Looming Effects on Attentional Modulation of Prepulse Inhibition Paradigm

In a hazardous environment, it is fundamentally important to successfully evaluate the motion of sounds. Previous studies demonstrated “auditory looming bias” in both macaques and humans, as looming sounds that increased in intensity were processed preferentially by the brain. In this study on rats, we used a prepulse inhibition (PPI) of the acoustic startle response paradigm to investigate whether auditory looming sound with intrinsic warning value could draw attention of the animals and dampen the startle reflex caused by the startling noise. We showed looming sound with a duration of 120 ms enhanced PPI compared with receding sound with the same duration; however, when both sound types were at shorter duration/higher change rate (i.e., 30 ms) or longer duration/lower rate (i.e., more than 160 ms), there was no PPI difference. This indicates that looming sound–induced PPI enhancement was duration dependent. We further showed that isolation rearing impaired the abilities of animals to differentiate looming and receding prepulse stimuli, although it did not abolish their discrimination between looming and stationary prepulse stimuli. This suggests that isolation rearing compromised their assessment of potential threats from approaching objects and receding objects.

Epigenetic-mediated N-methyl-D-aspartate receptor changes in the brain of isolated reared rats

Aim: We investigated: Grin1, Grin2a, Grin2b DNA methylation; NR1 and NR2 mRNA/protein in the prefrontal cortex (PFC); and hippocampus of male Wistar rats exposed to isolation rearing. Materials & methods: Animals were kept isolated or grouped (n = 10/group) from weaning for 10 weeks. Tissues were dissected for RNA/DNA extraction and N-methyl-D-aspartate receptor subunits were analyzed using quantitative reverse transcription (RT)-PCR, ELISA and pyrosequencing. Results: Isolated-reared animals had: decreased mRNA in PFC for all markers, increased NR1 protein in hippocampus and hypermethylation of Grin1 in PFC and Grin2b in hippocampus, compared with grouped rats. Associations between mRNA/protein and DNA methylation were found for both brain areas. Conclusion: This study indicates that epigenetic DNA methylation may underlie N-methyl-D-aspartate receptor mRNA/protein expression alterations caused by isolation rearing.

M9. RATS REARED IN SOCIAL ISOLATION INDUCES EPIGENETIC MODIFICATIONS IN THE NMDA RECEPTOR SUBUNITS

Background Early-life stress is a key risk for psychiatric disorders that may produce changes in the neurodevelopment. N-methyl-d-aspartate receptor (NMDAR) have been associated with the pathophysiology of schizophrenia and evidence supports that epigenetic changes in NMDAR imply deficiencies in excitatory neurotransmission suggest its role in the neurobiology of psychoses (Uno and Coyle, 2019; Fachim et al., 2019; Gulchina et al., 2017). Aims: Although previous studies have shown abnormalities in the glutamatergic system in animal model of schizophrenia, it is not known if there are equivalent mRNA/protein alterations and DNA methylation changes in the brains of rats reared in isolation. Thus, in order to improve the knowledge of glutamatergic system role in psychosis, we investigated the NR1 and NR2 mRNA/protein and the DNA methylation levels of Grin1, Grin2a and Grin2b promoter region in the prefrontal cortex (PFC) and hippocampus (HIPPO) of male Wistar rats after isolation rearing. Furthermore, because the Parvalbumin (PV) deficit is the most consistent finding across animal models and schizophrenia itself, we also evaluated the expression of PV and other related GABAergic genes (REL and GAD1) in the brain of rats undergoing social isolation rearing as a validation of this animal model. We hypothesized that isolation rearing reduces mRNA and protein expressions of NMDAR subunits and cause DNA methylation changes. Methods Wistar rats were kept isolated or grouped (n=10/group) from weaning (21 days after birth) to 10 weeks and then exposed to the Open Field Test to assess locomotion. Afterwards the behavioural tests, the tissues were dissected for RNA/DNA extraction and NMDAR subunits were analysed using qRT-PCR, ELISA and pyrosequencing. Data were analysed by parametric tests. Results Isolated-reared animals presented: (i) decreased mRNA levels of Grin1 (p=0.011), Grin2a (p=0.039) and Grin2b (p=0.037) in the PFC followed by reduction in the GABAergic markers; (ii) increased NR1 protein levels in the HIPPO (p=0.001); (iii) hypermethylation of Grin1 at CpG5 in the PFC (p=0.047) and Grin2b CpG4 in the HIPPO when compared to grouped (p=0.024). Moreover, isolated and grouped animals presented a negative correlation between Grin1 mRNA and Grin1 methylation levels at CpG5 in the PFC (r: -0.577; p=0.010) and isolated rats presented a negative correlation between Grin2b methylation at CpG4 and NR2 protein levels in the HIPPO (r: -0.753; p=0.012). Discussion This study supports the hypothesis that the NMDAR methylation changes found in the brain tissues may underlie the NMDAR mRNA/protein expression alterations caused by the isolation period. These results highlighted the importance of the environmental influence during the development that may lead to cognitive impairments in adulthood. Moreover, we demonstrated that the social isolation rearing during 10 weeks causes long-lasting behavioral changes that may be more associated with late stages of schizophrenia. Our study contributes to the identification of the epigenetic mechanisms involved in the neuropathophysiology of schizophrenia, which can bring new pharmacotherapeutic strategies and to identify biomarkers that can improve the early interventions in schizophrenia patients. Finally, our data thus reinforce the validity of rats reared in social isolation after weaning in modelling aspects of schizophrenia, highlighting the glutamatergic and GABAergic features involved principally in the cognitive impairments related to prefrontal cortex.

