Background Neuronal activity at gamma frequency is impaired in schizophrenia (SZ) and is considered critical for cognitive performance. Such impairments are thought to be due to reduced N-Methyl-D-Aspartate Receptor (NMDAR)-mediated inhibition from parvalbumin (PV) interneurons, rather than a direct role of impaired NMDAR signaling on pyramidal neurons. However, recent studies suggest a direct role of pyramidal neurons in regulating gamma oscillations. In particular, a computational model has been proposed in which phasic currents from pyramidal cells could drive synchronized feedback inhibition from interneurons. As such, impairments in pyramidal neuron activity could lead to abnormal gamma oscillations. However, this computational model has not been tested experimentally and the molecular mechanisms underlying pyramidal neuron dysfunction in SZ remain unclear. Methods In the present study, we tested the hypothesis that SZ-related phenotypes could arise from reduced NMDAR signaling in pyramidal neurons using forebrain pyramidal neurons specific NMDA-R1 knocked-out mice. Results The mice displayed increased baseline gamma power as well as socio-cognitive impairments. These phenotypes were associated with increased pyramidal cell excitability due to changes in inherent membrane properties. Interestingly, mutant mice showed decreased expression of GIRK2 channels, which has been linked to increase neuronal excitability. Conclusions Our data demonstrate for the first time that NMDAR hypofunction in pyramidal cells is sufficient to cause electrophysiological, molecular, neuropathological and behavioral changes related to SZ.

NMDA-receptor (NMDAR) hypofunction is strongly implicated in the pathophysiology of schizophrenia. Several convergent lines of evidence suggest that net excitation propagated by impaired NMDAR signaling on GABAergic interneurons may be of particular interest in mediating several aspects of schizophrenia. However, it is unclear which behavioral domains are governed by a net increase of excitation and whether modulating downstream GABAergic signaling can reverse neural and thus behavioral deficits. The current study determines the selective contributions of NMDAR dysfunction on PV-containing interneurons to electrophysiological, cognitive, and negative-symptom-related behavioral phenotypes of schizophrenia using mice with a PVcre-NR1flox-driven ablation of NR1 on PV-containing interneurons. In addition, we assessed the efficacy of one agent that directly modulates GABAergic signaling (baclofen) and one agent that indirectly modifies NMDAR-mediated signaling through antagonism of mGluR5 receptors (2-methyl-6-(phenylethynyl) pyridine (MPEP)). The data indicate that loss of NMDAR function on PV interneurons impairs self-care and sociability while increasing N1 latency and baseline gamma power, and reducing induction and maintenance of long-term potentiation. Baclofen normalized baseline gamma power without corresponding effects on behavior. MPEP further increased N1 latency and reduced social behavior in PVcre/NR1+/+ mice. These two indices were negatively correlated before and following MPEP such that as N1 latency increases, sociability decreases. This finding suggests a predictive role for N1 latency with respect to social function. Although previous data suggest that MPEP may be beneficial for core features of autism spectrum disorders, current data suggest that such effects require intact function of NMDAR on PV interneurons.

Autism is a disabling neurodevelopmental disorder characterized by social deficits, language impairment, and repetitive behaviors with few effective treatments. New evidence suggests that autism has reliable electrophysiological endophenotypes and that these measures may be caused by n-methyl-d-aspartic acid receptor (NMDAR) disruption on parvalbumin (PV)-containing interneurons. These findings could be used to create new translational biomarkers. Recent developments have allowed for cell-type selective knockout of NMDARs in order to examine the perturbations caused by disrupting specific circuits. This study examines several electrophysiological and behavioral measures disrupted in autism using a PV-selective reduction in NMDA R1 subunit. Mouse electroencephalograph (EEG) was recorded in response to auditory stimuli. Event-related potential (ERP) component amplitude and latency analysis, social testing, and premating ultrasonic vocalizations (USVs) recordings were performed. Correlations were examined between the ERP latency and behavioral measures. The N1 ERP latency was delayed, sociability was reduced, and mating USVs were impaired in PV-selective NMDA Receptor 1 Knockout (NR1 KO) as compared with wild-type mice. There was a significant correlation between N1 latency and sociability but not between N1 latency and premating USV power or T-maze performance. The increases in N1 latency, impaired sociability, and reduced vocalizations in PV-selective NR1 KO mice mimic similar changes found in autism. Electrophysiological changes correlate to reduced sociability, indicating that the local circuit mechanisms controlling N1 latency may be utilized in social function. Therefore, we propose that behavioral and electrophysiological alterations in PV-selective NR1 KO mice may serve as a useful model for therapeutic development in autism.

Rationale A number of studies have associated reduced Akt1 expression with vulnerability for schizophrenia. Although mice with deletion of a single copy of the Akt1 gene (Akt1+/−) show reduced Akt1 expression relative to wild-type (WT) animals, the extent to which these mice show schizophrenia-like phenotypic changes and/or increased susceptibility to epigenetic or non-genetic factors related to schizophrenia is unknown. Objectives Mutant mice were assessed on electroencephalographic/event related potential (EEG/ERP) and behavioral (acoustic startle and pre-pulse inhibition) measures relevant to schizophrenia. Mice were also assessed following exposure to the NMDA receptor antagonist ketamine, a potent psychotomimetic drug, in order to assess the role of reduced Akt1 expression as a vulnerability factor for schizophrenia. Methods Akt1+/−, Akt1−/− and WT mice received a series of paired-click, white noise stimuli, following ketamine (50 mg/kg) and saline injections. EEG was analyzed for ERPs and event-related power. Akt1+/− and WT mice were also assessed on PPI following ketamine (50 mg/kg) or saline injection. Results Akt1+/− and Akt1−/− mice displayed reduced amplitude of the P20 component of the ERP to the first click of a paired click stimulus, as well as reduced S1-S2 difference for P20 and N40 components, following ketamine. Mutant mice also showed increased reduction in gamma synchrony and theta suppression following ketamine. Akt1+/− mice displayed reduced pre-pulse inhibition. Conclusions Reduced genetic expression of Akt1 facilitated ketamine-induced changes of EEG and behavior in mice, suggesting that reduced Akt1 expression can serve as a vulnerability factor for schizophrenia.

