Steady-state concentrations of choline and acetylcholine in rat brain parts during a constant rate infusion of deuterated choline

Summary An intravenous infusion of deuterated choline at constant rate for 6 min (5 or 25 moles kg^–1 min^–1) significantly increases the concentration of choline in plasma, occipital cortex and striatum. Both 5 and 25 moles kg^–1 min^–1 increase the concentration of acetylcholine in cortex but only 25 moles kg^–1 min^–1 increases the acetylcholine content in striatum. In contrast, 1 mole kg^–1 min^–1 does not change the choline or acetylcholine content in cortex or striatum. A single pulse injection of choline (200 moles kg^–1) causes a significant increase in the concentration of choline in striatum 30 sec following injection. The choline content returns to normal values within 2 min. These studies show that when a pulse injection of a non-tracer dose of radioactive choline is used to measure brain acetylcholine turnover rate the maintenance of steady state must be verified within seconds after the pulse injection of radioactive choline. When constant infusion of deuterated choline is used to measure turnover rate of acetylcholine in the brain of rats, a dose of 1 mole kg^–1 min^–1 appears to be a maximal infusion rate.     

Effect of cyanide on the distribution of 60Co in mice

The effect of cyanide on the distribution of cobalt was studied by injecting mice i.p. with potassium cyanide 61.4 moles/kg, followed 1 min later by ⁶⁰CoCl₂ 38.5 moles/kg i.v. Blood and tissue concentrations of ⁶⁰Co were then determined up to 48 h after injection and the results were compared with those obtained from control animals receiving ⁶⁰CoCl₂ only. In animals treated with cobalt plus cyanide, considerably higher concentrations of ⁶⁰Co were found in the spleen in comparison with controls during the whole observation period, whereas the ⁶⁰Co concentration in the pancreas was lower than that of controls during the first 4 h. In other tissues no significant differences between cyanide-treated animals and controls were noticed. Determination of complex-bound cyanide demonstrated that the increased uptake of cobalt in the spleen observed in cyanide-treated animals was due to cobalt-cyanide complex(es). Cyanide did not affect the plasma protein binding of cobalt.     

Coenzyme Q10 attenuates cyanide-activation of the ATP-sensitive K+ channel current in single cardiac myocytes of the guinea-pig

Summary The effect of coenzyme Q₁₀ (CoQ₁₀) on the cyanide (CN^–)-induced ATP-sensitive K⁺ channel current (K_ATP) was examined in single atrial myocytes, using the patch clamp technique. Superfusion of the cells with a CN^–/low glucose bathing solution induced an outward current in the whole-cell clamp condition. Glibenclamide (1 M) abolished this current, indicating that the current was carried through the K_ATP channel. After steady-state activation by CN^–, pinacidil (a K_ATP channel opener, 300 M) failed to further increase the current. In cell-attached patches, CN^–, when applied to the bath, induced bursting openings of an 80 pS channel (the K_ATP channel). In cells preincubated for 30 min in a solution containing CoQ₁₀ (100 g/ml), CN^–-activation of the K_ATP channel was markedly attenuated both at the whole cell and at the single channel level. At the steady-state effect of CN^– in CoQ₁₀-treated cells, pinacidil (300 M) activated the current to the maximum level achieved by CN^– in the control cells. These results suggest that CoQ₁₀ reduces in the CN^–-induced KATP current not by affecting the channel itself but by preventing depletion of intracellular ATP caused by CN^–. Send offprint requests to Y. Kurachi at Mayo Foundation     

