Agnieszka Wąsik

The etiopathology of schizophrenia is still poorly understood. Still, it is widely accepted that oxidative stress, particularly during early stages of brain development, is associated with increased risk of developing schizophrenia. Several studies indicate that glutathione (GSH) is a key factor in maintaining redox balance in cells and is involved in numerous metabolic processes. Its deficiency in the neonatal period leads to permanent brain damage, manifested by schizophrenia-like symptoms in adults. Hence, administration of the GSH synthesis inhibitor L-buthionine-(S, R)-sulfoximine (BSO) alone and in co-treatment with the dopamine reuptake inhibitor 1-[2-[Bis-4(fluorophenyl)methoxy]ethyl]-4-3-(3-phenylpropyl) (GBR 12909) to rodents in neonatal period produces good neurodevelopmental models offering an opportunity to examine various neuroanatomical changes and different symptoms in schizophrenia spectrum. Schizophrenia is modeled by inducing lesions or changes in activity in specific brain regions of rodents (primarily the prefrontal cortex and hippocampus). Such artificially induced dysfunctions, discussed in this article, suggest the usefulness of these neurodevelopmental models in research on the pathomechanisms of schizophrenia. The aim of this review is to analyze the literature on the impact of GSH deficiency on the etiopathology of schizophrenia, with particular emphasis on neurodevelopmental animal models in which oxidative stress during early postnatal development causes schizophrenia-like symptoms in adulthood.

Background: Iron is one of the key microelements in the mammalian body and is the most abundant metal in the brain. Iron, a very important chemical element in the body of mammals, is the most abundant metal in the brain. It participates in many chemical reactions taking place in the central nervous system acting as a cofactor in key enzymatic reactions involved in neurotransmitter synthesis and degradation, dendritic arborization, and myelination. Moreover, iron accumulation in the brain has been implicated in the pathogenesis of neurogenerative disorders. Material and methods: The aim of our study was to assess the influence of iron administered orally (30 mg/kg) to rats in the neonatal period (p12-p14) by testing the performance of rats in the open field and social interaction tests, and by evaluating the recognition memory, monoamine levels in some brain structures, and BDNF mRNA expression. The behavioral and biochemical tests were performed in adult p88-p92 rats. Results: Iron administered to rats in the neonatal period induced long-term deficits in behavioral tests in adult rats. It reduced the exploratory activity in the open field test. In the social interaction test, it induced deficits in the parameters studied, and decreased memory retention. Moreover, iron changed the brain monoamine levels in some studied brain structures and decreased the expression of BDNF mRNA in the hippocampus. Conclusions: All earlier and our present results indicated that iron administered to rats in the neonatal period induced an increase in oxidative stress which resulted in a change in the brain monoamine levels and decreased BDNF mRNA expression which may play a role in iron-induced memory impairment in adult rats.

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor that indirectly elevates the glucagon-like peptide-1 (GLP-1) level. The aim of the present study was to check whether linagliptin has an influence on neurotransmission in rat brain. Rats were acutely and chronically exposed to linagliptin (10 and 20 mg/kg, intraperitoneally (i.p.)). Twenty-four hours later, the striatum and hippocampus were selected for further studies. In neurochemical experiments, using high-performance liquid chromatography with electrochemical detection (HPLC-ED), the concentrations of three major neurotransmitters—dopamine, serotonin and noradrenaline—and their metabolites were measured. The analysis of mRNA expression of dopamine (D1 and D2), serotonin (5-HT-1 and 5-HT-2) and noradrenaline (α1 and α2a) receptors was also investigated using real-time quantitative reverse transcription polymerase chain reaction (RQ-PCR) in the same brain areas. Linagliptin has the ability to influence the dopaminergic system. In the striatum, the elevation of dopamine and its metabolites was observed after repeated administration of that linagliptin, and in the hippocampus, a reduction in dopamine metabolism was demonstrated. Acute linagliptin exposure increases the serotonin level in both areas, while after chronic linagliptin administration a tendency for the mRNA expression of serotoninergic receptors (5-HT1A and 5-HT2A) to increase was observed. A single instance of exposure to linagliptin significantly modified the noradrenaline level in the striatum and intensified noradrenaline turnover in the hippocampus. The recognition of the interactions in the brain between DPP-4 inhibitors and neurotransmitters and/or receptors is a crucial step for finding novel discoveries in the pharmacology of DPP-4 inhibitors and raises hope for further applications of DPP-4 inhibitors in clinical practices.

