Phencyclidine administration during neurodevelopment alters network activity in prefrontal cortex and hippocampus in adult rats

Postnatal hypofunction of N-methyl-D-aspartate receptors alters perforant path synaptic plasticity and filtering and impairs dentate gyrus-mediated spatial discrimination

BACKGROUND AND PURPOSE

Transient hypofunction of the NMDA receptor represents a convergence point for the onset and further development of psychiatric disorders, including schizophrenia. Although the cumulative evidence indicates dysregulation of the hippocampal formation in schizophrenia, the integrity of the synaptic transmission and plasticity conveyed by the somatosensorial inputs to the dentate gyrus, the perforant pathway synapses, have barely been explored in this pathological condition.

EXPERIMENTAL APPROACH

We identified a series of synaptic alterations of the lateral and medial perforant paths in animals postnatally treated with the NMDA antagonist MK-801. This dysregulation suggests decreased cognitive performance, for which the dentate gyrus is critical.

KEY RESULTS

We identified alterations in the synaptic properties of the lateral and medial perforant paths to the dentate gyrus synapses in slices from MK-801-treated animals. Altered glutamate release and decreased synaptic strength precede an impairment in the induction and expression of long-term potentiation (LTP) and CB1 receptor-mediated long-term depression (LTD). Remarkably, by inhibiting the degradation of 2-arachidonoylglycerol (2-AG), an endogenous ligand of the CB1 receptor, we restored the LTD in animals treated with MK-801. Additionally, we showed for the first time, that spatial discrimination, a cognitive task that requires dentate gyrus integrity, is impaired in animals exposed to transient hypofunction of NMDA receptors.

CONCLUSION AND IMPLICATIONS

Dysregulation of glutamatergic transmission and synaptic plasticity from the entorhinal cortex to the dentate gyrus has been demonstrated, which may explain the cellular dysregulations underlying the altered cognitive processing in the dentate gyrus associated with schizophrenia.

Inhibition of fatty acid amide hydrolase reverses aberrant prefrontal gamma oscillations in the sub-chronic PCP model for schizophrenia

Hypofunctioning of NMDA receptors, and the resulting shift in the balance between excitation and inhibition, is considered a key process in the pathophysiology of schizophrenia. One important manifestation of this phenomenon is changes in neural oscillations, those above 30 Hz (i.e., gamma-band oscillations), in particular. Although both preclinical and clinical studies observed increased gamma activity following acute administration of NMDA receptor antagonists, the relevance of this phenomenon has been recently questioned given the reduced gamma oscillations typically observed during sensory and cognitive tasks in schizophrenia. However, there is emerging, yet contradictory, evidence for increased spontaneous gamma-band activity (i.e., at rest or under baseline conditions). Here, we use the sub-chronic phencyclidine (PCP) rat model for schizophrenia, which has been argued to model the pathophysiology of schizophrenia more closely than acute NMDA antagonism, to investigate gamma oscillations (30-100 Hz) in the medial prefrontal cortex of anesthetized animals. While baseline gamma oscillations were not affected, oscillations induced by train stimulation of the posterior dorsal CA1 (pdCA1) field of the hippocampus were enhanced in PCP-treated animals (5 mg/kg, twice daily for 7 days, followed by a 7-day washout period). This effect was reversed by pharmacological enhancement of endocannabinoid levels via systemic administration of URB597 (0.3 mg/kg), an inhibitor of the catabolic enzyme of the endocannabinoid anandamide. Intriguingly, the pharmacological blockade of CB1 receptors by AM251 unmasked a reduced gamma oscillatory activity in PCP-treated animals. The findings are consistent with the observed effects of URB597 and AM251 on behavioral deficits reminiscent of the symptoms of schizophrenia and further validate the potential for cannabinoid-based drugs as a treatment for schizophrenia.

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.

NMDA receptor activity during postnatal development determines intrinsic excitability and mossy fiber long-term potentiation of CA3 pyramidal cells

Experimental manipulations that interfere with the functional expression of N-methyl-D-aspartate receptors (NMDARs) during prenatal neurodevelopment or critical periods of postnatal development are models that mimic behavioral and neurophysiological abnormalities of schizophrenia. Blockade of NMDARs with MK-801 during early postnatal development alters glutamate release and impairs the induction of NMDAR-dependent long-term plasticity at the CA1 area of the hippocampus. However, it remains unknown if other forms of hippocampal plasticity, such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated short- and long-term potentiation, are compromised in response to neonatal treatment with MK-801. Consistent with this tenet, short- and long-term potentiation between dentate gyrus axons, the mossy fibers (MF), onto CA3 pyramidal cells (CA3 PCs) are mediated by AMPARs. By combining whole-cell patch clamp and extracellular recordings, we have demonstrated that transient blockade of NMDARs during early postnatal development induces a series of pre- and postsynaptic modifications at the MF-CA3 synapse. We found reduced glutamate release from the mossy boutons, increased paired-pulse ratio, and reduced AMPAR-mediated MF LTP levels. At the postsynaptic level, we found an altered NMDA/AMPA ratio and dysregulation of several potassium conductances that increased the excitability of CA3 PCs. In addition, MK-801-treated animals exhibited impaired spatial memory retrieval in the Barnes maze task. Our data demonstrate that transient hypofunction of NMDARs impacts NMDAR-independent forms of synaptic plasticity of the hippocampus.

