Decrease in gamma-band auditory steady-state response in patients with treatment-resistant schizophrenia

Acute administration of NLX-101, a Serotonin 1A receptor agonist, improves auditory temporal processing during development in a mouse model of Fragile X Syndrome

BACKGROUND

Fragile X syndrome (FXS) is a leading known genetic cause of intellectual disability and autism spectrum disorders (ASD)-associated behaviors. A consistent and debilitating phenotype of FXS is auditory hypersensitivity that may lead to delayed language and high anxiety. Consistent with findings in FXS human studies, the mouse model of FXS, the Fmr1 knock out (KO) mouse, shows auditory hypersensitivity and temporal processing deficits. In electroencephalograph (EEG) recordings from humans and mice, these deficits manifest as increased N1 amplitudes in event-related potentials (ERP), increased gamma band single trial power (STP) and reduced phase locking to rapid temporal modulations of sound. In our previous study, we found that administration of the selective serotonin-1 A (5-HT1A)receptor biased agonist, NLX-101, protected Fmr1 KO mice from auditory hypersensitivity-associated seizures. Here we tested the hypothesis that NLX-101 will normalize EEG phenotypes in developing Fmr1 KO mice.

METHODS

To test this hypothesis, we examined the effect of NLX-101 on EEG phenotypes in male and female wildtype (WT) and Fmr1 KO mice. Using epidural electrodes, we recorded auditory event related potentials (ERP) and auditory temporal processing with a gap-in-noise auditory steady state response (ASSR) paradigm at two ages, postnatal (P) 21 and 30 days, from both auditory and frontal cortices of awake, freely moving mice, following NLX-101 (at 1.8 mg/kg i.p.) or saline administration.

RESULTS

Saline-injected Fmr1 KO mice showed increased N1 amplitudes, increased STP and reduced phase locking to auditory gap-in-noise stimuli versus wild-type mice, reproducing previously published EEG phenotypes. An acute injection of NLX-101 did not alter ERP amplitudes at either P21 or P30, but significantly reduces STP at P30. Inter-trial phase clustering was significantly increased in both age groups with NLX-101, indicating improved temporal processing. The differential effects of serotonin modulation on ERP, background power and temporal processing suggest different developmental mechanisms leading to these phenotypes.

CONCLUSIONS

These results suggest that NLX-101 could constitute a promising treatment option for targeting post-synaptic 5-HT1A receptors to improve auditory temporal processing, which in turn may improve speech and language function in FXS.

Discovery of VU6024578/BI02982816: An mGlu1 Positive Allosteric Modulator with Efficacy in Preclinical Antipsychotic and Cognition Models

Herein, we report progress toward a metabotropic glutamate receptor subtype 1 (mGlu1) positive allosteric modulator (PAM) clinical candidate and the discovery of VU6024578/BI02982816. From a weak high-throughput screening hit (VU0538160, EC50 > 10 μM, 71% Glumax), optimization efforts improved functional potency over 185-fold to deliver the selective (inactive on mGlu2-5,7,8) and CNS penetrant (rat Kp = 0.99, Kp,uu = 0.82; MDCK-MDR1 ER = 1.7, Papp = 73 × 10-6 cm/s) mGlu1 PAM (VU6024578/BI02982816, EC50 = 54 nM, 83% Glumax). An excellent rat pharmacokinetic profile allowed the evaluation of VU6024578/BI02982816 in both amphetamine-induced hyperlocomotion (minimum effective dose (MED) = 3 mg/kg, p.o.) and MK-801 induced disruptions of novel object recognition (MED = 10 mg/kg p.o.), thus providing efficacy in preclinical models of psychosis and cognition. However, unanticipated AEs in dog prevented further consideration as a candidate. Thus, VU6024578/BI02982816 can serve as a best-in-class in vivo rodent tool to study selective mGlu1 activation.

The influence of novelty detection on the 40-Hz auditory steady-state response in schizophrenia: A novel hypothesis from meta-analysis

