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P.2.007 Pergolide attenuates memory impairment and oxidative stress in a 6-hydroxydopamine model of Parkinson's disease
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Behavioural pharmacology
choice behaviour remained stable throughout cocaine self-administration and extinction. Over all ten weeks of self-administration and extinction Cronbach’s alpha of the indifference points was 0.90. Although transient changes occurred within low impulsive individuals, these changes were gradually restored over time. Moreover, these transient changes in impulsive choice, were not predictive of any addiction-like behaviour. Discussion: This study shows that, similar to our observations with nicotine [2], impulsive decision making is a strong predictor of prolonged cocaine seeking during extinction and enhanced vulnerability to cue-induced relapse. Although cocaine intake did induce transient changes in impulsive choice, this was not predictive of cocaine taking or seeking. It is important to note here, that the predictive value of trait and not state impulsivity has also been observed for impulsive actions and cocaine intake [1]. This leaves us with the question whether or not pharmacological reduction of impulsive decision making would be a promising approach to reduce relapse vulnerability. Reference(s) [1] Dalley, J.W., Fryer, T.D., Brichard, L., Robinson, E.S., Theobald, D.E., Laane, K., Pena, Y., Murphy, E.R., Shah, Y., Probst, K., Abakumova, I., Aigbirhio, F.I., Richards, H.K., Hong, Y., Baron, J.C., Everitt, B.J., Robbins, T.W., 2007. Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science 315, 1267–1270. [2] Diergaarde, L., Pattij, T., Poortvliet, I., Hogenboom, F., De Vries, W., Schoffelmeer, A.N., De Vries, T.J., 2008. Impulsive choice and impulsive action predict vulnerability to distinct stages of nicotine seeking in rats. Biological Psychiatry 63, 301–308. P.2.007 Pergolide attenuates memory impairment and oxidative stress in a 6-hydroxydopamine model of Parkinson’s disease A. Ciobica1 ° , L. Hritcu2 , V. Artenie2 , W. Bild3 , 1 Romanian Academy, Laboratory for M. Padurariu3 . Experimental and Applied Physiology, Iasi, Romania; 2 Alexandru Ioan Cuza University, of Biology, Iasi, Romania; 3 Gr.T. Popa University, Medicine, Iasi, Romania Background: Parkinson’s disease (PD) is a human neurodegenerative disorder which is mainly characterized by a massive and progressive degeneration of the dopaminergic neurons in the substantia nigra (SN). As a result, one of the most widely used animal models of PD involve injecting of 6-OHDA directly into the SN, in
order to induce selective neurodegeneration of dopamine nerve terminals [1]. We previously demonstrated that 6-OHDA-induced lesion of SN results in memory deficits and increase brain oxidative stress [2]. Some authors speculated that dopaminergic drugs may exert brain antioxidant activity which could explain some of their protective actions [3]. The aim of the present study was to examine the effects of pergolide, a mixed D1/D2 agonist, on behavioral deficits and brain oxidative stress induced by 6-OHDA in a rat model of PD. Material and Methods: 30 male Wistar rats weighing 200–250 g at the start of the experiment were used. Specific right-unilateral lesions of the dopaminergic neurons located in the SN were produced with 6-OHDA (Sigma). 8 mg 6-OHDA, dissolved in 4 ml physiological saline containing 0.1% ascorbic acid were administrated through Hamilton syringe. The following coordinates were used: 5.5 mm posterior to bregma; 2.0 mm lateral to the midline; 7.4 mm ventral to the surface of the cortex. Two weeks after operation, all surviving animals showing no evident neurological abnormalities were admitted to drug treatment. Pergolide was dissolved in saline and injected intraperitoneally at the dose of 0.3 mg/kg/day for consecutive 10 days. Control animals received an injection of saline alone with the same procedure. Radial 8-arm maze and Y maze tasks were used for memory assessment. We also assessed the levels of some enzymatic antioxidant defences like superoxide dismutase (SOD) and glutathione peroxidase (GPX), as well as lipid oxidation makers like MDA (malondialdehyde), from the temporal lobe, using chemiluminometric and spectrophotometric methods. Results: Administration of pergolide resulted in a significant facilitation of short-term memory, explored by Y-maze task, as indicated by a increase of spontaneous alternation percentage (F(1,2) = 3.44, p < 0.05). This effect could not be attributed to increased motor activity, since the number of arm entries was not significantly changed (F(1,2) = 0.23; p>0.05). Also, pergolide induced a significant decrease in the number of working (F(2,7) = 3.52, P < 0.05) and reference memory (F(2,7) = 25.74, P < 0.0003) errors, explored in the radial arm maze, suggesting significant positive effects on spatial memory. At the biochemical level, we observed an increase in the specific activity of superoxide dismutase (p < 0.001) and glutathione peroxidase (p < 0.002), in temporal lobe of pergolide-treated rats, compared to control group. Moreover, Pearson’s correlation coefficient and regression analysis revealed a significant positive correlation between spontaneous alternation in Y maze and SOD specific activity (n = 30, r = 0.898, p = 10−9 ).
