Deficits in prepulse inhibition and habituation in never-medicated, first-episode schizophrenia

Differential depletion of GluN2A induces heterogeneous schizophrenia-related phenotypes in mice

BACKGROUND

Schizophrenia, a debilitating psychiatric disorder, displays considerable interindividual variation in clinical presentations. The ongoing debate revolves around whether this heterogeneity signifies a continuum of severity linked to a singular causative factor or a collection of distinct subtypes with unique origins. Within the realm of schizophrenia, the functional impairment of GluN2A, a subtype of the NMDA receptor, has been associated with an elevated risk. Despite GluN2A's expression across various neuronal types throughout the brain, its specific contributions to schizophrenia and its involvement in particular cell types or brain regions remain unexplored.

METHODS

We generated age-specific, cell type-specific or brain region-specific conditional knockout mice targeting GluN2A and conducted a comprehensive analysis using tests measuring phenotypes relevant to schizophrenia.

FINDINGS

Through the induction of germline ablation of GluN2A, we observed the emergence of numerous schizophrenia-associated abnormalities in adult mice. Intriguingly, GluN2A knockout performed at different ages, in specific cell types and within distinct brain regions, we observed overlapping yet distinct schizophrenia-related phenotypes in mice.

INTERPRETATION

Our interpretation suggests that the dysfunction of GluN2A is sufficient to evoke heterogeneous manifestations associated with schizophrenia, indicating that GluN2A stands as a prominent risk factor and a potential therapeutic target for schizophrenia.

FUNDING

This project received support from the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX02) awarded to Y.C. and the Natural Science Foundation of Shanghai (Grant No. 19ZR1468600 and 201409003800) awarded to G.Y.

Neonatal phencyclidine as a model of sex-biased schizophrenia symptomatology in adolescent mice

Sex-biased differences in schizophrenia are evident in several features of the disease, including symptomatology and response to pharmacological treatments. As a neurodevelopmental disorder, these differences might originate early in life and emerge later during adolescence. Considering that the disruption of the glutamatergic system during development is known to contribute to schizophrenia, we hypothesized that the neonatal phencyclidine model could induce sex-dependent behavioral and neurochemical changes associated with this disorder during adolescence. C57BL/6 mice received either saline or phencyclidine (5, 10, or 20 mg/kg) on postnatal days (PN) 7, 9, and 11. Behavioral assessment occurred in late adolescence (PN48-50), when mice were submitted to the open field, social interaction, and prepulse inhibition tests. Either olanzapine or saline was administered before each test. The NMDAR obligatory GluN1 subunit and the postsynaptic density protein 95 (PSD-95) were evaluated in the frontal cortex and hippocampus at early (PN30) and late (PN50) adolescence. Neonatal phencyclidine evoked dose-dependent deficits in all analyzed behaviors and males were more susceptible. Males also had reduced GluN1 expression in the frontal cortex at PN30. There were late-emergent effects at PN50. Cortical GluN1 was increased in both sexes, while phencyclidine increased cortical and decreased hippocampal PSD-95 in females. Olanzapine failed to mitigate most phencyclidine-evoked alterations. In some instances, this antipsychotic aggravated the deficits or potentiated subthreshold effects. These results lend support to the use of neonatal phencyclidine as a sex-biased neurodevelopmental preclinical model of schizophrenia. Olanzapine null effects and deleterious outcomes suggest that its use during adolescence should be further evaluated.

Mice lacking Ptprd exhibit deficits in goal-directed behavior and female-specific impairments in sensorimotor gating

Protein Tyrosine Phosphatase receptor type D (PTPRD) is a member of the protein tyrosine phosphatase family that mediates cell adhesion and synaptic specification. Genetic studies have linked Ptprd to several neuropsychiatric phenotypes, including Restless Leg Syndrome (RLS), opioid abuse disorder, and antipsychotic-induced weight gain. Genome-wide association studies (GWAS) of either pediatric obsessive-compulsive traits, or Obsessive-Compulsive Disorder (OCD), have identified loci near PTPRD as genome-wide significant, or strongly suggestive for this trait. We assessed Ptprd wild-type (WT), heterozygous (HT), and knockout (KO) mice for behavioral dimensions that are altered in OCD, including anxiety and exploration (open field test, dig test), perseverative behavior (splash-induced grooming, spatial d), sensorimotor gating (prepulse inhibition), and home cage goal-directed behavior (nest building). No effect of genotype was observed in any measure of the open field test, dig test, or splash test. However, Ptprd KO mice of both sexes showed impairments in nest building behavior. Finally, female, but not male, Ptprd KO mice showed deficits in prepulse inhibition, an operational measure of sensorimotor gating that is reduced in female, but not male, OCD patients. Our results indicate that constitutive lack of Ptprd may contribute to the development of certain domains that are altered OCD, including goal-directed behavior, and reduced sensorimotor gating specifically in females.

Negative emotion-conditioned prepulse induces the attentional enhancement of prepulse inhibition in humans

Prepulse inhibition (PPI) is a reduction of the acoustic startle reflex (ASR) when the startling stimulus is preceded by a weaker and non-startling stimulus (i.e., prepulse). Previous studies have revealed that PPI can be top-down modulated by selective attention to the fear-conditioned prepulse in animals. However, few researchers have tested this assumption in humans. Thus, in this study, the negative emotional-conditioned prepulse (CS+) was used to explore whether it could improve participants' attention, and further improve the PPI. The results showed that the CS+ prepulse increased the PPI only in females, PPI produced by CS+ prepulse was larger in females than in males, and the perceptual spatial attention further improved the PPI in both females and males. The results suggested that the PPI was affected by emotional, perceptual spatial attention, and sex. These findings highlight an additional method to measure top-down attentional regulation of PPI in humans. Which may offer a useful route to enhance the diagnosis of affective disorders, such as anxiety, depression, and post-traumatic stress disorder.

Systematic review of visual illusions in schizophrenia

Visual illusions have long been used as tools to investigate sensory-perceptual deficits in schizophrenia. Recent conflicting accounts have called into question the assumption of abnormal illusion perception in patients and, therefore, the validity of this approach. Here, we present a systematic review of the current evidence regarding visual illusion perception abnormalities in patients with schizophrenia. Relevant publications were identified by a systematic search of PubMed, Literatura LILACS, PsycINFO, Embase, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), IBECS, BIOSIS, and Web of Science. Forty-five studies were selected which included illusions classified as 'Motion illusions', 'Geometric-optical illusions', 'Illusory contours', 'Depth inversion illusion', and 'Non-specific'. There is concordant evidence of abnormal processing of illusions in patients for most categories, especially in facial Depth Inversion and Müller-Lyer illusions. There were significant methodological disparities and shortcomings, but risk of bias was overall low for individual studies. The usefulness of visual illusions as tools in clinical settings as well as in basic research may be contingent on significant methodological refinements.

Cerebrospinal fluid concentration of complement component 4A is increased in first episode schizophrenia

Postsynaptic density is reduced in schizophrenia, and risk variants increasing complement component 4A (C4A) gene expression are linked to excessive synapse elimination. In two independent cohorts, we show that cerebrospinal fluid (CSF) C4A concentration is elevated in patients with first-episode psychosis (FEP) who develop schizophrenia (FEP-SCZ: median 0.41 fmol/ul [CI = 0.34-0.45], FEP-non-SCZ: median 0.29 fmol/ul [CI = 0.22-0.35], healthy controls: median 0.28 [CI = 0.24-0.33]). We show that the CSF elevation of C4A in FEP-SCZ exceeds what can be expected from genetic risk variance in the C4 locus, and in patient-derived cellular models we identify a mechanism dependent on the disease-associated cytokines interleukin (IL)-1beta and IL-6 to selectively increase neuronal C4A mRNA expression. In patient-derived CSF, we confirm that IL-1beta correlates with C4A controlled for genetically predicted C4A RNA expression (r = 0.39; CI: 0.01-0.68). These results suggest a role of C4A in early schizophrenia pathophysiology.