Formation of cyanide after i. v. administration of the oxime HI 6 to dogs

HI6(pyridinium, 1-[[[4-(aminocarbonyl)pyridinio] methoxy]methyl]-2-[(hydroxyimino)methyl]-dichloride belongs to a series of bisquaternary pyridinium oximes that are effective against poisoning with extremely toxic organophosphates. Since HI6 has been shown to be unstable at pH 7.4 and to release significant amounts of cyanide, a study was undertaken to determine the degree of cyanide formation from HI 6 in vivo. When HI 6 (100 mol/kg) was administered i. v. to dogs, the animals showed no signs of cyanide toxicity but exhibited some cholinomimetic symptoms, including retching, hypersalivation and enhanced intestinal motility. Cyanide content in whole blood was monitored after production of methemoglobinemia (30%) by 4-dimethylaminophenol in order to sequester cyanide within red cells. Maximal cyanide contents of 20 mol/l were found in blood after 90 min. Calculation of the area under the concentration versus time curve for blood cyanide indicates that about 4% of HI 6 produced cyanide. Determination of the pharmacokinetic parameters of HI 6 (V_D=0.31 l/kg; k_el=0.76 h^–1) and of cyanide (V_D=0.086 l/kg; k_el=0.52 h^–1) together with the apparent first order rate constant of cyanide formation from HI 6 in vitro (0.174 h^–1, pH 7.4, 37°) allowed the simulation of a cyanide concentration curve that fitted with the experimental data points, indicating that cyanide formation in vivo was not bio-catalyzed. It is concluded that cyanide formation from HI 6 may not be regarded as a potential hazard, since cyanide elimination exceeded markedly its formation. Whether this conclusion also holds true for man has to be established.     

Calcium channel modulation by dihydropyridines modifies sufentanil-induced antinociception in acute and tolerant conditions

Summary The study was aimed at elucidating the possible participation of l-type Ca²⁺ channel in the acute analgesic effect of an opiate and the development of tolerance to this action. Sufentanil, a selective p agonist, and two dihydropyridines, the Ca²⁺ antagonist nimodipine and the Ca²⁺ agonist Bay K 8644, were selected. The tail-flick test was used to assess the nociceptive threshold. In naive rats, nimodipine (200 g/kg) potentiated the analgesic effect of sufentanil reducing the ED₅₀ from 0.26 to 0.08 g/kg. Similar results were observed with its (–)-enantiomer Bay N 5248, while the (+) enantiomer Bay N 5247 was ineffective. Tolerance to the opiate was induced by chronic subcutaneous administration of sufentanil with minipumps (2 g/h, 7 days). In these conditions the dose-response curve to sufentanil was displaced to the right and the ED₅₀ was increased to 1.49 g/kg. In tolerant rats, nimodipine preserved its potentiating ability and prevented the displacement to the right of the sufentanil dose response-curve (ED₅₀ = 0.48 g/kg). When nimodipine was pumped (1 g/h, 7 days) concurrently with sufentanil, the development of tolerance to the opioid was not disturbed. However, the expression of tolerance was abolished and even the effect of acutely administered sufentanil was markedly potentiated (ED₅₀ = 0.03 g/kg). Similar experiments were performed with Bay K 8644. In naive rats, Bay K 8644 at a low dose (20 g/kg) that behaves as a calcium agonist, antagonized the analgesic effect of sufentanil (ED₅₀ = 0.58 g/kg), whereas at a high dose (200 g/kg) it potentiated this action (ED₅₀ = 0.15 g/kg). In tolerant rats, Bay K 8644 (20 g/kg) preserved its antagonizing ability inducing a displacement to the right of the sufentanildose-response curve (ED₅₀ = 4.2 g/kg). When Bay K 8644 was pumped (1 g/h, 7 days) concurrently with sufentanil, it enhanced the expression of tolerance to the opiate (ED₅₀ = 3.8 g/kg). These results suggest that the calcium fluxes through the l-type channel in neurones are functionally linked to the activation of the opiate receptor: the blockade of the channel increased the potency of sufentanil, whereas its activation reduced the potency of the opiate. In chronic experiments, DHPs concurrently administered with sufentanil did not affect the development of tolerance to the opiate. However, nimodipine prevented the expression of this phenomenon. Even more, the animals became hypersensitive to the opiate suggesting that the adaptative mechanisms induced by chronic opiate could be affected by chronic nimodipine.This work was supported by grants from Universidad de Cantabria-Caja Cantabria (1988) and Bayer AG, Wuppertal, FRGPredoctoral Fellow: Fondo de Investigaciones Sanitarias de la Seguridad Social.Send offprint requests to: M. A. Hurlé at the above address     

