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P.1.12 Response to chronic social stress in the rat depends on persistent differences in sucrose consumption
Poster sessions periods of its development. Prenatal manipulations with neutotransmitter activity by means of administration of nicotine or insectisides led to different structural and functional changes in the developing brain [2]. The purpose of the paper was to study the effects of selective M- and N-cholinoblockers administered in prenatal period on dynamics of development of neurotransmitter systems in the brain of 20th days embryos. Methods: Pregnant Wistar rats were injected thirdly with cholinergic drugs (M-cholinoblocker methamizil 2 mg/kg or N-cholinoblocker gangleron 12 mg/kg i.m. once a day) on 9−12, 12−14 and 17−19 days of gestation. On the 20th day of pregnancy the extraction and decapitation of embryos were produced (the brain without cerebellum was freezed in liquied nitrogen). The concentrations of dopamine (DA), 5-hydroxytriptamine (5-HT) and their metabolites were examined with HPLCED in the Beckman System Gold with electrochemical detector. In the other part of the experiment the delayed behavioral effects were assessed in adult rats of 3−4 months of age. Results: Prenatal exposure of pregnant rats with both cholinergic drugs (methamizil and gangleron) induced imbalance of DA, 5-HT and their metabolites contents in the 20th day embryo brain. The com-parative analysis revealed that 5-HT-ergic neurotransmitter system was more sensitive to cholinergic drugs in comparison with DAergic system. The reduced level of 5-HT and change of its turnover was registered within all second part of pregnancy after exposure with mathamizil and gangleron. The DA-ergic system of the embryo brain (both genotypic males and females) was more sensitive to exposure of Ncholinoblocker gangleron. The more significant changes of neurotransmitter status were obtained in early period of gestation (10 and 13 days) in embryos of different genetic gender. Prenatal exposure with methamizil did not effect on DA level in the embryo brain both in males and in females. The tendency of decreasing in DA content was revealed at the same time. Besides, the behavioral studies showed that the delayed disorders of sexual function were registered in adult off-springs. After 4 consequent tests on learning of sexual experience the persentage of naive rats after gangleron administration was 40−70%, and after methamizil administration was 20% versus 0% in control group (nontreated with cholinoblockers). Conclusion: Therefore, prenatal exposure of pregnant rats with cholinergic drugs in early ontogeny induces imbalance in neurotransmitter systems of the 20th day embryo brain. The data suggested that the change of cholinergic neuronal activity in prenatal period with cholinergic drugs can lead to disturbance of sexual differentiation in neonatal period and behavioral disorders
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in pubertate age. At this time the sexual experience depended preferably on N-cholinergic mechanisms. Reference(s) [1] Bairamov, A.A., Sapronov, N.S., 2004 Effect of dehydroepiandrosterone on radioligand binding of [3H]-testosterone by androgen receptors in rat hypothalamus. Bull. Exp. Biol. Med., 138(4), 387– 389. [2] Bairamov, A.A., Efremov, O.M., Senchik, K.J., Losev, N.A., Sapronov, N.S., 2005 Cholinergic modulation of sexual behavior after stress: Neurochemical correlations. Eur. J. Neuropsychopharmacol., 15(Suppl.2), 176–177. P.1.12 Response to chronic social stress in the rat depends on persistent differences in sucrose consumption M. Kanarik1 ° , K. K˜oiv1 , D. Matrov1 , J. Harro1 . 1 University of Tartu, Department of Psychology, Tartu, Estonia The majority of stressors in human everyday life are of social nature; therefore social stress could be a valuable method to model stress on rodents. Chronic social defeat with resident-intruder paradigm is an ecologically valid method to evoke depressive-like and anxious behaviour in rodents [1]. In this model an intruder rat is placed into the home-cage of a resident, who will in defence of its territory attack and defeat the intruder. Consumption of sucrose solution is considered the standard measure of anhedonia inflicted by chronic stress, the reduction in sucrose intake interpreted as inability to experience positive reward. There is a large individual variation in sucrose consumption and it has been shown to be a stable parameter that can be regarded as a trait [2]. The aim of the current study was to determine whether chronic social stress influences rats with persistently high and