European Journal of Pharmacology (v.455, #1)

During the four decades that research has been carried out on antipsychotic drugs, a variety of methods have been used to study the effects of these compounds on dopamine neurotransmission. An important issue in this research was to find an explanation for the difference between “typical” and “atypical” antipsychotic drugs. The hypothesis that the beneficial properties and the motor side effects of antipsychotic drugs result from their effects on different groups of dopamine neurons has received considerable attention. Numerous researchers have tried to discover regiospecific actions of antipsychotic drugs in mesolimbic and in mesocortical dopamine neurons. An overview of these research attempts is presented here. Electrophysiological studies showed a selective action of atypical antipsychotic drugs on A10 dopamine neurons. It was found that chronic treatment with these compounds induced a preferential depolarisation block of the A10 neurons that project to the mesolimbic areas. The model represents certain clinical features of antipsychotic drug use and offers a possible explanation for the lack of extrapyramidal side effects of atypical antipsychotic drugs. Dopamine neurons projecting from A10 to the frontal cortex are also considered as a possible site of action of atypical antipsychotic drugs. Microdialysis studies have shown that certain atypical antipsychotic drugs selectively enhance the release of dopamine in the prefrontal cortex when compared with typical antipsychotic drugs. The finding that repeated treatment with antipsychotic drugs increased dopamine D2 receptor binding in the frontal cortex confirms the significance of this brain area. These properties might indeed explain certain beneficial effects of atypical antipsychotic drugs such as improvement of cognitive dysfunction. However the effects of typical and atypical antipsychotic drugs in the frontal cortex could not be fully differentiated, which illustrates the difficulty of localising clinical effects of antipsychotic drugs in terms of regional dopamine neurons. Recently new insights into the mechanism of action of typical and atypical antipsychotic drugs have been published. Clinical positron emission tomography (PET) studies have indicated that a moderate dopamine D2 receptor occupancy, probably combined with a high dissociation rate, might provide the optimal clinical conditions for an antipsychotic drug, without inducing extrapyramidal side effects. Moreover the efficacy of benzamides as atypical antipsychotic drugs suggests that low to moderate dopamine D2 blockade is probably the most important—if not the only—criterion that determines “atypicality”. Interestingly these new insights are based on PET studies of the human basal ganglia and not on the comparison of different brain areas. Apparently, according to this concept an ideal antipsychotic drug need not to act on a particular type of dopamine neurons, as it is the moderate dopamine D2 receptor occupancy that determines the desirable clinical effects. It is concluded that both beneficial actions and side effects, of antipsychotic drugs might be dose dependently localised in A9 as well as A10 dopamine neurons.
Keywords: Dopamine; Mesolimbic; Antipsychotic drug; Clozapine; Prefrontal cortex;

Two-phase response of acid extrusion triggered by purinoceptor in Chinese hamster ovary cells by Yuichi Okada; Takanobu Taniguchi; Yoshio Akagi; Ikunobu Muramatsu (19-25).
The functional characteristics of purinoceptors in Chinese hamster ovary (CHO) cells were investigated using a microphysiometer which detects small metabolic changes to living cells in real-time as variations of pH in the extracellular microenvironment. Uridine 5′-triphosphate (UTP) increased the extracellular acidification rate biphasically, namely a transient and a steady response were observed. The transient phase reached a peak (four- to fivefold the basal extracellular acidification rate in amplitude) within 20 s and was followed by the steady phase which was sustained for more than 1 min at an amplitude less than twofold the basal extracellular acidification rate. Both phases showed a concentration-dependent increase in response to UTP. However, there was a significant difference in the pEC50 value for UTP between the transient (4.8) and steady phases (6.1). Like UTP, ATP increased the extracellular acidification rate, but α,β-methyleneATP (α,β-MeATP), 2-methylthioATP (2-MeSATP), ADP, UDP and adenosine did not. This result suggests that the acid is extruded through a P2Y2 or P2Y2-like purinoceptor. 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and 4-isopropyl-3-methylsulphonylbenzoyl-guanidine methanesulphonate (HOE642) suppressed both phases of the UTP-stimulated extracellular acidification rate response with high affinity (pIC50: approximately 7.0). This result suggests that the Na+/H+ exchanger 1 (NHE-1) predominantly mediates the UTP-induced acid extrusion response in CHO cells. Elimination of extracellular Ca2+ or treatment with thapsigargin diminished both phases of the UTP-stimulated extracellular acidification rate. In addition, N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide hydrochloride (W-7) also abrogated the two phases. These results are consistent with the involvement of NHE-1 which is activated via Ca2+/calmodulin. Persistent exposure to UTP reduced both extracellular acidification rate phases, causing desensitization of the P2Y purinoceptor. This desensitization did not affect the acid extrusion response mediated by the α1-adrenoceptor.
Keywords: Acid extrusion; Microphysiometer; P2Y purinoceptor; Na+/H+ exchanger;

