European Journal of Pharmacology (v.471, #2)

Positive regulation of GABAB receptors dually coupled to cyclic AMP by the allosteric agent CGP7930 by Pierluigi Onali; Francesca M. Mascia; Maria C. Olianas (77-84).
The ability of 2,6Di-tert-butyl-4-(-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930), a positive allosteric modulator of GABAB receptors, to regulate GABAB receptor-induced stimulation and inhibition of adenylyl cyclase activity in rat brain was investigated. In olfactory bulb granule cell layer and in frontal cortex, CGP7930 potentiated the stimulatory effects of (−)-baclofen and γ-aminobutyric acid (GABA) on basal and corticotropin-releasing hormone-stimulated adenylyl cyclase activities, respectively. In these stimulatory responses, CGP7930 enhanced both agonist potencies and maximal effects. When GABAB receptor-mediated inhibition of forskolin-stimulated adenylyl cyclase activity of frontal cortex was examined, CGP7930 increased the agonist potencies but failed to affect the maximal effect of (−)-baclofen and modestly increased that of GABA. Similar results were obtained for the inhibition of Ca2+/calmodulin-stimulated adenylyl cyclase in striatum and cerebellum. Western blot analysis of each membrane preparation showed the presence of GABAB2 receptor subunit, a putative site of action of CGP7930. These data indicate that CGP7930 positively modulates brain GABAB receptors coupled to either stimulation or inhibition of cyclic AMP signalling.
Keywords: GABAB receptor; cAMP; CGP7930; Allosteric modulation; Brain;

Nitrogen substitution modifies the activity of cytisine on neuronal nicotinic receptor subtypes by Eric Carbonnelle; Fabio Sparatore; Caterina Canu-Boido; Cristian Salvagno; Barbara Baldani-Guerra; Georg Terstappen; Ruud Zwart; Henk Vijverberg; Francesco Clementi; Cecilia Gotti (85-96).
Cytisine very potently binds and activates the α3β4 and α7 nicotinic subtypes, but only partially agonises the α4β2 subtype. Although with a lower affinity than cytisine, new cytisine derivatives with different substituents on the basic nitrogen (CC1–CC8) bind to both the heteromeric and homomeric subtypes, with higher affinity for brain [3H]epibatidine receptors. The cytisine derivatives were tested on the Ca2+ flux of native or transfected cell lines expressing the rat α7, or human α3β4 or α4β2 subtypes using Ca2+ dynamics in conjunction with a fluorescent image plate reader. None elicited any response at doses of up to 30–100 μM, but all inhibited agonist-induced responses. Compounds CC5 and CC7 were also electrophysiologically tested on oocyte-expressed rat α4β2, α3β4 and α7 subtypes. CC5 competitively antagonised the α4β2 and α3β4 subtypes with similar potency, whereas CC7 only partially agonised them with maximum responses of respectively 3% and 11% of those of 1 mM acetylcholine. Neither compound induced any current in the oocyte-expressed α7 subtype, and both weakly inhibited acetylcholine-induced currents. Adding chemical groups of a different class or size to the basic nitrogen of cytisine leads to compounds that lose full agonist activity on the α3β4 and α7 subtypes.
Keywords: Cytisine; Nicotinic receptor; Agonist; Antagonist; Partial agonist; Binding; FLIPR; Electrophysiology;

