Glutamate and modeling of schizophrenia symptoms: Review of our Findings: 1990–2014

A narrative review of treatment interventions to improve cognitive performance in schizophrenia, with an emphasis on at-risk and early course stages

Cognitive dysfunction is a core feature of schizophrenia (SCZ), which unfavorably affects SCZ patients' daily functioning and overall clinical outcome. An increasing body of evidence has shown that cognitive deficits are present not only at the beginning of the illness but also several years before the onset of psychosis. Nonetheless, the majority of treatment interventions targeting cognitive dysfunction in SCZ, using both pharmacological and nonpharmacological approaches, have focused on chronic patients rather than individuals at high risk or in the early stages of the disease. In this article, we provide a narrative review of cognitive interventions in SCZ patients, with a particular focus on pre-emptive interventions in at-risk/early course individuals when available. Furthermore, we discuss current challenges for these pre-emptive treatment interventions and provide some suggestions on how future work may ameliorate cognitive dysfunction in these individuals.

Effects of Cycloleucine in the Nucleus Accumbens Septi on the Elevated plus Maze Test in Rats

INTRODUCTION

In recent years, an important number of studies have emphasized the psychopharmacological actions of cycloleucine (1-aminocyclopentanecarboxylic acid) acting on the NR1 subunit (glycine allosteric site) of NMDA (N-methyl-D-aspartic acid) receptor. We studied the effects of its injection in an anxiety test.

METHODS

The elevated plus maze test was used. Male rats bilaterally cannulated into the nucleus accumbens septi (NAS) were employed. Rats were divided into 5 groups that received either 1 µL injections of saline or cycloleucine (0.5, 1, 2, or 4 µg) 15 min before testing.

RESULTS

Time spent in the open arm was significantly increased by cycloleucine treatment with all doses (1 and 2 µg, p < 0.05; 0.5 and 4 µg, p < 0.01), like number of extreme arrivals (0.5 and 1 µg, p < 0.05; 2 µg, p < 0.01; and 4 µg, p < 0.001). Open arm entries were increased by the highest dose only (4 µg, p < 0.01).

DISCUSSION/CONCLUSION

Present results show no difference between all doses in the time spent in the open arm, suggesting an indirect, noncompetitive action of the drug. The increase in extreme arrivals and open arm entries suggests a dose influence in these parameters. We conclude that cycloleucine influence on the NMDA receptors within NAS leads to anxiolytic-like effects and behavioral disinhibition, which once more confirms the involvement of NAS in anxiety processing.

Effects of atenolol injected into the nucleus accumbens septi in rats in the elevated plus-maze test

Background In previous studies, we have observed that glutamate antagonists injected within the nucleus accumbens septi (NAS) induced an anxiolytic-like effect in the elevated plus maze (EPM) test in rats. In the present study, the effect of Atenolol, a specific Beta Adreno-receptor antagonist in the EPM was studied in male rats bilaterally cannulated NAS. Methods Rats were divided into five groups that received either 1 μL injections of saline or atenolol in different doses (0.75, 1 or 2 μg/1 μL, n=15-16) 15 min before testing. Results Time Spent in the Open Arm was modified by treatment (F=4.563, p=0.006, df 3). This was increased by the lowest dose of atenolol (p<0.05), by the medium doses (p<0.001) and also by the highest dose (p<0.01). Time per Entry was modified by treatment (F=4.54, p=0.06, df 3). This parameter was increased by the lowest dose of atenolol (p<0.01), but not for the medium and higher doses. Conclusions We conclude that Atenolol beta receptor blockade in the accumbens lead to an anxiolytic-like effect related to an increase in the time spent in the open arm and in the time per entry, showing specific behavioral patterns.