Rhynchophylline and isorhynchophylline inhibit NMDA receptors expressed in Xenopus oocytes by Tai-Hyun Kang; Yukihisa Murakami; Kinzo Matsumoto; Hiromitsu Takayama; Mariko Kitajima; Norio Aimi; Hiroshi Watanabe (27-34).
Rhynchophylline and isorhynchophylline are major tetracyclic oxindole alkaloid components of Uncaira species, which have been long used as medicinal plants. In this study, the effects of rhynchophylline and isorhynchophylline on the ionotropic and metabotropic glutamate receptor-mediated current responses were examined using Xenopus oocytes injected with total RNA prepared from rat cortices or cerebelli. Rhynchophylline and isorhynchophylline (1–100 μM) per se failed to induce membrane current, but these alkaloids reversibly reduced N-methyl-d-aspartate (NMDA)-induced current in a concentration-dependent but voltage-independent manner. The IC50 values of rhynchophylline and isorhynchophylline were 43.2 and 48.3 μM, respectively. Substitution of Ba2+ for Ca2+ in the recording medium did not alter the extent of rhynchophylline- and isorhynchophylline-induced suppression of NMDA currents. In contrast, neither alkaloid had an effect on the currents mediated by ionotropic kainic acid-type and (±)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors or by the metabotropic glutamate receptor1 and 5 (mGlu1/5). Rhynchophylline and isorhynchophylline (30 μM) significantly reduced the maximal current responses evoked by NMDA and glycine (a co-agonist of NMDA receptor), but had no effect on the EC50 values and Hill coefficients of NMDA and glycine for inducing currents. These alkaloids showed no interaction with the polyamine binding site, the Zn2+ site, proton site or redox modulatory site on the NMDA receptor. These results suggest that rhynchophylline and isorhynchophylline act as noncompetitive antagonists of the NMDA receptor and that this property may contribute to the neuroprotective and anticonvulsant activity of the Uncaira species plant extracts.
Keywords: Rhynchophylline; Isorhynchophylline; NMDA receptor; Glycine site;

Sleep–wake effects of meta-chlorophenyl piperazine and mianserin in the behaviorally depressed rat by Vijayakumar Mavanji; Basavalingappa Meti; Subimal Datta (35-41).
The present study examined the effects of meta-chlorophenyl piperazine (mCPP) and mianserin on the sleep–wake cycle of the clomipramine-induced behaviorally screened depressed rats. Six-hour polygraphic recordings were made between 06:00 and 12:00 h, after a single injection of either saline or mianserin or mCPP into the lateral cerebral ventricle (i.c.v.) of both the depressed (n=12) and control rats (n=12). The injection of mCPP in the depressed rats caused a significant reduction in the total duration and number of rapid eye movement (REM) sleep episodes while it increased the REM sleep onset latency compared to the control saline injections. The injection of mianserin in the depressed rats also caused a significant reduction in the total duration and number of REM sleep episodes without changing the REM sleep latency. These results demonstrate for the first time that the central administration of mCPP and mianserin could act as an antidepressant in the clomipramine-induced rat model of depression.
Keywords: Animal model; Depression; 5-HT (5-hydroxytryptamine, serotonin); REM (rapid eye movement) sleep; Mianserin; mCPP;