AMPA receptors in schizophrenia: A systematic review of postmortem studies on receptor subunit expression and binding

BACKGROUND

While altered expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type receptor has been reported in postmortem studies of schizophrenia, these findings are inconsistent. Therefore, we aimed to systematically review postmortem studies that investigated AMPA receptor expressions in schizophrenia.

METHODS

A systematic literature search was conducted for postmortem studies that measured AMPA receptor subunit expressions or receptor bindings in schizophrenia compared to healthy individuals on February 3, 2021, using Medline and Embase.

RESULTS

A total of 39 relevant articles were identified from 1360 initial reports. The dorsolateral prefrontal cortex (DLPFC) was the most investigated region (15 studies), followed by the medial temporal lobe (8 studies). For the DLPFC, 4/15 studies (26.7%) showed increased AMPA receptor binding or subunit expression in patients with schizophrenia compared to that in controls, especially in GRIA1 and GRIA4, 2/15 studies (13.3%) reported a decrease, particularly in GRIA2, and 8/15 studies (56.7%) found no significant differences. A decreased expression or receptor binding was observed in 6/8 studies (75.0%) in the subregions of the hippocampus in patients with schizophrenia compared to that in controls, whereas the other two studies found no significant differences.

CONCLUSION

Published data have reported decreased subunit expression or receptor binding in the hippocampus in schizophrenia. These findings were inconsistent in other brain regions, which might be due to the heterogeneity of this population, various study design, physiological changes after death, and limited number of studies. Future in vivo studies are warranted to examine AMPA receptor expressions in human brains, together with their comprehensive clinical characterization.

Glycogen Synthase Kinase 3: Ion Channels, Plasticity, and Diseases

Glycogen synthase kinase 3β (GSK3) is a multifaceted serine/threonine (S/T) kinase expressed in all eukaryotic cells. GSK3β is highly enriched in neurons in the central nervous system where it acts as a central hub for intracellular signaling downstream of receptors critical for neuronal function. Unlike other kinases, GSK3β is constitutively active, and its modulation mainly involves inhibition via upstream regulatory pathways rather than increased activation. Through an intricate converging signaling system, a fine-tuned balance of active and inactive GSK3β acts as a central point for the phosphorylation of numerous primed and unprimed substrates. Although the full range of molecular targets is still unknown, recent results show that voltage-gated ion channels are among the downstream targets of GSK3β. Here, we discuss the direct and indirect mechanisms by which GSK3β phosphorylates voltage-gated Na⁺ channels (Na_v1.2 and Na_v1.6) and voltage-gated K⁺ channels (K_v4 and K_v7) and their physiological effects on intrinsic excitability, neuronal plasticity, and behavior. We also present evidence for how unbalanced GSK3β activity can lead to maladaptive plasticity that ultimately renders neuronal circuitry more vulnerable, increasing the risk for developing neuropsychiatric disorders. In conclusion, GSK3β-dependent modulation of voltage-gated ion channels may serve as an important pharmacological target for neurotherapeutic development.

Early Schizophrenia and Bipolar Disorder Patients Display Reduced Neural Prepulse Inhibition

BACKGROUND

Altered sensorimotor gating has been demonstrated by Prepulse Inhibition (PPI) tests in patients with psychosis. Recent advances in signal processing methods allow assessment of neural PPI through electroencephalogram (EEG) recording during acoustic startle response measures (classic muscular PPI). Simultaneous measurements of muscular (eye-blink) and neural gating phenomena during PPI test may help to better understand sensorial processing dysfunctions in psychosis. In this study, we aimed to assess simultaneously muscular and neural PPI in early bipolar disorder and schizophrenia patients.

METHOD

Participants were recruited from a population-based case-control study of first episode psychosis. PPI was measured using electromyography (EMG) and EEG in pulse alone and prepulse + pulse with intervals of 30, 60, and 120 ms in early bipolar disorder (n = 18) and schizophrenia (n = 11) patients. As control group, 15 socio-economically matched healthy subjects were recruited. All subjects were evaluated with Rating Scale, Hamilton Rating Scale for Depression, and Young Mania Rating Scale questionnaires at recruitment and just before PPI test. Wilcoxon ranked sum tests were used to compare PPI test results between groups.

RESULTS

In comparison to healthy participants, neural PPI was significantly reduced in PPI 30 and PPI60 among bipolar and schizophrenia patients, while muscular PPI was reduced in PPI60 and PPI120 intervals only among patients with schizophrenia.

CONCLUSION

The combination of muscular and neural PPI evaluations suggested distinct impairment patterns among schizophrenia and bipolar disorder patients. Simultaneous recording may contribute with novel information in sensory gating investigations.

Impaired prepulse inhibition in mice with IRSp53 deletion in modulatory neurotransmitter neurons including dopamine, acetylcholine, oxytocin, and serotonin

Prepulse inhibition (PPI) is a neurophysiological finding that is decreased in schizophrenia patients and has been used in pathophysiology studies of schizophrenia and the development of antipsychotic drugs. PPI is affected by several drugs including amphetamine, ketamine, and nicotinic agents, and it is reported that several brain regions and modulatory neurotransmitters are involved in PPI. Here we showed that mice with IRSp53 deletion in each dopaminergic, cholinergic, oxytocinergic, and serotoninergic modulatory neurons showed a decrease in PPI. Other than PPI, there were no other behavioral changes among IRSp53 deletion mice. Through this study, we could reconfirm that dysfunction of each modulatory neuron such as dopamine, acetylcholine, oxytocin, and serotonin can result in PPI impairment, and it should be considered that PPI could be broadly affected by changes in one of a certain kind of modulatory neurons.

Physiological and pathological functions of βB2-crystallins in multiple organs: a systematic review

Crystallins, the major constituent proteins of mammalian lenses, are significant not only for the maintenance of eye lens stability, transparency, and refraction, but also fulfill various physiopathological functions in extraocular tissues. βB2-crystallin, for example, is a multifunctional protein expressed in the human retina, brain, testis, ovary, and multiple tumors. Mutations in the βB2 crystallin gene or denaturation of βB2-crystallin protein are associated with cataracts, ocular pathologies, and psychiatric disorders. A prominent role for βB2-crystallins in axonal growth and regeneration, as well as in dendritic outgrowth, has been demonstrated after optic nerve injury. Studies in βB2-crystallin-null mice revealed morphological and functional abnormalities in testis and ovaries, indicating βB2-crystallin contributes to male and female fertility in mice. Interestingly, although pathogenic significance remains obscure, several studies identified a clear correlation between βB2 crystallin expression and the prognosis of patients with breast cancer, colorectal cancer, prostate cancer, renal cell carcinoma, and glioblastoma in the African American population. This review summarizes the physiological and pathological functions of βB2-crystallin in the eye and other organs and tissues and discusses findings related to the expression and potential role of βB2-crystallin in tumors.

Disrupted sensorimotor gating in first-episode psychosis patients is not affected by short-term antipsychotic treatment

BACKGROUND

Impaired sensorimotor gating, commonly measured as disrupted prepulse inhibition (PPI) of the acoustic startle response, has been widely observed in psychotic diseases. However, most PPI studies published so far involve patients with long illness duration and different drug treatments. Few studies have investigated untreated patients at their first episode of psychotic symptoms.

METHOD

PPI is an acoustic startle paradigm (30, 60-, 120-ms interstimulus intervals). Startle reactivity and habituation were succesfully assessed in 49 antipsychotic-naïve first-episode psychosis (FEP) patients and compared with 35 age- and gender-matched healthy control subjects. Mean age of patients was 28 years and 27 for controls. Patients treated with antipsychotics more than 30 days were not included in the study and twenty-three out of forty-nine patients received antipsychotic treatment with a mean treatment time of 13 days.

RESULTS

PPI was significantly lower in FEP patients, compared to healthy controls. The PPI deficiency found in these patients was not due to antipsychotic treatment since PPI did not differ between treated (n=23) and untreated patients n=(26). By using the latent curve modeling we identified a delayed habituation in patients treated with antipsychotics, suggesting that antipsychotic treatment should be considered as a confound when investigating habituation in schizophrenia.