Behavioural pharmacology Conclusions: Taken together, our data suggest that pergolide (0.3 mg/kg/day) may counteract both behavioral and biochemical changes induced by 6-OHDA in a rat model of PD. Our study also suggests that these positive behavioral responses could be correlated with some antioxidant actions of pergolide. This could be useful for future investigations and clinical applications of dopaminergic drugs. Reference(s) [1] Hefco V., Yamada K., Hefco A., Hritcu L., Tiron A., Nabeshima T., 2003 Role of the mesotelencephalic dopamine system in learning and memory processes in the rat. Eur. J. Pharmacol. 475, 55−60. [2] Hritcu L, Ciobica A, Artenie V., 2008 Effects of right-unilateral 6-hydroxydopamine infusion-induced memory impairment and oxidative stress: relevance for Parkinson’s disease. Central European Journal of Biology 3, 250–257. [3] Micale V, Incognito T, Ignoto A, Rampello L, Spart`a M, Drago F., 2006 Dopaminergic drugs may counteract behavioral and biochemical changes induced by models of brain injury. Eur Neuropsychopharmacol. 16 195–203. Disclosure statement: This research was supported by the National Council of Scientific Research and University Education (Grant TD CNCSIS no. 464), Romania. P.2.008 Duration over time of learned placebo analgesic responses L. Colloca1 ° , F. Benedetti1 . 1 University of Turin, Department of Neuroscience, Turin, Italy In the last few years, there has been an increased emphasis on learning as modulator factor of placebo effects. The main reason for this is the awareness that a previous direct experience of benefit via pharmacological or biologically-significant cue exposure powerfully change behavior and clinical outcomes [1−3]. In fact, conditioning approaches used in many placebo studies, have provided strong evidence that placebo responses that are obtained via conditioning are more robust than those induced by verbal suggestions alone. A direction for future research is to determine the number of conditioning trials that is necessary to obtain placebo responses and to ensure their resistance to extinction. Here we test the effects of two sessions of conditioning (72 trials) on placebo modulation of repetitive painful stimuli (144 trials) delivered on the dorsum of the foot. Placebo procedure consisted in a simulation of a painkiller and was obtained by pairing green light to a series
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of stimuli that were made analgesic by lowering the intensity of stimulation surprisingly. Subjects were told that the activation of ankle’s electrodes (actually sham electrodes) respectively, induced analgesia. A red light was associated with a series of control painful stimuli. Eighteen subjects (5M; age 36±13 years) received two sessions of conditioning and 4 sessions of testing, whereby all the stimuli were delivered at the same intensity. Before the experimental session started, subjects were asked to rate in percentage, how much they expected that the treatment would work. In all the experimental conditions, at the end of each stimulation, pain intensity was assessed by means of Numerical Rating Scale (NRS), ranging from 0=no pain to 10=maximum imaginable pain. Within-subjects repeated ANOVAs were used to assess the effects of treatment (levels 2) and time (18 trials). The main effects of treatment were tested for each session (conditioning 1, 2 and testing sessions 1−4). The F-tests were followed by simple contrasts and the Bonferroni post-hoc tests for multiple comparisons. Spearman correlations were calculated between size of placebo responses and level of expectancy. After two sessions of conditioning, we observed strong placebo analgesic responses to painful stimulation (session 1, p < 0.001; session 2, p < 0.001; session 3, p < 0.01; session 4, p < 0.001). Interestingly, these effects did extinct over time. No significant correlations were found between the magnitude of placebo responses and subject’s expectations, thus suggesting that direct experience of effectiveness (via conditioning) is able to change and to “drive” subjects expectations. These findings contribute to increase our knowledge about the role of learning in creating placebo responses. Overall, from this research emerges that learning, via classical conditioning, powerfully shapes clinical and behavior outcomes. From a clinical perspective, it is plausible thinking that learning via prior exposure to effective treatments and repetitive reinforcements, may represent one of the most promising strategy to harness placebo responses in the clinical routine. Thus, understanding how to enhance placebo responses could have an important positive impact on scientific knowledge and health care. Reference(s) [1] Colloca, L., Benedetti, F., 2005 Placebo and painkillers: is mind as real as matter? Nature Rev Neurosci, 6(7): 245−52. [2] Colloca, L., Benedetti, F., 2006 How prior experience shapes placebo analgesia. Pain, 124(1−2):126−33. [3] Colloca, L., Tinazzi, M., Recchia, S., Le Pera, D., Fiaschi, A., Benedetti, F., Valeriani, M., 2008 Learning potentiates neurophysiological and behavioral placebo analgesic responses. Pain, 139(2):306−14.
