Hippocampal Hyperactivity as a Druggable Circuit-Level Origin of Aberrant Salience in Schizophrenia

The excitatory-inhibitory balance as a target for the development of novel drugs to treat schizophrenia

The intricate balance between excitation and inhibition (E/I) in the brain plays a crucial role in normative information processing. Dysfunctions in the E/I balance have been implicated in various psychiatric disorders, including schizophrenia (SCZ). In particular, abnormalities in GABAergic signaling, specifically in parvalbumin (PV)-containing interneurons, have been consistently observed in SCZ pathophysiology. PV interneuron function is vital for maintaining an ideal E/I balance, and alterations in PV interneuron-mediated inhibition contribute to circuit deficits observed in SCZ, including hippocampus hyperactivity and midbrain dopamine system overdrive. While current antipsychotic medications primarily target D2 dopamine receptors and are effective primarily in treating positive symptoms, novel therapeutic strategies aiming to restore the E/I balance could potentially mitigate not only positive symptoms but also negative symptoms and cognitive deficits. This could involve, for instance, increasing the inhibitory drive onto excitatory neurons or decreasing the putative enhanced pyramidal neuron activity due to functional loss of PV interneurons. Compounds targeting the glycine site at glutamate NMDA receptors and muscarinic acetylcholine receptors on PV interneurons that can increase PV interneuron drive, as well as drugs that increase the postsynaptic action of GABA, such as positive allosteric modulators of α5-GABA-A receptors, and decrease glutamatergic output, such as mGluR2/3 agonists, represent promising approaches. Preventive strategies aiming at E/I balance also represent a path to reduce the risk of transitioning to SCZ in high-risk individuals. Therefore, compounds with novel mechanisms targeting E/I balance provide optimism for more effective and tailored interventions in the management of SCZ.

Inhibition of 14-3-3 proteins increases the intrinsic excitability of mouse hippocampal CA1 pyramidal neurons

14-3-3 proteins are a family of regulatory proteins that are abundantly expressed in the brain and enriched at the synapse. Dysfunctions of these proteins have been linked to neurodevelopmental and neuropsychiatric disorders. Our group has previously shown that functional inhibition of these proteins by a peptide inhibitor, difopein, in the mouse brain causes behavioural alterations and synaptic plasticity impairment in the hippocampus. Recently, we found an increased cFOS expression in difopein-expressing dorsal CA1 pyramidal neurons, indicating enhanced neuronal activity by 14-3-3 inhibition in these cells. In this study, we used slice electrophysiology to determine the effects of 14-3-3 inhibition on the intrinsic excitability of CA1 pyramidal neurons from a transgenic 14-3-3 functional knockout (FKO) mouse line. Our data demonstrate an increase in intrinsic excitability associated with 14-3-3 inhibition, as well as reveal action potential firing pattern shifts after novelty-induced hyperlocomotion in the 14-3-3 FKO mice. These results provide novel information on the role 14-3-3 proteins play in regulating intrinsic and activity-dependent neuronal excitability in the hippocampus.

Correlation between desynchrony of hippocampal neural activity and hyperlocomotion in the model mice of schizophrenia and therapeutic effects of aripiprazole

AIMS

The hippocampus has been reported to be morphologically and neurochemically altered in schizophrenia (SZ). Hyperlocomotion is a characteristic SZ-associated behavioral phenotype, which is associated with dysregulated dopamine system function induced by hippocampal hyperactivity. However, the neural mechanism of hippocampus underlying hyperlocomotion remains largely unclear.

METHODS

Mouse pups were injected with N-methyl-D-aspartate receptor antagonist (MK-801) or vehicle twice daily on postnatal days (PND) 7-11. In the adulthood phase, one cohort of mice underwent electrode implantation in field CA1 of the hippocampus for the recording local field potentials and spike activity. A separate cohort of mice underwent surgery to allow for calcium imaging of the hippocampus while monitoring the locomotion. Lastly, the effects of atypical antipsychotic (aripiprazole, ARI) were evaluated on hippocampal neural activity.

RESULTS

We found that the hippocampal theta oscillations were enhanced in MK-801-treated mice, but the correlation coefficient between the hippocampal spiking activity and theta oscillation was reduced. Consistently, although the rate and amplitude of calcium transients of hippocampal neurons were increased, their synchrony and correlation to locomotion speed were disrupted. ARI ameliorated perturbations produced by the postnatal MK-801 treatment.

