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Poster #M12 REWARD DEFICITS IN THE MATERNAL IMMUNE ACTIVATION MODEL
Abstracts of the 4th Biennial Schizophrenia International Research Conference / Schizophrenia Research 153, Supplement 1 (2014) S1–S384
locomotor activity and prepulse inhibition were investigated at PN60. Their frontal cortices at PN7 (1 h after injection), PN8, PN21, PN42, and PN60 were examined to investigate the long-term effects on the molecules in signal pathway of protein translation. Results: At PN60, the rats treated with MK-801 at PN7 showed psychotomimetic behaviors, including increased locomotor activity and deficits in prepulse inhibition. Accompanied with the behavioral changes, the phosphorylation level of S6 at S240/244, which promotes protein translation initiation, was increased, and the phosphorylation of raptor at S792, which inhibits the activity of mTOR signal pathway, was reduced in the rat frontal cortex at PN60. The phosphorylation level of S6 in neonatal MK-801-treated group was significantly lower at 1h after injection, higher at PN8, PN21, PN42, PN60 in the rat frontal cortex compared to the vehicle-treated group. Discussion: Neonatal MK-801 treatment induced acute reduction followed by increase in the phosphorylation of ribosomal S6 protein through developmental process with the long-term psychotomimetic behavioral changes in adult rats. These findings could suggest an important role of aberrant long-term activation of protein translation machinery in the MK-801 neurodevelopmental animal model of schizophrenia.
Poster #M12 REWARD DEFICITS IN THE MATERNAL IMMUNE ACTIVATION MODEL Marie A. Labouesse, Wolfgang Langhans, Urs Meyer Physiology and Behavior Laboratory, ETH Zurich Background: Prenatal maternal infection is an environmental risk factor of schizophrenia and disease-associated behavioral abnormalities. Modeling this epidemiological link in animals shows that maternal immune activation is capable of inducing long-term deficits in numerous behavioral and cognitive domains. However, whether maternal immune activation causes deficits in central reward processing thus far remains unknown. Exploring this issue seems highly warranted because impaired reward processing is a core symptom related to the negative symptoms of schizophrenia. Methods: Pregnant C57BL6/N mice were treated with the synthetic viral mimetic poly(I:C) (5 mg/kg, i.v.) or control (saline, i.v.) solution on gestation day 17. All offspring were subjected to behavioral testing in adulthood (PND70-100) using a running alley paradigm to assess willingness to run for food reward, and a sucrose-driven conditioned place preference (CPP) paradigm. Poly(I:C) and control animals were further compared in conditioned active avoidance and contextual fear paradigms to evaluate their capacities for instrumental learning and context-dependent conditioning. Finally, brains were harvested for immunohistochemical analyses of brain markers of interest, which included dopamine receptors 1 (D1R) and 2 (D2R), tyrosine hydroxylase (TH), and dopamine transporter (DAT) in the nucleus accumbens (NAc) and caudate putamen (CPu). Results: We found that prenatal poly(I:C) treatment induced deficits in the running alley paradigm, in which the completion speed of poly(I:C) offspring was significantly lower over time as compared to control mice. Such deficits could not be explained by deficient instrumental learning per se because conditioned active avoidance performance was similar in poly(I:C) and control offspring. Hence, the poly(I:C)-induced deficit emerging in the running alley test likely represents a genuine impairment in the willingness to work for food reward. This impression was further confirmed by the CPP test, in which control mice significantly preferred the sucrose-paired (vs. water) chamber while poly(I:C) offspring spent an equal amount of time in both chambers. Such deficits are unlikely to be accounted for by abnormal contextual processing given that the performance of poly(I:C) offspring in contextual fear conditioning was fully intact. The reward-related behavioral manifestations were further accompanied by marked changes in the mesolimbic dopaminergic system, known to represent a major neural contributor to reward-related functions. Our data reveal that striatal DAT and TH levels were significantly decreased and increased, respectively, indicating the existence of an augmented dopaminergic tone at the presynapse. On the other hand, D1R and D2R were reduced in the CPu and NAc, suggesting reduced dopaminergic signaling at the post-synapse. Discussion: Our findings demonstrate for the first time that in-utero immune challenge results in the emergence of deficits in reward-related behaviors in mice, which are accompanied by abnormalities in several key dopaminergic markers of the mesolimbic system. Such data support the hypothesis that immune-mediated disruption of neurodevelopmental
S193
processes may contribute to the appearance of aberrant reward function. Our etiologically informed model suggests that prenatal immune abnormalities may be a causal environmental factor contributing to behavioral and dopaminergic abnormalities relevant especially to the negative symptoms of schizophrenia.