Methoxphenidine (MXP) induced abnormalities: Addictive and schizophrenia-related behaviours based on an imbalance of neurochemicals in the brain

BACKGROUND AND PURPOSE

Methoxphenidine is a dissociative-based novel psychoactive designer drug. Although fatal accidents from methoxphenidine abuse have been reported, recreational use of the drug continues. We aim to provide scientific supportfor legal regulation of recreational abuse of methoxphenidine by demonstrating its the pharmacological action.

EXPERIMENTAL APPROACH

Addictive potential of methoxphenidine was examined using intravenous self-administration test with rats and conditioned place preference test with mice. Further, a series of behavioural tests (open field test, elevated plus maze test, novel object recognition test, social interaction test and tail suspension test) performed to assess whether methoxphenidine caused schizophrenia-related symptoms in mice. Additionally, neurotransmitter enzyme-linked immunosorbent assay and western blot were used to confirm methoxphenidine-induced neurochemical changes in specific brain regions related to abnormal behaviours.

KEY RESULTS

Methoxphenidine caused addictive behaviours via reinforcing and rewarding effects. Consistently, methoxphenidine induced over-activation of dopamine pathways in the nuclear accumbens, indicating activation of the brain reward circuit. Also, methoxphenidine caused all categories of schizophrenia-related symptoms, including positive symptoms (hyperactivity, impulsivity), negative symptoms (anxiety, social withdrawal, depression) and cognitive impairment. Consistently, methoxphenidine led to the disruption of the hippocampal-prefrontal cortex pathway that is considered to be pathological involved in schizophrenia.

CONCLUSIONS AND IMPLICATIONS

We demonastrate that methoxphenidine causes addictive and schizophrenia-like behaviours and induces neurochemical changes in brain regions associated with these behaviours. We propose that methoxphenidine could be used in developing useful animal disease models and that it also requires legal restrictions on its recreational use.

Neonatal phencyclidine and social isolation in the rat: effects of clozapine on locomotor activity, social recognition, prepulse inhibition, and executive functions deficits

RATIONALE

There is a need to develop animal models of schizophrenia-like behaviors that have both construct and predictive validity. Recently, a neonatal phencyclidine (PCP) and post-weaning social isolation dual-hit model was developed; however, its face and predictive validities need to be further investigated.

OBJECTIVE

The aims of this study were to extend the characterization of the behavioral changes occurring in the neonatal PCP and post-weaning social isolation dual-hit rat model and to evaluate the effects of chronic treatment with clozapine on signs related to schizophrenia.

METHODS

Male Wistar rat pups were treated with PCP (10 mg/kg s.c.) on postnatal days (PND) 7, 9, and 11. Starting from weaning, neonatal PCP-treated rat pups were socially isolated, while control saline-treated rats were group housed. At adulthood, rats were assessed using behavioral tasks evaluating locomotor activity, social recognition, prepulse inhibition, and reversal learning. Clozapine (3 mg/kg i.p.) was administered daily starting from a week before behavioral tests and until the end of the study.

RESULTS

Neonatal PCP-treated and post-weaning social isolated (PCP-SI) rats displayed persistent and robust locomotor hyperactivity as well as social recognition impairment. The latter could not be explained by variations in the motivation to interact with a juvenile rat. Weak-to-moderate deficits in prepulse inhibition and reversal learning were also observed. Chronic treatment with clozapine attenuated the observed locomotor hyperactivity and social recognition deficits.

CONCLUSION

The PCP-SI model presents enduring and robust deficits (hyperactivity and social recognition impairment) associated with positive symptoms and cognitive/social deficits of schizophrenia, respectively. These deficits are normalized by chronic treatment with clozapine, thereby confirming the predictive validity of this animal model.

Polygenic effects of schizophrenia on hippocampal grey matter volume and hippocampus-medial prefrontal cortex functional connectivity

BACKGROUND

Schizophrenia is a complex mental disorder with high heritability and polygenic inheritance. Multimodal neuroimaging studies have also indicated that abnormalities of brain structure and function are a plausible neurobiological characterisation of schizophrenia. However, the polygenic effects of schizophrenia on these imaging endophenotypes have not yet been fully elucidated.