CONCLUSIONS

These results suggest that the disruption of neural coordination may underly the neuropathological mechanism for hyperlocomotion of SZ.

Modulation of hippocampal activity in schizophrenia with levetiracetam: a randomized, double-blind, cross-over, placebo-controlled trial

Hippocampal hyperactivity is a novel pharmacological target in the treatment of schizophrenia. We hypothesized that levetiracetam (LEV), a drug binding to the synaptic vesicle glycoprotein 2 A, normalizes hippocampal activity in persons with schizophrenia and can be measured using neuroimaging methods. Thirty healthy control participants and 30 patients with schizophrenia (28 treated with antipsychotic drugs), were randomly assigned to a double-blind, cross-over trial to receive a single administration of 500 mg oral LEV or placebo during two study visits. At each visit, we assessed hippocampal function using resting state fractional amplitude of low frequency fluctuations (fALFF), cerebral blood flow (CBF) with arterial spin labeling, and hippocampal blood-oxygen-level-dependent (BOLD) signal during a scene processing task. After placebo treatment, we found significant elevations in hippocampal fALFF in patients with schizophrenia, consistent with hippocampal hyperactivity. Additionally, hippocampal fALFF in patients with schizophrenia after LEV treatment did not significantly differ from healthy control participants receiving placebo, suggesting that LEV may normalize hippocampal hyperactivity. In contrast to our fALFF findings, we did not detect significant group differences or an effect of LEV treatment on hippocampal CBF. In the context of no significant group difference in BOLD signal, we found that hippocampal recruitment during scene processing is enhanced by LEV more significantly in schizophrenia. We conclude that pharmacological modulation of hippocampal hyperactivity in schizophrenia can be studied with some neuroimaging methods, but not others. Additional studies in different cohorts, employing alternate neuroimaging methods and study designs, are needed to establish levetiracetam as a treatment for schizophrenia.

Aberrant salience in cannabis-induced psychosis: a comparative study

Background

Natural Cannabis (NC) and Synthetic Cannabinoids (SCs) use can increase the risk and exacerbate the course of psychotic disorders. These could be influenced by the Aberrant Salience (AS) construct. It refers to an excess of attribution of meaning to stimuli that are otherwise regarded as neutral, thereby transform them into adverse, dangerous, or mysterious entities. This leads the patient to engage in aberrant and consequently incorrect interpretative efforts concerning the normal perception of reality and its relationship with our analytical abilities. AS appears to play a significant role in the onset and perpetuation of psychotic disorders. The internal conflict arising from aberrant attributions of significance leads to delusional thoughts, ultimately culminating in the establishment of a self-sustaining psychosis.

Aims

To examine the differences between psychoses course not associated with cannabis use and those associated with NC-use and SCs-use, in terms of psychotic and dissociative symptoms, AS, global functioning and suicidal ideation.

Methods

A sample of 62 patients with First Episode Psychosis (FEP) was divided into 3 groups: non cannabis users (non-users, N = 20); NC-users or rather Delta-9-tetrahydrocannabinol (THC) users (THC-users, N = 21); SCs-users, commonly referred to as SPICE-users (SPICE-users, N = 20). Each group underwent assessments at the onset of psychotic symptoms, as well as at the 3 months and 6 months marks, utilizing a range of psychopathological scales. These included the Positive and Negative Syndrome Scale (PANSS) for investigating psychotic symptoms, the Global Assessment of Functioning (GAF) scale for assessing overall functioning, the Dissociative Experiences Scale (DES-II) for measuring dissociative symptoms, the Scale for Suicide Ideation (SSI) for evaluating suicidal ideation and the Aberrant Salience Inventory (ASI) scale for gauging AS.

Results

SPICE-users showed more severe and persistent positive symptoms, while negative symptoms were mostly represented among non-users. Non-users showed better recovery than SPICE-users in global functioning. All groups showed a decrease in both ASI scores and subscale scores. SPICE-users exhibited higher global AS scores and less improvement in this aspect compared to other groups.

Conclusion

This study may help understanding the role of AS in both non-substance-related and substance-induced psychosis. This knowledge may lead clinician to a better diagnosis and identify patient-tailored psychopharmacological treatment.

