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P.6.d.007 The selective nicotinic alpha7 receptor agonist SSR180711 does not induce locomotor sensitisation
P.6.d Addiction – Drugs (basic) P.6.d.006 The in vivo modulation of the mesolimbic dopamine system by cannabinoid CB1 receptors J.L. Cornish ° , A. Wilson, S. Tye. Macquarie University, Psychology, Sydney, Australia Dopamine neurons of the midbrain are involved in psychopathologies such as addiction and psychosis. Research conducted at the cellular level demonstrates that these neurons are indirectly modulated by “cannabis (marijuana)-like” endocannabinoid neurotransmitters binding at cannabinoid type 1 (CB1) receptor binding sites. This research suggests involvement of CB1 receptors in dopamine-mediated pathologies. Drug addiction is a chronic relapsing disorder that currently has no effective pharmacological treatment. Recent trials utilizing cannabinoid antagonists have shown promising results in reducing relapse for most drugs of abuse. It has been suggested that the reduction of relapse produced by CB1 antagonists is due to the action at CB1 receptors to reduce midbrain dopamine neuron activity (for review see Gardner, 2005). However, studies to date have not selectively investigated if modulation of cannabinoid CB1 receptors in the midbrain alter dopamine release in vivo. Previous electrophysiological techniques have demonstrated that the activation of presynaptic CB1 receptors on GABAergic neurons disinhibits dopamine cells to increase dopamine cell firing (Gardner 2005). However recent electrophysiological studies also demonstrate that CB1 receptors are located presynaptically on glutamate terminals and act to inhibit glutamate release in the midbrain ventral tegmental area (VTA, Melis et al. 2004). This implies that during burst firing of dopamine cells, endocannabinoids may be released by dopamine cells to inhibit incoming input from both stimulatory (glutamate) and inhibitory (GABA) projections. The purpose of this study was to elucidate the effect on in vivo dopamine release in the forebrain nucleus accumbens (NAc) of directly stimulating or inhibiting the cannabinoid CB1 receptor in the midbrain VTA. This study is an in vivo examination of cannabinoid type one (CB1) receptor modulation of the midbrain dopamine reward system. The effects of CB1 receptor agonists and antagonists infused directly into the midbrain VTA were measured on dopamine release in the forebrain NAc following electrical stimulation of the Prefrontal Cortex (PFC) in rats. Methods: Urethane-anaesthetised male Lewis rats were instrumented with an electrode into the PFC, a drug infusion cannula into the VTA and a carbon fibre electrode into the NAc for the measurement of dopamine levels using fixed potential amperommetry. PFC stimulated changes in dopamine levels in the NAc were measured following the VTA infusion of vehicle, a CB1 agonist (WIN55212−2, 1 nmol, 3 nmol and 10 nmol) and a CB1 antagonist (AM251, 1 nmol, 3 nmol and 10 nmol). The results show that application of a CB1 agonist into the VTA produced a dose-dependent increase in PFC stimulated NAc dopamine release, indicating cannabinoid activity on GABA cells within the VTA. Conversely, application of a CB1 antagonist into the VTA only produced a predicted decrease in PFC stimulation-evoked dopamine release at the 10 nmol dose. At 3 nmol an increase in dopamine signal occurred, suggesting cannabinoid activity on glutamate afferents at the lower dose. In conclusion, these results may indicate that the midbrain dopamine reward system is modulated primarily by CB1 receptors on GABA cells within the VTA, and to a lesser extent glutamate cells.
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References [1] Gardner EL, 2005, Endocannabinoid signaling system and brain reward: emphasis on dopamine. Pharmacol Biochem Behav 81, 263– 284. [2] Melis M, Pistis M, Perra S, Muntoni AL, Pillolla G, Gessa GL, 2004, Endocannabinoids mediate presynaptic inhibition of glutamatergic transmission in rat ventral tegmental area dopamine neurons through activation of CB1 receptors. J Neurosci 24, 53−62.
