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P.1.d.002 The effect of chlordiazepoxide on reward reduction-induced decrease of operant performance
P.1.d Basic and clinical neuroscience – Animal models Technologies, West Warwick, RI, U.S.A) was used for amplification (about 2000 times) and initial filtration (0.1 – 100 Hz). The resulting signal was digitized (100 Hz), filtered (low-pass filter set at 10 Hz), stored and analyzed by using PowerLab/8SP system (ADInstruments, Oxfordshire, UK). The baseline EEG recordings were made for 15 min and then animals received respective drugs. Lamotrigine (10−30 mg/kg, i.p.) did not affect seizures-induced by pilocarpine. Topiramate significantly enhanced convulsive and neurodegenerative action of pilocarpine in mice and rats lowering the convulsant CD50 values (50% effective convulsant dose) of pilocarpine from 376.0 (361.5–391.1) to 228.5 (207.7–251.3) mg/kg and from 350.8 (329.2–373.8) to 254.6 mg/kg, respectively. Riluzole (1−4 mg/kg, i.p.) administered before pilocarpine dosedependently protected rats against seizures, status epilepticus and neurodegeneration with the anticonvulsant ED50 value (50% effective anticonvulsant dose) of 2.0 (1.57−2.53) mg/kg. In contrast, riluzole (8−12 mg/kg, i.p.) administered after the onset of pilocarpine-induced seizures affected neither status epilepticus nor mortality of rats. Because of growing number of clinical indications for the use of topiramate, the mechanism of its proconvulsant activity in pilocarpine-induced model of epilepsy deserves further investigation.
P.1.d Basic and clinical neuroscience – Animal models P.1.d.001 A selective mglu1 receptor antagonist, jnj16259685, suppresses isolation-induced aggression in male mice V. De Castro1 ° , M.M. Martin-Lopez1 , J.F. Navarro-Humanes1 . 1 University of Malaga, Department of Psychobiology, M´ alaga, Spain Glutamate plays a critical role as excitatory neurotransmitter in the central nervous system. It acts at several types of receptors, including ionotropic (cation-specific ion channels divided into three groups: NMDA, AMPA and kainate receptors) and metabotropic receptors (mGlu), which are members of the wider G-proteincoupled receptor family. Glutamate is involved in the modulation of aggression in laboratory animals. However, the implication of mGlu receptors in aggression is scarcely known. In a recent study, Navarro et al. [1] found that the acute administration of MPEP, a selective antagonist of mGlu5 receptors, reduces offensive behaviours (threat and attack) in male mice, suggesting a role for these receptors in aggression regulation. mGlu1 receptors are present in brain regions involved in aggression modulation, like the central periaquaductal gray, amygdala or lateral septum. So far, no studies have examined the functional role of mGlu1 antagonists in animal models of aggression. Therefore, the aim of this study was to analyze the effects of JNJ16259685 (0.125, 0.25, 0.5, 1, 2, 4 and 8 mg/kg, ip), a selective antagonist of the mGlu1 receptors, on agonistic interactions between male mice of the OF.1 strain. Individually housed mice were exposed to anosmic “standard opponents” 30 min after drug administration. Ten min of diadic interactions were staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped and the accumulated time allocated by subjects to ten broad behavioural categories was estimated using an ethologically based analysis. The categories and their constituent elements were as follows: (i) body care (including groom, self-groom, wash, shake,
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scratch); (ii) digging (dig, kick dig, push dig); (iii) non-social exploration (explore, rear, supported rear, scan); (iv) exploration from a distance (approach, attend, circle, head orient, streched attention); (v) social investigation (crawl over, crawl under, follow, groom, head groom, investigate, nose sniff, sniff, push past, walk around); (vi) threat (aggressive groom, sideways offensive, upright offensive, tail rattle); (vii) attack (charge, lunge, attack, chase); (viii) avoidance/flee (evade, flinch, retreat, ricochet, wheel, startle, jump, leave, wall, clutch); (ix) defence/submission (upright defensive, upright submissive, sideways defensive), and (x) immobility (squat, cringe). This ethoexperimental procedure allows a complete quantification of the behavioural elements shown by the subject during the agonistic encounters. Non-parametric KruskalWallis tests were used to assess the variance of the behavioural measures in the different treatment groups. Subsequently, appropriate