Modeling combined schizophrenia-related behavioral and metabolic phenotypes in rodents

Maternal choline supplementation in neurodevelopmental disorders: mechanistic insights from animal models and future directions

OBJECTIVES

To synthesize evidence from animal models of neurodevelopmental disorders (NDD) using maternal choline supplementation, to characterize current knowledge on the mechanisms of choline's protective effects against NDD, and to identify gaps in knowledge for future study.

METHODS

A literature review was conducted in PubMed to identify studies using prenatal choline supplementation interventions in rodent models of neurodevelopmental disorders. 24 studies were identified, and behavioral and biological findings were extracted from each. Studies examining both genetic and environmental risk factors were included.

RESULTS

Maternal choline supplementation during gestation is protective against both genetic and environmental NDD risk factors. Maternal choline supplementation improves both cognitive and affective outcomes throughout the lifespan in NDD models. Prenatal choline improved these outcomes through its participation in processes like neurogenesis, epigenetic regulation, and anti-inflammatory signaling.

DISCUSSION

Maternal choline supplementation improves behavioral and neurobiological outcomes in animal models of NDD, paralleling findings in humans. Animal models provide a unique opportunity to study the mechanisms by which gestational choline improves neurodevelopmental outcomes. This is especially important since nearly 90% of pregnant people in the United States are deficient in choline intake. However, much is still unknown about the mechanisms through which choline and its derivatives act. Further research into this topic, especially mechanistic studies in animal models, is critical to modernize maternal choline intake guidelines and to develop interventions to increase maternal choline intake in vulnerable populations.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

Zebrafish models of impulsivity and impulse control disorders

Impulse control disorders (ICDs) are characterized by generalized difficulty controlling emotions and behaviors. ICDs are a broad group of the central nervous system (CNS) disorders including conduct disorder, intermittent explosive, oppositional-defiant disorder, antisocial personality disorder, kleptomania, pyromania and other illnesses. Although they all share a common feature (aberrant impulsivity), their pathobiology is complex and poorly understood. There are also currently no ICD-specific therapies to treat these illnesses. Animal models are a valuable tool for studying ICD pathobiology and potential therapies. The zebrafish (Danio rerio) has become a useful model organism to study CNS disorders due to high genetic and physiological homology to mammals, and sensitivity to various pharmacological and genetic manipulations. Here, we summarize experimental models of impulsivity and ICD in zebrafish and highlight their growing translational significance. We also emphasize the need for further development of zebrafish ICD models to improve our understanding of their pathogenesis and to search for novel therapeutic treatments.

Ketogenic therapy in neurodegenerative and psychiatric disorders: From mice to men

Ketogenic diet is a low carbohydrate and high fat diet that has been used for over 100 years in the management of childhood refractory epilepsy. More recently, ketogenic diet has been investigated for a number of metabolic, neurodegenerative and neurodevelopmental disorders. In this comprehensive review, we critically examine the potential therapeutic benefits of ketogenic diet and ketogenic agents on neurodegenerative and psychiatric disorders in humans and translationally valid animal models. The preclinical literature provides strong support for the efficacy of ketogenic diet in a variety of diverse animal models of neuropsychiatric disorders. However, the evidence from clinical studies, while encouraging, particularly in Alzheimer's disease, psychotic and autism spectrum disorders, is limited to case studies and small pilot trials. Firm conclusion on the efficacy of ketogenic diet in psychiatric disorders cannot be drawn due to the lack of randomised, controlled clinical trials. The potential mechanisms of action of ketogenic therapy in these disorders with diverse pathophysiology may include energy metabolism, oxidative stress and immune/inflammatory processes. In conclusion, while ketogenic diet and ketogenic substances hold promise pre-clinically in a variety of neurodegenerative and psychiatric disorders, further studies, particularly randomised controlled clinical trials, are warranted to better understand their clinical efficacy and potential side effects.

