Rachel Anne Hill

Working memory relies on synchronised network oscillations involving complex interplay between pyramidal cells and GABAergic interneurons. NMDA receptor (NMDAR) antagonists influence both network oscillations and working memory, but the relationship between these two consequences has not been elucidated. This study aimed to determine the effect of NMDAR antagonists on network oscillations during a working memory task in mice, and the contribution of the GluN2D receptor subunit. After training wildtype (WT) and GluN2D-knockout (KO) mice on the Trial-Unique-Non-match to Location (TUNL) touchscreen task of working memory, recording electrodes were implanted into the prefrontal cortex (PFC) and hippocampus. Mice were challenged with either (S)-ketamine (30 mg/kg), (R)-ketamine (30 mg/kg), phencyclidine (PCP, 1 mg/kg), MK-801 (0.3 mg/kg) or saline prior to TUNL testing while simultaneous local field potential recordings were acquired. PCP disrupted working memory accuracy in WT ( p = 0.001) but not GluN2D-KO mice ( p = 0.79). MK-801 (p < 0.0001), (S)-ketamine (p < 0.0001) and (R)-ketamine ( p = 0.007) disrupted working memory accuracy in both genotypes. PCP increased baseline hippocampal gamma (30–80 Hz) power in WT ( p = 0.0015) but not GluN2D-KO mice ( p = 0.92). All drugs increased baseline gamma power in the PFC in both genotypes (p < 0.05). Low gamma was induced during the maintenance phase of the TUNL task and increased when mice correctly completed the task ( p = 0.024). This response-dependent increase in low gamma was disrupted by all drugs. In summary, PCP action involves the GluN2D subunit of the NMDA receptor in the hippocampus to alter baseline gamma power and working memory. Task-induced low gamma activity during maintenance aligns with task performance, and is disrupted by all NMDAR antagonists.

Working memory relies on synchronised network oscillations involving complex interplay between pyramidal cells and GABAergic interneurons. NMDA receptor (NMDAR) antagonists influence both network oscillations and working memory, but the relationship between these two consequences has not been elucidated. This study aimed to determine the effect of NMDAR antagonists on network oscillations during a working memory task in mice, and the contribution of the GluN2D receptor subunit. After training wildtype (WT) and GluN2D-knockout (KO) mice on the Trial-Unique-Non-match to Location (TUNL) touchscreen task of working memory, recording electrodes were implanted into the prefrontal cortex (PFC) and hippocampus. Mice were challenged with either (S)-ketamine (30mg/kg), (R)-ketamine (30mg/kg), phencyclidine (PCP, 1mg/kg), MK-801 (0.3mg/kg) or saline prior to TUNL testing while simultaneous local field potential recordings were acquired. PCP disrupted working memory accuracy in WT (p=0.001) but not GluN2D-KO mice (p=0.79). MK-801 (p<0.0001), (S)-ketamine (p<0.0001) and (R)-ketamine (p=0.007) disrupted working memory accuracy in both genotypes. PCP increased baseline gamma (30-80Hz) power in the hippocampus in WT (p=0.0015) but not GluN2D-KO mice (p=0.92). All drugs increased baseline gamma power in the PFC in both genotypes (p<0.05). Low gamma was induced during the maintenance phase of the TUNL task and increased when mice correctly completed the task (p=0.024). MK-801 disrupted task-induced low gamma in both genotypes (p=0.04). In summary, PCP action involves the GluN2D subunit of the NMDA receptor in the hippocampus to alter baseline gamma power and working memory. Task-induced low gamma activity during maintenance aligns with task performance, and is disrupted specifically by MK-801.