paired comparisons were carried out using Mann–Whitney U-tests to contrast behaviours in different treatment groups. JNJ16259685 (all doses) produced a significant reduction of offensive behaviours (threat and attack), without affecting immobility. The reduction of aggressive behaviours after treatment with JNJ16259685 was accompanied by a marked increase in nonsocial exploration behaviours as well as a decrease in digging behaviours. JNJ16259685 is a selective mGlu1 receptor antagonist with excellent potencies in inhibiting mGlu1 receptor function and binding and in occupying the mGlu1 receptor after systemic administration [2]. In conclusion, this is the first demonstration that an antagonist of mGlu1 receptors decreases aggressive behaviours (threat and attack) in mice. These findings suggest a role for mGlu1 receptors in the regulation of aggression. References [1] Navarro, J.F., Postigo, D., Mart´ın-L´opez, M., Bur´on, E., 2006. Antiaggressive effects of MPEP, a selective antagonist of mGlu5 receptor, in agonistic interactions between male mice. Eur. J. Pharmacol. 551, 67−70. [2] Lavreysen, H., Wouters, R., Bischoff, F., N´obrega, S., Langlois, X., Blockland, S., et al., 2004 JNJ16259685, a highly potent, selective and systemically active mGlu1 receptor antagonist. Neuropharmacology 47, 961–972.
P.1.d.002 The effect of chlordiazepoxide on reward reduction-induced decrease of operant performance A. Nikiforuk1 ° , P. Popik1 . 1 Polish Academy of Sciences, Department of Drug Development, Krakow, Poland Successive negative contrast (SNC) is a phenomenon, in which animals maintained on a high reward and unexpectedly offered a low reward exhibit a decrease in performance below the level displayed by the animals maintained on the low reward only [1]. The reduction of reward produces the emotional response (described as a frustration or a disappointment) that can be prevented by the administration of anxiolytic benzodiazepines. According to the methodology used and behavioral output, SNC may be differentiated into the consummatory (cSNC) and instrumental (iSNC). Although it is well known that the reduction of sucrose reward from 32% to 4% produces cSNC, the iSNC does not occur under these conditions as investigated in the runway or the operant conditioning tasks [2]. The purpose of the present study was to obtain iSNC following shift in sucrose solution in lever-pressing task under fixed ratio
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P.1.d Basic and clinical neuroscience – Animal models
(FR-5) and progressive ratio (PR) schedule of reinforcement in rats. Although existing data demonstrate that iSNC under FR-5 schedule is not possible to achieve, there is no information about that phenomenon under PR schedule. Moreover, the influence of chlordiazepoxide (CDP) on reward reduction-induced decrease in operant responding was also examined under both schedules of reinforcement. In experiment 1 male Sprague-Dawley rats responded under FR-5 schedule for 32% sucrose for 5 days and then were shifted to 4% sucrose solution for the next 5 days (shifted group). The performance of a control group was reinforced with 4% sucrose for all 10 days (unshifted group). In experiment 2, the performance of the shifted and unshifted groups was assessed under PR schedule of reinforcement according to the same experimental scheme. In experiment 3, the shifted group of rats received intraperitoneal injection of CDP (0, 2, 4 or 8 mg/kg) 60 min before test session, during the five shifted days under FR-5 and/or PR schedule. In FR-5 and PR schedules, the dependent variables were the number of lever presses and the break point, defined as the last ratio completed prior to the cessation of responding, respectively. An area under curve (AUC) data were calculated for the pre- and down-shift phases of experiments. The effect of CDP on rats’ performance during shifted conditions was evaluated by one-way ANOVA, followed by Dunnett’s post hoc test. The reduction in sucrose concentration from 32% to 4% produced a decrease in performance of rats under FR-5 and PR schedule, but only to the level of the unshifted group reinforced with 4% sucrose throughout the whole experiment. CDP did not affect the performance of shifted group of rats under FR-5 schedule, but prevented the reward reduction-induced decrement in responding under PR (F(3,24) = 12.34, p < 0.0001). This effect seems to be specific since there was no influence of CDP on performance of unshifted group. The present study demonstrated that despite of the lack of a distinct SNC effect, the reward reduction-induced decrement in operant responding may be modulated by CDP. The effectiveness of CDP during incentive reward reduction appears to be restricted to PR schedule of reinforcement. References [1] Flaherty, C.F., 1996. Incentive relativity. New York: Cambridge University Press. [2] Sastre, A., Lin, J-Y., Reilly, S., 2005. Failure to obtain instrumental successive negative contrast in tasks that support consummatory successive negative contrast. International Journal of Comparative Psychology 18, 307–319
