded that motor unit recruitment must play an important role in the compensation for the muscle weakening action of dantrolene sodium.
Inhibitory effects of caffeine on contractions and calcium movement in vascular and intestinal smooth muscle
Authors: Ahn H.Y. , Karaki H. , Urakawa N.
Published: July 2012

The mechanism of the inhibitory effect of caffeine was investigated using vascular smooth muscle of rabbit aorta and intestinal smooth muscle of taenia isolated from guinea‐pig caecum.

Caffeine, 0.5–10 mm, relaxed the sustained contraction induced by 65.4 mm KCl or 10−6 m noradrenaline in aorta, and by 45.4 mm KCl or 10−6 m carbachol in taenia. The inhibitory effect of caffeine on the high K+‐induced contraction was antagonized by external Ca2+ but not by the Ca2+ channel activators, Bay K 8644 (10−7 m) or CGP 28,392 (10−7 m). Forskolin (2 × 10−7 m) potentiated the inhibitory effect of caffeine on the noradrenaline‐induced contraction but not on the high K+‐ or carbachol‐induced contraction. Caffeine induced a time‐and concentration‐dependent increase in the cyclic AMP content of aorta and forskolin caused a further augmentation.

45Ca2+ uptake was increased by high K+ or noradrenaline in aorta and by high K+ or carbachol in taenia. The increments were inhibited by caffeine at concentrations needed to inhibit muscle contractions.

45Ca2+ in the cellular releasable site in aorta was decreased either by noradrenaline or by caffeine. Simultaneous application of noradrenaline and caffeine did not induce an additive decrease.

In aorta treated with a Ca2+‐free solution, caffeine induced only a small contraction. Noradrenaline induced a greater contraction which was inhibited by caffeine. After washout of caffeine and noradrenaline, the second application of noradrenaline induced a transient contraction suggesting that caffeine does not deplete the noradrenaline‐sensitive store. Caffeine did not inhibit Ca2+ accumulation by the noradrenaline‐sensitive store.

It was concluded that caffeine has multiple sites of action in smooth muscle. Caffeine releases Ca2+ from a store which is apparently not sensitive to noradrenaline. Caffeine may inhibit noradrenaline‐induced Ca2+ release. Caffeine itself induces only a small contraction possibly because it decreases the Ca2+ sensitivity of contractile filaments and/or increases Ca2+ extrusion. Further, caffeine seems to inhibit stimulated Ca2+ influx. Cyclic AMP may be only partly responsible for the inhibitory effect of caffeine.
The effects of neosurugatoxin on evoked catecholamine secretion from bovine adrenal chromaffin cells
Authors: Bourke Jane E. , Bunn Stephen J. , Marley Philip D. , Livett Bruce G.
Published: July 2012

The effect of neosurugatoxin (NSTX), a toxin from the Japanese ivory mollusc (Babylonia japonica), on the nicotinic response of bovine adrenal chromaffin cells was examined.

NSTX inhibited acetylcholine‐and nicotine‐induced catecholamine secretion from the cultured cells with an IC50 against 5 μm nicotine of 30 nm.

This inhibitory effect was reversible and independent of the presence of agonist.

NSTX had no effect on the catecholamine release from cultured cells evoked by 50 mm K+, or 1 μm histamine.

NSTX had no effect on the stimulation of phosphatidylinositol metabolism evoked by 100 μm muscarine.

These results suggest NSTX may be useful as a nicotinic receptor probe in tissues such as the adrenal and sympathetic ganglia where α‐bungarotoxin is ineffective.
Relationship between extracellular 5‐hydroxytryptamine and behaviour following monoamine oxidase inhibition and l‐tryptophan
Authors: Sleight A.J. , Marsden C.A. , Martin K.F. , Palfreyman M.G.
Published: July 2012

The present study investigates the effects of selective and a non‐selective monoamine oxidase (MAO) inhibitors combined with l‐tryptophan on MAO‐A and ‐B activity, hypothalamic extracellular 5‐hydroxytryptamine (5‐HT) in vivo and the occurrence of the 5‐HT behavioural syndrome.

Selective inhibition of intraneuronal MAO‐A with MDL 72394 (0.5 mg kg−1, i.p.) had no effect on extracellular 5‐HT and following administration of L‐tryptophan (50 mg kg−1, i.p.) the 5‐HT behavioural syndrome was not induced.