CONCLUSIONS

Our results suggest that acute pharmacological treatment does not normalize PPI in FEP patients but should be considered as a confound when investigating habituation in these patients.

Serotonin 2A receptors and cannabinoids

Accumulating evidence has proven that both exogenous cannabinoids as well as imbalances in the endocannabinoid system are involved in the onset and development of mental disorders such as anxiety, depression, or schizophrenia. Extensive recent research in this topic has mainly focused on the molecular mechanisms by which cannabinoid agonists may contribute to the pathophysiology of these disorders. Initially, serotonin neurotransmitter garnered most attention due to its relationship to mood disorders and mental diseases, with little attention to specific receptors. To date, the focus has redirected toward the understanding of different serotonin receptors, through a demonstration of its versatile pharmacology and synergy with different modulators. Serotonin 2A receptors are a good example of this phenomenon, and the complex signaling that they trigger appears of high relevance in the context of mental disorders, especially in schizophrenia. This chapter will analyze most relevant attributes of serotonin 2A receptors and the endocannabinoid system, and will highlight the evidence toward the functional bidirectional interaction between these elements in the brain as well as the impact of the endocannabinoid system dysregulation on serotonin 2A receptors functionality.

Loss of α7 nicotinic acetylcholine receptors in GABAergic neurons causes sex-dependent decreases in radial glia-like cell quantity and impairments in cognitive and social behavior

The dentate gyrus (DG) is a unique brain structure in that neurons can be generated postnatally and integrated within existing circuitry throughout life. The maturation process of these newly generated neurons (granule cells) is modulated by nicotinic acetylcholine receptors (nAChRs) through a variety of mechanisms such as neural stem pool proliferation, cell survival, signal modulation, and dendritic integration. Disrupted nAChR signaling has been implicated in neuropsychiatric and neurodegenerative disorders, potentially via alterations in DG neurogenesis. GABAergic interneurons are known to express nAChRs, predominantly the α7 subtype, and have been shown to shape development, integration, and circuit reorganization of DG granule cells. Therefore, we examined histological and behavioral effects of knocking out α7 nAChRs in GABAergic neurons. Deletion of α7 nAChRs resulted in a reduction of radial glia-like cells within the subgranular zone of the DG and a concomitant trend towards decreased immature neurons, specifically in male mice, as well as sex-dependent changes in several behaviors, including social recognition and spatial learning. Overall, these findings suggest α7 nAChRs expressed in GABAergic neurons play an important role in regulating the adult neural stem cell pool and behavior in a sex-dependent manner. This provides important insight into the mechanisms by which cholinergic dysfunction contributes to the cognitive and behavioral changes associated with neurodevelopmental and neurodegenerative disorders.

Involvement of nicotinic acetylcholine receptors in behavioral abnormalities and psychological dependence in schizophrenia-like model mice

The smoking incentive in patients with schizophrenia (SCZ) depends on stimulation of nicotinic acetylcholine receptors (nAChRs) in the central nervous system. To detect potential predictor genes for nicotine responses in SCZ, we explored common factor using research data in human and animal samples. In lymphoblastoid cell lines from SCZ, the mRNA expression level of α7 nAChR subunit was decreased. In SCZ-like model mice of phencyclidine (PCP; 10 mg/kg/day, subcutaneously for 14 days)-administered mice, the mRNA expression level of α7 nAChR subunit and protein expression level of α7 or α4 nAChR subunit were significantly decreased in the prefrontal cortex during PCP withdrawal. Protein, but not mRNA, expression levels of α7, α4, and β2 nAChR subunits were significantly increased in the nucleus accumbens. Acute (-)-nicotine [(-)-NIC: 0.3 mg/kg, s.c.] treatment attenuated impairments of social behaviors and visual recognition memory. These effects of (-)-NIC were completely blocked by both methyllycaconitine, a selective α7 nAChR antagonist, and dihydro-β-erythroidine (DHβE), a selective α4β2 nAChR antagonist. (-)-NIC did not induce conditioned place preference, but enhanced sensitivity to methamphetamine-induced hyperactivity. These findings suggest that α7 nAChR is associated with development of disease and is implicated in the therapeutic effect of nicotine in SCZ. The smoking incentive in SCZ might be attributed to treat their own symptoms, rather than a result of (-)-NIC dependence, by stimulating α7 and/or α4β2 nAChRs.

Meta-Analysis of Sensorimotor Gating Deficits in Patients With Schizophrenia Evaluated by Prepulse Inhibition Test

Prepulse inhibition (PPI) of startle is an operational measure of sensorimotor gating that is often impaired in patients with schizophrenia. Despite the large number of studies, there is considerable variation in PPI outcomes reported. We conducted a systematic review and meta-analysis investigating PPI impairment in patients with schizophrenia compared with healthy control subjects, and examined possible explanations for the variation in results between studies. Major databases were screened for observational studies comparing healthy subjects and patients with schizophrenia for the prepulse and pulse intervals of 60 and 120 ms as primary outcomes, ie, PPI-60 and PPI-120. Standardized mean difference (SMD) and 95% confidence intervals (CI) were extracted and pooled using random effects models. We then estimated the mean effect size of these measures with random effects meta-analyses and evaluated potential PPI heterogeneity moderators, using sensitivity analysis and meta-regressions. Sixty-seven primary studies were identified, with 3685 healthy and 4290 patients with schizophrenia. The schizophrenia group showed reduction in sensorimotor gating for both PPI-60 (SMD = -0.50, 95% CI = [-0.61, -0.39]) and PPI-120 (SMD = -0.44, 95% CI = [-0.54, -0.33]). The sensitivity and meta-regression analysis showed that sample size, gender proportion, imbalance for gender, source of control group, and study continent were sources of heterogeneity (P < .05) for both PPI-60 and PPI-120 outcomes. Our findings confirm a global sensorimotor gating deficit in schizophrenia patients, with overall moderate effect size for PPI-60 and PPI-120. Methodological consistency should decrease the high level of heterogeneity of PPI results between studies.

A Methyltransferase Inhibitor (Decitabine) Alleviates Intergenerational Effects of Paternal Neonatal Exposure to Anesthesia With Sevoflurane

BACKGROUND

Neonatal exposure to sevoflurane induces neurobehavioral and neuroendocrine abnormalities in exposed male rats (generation F0) and neurobehavioral, but not neuroendocrine, abnormalities in their male, but not female, offspring (generation F1). These effects of sevoflurane are accompanied by a hypermethylated neuron-specific K-2Cl (Kcc2) Cl exporter gene in the F0 spermatozoa and the F1 male hypothalamus, while the gene's expression is reduced in the F0 and F1 hypothalamus. We investigated whether inhibition of deoxyribonucleic acid methyltransferases (DNMTs) before paternal sevoflurane exposure could alleviate the anesthetic's F0 and F1 effects.

METHODS

Sprague-Dawley male rats were anesthetized with 2.1% sevoflurane for 5 hours on postnatal day (P) 5 and mated with control females on P90 to generate offspring. The nonselective DNMT inhibitor decitabine (0.5 mg/kg, intraperitoneally) was administered 30 minutes before sevoflurane exposure. The F0 and F1 male rats were evaluated in in vivo and in vitro tests in adulthood.

RESULTS

Paternal exposure to sevoflurane induced impaired prepulse inhibition of the acoustic startle response and exacerbated corticosterone responses to stress in F0 males and impaired prepulse inhibition of the startle responses in F1 males. These effects were accompanied in both generations by reduced and increased expressions of hypothalamic Kcc2 and Dnmt3a/b, respectively. Decitabine deterred the effects of paternal exposure to sevoflurane in F0 and F1 males.

CONCLUSIONS

These results suggest that similar decitabine-sensitive mechanisms regulating expression of multiple genes are involved in the mediation of neurobehavioral abnormalities in sires neonatally exposed to sevoflurane and in their future unexposed male offspring.