Behavioural pharmacology
choice behaviour remained stable throughout cocaine self-administration and extinction. Over all ten weeks of self-administration and extinction Cronbach’s alpha of the indifference points was 0.90. Although transient changes occurred within low impulsive individuals, these changes were gradually restored over time. Moreover, these transient changes in impulsive choice, were not predictive of any addiction-like behaviour. Discussion: This study shows that, similar to our observations with nicotine [2], impulsive decision making is a strong predictor of prolonged cocaine seeking during extinction and enhanced vulnerability to cue-induced relapse. Although cocaine intake did induce transient changes in impulsive choice, this was not predictive of cocaine taking or seeking. It is important to note here, that the predictive value of trait and not state impulsivity has also been observed for impulsive actions and cocaine intake [1]. This leaves us with the question whether or not pharmacological reduction of impulsive decision making would be a promising approach to reduce relapse vulnerability. Reference(s) [1] Dalley, J.W., Fryer, T.D., Brichard, L., Robinson, E.S., Theobald, D.E., Laane, K., Pena, Y., Murphy, E.R., Shah, Y., Probst, K., Abakumova, I., Aigbirhio, F.I., Richards, H.K., Hong, Y., Baron, J.C., Everitt, B.J., Robbins, T.W., 2007. Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science 315, 1267–1270. [2] Diergaarde, L., Pattij, T., Poortvliet, I., Hogenboom, F., De Vries, W., Schoffelmeer, A.N., De Vries, T.J., 2008. Impulsive choice and impulsive action predict vulnerability to distinct stages of nicotine seeking in rats. Biological Psychiatry 63, 301–308. P.2.007 Pergolide attenuates memory impairment and oxidative stress in a 6-hydroxydopamine model of Parkinson’s disease A. Ciobica1 ° , L. Hritcu2 , V. Artenie2 , W. Bild3 , 1 Romanian Academy, Laboratory for M. Padurariu3 . Experimental and Applied Physiology, Iasi, Romania; 2 Alexandru Ioan Cuza University, of Biology, Iasi, Romania; 3 Gr.T. Popa University, Medicine, Iasi, Romania Background: Parkinson’s disease (PD) is a human neurodegenerative disorder which is mainly characterized by a massive and progressive degeneration of the dopaminergic neurons in the substantia nigra (SN). As a result, one of the most widely used animal models of PD involve injecting of 6-OHDA directly into the SN, in
order to induce selective neurodegeneration of dopamine nerve terminals [1]. We previously demonstrated that 6-OHDA-induced lesion of SN results in memory deficits and increase brain oxidative stress [2]. Some authors speculated that dopaminergic drugs may exert brain antioxidant activity which could explain some of their protective actions [3]. The aim of the present study was to examine the effects of pergolide, a mixed D1/D2 agonist, on behavioral deficits and brain oxidative stress induced by 6-OHDA in a rat model of PD. Material and Methods: 30 male Wistar rats weighing 200–250 g at the start of the experiment were used. Specific right-unilateral lesions of the dopaminergic neurons located in the SN were produced with 6-OHDA (Sigma). 8 mg 6-OHDA, dissolved in 4 ml physiological saline containing 0.1% ascorbic acid were administrated through Hamilton syringe. The following coordinates were used: 5.5 mm posterior to bregma; 2.0 mm lateral to the midline; 7.4 mm ventral to the surface of the cortex. Two weeks after operation, all surviving animals showing no evident neurological abnormalities were admitted to drug treatment. Pergolide was dissolved in saline and injected intraperitoneally at the dose of 0.3 mg/kg/day for consecutive 10 days. Control animals received an injection of saline alone with the same procedure. Radial 8-arm maze and Y maze tasks were used for memory assessment. We also assessed the levels of some enzymatic antioxidant defences like superoxide dismutase (SOD) and glutathione peroxidase (GPX), as well as lipid oxidation makers like MDA (malondialdehyde), from the temporal lobe, using chemiluminometric and spectrophotometric methods. Results: Administration of pergolide resulted in a significant facilitation of short-term memory, explored by Y-maze task, as indicated by a increase of spontaneous alternation percentage (F(1,2) = 3.44, p < 0.05). This effect could not be attributed to increased motor activity, since the number of arm entries was not significantly changed (F(1,2) = 0.23; p>0.05). Also, pergolide induced a significant decrease in the number of working (F(2,7) = 3.52, P < 0.05) and reference memory (F(2,7) = 25.74, P < 0.0003) errors, explored in the radial arm maze, suggesting significant positive effects on spatial memory. At the biochemical level, we observed an increase in the specific activity of superoxide dismutase (p < 0.001) and glutathione peroxidase (p < 0.002), in temporal lobe of pergolide-treated rats, compared to control group. Moreover, Pearson’s correlation coefficient and regression analysis revealed a significant positive correlation between spontaneous alternation in Y maze and SOD specific activity (n = 30, r = 0.898, p = 10−9 ).