P.6.d.007 The selective nicotinic alpha7 receptor agonist SSR180711 does not induce locomotor sensitisation N. Mirza ° , K.B. Troelsen, L.S. Taouli. NeuroSearch A/S, In-vivo Pharmacology, Ballerup, Denmark The potential therapeutic benefit of selective nicotinic a7 receptor agonists in schizophrenia and Alzheimer’s disease has been an area of active pursuit. Recently available a7 selective tools (SSR180711, PNU282987, TC-1698, W-56203, ABBF) allow a more reliable determination of the therapeutic potential and sideeffects associated with a7 receptors. There is some literature, albeit mixed, which implicates nicotinic a7 receptors in drug abuse: (i) a7 receptors are localised on glutamatergic terminals apposed to ventral tegmental area dopamine cells which project to the nucleus accumbens (NAcc), a key pathway relevant to various drugs of abuse; and more specifically: (i) infusion of the selective nicotinic a7 receptor antagonist methyllycaconitine (MLA) into the VTA blocks (−)nicotine-induced dopamine release in the NAcc, (iii) MLA reduces (−)nicotine self-administration in rats in one study (Markou & Paterson, 2001) but not another (Grottick et al., 2000), and (iii) neither a7 selective partial (DMAC) or full (ARR17779) agonists affect locomotor activity in nicotine sensitised rats (Grottick et al., 2000). With respect to the locomotor studies, the brain/plasma ratio for AR R17779 is poor suggesting this is not an ideal tool with which to make definitive conclusions. Furthermore, no one to date has determined if chronic administration of a a7 selective agonist induces locomotor sensitisation per se. In the present study we address both these points utilising the nicotinic a7 selective drug SSR180711, an arguably better a7 selective tool than AR R17779 (Pichat et al., 2007). Separate groups of Sprague-dawley rats (n = 7) were treated (s.c.) with either saline, (−)nicotine (0.4 mg/kg) or SSR180711 (3 mg/kg), once daily for over 80 days, 7-days week. Immediately after drug administration animals were placed in locomotor activity cages for 36 minutes and activity levels (distance, m) monitored. All data was analysed by ANOVA followed relevant post hoc tests. Within 2 weeks a sensitised locomotor response to (−)nicotine developed (day 1: 89±15; day 14: 230±15), whereas activity levels in the vehicle and SSR180711 groups remained similar on day 1 (93±9 and 81±14, respectively) to day 14 (112±11 and 100±7, respectively). The sensitised locomotor response to (−)nicotine remained stable for over 80 days, over which time no significant change in locomotor response in vehicle or SSR180711 groups occurred. From day 21 cross-sensitisation dose-response curves were conducted in all three groups using a randomised within subject design whereby all animals in all groups were treated with vehicle and various doses of each drug. Cross-sensitisation test days were on Tuesdays/Fridays, with animals continuing to receive their chronic drug treatment on intervening days.
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P.6.d Addiction – Drugs (basic)
A dose-related sensitised response to (−)nicotine (0.1–0.4 mg/kg) in chronic (−)nicotine treated rats occurred, whereas (−)nicotine had no effect in chronic vehicle or SSR180711 treated rats. Conversely, SSR180711 (0.03−3 mg/kg) had little effect in rats treated chronically with (−)nicotine or saline. However, in chronic SSR180711 treated rats, SSR180711 itself significantly and dose-dependently (0.03−1 mg/kg) increased motility. SSR180711, a novel a7 selective agonist does not induce locomotor sensitisation per se and does not engender a sensitised locomotor response in animals sensitised to (−)nicotine. References [1] Grottick et al, 2000, JPET 294, 1112–1119. [2] Markou Paterson, 2001, Nicotine Tobacco Res 3, 361–373. [3] Pichat et al, 2007, Neuropharmacology 32, 17−34.
