A maturational shift in the frontal cortex synaptic transcriptional landscape underlies schizophrenia-relevant behavioural traits: A congenital rat model

Neonatal handling enhances behavioural and attentional domains, and frontocortical synaptic maturation in rat models of schizophrenia-like behaviour and anxiety-related responses

The Roman inbred rat strains are a neurodevelopmental model, with the Roman High Avoidance (RHA) presenting specific behaviours and frontal cortex (FC) gene expression changes relevant to schizophrenia symptoms. We wanted to assess the potentially positive modulatory and enduring effects of neonatal handling (NH) on the innate traits associated with both the RHA and their counterpart Roman Low Avoidance (RLA). Male rats received NH or were left untreated (controls). Two different age groups were considered: adolescent and adults. The assessment encompassed exploratory behaviour, social behaviour, anxiety-related behaviour (self-grooming), sensorimotor gating (prepulse inhibition; PPI), and the analysis of gene expression associated with synaptic processes, cortical maturation, and neuroplasticity in the FC. In adolescent rats, NH increased novelty exploration and activity, and reduced novelty-induced self-grooming in RLAs, whereas it improved PPI in RHAs. In adult rats, NH increased novelty-induced activity in both strains, reduced self-grooming in RLA rats, and enhanced social interaction and PPI in RHAs. NH produced significant effects on gene expression in adolescent RHA rats. These effects were observed at the presynaptic level by a reduction of Snap25 and increases of Cables1 and Cdk5, and at the postsynaptic level by increases of Grin2b, Homer1 and Nrg1, as well as by a NH-induced enhancement of Bdnf. NH also increased Nrg1 and Bdnf expression in adult RLA rats. These findings show for the first time that NH is able to modulate several genetically linked synaptic/neuroplasticity alterations in RHA vs. RLA rats, which are paralleled by NH-induced improvements in novelty exploration, social behaviour and sensorimotor gating (PPI).

The INO80E at 16p11.2 locus increases risk of schizophrenia in humans and induces schizophrenia-like phenotypes in mice

BACKGROUND

Chromosome 16p11.2 is one of the most significant loci in the genome-wide association studies (GWAS) of schizophrenia. Despite several integrative analyses and functional genomics studies having been carried out to identify possible risk genes, their impacts in the pathogenesis of schizophrenia remain to be fully characterized.

METHODS

We performed expression quantitative trait loci (eQTL) and summary-data-based Mendelian randomization (SMR) analyses to identify schizophrenia risk genes in the 16p11.2 GWAS locus. We constructed a murine model with dysregulated expression of risk gene in the medial prefrontal cortex (mPFC) using stereotaxic injection of adeno-associated virus (AAV), followed by behavioural assessments, dendritic spine analyses and RNA sequencing.

FINDINGS

We identified significant associations between elevated INO80E mRNA expression in the frontal cortex and risk of schizophrenia. The mice overexpressing Ino80e in mPFC (Ino80e-OE) exhibited schizophrenia-like behaviours, including increased anxiety behaviour, anhedonia, and impaired prepulse inhibition (PPI) when compared with control group. The neuronal sparse labelling assay showed that the density of stubby spines in the pyramidal neurons of mPFC was significantly increased in Ino80e-OE mice compared with control mice. Transcriptomic analysis in the mPFC revealed significant alterations in the mRNA levels of schizophrenia-related genes and processes related to synapses upon overexpressing Ino80e.

INTERPRETATION

Our results suggest that upregulation of the Ino80e gene in mPFC may induce schizophrenia-like behaviours in mice, further supporting the hypothesis that INO80E is an authentic risk gene.

FUNDING

This project received support from the National Key Research and Development Program of China, National Natural Science Foundation of China, Key Research and Development Projects of Hunan Provincial Science and Technology Department, Science and Technology Innovation team of Hunan Province, etc.

Cortical assembloids support the development of fast-spiking human PVALB+ cortical interneurons and uncover schizophrenia-associated defects

Disruption of parvalbumin positive (PVALB+) cortical interneurons is implicated in the pathogenesis of schizophrenia. However, how these defects emerge during brain development remains poorly understood. The protracted maturation of these cells during postnatal life has made their derivation from human pluripotent stem cells (hPSCs) extremely difficult, precluding hPSC-based disease modeling of their role in neuropsychiatric disease. Here we present a cortical assembloid system that supports the development of PVALB+ cortical interneurons which match the molecular profiles of primary PVALB+ interneurons and display their distinctive electrophysiological features. Further, we characterized cortical interneuron development in a series of CRISPR-generated isogenic structural variants associated with schizophrenia and identified variant-specific phenotypes affecting cortical interneuron migration and the molecular profile of PVALB+ cortical interneurons. These findings offer plausible mechanisms on how the disruption of cortical interneuron development may impact schizophrenia risk and provide the first human experimental platform to study of PVALB+ cortical interneurons.