P.1.d.003 Effects of early maternal separation during the development on the behavioral change in the forced swimming test in rats Y. Chung1 ° , S.H. Park1 , Y.M. Lee1 , B.D. Lee1 . 1 Pusan National University, Department of Psychiatry, Busan, South-Korea Objective: Early maternal separation during the development has been known to influence the alteration of behavior and neurochemical function in adulthood. There is increasing evidence that genetic and early environmental factors interact to disturb the normal development of brain. Nitric oxide (NO) may have been implicated to play a crucial role in the neurodevelopment as an intracellular and intercellular messenger in the brain glutamatergic N-methyl-D-aspartate (NMDA) pathway. The dysfunction of the glutamatergic NMDA – NO pathway may be involved in the
developmental pathophysiology of a variety of mental disorders. This study was designed to investigate the effects of early maternal separation on the behavioral change in the forced swim test in adult rats. It was also aimed to elucidate the implication of glutamatergic NMDA – NO pathway for the behavioral effects of early maternal separation in the forced swim test. Methods: Pregnant female Sprague-Dawley rats were observed for delivery (postnatal day 0). Subjects that were derived from the litters were divided into two groups. Experimental group (n = 48) consisted of subjects that were removed and weaned from the dams on postnatal day 15. Control group (n = 48) were the litters that experienced no maternal separation until postnatal day 21. The experimental and control groups were randomly divided into four subgroups, respectively. On postnatal day 35, baseline locomotor activity was measured using computrerized automatic analysis program (Neurovision Analysis, Department of Computing Engineering, Pusan National University, Korea). On the same day, the forced swimming test (FST) was carried out. The behavioral change in the FST was measured during the 5-minute retest 24 hour following the initial 15-minute swimming exposure. Test drugs including NMDA receptor antagonist MK-801 (0.5 mg/kg), nitric oxide synthase inhibitor Nw-nitro-L-arginine (L-NA, 20 mg/kg), and antidepressant paroxetine (20 mg/kg) and bupropion (150 mg/kg) were intraperitoneally administered respectively, I hour after the initial swimming exposure and I hour before the second swimming exposure. Results: The locomotor activity was significantly decreased in experimental group compared with control group (p < 0.05). The baseline immobility in the FST was significantly increased in experimental group compared with control group (p < 0.05). When test drugs were administered prior to the FST respectively, every drug decreased immobility significantly in experimental group (p < 0.01) as well as in control group (p < 0.05). The extent of decrease in immobility was greater in experimental group than in control group (p < 0.05). Conclusions: These results indicate that early maternal separation during the development can lead to behavioral abnormalities in adulthood. The underlying neurochemical mechanism of this behavioral effect of early maternal separation may be, in part, related to the glutamatergic NMDA – NO system. This suggests that glutamatergic NMDA – NO system may lead to a novel approach to the research and treatment of depression in that the behavioral change in the FST detects a wide range of antidepressant treatment. References [1] Padovan, C.M., Guimar˜aes, F.S. 2004. Antidepressant-like effects of NMDA-receptor antagonist injected into the dorsal hippocampus of rats. Pharmacol Biochem Behav 77:15−19. [2] Inan, S.Y., Yalcin, I., Aksu, F. 2004. Dual effects of nitric oxide in the mouse forced swimming test: possible contribution of nitric oxide mediated serotonin release and potassium channel modulation. Pharmacol Biochem Behav 77:457–464. [3] Joca, S.R.L., Guimar˜aes, F.S. 2006. Inhibition of neuronal nitric oxide synthase in the rat hippocampus induces antidepressant-like effects. Psychopharmacology 185:298–305.