Evans blue blocks P2X-purinoceptors in rat vas deferens

Summary In rat vas deferens, Evans blue 100 M increased contractions elicited by high K⁺ and by noradrenaline but markedly reduced contractions elicited by the P_2X-purinoceptor-selective agonist ,-methylene ATP (3 M). The concentration-response curve of ,-methylene ATP was shifted to the right by Evans blue 30 M and the maximal contraction was increased. In tissues incubated with nifedipine 10 M, Evans blue 100 M tended to increase the residual contraction elicited by noradrenaline and abolished the residual response to ,-methylene ATP (3 M). The concentration-response curve of ,-methylene ATP was progressively shifted to the right by increasing concentrations of Evans blue in the presence of nifedipine; maximal contractions were increased by Evans blue 10 and 30 but not 100 M. From the shifts to the right caused by Evans blue 30 M, apparent pK_B values of 5.9 (no nifedipine) and 6.0 (nifedipine present) were calculated. It is concluded that Evans blue blocks P_2X-purinoceptors in rat vas deferens and in addition causes a non-receptor-specific enhancement of contractions.Correspondence to: R. Bültmann at the above address     

Enhancement of adenosine A1 receptor functions by benzoylthiophenes in guinea pig tissues in vitro

Previous reports on a series of benzoylthiophenes, including PD 81,723 {2-amino-4,5-dimethyl-3-(3-trifluoromethyl-benzoyl)thiophene}, have shown specific enhancement of agonist binding at the adenosine A₁ receptor. We have studied the effects of two substituted benzoylthiophenes, PD 78,416 {thieno[2,3-c]pyridine-6(5H)-carboxylic acid, 2-amino-3-benzoyl-4,7-dihydro-ethyl ester} and RS-74513-000 {2-amino-4-ethyl-5-methyl-3-(3-trifluoro-methyl-benzoyl) thiophene} on response elicited by adenosine A₁ receptors in isolated guinea pig left atrium and ileum.In the electrically paced left atrium, PD 78,416 antagonized negative inotropic effect elicited by the agonist CPA {N⁶-cyclopentyladenosine} with a pK_B value of 6.2 ± 0.2 (n = 4) . At a low concentration which had no antagonistic effect (0.1 M), PD 78,416 enhanced the effect of CPA. The concentration-response curve to CPA was shifted leftward by 5.1 fold (95% confidence limits 2.4–11.2). In field stimulated isolated ileum, PD 78,416 (0.1, 0.3, 1 M) did not enhance or antagonize effects of CPA. At concentrations above 1 M, PD 78,416 decreased electrically induced contraction. This effect was not sensitive to adenosine deaminase and was not antagonized by the A₁ antagonist CPX {8-cyclopentyl-1,3-dipropyl-xanthine} (1 M).Unlike PD 78,416, RS-74513-000 (0.01, 0.1, 1, 3, 10 M) did not antagonize or enhance effects of CPA in the left atrium. However, effects of CPA in ileum were enhanced by RS-74513-000 (1 and 3 M). Maximum enhancement was observed at 3 M; the concentration-response curve to CPA was shifted leftward by 3.2 fold (95% confidence limits 2.4–4.2). Higher concentrations of RS-74513-000 (10 and 30 M) decreased electrically induced contraction, this effect was not reversed by CPX. These findings confirmed that functional effects of A₁ adenosine receptor may be enhanced by substituted benzoylthiophenes in vitro. The differential effect of PD 78,416 and RS-74513-000 on cardiac and ileal A₁ receptors suggests that it may be possible to design selective enhancers for cardiac and neural functions.     