BDNF Serum Levels are Associated With White Matter Microstructure in Schizophrenia - A Pilot Study

Brain derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of schizophrenia. As BDNF regulates axonal and dendritic growth, altered BDNF levels in schizophrenia patients might underlie changes in structural connectivity that have been identified by magnetic resonance imaging (MRI). We investigated a possible correlation between BDNF serum levels, fiber tract architecture, and regional grey matter volumes in 19 schizophrenia patients and a gender- and age-matched control group. Two patients had to be excluded due to abnormalities in their MRI scans. Serum samples were obtained to determine BDNF levels, and T1- as well as diffusion-weighted sequences were acquired. We, then, investigated correlations between BDNF serum levels with neuroimaging parameters, using Voxel-based Morphometry (VBM) and Tract-based Spatial Statistics (TBSS). We found a significant negative correlation between BDNF serum levels and FA values in the right inferior fronto-occipital fasciculus and the right superior longitudinal fasciculus. These regions also showed a decrease in AD values in schizophrenia patients. Grey matter volumes were reduced in patients but there was no correlation between regional grey matter volumes and BDNF. The right superior longitudinal fasciculus has been repeatedly identified to exhibit microstructural changes in schizophrenia patients. Our findings of a negative correlation between BDNF and FA values in patients might indicate that BDNF is upregulated to compensate decreased structural connectivity as it induces neural plasticity and shows increased levels in damaged tissue. These findings of our pilot study are encouraging leads for future research in larger samples.

Effects of dizocilpine-induced glutamatergic blockade in the nucleus accumbens septi on the plus maze test

BACKGROUND

In previous studies, we have observed that specific N-methyl-d-aspartic acid (NMDA) antagonists and non-NMDA antagonists injected within the nucleus accumbens septi (NAS) induced an anxiolytic-like effect in the plus maze test in rats. In the present study, the effect of intracanalicular blockade of NMDA receptors using dizocilpine in the plus maze was studied in male rats bilaterally cannulated NAS.

METHODS

Rats were divided into five groups that received either 1 μL injections of saline or dizocilpine (MK-801, [5R,10S]-[+]-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine) in different doses (0.5, 1, 2, or 4 μg) 15 min before testing.

RESULTS

Time spent in the open arm increased under dizocilpine treatment with the two higher doses (2 and 4 μg, p<0.05), extreme arrivals were increased by the three higher doses (1 μg, p<0.05; 2 and 4 μg, p<0.01), and open arm entries by the three higher doses (1, 2, and 4 μg, p<0.05). A dose-effect relationship was observed in all cases.

CONCLUSIONS

We conclude that dizocilpine-glutamatergic blockade in the accumbens lead to an anxiolytic-like effect and a behavioral disinhibition related to an increase in some motoric parameters, showing specific behavioral patterns.

Constitutive loss and acute pharmacological manipulation of ErbB4 signaling do not affect attention and inhibitory control in mice

The receptor tyrosine kinase ErbB4 and its ligand trophic factors of the neuregulin (NRG) family have been associated with schizophrenia and other mental disorders in human genetic studies. In vivo studies in mice have shown how abnormal Nrg-ErbB4 signaling leads to deviant behaviors relevant to distinct aspects of schizophrenia, including hyperactivity, sensory gating deficits, working and spatial memory deficits and impaired social behavior. However, so far little is known on the role of ErbB4 in attention and inhibitory control, two aspects of executive functions that are impaired in schizophrenia. Here we investigated the effects of constitutive loss of ErbB4 in the central nervous system of mice on performance in a 5-choice serial reaction time task (5CSRTT) assessing attention and inhibitory control. In this task, ErbB4^-/- mice did not show deficits in various parameters of attention, and premature responses as measure of inhibitory control. Nonetheless, ErbB4^-/- mice recapitulated a specific set of behavioral phenotypes associated with schizophrenia, including a deficit in spatial learning and memory in the Barnes Maze and in contextual fear learning, and a trend for a deficit in sensorimotor gating. Furthermore, we investigated the effect of acute pharmacological inhibition of ErbB tyrosine kinase receptor using the pan-ErbB kinase inhibitor JNJ-28871063 (JNJ), in an automated version of the 5CSRTT. JNJ did not affect attention and inhibitory control. In conclusion, our data suggest no direct involvement of a classical Nrg-ErbB4 pathway in attention and inhibitory control in mice, while it confirms the involvement of this pathway in other domains relevant to schizophrenia.

Cognitive impairment in schizophrenia across age groups: a case-control study

BACKGROUND

The potential dynamics of cognitive impairment in schizophrenia is discussed in the literature of the field. Recent publications suggest modest changes in level of cognitive impairment after first psychotic episode. Present article attempts to explore cognitive differences between patients and controls across age groups and differences between age groups in clinical group.