The contributions of neonatal inhalation of copper to air pollution-induced neurodevelopmental outcomes in mice

Exposures to ambient ultrafine particle (UFP) air pollution (AP) during the early postnatal period in mice (equivalent to human third trimester brain development) produce male-biased changes in brain structure, including ventriculomegaly, reduced brain myelination, alterations in neurotransmitters and glial activation, as well as impulsive-like behavioral characteristics, all of which are also features characteristic of male-biased neurodevelopmental disorders (NDDs). The purpose of this study was to ascertain the extent to which inhaled Cu, a common contaminant of AP that is also dysregulated across multiple NDDs, might contribute to these phenotypes. For this purpose, C57BL/6J mice were exposed from postnatal days 4-7 and 10-13 for 4 hr/day to inhaled copper oxide (CuxOy) nanoparticles at an environmentally relevant concentration averaging 171.9 ng/m3. Changes in brain metal homeostasis and neurotransmitter levels were determined following termination of exposure (postnatal day 14), while behavioral changes were assessed in adulthood. CuxOy inhalation modified cortical metal homeostasis and produced male-biased disruption of striatal neurotransmitters, with marked increases in dopaminergic function, as well as excitatory/inhibitory imbalance and reductions in serotonergic function. Impulsive-like behaviors in a fixed ratio (FR) waiting-for-reward schedule and a fixed interval (FI) schedule of food reward occurred in both sexes, but more prominently in males, effects which could not be attributed to altered locomotor activity or short-term memory. Inhaled Cu as from AP exposures, at environmentally relevant levels experienced during development, may contribute to impaired brain function, as shown by its ability to disrupt brain metal homeostasis and striatal neurotransmission. In addition, its ability to evoke impulsive-like behavior, particularly in male offspring, may be related to striatal dopaminergic dysfunction that is known to mediate such behaviors. As such, regulation of air Cu levels may be protective of public health.

The impact of maternal immune activation on GABAergic interneuron development: A systematic review of rodent studies and their translational implications

Mothers exposed to infections during pregnancy disproportionally birth children who develop autism and schizophrenia, disorders associated with altered GABAergic function. The maternal immune activation (MIA) model recapitulates this risk factor, with many studies also reporting disruptions to GABAergic interneuron expression, protein, cellular density and function. However, it is unclear if there are species, sex, age, region, or GABAergic subtype specific vulnerabilities to MIA. Furthermore, to fully comprehend the impact of MIA on the GABAergic system a synthesised account of molecular, cellular, electrophysiological and behavioural findings was required. To this end we conducted a systematic review of GABAergic interneuron changes in the MIA model, focusing on the prefrontal cortex and hippocampus. We reviewed 102 articles that revealed robust changes in a number of GABAergic markers that present as gestationally-specific, region-specific and sometimes sex-specific. Disruptions to GABAergic markers coincided with distinct behavioural phenotypes, including memory, sensorimotor gating, anxiety, and sociability. Findings suggest the MIA model is a valid tool for testing novel therapeutics designed to recover GABAergic function and associated behaviour.

VTA multifaceted modulation of CA1 local circuits

Excitatory pyramidal (PYR) cell activation of interneurons (INT) produces network oscillations that underlie cognitive processes in the CA1. Neural projections from the ventral tegmental area (VTA) to the hippocampus contribute to novelty detection by modulating CA1 PYR and INT activity. The role of the VTA in the VTA-hippocampus loop is mostly attributed to the dopamine neurons although the VTA glutamate-releasing terminals are dominant in the hippocampus. Because of the traditional focus on VTA dopamine circuits, how VTA glutamate inputs modulate PYR activation of INT in CA1 neuronal ensembles is poorly understood and has not been distinguished from the VTA dopamine inputs. By combining CA1 extracellular recording with VTA photostimulation in anesthetized mice, we compared the effects of VTA dopamine and glutamate input on CA1 PYR/INT connections. Stimulation of VTA glutamate neurons shortened PYR/INT connection time without altering the synchronization or connectivity strength. Conversely, activation of VTA dopamine inputs delayed CA1 PYR/INT connection time and increased the synchronization in putative pairs. Taken together, we conclude that VTA dopamine and glutamate projections produce tract-specific effects on CA1 PYR/INT connectivity and synchrony. As such, selective activation or co-activation of these systems will likely produce a range of modulatory effects on local CA1 circuits.

Aberrant memory and delusional ideation: A pernicious partnership?