Poster #M13 CHARACTERIZATION OF A ‘TWO-HIT’ MOUSE MODEL OF METHAMPHETAMINE-INDUCED PSYCHOSIS: EFFECTS OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) DEFICIENCY AND RELEVANCE TO SCHIZOPHRENIA Elizabeth E. Manning 1,2 , Maarten van den Buuse 1 The Florey Institute of Neuroscience and Mental Health; 2 The University of Melbourne
1
Background: Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, including cognitive and negative symptoms. For this reason animal models of methamphetamine psychosis may aid our understanding of both schizophrenia and psychotic disorders more broadly. Brain-derived neurotrophic factor (BDNF) had been implicated in the pathophysiology of schizophrenia and also the neuronal response to stimulant drugs. However the role of BDNF in METH-induced psychopathology remains unclear. Methods: We developed a “two hit” animal model where BDNF heterozygous mice (HETs) and wild-type (WT) littermates were treated with METH during young adulthood, from 6-9 weeks of age, using an escalating dosing protocol (Manning & van den Buuse, Front Cell Neurosci 2013). Following a two-week break, mice were tested in adulthood in behavioural paradigms relevant to schizophrenia. Specifically, we used amphetamine-induced locomotor hyperactivity as a model of psychosis and prepulse inhibition (PPI) and its disruption by an amphetamine challenge (5mg/kg) as a model of sensorimotor gating deficits in schizophrenia. Social interaction was assessed in a 3-chamber paradigm and short-term spatial memory was assessed in a Y-maze task. There were 8-14 animals per genotype/pretreatment group and data were analyzed using repeated-measures ANOVA. Results: The effects of young-adult METH treatment were altered in BDNF HETs in a task-dependent and sex-specific manner. As expected, in response to a challenge dose of amphetamine (3mg/kg) in adulthood, METH-treated WT mice showed locomotor sensitization compared to control WT mice. However, this increased hyperactive response following METH pre-treatment was absent in BDNF HETs. This genotype effect was observed in both male and female mice. BDNF deficiency and METH treatment had sex-specific and independent effects on the disruption of PPI by amphetamine. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. In addition, male, but not female BDNF HETs were more sensitive than WT to the effects of amphetamine on PPI, again irrespective of prior METH treatment. In contrast, in female mice, but not male mice, treatment with METH reduced sensitivity to the effects of an acute amphetamine challenge, irrespective of the genotype. There were no differences between the groups in terms of general sociability, measured by interaction time with a “stranger” mouse compared to that with an empty cup. However, in the subsequent social novelty preference phase of the test, male BDNF HETs treated with METH showed no preference to interact with a “novel stranger” mouse over a “familiar stranger” mouse. All other METH treated mice showed normal social novelty preference. Neither genotype nor METH treatment affected short term spatial memory. Discussion: These studies demonstrate that young-adult METH treatment can induce behavioural changes that are relevant to the symptoms observed in schizophrenia, and that BDNF HETs show an altered response to this treatment in some behavioural paradigms. Several sex differences were also observed in these studies, which may help to provide insight into the sex differences observed in schizophrenia. Ongoing molecular studies will aim to utilize this “two hit” model to address the question of how disruption of BDNF signalling alters the brain’s vulnerability to develop schizophrenia.