AIMS

To investigate the effects of polygenic risk for schizophrenia on the brain grey matter volume and functional connectivity, which are disrupted in schizophrenia.

METHOD

Genomic and neuroimaging data from a large sample of Han Chinese patients with schizophrenia (N = 509) and healthy controls (N = 502) were included in this study. We examined grey matter volume and functional connectivity via structural and functional magnetic resonance imaging, respectively. Using the data from a recent meta-analysis of a genome-wide association study that comprised a large number of Chinese people, we calculated a polygenic risk score (PGRS) for each participant.

RESULTS

The imaging genetic analysis revealed that the individual PGRS showed a significantly negative correlation with the hippocampal grey matter volume and hippocampus-medial prefrontal cortex functional connectivity, both of which were lower in the people with schizophrenia than in the controls. We also found that the observed neuroimaging measures showed weak but similar changes in unaffected first-degree relatives of patients with schizophrenia.

CONCLUSIONS

These findings suggested that genetically influenced brain grey matter volume and functional connectivity may provide important clues for understanding the pathological mechanisms of schizophrenia and for the early diagnosis of schizophrenia.

Neuroinflammation and glial cell activation in mental disorders

Mental disorders (MDs) are highly prevalent and potentially debilitating complex disorders which causes remain elusive. Looking into deeper aspects of etiology or pathophysiology underlying these diseases would be highly beneficial, as the scarce knowledge in mechanistic and molecular pathways certainly represents an important limitation. Association between MDs and inflammation/neuroinflammation has been widely discussed and accepted by many, as high levels of pro-inflammatory cytokines were reported in patients with several MDs, such as schizophrenia (SCZ), bipolar disorder (BD) and major depression disorder (MDD), among others. Correlation of pro-inflammatory markers with symptoms intensity was also reported. However, the mechanisms underlying the inflammatory dysfunctions observed in MDs are not fully understood yet. In this context, microglial dysfunction has recently emerged as a possible pivotal player, as during the neuroinflammatory response, microglia can be over-activated, and excessive production of pro-inflammatory cytokines, which can modify the kynurenine and glutamate signaling, is reported. Moreover, microglial activation also results in increased astrocyte activity and consequent glutamate release, which are both toxic to the Central Nervous System (CNS). Also, as a result of increased microglial activation in MDs, products of the kynurenine pathway were shown to be changed, influencing then the dopaminergic, serotonergic, and glutamatergic signaling pathways. Therefore, in the present review, we aim to discuss how neuroinflammation impacts on glutamate and kynurenine signaling pathways, and how they can consequently influence the monoaminergic signaling. The consequent association with MDs main symptoms is also discussed. As such, this work aims to contribute to the field by providing insights into these alternative pathways and by shedding light on potential targets that could improve the strategies for pharmacological intervention and/or treatment protocols to combat the main pharmacologically unmatched symptoms of MDs, as the SCZ.

Potential mechanisms for phencyclidine/ketamine-induced brain structural alterations and behavioral consequences

Evidence of structural abnormalities in the nervous system of recreational drug [e.g., phencyclidine (PCP) or ketamine] users and/or preclinical animal research models suggests interference with the activity of multiple neurotransmitters, particularly glutamate neurotransmission. The damage to the central nervous system (CNS) may include neuronal loss, synaptic changes, disturbed neural network formation and reduced projections to subcortical fields. Notably, the reduced projections may considerably compromise the establishment of the subcortical areas, such as the nucleus accumbens located in the basal forebrain. With its abundant dopaminergic innervation, the nucleus accumbens is believed to be directly associated with addictive behaviors and mental disorders. This review seeks to delineate the relationship between PCP/ketamine-induced loss of cortical neurons and the reduced level of polysialic acid neural cell adhesion molecule (PSA-NCAM) in the striatum, and the likely changes in striatal synaptogenesis during development. The basic mechanism of how PSA-NCAM cell surface expression may be regulated will also be discussed, as well as the hypothesis that PSA-NCAM activity is critical to the regulation of synaptic protein expression. Overall, the present review will address the general hypothesis that damage/interruption of cortico-striatal communication and subcortical synaptogenesis could underlie the erratic/sensitization or addictive states produced by chronic or prolonged PCP/ketamine usage.

In vivo electrophysiological recordings of the effects of antidepressant drugs

Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.