Partial adenosine A1 receptor agonists inhibit sarin-induced epileptiform activity in the hippocampal slice by Patrick K. Harrison; Tjerk J.H. Bueters; Adriaan P. Ijzerman; Herman P.M. van Helden; John E.H. Tattersall (97-104).
Organophosphate poisoning can result in seizures and subsequent neuropathology. One possible therapeutic approach would be to employ adenosine A1 receptor agonists, which have already been shown to have protective effects against organophosphate poisoning. Using an in vitro model of organophosphate-induced seizures, we have investigated the ability of several adenosine A1 receptor agonists to inhibit epileptiform activity induced by the organophosphate sarin, in the CA1 stratum pyramidale of the guinea pig hippocampal slice. Application of the adenosine A1 receptor agonist N 6-cyclopentyladenosine (CPA) or the partial adenosine A1 receptor agonists 2-deoxy-N 6-cyclopentyladenosine (2-deoxy-CPA) and 8-butylamino-N 6-cyclopentyladenosine (8-butylamino-CPA) abolished epileptiform activity in a concentration-related manner. The rank order of potency was CPA (IC50 4–5 nM)>2-deoxy-CPA (IC50 113–119 nM)=8-butylamino-CPA (IC50 90–115 nM). These data suggest that partial adenosine A1 receptor agonists, which have fewer cardiovascular effects, should be further evaluated in vivo as potential treatments for organophosphate poisoning.
Keywords: Epileptiform; Adenosine; Hippocampal slice; Organophosphate; Sarin; (Guinea pig);

Influence of histamine, cimetidine and pyrilamine on naloxone-induced jumping in morphine-dependent mice by Mohammad-Reza Zarrindast; Elham Assadi; Shahrbano Oryan; Anahita Torkaman-Boutorabi; Mousa Sahebgharani (105-112).
In the present study, the effects of histamine on naloxone-induced jumping in the presence or absence of adrenoceptor or acetylcholine receptor antagonists in morphine-dependent mice were examined. In these experiments, the drugs were used before s.c. injection of naloxone (2 mg/kg), to test their effects on the expression of jumping. The i.c.v. administration of histamine (5–20 μg/mouse) 15 min before naloxone injection decreased the number of jumps in mice. When the histamine H2 receptor antagonist, cimetidine (5–20 mg/kg), and the histamine H1 receptor antagonist, pyrilamine (5–20 mg/kg), were administered i.p. to morphine-dependent mice, only cimetidine enhanced the jumping behaviour. Administration of cimetidine (20 mg/kg, i.p.), 30 min, of the β-adrenoceptor antagonist, propranolol (2.5–10 mg/kg, i.p.), 15 min but not of pyrilamine (20 mg/kg, i.p.), 30 min before naloxone injection, decreased the histamine effect. The i.p. administration of an acetylcholine receptor antagonist, atropine (5 and 10 mg/kg, i.p.), the α1-adrenoceptor antagonist, prazosin (0.5, 1 and 2 mg/kg, i.p.), and α2-adrenoceptor antagonist, yohimbine (0.5, 1 and 2 mg/kg, i.p.), 15 min before naloxone injection, had no effect on the histamine response. Single administration of propranolol, atropine or prazosin decreased, while yohimbine increased the naloxone-induced jumping. It is concluded that the histamine H2 receptor mechanism may be involved in the influence of histamine on the expression of naloxone-induced jumping in morphine-dependent mice.
Keywords: Jumping; Histamine; Morphine; Naloxone; Adrenoceptor agent; (Mouse);

Our previous studies have shown an enhanced activity of the noradrenergic system in the heart in rats withdrawn from morphine. In the current study, we examined the role of protein kinase A, protein kinase C and Ca2+ entry through L-type Ca2+ channels in naloxone-precipitated increase turnover of noradrenaline in the right and left ventricle. Chronic pretreatment for 7 days with the selective protein kinase A inhibitor, HA-1004 (N-(2′ guanidinoethyl)-5-isoquinolinesulfonamide) concomitantly with morphine significantly antagonized the increase in normetanephrine/noradrenaline ratio (an index of noradrenaline turnover) observed in morphine withdrawn rats. However, the infusion of calphostin C (2-(12-(2-(benzoyloxy)propyl)-3,10-dihydro-4,9-dihydroxy-2,6,7,11-tetramethoxy-3,10-dioxo-1-perylenyl)-1 methylethy carbonic acid 4-hydroxyphenyl ester, a selective protein kinase C inhibitor) did not modify the morphine withdrawal-induced increase in noradrenaline turnover. In addition, when the selective L-type Ca2+ channel antagonist, nimodipine, was infused it diminished the increased in noradrenaline turnover observed after naloxone administration to morphine dependent rats. Taken together, these data might indicate that protein kinase A activity is necessary for the enhancement of noradrenaline turnover during morphine withdrawal and that an up-regulated Ca2+ system might contribute to the increase of noradrenaline turnover. The present finding suggests that protein kinase A and Ca2+ influx through L-type Ca2+ channels might contribute to the activation of noradrenergic system in the heart observed during morphine withdrawal.
Keywords: Morphine withdrawal; Protein kinase A; Protein kinase C; Ca2+ channel; Noradrenaline turnover; Heart;