Maternal infections during pregnancy can increase the risk to offspring of developing a neurodevelopmental disorder. Given the global prevalence and severity of infection with Severe Acute Respiratory Syndrome related Coronavirus 2 (SARS-CoV-2), the objective of this study was to determine if in utero exposure to severe maternal SARS-CoV-2 infection alters infant neurodevelopmental outcomes at 12 months and to identify potential biological markers of adverse infant outcomes. Mother-infant dyads exposed to severe SARS-CoV-2 infection (requiring hospitalization) during pregnancy and age and sociodemographic matched control dyads were recruited from Monash Medical Centre, Australia in 2021/22 and prospectively assessed over 12 months. Maternal serum cytokine levels and Edinburgh Postnatal Depression Scale (EPDS) scores were assessed at birth. DNA methylation was assessed from infant buccal swabs at birth (Illumina EPIC BeadChip). Infant neurodevelopmental outcomes at 12 months were assessed using the Ages and Stages Questionnaire (ASQ-3). Mothers exposed to severe SARS-CoV-2 exhibited elevated serum IL-6 and IL-17A and higher EPDS scores than controls at birth. Infants exposed to severe SARS-CoV-2 in utero demonstrated over 3000 significant differentially methylated sites within their genomes compared to non-exposed (adjusted p-value < 0.05), including genes highly relevant to ASD and synaptic pathways. At 12 months, severe SARS-CoV-2 exposed infants scored lower on the ASQ-3 than non-exposed infants, and communication and problem-solving scores negatively correlated with maternal IL-6 levels at birth. DNA methylation changes therefore unveil potential mechanisms linking infection exposure to delayed neurodevelopment and maternal serum IL-6 levels may be a potential biomarker of child developmental delay. Mothers exposed to severe SARS-CoV-2 infections show elevated pro-inflammatory cytokines. Infants exposed in utero to severe SARS-CoV-2 infection show altered DNA methylation at birth and delayed development at 12 months of age. Created in Biorender.com.

Maternal infections during pregnancy can increase the risk to offspring of developing a neurodevelopmental disorder. Given the global prevalence and severity of infection with Severe Acute Respiratory Syndrome related Coronavirus 2 (SARS-CoV-2), the objective of this study was to determine if in utero exposure to severe maternal SARS-CoV-2 infection alters infant neurodevelopmental outcomes at 12 months and to identify potential biological markers of adverse infant outcomes. Mother-infant dyads exposed to severe SARS-CoV-2 infection (requiring hospitalization) during pregnancy and age and sociodemographic matched control dyads were recruited from Monash Medical Centre, Australia in 2021/22 and prospectively assessed over 12 months. Maternal serum cytokine levels and Edinburgh Postnatal Depression Scale (EPDS) scores were assessed at birth. DNA methylation was assessed from infant buccal swabs at birth (Illumina EPIC BeadChip). Infant neurodevelopmental outcomes at 12 months were assessed using the Ages and Stages Questionnaire (ASQ-3). Mothers exposed to severe SARS-CoV-2 exhibited elevated serum IL-6 and IL-17A and higher EPDS scores than controls at birth. Infants exposed to severe SARS-CoV-2 in utero demonstrated over 3000 significant differentially methylated sites within their genomes compared to non-exposed (adjusted p-value < 0.05), including genes highly relevant to ASD and synaptic pathways. At 12 months, severe SARS-CoV-2 exposed infants scored lower on the ASQ-3 than non-exposed infants and communication and problem-solving scores negatively correlated with maternal Il-6 levels at birth. DNA methylation changes therefore unveil potential mechanisms linking infection exposure to delayed neurodevelopment and maternal serum IL-6 levels may be a potential biomarker of child developmental delay.

Noncompetitive NMDA receptor (NMDAR) antagonists like phencyclidine (PCP) and ketamine cause psychosis‐like symptoms in healthy humans, exacerbate schizophrenia symptoms in people with the disorder, and disrupt a range of schizophrenia‐relevant behaviors in rodents, including hyperlocomotion. This is negated in mice lacking the GluN2D subunit of the NMDAR, suggesting the GluN2D subunit mediates the hyperlocomotor effects of these drugs. However, the role of GluN2D in mediating other schizophrenia‐relevant NMDAR antagonist‐induced behavioral disturbances, and in both sexes, is unclear. This study aimed to investigate the role of the GluN2D subunit in mediating schizophrenia‐relevant behaviors induced by a range of NMDA receptor antagonists. Using both male and female GluN2D knockout (KO) mice, we examined the effects of the NMDAR antagonist's PCP, the S‐ketamine enantiomer (S‐ket), and the ketamine metabolite R‐norketamine (R‐norket) on locomotor activity, anxiety‐related behavior, and recognition and short‐term spatial memory. GluN2D‐KO mice showed a blunted locomotor response to R‐norket, S‐ket, and PCP, a phenotype present in both sexes. GluN2D‐KO mice of both sexes showed an anxious phenotype and S‐ket, R‐norket, and PCP showed anxiolytic effects that were dependent on sex and genotype. S‐ket disrupted spatial recognition memory in females and novel object recognition memory in both sexes, independent of genotype. This datum identifies a role for the GluN2D subunit in sex‐specific effects of NMDAR antagonists and on the differential effects of the R‐ and S‐ket enantiomers.