low sucrose consumption differently. Group-housed Wistar rats (n = 24) were submitted 18 times to social defeat sessions lasting one hour each. Apomorphine (1 mg/kg), a nonspecific dopamine agonist, was used to induce aggressive behaviour in residents [3]. Sucrose consumption was measured for 12 hours during the dark period in a twobottle test (water and 1% sucrose solution). Animals had free access to water and food at all time. Groups with high and low sucrose intake were formed by a median split on the basis of the average of 3 baseline test results. After the stress regimen behaviour of animals was assessed with the Forced Swimming Test (FST) − the time spent struggling, swimming and immobile measured
S140
Poster sessions
for 5 minutes on 2 consecutive days; and the Social Interaction Test (SIT) − the time two strange, weightmatched rats spent in active social contact measured during a 10 minute session. Sucrose consumption was highly stable with the correlations between the baseline tests approximately 0.8. The effect of social stress was expressed most prominently in a large decrease in normal weight gain: −4.8 for stressed and +17.5 grams for control animals by the end of the stress regimen, and irrespective of the sucrose consumption trait. Stressed animals spent more time in active social contact than control animals in the SIT. This result was more robust, with a more than twofold difference, in the subgroup of rats with high sucrose intake. On the second day of the FST control rats spent more time struggling than stressed animals, this result appearing only in animals with high sucrose intake. Control rats also struggled more on the second day of the FST compared to the first day, and even this was the case only in animals with high sucrose consumption. It can be concluded that rats persistently consuming more sucrose are more reactive to chronic stress than rats with lesser sucrose intake, and that high sucrose intake in general may reflect more active coping patterns. Reference(s) [1] Miczek, K.A., Yap, J.J., Covington III, H.E., 2008. Social stress, therapeutics and drug abuse: Preclinical models of escalated and depressed intake. Pharmacology & Therapeutics 120, 102–128. [2] T˜onissaar, M., Herm, L., Rinken, A., Harro, J., 2006. Individual differences in sucrose intake and preference in the rat: Circadian variation and association with dopamine D2 receptor function in striatum and nucleus accumbens. Neuroscience Letters 403, 119–124. [3] Matto, V., Vaarmann, A., Allikmets, L., 2001. Apomorphine-induced aggressive behaviour in parachlorophenylalanine-treated male rats: implications to brain. Pharmacology and Toxicology 88, 147–151. P.1.13 Identification of clusters of co-regulated genes that may underlie the phenotypes of high and low exploring rats A. Alttoa1 ° , T.A. Hinsley2 , K. K˜oiv1 , J. Harro1 . University of Tartu, Department of Psychology, Tartu, Estonia; 2 University of Manchester, Department of Computer Science, Manchester, United Kingdom 1
Behaviour in novel environments is a function of conflicting motivations to explore unfamiliar surroundings (curiosity) and avoid potential danger (neophobia). Affective disorders are often accompanied by changes in
these motivational processes, thus, we have developed the exploration box test that allows separation of rats into groups of inherent and stable high anxiety/low motivation to explore and low anxiety/high motivation to explore (low explorers and high explorers, LE and HE, respectively). In addition to several neurochemical differences between the HE- and LE-rats − most notably in dopamine- and serotonergic systems − LE-rats display higher anxietylike behaviour and more passive coping strategies also in other behavioural tests related to depression and anxiety, as compared to the HE-animals [1]. We have previously conducted a genome-wide microarray analysis on Illumina platform to identify differentially expressed genes in three brain regions, previously known to be involved in mood disorders (i.e., raphe, hippocampus and the frontal cortex), that underlie the distinct behavioural phenotypes of HE- and LE-animals [2]. We found a number of genes involved in neurotransmission and synaptic plasticity to be differentially expressed in HE- vs. LE-rats [2]. It is possible that at least some of the changes in the expression of genes that determine the HE/LE phenotype involve epigenetic modifications. The present study is thus an extension of the previous work, and, using the REEF (REgionally Enriched Features) software [3], aims at identifying clusters of differentially expressed genes whose expression is potentially co-regulated