Responding of rats was maintained under a 120-response fixed ratio (FR) schedule of food delivery, and animals received individual and combined injections of N-methyl-d-aspartic acid (NMDA), phencyclidine hydrochloride, (+)-MK-801 hydrogen maleate (MK-801), (±)-2-amino-5-phosphonopentanoic acid (AP5), 7-chlorokynurenic acid (7CK), ifenprodil tartrate, N G-nitro-l-arginine methyl ester hydorchloride (l-NAME), 7-nitroindazole, aminoguanidine hemisulfate, l-arginine, molsidomine, sodium nitroprusside, and 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8). Behavioral suppression after NMDA was completely and dose-dependently reversed by MK-801, phencyclidine, AP5, and aminoguanidine; partially and dose-dependently attenuated by molsidomine, ifenprodil, and 7CK; and not attenuated at all by l-NAME, 7-nitroindazole, or TMB-8. These findings suggested that behavioral suppression after NMDA was associated with nitric oxide from the inducible synthase. In a second series of experiments, comparable behavioral suppression by 0.1 mg/kg MK-801, but not 3 mg/kg phencyclidine, was attenuated by nitroprusside, molsidomine, and l-arginine, suggesting that suppressions from MK-801 and phencyclidine were mediated by different final common pathways, and that behavioral suppression from MK-801, but not phencyclidine, may be associated with Ca2+-dependent nitric oxide.
Keywords: NMDA; Nitric oxide (NO); Operant behavior; Fixed ratio; (Rat);

Conditioned taste aversion: modulation by 5-HT receptor activity and corticosterone by Boris Gorzalka; Laura Hanson; Jennifer Harrington; Sisley Killam; Dan Campbell-Meiklejohn (129-134).
Two experiments were designed to elucidate the involvement of the hypothalamic–pituitary–adrenal axis and the 5-hydroxytryptamine (5-HT) system in the acquisition of lithium chloride-conditioned taste aversion. In Experiment 1, rats were administered either vehicle or 50 mg/kg nefazodone daily for 4 weeks. Rats were treated with 22 mg/kg of lithium chloride in order to produce conditioned taste aversion to a sucrose solution. Three days later, nefazodone completely blocked the lithium chloride-conditioned taste aversion. In Experiment 2, the effects of chronic corticosterone administration on lithium chloride-conditioned taste aversion were investigated. Twenty male rats received either corticosterone at a dose of (50 mg/kg) or vehicle injections over a period of 14 consecutive days. Lithium chloride-conditioned taste aversion was potentiated in rats treated with corticosterone. Additionally, corticosterone-treated animals required more trials to reach extinction. These results suggest the involvement of both the 5-HT system and the hypothalamic–pituitary–adrenal axis in lithium chloride-conditioned taste aversion.
Keywords: Lithium chloride; Conditioned taste aversion; Nefazodone; Corticosterone;