P.1.d Basic and clinical neuroscience – Animal models P.1.d.001 A selective mglu1 receptor antagonist, jnj16259685, suppresses isolation-induced aggression in male mice V. De Castro1 ° , M.M. Martin-Lopez1 , J.F. Navarro-Humanes1 . 1 University of Malaga, Department of Psychobiology, M´ alaga, Spain Glutamate plays a critical role as excitatory neurotransmitter in the central nervous system. It acts at several types of receptors, including ionotropic (cation-specific ion channels divided into three groups: NMDA, AMPA and kainate receptors) and metabotropic receptors (mGlu), which are members of the wider G-proteincoupled receptor family. Glutamate is involved in the modulation of aggression in laboratory animals. However, the implication of mGlu receptors in aggression is scarcely known. In a recent study, Navarro et al. [1] found that the acute administration of MPEP, a selective antagonist of mGlu5 receptors, reduces offensive behaviours (threat and attack) in male mice, suggesting a role for these receptors in aggression regulation. mGlu1 receptors are present in brain regions involved in aggression modulation, like the central periaquaductal gray, amygdala or lateral septum. So far, no studies have examined the functional role of mGlu1 antagonists in animal models of aggression. Therefore, the aim of this study was to analyze the effects of JNJ16259685 (0.125, 0.25, 0.5, 1, 2, 4 and 8 mg/kg, ip), a selective antagonist of the mGlu1 receptors, on agonistic interactions between male mice of the OF.1 strain. Individually housed mice were exposed to anosmic “standard opponents” 30 min after drug administration. Ten min of diadic interactions were staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped and the accumulated time allocated by subjects to ten broad behavioural categories was estimated using an ethologically based analysis. The categories and their constituent elements were as follows: (i) body care (including groom, self-groom, wash, shake,
S249
scratch); (ii) digging (dig, kick dig, push dig); (iii) non-social exploration (explore, rear, supported rear, scan); (iv) exploration from a distance (approach, attend, circle, head orient, streched attention); (v) social investigation (crawl over, crawl under, follow, groom, head groom, investigate, nose sniff, sniff, push past, walk around); (vi) threat (aggressive groom, sideways offensive, upright offensive, tail rattle); (vii) attack (charge, lunge, attack, chase); (viii) avoidance/flee (evade, flinch, retreat, ricochet, wheel, startle, jump, leave, wall, clutch); (ix) defence/submission (upright defensive, upright submissive, sideways defensive), and (x) immobility (squat, cringe). This ethoexperimental procedure allows a complete quantification of the behavioural elements shown by the subject during the agonistic encounters. Non-parametric KruskalWallis tests were used to assess the variance of the behavioural measures in the different treatment groups. Subsequently, appropriate paired comparisons were carried out using Mann–Whitney U-tests to contrast behaviours in different treatment groups. JNJ16259685 (all doses) produced a significant reduction of offensive behaviours (threat and attack), without affecting immobility. The reduction of aggressive behaviours after treatment with JNJ16259685 was accompanied by a marked increase in nonsocial exploration behaviours as well as a decrease in digging behaviours. JNJ16259685 is a selective mGlu1 receptor antagonist with excellent potencies in inhibiting mGlu1 receptor function and binding and in occupying the mGlu1 receptor after systemic administration [2]. In conclusion, this is the first demonstration that an antagonist of mGlu1 receptors decreases aggressive behaviours (threat and attack) in mice. These findings suggest a role for mGlu1 receptors in the regulation of aggression. References [1] Navarro, J.F., Postigo, D., Mart´ın-L´opez, M., Bur´on, E., 2006. Antiaggressive effects of MPEP, a selective antagonist of mGlu5 receptor, in agonistic interactions between male mice. Eur. J. Pharmacol. 551, 67−70. [2] Lavreysen, H., Wouters, R., Bischoff, F., N´obrega, S., Langlois, X., Blockland, S., et al., 2004 JNJ16259685, a highly potent, selective and systemically active mGlu1 receptor antagonist. Neuropharmacology 47, 961–972.