Delusions can be conceptualized as beliefs that are both at odds with consensus reality and espoused with high conviction. While delusions represent a cardinal symptom of schizophrenia, delusion-like beliefs can be found in the general population. Do similar cognitive mechanisms support delusionality across this spectrum? If so, what are they? Here, we examine evidence for a mechanistic role of the (associative) memory system in the formation and maintenance of delusions and delusion-like beliefs. While general neurocognitive metrics do not tend to associate with delusionality, our scoping review of the clinical and subclinical literature reveals several subdomains of memory function that do. These include a propensity to commit errors of commission (i.e., false alarms and intrusions), source memory biases, and metamemory impairment. We discuss how several of these effects may stem from aberrant associative memory function and offer recommendations for future research. Further, we propose a state/trait interaction model in which underlying traits (i.e., impaired associative and metamemory function) may become coupled with delusionality during states of acute psychosis, when memory function is particularly challenged by aberrant salience attribution and noisy perceptual input. According to this model, delusions may arise as explanations to high-salience (but low-source) mnemonic content that is endorsed with high confidence.

Levetiracetam Attenuates Adolescent Stress-induced Behavioral and Electrophysiological Changes Associated With Schizophrenia in Adult Rats

BACKGROUND AND HYPOTHESIS

Stress during adolescence is a major risk factor for schizophrenia. We have found previously in rats that adolescent stress caused, in adulthood, behavioral changes and enhanced ventral tegmental area (VTA) dopamine system activity, which were associated with dysregulation of the excitatory-inhibitory (E/I) balance in the ventral hippocampus (vHip). Levetiracetam, an anticonvulsant drug, regulates the release of neurotransmitters, including glutamate, via SV2A inhibition. It also modulates parvalbumin interneuron activity via Kv3.1 channels. Therefore, levetiracetam could ameliorate deficits in the E/I balance. We tested whether levetiracetam attenuate the adolescent stress-induced behavioral changes, vHip hyperactivity, and enhanced VTA dopamine system activity in adult rats.

STUDY DESIGN

Male Sprague-Dawley rats were subjected to a combination of daily footshock (postnatal day [PD] 31-40), and three 1 h-restraint stress sessions (at PD31, 32, and 40). In adulthood (PD62), animals were tested for anxiety responses (elevated plus-maze and light-dark box), social interaction, and cognitive function (novel object recognition test). The activity of vHip pyramidal neurons and VTA dopamine neurons was also recorded.

STUDY RESULTS

Adolescent stress produced anxiety-like responses and impaired sociability and cognitive function. Levetiracetam (10 mg/kg) reversed these changes. Levetiracetam also reversed the increased VTA dopamine neuron population activity and the enhanced firing rate of vHip pyramidal neurons induced by adolescent stress.

CONCLUSIONS

These findings suggest that levetiracetam attenuates the adverse outcomes associated with schizophrenia caused by stress during adolescence.

Chronic N-acetylcysteine treatment improves anhedonia and cognition in a mouse model of the schizophrenia prodrome

Schizophrenia is a severe psychiatric disorder whose neurodevelopmental pathogenesis includes a prodromal phase before its diagnostically decisive—namely psychotic—symptoms are present. This prodrome is characterized by cognitive and affective deficits, and it may constitute a critical time period for an early therapeutic intervention to improve or even prevent further disease development. N-acetylcysteine (NAC) is an easily repurposable compound that has recently shown promise in improving non-psychotic symptoms in patients with established schizophrenia. Its therapeutic mechanism may involve the amelioration of circuit abnormalities like a hyper-glutamatergic state and oxidative stress in cortex which have been proposed to drive the pathogenesis of this disease. However, it is currently unknown to what extent NAC can actually improve prodromal aberrations. To investigate this preclinically, we deployed the cyclin-D2 knockout mouse model (CD2-KO) that shares physiological and behavioral abnormalities with the schizophrenia prodrome, including a hyperactive CA1 region, and cognitive and affective deficits. Applying NAC chronically in drinking water (0.9 g/l) during development (∼P22–P70), we found that excessive novelty-induced hyperlocomotion was neither ameliorated during (∼P68) nor after (∼P75) treatment; similarly, T-maze working memory (tested after treatment; ∼P84) was unaffected. However, once chronic NAC treatment was resumed (at approximately P134) in those mice that had received it before, working memory, cognitive flexibility (tested under NAC), and anhedonia (sucrose-preference, tested 1 day after NAC-treatment stopped) were improved in CD2-KO mice. This suggests that chronic NAC treatment may be a therapeutic strategy to improve some cognitive and affective dysfunctions in the schizophrenia prodrome.