Previously, we reported that the α1A-adrenoceptor, but not the α1D-adrenoceptor, mediates pupillary dilation elicited by sympathetic nerve stimulation in rats. This study was undertaken to further characterize the α-adrenoceptor subtypes mediating pupillary dilation in response to both neural and agonist activation. Pupillary dilator response curves were generated by intravenous injection of norepinephrine in pentobarbital-anesthetized rats. Involvement of α1-adrenoceptors was established as mydriatic responses were inhibited by systemic administration of nonselective α-adrenoceptor antagonists, phentolamine (0.3–3 mg/kg) and phenoxybenzamine (0.03–0.3 mg/kg), as well as by the selective α1-adrenoceptor antagonist, prazosin (0.3 mg/kg). The α2-adrenoceptor antagonist, rauwolscine (0.5 mg/kg), was without antagonistic effects. α1A-Adrenoceptor selective antagonists, 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101; 0.1–1 mg/kg) and 5-methylurapidil (0.1–1 mg/kg), the α1B-adrenoceptor selective antagonist, 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)- [[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765314; 0.3–1 mg/kg), as well as the α1D-adrenoceptor selective antagonist, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY-7378; 1 mg/kg), were used to delineate the adrenoceptor subtypes involved. Mydriatic responses to norepinephrine were significantly antagonized by intravenous administration of both WB-4101 and 5-methylurapidil, but neither by L-765314 nor by BMY-7378. L-765314 (0.3–3 mg/kg, i.v.) was also ineffective in inhibiting the mydriasis evoked by cervical sympathetic nerve stimulation. These results suggest that α1B-adrenoceptors do not mediate sympathetic mydriasis in rats, and that the α1A-adrenoceptor is the exclusive subtype mediating mydriatic responses in this species.
Keywords: Adrenoceptor subtype; Mydriasis; (Rat); Norepinephrine; 5-Methylurapidil; L-765314;

Functions of thrombin as a modulator of inflammation and tissue repair are mediated by the proteinase-activated receptor (PAR) family. Some of these effects may be induced by activation of mast cells. To characterize the degranulation of rat peritoneal mast cells in response to PAR agonists, the effects of thrombin, trypsin and peptide agonists of PARs (PAR-AP, proteinase-activated receptor-activating peptides) on secretion were investigated. The release of β-hexosaminidase by thrombin (0.01–1 μM) was concentration-dependent and mediated via PAR1, as evidenced by cathepsin G (100 μM)-induced inactivation of PAR1 and thrombin-stimulated PAR1 desensitization. Trypsin (1 μM) accelerated histamine secretion. The PAR1-AP, TRAP (SFFLRN, 1–100 μM) and the PAR2-AP SLIGRL (5–100 μM) caused the release of histamine, and β-hexosaminidase from inflammatory mast cells were obtained from a model of acute peritonitis in rats. Relative to the response to compound 48/80, the thrombin- and TRAP-induced release of β-hexosaminidase was higher in inflammatory mast cells than in the control. This suggests that additional exposure of PAR1 on mast cells to PAR agonists or an increase in PARs sensitivity to PAR agonists probably occurred during acute inflammation.
Keywords: Mast cell; PAR (proteinase-activated receptor); PAR-activating peptide (PAR-AP); Thrombin; Histamine; Peritonitis;

Effects of castration and of testosterone replacement on α1-adrenoceptor subtypes in the rat vas deferens by Marcelo Campos; Paola de Lucena Morais; André S. Pupo (149-155).
The contractions of the rat vas deferens in response to noradrenaline are mediated through α1A-adrenoceptors. We observed participation of α1B-adrenoceptors in these contractions after castration. We now investigated the time course of this plasticity and the effects of testosterone by determining the actions of competitive antagonists on noradrenaline-induced contractions after 7, 14, 21 and 30 days of castration. BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride) antagonised noradrenaline-induced contractions in control and castrated rats with low pA 2 values (≅6.8). In control vas deferens, WB 4101 (2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride) had a slope in the Schild plot no different from 1.0, while slopes lower than 1.0 (≈0.6) were observed for vas deferens from castrated rats. Chloroethylclonidine was ineffective in the control vas while it inhibited noradrenaline-induced contractions in vasa from castrated rats and converted the complex antagonism by WB 4101 into simple competitive antagonism. Treatment of castrated rats with testosterone prevented the effects of castration. The results suggest that α1B-adrenoceptors are detectable in vas deferens from at least the 7th through the 30th day after castration and that testosterone prevents this plasticity.
Keywords: α1-Adrenoceptor; Vas deferens; (Rat); Castration; Testosterone;