Behavioural pharmacology Conclusions: Taken together, our data suggest that pergolide (0.3 mg/kg/day) may counteract both behavioral and biochemical changes induced by 6-OHDA in a rat model of PD. Our study also suggests that these positive behavioral responses could be correlated with some antioxidant actions of pergolide. This could be useful for future investigations and clinical applications of dopaminergic drugs. Reference(s) [1] Hefco V., Yamada K., Hefco A., Hritcu L., Tiron A., Nabeshima T., 2003 Role of the mesotelencephalic dopamine system in learning and memory processes in the rat. Eur. J. Pharmacol. 475, 55−60. [2] Hritcu L, Ciobica A, Artenie V., 2008 Effects of right-unilateral 6-hydroxydopamine infusion-induced memory impairment and oxidative stress: relevance for Parkinson’s disease. Central European Journal of Biology 3, 250–257. [3] Micale V, Incognito T, Ignoto A, Rampello L, Spart`a M, Drago F., 2006 Dopaminergic drugs may counteract behavioral and biochemical changes induced by models of brain injury. Eur Neuropsychopharmacol. 16 195–203. Disclosure statement: This research was supported by the National Council of Scientific Research and University Education (Grant TD CNCSIS no. 464), Romania. P.2.008 Duration over time of learned placebo analgesic responses L. Colloca1 ° , F. Benedetti1 . 1 University of Turin, Department of Neuroscience, Turin, Italy In the last few years, there has been an increased emphasis on learning as modulator factor of placebo effects. The main reason for this is the awareness that a previous direct experience of benefit via pharmacological or biologically-significant cue exposure powerfully change behavior and clinical outcomes [1−3]. In fact, conditioning approaches used in many placebo studies, have provided strong evidence that placebo responses that are obtained via conditioning are more robust than those induced by verbal suggestions alone. A direction for future research is to determine the number of conditioning trials that is necessary to obtain placebo responses and to ensure their resistance to extinction. Here we test the effects of two sessions of conditioning (72 trials) on placebo modulation of repetitive painful stimuli (144 trials) delivered on the dorsum of the foot. Placebo procedure consisted in a simulation of a painkiller and was obtained by pairing green light to a series
S35
of stimuli that were made analgesic by lowering the intensity of stimulation surprisingly. Subjects were told that the activation of ankle’s electrodes (actually sham electrodes) respectively, induced analgesia. A red light was associated with a series of control painful stimuli. Eighteen subjects (5M; age 36±13 years) received two sessions of conditioning and 4 sessions of testing, whereby all the stimuli were delivered at the same intensity. Before the experimental session started, subjects were asked to rate in percentage, how much they expected that the treatment would work. In all the experimental conditions, at the end of each stimulation, pain intensity was assessed by means of Numerical Rating Scale (NRS), ranging from 0=no pain to 10=maximum imaginable pain. Within-subjects repeated ANOVAs were used to assess the effects of treatment (levels 2) and time (18 trials). The main effects of treatment were tested for each session (conditioning 1, 2 and testing sessions 1−4). The F-tests were followed by simple contrasts and the Bonferroni post-hoc tests for multiple comparisons. Spearman correlations were calculated between size of placebo responses and level of expectancy. After two sessions of conditioning, we observed strong placebo analgesic responses to painful stimulation (session 1, p < 0.001; session 2, p < 0.001; session 3, p < 0.01; session 4, p < 0.001). Interestingly, these effects did extinct over time. No significant correlations were found between the magnitude of placebo responses and subject’s expectations, thus suggesting that direct experience of effectiveness (via conditioning) is able to change and to “drive” subjects expectations. These findings contribute to increase our knowledge about the role of learning in creating placebo responses. Overall, from this research emerges that learning, via classical conditioning, powerfully shapes clinical and behavior outcomes. From a clinical perspective, it is plausible thinking that learning via prior exposure to effective treatments and repetitive reinforcements, may represent one of the most promising strategy to harness placebo responses in the clinical routine. Thus, understanding how to enhance placebo responses could have an important positive impact on scientific knowledge and health care. Reference(s) [1] Colloca, L., Benedetti, F., 2005 Placebo and painkillers: is mind as real as matter? Nature Rev Neurosci, 6(7): 245−52. [2] Colloca, L., Benedetti, F., 2006 How prior experience shapes placebo analgesia. Pain, 124(1−2):126−33. [3] Colloca, L., Tinazzi, M., Recchia, S., Le Pera, D., Fiaschi, A., Benedetti, F., Valeriani, M., 2008 Learning potentiates neurophysiological and behavioral placebo analgesic responses. Pain, 139(2):306−14.