via epigenetic mechanisms. The assumption for this analysis is that genes are not uniformly distributed, and functionally related features (or genes) tend to be clustered within the genome. Using a sliding window approach, the REEF program compares the density of specific and reference features within the genome and calculates the significance of regional enrichment in specific features observed in each window. We found 28 clusters of co-regulated genes among the transcripts that were upregulated in HE vs. LE; 2 clusters among the genes that were downregulated in HE vs. LE; and 14 additional clusters of co-expressed genes when both up- and downregulated genes in the HE vs. LE comparison were analyzed. To characterize the clustered genes we used the DAVID2008 Functional Annotation Tool to find significantly enriched Gene Ontology categories. The results suggest that the clusters were significantly enriched in genes involved in nucleic acid binding, translation factor activity, and cytoskeletal protein binding. When the clustered genes were mapped onto KEGG pathways, a significant over-representation of genes involved in the Wnt signalling pathway was found. Together with the results from the previous study [2] this finding strengthens the case for the importance of Wnt signalling in determining the divergence between the HEand LE-animals. In conclusion, we have identified several clusters of genes within the rat genome that may be responsible for the
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in pubertate age. At this time the sexual experience depended preferably on N-cholinergic mechanisms. Reference(s) [1] Bairamov, A.A., Sapronov, N.S., 2004 Effect of dehydroepiandrosterone on radioligand binding of [3H]-testosterone by androgen receptors in rat hypothalamus. Bull. Exp. Biol. Med., 138(4), 387– 389. [2] Bairamov, A.A., Efremov, O.M., Senchik, K.J., Losev, N.A., Sapronov, N.S., 2005 Cholinergic modulation of sexual behavior after stress: Neurochemical correlations. Eur. J. Neuropsychopharmacol., 15(Suppl.2), 176–177. P.1.12 Response to chronic social stress in the rat depends on persistent differences in sucrose consumption M. Kanarik1 ° , K. K˜oiv1 , D. Matrov1 , J. Harro1 . 1 University of Tartu, Department of Psychology, Tartu, Estonia The majority of stressors in human everyday life are of social nature; therefore social stress could be a valuable method to model stress on rodents. Chronic social defeat with resident-intruder paradigm is an ecologically valid method to evoke depressive-like and anxious behaviour in rodents [1]. In this model an intruder rat is placed into the home-cage of a resident, who will in defence of its territory attack and defeat the intruder. Consumption of sucrose solution is considered the standard measure of anhedonia inflicted by chronic stress, the reduction in sucrose intake interpreted as inability to experience positive reward. There is a large individual variation in sucrose consumption and it has been shown to be a stable parameter that can be regarded as a trait [2]. The aim of the current study was to determine whether chronic social stress influences rats with persistently high and low sucrose consumption differently. Group-housed Wistar rats (n = 24) were submitted 18 times to social defeat sessions lasting one hour each. Apomorphine (1 mg/kg), a nonspecific dopamine agonist, was used to induce aggressive behaviour in residents [3]. Sucrose consumption was measured for 12 hours during the dark period in a twobottle test (water and 1% sucrose solution). Animals had free access to water and food at all time. Groups with high and low sucrose intake were formed by a median split on the basis of the average of 3 baseline test results. After the stress regimen behaviour of animals was assessed with the Forced Swimming Test (FST) − the time spent struggling, swimming and immobile measured
S140
Poster sessions
for 5 minutes on 2 consecutive days; and the Social Interaction Test (SIT) − the time two strange, weightmatched rats spent in active social contact measured during a 10 minute session. Sucrose consumption was highly stable with the correlations between the baseline tests approximately 0.8. The effect of social stress was expressed most prominently in a large decrease in normal weight gain: −4.8 for stressed and +17.5 grams for control animals by the end of the stress regimen, and irrespective of the sucrose consumption trait. Stressed animals spent more time in active social contact than control animals in the SIT. This result was more robust, with a more than twofold difference, in the subgroup of rats with high sucrose intake. On