Impaired Sensorimotor Gating Using the Acoustic Prepulse Inhibition Paradigm in Individuals at a Clinical High Risk for Psychosis

Many robust studies have investigated prepulse inhibition (PPI) in patients with schizophrenia. Recent evidence indicates that PPI may help identify individuals who are at clinical high risk for psychosis (CHR). Selective attention to prepulse stimulus can specifically enhance PPI in healthy subjects; however, this enhancement effect is not observed in patients with schizophrenia. Modified PPI measurement with selective attentional modulation using perceived spatial separation (PSS) condition may be a more robust and sensitive index of PPI impairment in CHR individuals. The current study investigated an improved PSSPPI condition in CHR individuals compared with patients with first-episode schizophrenia (FES) and healthy controls (HC) and evaluated the accuracy of PPI in predicting CHR from HC. We included 53 FESs, 55 CHR individuals, and 53 HCs. CHRs were rated on the Structured Interview for Prodromal Syndromes. The measures of perceived spatial co-location PPI (PSCPPI) and PSSPPI conditions were applied using 60- and 120-ms lead intervals. Compared with HC, the CHR group had lower PSSPPI level (Inter-stimulus interval [ISI] = 60 ms, P < .001; ISI = 120 ms, P < .001). PSSPPI showed an effect size (ES) between CHR and HC (ISI = 60 ms, Cohen's d = 0.91; ISI = 120 ms, Cohen's d = 0.98); on PSSPPI using 60-ms lead interval, ES grade increased from CHR to FES. The area under the receiver operating characteristic curve for PSSPPI was greater than that for PSCPPI. CHR individuals showed a PSSPPI deficit similar to FES, with greater ES and sensitivity. PSSPPI appears a promising objective approach for preliminary identification of CHR individuals.

Controlled sleep deprivation as an experimental medicine model of schizophrenia: An update

In recent years there has been a surge of interest and corresponding accumulation of knowledge about the role of sleep disturbance in schizophrenia. In this review, we provide an update on the current status of experimentally controlled sleep deprivation (SD) as an experimental medicine model of psychosis, and also consider, given the complexity and heterogeneity of schizophrenia, whether this (state) model can be usefully combined with other state or trait model systems to more powerfully model the pathophysiology of psychosis. We present evidence of dose-dependent aberrations that qualitatively resemble positive, negative and cognitive symptoms of schizophrenia as well as deficits in a range of translational biomarkers for schizophrenia, including prepulse inhibition, smooth pursuit and antisaccades, following experimentally controlled SD, relative to standard sleep, in healthy volunteers. Studies examining the combination of SD and schizotypy, a trait model of schizophrenia, revealed only occasional, task-dependent superiority of the combination model, relative to either of the two models alone. Overall, we argue that experimentally controlled SD is a valuable experimental medicine model of schizophrenia to advance our understanding of the pathophysiology of the clinical disorder and discovery of more effective or novel treatments. Future studies are needed to test its utility in combination with other, especially state, model systems of psychosis such as ketamine.

A novel optical non-intrusive method for measuring acoustic startle reflex in humans

OBJECTIVE

The development of a new non-intrusive optical system for remotely measuring acoustic startle reflex (ASR) in humans.

APPROACH

The eye reflex movement during an acoustic stimulation session is recorded through a high-speed digital camera. The eyes region is isolated by the rest of the face by an advanced pyramid-like feature detection algorithm, which greatly reduces the number of false positives. A separate Lucas-Kanade optical flow routine is designed for the eyeblink movement detection and the startle eyeblink reflex (SEBR) curve extraction. Image masking is implemented for the elimination of unwanted artifacts caused mainly by voluntary eye movement. The proposed system was tested along with a valid EMG system on a sample of 32 healthy randomly selected adults, and the results were compared in order to measure the system's degree of reliability.

MAIN RESULTS

To assess the proposed method's validity the EMG data was used as a benchmark. The results showed strong correlation between EMG and Camera acquired results, which proves the validity of the proposed method. Furthermore, by comparing the response probability and the signal to noise ratio (SNR) for the two techniques, we proved that the proposed method can surpass the traditional EMG system in terms of accuracy and reliability.

SIGNIFICANCE

The proposed technique presents a simple, robust and reliable non-intrusive means of measuring ASR in humans, with the potential of future implementation on various ASR psychophysiology experiments, such as the study of PPI.

Threat vs control: Potentiation of the trigeminal blink reflex by threat proximity is overruled by self-stimulation

The magnitude of the defensive blink reflex is modulated by continuous assessment of its protective value. Here, we studied whether the trigeminal blink reflex (TBR) is modulated by a potentially offensive object close to the face, and, if so, whether self-stimulation or observation of the act of stimulus triggering counteracts such modulation. In all, 26 healthy volunteers participated in various experimental conditions. At baseline, an experimenter triggered supraorbital nerve stimuli remotely, unseen by the participants; in experimental conditions, the experimenter held a stimulation probe close to the participant's face but triggered the stimuli either remotely, "surprising" participants (S₁ ), or directly on the probe, observed by participants (S₂ ). In other conditions, participants triggered stimuli themselves on the probe held next to their body (S₃ ) or held in front of their face (S₄ ). The latter condition was repeated similarly, but pressing the button only randomly generated electrical stimuli (S5, "Russian roulette"). The size of the R2 component of the TBR (TBR-R2) was the main outcome measure. Compared to baseline, TBR-R2 area was significantly larger in S₁ when the "threatening" probe was close to the face and the participant had no control over stimulation. Conversely, TBR-R2 was suppressed when participants either saw the action of triggering, thus being aware (S₂ ), or had full initiative over stimulation (S₃ , S₄ ). Random self-generated stimuli (S₅ ) inhibited TBR-R2, but to a lesser extent than S₃ and S_4. Perceived threat close to the face facilitates TBR-R2, but knowledge about impending stimulation or self-agency overrules this effect.

Control of neuronal excitability by GSK-3beta: Epilepsy and beyond

Glycogen synthase kinase 3beta (GSK-3β) is an enzyme with a variety of cellular functions in addition to the regulation of glycogen metabolism. In the central nervous system, different intracellular signaling pathways converge on GSK-3β through a cascade of phosphorylation events that ultimately control a broad range of neuronal functions in the development and adulthood. In mice, genetically removing or increasing GSK-3β cause distinct functional and structural neuronal phenotypes and consequently affect cognition. Precise control of GSK-3β activity is important for such processes as neuronal migration, development of neuronal morphology, synaptic plasticity, excitability, and gene expression. Altered GSK-3β activity contributes to aberrant plasticity within neuronal circuits leading to neurological, psychiatric disorders, and neurodegenerative diseases. Therapeutically targeting GSK-3β can restore the aberrant plasticity of neuronal networks at least in animal models of these diseases. Although the complete repertoire of GSK-3β neuronal substrates has not been defined, emerging evidence shows that different ion channels and their accessory proteins controlling excitability, neurotransmitter release, and synaptic transmission are regulated by GSK-3β, thereby supporting mechanisms of synaptic plasticity in cognition. Dysregulation of ion channel function by defective GSK-3β activity sustains abnormal excitability in the development of epilepsy and other GSK-3β-linked human diseases.

Polymorphisms in CRYBB2 encoding βB2-crystallin are associated with antisaccade performance and memory function

βB2-crystallin (gene symbol: Crybb2/CRYBB2) was first described as a structural protein of the ocular lens before it was detected in various brain regions of the mouse, including the hippocampus and the cerebral cortex. Mutations in the mouse Crybb2 gene lead to alterations of sensorimotor gating measured as prepulse inhibition (PPI) and reduced hippocampal size, combined with an altered number of parvalbumin-positive GABAergic interneurons. Decreased PPI and alterations of parvalbumin-positive interneurons are also endophenotypes that typically occur in schizophrenia. To verify the results found in mice, we genotyped 27 single nucleotide polymorphisms (SNPs) within the CRYBB2 gene and its flanking regions and investigated different schizophrenia typical endophenotypes in a sample of 510 schizophrenia patients and 1322 healthy controls. In the case-control study, no association with schizophrenia was found. However, 3 of the 4 investigated haplotype blocks indicated a decreased CRYBB2 mRNA expression. Two of these blocks were associated with poorer antisaccade task performance and altered working memory-linked functional magnetic resonance imaging signals. For the two haplotypes associated with antisaccade performance, suggestive evidence was found with visual memory and in addition, haplotype block 4 showed a nominally significant association with reduced sensorimotor gating, measured as P50 ratio. These results were not schizophrenia-specific, but could be detected in a combined sample of patients and healthy controls. This is the first study to demonstrate the importance of βB2-crystallin for antisaccade performance and memory function in humans and therefore provides implications for βB2-crystallin function in the human brain.