The 40-Hz auditory steady-state response (ASSR) is influenced not only by parameters such as attention, stimulus type, and analysis level but also by stimulus duration and inter-stimulus interval (ISI). In this meta-analysis, we examined these parameters in 33 studies that investigated 40-Hz ASSRs in patients with schizophrenia. The average Hedges' g random effect sizes were - 0.47 and - 0.43 for spectral power and phase-locking, respectively. We also found differences in ASSR measures based on stimulus duration and ISI. In particular, ISI was shown to significantly influence differences in the 40-Hz ASSR between healthy controls and patients with schizophrenia. We proposed a novel hypothesis focusing on the role of novelty detection, dependent on stimulus duration and ISI, as a critical factor in determining these differences. Specifically, longer stimulus durations and shorter ISIs under random presentation, or shorter stimulus durations and longer ISIs under repetitive presentation, decrease the 40-Hz ASSR in healthy controls. Patients with schizophrenia show minimal changes in response to stimulus duration and ISI, thus reducing the difference between controls and patients. This hypothesis can consistently explain most of the studies that have failed to show a reduction in 40-Hz ASSR in patients with schizophrenia. Increased novelty-related activity, reflected as an increase in auditory evoked potential components at stimulus onset, such as the N1, could suppress the 40-Hz ASSR, potentially reducing the peak measures of spectral power and phase-locking. To establish the 40-Hz ASSR as a truly valuable biomarker for schizophrenia, further systematic research using paradigms with various stimulus durations and ISIs is needed.

Aberrant heartbeat-evoked potential in schizophrenia

Self-disturbance is considered a core feature underlying the psychopathology of schizophrenia. Interoception has an important role in the development of a sense of self, leading to increased interest in the potential contribution of abnormal interoception to self-disturbances in schizophrenia. Several neuropsychological studies have demonstrated aberrant interoception in schizophrenia. However, cortical interoceptive processing has not yet been thoroughly investigated. Thus, we sought to examine resting-state heartbeat-evoked potential (HEP) in this population. We hypothesized that patients with schizophrenia would exhibit significant alterations in HEP compared to healthy controls (HCs). In this cross-sectional electroencephalogram (EEG) study, we compared the HEPs between age- and sex-matched groups of patients with schizophrenia and HCs. A 10-min resting-state EEG with eyes closed and an electrocardiogram (ECG) were recorded and analyzed for the time window of 450 ms to 500 ms after an ECG R peak. A positive HEP shift was observed in the frontal-central regions (F [1, 82] = 7.402, p = 0.008, partial η2 = 0.009) in patients with schizophrenia (n = 61) when compared with HCs (n = 31) after adjusting for confounders such as age, sex, and heart rate. A cluster-based correction analysis revealed that the HEP around the right frontal area (Fp2, F4, and F8) showed the most significant group differences (F [1, 82] = 10.079, p = 0.002, partial η2 = 0.021), with a peak at the F4 electrode site (F [1, 82] = 12.646, p < 0.001, partial η2 = 0.069). We observed no correlation between HEP and symptoms in patients with schizophrenia. A positive shift of HEP during the late component could reflect a trait abnormality in schizophrenia. Further research is required to determine the association between the altered cortical interoceptive processing indexed with HEP and self-disturbances in schizophrenia.

Therapeutic potential of gamma entrainment using sensory stimulation for cognitive symptoms associated with schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with significant morbidity. Treatment options that address the spectrum of symptoms are limited, highlighting the need for innovative therapeutic approaches. Gamma Entrainment Using Sensory Stimulation (GENUS) is an emerging treatment for neuropsychiatric disorders that uses sensory stimulation to entrain impaired oscillatory network activity and restore brain function. Aberrant oscillatory activity often underlies the symptoms experienced by patients with schizophrenia. We propose that GENUS has therapeutic potential for schizophrenia. This paper reviews the current status of schizophrenia treatment and explores the use of sensory stimulation as an adjunctive treatment, specifically through gamma entrainment. Impaired gamma frequency entrainment is observed in patients, particularly in response to auditory and visual stimuli. Thus, sensory stimulation, such as music listening, may have therapeutic potential for individuals with schizophrenia. GENUS holds novel therapeutic potential to improve the lives of individuals with schizophrenia, but further research is required to determine the efficacy of GENUS, optimize its delivery and therapeutic window, and develop strategies for its implementation in specific patient populations.

Associations Between Structural Covariance Network and Antipsychotic Treatment Response in Schizophrenia

BACKGROUND AND HYPOTHESIS

Schizophrenia is associated with widespread cortical thinning and abnormality in the structural covariance network, which may reflect connectome alterations due to treatment effect or disease progression. Notably, patients with treatment-resistant schizophrenia (TRS) have stronger and more widespread cortical thinning, but it remains unclear whether structural covariance is associated with treatment response in schizophrenia.

STUDY DESIGN

We organized a multicenter magnetic resonance imaging study to assess structural covariance in a large population of TRS and non-TRS, who had been resistant and responsive to non-clozapine antipsychotics, respectively. Whole-brain structural covariance for cortical thickness was assessed in 102 patients with TRS, 77 patients with non-TRS, and 79 healthy controls (HC). Network-based statistics were used to examine the difference in structural covariance networks among the 3 groups. Moreover, the relationship between altered individual differentiated structural covariance and clinico-demographics was also explored.