Relevance of interactions between dopamine and glutamate neurotransmission in schizophrenia

Dopamine (DA) and glutamate neurotransmission are strongly implicated in schizophrenia pathophysiology. While most studies focus on contributions of neurons that release only DA or glutamate, neither DA nor glutamate models alone recapitulate the full spectrum of schizophrenia pathophysiology. Similarly, therapeutic strategies limited to either system cannot effectively treat all three major symptom domains of schizophrenia: positive, negative, and cognitive symptoms. Increasing evidence suggests extensive interactions between the DA and glutamate systems and more effective treatments may therefore require the targeting of both DA and glutamate signaling. This offers the possibility that disrupting DA-glutamate circuitry between these two systems, particularly in the striatum and forebrain, culminate in schizophrenia pathophysiology. Yet, the mechanisms behind these interactions and their contributions to schizophrenia remain unclear. In addition to circuit- or system-level interactions between neurons that solely release either DA or glutamate, here we posit that functional alterations involving a subpopulation of neurons that co-release both DA and glutamate provide a novel point of integration between DA and glutamate systems, offering a key missing link in our understanding of schizophrenia pathophysiology. Better understanding of mechanisms underlying DA/glutamate co-release from these neurons may therefore shed new light on schizophrenia pathophysiology and lead to more effective therapeutics.

Comparison of electroconvulsive therapy and magnetic seizure therapy in schizophrenia: Structural changes/neuroplasticity

Electroconvulsive therapy (ECT) can effectively reduce the symptoms of schizophrenia, but may also impair cognitive function. A potential alternative is magnetic seizure therapy (MST), which has shown comparable efficacy with less severe cognitive disruption. This study compared ECT to MST for clinical efficacy and cognitive side effects. In addition, we examined the possible contributions of hippocampal volume changes and enhanced brain derived neurotrophic factor (BDNF) signaling to the therapeutic responses. Thirty-four confirmed schizophrenia patients were allocated to receive ECT (n = 16) or MST (n = 18) over a 4-week period. Schizophrenia symptoms were measured by PANSS, cognition by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), and serum BDNF and its precursor proBDNF by ELISA at baseline and following ECT or MST. Both treatments reduced PANSS scores with comparable efficacy, while MST was superior for preservation of RBANS language score. ECT significantly increased the volumes of the bilateral hippocampus and multiple subfields, while MST had no effect on hippocampal volume. The change in right hippocampal volume was correlated with proBDNF change among ECT and MST non-responders (< 25% decrease in PANSS score). MST reduced schizophrenia symptoms as effectively as ECT with slightly better preservation of cognitive function.

The shallow cognitive map hypothesis: A hippocampal framework for thought disorder in schizophrenia

Memories are not formed in isolation. They are associated and organized into relational knowledge structures that allow coherent thought. Failure to express such coherent thought is a key hallmark of Schizophrenia. Here we explore the hypothesis that thought disorder arises from disorganized Hippocampal cognitive maps. In doing so, we combine insights from two key lines of investigation, one concerning the neural signatures of cognitive mapping, and another that seeks to understand lower-level cellular mechanisms of cognition within a dynamical systems framework. Specifically, we propose that multiple distinct pathological pathways converge on the shallowing of Hippocampal attractors, giving rise to disorganized Hippocampal cognitive maps and driving conceptual disorganization. We discuss the available evidence at the computational, behavioural, network, and cellular levels. We also outline testable predictions from this framework, including how it could unify major chemical and psychological theories of schizophrenia and how it can provide a rationale for understanding the aetiology and treatment of the disease.

Distinct contributions of GluA1-containing AMPA receptors of different hippocampal subfields to salience processing, memory and impulse control

