Vulnerability to omega-3 deprivation in a mouse model of NMDA receptor hypofunction

Cannabidiol, but Not Δ9-Tetrahydrocannabinol, Has Strain- and Genotype-Specific Effects in Models of Psychosis

Introduction: Cannabis use has been associated with an increased incidence of psychiatric disorders, yet the underlying neurobiological processes mediating these associations are poorly understood. Whereas exposure to Δ9-tetrahydrocannabinol (THC) has been associated with the development or exacerbation of psychosis, treatment with cannabidiol (CBD) has been associated with amelioration of psychosis. In this study, we demonstrate a complex effect of CBD in mouse models of psychosis, based on factors, including dose, strain, and genotype. Methods: Adult GluN1 knockdown (GluN1KD) and dopamine transporter knockout (DATKO) mice (almost equally balanced for male/female) were acutely treated with vehicle, THC (4 mg/kg), CBD (60, 120 mg/kg), or THC:CBD (1:15, 4:60 mg/kg) and tested in behavioral assays. Results: GluN1KD and DATKO mice displayed hyperactivity, impaired habituation, and sensorimotor gating, along with increased stereotypy and vertical activity. THC, alone and in combination with CBD, produced a robust "dampening" effect on the exploratory behavior regardless of strain or genotype. CBD exhibited a more complex profile. At 60 mg/kg, CBD had minimal effects on horizontal activity, but the effects varied in terms of directionality (increase vs. decrease) in other parameters; effects on stereotypic behaviors differ by genotype, while effects on vertical exploration differ by strain×genotype. CBD at 120 mg/kg had a "dampening" effect on exploration overall, except in GluN1KD mice, where no effect was observed. In terms of sensorimotor gating, both THC and CBD had minimal effects, except for 120 mg/kg CBD, which exacerbated the acoustic startle response. Conclusions: Here, we present a study that highlights the complex mechanism of phytocannabinoids, particularly CBD, in models of psychosis-like behavior. These data require careful interpretation, as agonism of the cannabinoid receptor 1 (CB1) resulting in a decrease in locomotion can be misinterpreted as "antipsychotic-like" activity in murine behavioral outputs of psychosis. Importantly, the THC-mediated decrease in hyperexploratory behavior observed in our models (alone or in combination) was not specific to the genetic mutants, but rather was observed regardless of strain or genotype. Furthermore, CBD treatment, when comparing mutants with their wild-type littermate controls, showed little to no "antipsychotic-like" activity in our models. Therefore, it is not only important to consider dose when designing/interpreting therapeutically driven phytocannabinoid studies, but also effects of strain or genetic vulnerability respective to the general population.

Abnormal sensory perception masks behavioral performance of Grin1 knockdown mice

The development and function of sensory systems require intact glutamatergic neurotransmission. Changes in touch sensation and vision are common symptoms in autism spectrum disorders, where altered glutamatergic neurotransmission is strongly implicated. Further, cortical visual impairment is a frequent symptom of GRIN disorder, a rare genetic neurodevelopmental disorder caused by pathogenic variants of GRIN genes that encode NMDA receptors. We asked if Grin1 knockdown mice (Grin1KD), as a model of GRIN disorder, had visual impairments resulting from NMDA receptor deficiency. We discovered that Grin1KD mice had deficient visual depth perception in the visual cliff test. Since Grin1KD mice are known to display robust changes in measures of learning, memory, and emotionality, we asked whether deficits in these higher-level processes could be partly explained by their visual impairment. By changing the experimental conditions to improve visual signals, we observed significant improvements in the performance of Grin1KD mice in tests that measure spatial memory, executive function, and anxiety. We went further and found destabilization of the outer segment of retina together with the deficient number and size of Meissner corpuscles (mechanical sensor) in the hind paw of Grin1KD mice. Overall, our findings suggest that abnormal sensory perception can mask the expression of emotional, motivational and cognitive behavior of Grin1KD mice. This study demonstrates new methods to adapt routine behavioral paradigms to reveal the contribution of vision and other sensory modalities in cognitive performance.

Consequences of NMDA receptor deficiency can be rescued in the adult brain

N-methyl-D-aspartate receptors (NMDARs) are required to shape activity-dependent connections in the developing and adult brain. Impaired NMDAR signalling through genetic or environmental insults causes a constellation of neurodevelopmental disorders that manifest as intellectual disability, epilepsy, autism, or schizophrenia. It is not clear whether the developmental impacts of NMDAR dysfunction can be overcome by interventions in adulthood. This question is paramount for neurodevelopmental disorders arising from mutations that occur in the GRIN genes, which encode NMDAR subunits, and the broader set of mutations that disrupt NMDAR function. We developed a mouse model where a congenital loss-of-function allele of Grin1 can be restored to wild type by gene editing with Cre recombinase. Rescue of NMDARs in adult mice yields surprisingly robust improvements in cognitive functions, including those that are refractory to treatment with current medications. These results suggest that neurodevelopmental disorders arising from NMDAR deficiency can be effectively treated in adults.