Behavioral effects in adult rats exposed to low doses of a phthalate mixture during the perinatal or adolescent period

Hormones influence neurodevelopment which can result in vulnerability to endocrine disruptors such as phthalates during both the perinatal period and adolescence. Using a rat model, we have previously shown that perinatal exposure to an environmentally relevant phthalate mixture at low doses results in cognitive flexibility deficits in adults and a reduction in neuron and synapse number within the medial prefrontal cortex. Here, we further examined the behavioral effects of exposure to an environmentally relevant mixture of phthalates at low doses during either perinatal development or adolescence. Using the elevated plus maze, adult females, not males, exposed to phthalates during adolescence showed indications of reduced anxiety-like behavior while perinatal exposed animals were unaffected. There was no effect of adolescent phthalate exposure on cognitive flexibility using the attentional set shift paradigm in either sex, unlike the impairments we have previously reported following perinatal exposure (Kougias et al., 2018b). Finally, there was no effect of phthalate exposure during either time frame on sensorimotor gating measured using prepulse inhibition. Environmentally relevant phthalate exposure during the perinatal period or during adolescence did not induce widespread changes in the adult behaviors measured here.

Prepulse inhibition and “psychosis-proneness” in healthy individuals: An fMRI study

Objective

Prepulse inhibition (PPI) of the startle response provides an operational index of sensorimotor gating that is reliably demonstrable in both human and animal subjects. Patients with schizophrenia, first-degree relatives of patients with schizophrenia, patients with schizotypal personality disorder and healthy individuals scoring high on psychometric measures of psychosis-proneness display reduced PPI. This study examined associations between individual differences in “psychosis-proneness” and brain activity during a tactile prepulse inhibition paradigm previously found to reveal activation in controls and deficient activation in schizophrenia patients in the striatum, thalamus, insula, hippocampal, temporal, inferior frontal, and inferior parietal regions.

Methods

Fourteen right-handed healthy men underwent psychophysiological testing and functional magnetic resonance imaging (fMRI) during a 15-min tactile PPI paradigm involving the use of tactile stimuli as both the pulse (a 40-ms presentation of 30 psi air-puff) and the prepulse (a 20-ms presentation of 6 psi air-puff presented 30-ms or 120-ms before the pulse). Individual differences in “psychosis-proneness” were assessed with Psychoticism scale of the Eysenck Personality Questionnaire-Revised (EPQ-R).

Results

High psychosis-proneness was associated with lower PPI and reduced activity in the inferior frontal gyrus, insula extending to putamen and thalamus, parahippocampal gyrus, and inferior parietal and middle temporal regions. No regional activity correlated positively with psychosis-proneness.

Conclusions

The present observations extend the findings observed previously in people with schizophrenia to people with high psychosis-proneness, providing support to continuum theories of psychosis with implications for understanding trait-related neural deficits in schizophrenia.

Do young adolescents with first-episode psychosis or ADHD show sensorimotor gating deficits?

BACKGROUND

Early identification is important for patients with early-onset schizophrenia (SZ). Assessment of (candidate) endophenotypic markers for SZ, such as prepulse inhibition of the startle reflex (PPI), may help distinguish between the early-onset SZ and other psychiatric disorders. We explored whether PPI deficits usually seen in adult-onset SZ are present in young adolescents with either early-onset psychosis or attention deficit/hyperactivity disorder (ADHD).

METHODS

Twenty-five adolescents with first-episode, non-affective psychosis (FEP), 28 adolescents with ADHD and 43 healthy controls (HC), aged 12-17 years, were assessed with an auditory PPI paradigm.

RESULTS

No significant group differences were found in PPI. However, when the FEP group was divided into those already diagnosed with SZ (n = 13) and those without (N-SZ) (n = 12), and all four groups (SZ, N-SZ, ADHD and HC) were compared on percentage PPI in the 85/60 trials, significantly less PPI was found in patients with SZ than in the HC as well as the ADHD group. No significant group differences were found in explorative analyses on the other trial types. Additionally, startle magnitude was significantly higher in SZ than in N-SZ patients.

CONCLUSION

Young adolescents with SZ showed sensorimotor gating deficits similar to those usually found in adults with SZ and had larger startle magnitude than patients with other types of non-affective early-onset psychosis. No sensorimotor gating deficits were found in adolescents with ADHD. Our findings support the theory that deficient PPI is endophenotypic for SZ.

Interaction of reelin and stress on immobility in the forced swim test but not dopamine-mediated locomotor hyperactivity or prepulse inhibition disruption: Relevance to psychotic and mood disorders

RATIONALE

Psychotic disorders, such as schizophrenia, as well as some mood disorders, such as bipolar disorder, have been suggested to share common biological risk factors. One such factor is reelin, a large extracellular matrix glycoprotein that regulates neuronal migration during development as well as numerous activity-dependent processes in the adult brain. The current study sought to evaluate whether a history of stress exposure interacts with endogenous reelin levels to modify behavioural endophenotypes of relevance to psychotic and mood disorders.

METHODS

Heterozygous Reeler Mice (HRM) and wildtype (WT) controls were treated with 50mg/L of corticosterone (CORT) in their drinking water from 6 to 9weeks of age, before undergoing behavioural testing in adulthood. We assessed methamphetamine-induced locomotor hyperactivity, prepulse inhibition (PPI) of acoustic startle, short-term spatial memory in the Y-maze, and depression-like behaviour in the Forced-Swim Test (FST).

RESULTS

HRM genotype or CORT treatment did not affect methamphetamine-induced locomotor hyperactivity, a model of psychosis-like behaviour. At baseline, HRM showed decreased PPI at the commonly used 100msec interstimulus interval (ISI), but not at the 30msec ISI or following challenge with apomorphine. A history of CORT exposure potentiated immobility in the FST amongst HRM, but not WT mice. In the Y-maze, chronic CORT treatment decreased novel arm preference amongst HRM, reflecting reduced short-term spatial memory.

CONCLUSION

These data confirm a significant role of endogenous reelin levels on stress-related behaviour, supporting a possible role in both bipolar disorder and schizophrenia. However, an interaction of reelin deficiency with dopaminergic regulation of psychosis-like behaviour remains unclear.

Reduced Acoustic Startle Response and Prepulse Inhibition in the Tg4-42 Model of Alzheimer's Disease

Sensorimotor deficits have been described in several neuropsychiatric disorders including Alzheimer’s disease. The aim of the present study was to evaluate possible sensorimotor gating deficits in the Tg4-42 mouse model of Alzheimer’s disease using the prepulse inhibition task (PPI). Previous studies indicated that the hippocampus is essentially involved in the regulation of PPI. We analyzed 7-month-old homozygous Tg4-42 mice as mice at this age display severe neuron loss especially in the CA1 region of the hippocampus. Our results revealed a reduced startle response and PPI in Tg4-42 mice. The observed deficits in startle response and PPI are likely due to altered sensory processing abilities rather than hearing deficits as Tg4-42 displayed intact hearing in the fear conditioning task. The present study demonstrates for the first time that sensorimotor gating is impaired in Tg4-42 mice. Analyzing startle response as well as the PPI may offer valuable measurements to assess the efficacy of therapeutic strategies in the future in this Alzheimer’s disease model.