Schizophrenia is associated with a broad range of severe and currently pharmacoresistant cognitive deficits. Prior evidence suggests that hypofunction of AMPA-type glutamate receptors (AMPARs) containing the subunit GLUA1, encoded by GRIA1, might be causally related to impairments of selective attention and memory in this disorder, at least in some patients. In order to clarify the roles of GluA1 in distinct cell populations, we investigated behavioural consequences of selective Gria1-knockout in excitatory neurons of subdivisions of the prefrontal cortex and the hippocampus, assessing sustained attention, impulsivity, cognitive flexibility, anxiety, sociability, hyperactivity, and various forms of short-term memory in mice. We found that virally induced reduction of GluA1 across multiple hippocampal subfields impaired spatial working memory. Transgene-mediated ablation of GluA1 from excitatory cells of CA2 impaired short-term memory for conspecifics and objects. Gria1 knockout in CA3 pyramidal cells caused mild impairments of object-related and spatial short-term memory, but appeared to partially increase social interaction and sustained attention and to reduce motor impulsivity. Our data suggest that reduced hippocampal GluA1 expression-as seen in some patients with schizophrenia-may be a central cause particularly for several short-term memory deficits. However, as impulse control and sustained attention actually appeared to improve with GluA1 ablation in CA3, strategies of enhancement of AMPAR signalling likely require a fine balance to be therapeutically effective across the broad symptom spectrum of schizophrenia.

Disrupted mossy fiber connections from defective embryonic neurogenesis contribute to SOX11-associated schizophrenia

Abnormal mossy fiber connections in the hippocampus have been implicated in schizophrenia. However, it remains unclear whether this abnormality in the patients is genetically determined and whether it contributes to the onset of schizophrenia. Here, we showed that iPSC-derived hippocampal NPCs from schizophrenia patients with the A/A allele at SNP rs16864067 exhibited abnormal NPC polarity, resulting from the downregulation of SOX11 by this high-risk allele. In the SOX11-deficient mouse brain, abnormal NPC polarity was also observed in the hippocampal dentate gyrus, and this abnormal NPC polarity led to defective hippocampal neurogenesis-specifically, irregular neuroblast distribution and disrupted granule cell morphology. As granule cell synapses, the mossy fiber pathway was disrupted, and this disruption was resistant to activity-induced mossy fiber remodeling in SOX11 mutant mice. Moreover, these mutant mice exhibited diminished PPI and schizophrenia-like behaviors. Activation of hippocampal neurogenesis in the embryonic brain, but not in the adult brain, partially alleviated disrupted mossy fiber connections and improved schizophrenia-related behaviors in mutant mice. We conclude that disrupted mossy fiber connections are genetically determined and strongly correlated with schizophrenia-like behaviors in SOX11-deficient mice. This disruption may reflect the pathological substrate of SOX11-associated schizophrenia.

14-3-3 Dysfunction in Dorsal Hippocampus CA1 (dCA1) Induces Psychomotor Behavior via a dCA1-Lateral Septum-Ventral Tegmental Area Pathway

While hippocampal hyperactivity is implicated in psychosis by both human and animal studies, whether it induces a hyperdopaminergic state and the underlying neural circuitry remains elusive. Previous studies established that region-specific inhibition of 14-3-3 proteins in the dorsal hippocampus CA1 (dCA1) induces schizophrenia-like behaviors in mice, including a novelty-induced locomotor hyperactivity. In this study, we showed that 14-3-3 dysfunction in the dCA1 over-activates ventral tegmental area (VTA) dopaminergic neurons, and such over-activation is necessary for eliciting psychomotor behavior in mice. We demonstrated that such hippocampal dysregulation of the VTA during psychomotor behavior is dependent on an over-activation of the lateral septum (LS), given that inhibition of the LS attenuates over-activation of dopaminergic neurons and psychomotor behavior induced by 14-3-3 inhibition in the dCA1. Moreover, 14-3-3 inhibition-induced neuronal activations within the dCA1-LS-VTA pathway and psychomotor behavior can be reproduced by direct chemogenetic activation of LS-projecting dCA1 neurons. Collectively, these results suggest that 14-3-3 dysfunction in the dCA1 results in hippocampal hyperactivation which leads to psychomotor behavior via a dCA1-LS-VTA pathway.

Hippocampal Glutamate and Positive Symptom Severity in Clinical High Risk for Psychosis

This study examines the association between increased hippocampal glutamate and higher total positive symptom severity in converters to psychosis.

Ventral Striatal-Hippocampus Coupling During Reward Processing as a Stratification Biomarker for Psychotic Disorders

BACKGROUND

Altered ventral striatal (vST) activation to reward expectancy is a well-established intermediate phenotype for psychiatric disorders, specifically schizophrenia (SZ). Preclinical research suggests that striatal alterations are related to a reduced inhibition by the hippocampal formation, but its role in human transdiagnostic reward-network dysfunctions is not well understood.