Selective inhibition of MAO‐A at all sites with clorgyline (5 mg kg−1, i.p.) increased extracellular 5‐HT but did not induce the 5‐HT behavioural syndrome when combined with l‐tryptophan administration.

Selective inhibition of MAO‐B with selegiline (10 mg kg−1, i.p.) had no effect on extracellular 5‐HT and the 5‐HT behavioural syndrome was not observed after L‐tryptophan administration.

Inhibition of MAO‐A and ‐B with a higher and therefore non‐selective, dose of MDL 72394 (2 mg kg−1) markedly increased extracellular 5‐HT but failed to induce the 5‐HT behavioural syndrome after l‐tryptophan administration.

Inhibition of MAO‐A and ‐B at all sites in the brain (tranylcypromine 20 mg kg−1, i.p. or clorgyline 5 mg kg−1 plus selegiline 10 mg kg−1) increased extracellular 5‐HT and induced the behavioural syndrome on administration of l‐tryptophan.

The results demonstrate that inhibition of MAO‐A and ‐B both within amine neurones and elsewhere in the brain is essential for the development of the 5‐HT behavioural syndrome. Whilst the syndrome is associated with increased extracellular 5‐HT this does not appear necessarily to result in the syndrome and may indicate that increased extracellular 5‐HT is not solely involved in the induction of the ‘5‐HT behavioural syndrome’.
Neuroeffector actions of thromboxane B2 in dog isolated mesenteric arteries
Authors: Okamura Tomio , Nakajima Masatoshi , Toda Noboru
Published: July 2012

Thromboxane (TX) B2 and epithiomethano (sTXA2), in concentrations that were insufficient to alter the basal tone, potentiated contractile responses of helical strips of dog mesenteric arteries to transmural electrical stimulation. The potentiating effect of TXB2 (up to 10−6 m) was not abolished by diphloretin phosphate (DPP), a prostaglandin antagonist, whereas the potentiation by sTXA2 was abolished by the antagonist.

sTXA2 and TXB2 (3 × 10−6 m or higher) potentiated the responses to noradrenaline, the potentiation being antagonized by DPP.

3H‐overflow evoked by transmural stimulation in superfused arterial strips previously soaked in medium containing [3H]‐noradrenaline was increased by TXB2, but not altered by sTXA2.

TXB2 in low concentrations potentiated the contractile response to adrenergic nerve stimulation, possibly by increasing the release of noradrenaline, while the potentiation by the TXA2 analogue appears to be due to increased sensitivity of the arteries to noradrenaline. Prejunctional effects of TXB2 may be mediated by receptor sites functionally different from those located postjunctionally.
A comparative study of the cardiovascular and biochemical actions of the imidazo [4,5b] pyridine sulmazole and an imidazo [4,5c] pyridine analogue, BW A746C
Authors: Allan G. , Cambridge D. , Follenfant M.J. , Stone D. , Whiting M.V.
Published: July 2012

BW A746C is a chemical analogue of the imidazo [4,5b] pyridine, sulmazole (AR‐L115 BS). Like sulmazole, BW A746C possesses positive inotropic and vasodilator activity in vivo.

In anaesthetized guinea‐pigs, dogs and primates, a bolus i.v. injection of BW A746C, (0.001‐1.0 mg kg−1) caused a significant, dose‐related increase in ventricular dP/dt, and reduction in diastolic blood pressure, with small increases in heart rate. In these species, a significantly higher dose of BW A746C was required to lower blood pressure by 30% from basal, than was needed to raise ventricular dP/dt by 50% over basal.

In anaesthetized guinea‐pigs and dogs, bolus i.v. injections of sulmazole (0.1–10.0 mg kg−1) caused similar effects to those observed with BW A746C. In these species, however, there was no significant difference between the dose of sulmazole required to lower blood pressure by 30% from basal and that required to raise ventricular dP/dt by 50%.

In conscious dogs, i.v. infusion of BW A746C (to a total dose of 0.3 mg kg−1) caused a significant increase in ventricular dP/dt, but no significant change in either diastolic blood pressure or heart rate.

In cell‐free biochemical assays, there were no clear differences between the observed activities of BW A746C and sulmazole. Both compounds are cyclic nucleotide phosphodiesterase inhibitors with similar potencies and selectivities for the Type III enzyme (IC50 BW A746C = 3.0 ± 0.5 × 10−5 m, sulmazole 5.0 ± 1.9 × 10−5 m). The compounds had little or no effects on sarcolemmal Na+/K+‐ATPase, Ca2+ ATPase or Na+/Ca2+ exchange, and sulmazole, but not BW A746C, had a small, stimulatory effect on myofibrillar ATPase.