Drosophila Bruton's Tyrosine Kinase Regulates Habituation Latency and Facilitation in Distinct Mushroom Body Neurons

Habituation is the adaptive behavioral outcome of processes engaged in timely devaluation of non-reinforced repetitive stimuli, but the neuronal circuits and molecular mechanisms that underlie them are not well understood. To gain insights into these processes we developed and characterized a habituation assay to repetitive footshocks in mixed sex Drosophila groups and demonstrated that acute neurotransmission from adult α/β mushroom body (MB) neurons prevents premature stimulus devaluation. Herein we demonstrate that activity of the non-receptor tyrosine kinase dBtk protein is required within these neurons to prevent premature habituation. Significantly, we also demonstrate that the complementary process of timely habituation to the repetitive stimulation is facilitated by α'/β' MB neurons and also requires dBtk activity. Hence our results provide initial insights into molecular mechanisms engaged in footshock habituation within distinct MB neurons. Importantly, dBtk attenuation specifically within α'/β' neurons leads to defective habituation, which is readily reversible by administration of the antipsychotics clozapine and risperidone suggesting that the loss of the kinase may dysregulate monoamine receptors within these neurons, whose activity underlies the failure to habituate.SIGNIFICANCE STATEMENT Habituation refers to processes underlying decisions to attend or ignore stimuli, which are pivotal to brain function as they underlie selective attention and learning, but the circuits involved and the molecular mechanisms engaged by the process therein are poorly understood. We demonstrate that habituation to repetitive footshock involves two phases mediated by distinct neurons of the Drosophila mushroom bodies and require the function of the dBtk non-receptor tyrosine kinase. Moreover, habituation failure upon dBtk abrogation in neurons where it is required to facilitate the process is readily reversible by antipsychotics, providing conceptual links to particular symptoms of schizophrenia in humans, also characterized by habituation defects and ameliorated by these pharmaceuticals.

Rhodiola rosea root extract has antipsychotic-like effects in rodent models of sensorimotor gating

ETHNOPHARMACOLOGICAL RELEVANCE: The plant arctic root (Rhodiola rosea, L.) is growing in northern regions of Europe, Asia and North America. Extracts of R. rosea are used in traditional medicine for various conditions related to nervous system function. According to scientific studies from the last decades, the plant might have potential for use in the treatment of memory impairments, stress and depression, but reports concerning other neuropsychiatric disorders are scarce.

AIM OF THE STUDY

In this context, our study aimed to examine potential antipsychotic-like effects of R. rosea root extract.

MATERIALS AND METHODS

We tested the effects of R. rosea root extract on prepulse inhibition in rats and mice. Prepulse inhibition is an established operational measure of sensorimotor gating, which is impaired in schizophrenia and other psychotic disorders.

RESULTS

R. rosea root extract increased prepulse inhibition in rats and mice. Interestingly, the R. rosea extract had stronger effects in those individual animals that had low baseline levels of prepulse inhibition. Therefore, we performed further experiments in which we pharmacologically induced a prepulse inhibition deficit by two different psychostimulants, either the dopamine D2 receptor agonist apomorphine or the NMDA receptor antagonist dizocilpine (MK-801). Pre-treatment with the R. rosea extract significantly restored both, apomorphine- and dizocilpine-induced prepulse inhibition deficits.

CONCLUSIONS

The present study demonstrates that R. rosea extract robustly reverses prepulse inhibition deficits in rodents. This suggests antipsychotic-like effects of R. rosea extract. Future studies should focus on the pharmacological mechanisms underlying these effects.

Distinct Time-Course of Alterations of Groups I and II Metabotropic Glutamate Receptor and GABAergic Receptor Expression Along the Dorsoventral Hippocampal Axis in an Animal Model of Psychosis

Psychosis is a clinical state that encompasses a range of abnormal conditions, including distortions in sensory information processing and the resultant delusional thinking, emotional discordance and cognitive impairments. Upon developing this condition, the rate at which cognitive and behavioral deteriorations progress steadily increases suggesting an active contribution of the first psychotic event to the progression of structural and functional abnormalities and disease establishment in diagnosed patients. Changes in GABAergic and glutamatergic function, or expression, in the hippocampus have been proposed as a key factor in the pathophysiology of psychosis. However, little is known as to the time-point of onset of putative changes, to what extent they are progressive, and their relation to disease stabilization. Here, we characterized the expression and distribution patterns of groups I and II metabotropic glutamate (mGlu) receptors and GABA receptors 1 week and 3 months after systemic treatment with an N-methyl-D-aspartate receptor (NMDAR) antagonist (MK801) that is used to model a psychosis-like state in adult rats. We found an early alteration in the expression of mGlu1, mGlu2/3, and GABA_B receptors across the hippocampal dorsoventral and transverse axes. This expanded to include an up-regulation of mGlu5 levels across the entire CA1 region and a reduction in GABA_B expression, as well as GAD67-positive interneurons particularly in the dorsal hippocampus that appeared 3 months after treatment. Our findings indicate that a reduction of excitability may occur in the hippocampus soon after first-episode psychosis. This changes, over time, into increased excitability. These hippocampus-specific alterations are likely to contribute to the pathophysiology and stabilization of psychosis.

Temporally specific engagement of distinct neuronal circuits regulating olfactory habituation in Drosophila

Habituation is the process that enables salience filtering, precipitating perceptual changes that alter the value of environmental stimuli. To discern the neuronal circuits underlying habituation to brief inconsequential stimuli, we developed a novel olfactory habituation paradigm, identifying two distinct phases of the response that engage distinct neuronal circuits. Responsiveness to the continuous odor stimulus is maintained initially, a phase we term habituation latency and requires Rutabaga Adenylyl-Cyclase-depended neurotransmission from GABAergic Antennal Lobe Interneurons and activation of excitatory Projection Neurons (PNs) and the Mushroom Bodies. In contrast, habituation depends on the inhibitory PNs of the middle Antenno-Cerebral Track, requires inner Antenno-Cerebral Track PN activation and defines a temporally distinct phase. Collectively, our data support the involvement of Lateral Horn excitatory and inhibitory stimulation in habituation. These results provide essential cellular substrates for future analyses of the molecular mechanisms that govern the duration and transition between these distinct temporal habituation phases.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Changes in global and thalamic brain connectivity in LSD-induced altered states of consciousness are attributable to the 5-HT2A receptor

Background:

Lysergic acid diethylamide (LSD) has agonist activity at various serotonin (5-HT) and dopamine receptors. Despite the therapeutic and scientific interest in LSD, specific receptor contributions to its neurobiological effects remain unknown.

Methods:

We therefore conducted a double-blind, randomized, counterbalanced, cross-over studyduring which 24 healthy human participants received either (i) placebo+placebo, (ii) placebo+LSD (100 µg po), or (iii) Ketanserin, a selective 5-HT2A receptor antagonist,+LSD. We quantified resting-state functional connectivity via a data-driven global brain connectivity method and compared it to cortical gene expression maps.

Results:

LSD reduced associative, but concurrently increased sensory-somatomotor brain-wide and thalamic connectivity. Ketanserin fully blocked the subjective and neural LSD effects. Whole-brain spatial patterns of LSD effects matched 5-HT2A receptor cortical gene expression in humans.

Conclusions:

Together, these results strongly implicate the 5-HT2A receptor in LSD’s neuropharmacology. This study therefore pinpoints the critical role of 5-HT2A in LSD’s mechanism, which informs its neurobiology and guides rational development of psychedelic-based therapeutics.

Funding:

Funded by the Swiss National Science Foundation, the Swiss Neuromatrix Foundation, the Usona Institute, the NIH, the NIAA, the NARSAD Independent Investigator Grant, the Yale CTSA grant, and the Slovenian Research Agency.

Clinical trial number:

NCT02451072.

The psychedelic drug LSD alters thinking and perception. Users can experience hallucinations, in which they, for example, see things that are not there. Colors, sounds and objects can appear distorted, and time can seem to speed up or slow down. These changes bear some resemblance to the changes in thinking and perception that occur in certain psychiatric disorders, such as schizophrenia. Studying how LSD affects the brain could thus offer insights into the mechanisms underlying these conditions. There is also evidence that LSD itself could help to reduce the symptoms of depression and anxiety disorders.