P.1.d.002 The effect of chlordiazepoxide on reward reduction-induced decrease of operant performance A. Nikiforuk1 ° , P. Popik1 . 1 Polish Academy of Sciences, Department of Drug Development, Krakow, Poland Successive negative contrast (SNC) is a phenomenon, in which animals maintained on a high reward and unexpectedly offered a low reward exhibit a decrease in performance below the level displayed by the animals maintained on the low reward only [1]. The reduction of reward produces the emotional response (described as a frustration or a disappointment) that can be prevented by the administration of anxiolytic benzodiazepines. According to the methodology used and behavioral output, SNC may be differentiated into the consummatory (cSNC) and instrumental (iSNC). Although it is well known that the reduction of sucrose reward from 32% to 4% produces cSNC, the iSNC does not occur under these conditions as investigated in the runway or the operant conditioning tasks [2]. The purpose of the present study was to obtain iSNC following shift in sucrose solution in lever-pressing task under fixed ratio
S250
P.1.d Basic and clinical neuroscience – Animal models
(FR-5) and progressive ratio (PR) schedule of reinforcement in rats. Although existing data demonstrate that iSNC under FR-5 schedule is not possible to achieve, there is no information about that phenomenon under PR schedule. Moreover, the influence of chlordiazepoxide (CDP) on reward reduction-induced decrease in operant responding was also examined under both schedules of reinforcement. In experiment 1 male Sprague-Dawley rats responded under FR-5 schedule for 32% sucrose for 5 days and then were shifted to 4% sucrose solution for the next 5 days (shifted group). The performance of a control group was reinforced with 4% sucrose for all 10 days (unshifted group). In experiment 2, the performance of the shifted and unshifted groups was assessed under PR schedule of reinforcement according to the same experimental scheme. In experiment 3, the shifted group of rats received intraperitoneal injection of CDP (0, 2, 4 or 8 mg/kg) 60 min before test session, during the five shifted days under FR-5 and/or PR schedule. In FR-5 and PR schedules, the dependent variables were the number of lever presses and the break point, defined as the last ratio completed prior to the cessation of responding, respectively. An area under curve (AUC) data were calculated for the pre- and down-shift phases of experiments. The effect of CDP on rats’ performance during shifted conditions was evaluated by one-way ANOVA, followed by Dunnett’s post hoc test. The reduction in sucrose concentration from 32% to 4% produced a decrease in performance of rats under FR-5 and PR schedule, but only to the level of the unshifted group reinforced with 4% sucrose throughout the whole experiment. CDP did not affect the performance of shifted group of rats under FR-5 schedule, but prevented the reward reduction-induced decrement in responding under PR (F(3,24) = 12.34, p < 0.0001). This effect seems to be specific since there was no influence of CDP on performance of unshifted group. The present study demonstrated that despite of the lack of a distinct SNC effect, the reward reduction-induced decrement in operant responding may be modulated by CDP. The effectiveness of CDP during incentive reward reduction appears to be restricted to PR schedule of reinforcement. References [1] Flaherty, C.F., 1996. Incentive relativity. New York: Cambridge University Press. [2] Sastre, A., Lin, J-Y., Reilly, S., 2005. Failure to obtain instrumental successive negative contrast in tasks that support consummatory successive negative contrast. International Journal of Comparative Psychology 18, 307–319