Reductions in the levels of the neuropeptide vasopressin (VP) and its receptors have been associated with schizophrenia. VP is also critical for appropriate social behaviors in humans as well as rodents. One of the prominent symptoms of schizophrenia is asociality and these symptoms may develop prodromally. A reduction in event-related potential (ERP) peak amplitudes is an endophenotype of schizophrenia. In this study, we use the Brattleboro (BRAT) rat to assess the role of VP deficiency in vocal communication during early development and on auditory ERPs during adulthood. BRAT rats had similar vocal communication to wild-type littermate controls during postnatal days 2 and 5 but the time between vocalizations was increased and the power of the vocalizations was reduced beginning at postnatal day 9. During adulthood, BRAT rats had deficits in auditory ERPs including reduced N40 amplitude and reduced low and high gamma intertrial coherence. These results suggest that the role of VP on vocal communication is an age-dependent process. Additionally, the deficits in ERPs indicate an impairment of auditory information processing related to the reduction in VP. Therefore, manipulation of the VP system could provide a novel mechanism for treatment for negative symptoms of schizophrenia.

Background: Advanced cardiac imaging(ACI) with cardiac CT (CCT) and cardiac MR (CMR) are valuable noninvasive investigative tools to assess cardiac structure in cryptogenic stroke assessment. In this study, we examine patient, electrocardiographic (EKG), and TTE variables associated with subsequent detection of intracardiac thrombus using CCT and CMR in patients with cryptogenic stroke. Methods: The Medical University of South Carolina Comprehensive stroke center database was used to identify acute ischemic stroke patients who received inpatient CCT or CMR between January 2017 to May 2018. Patient demographics, past medical history, EKG, and TTE related variables were abstracted by 2 physicians. Univariate and multivariable logistic regression was used to identify factors associated with detection of intracardiac thrombus on CCT/CMR. Negative and positive predictive value (NPV and PPV) were calculated for TTE, with CCT/CMR considered as gold standard. Results: 256 subjects received CCT/CMR after TTE during the study period; with 25 (9.7%) found to have an intracardiac thrombus [12 (4.7%) LV thrombus, 6 (2.3%) LA thrombus, 7 (2.8%) Others including myxoma,valve aortic arch thrombus]. The PPV and NPV of TTE were 57% and 93% respectively. Mild-Modertely Reduced (30-50% EF was associated with subsequent detection of intracardiac thrombus onCCT/CMR in univariate model, but did not reach significance after adjusting for other variables. Atrial fibrillation, P wave abnormality on EKG, ST changes on EKG, Left Ventricle wall motion akinesia on TTE were associated with intracardiac thrombus on CCT/CMR in both models. Conclusion: Advanced cardiac imaging is a useful noninvasive tool to identify cardiac source of ischemic stroke. Although small sample size and inadequate power may limit generalizability, patients with atrial fibrillation, P wave and ST changes on EKG, and LV wall motion akinesis should be considered for advanced cardiac.

Background: The vasopressin deficient Brattleboro (BRAT) rats have behavioral impairments which mimic those seen in other schizophrenia models. However, the mechanism by which vasopressin produces these behavioral abnormalities is unclear. Notably, elevations in dopamine signaling as well as reductions in glutamatergic signaling have been associated with behavioral impairments consistent with those observed in the BRAT rats. Therefore, a potential mechanism for vasopressin induces behavioral abnormalities could be through modulation of dopamine or glutamate signaling. Consequently, the aim of this study was to assess the modulatory function of vasopressin on dopamine and NMDA signaling. Methods: Single intraperitoneal injection of amphetamine (0.5 mg/kg), a dopamine agonist, and MK801 (0.25 mg/kg), a NMDA antagonist, were used to assess vasopressin (VP) modulatory activity on dopaminergic and glutamatergic pre-pulse inhibition of startle (PPI), social interaction and auditory event related potential (ERPs) impairments in BRAT and littermate control WT rats. Results: MK801-induced impairments were consistent and not significantly different between WT and BRAT rats suggesting minimal modulatory activity of vasopressin on NMDA signaling. In contrast, amphetamine-induced deficits were genotype dependent. In control animals, amphetamine caused a statistically significant deficit in PPI and social interaction whereas there was no effect in BRAT rats. Conversely, ERP components were unaltered in control rats, whereas N40 amplitude, evoked gamma power, and gamma signal to noise ratio were all elevated in BRAT rats. Conclusions:The ERP component analyses of BRAT rats treated with amphetamine suggest modulation of auditory information processing through interplay between dopaminergic and vasopressin. However, the behavioral and electrophysiological evidence presented here also suggest that vasopressin does not modulate glutamatergic signaling through NMDA receptors. Further evidence in necessary to determine the interaction between vasopressin and dopamine signaling and future studies are necessary to comprehend glutamatergic interactions with vasopressin that are not NMDA-mediated.