Preller et al. have now used brain imaging to explore the effects of LSD on the brains of healthy volunteers. This revealed that LSD reduced communication among brain areas involved in planning and decision-making, but it increased communication between areas involved in sensation and movement. Volunteers whose brains showed the most communication between sensory and movement areas also reported the strongest effects of LSD on their thinking and perception.

Preller et al. also found that another drug called Ketanserin prevented LSD from altering how different brain regions communicate. It also prevented LSD from inducing changes in thinking and perception. Ketanserin blocks a protein called the serotonin 2A receptor, which is activated by a brain chemical called serotonin that, amongst other roles, helps to regulate mood. By mapping the location of the gene that produces the serotonin 2A receptor, Preller et al. showed that the receptor is present in brain regions that show altered communication after LSD intake, therefore pinpointing the importance of this receptor in the effects of LSD.

Psychiatric disorders that produce psychotic symptoms affect vast numbers of people worldwide. Further research into how LSD affects the brain could help us to better understand how such symptoms arise, and may also lead to the development of more effective treatments for a range of mental health conditions.

Chronic cannabis promotes pro-hallucinogenic signaling of 5-HT2A receptors through Akt/mTOR pathway

Long-term use of potent cannabis during adolescence increases the risk of developing schizophrenia later in life, but to date, the mechanisms involved remain unknown. Several findings suggest that the functional selectivity of serotonin 2A receptor (5-HT2AR) through inhibitory G-proteins is involved in the molecular mechanisms responsible for psychotic symptoms. Moreover, this receptor is dysregulated in the frontal cortex of schizophrenia patients. In this context, studies involving cannabis exposure and 5-HT2AR are scarce. Here, we tested in mice the effect of an early chronic Δ9-tetrahydrocannabinol (THC) exposure on cortical 5-HT2AR expression, as well as on its in vivo and in vitro functionality. Long-term exposure to THC induced a pro-hallucinogenic molecular conformation of the 5-HT2AR and exacerbated schizophrenia-like responses, such as prepulse inhibition disruption. Supersensitive coupling of 5-HT2AR toward inhibitory Gαi1-, Gαi3-, Gαo-, and Gαz-proteins after chronic THC exposure was observed, without changes in the canonical Gαq/11-protein pathway. In addition, we found that inhibition of Akt/mTOR pathway by rapamycin blocks the changes in 5-HT2AR signaling pattern and the supersensitivity to schizophrenia-like effects induced by chronic THC. The present study provides the first evidence of a mechanistic explanation for the relationship between chronic cannabis exposure in early life and increased risk of developing psychosis-like behaviors in adulthood.

Effects of Panax ginseng C.A. Meyer extract on the offspring of adult mice with maternal immune activation

To understand maternal immune activation (MIA) during prenatal development, the synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid [poly(I:C)] has been widely used in animal models to induce behavioral deficits similar to those in schizophrenia and other psychotic disorders. Panax ginseng C.A. Meyer (PG) extract is widely used to treat various kinds of nervous system disorders in Asia particularly China and Korea. The present study aimed to examine the effects of PG extract on MIA offspring using behavioral activity tests and protein expression analyses. Pregnant mice were exposed to poly(I:C) (5 mg/kg) or vehicle treatment on gestation day 9, and the resulting MIA offspring were subjected to vehicle or PG (300 mg/kg) treatment. In the acoustic startle response test, MIA-induced sensorimotor gating deficit was ameliorated by PG. The majority of behavioral parameters measured in the social interaction (non-aggressive or/and aggressive pattern), open field (number/duration of behavior) and forced swimming test (immobility behavior) were significantly altered in the MIA offspring. Western blot and immunohistochemical analyses of the medial prefrontal cortex indicated that the expression levels of certain neurodevelopmental proteins, including dihydropyrimidinase-related 2, LIM and SH3 domain 1, neurofilament medium, and discs large homolog 4, were decreased in the untreated MIA offspring, whereas PG treatment improved behavioral impairments and increased neurodevelopmental protein expression in MIA offspring. These results suggested that PG may be useful in neurodevelopmental disorder therapy, including psychiatric disorders such as schizophrenia, owing to its antipsychotic effects.

Meta-analysis on the association between genetic polymorphisms and prepulse inhibition of the acoustic startle response

Sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle response (ASR) has been proposed as one of the most promising electrophysiological endophenotypes of schizophrenia. During the past decade, a number of publications have reported significant associations between genetic polymorphisms and PPI in samples of schizophrenia patients and healthy volunteers. However, an overall evaluation of the robustness of these results has not been published so far. Therefore, we performed the first meta-analysis of published and unpublished associations between gene polymorphisms and PPI of ASR. Unpublished associations between genetic polymorphisms and PPI were derived from three independent samples. In total, 120 single observations from 16 independent samples with 2660 study participants and 43 polymorphisms were included. After correction for multiple testing based on false discovery rate and considering the number of analyzed polymorphisms, significant associations were shown for four variants, even though none of these associations survived a genome-wide correction (P<5∗10-8). These results imply that PPI might be modulated by four genotypes - COMT rs4680 (primarily in males), GRIK3 rs1027599, TCF4 rs9960767, and PRODH rs385440 - indicating a role of these gene variations in the development of early information processing deficits in schizophrenia. However, the overall impact of single genes on PPI is still rather small suggesting that PPI is - like the disease phenotype - highly polygenic. Future genome-wide analyses studies with large sample sizes will enhance our understanding on the genetic architecture of PPI.

Sensorimotor gating deficits in "two-hit" models of schizophrenia risk factors

Genetic and environmental models of neuropsychiatric disease have grown exponentially over the last 20years. One measure that is often used to evaluate the translational relevance of these models to human neuropsychiatric disease is prepulse inhibition of startle (PPI), an operational measure of sensorimotor gating. Deficient PPI characterizes several neuropsychiatric disorders but has been most extensively studied in schizophrenia. It has become a useful tool in translational neuropharmacological and molecular genetics studies because it can be measured across species using almost the same experimental parameters. Although initial studies of PPI in rodents were pharmacological because of the robust predictive validity of PPI for antipsychotic efficacy, more recently, PPI has become standard common behavioral measures used in genetic and neurodevelopmental models of schizophrenia. Here we review "two hit" models of schizophrenia and discuss the utility of PPI as a tool in phenotyping these models of relevant risk factors. In the review, we consider approaches to rodent models of genetic and neurodevelopmental risk factors and selectively review "two hit" models of gene×environment and environment×environment interactions in which PPI has been measured.

The effect of antipsychotic medications on acoustic startle latency in schizophrenia

Prepulse inhibition of the acoustic startle reflex (PPI) is extensively studied as a biomarker of schizophrenia (SCZ); however, antipsychotic medication can confound the measure. Latency, the time between the startling stimulus and the reflexive eye blink, provides an index of neural processing speed and is 90% heritable. SCZ subjects have slower latency than controls (CON). This study examined the effects of antipsychotic medication on startle latency. 108 CON and 132 SCZ subjects in three medication subgroups (94 on second-generation antipsychotics (SGA), 25 on first-generation antipsychotics (FGA), 13 unmedicated (NoMed)) were tested on a standard acoustic startle paradigm designed to measure startle magnitude, PPI, and latency. Latency was slower in SCZ compared to CON subjects (p=0.005). Latency did not differ between the three SCZ medication groups. When CON were added to that model, both the NoMed subjects (p=0.04) and the SGA subjects (p=0.003) were slower than CON subjects. For PPI, CON did not differ from SCZ analyzed as a single group. When SCZ subjects were divided into medication groups, PPI was lower in NoMed subjects than the CON group (p=0.03), the SGA group (p=0.02) and the FGA group (p=0.05). SCZ subjects on any medication did not differ from CON. Thus, latency was partially normalized by antipsychotic medication, but this did not obscure the slower latency in SCZ compared to CON. Therefore latency is both trait and state related, whereas medication normalized PPI and obscured any difference between SCZ and CON.