An Overview of Animal Models Related to Schizophrenia

Schizophrenia is a heterogeneous psychiatric disorder that is poorly treated with current therapies. In this brief review, we provide an update regarding the use of animal models to study schizophrenia in an attempt to understand its aetiology and develop novel therapeutic strategies. Tremendous progress has been made developing and validating rodent models that replicate the aetiologies, brain pathologies, and behavioural abnormalities associated with schizophrenia in humans. Here, models are grouped into 3 categories-developmental, drug induced, and genetic-to reflect the heterogeneous risk factors associated with schizophrenia. Each of these models is associated with varied but overlapping pathophysiology, endophenotypes, behavioural abnormalities, and cognitive impairments. Studying schizophrenia using multiple models will permit an understanding of the core features of the disease, thereby facilitating preclinical research aimed at the development and validation of better pharmacotherapies to alter the progression of schizophrenia or alleviate its debilitating symptoms.

Can N-Methyl-D-Aspartate Receptor Hypofunction in Schizophrenia Be Localized to an Individual Cell Type?

Hypofunction of N-methyl-D-aspartate glutamate receptors (NMDARs), whether caused by endogenous factors like auto-antibodies or mutations, or by pharmacological or genetic manipulations, produces a wide variety of deficits which overlap with-but do not precisely match-the symptom spectrum of schizophrenia. In order to understand how NMDAR hypofunction leads to different components of the syndrome, it is necessary to take into account which neuronal subtypes are particularly affected by it in terms of detrimental functional alterations. We provide a comprehensive overview detailing findings in rodent models with cell type-specific knockout of NMDARs. Regarding inhibitory cortical cells, an emerging model suggests that NMDAR hypofunction in parvalbumin (PV) positive interneurons is a potential risk factor for this disease. PV interneurons display a selective vulnerability resulting from a combination of genetic, cellular, and environmental factors that produce pathological multi-level positive feedback loops. Central to this are two antioxidant mechanisms-NMDAR activity and perineuronal nets-which are themselves impaired by oxidative stress, amplifying disinhibition. However, NMDAR hypofunction in excitatory pyramidal cells also produces a range of schizophrenia-related deficits, in particular maladaptive learning and memory recall. Furthermore, NMDAR blockade in the thalamus disturbs thalamocortical communication, and NMDAR ablation in dopaminergic neurons may provoke over-generalization in associative learning, which could relate to the positive symptom domain. Therefore, NMDAR hypofunction can produce schizophrenia-related effects through an action on various different circuits and cell types.

The dynamics of disordered dialogue: Prefrontal, hippocampal and thalamic miscommunication underlying working memory deficits in schizophrenia

The prefrontal cortex is central to the orchestrated brain network communication that gives rise to working memory and other cognitive functions. Accordingly, working memory deficits in schizophrenia are increasingly thought to derive from prefrontal cortex dysfunction coupled with broader network disconnectivity. How the prefrontal cortex dynamically communicates with its distal network partners to support working memory and how this communication is disrupted in individuals with schizophrenia remain unclear. Here we review recent evidence that prefrontal cortex communication with the hippocampus and thalamus is essential for normal spatial working memory, and that miscommunication between these structures underlies spatial working memory deficits in schizophrenia. We focus on studies using normal rodents and rodent models designed to probe schizophrenia-related pathology to assess the dynamics of neural interaction between these brain regions. We also highlight recent preclinical work parsing roles for long-range prefrontal cortex connections with the hippocampus and thalamus in normal and disordered spatial working memory. Finally, we discuss how emerging rodent endophenotypes of hippocampal- and thalamo-prefrontal cortex dynamics in spatial working memory could translate into richer understanding of the neural bases of cognitive function and dysfunction in humans.

Olanzapine Reverses MK-801-Induced Cognitive Deficits and Region-Specific Alterations of NMDA Receptor Subunits

Cognitive dysfunction constitutes an essential component in schizophrenia for its early presence in the pathophysiology of the disease and close relatedness to life quality of patients. To develop effective treatment of cognitive deficits, it is important to understand their neurobiological causes and to identify potential therapeutic targets. In this study, adopting repeated MK-801 treatment as an animal model of schizophrenia, we investigated whether antipsychotic drugs, olanzapine and haloperidol, can reverse MK-801-induced cognitive deficits and how the reversal processes recruited proteins involved in glutamate neurotransmission in rat medial prefrontal cortex (mPFC) and hippocampus. We found that low-dose chronic MK-801 treatment impaired object-in-context recognition memory and reversal learning in the Morris water maze, leaving reference memory relatively unaffected, and that these cognitive deficits can be partially reversed by olanzapine, not haloperidol, treatment. At the molecular level, chronic MK-801 treatment resulted in the reduction of multiple N-methyl-D-aspartate (NMDA) receptor subunits in rat mPFC and olanzapine, not haloperidol, treatment restored the levels of GluN1 and phosphorylated GluN2B in this region. Taken together, MK-801-induced cognitive deficits may be associated with region-specific changes in NMDA receptor subunits and the reversal of specific NMDA receptor subunits may underlie the cognition-enhancing effects of olanzapine.