METHODS

We performed functional magnetic resonance imaging during reward processing in 728 individuals including healthy control subjects (n = 396), patients (SZ: n = 46; bipolar disorder: n = 45; major depressive disorder: n = 60), and unaffected first-degree relatives (SZ: n = 46; bipolar disorder: n = 50; major depressive disorder: n = 85). We assessed disorder-specific differences in functional vST-hippocampus coupling and transdiagnostic associations with dimensional measures of positive, negative, and cognitive symptoms. We also probed the genetic underpinning using polygenic risk scores for SZ in a subset of healthy participants (n = 295).

RESULTS

Functional vST-hippocampus coupling was 1) reduced in patients with SZ and bipolar disorder (p_FWE < .05, small-volume corrected [SVC]); 2) associated transdiagnostically to dimensional measures of positive (p_FWE = .01, SVC) and cognitive (p_FWE = .02, SVC), but not negative, (p_FWE > .05, SVC) symptoms; and 3) reduced in first-degree relatives of patients with SZ (p_FWE = .017, SVC) and linked to the genetic risk for SZ in healthy participants (p = .035).

CONCLUSIONS

We provide evidence that reduced vST-hippocampus coupling during reward processing is an endophenotype for SZ linked to positive and cognitive symptoms, supporting current preclinical models of the emergence of psychosis. Moreover, our data indicate that vST-hippocampus coupling is familial and linked to polygenic scores for SZ, supporting the use of this measure as an intermediate phenotype for psychotic disorders.

Hippocampal Disinhibition Reduces Contextual and Elemental Fear Conditioning While Sparing the Acquisition of Latent Inhibition

Hippocampal neural disinhibition, i.e., reduced GABAergic inhibition, is a key feature of schizophrenia pathophysiology. The hippocampus is an important part of the neural circuitry that controls fear conditioning and can also modulate prefrontal and striatal mechanisms, including dopamine signaling, which play a role in salience modulation. Consequently, hippocampal neural disinhibition may contribute to impairments in fear conditioning and salience modulation reported in schizophrenia. Therefore, we examined the effect of ventral hippocampus (VH) disinhibition in male rats on fear conditioning and salience modulation, as reflected by latent inhibition (LI), in a conditioned emotional response (CER) procedure. A flashing light was used as the conditioned stimulus (CS), and conditioned suppression was used to index conditioned fear. In experiment 1, VH disinhibition via infusion of the GABA-A receptor antagonist picrotoxin before CS pre-exposure and conditioning markedly reduced fear conditioning to both the CS and context; LI was evident in saline-infused controls but could not be detected in picrotoxin-infused rats because of the low level of fear conditioning to the CS. In experiment 2, VH picrotoxin infusions only before CS pre-exposure did not affect the acquisition of fear conditioning or LI. Together, these findings indicate that VH neural disinhibition disrupts contextual and elemental fear conditioning, without affecting the acquisition of LI. The disruption of fear conditioning resembles aversive conditioning deficits reported in schizophrenia and may reflect a disruption of neural processing both within the hippocampus and in projection sites of the hippocampus.

Upregulation of heat-shock protein HSP-70 and glutamate transporter-1/glutamine synthetase in the striatum and hippocampus in haloperidol-induced dopamine-supersensitivity-state rats

BACKGROUND

The excessive blockade of dopamine D2 receptors (DRD2s) with long-term antipsychotic treatment is known to induce a dopamine supersensitivity state (DSS). The mechanism of DSS is speculated to be a compensatory up-regulation of DRD2s, but an excess blockade of DRD2s can also cause glutamatergic neuronal damage. Herein, we investigated whether antipsychotic-induced neuronal damage plays a role in the development of DSS.

METHODS

Haloperidol (HAL; 0.75 mg/kg/day for 14 days) or vehicle was administered to rats via an osmotic mini-pump. Haloperidol-treated rats were divided into groups of DSS rats and non-DSS rats based on their voluntary locomotion data. We then determined the tissue levels of glutamate transporter-1 (GLT-1)/glutamine synthetase (GS) and heat shock protein-70 (HSP-70) in the rats' brain regions.

RESULTS

The levels of HSP-70 in the striatum and CA-3 region of the DSS rats were significantly higher than those of the control and non-DSS rats, whereas the dentate gyrus HSP-70 levels in both the DSS and non-DSS rats were increased versus the controls. The levels of GLT-1/GS in the CA-3 and nucleus accumbens were increased in the DSS rats.