Ketogenic diet for schizophrenia: clinical implication

PURPOSE OF REVIEW

The aim of this article is to review recent findings on the efficacy of ketogenic diet in preclinical models and in patients with schizophrenia. This review will also highlight emerging evidence for compromised glucose and energy metabolism in schizophrenia, which provides a strong rationale and a potential mechanism of action for ketogenic diet.

RECENT FINDINGS

Recent transcriptomic, proteomic and metabolomic evidence from postmortem prefrontal cortical samples and in-vivo NMR spectroscopy results support the hypothesis that there is a bioenergetics dysfunction characterized by abnormal glucose handling and mitochondrial dysfunctions resulting in impaired synaptic communication in the brain of people with schizophrenia. Ketogenic diet, which provides alternative fuel to glucose for bioenergetic processes in the brain, normalizes schizophrenia-like behaviours in translationally relevant pharmacological and genetic mouse models. Furthermore, recent case studies demonstrate that ketogenic diet produces improvement in psychiatric symptoms as well as metabolic dysfunctions and body composition in patients with schizophrenia.

SUMMARY

These results support that ketogenic diet may present a novel therapeutic approach through restoring brain energy metabolism in schizophrenia. Randomized controlled clinical trials are needed to further show the efficacy of ketogenic diet as a co-treatment to manage both clinical symptoms and metabolic abnormalities inherent to the disease and resulted by antipsychotic treatment.

Galphimia glauca and Natural Galphimines Block Schizophrenia-Like Symptoms Induced with Apomorphine and MK-801 in Mice

BACKGROUND

Galphimia glauca has been used for many years in Mexican Traditional Medicine to calm "insane people." Triterpenes, known as galphimines, were identified in this species. One of them, Galphimine-B (G-B), acts selectively on dopaminergic neurons by antagonizing the effect of glutamate on NMDA receptors. The objective of this study was to evaluate the effect of G. glauca methanolic extract (GgMeOH), a Galphimine-Rich Fraction (GRF), as well as the galphimines G-A, G-B, and G-E, on the acute psychosis induced by Apomorphine (APO) in mice and on schizophrenia-like symptoms induced by subchronic administration of MK-801.

METHOD

On the first day, ICR male mice were given GgMeOH, GRF, or one of the galphimines. On day two, animals were treated with APO, and on day 3, they were subjected to behavioral tests. In a second test, MK-801 was administered daily for 28 days. In this case, animals were treated daily with G. glauca products from day 9 to day 28 and then subjected to behavioral tests (passive avoidance test, open field test, forced swimming test, and social interaction test).

RESULTS

The increased number of stereotyped behaviors and grooming behaviors induced with APO were counteracted by all of the experimental treatments. MK-801 induced an increase in immobility time, which was blocked with G-B; GRF counteracted the decreased social interaction, and GgMeOH and GRF prevented the memory loss induced by MK-801.

CONCLUSION

G. glauca and their derivatives products (GRF and galphimines) were able to interact with the dopaminergic and glutamatergic drugs and to block different behaviors associated with some of the positive, negative, and cognitive symptoms of induced schizophrenia in mice. It is necessary to continue with this research, in order to identify their mechanism of action.

Hypervulnerability of the adolescent prefrontal cortex to nutritional stress via reelin deficiency

Overconsumption of high-fat diets (HFDs) can critically affect synaptic and cognitive functions within telencephalic structures such as the medial prefrontal cortex (mPFC). The underlying mechanisms, however, remain largely unknown. Here we show that adolescence is a sensitive period for the emergence of prefrontal cognitive deficits in response to HFD. We establish that the synaptic modulator reelin (RELN) is a critical mediator of this vulnerability because (1) periadolescent HFD (pHFD) selectively downregulates prefrontal RELN⁺ cells and (2) augmenting mPFC RELN levels using transgenesis or prefrontal pharmacology prevents the pHFD-induced prefrontal cognitive deficits. We further identify N-methyl-d-aspartate-dependent long-term depression (NMDA-LTD) at prefrontal excitatory synapses as a synaptic signature of this association because pHFD abolishes NMDA-LTD, a function that is restored by RELN overexpression. We believe this study provides the first mechanistic insight into the vulnerability of the adolescent mPFC towards nutritional stress, such as HFDs. Our findings have primary relevance to obese individuals who are at an increased risk of developing neurological cognitive comorbidities, and may extend to multiple neuropsychiatric and neurological disorders in which RELN deficiency is a common feature.