P.6.d.008 Cannabinoid CB1 receptor modulation of the acute and semichronic effects of MDMA in locomotor activity in mice
activity (42%; p < 0.05) and locomotion (49%; p < 0.01) without effects in corner time respect control group. In this case, WIN 55,212−2 did not change the increase ecstasy-induced effects on horizontal activity, peripheral activity, rearing activity, corner time and locomotion. However, the CB1 cannabinoid antagonist AM251 block completely the horizontal activity, peripheral activity, rearing activity and locomotion increased after ectasy semichronic administration but had no effect on the corner time. Overall, our findings suggest that the administration of CB1 agonist/antagonist differentially modulates the locomotor effcts of MDMA in a time-dependent manner. Thus, the endocannabinoid seems to mediate, at least in part, the locomotor effects of MDMA. Jos´e-M. Oliva is a recipient of a Post-Doctoral Fellowship from the Spanish Ministry of Education
P.6.d.009 A novel approach to assess drug-induced aversion to ethanol
P. Svenningsson. Karolinska Institute, Department J.M. Physiology and Pharmacology, Stockholm, Sweden
O. Dravolina ° , I. Sukhotina, E. Zvartau, A. Bespalov. Pavlov Medical University, Institute of Pharmacology, St. Petersburg, Russia
The hyperactivity induced by 3,4-methylenedioxymethamphetamine (MDMA; “ecstasy”) is characterized by increased forward locomotion in the periphery of the chamber and decreased investigatory behaviors, e.g., hole-pokes and rearing activity and elicitation of the serotonin (5-HT; 5-hydroxytryptamine) syndrome are also observed after MDMA administration. Both the 5-HT and dopamine (DA) systems may mediate hyperactivity induced by MDMA. First, MDMA evokes the release of DA as well as 5-HT in vivo. Second, the pattern of behavior evoked by MDMA is more similar to that induced by substituted amphetamines that enhance 5-HT, but not DA, release than to that evoked by amphetamine, which is predominantly a DA releaser. The aim of this study was to examine the role of CB1 cannabinoid receptor in the acute (1 day) and semichronic (5 days) effects of ectasy in locomotor activity. To this purpose, we administer the CB1 cannabinoid agonist WIN 55212,2 (0.5 mg/kg; p.o.) or the CB1 cannabinoid antagonist AM251 (2 mg/kg; p.o.) 45 minutes prior MDMA (3 mg/kg; p.o.). Thus, we had the following groups (n = 8−10): (1) control group, (2) MDMA group, (3) WIN 55212,2 group, (4) WIN 55212,2 + MDMA group, (5) AM251 group and (6) AM251 + MDMA group. After 1 hour, we studied the locomotor activity in the open-field during 2 hours. In our study we measure different parameters related to locomotor activity as horizontal activity, peripheral activity, rearing activity, corner time and locomotion. Statistical analyses was carried out using the ANOVA followed by the Student Newman-Keul’s test. The acute administration of MDMA (3 mg/kg) induced a significant increase in horizontal activity (48%; p < 0.01), rearing activity (42%; p < 0.05) and locomotion (85%; p < 0.001) and a decrease in corner time (45%; p < 0.001) respect control group. No differences were found in peripheral activity. The administration of WIN 55212,2 prior a single administration of MDMA decreased the effects seen by ecstasy in horizontal activity, rearing activity and locomotion, meanwhile the administration of AM251 had no effects on horizontal activity, rearing activity, corner time or locomotion but decreased the peripheral activity (28%; p < 0.01). After a semichronic administration period (5 days), MDMA also increased the horizontal activity (39%; p < 0.01), rearing
One of currently approved drugs for the treatment of alcohol dependence, disulfiram (tetraethylthiuram disulfide), non-specifically inhibits aldehyde dehydrogenase (ALDH2−1) by reacting with sulphhydryl groups in the enzyme and acts as an alcohol-deterrent drug. Current perspectives on clinical use of disulfiram are mixed; it is a second-line medication compared with other drugs, and is probably most effective in reducing alcohol consumption when used in a supervised setting (Brewer, 1993). However, introduction of depot forms of disulfiram may revive interest in this type of therapy and this necessitates the development of experimental methods to evaluate efficacy of disulfiram preparations. The aim of this study was to develop an experimental paradigm in which the malaise of drug-ethanol reaction is quickly recognized by rats as derived from ethanol. For this purpose, several experiments were conducted using a variant of the conditioned taste aversion paradigm based on the gustatory long-term memory established after association of the taste of food (conditioned stimulus, CS) with visceral signals