locomotor activity and prepulse inhibition were investigated at PN60. Their frontal cortices at PN7 (1 h after injection), PN8, PN21, PN42, and PN60 were examined to investigate the long-term effects on the molecules in signal pathway of protein translation. Results: At PN60, the rats treated with MK-801 at PN7 showed psychotomimetic behaviors, including increased locomotor activity and deficits in prepulse inhibition. Accompanied with the behavioral changes, the phosphorylation level of S6 at S240/244, which promotes protein translation initiation, was increased, and the phosphorylation of raptor at S792, which inhibits the activity of mTOR signal pathway, was reduced in the rat frontal cortex at PN60. The phosphorylation level of S6 in neonatal MK-801-treated group was significantly lower at 1h after injection, higher at PN8, PN21, PN42, PN60 in the rat frontal cortex compared to the vehicle-treated group. Discussion: Neonatal MK-801 treatment induced acute reduction followed by increase in the phosphorylation of ribosomal S6 protein through developmental process with the long-term psychotomimetic behavioral changes in adult rats. These findings could suggest an important role of aberrant long-term activation of protein translation machinery in the MK-801 neurodevelopmental animal model of schizophrenia.
Poster #M12 REWARD DEFICITS IN THE MATERNAL IMMUNE ACTIVATION MODEL Marie A. Labouesse, Wolfgang Langhans, Urs Meyer Physiology and Behavior Laboratory, ETH Zurich Background: Prenatal maternal infection is an environmental risk factor of schizophrenia and disease-associated behavioral abnormalities. Modeling this epidemiological link in animals shows that maternal immune activation is capable of inducing long-term deficits in numerous behavioral and cognitive domains. However, whether maternal immune activation causes deficits in central reward processing thus far remains unknown. Exploring this issue seems highly warranted because impaired reward processing is a core symptom related to the negative symptoms of schizophrenia. Methods: Pregnant C57BL6/N mice were treated with the synthetic viral mimetic poly(I:C) (5 mg/kg, i.v.) or control (saline, i.v.) solution on gestation day 17. All offspring were subjected to behavioral testing in adulthood (PND70-100) using a running alley paradigm to assess willingness to run for food reward, and a sucrose-driven conditioned place preference (CPP) paradigm. Poly(I:C) and control animals were further compared in conditioned active avoidance and contextual fear paradigms to evaluate their capacities for instrumental learning and context-dependent conditioning. Finally, brains were harvested for immunohistochemical analyses of brain markers of interest, which included dopamine receptors 1 (D1R) and 2 (D2R), tyrosine hydroxylase (TH), and dopamine transporter (DAT) in the nucleus accumbens (NAc) and caudate putamen (CPu). Results: We found that prenatal poly(I:C) treatment induced deficits in the running alley paradigm, in which the completion speed of poly(I:C) offspring was significantly lower over time as compared to control mice. Such deficits could not be explained by deficient instrumental learning per se because conditioned active avoidance performance was similar in poly(I:C) and control offspring. Hence, the poly(I:C)-induced deficit emerging in the running alley test likely represents a genuine impairment in the willingness to work for food reward. This impression was further confirmed by the CPP test, in which control mice significantly preferred the sucrose-paired (vs. water) chamber while poly(I:C) offspring spent an equal amount of time in both chambers. Such deficits are unlikely to be accounted for by abnormal contextual processing given that the performance of poly(I:C) offspring in contextual fear conditioning was fully intact. The reward-related behavioral manifestations were further accompanied by marked changes in the mesolimbic dopaminergic system, known to represent a major neural contributor to reward-related functions. Our data reveal that striatal DAT and TH levels were significantly decreased and increased, respectively, indicating the existence of an augmented dopaminergic tone at the presynapse. On the other hand, D1R and D2R were reduced in the CPu and NAc, suggesting reduced dopaminergic signaling at the post-synapse. Discussion: Our findings demonstrate for the first time that in-utero immune challenge results in the emergence of deficits in reward-related behaviors in mice, which are accompanied by abnormalities in several key dopaminergic markers of the mesolimbic system. Such data support the hypothesis that immune-mediated disruption of neurodevelopmental
S193
processes may contribute to the appearance of aberrant reward function. Our etiologically informed model suggests that prenatal immune abnormalities may be a causal environmental factor contributing to behavioral and dopaminergic abnormalities relevant especially to the negative symptoms of schizophrenia.