METHODS

One hundred and twenty-eight hospitalized patients with schizophrenia (64 women and 64 men) and 68 individuals from the control group (32 women and 32 men) aged 18-55 years were examined. The patients were divided into age groups (18-25, 26-35, 36-45, 46-55). Both groups were examined using Wisconsin Card Sorting Test, Rey Auditory Verbal Learning Test, Rey Osterrieth Complex Figure Test, Trail Making Test (A and B), Stroop Test, verbal fluency test and Wechsler digit span.

RESULTS

Patients with schizophrenia obtained significantly lower scores versus the control group in regard to all the measured cognitive functions (Mann-Whitney U; p < 0.05. Most deficits were present in all age groups, however, statistically important impairment in executive functions (WCST) were present only in "older" groups.

CONCLUSIONS

Patients with schizophrenia obtained less favourable results than the control group in all age groups. Deficits regarding executive functions do not seem to be at a significant level among the youngest group, whereas they are more noticeable in the group of 46-55-year-olds. Executive functions are significantly lowered in the group aged 36-45 in comparison to the "younger" groups. The level of cognitive functions shows a mild exacerbation in connection with age, whereas cognitive rigidity proved to be related to the number of years spent without hospital treatment.

Rasd2 Modulates Prefronto-Striatal Phenotypes in Humans and 'Schizophrenia-Like Behaviors' in Mice

Rasd2 is a thyroid hormone target gene, which encodes for a GTP-binding protein enriched in the striatum where, among other functions, it modulates dopaminergic neurotransmission. Here we report that human RASD2 mRNA is abundant in putamen, but it also occurs in the cerebral cortex, with a distinctive expression pattern that differs from that present in rodents. Consistent with its localization, we found that a genetic variation in RASD2 (rs6518956) affects postmortem prefrontal mRNA expression in healthy humans and is associated with phenotypes of relevance to schizophrenia, including prefrontal and striatal grey matter volume and physiology during working memory, as measured with magnetic resonance imaging. Interestingly, quantitative real-time PCR analysis indicated that RASD2 mRNA is slightly reduced in postmortem prefrontal cortex of patients with schizophrenia. In the attempt to uncover the neurobiological substrates associated with Rasd2 activity, we used knockout mice to analyze the in vivo influence of this G-protein on the prepulse inhibition of the startle response and psychotomimetic drug-related behavioral response. Data showed that Rasd2 mutants display deficits in basal prepulse inhibition that, in turn, exacerbate gating disruption under psychotomimetic drug challenge. Furthermore, we documented that lack of Rasd2 strikingly enhances the behavioral sensitivity to motor stimulation elicited by amphetamine and phencyclidine. Based on animal model data, along with the finding that RASD2 influences prefronto-striatal phenotypes in healthy humans, we suggest that genetic mutation or reduced levels of this G-protein might have a role in cerebral circuitry dysfunction underpinning exaggerated psychotomimetic drugs responses and development of specific biological phenotypes linked to schizophrenia.

Physical Exercise Alleviates Health Defects, Symptoms, and Biomarkers in Schizophrenia Spectrum Disorder

Schizophrenia spectrum disorders are characterized by symptom profiles consisting of positive and negative symptoms, cognitive impairment, and a plethora of genetic, epigenetic, and phenotypic biomarkers. Assorted animal models of these disorders and clinical neurodevelopmental indicators have implicated neurodegeneration as an element in the underlying pathophysiology. Physical exercise or activity regimes--whether aerobic, resistance, or endurance--ameliorate regional brain and functional deficits not only in affected individuals but also in animal models of the disorder. Cognitive deficits, often linked to regional deficits, were alleviated by exercise, as were quality-of-life, independent of disorder staging and risk level. Apoptotic processes intricate to the etiopathogenesis of schizophrenia were likewise attenuated by physical exercise. There is also evidence of manifest benefits endowed by physical exercise in preserving telomere length and integrity. Not least, exercise improves overall health and quality-of-life. The notion of scaffolding as the outcome of physical exercise implies the "buttressing" of regional network circuits, neurocognitive domains, anti-inflammatory defenses, maintenance of telomeric integrity, and neuro-reparative and regenerative processes.