In anaesthetized guinea‐pigs and dogs, BW A746C was significantly more potent as a positive inotrope than sulmazole. In contrast with sulmazole, BW A746C produced its inotropic effects at significantly lower doses than those required to reduce diastolic blood pressure. This was also apparent from the results obtained in the anaesthetised primates and the conscious dogs. It was therefore concluded that the inotropic/vasodilator profile of BW A746C favours its positive inotrope activity. This profile cannot be explained on the basis of any biochemical differences from sulmazole.
4‐Hydroxy‐2‐methyl‐4‐phenyl‐1,2,3,4‐tetrahydroisoquinoline (PI‐OH): a new potentiator of sympathomimetic amines on the rat anococcygeus muscle
Authors: Ishida Y. , Koga N. , Nanbu T. , Kihara M. , Kobayashi S.
Published: July 2012

The potentiating effects of racemic 4‐hydroxy‐2‐methyl‐4‐phenyl‐1,2,3,4‐tetrahydroisoquinoline (PI‐OH), cocaine, desipramine and nomifensine on the concentration‐response curves of the rat anococcygeus muscle to noradrenaline (NA) and field stimulation were examined.

PI‐OH and cocaine concentration‐dependently potentiated the responses of anococcygeus muscle to NA and field stimulation, but the activity of PI‐OH was stronger than that of cocaine on both responses.

At high concentrations the potentiating activities of desipramine and nomifensine were less, a fact that was explained by their postsynaptic inhibitory properties; the actions of nomifensine and desipramine as antagonists against NA were competitive and non‐competitive, respectively.

It is concluded that PI‐OH may be an ideal potentiator of the response to NA in adrenergically‐innervated tissues because it has no side effects such as postsynaptic inhibition.
The involvement of afferent nerve terminals in the stimulation of ion transport by bradykinin in rat isolated colon
Authors: Perkins M.N. , Forster P.L. , Dray A.
Published: July 2012

The actions of bradykinin (Bk) were investigated on rat colon epithelium preparations that had been stripped of the muscle layers. The electrogenic ion flux was monitored by measuring changes in the short circuit current (SCC) produced by addition of drugs. Bk, administered to the basolateral side, but not apical side, of the epithelium evoked an increase in SCC which was separable into two distinct components, both of which were mediated mainly by chloride efflux.

The early component was robust, reproducible and exhibited clear concentration‐dependency with an EC50 of 6.2 nm. The second phase of the response exhibited a much slower time course than the first phase and diminished amplitude with repeated applications of Bk.

In preparations of unstripped epithelium, bradykinin (Bk) evoked mainly a slow neurogenic response which was attenuated or abolished by tetrodotoxin (TTX). When the epithelium was stripped off, TTX had little effect either on the baseline SCC or on responses to Bk.

Perfusion with zero calcium solution did not affect the early phase but abolished the late phase of the Bk response. Verapamil (20 μm), but not nifedipine (20 μm), also attenuated the later phase of the response.

Capsaicin (20 μm) administered to the basolateral, but not the apical, side produced an increase in SCC. Following desensitization to capsaicin the second phase of the response to Bk was abolished with little effect on the initial response to Bk.

The data suggest that Bk increases the efflux of chloride ions across the colonic epithelium in at least two ways: (a) by an action on the epithelial cells and (b) by an action on neuronal elements within the epithelium. This latter effect of Bk is due to stimulation of capsaicin‐sensitive nerve terminals within the mucosa of the colon epithelium causing the release of a mediator which is responsible for the second phase of the response to Bk.
In vivo EDRF activity influences platelet function
Authors: Hogan J.C. , Lewis M.J. , Henderson A.H.
Published: July 2012

The administration of carbachol to rabbits to stimulate the release of endothelium derived relaxing factor (EDRF) results in inhibition of platelet aggregation and elevation of platelet cyclic GMP content. These effects are reversed by simultaneous administration of the EDRF inhibitors methylene blue or haemoglobin. The data provide the first direct biochemical evidence of in vivo EDRF activity.
Phospholipase A2 induced airway hyperreactivity to cooling and acetylcholine in rat trachea: pharmacological modulation
Authors: Chand N. , Diamantis W. , Mahoney T.P. , Sofia R.D.
Published: July 2012

Rat isolated tracheal smooth muscle preparations respond to phospholipase A2 (PLA2) and phospholipase C (PLC) with contractile responses of highly variable magnitudes. Rat tracheae exposed to PLA2 or PLC for a period of 10–30 min, exhibit airway hyperreactivity (AH) to cooling (10°C), i.e., respond with strong contractile responses. Phospholipase D neither contracted rat tracheae nor induced AH to cooling.