T191. FRONTO-CORTICAL ROLES OF NIGELLA SATIVA IN SOCIALLY ISOLATED MICE

Background Schizophrenia is a chronic debilitating mental disorder, modelled developmentally in animals by social isolation rearing (SIR). This study investigated the roles of Nigella sativa, a multi-therapeutic plant oil, on the fronto-cortical functions and alterations in socially isolated BALB/c mice. Methods Body weights, relative brain weights, dopamine, glutamate and GPX levels, as well as recognition memory were measured in 75 albino pups of 10 weeks age. These pups were divided into CTRL,NS,SIR, SIR NS and NS SIR. CTRL (socialised) and SIR (isolated) received 10ml/kg normal saline orally for 10 days, while the NS-SIR, NS and SIR-NS received 1ml/kg Nigella sativa oil orally for 10 days either prophylactically (prenatal exposure), alone without isolation, or interventionally respectively. Recognition memory was assayed through novel object recognition test and the animals were euthanized. Brains were excised for histological examination of the frontal Cortex using the H&E stain. Results Significant increase (p<0.05) in fronto-cortical glutamate, dopamine, and glutathione peroxidase (GPX), as well as recognition memory index, relative brain weight and total body weights were recorded in the isolated mice that were pre-treated and post-treated with Nigella sativa, compared with the untreated ones. However, no significant neuroarchitectural difference was observed histologically across the frontal cortices of the mice. Discussion Nigella sativa was significantly prophylactic and ameliorative of the neurochemical and neurobehavioural schizotypic deficits induced in socially isolated BALB/c mice. This was revealed by glutamate, dopamine, GPX, recognition index and relative brain weight values of the pretreated and post-treated mice. Use of dendritic and Nissl markers are recommended for better histological appreciation

Social isolation improves the performance of rodents in a novel cognitive flexibility task

Background Social isolation, i.e., the deprivation of social contact, is a highly stressful circumstance that affects behavioral and functional brain development in social animals. Cognitive flexibility, one of the essential executive brain function that facilitates survival problem solving, was reported to be impaired after social isolation rearing. However, most of the previous studies have focused on the constrained aspect of flexibility and little is known about the unconstrained aspect. In the present study, the unconstrained cognitive flexibility of Kunming mice (Mus musculus, Km) reared in isolation was examined by a novel digging task. The exploratory behavior of the mice was also tested utilizing the hole-board and elevated plus maze tests to explain the differences in cognitive flexibility between the mice reared socially and in isolation. Results The results demonstrated that the isolated mice had a higher success rate in solving the novel digging problem and showed a higher rate of exploratory behavior compared with the controls. Linear regression analysis revealed that the time it took the mice to solve the digging problem was negatively associated with exploratory behavior. Conclusions The data suggest that social isolation rearing improves unconstrained cognitive flexibility in mice, which is probably related to an increase in their exploratory behavior. Such effects may reflect the behavioral and cognitive evolutionary adaptations of rodents to survive under complex and stressful conditions.