STUDY RESULTS

Patients with non-TRS exhibited greater structural covariance compared with HC, mainly in the fronto-temporal and fronto-occipital regions, while there were no significant differences in structural covariance between TRS and non-TRS or HC. Higher individual differentiated structural covariance was associated with lower general scores of the Positive and Negative Syndrome Scale in the non-TRS group, but not in the TRS group.

CONCLUSIONS

These findings suggest that reconfiguration of brain networks via coordinated cortical thinning is related to treatment response in schizophrenia. Further longitudinal studies are warranted to confirm if greater structural covariance could serve as a marker for treatment response in this disease.

Auditory Steady-State Responses in Schizophrenia: An Updated Meta-Analysis

This meta-analysis investigates auditory steady-state responses (ASSRs) as potential biomarkers of schizophrenia, focusing on previously unexplored clinical populations, frequencies, and variables. We examined 37 studies, encompassing a diverse cohort of 1788 patients with schizophrenia, including 208 patients with first-episode psychosis, 281 at-risk individuals, and 1603 healthy controls. The results indicate moderate reductions in 40 Hz ASSRs in schizophrenia patients, with significantly greater reductions in first-episode psychosis patients and minimal changes in at-risk individuals. These results call into question the expected progression of ASSR alterations across all stages of schizophrenia. The analysis also revealed the sensitivity of ASSR alterations at 40 Hz to various factors, including stimulus type, level of analysis, and attentional focus. In conclusion, our research highlights ASSRs, particularly at 40 Hz, as potential biomarkers of schizophrenia, revealing varied implications across different stages of the disorder. This study enriches our understanding of ASSRs in schizophrenia, highlighting their potential diagnostic and therapeutic relevance, particularly in the early stages of the disease.

Click-train evoked steady state harmonic response as a novel pharmacodynamic biomarker of cortical oscillatory synchrony

Sensory networks naturally entrain to rhythmic stimuli like a click train delivered at a particular frequency. Such synchronization is integral to information processing, can be measured by electroencephalography (EEG) and is an accessible index of neural network function. Click trains evoke neural entrainment not only at the driving frequency (F), referred to as the auditory steady state response (ASSR), but also at its higher multiples called the steady state harmonic response (SSHR). Since harmonics play an important and non-redundant role in acoustic information processing, we hypothesized that SSHR may differ from ASSR in presentation and pharmacological sensitivity. In female SD rats, a 2 s-long train stimulus was used to evoke ASSR at 20 Hz and its SSHR at 40, 60 and 80 Hz, recorded from a prefrontal epidural electrode. Narrow band evoked responses were evident at all frequencies; signal power was strongest at 20 Hz while phase synchrony was strongest at 80 Hz. SSHR at 40 Hz took the longest time (∼180 ms from stimulus onset) to establish synchrony. The NMDA antagonist MK801 (0.025-0.1 mg/kg) did not consistently affect 20 Hz ASSR phase synchrony but robustly and dose-dependently attenuated synchrony of all SSHR. Evoked power was attenuated by MK801 at 20 Hz ASSR and 40 Hz SSHR only. Thus, presentation as well as pharmacological sensitivity distinguished SSHR from ASSR, making them non-redundant markers of cortical network function. SSHR is a novel and promising translational biomarker of cortical oscillatory dynamics that may have important applications in CNS drug development and personalized medicine.

40-Hz Auditory Steady-State Responses in Schizophrenia: Toward a Mechanistic Biomarker for Circuit Dysfunctions and Early Detection and Diagnosis

There is converging evidence that 40-Hz auditory steady-state responses (ASSRs) are robustly impaired in schizophrenia and could constitute a potential biomarker for characterizing circuit dysfunctions as well as enable early detection and diagnosis. Here, we provide an overview of the mechanisms involved in 40-Hz ASSRs, drawing on computational, physiological, and pharmacological data with a focus on parameters modulating the balance between excitation and inhibition. We will then summarize findings from electro- and magnetoencephalographic studies in participants at clinical high risk for psychosis, patients with first-episode psychosis, and patients with schizophrenia to identify the pattern of deficits across illness stages, the relationship with clinical variables, and the prognostic potential. Finally, data on genetics and developmental modifications will be reviewed, highlighting the importance of late modifications of 40-Hz ASSRs during adolescence, which are closely related to the underlying changes in GABA (gamma-aminobutyric acid) interneurons. Together, our review suggests that 40-Hz ASSRs may constitute an informative electrophysiological approach to characterize circuit dysfunctions in psychosis that could be relevant for the development of mechanistic biomarkers.