A Review of Oxytocin's Effects on the Positive, Negative, and Cognitive Domains of Schizophrenia

Schizophrenia is a disabling, heterogeneous disorder with clinical features that can be parsed into three domains: positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic drugs produce fairly robust clinical benefit against positive symptoms but typically have minimal therapeutic effects on negative symptoms and cognitive deficits. Oxytocin (OT) is a nonapeptide that, in addition to its role as a hormone regulating peripheral reproductive-relevant functions, acts as a neurotransmitter in the brain. Several lines of preclinical and clinical research suggest that the OT system may play a role in regulating the expression of schizophrenia spectrum disorders and that targeting the central OT system may yield novel treatments to address these symptoms. In this review, we summarize the extant preclinical and clinical evidence relevant to the role of OT in schizophrenia with particular emphasis on its putative therapeutic effects on each of the three above-mentioned clinical domains.

Slow Physical Growth, Delayed Reflex Ontogeny, and Permanent Behavioral as Well as Cognitive Impairments in Rats Following Intra-generational Protein Malnutrition

Environmental stressors including protein malnutrition (PMN) during pre-, neo- and post-natal age have been documented to affect cognitive development and cause increased susceptibility to neuropsychiatric disorders. Most studies have addressed either of the three windows and that does not emulate the clinical conditions of intra-uterine growth restriction (IUGR). Such data fail to provide a complete picture of the behavioral alterations in the F1 generation. The present study thus addresses the larger window from gestation to F1 generation, a new model of intra-generational PMN. Naive Sprague Dawley (SD) dams pre-gestationally switched to LP (8% protein) or HP (20% protein) diets for 45 days were bred and maintained throughout gestation on same diets. Pups born (HP/LP dams) were maintained on the respective diets post-weaningly. The present study aimed to show the sex specific differences in the neurobehavioral evolution and behavioral phenotype of the HP/LP F1 generation pups. A battery of neurodevelopmental reflex tests, behavioral (Open field and forelimb gripstrength test), and cognitive [Elevated plus maze (EPM) and Morris water maze (MWM)] assays were performed. A decelerated growth curve with significantly restricted body and brain weight, delays in apparition of neuro-reflexes and poor performance in the LP group rats was recorded. Intra-generational PMN induced poor habituation-with-time in novel environment exploration, low anxiety and hyperactive like profile in open field test in young and adult rats. The study revealed poor forelimb neuromuscular strength in LP F1 pups till adulthood. Group occupancy plots in MWM test revealed hyperactivity with poor learning, impaired memory retention and integration, thus modeling the signs of early onset Alzehemier phenotype. In addition, a gender specific effect of LP diet with severity in males and favoring female sex was also noticed.

Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders

Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms.

Converging models of schizophrenia--Network alterations of prefrontal cortex underlying cognitive impairments

The prefrontal cortex (PFC) and its connections with other brain areas are crucial for cognitive function. Cognitive impairments are one of the core symptoms associated with schizophrenia, and manifest even before the onset of the disorder. Altered neural networks involving PFC contribute to cognitive impairments in schizophrenia. Both genetic and environmental risk factors affect the development of the local circuitry within PFC as well as development of broader brain networks, and make the system vulnerable to further insults during adolescence, leading to the onset of the disorder in young adulthood. Since spared cognitive functions correlate with functional outcome and prognosis, a better understanding of the mechanisms underlying cognitive impairments will have important implications for novel therapeutics for schizophrenia focusing on cognitive functions. Multidisciplinary approaches, from basic neuroscience to clinical studies, are required to link molecules, circuitry, networks, and behavioral phenotypes. Close interactions among such fields by sharing a common language on connectomes, behavioral readouts, and other concepts are crucial for this goal.