P.1.d.003 Effects of early maternal separation during the development on the behavioral change in the forced swimming test in rats Y. Chung1 ° , S.H. Park1 , Y.M. Lee1 , B.D. Lee1 . 1 Pusan National University, Department of Psychiatry, Busan, South-Korea Objective: Early maternal separation during the development has been known to influence the alteration of behavior and neurochemical function in adulthood. There is increasing evidence that genetic and early environmental factors interact to disturb the normal development of brain. Nitric oxide (NO) may have been implicated to play a crucial role in the neurodevelopment as an intracellular and intercellular messenger in the brain glutamatergic N-methyl-D-aspartate (NMDA) pathway. The dysfunction of the glutamatergic NMDA – NO pathway may be involved in the
developmental pathophysiology of a variety of mental disorders. This study was designed to investigate the effects of early maternal separation on the behavioral change in the forced swim test in adult rats. It was also aimed to elucidate the implication of glutamatergic NMDA – NO pathway for the behavioral effects of early maternal separation in the forced swim test. Methods: Pregnant female Sprague-Dawley rats were observed for delivery (postnatal day 0). Subjects that were derived from the litters were divided into two groups. Experimental group (n = 48) consisted of subjects that were removed and weaned from the dams on postnatal day 15. Control group (n = 48) were the litters that experienced no maternal separation until postnatal day 21. The experimental and control groups were randomly divided into four subgroups, respectively. On postnatal day 35, baseline locomotor activity was measured using computrerized automatic analysis program (Neurovision Analysis, Department of Computing Engineering, Pusan National University, Korea). On the same day, the forced swimming test (FST) was carried out. The behavioral change in the FST was measured during the 5-minute retest 24 hour following the initial 15-minute swimming exposure. Test drugs including NMDA receptor antagonist MK-801 (0.5 mg/kg), nitric oxide synthase inhibitor Nw-nitro-L-arginine (L-NA, 20 mg/kg), and antidepressant paroxetine (20 mg/kg) and bupropion (150 mg/kg) were intraperitoneally administered respectively, I hour after the initial swimming exposure and I hour before the second swimming exposure. Results: The locomotor activity was significantly decreased in experimental group compared with control group (p < 0.05). The baseline immobility in the FST was significantly increased in experimental group compared with control group (p < 0.05). When test drugs were administered prior to the FST respectively, every drug decreased immobility significantly in experimental group (p < 0.01) as well as in control group (p < 0.05). The extent of decrease in immobility was greater in experimental group than in control group (p < 0.05). Conclusions: These results indicate that early maternal separation during the development can lead to behavioral abnormalities in adulthood. The underlying neurochemical mechanism of this behavioral effect of early maternal separation may be, in part, related to the glutamatergic NMDA – NO system. This suggests that glutamatergic NMDA – NO system may lead to a novel approach to the research and treatment of depression in that the behavioral change in the FST detects a wide range of antidepressant treatment. References [1] Padovan, C.M., Guimar˜aes, F.S. 2004. Antidepressant-like effects of NMDA-receptor antagonist injected into the dorsal hippocampus of rats. Pharmacol Biochem Behav 77:15−19. [2] Inan, S.Y., Yalcin, I., Aksu, F. 2004. Dual effects of nitric oxide in the mouse forced swimming test: possible contribution of nitric oxide mediated serotonin release and potassium channel modulation. Pharmacol Biochem Behav 77:457–464. [3] Joca, S.R.L., Guimar˜aes, F.S. 2006. Inhibition of neuronal nitric oxide synthase in the rat hippocampus induces antidepressant-like effects. Psychopharmacology 185:298–305.