Arteriolar changes in nitric oxide activity and sensitivity during the course of streptozotocin-induced diabetes by Bastiaan van Dam; Cihan Demirci; Hans J Reitsma; Anton A van Lambalgen; Gerard C van den Bos; Geert Jan Tangelder; Coen D.A Stehouwer (43-51).
Nitric oxide (NO) may play an important role in the pathogenesis of diabetic microangiopathy. However, arteriolar changes in NO activity and sensitivity to NO may be dependent on both the type of arteriole and the duration of diabetes. Therefore, we assessed, in the in situ spinotrapezius muscle preparation of streptozotocin-diabetic rats and of controls, inside diameters of A2–A4 arterioles and the reactivity to topically applied acetylcholine and nitroprusside, before and after N G-nitro-l-arginine (l-NNA) at 2, 4, 6 and 12 weeks of diabetes. In A2 arterioles, basal diameters and the contribution of NO to basal diameter were not affected during the course of streptozotocin-induced diabetes. However, the maximal response to acetylcholine in these arterioles was attenuated after 2 until 4 weeks, and from 4 weeks on a sustained decrease in reactivity to sodium nitroprusside was observed. In A3 arterioles, both the basal diameter and the contribution of NO to basal diameter were decreased after 2 weeks and increased after 6 weeks, while the response to sodium nitroprusside was unaffected. In A4 arterioles, a significant increase in basal diameter was observed after 6 weeks only. Thus, this study shows that streptozotocin-induced diabetes causes microvascular changes in NO activity and sensitivity that depend on the type of arteriole. For each order of arteriole, these changes show a specific pattern during the course of diabetes.
Keywords: Hyperglycemia; Microcirculation; Streptozotocin; Acetylcholine; Sodium nitroprusside; Nitric oxide; Diabetes mellitus;

Diet can be the most important factor that influences risks for cardiovascular diseases. Genistein included in soy is one candidate that may benefit the cardiovascular system. Here, we investigated the inhibitory effects of genistein on thrombotic vessel occlusion in the mouse femoral artery using a photochemical reaction, and in vitro platelet aggregation in whole blood measured by single platelet counting. Genistein (10 mg/kg), intravenously administered 10 min before the rose bengal injection, significantly prolonged the thrombotic occlusion time from 6.1±0.4 to 8.4±0.8 min (P<0.05). Genistein at doses higher than 30 μM significantly (P<0.01) inhibited in vitro platelet aggregation induced by collagen (1 and 3 μg/ml). When 10 mg/kg genistein was intravenously administered, ex vivo platelet aggregation induced by collagen (1 and 3 μg/ml) was significantly suppressed (P<0.01). In conclusion, genistein prevented in vivo thrombogenesis and suppressed in vitro platelet aggregation. These results suggest that dietary supplementation of soy may prevent the progression of thrombosis and atherosclerosis.
Keywords: Genistein; Thrombosis; Soy; Isoflavone; Platelet aggregation;

Evidence that NAN-190-induced hypotension involves vascular α1-adrenoceptor antagonism in the rat by Rafael Villalobos-Molina; Itzell A Gallardo-Ortı́z; J.Javier López-Guerrero; Maximiliano Ibarra (59-64).
The effect of NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phthalimido]-butyl] piperazine), described as a mixed 5-HT1A receptor agonist/antagonist, on cardiovascular function was studied. The i.v. injection of NAN-190 (1–300 μg/kg) dose-dependently decreased blood pressure (p<0.001), while heart rate was not significantly modified compared to saline-treated, anaesthetized adult rats. WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl] ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide), a highly selective 5-HT1A receptor antagonist, increased NAN-190-induced hypotension (p<0.05). In the pithed rat NAN-190 displaced the phenylephrine dose–pressor response curve to the right; ED50 values were: ≈14, 20, 40 and 270 μg/kg for saline and NAN-190 (1, 10 and 100 μg/kg, respectively); similar ED50 values were obtained with prazosin (≈20, 69 and 358 μg/kg for 1, 10 and 100 μg/kg of prazosin, respectively). NAN-190 shifted to the right the concentration–response curves to phenylephrine in rat tail artery (α1A-adrenoceptors), in rabbit aorta (α1B-adrenoceptors) and in rat aorta (α1D-adrenoceptors), with pA 2 values of 9.47, 9.02 and 9.99; while Schild slopes were −0.78, −1.13 and −0.90, respectively (not significantly different from unity). The results show that NAN-190 induced hypotension in the anaesthetized, adult rat and suggest that this effect could be explained by antagonism of vascular α1-adrenoceptors.
Keywords: NAN-190; Hypotension; Rat; Rat; α1-Adrenoceptor;