Differential effects of the stereoisomers of 3PPP in dopaminergic and cholinergic neurotransmission in superfused slices of the corpus striatum

Summary The two enantiomers of 3PPP were tested on the spontaneous and electrically-evoked release of ³H-dopamine from slices of the rabbit caudate nucleus and of ³H-acetylcholine (³H-ACh) from slices of the rat caudate nucleus.In caudate slices labelled with ³H-dopamine, exposure to (+)3PPP (0.1–1 M) facilitated the spontaneous outflow of radioactivity with a concomitant inhibition of the electrically-evoked release of ³H-dopamine. In the presence of cocaine 10 M, exposure to (+)3PPP (1 M) inhibited the electrically evoked release of ³H-dopamine without modifying the spontaneous outflow of radioactivity. This inhibitory effect was not significantly antagonized by S-sulpiride 0.01 M.Exposure to (+)3PPP 1 M inhibited the electrically-evoked release of ³H-ACh, and this effect was not modified by pretreatment with reserpine alone, or in combination with -methyl-p-tyrosine (-MT).In contrast to the (+) enantiomer, exposure to (-)3PPP (0.1–1 M) facilitated the electrically-evoked release of ³H-dopamine without affecting the spontaneous outflow of radioactivity. (-)3PPP antagonized the inhibitory effect of apomorphine on the electrically-evoked release of ³H-dopamine.Exposure to (-)3PPP 1 M did not modify the spontaneous or the electrically-evoked release of ³H-ACh. Yet, this concentration of (-)3PPP antagonized significantly the inhibitory effect of 0.03 M apomorphine, 1 M d-amphetamine, and 1 M (+)3PPP on the electrically-evoked release of ³H-ACh (-)3PPP (0.1–1 M) was about 100 times less potent than S-sulpiride at antagonizing the inhibitory effect of apomorphine on the electrically-evoked release of ³H-ACh.It is concluded that under in vitro conditions at the level of the dopamine receptor modulating the release of ³H-ACh from the cholinergic interneuron in the striatum, (+)3PPP behaves as a dopamine receptor agonist while (-)3PPP possesses dopamine receptor-antagonist properties. At the level of the dopaminergic nerve terminal, (-)3PPP facilitates the release of ³H-dopamine probably through the blockade of the dopamine autoreceptors. The dopamine autoreceptor agonists properties of (+)3PPP are difficult to establish in our model because of the dopamine releasing action of this enantiomer.Some of the results described in this publication have been presented at the British Pharmacological Society Meeting (Arbilla and Langer 1983).     

Pharmacokinetics and endocrine effects of terguride in healthy subjects

Summary Plasma levels of the partial dopamine agonist, terguride, were measured by RIA in healthy volunteers after a single i. v. dose of 50 g and on the first and seventh day of an oral treatment with 250 g, 500 g and 750 g b. d. Basal and releasing hormone (TRH, GHRH, CRF, LHRH) — stimulated pituitary hormone secretion (PRL, TSH, GH, FSH, LH) and cortisol were also determined by RIA.Following the i. v. injection, plasma terguride levels declined biphasically, with half-lives of 0.2 and 1.5 h; total clearance was 17 ml·min^–1·kg^–1. the oral bioavailability of terguride over all doses was about 20%. Basal and TRH-stimulated prolactin levels were dose-dependently depressed, but the secretion of other hormones remained unaffected. Tolerance of terguride was excellent and there was no negative effect on performance or mood, nor on mixed-function oxygenase activity, assessed as urinary 6-OH cortisol.     

Stimulatory effects of clonidine,cirazoline and rilmenidine on locus coeruleus noradrenergic neurones: possible involvement of imidazoline-preferring receptors

Summary Clonidine and related drugs not only interact with ₂-adrenoceptors but also recognise non-adrenoceptor sites in the brain. The involvement of these imidazoline-preferring receptors in the regulation of the activity of locus coeruleus noradrenergic neurones (NA-LC) was investigated after inactivation of ₂-adrenoceptors with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). In EEDQ-pretreated rats (6 mg/kg, i.p., 6 h), the characteristic inhibitory effect of low doses of clonidine on these neurones was abolished and a paradoxical, dose-dependent increase in firing rate was observed at higher doses (640–5120 g/kg, i.v.) (ED₅₀ = 702 g/kg, E_max = 83 %, n = 14). Guanfacine (0.3–20 mg/kg) did not modify neuronal activity but antagonised the stimulatory effect of clonidine. Cirazoline (80–640 g/kg) and rilmenidine (0.3–10 mg/kg) also stimulatedneuronal activity(ED₅₀ = 192 g/kg, E_max = 102%, n = 5; ED₅₀ = 1563 g/kg, E_max = 70%, n = 1–5, respectively) by an ₂-adrenoceptor-independent mechanism. The results suggest that these drugs can modulate the activity of locus coeruleus noradrenergic neurones through the activation of I₁-imidazoline-preferring receptors.     