of poisoning (unconditioned stimulus, US). The conditioned taste aversion is an acquired adaptive reaction preventing animals from repeated ingestion of a novel tastant, which has induced illness (Garcia and Ervin, 1968). After the acquisition of conditioned taste aversion in a single conditioning trial, the gustatory CS becomes hedonically aversive as indicated by reduced ingestive and increased aversive taste reactivity in response to re-exposures to the CS. Experimentally naive male Wistar rats (200–250 g) were used. As a preliminary, we defined: (1) the dose of disulfiram that made animals to cease consuming alcohol, indicating that the ethanol-disulfiram reaction was associated with alcohol ingestion; (2) the highest dose of ethanol that did not cause the acquisition of conditioned taste aversion. For subsequent experiments, separate groups of rats were pretreated by disulfiram (200 mg/kg, subcutaneously) or vehicle (0.5% methylcellulose) 24 h before the acquisition of conditioned taste aversion. During the acquisition of conditioned taste aversion, rats were allowed to eat food pellets (Formula F, Noyes Precision Pellets, Research Diets, Inc., New Brunswick, NJ) for 30 min, and immediately after that each animal received an intraperitoneal injection of ethanol (0.56 g/kg, 15% v/v in sterile water) or vehicle.
Oliva ° ,
S555
References [1] Gardner EL, 2005, Endocannabinoid signaling system and brain reward: emphasis on dopamine. Pharmacol Biochem Behav 81, 263– 284. [2] Melis M, Pistis M, Perra S, Muntoni AL, Pillolla G, Gessa GL, 2004, Endocannabinoids mediate presynaptic inhibition of glutamatergic transmission in rat ventral tegmental area dopamine neurons through activation of CB1 receptors. J Neurosci 24, 53−62.
P.6.d.007 The selective nicotinic alpha7 receptor agonist SSR180711 does not induce locomotor sensitisation N. Mirza ° , K.B. Troelsen, L.S. Taouli. NeuroSearch A/S, In-vivo Pharmacology, Ballerup, Denmark The potential therapeutic benefit of selective nicotinic a7 receptor agonists in schizophrenia and Alzheimer’s disease has been an area of active pursuit. Recently available a7 selective tools (SSR180711, PNU282987, TC-1698, W-56203, ABBF) allow a more reliable determination of the therapeutic potential and sideeffects associated with a7 receptors. There is some literature, albeit mixed, which implicates nicotinic a7 receptors in drug abuse: (i) a7 receptors are localised on glutamatergic terminals apposed to ventral tegmental area dopamine cells which project to the nucleus accumbens (NAcc), a key pathway relevant to various drugs of abuse; and more specifically: (i) infusion of the selective nicotinic a7 receptor antagonist methyllycaconitine (MLA) into the VTA blocks (−)nicotine-induced dopamine release in the NAcc, (iii) MLA reduces (−)nicotine self-administration in rats in one study (Markou & Paterson, 2001) but not another (Grottick et al., 2000), and (iii) neither a7 selective partial (DMAC) or full (ARR17779) agonists affect locomotor activity in nicotine sensitised rats (Grottick et al., 2000). With respect to the locomotor studies, the brain/plasma ratio for AR R17779 is poor suggesting this is not an ideal tool with which to make definitive conclusions. Furthermore, no one to date has determined if chronic administration of a a7 selective agonist induces locomotor sensitisation per se. In the present study we address both these points utilising the nicotinic a7 selective drug SSR180711, an arguably better a7 selective tool than AR R17779 (Pichat et al., 2007). Separate groups of Sprague-dawley rats (n = 7) were treated (s.c.) with either saline, (−)nicotine (0.4 mg/kg) or SSR180711 (3 mg/kg), once daily for over 80 days, 7-days week. Immediately after drug administration animals were placed in locomotor activity cages for 36 minutes and activity levels (distance, m) monitored. All data was analysed by ANOVA followed relevant post hoc tests. Within 2 weeks a sensitised locomotor response to (−)nicotine developed (day 1: 89±15; day 14: 230±15), whereas activity levels in the vehicle and SSR180711 groups remained similar on day 1 (93±9 and 81±14, respectively) to day 14 (112±11 and 100±7, respectively). The sensitised locomotor response to (−)nicotine remained stable for over 80 days, over which time no significant change in locomotor response in vehicle or SSR180711 groups occurred. From day 21 cross-sensitisation dose-response curves were conducted in all three groups using a randomised within subject design whereby all animals in all groups were treated with vehicle and various doses of each drug. Cross-sensitisation test days were on Tuesdays/Fridays, with animals continuing to receive their chronic drug treatment on intervening days.