PLA2‐induced AH to cooling was dependent on the presence of extracellular Ca2+ in the physiological solution.

Verapamil, azelastine, diltiazem and TMB‐8 (each 10 μm) significantly attenuated PLA2‐induced AH. This effect was not shared by nifedipine (10 μm).

Bepridil (10 μm), a Ca2+ and calmodulin antagonist, also significantly attenuated AH induced by PLA2.

Indomethacin (a cyclo‐oxygenase inhibitor), AA‐861 (a selective 5‐lipoxygenase inhibitor), FPL 55712 (a leukotriene receptor antagonist), methysergide (a 5‐hydroxytryptamine D‐receptor antagonist) and pyrilamine (a histamine H1‐receptor antagonist) exerted little or no effect on PLA2‐induced AH to cooling.

Atropine significantly attenuated PLA2‐induced AH suggesting the participation of acetylcholine.

Nordihydroguaiaretic acid (an antioxidant; 5‐lipoxygenase inhibitor) and BW 755C (an antioxidant; a dual inhibitor of cyclo‐oxygenase and 5‐lipoxygenase) significantly attenuated PLA2‐induced AH to cooling.

In conclusion, these data show that PLA2 (an enzyme involved in the synthesis of Paf‐acether, prostaglandins, thromboxanes, leukotrienes, diacylglycerol, superoxide free radicals and lipid peroxides, etc.) induces AH to cooling and acetylcholine in rat trachea. The induction of AH to cooling is dependent on the presence of extracellular Ca2+ and is significantly attenuated by verapamil, diltiazem, bepridil, atropine and azelastine (an antiallergic/antiasthmatic drug).
Responses to 5‐hydroxytryptamine evoked in the hemisected spinal cord of the neonate rat
Authors: Connell L.A. , Wallis D.I.
Published: July 2012

Superfusion of isolated hemisected spinal cord from neonate rats with 5‐hydroxytryptamine (5‐HT) (10−6 to 10−3 m) evoked concentration‐related depolarizations. The maximal depolarization elicited by a concentration of 10−4 m was 1.0 ± 0.1 mV (mean ± s.e.mean, n = 30). Noradrenaline in a similar range of concentrations also elicited depolarizations.

The depolarizations probably originate in motoneurones as a result of direct interaction of the amines with these cells, since responses were unaltered by tetrodotoxin (10−7 m) or Ca2+‐free/Mg2+‐rich medium.

5‐Carboxamidotryptamine (5‐CT), S(+)−α‐methyl‐5‐hydroxytryptamine (α‐Me5‐HT) and 5‐methoxytryptamine (5‐MeOT) evoked similar depolarizations to 5‐HT. Tryptamine evoked depolarizations of smaller maximal amplitude. 5‐Hydroxytryptophan, 2‐methyl‐5‐hydroxytryptamine, 8‐hydroxy‐2‐(di‐N‐propylamino) tetralin hydrobromide (8‐OH‐DPAT) and 5‐methoxy‐3‐[1,2,3,6‐tetrahydro‐4‐pyridinyl]‐1‐H‐indole succinate (RU 24969) had no depolarizing action.

Concentration‐response (CR) curves were determined for 5‐HT, 5‐CT, α‐Me5‐HT, 5‐MeOT and tryptamine. The ED50 value for 5‐HT was 20.5 ± 1.2 μm. The equipotent molar ratios (EPMRs) for 5‐CT and α‐Me5‐HT were close to unity, while 5‐MeOT was approximately 3 times and tryptamine 13 to 14 times less potent than 5‐HT.

The relative agonist potency of 5‐HT with respect to other tryptamine analogues capable of depolarizing motoneurones was increased when 5‐HT uptake was blocked by citalopram (10−7 m). In the presence of citalopram, 5‐HT was 2.7 times more potent than α‐Me5‐HT and 16.9 times more potent than 5‐CT. The apparent order of potency was 5‐HT > α‐Me5‐HT > 5‐CT (> 5‐MeOT > tryptamine).

The monoamine oxidase inhibitor, pargyline (5 × 10−4 m), had no effect on depolarizations to 5‐HT, 5‐CT or α‐Me5‐HT.