Tolbutamide- and diazoxide-sensitive K+ channel in neurons of substantia nigra pars reticulata

Summary Single-channel K⁺ currents were recorded in cell-attached patches from slices of rat substantia nigra. On the somata of neurons in the caudal half of the substantia nigra pars reticulata a K⁺ selective channel with a unitary conductance of 71 pS (154 mmol/l K⁺ in pipette filling solution) was identified. The channel was activated both by application of diazoxide (300 mol/l) and by energy-depleting conditions (200 mol/l cyanide) and was reversibly blocked by tolbutamide (0.1–1 mmol/l). It is concluded that neurons in the substantia nigra pars reticulata of the rat contain a typical ATP-sensitive K⁺ channel the activity of which can be modulated by diazoxide and sulfonylureas.Correspondence to: C. Schwanstecher at the above address     

Inhibition of furosemide-induced renin release by vasoconstrictors

Summary The effect of i. v. infused (asp¹--amid, val⁵)-angiotensin II (1.0 g/kg min), octapressin (phe², lys⁸-vasopressin) (10.0 mU/kg min) and of the -sympathomimetic amine phenylephrine (40.0 g/kg min) on the stimulation of renin secretion by furosemide (10.0 mg/kg i.v.) was investigated. The vasoconstrictors abolished the renin release induced by furosemide. Studies on the clearance of p-aminohippuric acid (PAH) (i.e. renal plasma flow) showed that the action of the vasoconstrictors cannot be explained by a decrease in access of furosemide to its intrarenal sites of action.The mechanism of the suppressive action of the vasoconstrictors on renin release is discussed.Supported by DFG grant Me 541/1.     

The cardiovascular effects of intraventricularly administered histamine in the anaesthetised rat

Summary In urethane-anaesthetised rats intraventricular (i.c.v.) injections of histamine (0.1–10.0 g) elicited dose-related rises in both the resting blood pressure and heart rate. These cardiovascular effects of histamine were antagonised in a dose-dependent manner by i.c.v. pretreatments with the histamine H₁-receptor antagonists mepyramine (10, 50 and 100 g) and diphenylpyraline (100 and 200 g). Pretreatment with the histamine H₂-receptor antagonist metiamide (100 and 200 g i.c.v.) failed to modify either of the responses. A dose-related antagonism of the hypertensive response to histamine i.c.v. was elicited by phentolamine (100 and 200 g i.c.v.) but the positive chronotropic effect was not modified by this pretreatment. The cardiovascular responses to histamine i.c.v. were abolished by mecamylamine (5.0 mg/kg i.v.) and greatly reduced by 6-hydroxydopamine (3×250 g i.c.v.), but only the tachycardia was significantly modified by atropine (100 g i.c.v.) and propranolol (1 mg/kg i.v.). Propranolol (100 g i.c.v.), bilateral vagotomy, or acute bilateral adrenal demedullation failed to modify the cardiovascular responses to histamine i.c.v. The results suggest that histamine is able to modify the resting blood pressure and heart rate by independent central modes of action, which involve central adrenergic and cholinergic mechanisms.Preliminary findings of this study were presented at the Autumn meeting of the British Pharmacological Society (Finch and Hicks, 1975).     

Further studies on the action of 5-hydroxytryptamine on lumbar motoneurones in the rat isolated spinal cord