Poster #M13 CHARACTERIZATION OF A ‘TWO-HIT’ MOUSE MODEL OF METHAMPHETAMINE-INDUCED PSYCHOSIS: EFFECTS OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF) DEFICIENCY AND RELEVANCE TO SCHIZOPHRENIA Elizabeth E. Manning 1,2 , Maarten van den Buuse 1 The Florey Institute of Neuroscience and Mental Health; 2 The University of Melbourne
1
Background: Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, including cognitive and negative symptoms. For this reason animal models of methamphetamine psychosis may aid our understanding of both schizophrenia and psychotic disorders more broadly. Brain-derived neurotrophic factor (BDNF) had been implicated in the pathophysiology of schizophrenia and also the neuronal response to stimulant drugs. However the role of BDNF in METH-induced psychopathology remains unclear. Methods: We developed a “two hit” animal model where BDNF heterozygous mice (HETs) and wild-type (WT) littermates were treated with METH during young adulthood, from 6-9 weeks of age, using an escalating dosing protocol (Manning & van den Buuse, Front Cell Neurosci 2013). Following a two-week break, mice were tested in adulthood in behavioural paradigms relevant to schizophrenia. Specifically, we used amphetamine-induced locomotor hyperactivity as a model of psychosis and prepulse inhibition (PPI) and its disruption by an amphetamine challenge (5mg/kg) as a model of sensorimotor gating deficits in schizophrenia. Social interaction was assessed in a 3-chamber paradigm and short-term spatial memory was assessed in a Y-maze task. There were 8-14 animals per genotype/pretreatment group and data were analyzed using repeated-measures ANOVA. Results: The effects of young-adult METH treatment were altered in BDNF HETs in a task-dependent and sex-specific manner. As expected, in response to a challenge dose of amphetamine (3mg/kg) in adulthood, METH-treated WT mice showed locomotor sensitization compared to control WT mice. However, this increased hyperactive response following METH pre-treatment was absent in BDNF HETs. This genotype effect was observed in both male and female mice. BDNF deficiency and METH treatment had sex-specific and independent effects on the disruption of PPI by amphetamine. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. In addition, male, but not female BDNF HETs were more sensitive than WT to the effects of amphetamine on PPI, again irrespective of prior METH treatment. In contrast, in female mice, but not male mice, treatment with METH reduced sensitivity to the effects of an acute amphetamine challenge, irrespective of the genotype. There were no differences between the groups in terms of general sociability, measured by interaction time with a “stranger” mouse compared to that with an empty cup. However, in the subsequent social novelty preference phase of the test, male BDNF HETs treated with METH showed no preference to interact with a “novel stranger” mouse over a “familiar stranger” mouse. All other METH treated mice showed normal social novelty preference. Neither genotype nor METH treatment affected short term spatial memory. Discussion: These studies demonstrate that young-adult METH treatment can induce behavioural changes that are relevant to the symptoms observed in schizophrenia, and that BDNF HETs show an altered response to this treatment in some behavioural paradigms. Several sex differences were also observed in these studies, which may help to provide insight into the sex differences observed in schizophrenia. Ongoing molecular studies will aim to utilize this “two hit” model to address the question of how disruption of BDNF signalling alters the brain’s vulnerability to develop schizophrenia.