S556
P.6.d Addiction – Drugs (basic)
A dose-related sensitised response to (−)nicotine (0.1–0.4 mg/kg) in chronic (−)nicotine treated rats occurred, whereas (−)nicotine had no effect in chronic vehicle or SSR180711 treated rats. Conversely, SSR180711 (0.03−3 mg/kg) had little effect in rats treated chronically with (−)nicotine or saline. However, in chronic SSR180711 treated rats, SSR180711 itself significantly and dose-dependently (0.03−1 mg/kg) increased motility. SSR180711, a novel a7 selective agonist does not induce locomotor sensitisation per se and does not engender a sensitised locomotor response in animals sensitised to (−)nicotine. References [1] Grottick et al, 2000, JPET 294, 1112–1119. [2] Markou Paterson, 2001, Nicotine Tobacco Res 3, 361–373. [3] Pichat et al, 2007, Neuropharmacology 32, 17−34.
P.6.d.008 Cannabinoid CB1 receptor modulation of the acute and semichronic effects of MDMA in locomotor activity in mice
activity (42%; p < 0.05) and locomotion (49%; p < 0.01) without effects in corner time respect control group. In this case, WIN 55,212−2 did not change the increase ecstasy-induced effects on horizontal activity, peripheral activity, rearing activity, corner time and locomotion. However, the CB1 cannabinoid antagonist AM251 block completely the horizontal activity, peripheral activity, rearing activity and locomotion increased after ectasy semichronic administration but had no effect on the corner time. Overall, our findings suggest that the administration of CB1 agonist/antagonist differentially modulates the locomotor effcts of MDMA in a time-dependent manner. Thus, the endocannabinoid seems to mediate, at least in part, the locomotor effects of MDMA. Jos´e-M. Oliva is a recipient of a Post-Doctoral Fellowship from the Spanish Ministry of Education
P.6.d.009 A novel approach to assess drug-induced aversion to ethanol
P. Svenningsson. Karolinska Institute, Department J.M. Physiology and Pharmacology, Stockholm, Sweden
O. Dravolina ° , I. Sukhotina, E. Zvartau, A. Bespalov. Pavlov Medical University, Institute of Pharmacology, St. Petersburg, Russia
The hyperactivity induced by 3,4-methylenedioxymethamphetamine (MDMA; “ecstasy”) is characterized by increased forward locomotion in the periphery of the chamber and decreased investigatory behaviors, e.g., hole-pokes and rearing activity and elicitation of the serotonin (5-HT; 5-hydroxytryptamine) syndrome are also observed after MDMA administration. Both the 5-HT and dopamine (DA) systems may mediate hyperactivity induced by MDMA. First, MDMA evokes the release of DA as well as 5-HT in vivo. Second, the pattern of behavior evoked by MDMA is more similar to that induced by substituted amphetamines that enhance 5-HT, but not DA, release than to that evoked by amphetamine, which is predominantly a DA releaser. The aim of this study was to examine the role of CB1 cannabinoid receptor in the acute (1 day) and semichronic (5 days) effects of ectasy in locomotor activity. To this purpose, we administer the CB1 cannabinoid agonist WIN 55212,2 (0.5 mg/kg; p.o.) or the CB1 cannabinoid antagonist AM251 (2 mg/kg; p.o.) 45 minutes prior MDMA (3 mg/kg; p.o.). Thus, we had the following groups (n = 8−10): (1) control group, (2) MDMA group, (3) WIN 55212,2 group, (4) WIN 55212,2 + MDMA group, (5) AM251 group and (6) AM251 + MDMA group. After 1 hour, we studied the locomotor activity in the open-field during 2 hours. In our study we measure