Summary Using the hemisected spinal cord of the neonate rat, the effects of altered external Ca, thyrotrophin-releasing hormone (TRH) and a number of antagonists were tested on depolarizations evoked by 5-hydroxytryptamine (5-HT). Responses of populations of motoneurones were recorded via a ventral root. 5-Hydroxytryptamine depolarizations were not Ca-dependent but were enhanced in amplitude in Ca-free solutions. Raised Mg reversed this enhancement. 5-Hydroxytryptamine depolarizations persisted in the presence of Mn (1.53 mmol/l). TRH depolarized motoneurones; there was no evidence of modulation of 5-HT responses on concurrent application of TRH. Ritanserin (0.1 mol/l) had a modest blocking action on 5-hydroxytryptamine depolarizations reducing the maximum; 1mol/l ritanserin caused a greater antagonism which was unsurmountable (pIC₅₀ 5.2). Ritanserin (0.1 or 1 mol/l) did not depress responses to noradrenaline (NA). Ketanserin (0.1 mol/l) caused a blockade of slow onset, equilibrium with the receptors requiring 1 h. Blockade by 0.01, 0.1 and 1 mol/l ketanserin was concentration-dependent (pIC₅₀ 6.2). Ketanserin 1 mol/l, but not at lower concentrations, depressed noradrenaline responses. Mianserin (0.1 mol/l) also caused a blockade of slow onset; 0.1 or 1 mol/l produced a flattening of the 5-hydroxytryptamine concentration-response curve but did not depress noradrenaline responses (pIC₅₀ 4.7). The pIC₅₀ for spiperone was 8.0. DOI (10–100 mol/l) had no detectable agonist action but at concentrations of 0.01 and 0.1 mol/l it acted as an antagonist. Equilibration with the receptors occurred over 2 h. DOI (0.01 mol/l) depressed 5-hydroxytryptamine but not noradrenaline responses; higher concentrations of DOI also depressed noradrenaline responses. The pharmacological profile of the 5-hydroxytryptamine receptor mediating depolarization of spinal and facial motoneurones suggests that it belongs to the 5-HT_1C-5-HT₂, group of 5-hydroxytryptamine receptors but is not identical to 5-HT_1C or the 5-HT₂ CNS binding sites. Alternatively, the response might arise from a mixed population of 5-HT₁-like and 5-HT₂ receptors. Send offprint requests to D. I. Wallis at the above address     

Effects of flunarizine on induced calcium transients as measured in fura-2-loaded neurons of the rat dorsal root ganglion

Summary The effect of the calcium entry blocker flunarizine on a high-potassium induced increase of intracellular free calcium was studied. The experiments were done with neurons isolated from rat dorsal root ganglia and loaded with the calcium-sensitive dye fura-2. The increase of calcium induced by 60 mmol/1 potassium was abolished after removal of extracellular calcium, was reversibly reduced by 50 mol/l cadmium (76% inhibition), 50 mol/1 nickel (25% inhibition) and 10 mol/1 nifedipine (18°10 inhibition), and reversibly increased after removal of extracellular sodium (26% increase). The potassium induced increase of intracellular calcium is, therefore, mediated by transmembrane calcium influx, probably to a large extent through cadmium-sensitive calcium channels. Flunarizine (5 min incubation followed 1 min wash-out) reduced the amplitude of the high-potassium induced calcium increase in a dose-dependent manner (K _d = 370 ± 100 nmol/l; mean ± SEM; n = 8), causing complete inhibition at a concentration of 10 mol/1 in the majority of cells. Flunarizine ( 1 mol/1) caused a reversible increase of the resting level of intracellular calcium in some cells, an effect which disappeared in the absence of extracellular calcium. The drug (1 mol/1 had no influence on the time course of recovery of intracellular calcium subsequent to a rise induced by high-potassium or by the calcium ionophore A23187. It is concluded that flunarizine acts as an inhibitor of depolarization-mediated calcium influx. At a concentration of 1 mol/1, the drug presumably has no effect on cellular calcium extrusion and/or sequestration mechanisms. Correspondence to L. Leybaert at the above address     

Effects of verapamil,diltiazem and ryosidine on the release of dopamine and acetylcholine in rabbit caudate nucleus slices