Characterization of a Novel Mutation in SLC1A1 Associated with Schizophrenia

We have recently described a hemi-deletion on chromosome 9p24.2 at the SLC1A1 gene locus and its co-segregation with schizophrenia in an extended Palauan pedigree. This finding represents a point of convergence for several pathophysiological models of schizophrenia. The present report sought to characterize the biological consequences of this hemi-deletion. Dual luciferase assays demonstrated that the partially deleted allele (lacking exon 1 and the native promoter) can drive expression of a 5'-truncated SLC1A1 using sequence upstream of exon 2 as a surrogate promoter. However, confocal microscopy and electrophysiological recordings demonstrate that the 5'-truncated SLC1A1 lacks normal membrane localization and glutamate transport ability. To identify downstream consequences of the hemi-deletion, we first used a themed qRT-PCR array to compare expression of 84 GABA and glutamate genes in RNA from peripheral blood leukocytes in deletion carriers (n = 11) versus noncarriers (n = 8) as well as deletion carriers with psychosis (n = 5) versus those without (n = 3). Then, targeted RNA-Seq (TREx) was used to quantify expression of 375 genes associated with neuropsychiatric disorders in HEK293 cells subjected to either knockdown of SLC1A1 or overexpression of full-length or 5'-truncated SLC1A1. Expression changes of several genes strongly implicated in schizophrenia pathophysiology were detected (e.g. SLC1A2, SLC1A3, SLC1A6, SLC7A11, GRIN2A, GRIA1 and DLX1).

Hippocampal Proteomic and Metabonomic Abnormalities in Neurotransmission, Oxidative Stress, and Apoptotic Pathways in a Chronic Phencyclidine Rat Model

Schizophrenia is a neuropsychiatric disorder affecting 1% of the world's population. Due to both a broad range of symptoms and disease heterogeneity, current therapeutic approaches to treat schizophrenia fail to address all symptomatic manifestations of the disease. Therefore, disease models that reproduce core pathological features of schizophrenia are needed for the elucidation of pathological disease mechanisms. Here, we employ a comprehensive global label-free liquid chromatography-mass spectrometry proteomic (LC-MS(E)) and metabonomic (LC-MS) profiling analysis combined with the targeted proteomics (selected reaction monitoring and multiplex immunoassay) of serum and brain tissues to investigate a chronic phencyclidine (PCP) rat model in which glutamatergic hypofunction is induced through noncompetitive NMDAR-receptor antagonism. Using a multiplex immunoassay, we identified alterations in the levels of several cytokines (IL-5, IL-2, and IL-1β) and fibroblast growth factor-2. Extensive proteomic and metabonomic brain tissue profiling revealed a more prominent effect of chronic PCP treatment on both the hippocampal proteome and metabonome compared to the effect on the frontal cortex. Bioinformatic pathway analysis confirmed prominent abnormalities in NMDA-receptor-associated pathways in both brain regions, as well as alterations in other neurotransmitter systems such as kainate, AMPA, and GABAergic signaling in the hippocampus and in proteins associated with neurodegeneration. We further identified abundance changes in the level of the superoxide dismutase enzyme (SODC) in both the frontal cortex and hippocampus, which indicates alterations in oxidative stress and substantiates the apoptotic pathway alterations. The present study could lead to an increased understanding of how perturbed glutamate receptor signaling affects other relevant biological pathways in schizophrenia and, therefore, support drug discovery efforts for the improved treatment of patients suffering from this debilitating psychiatric disorder.