Methiothepin, 1αH, 3α, 5H‐tropan‐3‐yl‐3,5‐dichlorobenzoate methanesulphonate (MDL 72222) and [3α‐tropanyl]‐1H‐indole‐3‐carboxylic acid ester hydrochloride (ICS 205–930) had no effect on 5‐HT depolarizations elicited in motoneurones. Ketanserin (0.75 × 10−7 m to 10−6 m) showed modest antagonistic action and depressed maximal response amplitude; the pIC50 was 6.5.

Methysergide (10−8 to 10−7 m) was a potent antagonist of responses to 5‐HT. CR curves were displaced to the right and flattened in the presence of the antagonist. The pIC50 assessed from the effect on depolarizations evoked by 5‐HT 10−4 m was 7.5.

It is concluded that 5‐HT acts directly to depolarize mammalian spinal motoneurones through receptors that are also activated by 5‐CT, α‐Me5‐HT and 5‐MeOT and are blocked by methysergide. The receptor profile, although not 5‐HT3‐like, does not clearly coincide with that for either 5‐HT1‐like or 5‐HT2 receptors.
Effects of REV 5901, a 5‐lipoxygenase inhibitor and leukotriene antagonist, on pulmonary responses to platelet activating factor in the guinea‐pig
Authors: Anderson Gary , Fennessy Max
Published: July 2012

The effects of REV 5901 on the platelet activating factor (Paf)‐induced (a) bronchoconstriction, (b) contraction of lung parenchymal strips and (c) increased airways responsiveness to histamine, were assessed in the guinea‐pig. REV 5901 is a 5‐lipoxygenase inhibitor and competitive peptidoleukotriene antagonist which does not inhibit multiple forms of phosphodiesterase.

In urethane/pentobarbitone anaesthetized animals, REV 5901 (10 or 30 mg kg−1 i.v.) substantially inhibited the bronchoconstriction, measured as changes in airways resistance (RL) and dynamic lung compliance (Cdyn), induced by leukotriene D4 (2.5 μg kg−1, i.v.) but did not attenuate that induced by Paf (50 ng kg−l, i.v.).

Paf contracted the lung parenchymal strip in a concentration‐dependent manner. REV 5901 (25 μm) neither altered the magnitude of the contractions nor the tissue sensitivity to Paf. The sustained contraction induced by Paf was not affected when REV 5901 was added after the response had reached a plateau.

Contractions of parenchymal strips to Paf (50 nm) were prevented by pretreatment with the competitive Paf antagonists, SRI 63441 and WEB 2086. Also WEB 2086, but not SRI 63441, reversed established Paf‐induced contractions and relaxed parenchymal strips from intrinsic tone in the absence of Paf.

Paf (20 ng kg−1, i.v.) caused an acute increase in airways responsiveness to histamine (4–12 μg kg−1, i.v.) which was attenuated by REV 5901 at 10 mg kg−1, i.v. and abolished by 30 mg kg−1, i.v.

These data suggest that leukotrienes do not participate in Paf‐induced bronchoconstriction or contraction of the lung parenchymal strip, but may play a role in the increased responsiveness of the airways to histamine observed after Paf challenge in the guinea‐pig.
Gastric motor responses elicited by vagal stimulation and purine compounds in the atropine‐treated rabbit
Authors: Beck K. , Calamai F. , Staderini G. , Susini T.
Published: July 2012

The effects of vagal inhibitory stimulation and of purine compounds were studied in the rabbit stomach.

Gastric motility was assessed by the balloon method. Vagal nerves were electrically stimulated at the neck. Purine compounds were injected intra‐arterially.

In the atropine‐treated rabbit, vagal stimulation caused relaxant motor responses followed by a rebound contraction.

Among the purine compounds, only ADP and ATP caused relaxant motor responses similar to the effects of vagal inhibitory stimulation. However, the relaxation produced by ATP was more powerful than that due to ADP, especially at lower infusion rates.

Vagal inhibitory responses were recorded during and after infusion of ATP. When relaxation by ATP was fully developed, vagal inhibitory stimulation was ineffective. At the highest infusion rates of ATP, a depression of the vagal inhibitory motility was also observed after cessation of the infusion.

Relaxant responses to ATP and vagal inhibitory stimulation were not influenced by theophylline, scarcely affected by α,β‐methylene ATP, but were reduced or blocked by reactive blue 2.

The results are consistent with ATP being an inhibitory neurotransmitter in the stomach of the rabbit.