Summary Slices of the rabbit caudate nucleus were preincubated with ³H-dopamine or ³H-choline and then superfused with label-free medium. Release of ³H-dopamine and ³H-acetylcholine was elicited by either electrical stimulation at 8 (in one series 2) Hz, or an increase in the K⁺ concentration by 50 mmol/l, or addition of L-glutamate 1 mmol/l. Verapamil 1 mol/l, diltiazem 1 and 10 mol/l, and ryosidine 1 mol/l failed to the reduce the electrically-, K⁺- and glutamate-evoked overflow of tritium. Verapamil 1 mol/l and diltiazem 10 mol/l also failed to reduce the electricallyevoked overflow (2 Hz) when dopamine receptors, neuronal dopamine uptake, and neuronal choline uptake were blocked by domperidone, nomifensine and hemicholinium, respectively. Inhibition of the evoked overflow of tritium was only obtained when concentrations were increased to verapamil 10 mol/l, diltiazem 100 mol/l and ryosidine 10 mol/l. The inhibition was generally small. It was more evident for slices preincubated with ³H-choline than for those preincubated with ³H-dopamine, because in the latter verapamil, diltiazem and (much less) ryosidine accelerated the basal efflux of tritium. The inhibition of the K⁺-evoked overflow of tritium was probably due to blockade of Ca²⁺ channels because this overflow was Ca²⁺-dependent but tetrodotoxin-resistant. In contrast, the inhibition of the electrically- and glutamateevoked overflow possibly involved blockade of Na⁺ channels as well. The results indicate that three calcium antagonists from different chemical classes are very weak inhibitors of Ca²⁺ entry into, and hence transmitter release from, the terminal axons of central dopaminergic and cholinergic neurones. The function of the high affinity calcium antagonist binding sites that have been identified in brain remains unknown.     

Mesolimbic dopamine and its control of locomotor activity in rats: differences in pharmacology and light/dark periodicity between the olfactory tubercle and the nucleus accumbens

To compare the functions of the lateral olfactory tubercle (OT) and the medial nucleus accumbens (ACC), dopamine (DA), (3,4-dihydroxyphenylimino)-2-imidazoline (DPI), and ergometrine were injected into the brain of rats familiarized with the experimental cage in which locomotor activity was assessed. In all tests a volume of 0.5 l per side was used. Both DA (1–10 g) and apomorphine (1–10 g) increased locomotor activity when injected into the OT; similar injections into the ACC produced inconsistent effects. The OT effects were short-lasting, dose-dependent and antagonized by haloperidol (0.5–2.5 g) in a dose-dependent manner. DPI (1–10 g) too produced an increase when injected into the OT; this response was long-lasting, dose-dependent and potentiated by ergometrine (0.1–1.0 g). Ergometrine (0.1–1.0 g) dose-dependently increased activity over a period of 200 min in ACC and OT rats, although the response in OT rats was much smaller than that in ACC rats. Only the ergometrine response in ACC rats was dose-dependently suppressed by DPI (1–10 g). ACC rats tested during the light period showed a weak stimulatory response to ergometrine in comparison with ACC rats tested during the dark period; OT rats showed reversed light/dark periodicity. Thus, OT rats significantly differed from ACC rats with respect to locomotor responses to dopaminergic agents, their pharmacological profile and their light/dark periodicity. Evidence is provided that the lateral tuberculum, but not the medial accumbens, is responsible for the stimulatory effect of dopamine and related compounds.The results were presented during the 14th C.I.N.P. Congress (Collegium International Neuro-Psychopharmacologicum), held at Florence (Italy), June 19–23, 1984     

Different types of opioid receptors mediating analgesia induced by morphine,DAMGO, DPDPE,DADLE and β-endorphin in mice