Shared Biological Pathways between Antipsychotics and Omega-3 Fatty Acids: A Key Feature for Schizophrenia Preventive Treatment?

Schizophrenia typically emerges during adolescence, with progression from an ultra-high risk state (UHR) to the first episode of psychosis (FEP) followed by a chronic phase. The detailed pathophysiology of schizophrenia and the factors leading to progression across these stages remain relatively unknown. The current treatment relies on antipsychotics, which are effective for FEP and chronic schizophrenia but ineffective for UHR patients. Antipsychotics modulate dopaminergic and glutamatergic neurotransmission, inflammation, oxidative stress, and membrane lipids pathways. Many of these biological pathways intercommunicate and play a role in schizophrenia pathophysiology. In this context, research of preventive treatment in early stages has explored the antipsychotic effects of omega-3 supplementation in UHR and FEP patients. This review summarizes the action of omega-3 in various biological systems involved in schizophrenia. Similar to antipsychotics, omega-3 supplementation reduces inflammation and oxidative stress, improves myelination, modifies the properties of cell membranes, and influences dopamine and glutamate pathways. Omega-3 supplementation also modulates one-carbon metabolism, the endocannabinoid system, and appears to present neuroprotective properties. Omega-3 has little side effects compared to antipsychotics and may be safely prescribed for UHR patients and as an add-on for FEP patients. This could to lead to more efficacious individualised treatments, thus contributing to precision medicine in psychiatry.

A novel allosteric modulator of the cannabinoid CB1 receptor ameliorates hyperdopaminergia endophenotypes in rodent models

The endocannabinoid system (eCBs) encompasses the endocannabinoids, their synthetic and degradative enzymes, and cannabinoid (CB) receptors. The eCBs mediates inhibition of neurotransmitter release and acts as a major homeostatic system. Many aspects of the eCBs are altered in a number of psychiatric disorders including schizophrenia, which is characterized by dysregulation of dopaminergic signaling. The GluN1-Knockdown (GluN1KD) and Dopamine Transporter Knockout (DATKO) mice are models of hyperdopaminergia, which display abnormal psychosis-related behaviors, including hyperlocomotion and changes in pre-pulse inhibition (PPI). Here, we investigate the ability of a novel CB₁ receptor (CB₁R) allosteric modulator, ABM300, to ameliorate these dysregulated behaviors. ABM300 was characterized in vitro (receptor binding, β-arrestin2 recruitment, ERK1/2 phosphorylation, cAMP inhibition) and in vivo (anxiety-like behaviors, cannabimimetic effects, novel environment exploratory behavior, pre-pulse inhibition, conditioned avoidance response) to assess the effects of the compound in dysregulated behaviors within the transgenic models. In vitro, ABM300 increased CB₁R agonist binding but acted as an inhibitor of CB₁R agonist induced signaling, including β-arrestin2 translocation, ERK phosphorylation and cAMP inhibition. In vivo, ABM300 did not elicit anxiogenic-like or cannabimimetic effects, but it decreased novelty-induced hyperactivity, exaggerated stereotypy, and vertical exploration in both transgenic models of hyperdopaminergia, as well as normalizing PPI in DATKO mice. The data demonstrate for the first time that a CB₁R allosteric modulator ameliorates the behavioral deficits in two models of increased dopamine, warranting further investigation as a potential therapeutic target in psychiatry.

Discordant Dose-Dependent Metabolic Effects of Eicosapentanoic Acid in Diet-Induced Obese Mice

Obesity is a widespread epidemic that increases the risk for several metabolic diseases. Despite several beneficial health effects of eicosapentaenoic acid (C20:5n-3, EPA), previous studies have used very high doses of EPA. In this study, dose-dependent effects of EPA on metabolic outcomes were determined in diet-induced obese mice. We used B6 male mice, fed high-fat diet (HF, 45% kcal fat) or HF diet supplemented with 9, 18, and 36 g/kg of EPA-enriched fish oil for 14 weeks. We conducted metabolic phenotyping during the feeding period, and harvested tissues and blood at termination. Only mice fed 36 g/kg of EPA significantly (p < 0.05) lowered body weight, fat content and epididymal fat pad weight, compared to HF. Both 18 and 36 g/kg doses of EPA significantly increased glucose clearance and insulin sensitivity, compared to HF or 9 g/kg of EPA. Locomotor activity was significantly increased with both 18 and 36 g/kg doses of EPA. Interestingly, all doses of EPA compared to HF, significantly increased energy expenditure and oxygen consumption and significantly reduced serum insulin, leptin, and triglycerides levels. These results demonstrate weight- and adiposity-independent metabolic benefits of EPA, at doses comparable to those currently used to treat hypertriglyceridemia.