CONCLUSIONS

These results suggest that the DSS rats experienced striatal neuronal damage and indicate that a HAL-induced upregulation of HSP-70 and the GLT-1/GS system in the CA3 may be involved in the development of DSS. It remains unknown why the non-DSS rats did not suffer neuronal damage. In view of the need for therapeutic strategies for treatment-resistant schizophrenia, dopamine supersensitivity psychosis, and tardive dyskinesia, further investigations of our findings are warranted.

Nanotechnology Approaches for Enhanced CNS Drug Delivery in the Management of Schizophrenia

Schizophrenia is a neuropsychiatric disorder mainly affecting the central nervous system, presented with auditory and visual hallucinations, delusion and withdrawal from society. Abnormal dopamine levels mainly characterise the disease; various theories of neurotransmitters explain the pathophysiology of the disease. The current therapeutic approach deals with the systemic administration of drugs other than the enteral route, altering the neurotransmitter levels within the brain and providing symptomatic relief. Fluid biomarkers help in the early detection of the disease, which would improve the therapeutic efficacy. However, the major challenge faced in CNS drug delivery is the blood-brain barrier. Nanotherapeutic approaches may overcome these limitations, which will improve safety, efficacy, and targeted drug delivery. This review article addresses the main challenges faced in CNS drug delivery and the significance of current therapeutic strategies and nanotherapeutic approaches for a better understanding and enhanced drug delivery to the brain, which improve the quality of life of schizophrenia patients.

Modeling intrahippocampal effects of anterior hippocampal hyperactivity relevant to schizophrenia using chemogenetic excitation of long axis-projecting mossy cells in the mouse dentate gyrus

Background

The anterior hippocampus of individuals with early psychosis or schizophrenia is hyperactive, as is the ventral hippocampus in many rodent models for schizophrenia risk. Mossy cells (MCs) of the ventral dentate gyrus (DG) densely project in the hippocampal long axis, targeting both dorsal DG granule cells and inhibitory interneurons. MCs are responsive to stimulation throughout hippocampal subfields and thus may be suited to detect hyperactivity in areas where it originates such as CA1. Here, we tested the hypothesis that hyperactivation of ventral MCs activates dorsal DG granule cells to influence dorsal hippocampal function.

Methods

In CD-1 mice, we targeted dorsal DG-projecting ventral MCs using an adeno-associated virus intersectional strategy. In vivo fiber photometry recording of ventral MCs was performed during exploratory behaviors. We used excitatory chemogenetic constructs to test the effects of ventral MC hyperactivation on long-term spatial memory during an object location memory task.

Results

Photometry revealed that ventral MCs were activated during exploratory rearing. Ventral MCs made functional monosynaptic inputs to dorsal DG granule cells, and chemogenetic activation of ventral MCs modestly increased activity of dorsal DG granule cells measured by c-Fos. Finally, chemogenetic activation of ventral MCs during the training phase of an object location memory task impaired test performance 24 hours later, without effects on locomotion or object exploration.

Conclusions

These data suggest that ventral MC activation can directly excite dorsal granule cells and interfere with dorsal DG function, supporting future study of their in vivo activity in animal models for schizophrenia featuring ventral hyperactivity.

The Medial Septum as a Potential Target for Treating Brain Disorders Associated With Oscillopathies

The medial septum (MS), as part of the basal forebrain, supports many physiological functions, from sensorimotor integration to cognition. With often reciprocal connections with a broad set of peers at all major divisions of the brain, the MS orchestrates oscillatory neuronal activities throughout the brain. These oscillations are critical in generating sensory and emotional salience, locomotion, maintaining mood, supporting innate anxiety, and governing learning and memory. Accumulating evidence points out that the physiological oscillations under septal influence are frequently disrupted or altered in pathological conditions. Therefore, the MS may be a potential target for treating neurological and psychiatric disorders with abnormal oscillations (oscillopathies) to restore healthy patterns or erase undesired ones. Recent studies have revealed that the patterned stimulation of the MS alleviates symptoms of epilepsy. We discuss here that stimulus timing is a critical determinant of treatment efficacy on multiple time scales. On-demand stimulation may dramatically reduce side effects by not interfering with normal physiological functions. A precise pattern-matched stimulation through adaptive timing governed by the ongoing oscillations is essential to effectively terminate pathological oscillations. The time-targeted strategy for the MS stimulation may provide an effective way of treating multiple disorders including Alzheimer's disease, anxiety/fear, schizophrenia, and depression, as well as pain.