Summary The effects of intracerebroventricular (i.c.v.) administration of d-Phe-Cys-Tyr-d-Try-Orn-Thr-Pen-Thr-NH₂ (CTOP), a selective mu-opioid receptor antagonist, (Allyl)2-Tyr-Aib-Aib-Phe-Leu-OH (ICI 174864) and (N,N-Bisallyl-Tyr-Gly-Gly--(CH₂S)-Phe-Leu-OH (ICI 154129), selective delta-opioid receptor antagonists on blocking analgesia induced by -endorphin, morphine, d-Ala²-NMePhe⁴-Gly-ol-enkephalin (DAMGO), d-Ala²-d-Leu⁵-enkephalin (DADLE) and d-Pen²-enkephalin (DPDPE) administered i.c.v. were studied in male ICR mice. The analgesia was assessed by the tail-flick and paw-licking (hot-plate) tests. The potencies of opioid agonists injected i.c.v. for producing analgesia were DAMGO > DADLE > -endorphin > morphine > DPDPE. Intracerebroventricular administration of CTOP (0.05 g) selectively antagonized inhibition of the tail-flick and paw-licking response induced by morphine, DAMGO or DADLE but not -endorphin or DPDPE. ICI 174864 (5 g) and ICI 154129 (5 g) injected i.c.v. selectively antagonized analgesia induced by DPDPE or DADLE but not -endorphin, morphine or DAMGO injected i.c.v. These results indicate that analgesia induced by morphine and DAMGO is mediated by the stimulation of mu-opioid receptors while analgesia induced by DPDPE is mediated by the stimulation of delta-opioid receptors. DADLE-induced analgesia is mediated by the stimulation of both mu- and delta-opioid receptors. Analgesia induced by -endorphin is mediated by neither munor delta-opioid receptors.Abbreviations i.c.v. intracerebroventricular - i.t. intrathecal - CTOP d-Phe-Cys-Tyr-d-Try-Orn-Thr-Pen-Thr-NHZ - DAMGO d-Ala²-NMePhe²-Gly-ol-enkephalin - DADLE d-Ala²-d-Leus-enke-phalin - DPDPE dd-Pen²-dd-Pen⁵-enkephalin - ICI 174864 (Allyl)2Tyr-Aib-Aib-Phe-Leu-OH - ICI 154129 (N,N-Bisallyl-Tyr-Gly-Gly-(CH₂S)-Phe-Leu-OH     

Entstehung eines DOPA-pools bei Blockierung der DOPA-Decarboxylase

Summary ³H-tyrosine was administered to cats as a continuous i.v. infusion of 30 min duration after inhibition of DOPA-decarboxylase by N-methyl-N(3-hydroxybenzyl) hydrazine dihydrogen phosphate (= NSD-1034). Subsequently, the content of³H-DOPA in the arterial blood, adrenal glands and adrenal venous blood was measured. For this purpose DOPA was separated from tyrosine and other radioactive tyrosine catabolites by ion exchange chromatography after adsorption onto and elution from alumina. ³H-DOPA was not only detectable in the adrenal glands and in the adrenal venous blood but also in the arterial blood. The content of DOPA in the arterial blood increased linearly during the 30 min infusion period and was 0.5 mmole/ml at the end of the experiment. This corresponds to a DOPA content in the total blood volume of about 27.5 mmole/kg body weight. Both adrenals synthesized 0.3 mmole DOPA per minute and per kg body weight. The significance of the formation of a DOPA pool for the therapeutic use of DOPA decarboxylase inhibitors is discussed.

Herrn Prof. Dr. W. Maurer danken wir für die stets großzügige Förderung der Arbeit. Fräulein Regina Kreutz, Frau Susanne Schmidt und Herrn Abdallah Ahmed El Hindy sind wir für interessierte Mitarbeit zu Dank verpflichtet. NSD-1034 wurde freundlicherweise von Smith & Nephew, Research Ltd., Harlow, England, zur Verfügung gestellt. Der Deutschen Forschungsgemeinschaft danken wir für die Gewährung von Sach- und Personalmitteln.     

Activation of central ATP-sensitive potassium channels produces the antinociception and spinal noradrenaline turnover-enhancing effect in mice

ICV cromakalim, a K⁺ channel opener, produced antinociception. This effect was completely antagonized by ICV glibenclamide, a selective adenosine triphosphate-sensitive K⁺ channel (K_ATP channel) blocker. Furthermore, direct opening of central K_ATP channels by ICV cromakalim increased the spinal noradrenaline (NA) turnover. On the other hand, the antinociception induced by ICV morphine ( opioid agonist), but not ICV U-50,488H ( opioid agonist) was markedly potentiated by cromakalim. These findings suggest that the opening of central K_ATP channels may elicit the antinociceptive effect and activate the descending NAergic pathway, and central K_ATP channels play an important role as a modulator of the antinociception induced by agonists but not agonists.