Effects of mibefradil on uterine contractility by Keerai T Asokan; Souvendra N Sarkar; Santosh K Mishra; Vellanki Raviprakash (65-71).
Mibefradil, a benzimidazolyl tetralol derivative, is a new Ca2+ channel antagonist which is structurally distinct from other Ca2+ channel antagonists such as nifedipine, verapamil and diltiazem. It is a very effective antihypertensive agent that is thought to achieve its action via a higher affinity block for low-voltage activated (T) than for high-voltage-activated (L) Ca2+ channels. Nevertheless, it blocks L-type Ca2+ channels in several tissues. In the present study, the effects of mibefradil on spontaneous rhythmic contractions and on contractions elicited by CaCl2 (K+-depolarized preparations) and oxytocin (in low Ca2+/Ca2+-free solutions) were investigated on uterus strips from pregnant and non-pregnant rats. Mibefradil (10−8–3×10−6 M) caused concentration-dependent inhibition of spontaneous contractions of uterus strips from pregnant and non-pregnant rats with the IC50 values of 8.83×10−7 M; 5.94×10−7 M (amplitude) and 1.03×10−6 M; 5.48×10−7 M (frequency), respectively. Mibefradil (3 μM) caused a rightward shift in the concentration–response curves for CaCl2 in K+ (40 mM)-depolarized uterus strips taken from both pregnant and non-pregnant rats. Mibefradil (3 μM) was, however, more potent for antagonising CaCl2 responses in uterus strips obtained from pregnant rats than in those from non-pregnant rats. Mibefradil (3 μM) had no effect on oxytocin-induced contraction in Ca2+-free physiological salt solution (PSS) on uterus strips from non-pregnant rats. However, it markedly inhibited oxytocin-induced contraction of pregnant rat uterus strips in Ca2+-free PSS. Thus, mibefradil probably antagonizes L-type Ca2+ channels as well as interferes with the intracellular Ca2+ release mechanism, which would be helpful in the development of a tocolytic agent.
Keywords: Uterus; Ca2+ channel; Mibefradil;

Nitric oxide (NO) has been recognized as a neurotransmitter or a neuromodulator in the central nervous system. Brain NO is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. Previously we reported that central NO is involved in the elevation of plasma noradrenaline levels induced by intracerebroventricularly (i.c.v.) administered interleukin-1β in rats [Eur. J. Phamacol. 317 (1996) 61]. In the present study, therefore, we tried to characterize which type of NOS isoforms is involved in the cytokine-induced responses using selective inhibitors of each NOS isoform in urethane-anesthetized rats. I.c.v. administered interleukin-1β (100 ng/animal) elevated plasma levels of noradrenaline but not adrenaline. The cytokine-induced elevation of plasma noradrenaline levels was attenuated by cycloheximide, an inhibitor of protein synthesis, in a dose-dependent manner (10 and 20 μg/animal, i.c.v.). S-ethylisothiourea (0.1 and 0.5 μg/animal, i.c.v.), an inhibitor of inducible NOS, dose-dependently reduced the cytokine-induced elevation of plasma noradrenaline levels, while 7-nitroindazole (5 and 10 μg/animal, i.c.v.), an inhibitor of neuronal NOS, had no effect. These results suggest the involvement of brain inducible NOS in the interleukin-1β-induced activation of the central sympathetic outflow in rats.
Keywords: Noradrenaline; Plasma; Interleukin-1β; Nitric oxide (NO) synthase; Brain;

Erratum to “Role of nitric oxide in allergic inflammation and bronchial hyperresponsiveness” [Eur. J. Pharmacol. 452 (2002) 123–133] by Paul R Eynott; David A Groneberg; Gaetano Caramori; Ian M Adcock; Louise E Donnelly; Sergei Kharitonov; Peter J Barnes; K.Fan Chung (79).