the second day of the FST control rats spent more time struggling than stressed animals, this result appearing only in animals with high sucrose intake. Control rats also struggled more on the second day of the FST compared to the first day, and even this was the case only in animals with high sucrose consumption. It can be concluded that rats persistently consuming more sucrose are more reactive to chronic stress than rats with lesser sucrose intake, and that high sucrose intake in general may reflect more active coping patterns. Reference(s) [1] Miczek, K.A., Yap, J.J., Covington III, H.E., 2008. Social stress, therapeutics and drug abuse: Preclinical models of escalated and depressed intake. Pharmacology & Therapeutics 120, 102–128. [2] T˜onissaar, M., Herm, L., Rinken, A., Harro, J., 2006. Individual differences in sucrose intake and preference in the rat: Circadian variation and association with dopamine D2 receptor function in striatum and nucleus accumbens. Neuroscience Letters 403, 119–124. [3] Matto, V., Vaarmann, A., Allikmets, L., 2001. Apomorphine-induced aggressive behaviour in parachlorophenylalanine-treated male rats: implications to brain. Pharmacology and Toxicology 88, 147–151. P.1.13 Identification of clusters of co-regulated genes that may underlie the phenotypes of high and low exploring rats A. Alttoa1 ° , T.A. Hinsley2 , K. K˜oiv1 , J. Harro1 . University of Tartu, Department of Psychology, Tartu, Estonia; 2 University of Manchester, Department of Computer Science, Manchester, United Kingdom 1
Behaviour in novel environments is a function of conflicting motivations to explore unfamiliar surroundings (curiosity) and avoid potential danger (neophobia). Affective disorders are often accompanied by changes in
these motivational processes, thus, we have developed the exploration box test that allows separation of rats into groups of inherent and stable high anxiety/low motivation to explore and low anxiety/high motivation to explore (low explorers and high explorers, LE and HE, respectively). In addition to several neurochemical differences between the HE- and LE-rats − most notably in dopamine- and serotonergic systems − LE-rats display higher anxietylike behaviour and more passive coping strategies also in other behavioural tests related to depression and anxiety, as compared to the HE-animals [1]. We have previously conducted a genome-wide microarray analysis on Illumina platform to identify differentially expressed genes in three brain regions, previously known to be involved in mood disorders (i.e., raphe, hippocampus and the frontal cortex), that underlie the distinct behavioural phenotypes of HE- and LE-animals [2]. We found a number of genes involved in neurotransmission and synaptic plasticity to be differentially expressed in HE- vs. LE-rats [2]. It is possible that at least some of the changes in the expression of genes that determine the HE/LE phenotype involve epigenetic modifications. The present study is thus an extension of the previous work, and, using the REEF (REgionally Enriched Features) software [3], aims at identifying clusters of differentially expressed genes whose expression is potentially co-regulated via epigenetic mechanisms. The assumption for this analysis is that genes are not uniformly distributed, and functionally related features (or genes) tend to be clustered within the genome. Using a sliding window approach, the REEF program compares the density of specific and reference features within the genome and calculates the significance of regional enrichment in specific features observed in each window. We found 28 clusters of co-regulated genes among the transcripts that were upregulated in HE vs. LE; 2 clusters among the genes that were downregulated in HE vs. LE; and 14 additional clusters of co-expressed genes when both up- and downregulated genes in the HE vs. LE comparison were analyzed. To characterize the clustered genes we used the DAVID2008 Functional Annotation Tool to find significantly enriched Gene Ontology categories. The results suggest that the clusters were significantly enriched in genes involved in nucleic acid binding, translation factor activity, and cytoskeletal protein binding. When the clustered genes were mapped onto KEGG pathways, a significant over-representation of genes involved in the Wnt signalling pathway was found. Together with the results from the previous study [2] this finding strengthens the case for the importance of Wnt signalling in determining the divergence between the HEand LE-animals. In conclusion, we have identified several clusters of genes within the rat genome that may be responsible for the