different parameters related to locomotor activity as horizontal activity, peripheral activity, rearing activity, corner time and locomotion. Statistical analyses was carried out using the ANOVA followed by the Student Newman-Keul’s test. The acute administration of MDMA (3 mg/kg) induced a significant increase in horizontal activity (48%; p < 0.01), rearing activity (42%; p < 0.05) and locomotion (85%; p < 0.001) and a decrease in corner time (45%; p < 0.001) respect control group. No differences were found in peripheral activity. The administration of WIN 55212,2 prior a single administration of MDMA decreased the effects seen by ecstasy in horizontal activity, rearing activity and locomotion, meanwhile the administration of AM251 had no effects on horizontal activity, rearing activity, corner time or locomotion but decreased the peripheral activity (28%; p < 0.01). After a semichronic administration period (5 days), MDMA also increased the horizontal activity (39%; p < 0.01), rearing
One of currently approved drugs for the treatment of alcohol dependence, disulfiram (tetraethylthiuram disulfide), non-specifically inhibits aldehyde dehydrogenase (ALDH2−1) by reacting with sulphhydryl groups in the enzyme and acts as an alcohol-deterrent drug. Current perspectives on clinical use of disulfiram are mixed; it is a second-line medication compared with other drugs, and is probably most effective in reducing alcohol consumption when used in a supervised setting (Brewer, 1993). However, introduction of depot forms of disulfiram may revive interest in this type of therapy and this necessitates the development of experimental methods to evaluate efficacy of disulfiram preparations. The aim of this study was to develop an experimental paradigm in which the malaise of drug-ethanol reaction is quickly recognized by rats as derived from ethanol. For this purpose, several experiments were conducted using a variant of the conditioned taste aversion paradigm based on the gustatory long-term memory established after association of the taste of food (conditioned stimulus, CS) with visceral signals of poisoning (unconditioned stimulus, US). The conditioned taste aversion is an acquired adaptive reaction preventing animals from repeated ingestion of a novel tastant, which has induced illness (Garcia and Ervin, 1968). After the acquisition of conditioned taste aversion in a single conditioning trial, the gustatory CS becomes hedonically aversive as indicated by reduced ingestive and increased aversive taste reactivity in response to re-exposures to the CS. Experimentally naive male Wistar rats (200–250 g) were used. As a preliminary, we defined: (1) the dose of disulfiram that made animals to cease consuming alcohol, indicating that the ethanol-disulfiram reaction was associated with alcohol ingestion; (2) the highest dose of ethanol that did not cause the acquisition of conditioned taste aversion. For subsequent experiments, separate groups of rats were pretreated by disulfiram (200 mg/kg, subcutaneously) or vehicle (0.5% methylcellulose) 24 h before the acquisition of conditioned taste aversion. During the acquisition of conditioned taste aversion, rats were allowed to eat food pellets (Formula F, Noyes Precision Pellets, Research Diets, Inc., New Brunswick, NJ) for 30 min, and immediately after that each animal received an intraperitoneal injection of ethanol (0.56 g/kg, 15% v/v in sterile water) or vehicle.
Oliva ° ,