Mental illness modeling is still a major challenge for scientists. Animal models of schizophrenia are essential to gain a better understanding of the disease etiopathology and mechanism of action of currently used antipsychotic drugs and help in the search for new and more effective therapies. We can distinguish among pharmacological, genetic, and neurodevelopmental models offering various neuroanatomical disorders and a different spectrum of symptoms of schizophrenia. Modeling schizophrenia is based on inducing damage or changes in the activity of relevant regions in the rodent brain (mainly the prefrontal cortex and hippocampus). Such artificially induced dysfunctions approximately correspond to the lesions found in patients with schizophrenia. However, notably, animal models of mental illness have numerous limitations and never fully reflect the disease state observed in humans.

Recent studies suggest that impaired glutathione synthesis and distorted dopaminergic transmission are important factors in the pathophysiology of schizophrenia. In the present study, on the postnatal days p5–p16, male pups were treated with the inhibitor of glutathione synthesis, L-buthionine-(S,R)- sulfoximine (BSO, 3.8 or 7.6 mmol/kg), and the dopamine uptake inhibitor, GBR 12,909 (5 mg/kg) alone or in combination, and prepulse inhibition of the acoustic startle response (PPI) was evaluated in adult 90-day-old rats. Moreover, the monoamine levels in the cortex and hippocampus of 16-day-old rats or 91-day-old rats were measured. The present results showed that administration of BSO at 3.8 mmol/kg led to a decreasing tendency in PPI for all tested prepulse intensities. In contrast, a combined treatment with BSO in both studied doses and GBR 12,909 did not induce significant deficits in PPI. Moreover, the results of biochemical studies indicated that treatment with BSO or GBR 12,909 alone induced a weak increase in the activity of dopaminergic, serotonergic, and noradrenergic systems in the frontal cortex and hippocampus of 16-day-old rats and 91-day-old rats. However, the combined administration of both substances allowed for maintaining the normal activity of monoaminergic systems in the rat brain. The most significant changes in the functioning of monoaminergic systems were observed in the frontal cortex of 16-day-old rats. Therefore, it seems that the frontal cortex of rat puppies is most sensitive to glutathione deficiencies resulting in increased oxidative stress in neurons. As a result, it can lead to cognitive and memory impairment.

MK-801, as an N-methyl-D-aspartate (NMDA) receptor inhibitor, causes elevation in glutamate release, which may lead to an increase in excitotoxicity, oxidative stress and, consequently, cell death. 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) shows antioxidant activity. The aim of the present study was to evaluate the effect of combined treatment with 1MeTIQ and MK-801 on cell viability, antioxidant enzyme activity, and glutamate release in the rat hippocampus. Cytotoxicity was measured using lactate dehydrogenase leakage assay (LDH) and the methyl tetrazolium (MTT) assay; antioxidant enzyme activity (glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT)) were measured by ELISA kits. The release of glutamate in the rat hippocampus was measured using in vivo microdialysis methodology. An in vitro study showed that MK-801 induced cell death in a concentration-dependent manner and that 1MeTIQ partially reduced this adverse effect of MK-801. An ex vivo study indicated that MK-801 produced an increase in antioxidant enzyme activity (GPx, GR, and SOD), whereas coadministration of MK-801 and 1MeTIQ restored the activity of these enzymes to the control level. An in vivo microdialysis study demonstrated that combined treatment with both drugs decreased the release of glutamate in the rat hippocampus. The above results revealed that 1MeTIQ shows limited neuroprotective activity under conditions of glutamate-induced neurotoxicity.

Background: The aim of the present study was to evaluate the effect of 1MeTIQ on fear memory and social interaction in an MK-801-induced model of schizophrenia. The results obtained after administration of 1MeTIQ were compared with those obtained with olanzapine, an antipsychotic drug. Methods: Sprague–Dawley rats received a single injection of MK-801 to induce behavioral disorders. 1MeTIQ was given either acutely in a single dose or chronically for 7 consecutive days. Olanzapine was administered once. In groups receiving combined treatments, 1MeTIQ or olanzapine was administered 20 min before MK-801 injection. Contextual fear conditioning was used to assess disturbances in fear memory (FM), and the sociability of the rats was measured in the social interaction test (SIT). Biochemical analysis was carried out to evaluate monoamine levels in selected brain structures after treatment. Results: Our results are focused mainly on data obtained from neurochemical studies, demonstrating that 1MeTIQ inhibited the MK-801-induced reduction in dopamine levels in the frontal cortex and increased the 5-HT concentration. The behavioral tests revealed that acute administration of MK-801 caused disturbances in both the FM and SIT tests, while neither 1MeTIQ nor olanzapine reversed these deficits. Conclusion: 1MeTIQ, although pharmacologically effective (i.e., it reverses MK-801-induced changes in monoamine activity), did not influence MK-801-induced social and cognitive deficits. Thus, our FM tests and SIT did not support the main pharmacological hypotheses that focus on dopamine system stabilization and dopamine–serotonin system interactions as probable mechanisms for inhibiting the negative symptoms of schizophrenia.