Deficient prepulse inhibition in schizophrenia in a multi-site cohort: Internal replication and extension

BACKGROUND

The Consortium on the Genetics of Schizophrenia (COGS) collected case-control endophenotype and genetic information from 2457 patients and healthy subjects (HS) across 5 test sites over 3.5 years. Analysis of the first "wave" (W1) of 1400 subjects identified prepulse inhibition (PPI) deficits in patients vs. HS. Data from the second COGS "wave" (W2), and the combined W(1+2), were used to assess: 1) the replicability of PPI deficits in this design; 2) the impact of response criteria on PPI deficits; and 3) PPI in a large cohort of antipsychotic-free patients.

METHODS

PPI in W2 HS (n=315) and schizophrenia patients (n=326) was compared to findings from W1; planned analyses assessed the impact of diagnosis, "wave" (1 vs. 2), and startle magnitude criteria. Combining waves allowed us to assess PPI in 120 antipsychotic-free patients, including many in the early course of illness.

RESULTS

ANOVA of all W(1+2) subjects revealed robust PPI deficits in patients across "waves" (p<0.0004). Strict response criteria excluded almost 39% of all subjects, disproportionately impacting specific subgroups; ANOVA in this smaller cohort confirmed no significant effect of "wave" or "wave x diagnosis" interaction, and a significant effect of diagnosis (p<0.002). Antipsychotic-free, early-illness patients had particularly robust PPI deficits.

DISCUSSION

Schizophrenia-linked PPI deficits were replicable across two multi-site "waves" of subjects collected over 3.5years. Strict response criteria disproportionately excluded older, male, non-Caucasian patients with low-normal hearing acuity. These findings set the stage for genetic analyses of PPI using the combined COGS wave 1 and 2 cohorts.

Relationships between the acoustic startle response and prepulse inhibition in C57BL/6J mice: a large-scale meta-analytic study

Prepulse inhibition (PPI) is the suppression of a startle reflex response to a startle stimulus that occurs when a weak prepulse stimulus precedes the startle stimulus. PPI is measured to assess sensorimotor gating across species, including humans and rodents. Reduced PPI, which is thought to reflect dysfunction of sensorimotor gating, is reported in patients with psychiatric disorders, such as schizophrenia, bipolar disorder, and post-traumatic stress disorder (PTSD), and in animal models of these disorders. Individual differences in basal startle reactivity occur even in a genetically homogenous group of animals; however, there is limited information regarding whether basal levels of the startle response are associated with variations in PPI levels. Here, to explore the relationship between an acoustic startle response (ASR) and PPI, we performed a meta-analysis of data obtained from more than 1300 C57BL/6J male mice on the influence of an ASR to 110- and 120-dB startle stimuli on the PPI levels of the ASR at 74- and 78-dB prepulse intensities. Examination of scatter plots of the ASR amplitudes and PPI levels followed by correlation analyses indicated that there is no simple linear relationship between the two measures; when mice were divided into three groups on the basis of their startle amplitudes, there were positive correlations between the amplitude of the ASR to the 110-dB stimulus and PPI levels in a group of mice that showed lower ASR amplitudes among the genetically homogenous group, whereas no significant correlations were identified in groups of mice that showed intermediate and higher ASR amplitudes. As indicated by the correlation analysis, the lowest responders to the 110-dB stimulus exhibited lower levels of PPI than the intermediate or higher responders. In contrast, for the 120-dB stimulus, a negative correlation was identified between the amplitude of the ASR to the 120-dB stimulus and the PPI levels in the groups of mice that showed intermediate or higher ASR amplitudes. Lower and intermediate responders showed higher levels of PPI than higher responders to the 120-dB stimulus. These findings suggest that basal startle reactivity may affect PPI levels in male C57BL/6J mice, thus representing one potential confounding factor that may confuse the interpretation of PPI results. These findings emphasize the importance of careful examination of startle reactivity to ensure a reliable assessment of PPI.

Meta-analysis of sensorimotor gating in patients with autism spectrum disorders

Prepulse inhibition (PPI) of startle response is a well-established neurophysiological marker of sensorimotor gating ability in psychiatric patients including those with autism spectrum disorders (ASD). PPI has been utilized as an indicator of the central inhibitory function and is potentially linked to the clinical features of this disease. However, it remains inconclusive whether ASD patients exhibit PPI deficits compared with healthy controls. The present meta-analysis aimed to explore the pooled effect sizes of PPI in ASD patients. We searched major electronic databases from 1990 to January 2017. Seven studies, consisting of 21 individual investigations with 135 healthy controls and 99 ASD patients, were obtained. The effect size, calculated as Hedges's g and 95% confidence interval, were estimated. Overall, we found ASD patients exhibited an impaired PPI compared with healthy controls (p = 0.008). Specifically, significant PPI deficits were observed among ASD children/adolescents, compared with their healthy counterparts (p = 0.019). However, differences in PPI responses were not observed among adults. Conclusively, our results reconciled the previous studies and showed that ASD children/adolescents, but not adults, exhibit reduced sensorimotor gating function compared to healthy controls. We also suggest that the parameters of PPI are particularly important and the results should be interpreted with cautions.

The effect of estrogenic compounds on psychosis-like behaviour in female rats

17β-estradiol treatment has shown benefit against schizophrenia symptoms, however long-term use may be associated with negative side-effects. Selective estrogen receptor modulators, such as raloxifene and tamoxifen, have been proposed as suitable alternatives to 17β-estradiol. An isomer of 17β-estradiol, 17α-estradiol, is considered less carcinogenic, and non-feminising in males, however little is known about its potential as a treatment for schizophrenia. Moreover, the mechanism underlying the therapeutic action of estrogens remains unclear. We aimed to investigate the ability of these estrogenic compounds to attenuate psychosis-like behaviour in rats. We used two acute pharmacologically-induced assays of psychosis-like behaviour: psychotomimetic drug-induced hyperlocomotion and disruption of prepulse inhibition (PPI). Female Long Evans rats were either intact, ovariectomised (OVX), or OVX and chronically treated with 17β-estradiol, 17α-estradiol, raloxifene or tamoxifen. Only 17β-estradiol treatment attenuated locomotor hyperactivity induced by the indirect dopamine receptor agonist, methamphetamine. 17β-estradiol- and tamoxifen-treated rats showed attenuated methamphetamine- and apomorphine (dopamine D1/D2 receptor agonist)-induced disruption of PPI. Raloxifene-treated rats showed attenuated apomorphine-induced PPI disruption only. Baseline PPI was significantly reduced following OVX, and this deficit was reversed by all estrogenic compounds. Further, PPI in OVX rats was increased following administration of apomorphine. This study confirms a protective effect of 17β-estradiol in two established animal models of psychosis, while tamoxifen showed beneficial effects against PPI disruption. In contrast, 17α-estradiol and raloxifene showed little effect on dopamine receptor-mediated psychosis-like behaviours. This study highlights the utility of some estrogenic compounds to attenuate psychosis-like behaviour in rats, supporting the notion that estrogens have therapeutic potential for psychotic disorders.

Dlgap1 knockout mice exhibit alterations of the postsynaptic density and selective reductions in sociability

The scaffold protein DLGAP1 is localized at the post-synaptic density (PSD) of glutamatergic neurons and is a component of supramolecular protein complexes organized by PSD95. Gain-of-function variants of DLGAP1 have been associated with obsessive-compulsive disorder (OCD), while haploinsufficient variants have been linked to autism spectrum disorder (ASD) and schizophrenia in human genetic studies. We tested male and female Dlgap1 wild type (WT), heterozygous (HT), and knockout (KO) mice in a battery of behavioral tests: open field, dig, splash, prepulse inhibition, forced swim, nest building, social approach, and sucrose preference. We also used biochemical approaches to examine the role of DLGAP1 in the organization of PSD protein complexes. Dlgap1 KO mice were most notable for disruption of protein interactions in the PSD, and deficits in sociability. Other behavioral measures were largely unaffected. Our data suggest that Dlgap1 knockout leads to PSD disruption and reduced sociability, consistent with reports of DLGAP1 haploinsufficient variants in schizophrenia and ASD.