Contrasting Effects of Oxytocin on MK801-Induced Social and Non-Social Behavior Impairment and Hyperactivity in a Genetic Rat Model of Schizophrenia-Linked Features

Social withdrawal in rodents is a measure of asociality, an important negative symptom of schizophrenia. The Roman high- (RHA) and low-avoidance (RLA) rat strains have been reported to exhibit differential profiles in schizophrenia-relevant behavioral phenotypes. This investigation was focused on the study of social and non-social behavior of these two rat strains following acute administration of dizocilpine (MK801, an NMDA receptor antagonist), a pharmacological model of schizophrenia-like features used to produce asociality and hyperactivity. Also, since oxytocin (OXT) has been proposed as a natural antipsychotic and a potential adjunctive therapy for social deficits in schizophrenia, we have evaluated the effects of OXT administration and its ability to reverse the MK801-impairing effects on social and non-social behavior and MK801-induced hyperactivity. MK801 administration produced hyperlocomotion and a decrease in social and non-social behavior in both rat strains, but these drug effects were clearly more marked in RHA rats. OXT (0.04 mg/kg and 0.2 mg/kg) attenuated MK801-induced hyperlocomotion in both rat strains, although this effect was more marked in RHA rats. The MK801-decreasing effect on exploration of the "social hole" was moderately but significantly attenuated only in RLA rats. This study is the first to demonstrate the differential effects of OXT on MK801-induced impairments in the two Roman rat strains, providing some support for the potential therapeutic effects of OXT against schizophrenia-like symptoms, including both a positive-like symptom (i.e., MK801-induced hyperlocomotion) and a negative-like symptom (i.e., MK801 decrease in social behavior), while highlighting the importance of the genetic background (i.e., the rat strain) in influencing the effects of both MK801 and oxytocin.

Schizophrenia-relevant social, attentional and cognitive traits in female RHA vs. RLA rats: Effects of neonatal handling

The Roman high- (RHA) and low-avoidance (RLA) rats were bidirectionally selected and bred for, respectively, their rapid vs. extremely poor acquisition in the two-way active avoidance task. Consistent between-strain neurobehavioural differences have been found in anxiety- and stress-linked traits, as well as in schizophrenia-related phenotypes. RLAs display enhanced anxious- and stress-related phenotypes, whereas RHA rats show impulsivity, hyperactivity and attention/cognition-related impairments. Many of these typical behavioural phenotypes have been reported to be positively modulated by environmental treatments such as neonatal handling (NH). However, most studies on the Roman rat strains have been carried out in males. Thus, the present study for the first time focused on the joint evaluation of differences in novel object exploration (NOE), social interaction (SI), prepulse inhibition of the startle response (PPI), and cognitive performance and flexibility in various spatial tasks (using the Morris water maze, MWM) in females of both Roman rat strains. We also aimed at evaluating the long-lasting effects of NH treatment on the RHA vs. RLA profiles in these tests/tasks. Results show that anxiety-related behavior, as measured by the NOE test and self-grooming in the SI test, was increased in RLA rats, and dramatically reduced by NH. In the SI test RLA rats displayed diminished social interaction, which was rescued by NH. RHA females exhibited a deficit of PPI, which was not affected by NH. Spatial tasks in the MWM showed impairments of working memory, reference learning/memory and spatial reversal learning (i.e., cognitive flexibility) in RHA females. Spatial reference learning and cognitive flexibility (i.e., reversal task) showed some improvement in rats (mainly in RHAs) that had received NH during the first three weeks of life. With the exception of the SI test, the pattern of differences between female RHA vs. RLA profiles was overall consistent with what has previously been found in males of both strains, and NH treatment was able to enduringly improve some emotion-related and (spatial) cognitive outcomes in both strains.

Contribution of the Roman rat lines/strains to personality neuroscience: neurobehavioral modeling of internalizing/externalizing psychopathologies

The Roman high-avoidance (RHA) and low-avoidance (RLA) rat lines/strains were established in Rome through bidirectional selection of Wistar rats for rapid (RHA) or extremely poor (RLA) acquisition of a two-way active avoidance task. Relative to RHAs, RLA rats exhibit enhanced threat sensitivity, anxiety, fear and vulnerability to stress, a passive coping style and increased sensitivity to frustration. Thus, RLA rats' phenotypic profile falls well within the "internalizing" behavior spectrum. Compared with RLAs and other rat strains/stocks, RHAs present increased impulsivity and reward sensitivity, deficits in social behavior and attentional/cognitive processes, novelty-induced hyper-locomotion and vulnerability to psychostimulant sensitization and drug addiction. Thus, RHA rats' phenotypes are consistent with a "disinhibiting externalizing" profile. Many neurobiological/molecular traits differentiate both rat lines/strains. For example, relative to RLA rats, RHAs exhibit decreased function of the prefrontal cortex (PFC), hippocampus and amygdala, increased functional tone of the mesolimbic dopamine system, a deficit of central metabotropic glutamate-2 (mGlu2) receptors, increased density of serotonin 5-HT2A receptors in the PFC, impairment of GABAergic transmission in the PFC, alterations of several synaptic markers and increased density of pyramidal immature dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. We review evidence supporting RLA rats as a valid model of anxiety/fear, stress and frustration vulnerability, whereas RHA rats represent a promising translational model of neurodevelopmental alterations related to impulsivity, schizophrenia-relevant features and comorbidity with drug addiction vulnerability.