Remembering Mechanosensitivity of NMDA Receptors

An increase in post-synaptic Ca²⁺ conductance through activation of the ionotropic N-methyl-D-aspartate receptor (NMDAR) and concomitant structural changes are essential for the initiation of long-term potentiation (LTP) and memory formation. Memories can be initiated by coincident events, as occurs in classical conditioning, where the NMDAR can act as a molecular coincidence detector. Binding of glutamate and glycine, together with depolarization of the postsynaptic cell membrane to remove the Mg²⁺ channel pore block, results in NMDAR opening for Ca²⁺ conductance. Accumulating evidence has implicated both force-from-lipids and protein tethering mechanisms for mechanosensory transduction in NMDAR, which has been demonstrated by both, membrane stretch and application of amphipathic molecules such as arachidonic acid (AA). The contribution of mechanosensitivity to memory formation and consolidation may be to increase activity of the NMDAR leading to facilitated memory formation. In this review we look back at the progress made toward understanding the physiological and pathological role of NMDA receptor channels in mechanobiology of the nervous system and consider these findings in like of their potential functional implications for memory formation. We examine recent studies identifying mechanisms of both NMDAR and other mechanosensitive channels and discuss functional implications including gain control of NMDA opening probability. Mechanobiology is a rapidly growing area of biology with many important implications for understanding form, function and pathology in the nervous system.

Influence of omega-3 polyunsaturated fatty acids from fish oil or meal on the structure of lipid microdomains in bovine luteal cells

Biological membranes are composed of a lipid bilayer and proteins that form lipid microdomains. This study examined the effects of fish byproducts on lipid-protein interactions within lipid microdomains of bovine luteal cells. In Exp. 1 and 2, luteal cells were prepared from corpora lutea (CL; n = 4 to 8) collected at an abattoir. Exp. 1 was conducted to optimize ultrasonication in a detergent-free protocol for isolation of lipid microdomains. A power setting of 10 to 20% was effective in isolating lipid microdomains from bulk lipid. In Exp. 2, cells were cultured in control medium or fish oil to determine influence of fish oil on distribution of lipid microdomain markers and prostaglandin F_2α (FP) receptors. Cells treated with fish oil had a smaller percentage of microdomain markers and FP receptor in microdomains (P < 0.05). In Exp. 3 and 4, cells were prepared from mid-cycle CL obtained from cows supplemented with corn gluten meal (n = 4) or fish meal (n = 4). Exp. 3 examined effects of dietary supplementation on distribution of lipid microdomain markers and FP receptor and Exp. 4 on fatty acid composition within lipid microdomains. A smaller percentage of lipid microdomain markers and FP receptor was detected in microdomains of cells collected from fish meal supplemented animals (P < 0.05). In Exp. 4, a greater percentage of omega-3 polyunsaturated fatty acids was detected in bulk lipid from fish meal supplemented cows (P < 0.05). Results show that fish byproducts influence lipid-protein interactions in lipid microdomains in bovine luteal cells.

The use of antioxidant compounds in the treatment of first psychotic episode: Highlights from preclinical studies

Recent evidence highlighted a pathogenetic link between redox dysregulation and the early stages of psychosis. Indeed, an increasing number of studies have pointed toward an association between oxidative stress, both at central and peripheral levels, and first psychotic episode. Moreover, basal low antioxidant capacity has been shown to directly correlate with cognitive impairment in the early onset of psychosis. In this context, the possibility to use antioxidant compounds in first psychotic episode, especially as supplementation to antipsychotic therapy, has become the focus of numerous investigations on rodents with the aim to translate data on the possible effects of antioxidant therapies to large populations of patients, with a diagnosis of the first psychotic episode. In this review, we will discuss studies, published from January 1st, 2007 to July 31st, 2017, investigating the effects of antioxidant compounds on neuropathological alterations observed in different rodent models characterized by a cluster of psychotic-like symptoms reminiscent of what observed in human first psychotic episode. A final focus on the effective possibility to directly translate data obtained on rodents to humans will be also provided.

N-3 (Omega-3) Fatty Acids: Effects on Brain Dopamine Systems and Potential Role in the Etiology and Treatment of Neuropsychiatric Disorders

BACKGROUND & OBJECTIVE

A number of neuropsychiatric disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and, to some extent, depression, involve dysregulation of the brain dopamine systems. The etiology of these diseases is multifactorial, involving genetic and environmental factors. Evidence suggests that inadequate levels of n-3 (omega- 3) polyunsaturated fatty acids (PUFA) in the brain may represent a risk factor for these disorders. These fatty acids, which are derived from the diet, are a major component of neuronal membranes and are of particular importance in brain development and function. Low levels of n-3 PUFAs in the brain affect the brain dopamine systems and, when combined with appropriate genetic and other factors, increase the risk of developing these disorders and/or the severity of the disease. This article reviews the neurobiology of n-3 PUFAs and their effects on dopaminergic function.

CONCLUSION

Clinical studies supporting their role in the etiologies of diseases involving the brain dopamine systems and the potential of n-3 PUFAs in the treatment of these disorders are discussed.