Vol 12, No 1 (2018)

The group of compounds of the cardiotonic steroid (CTS) class includes steroid compounds that inhibit Na⁺,K⁺-ATPase. Recently, a large amount of data has been accumulating on the important role of CTS in regulating brain function through binding to Na⁺,K⁺-ATPase, which can perform a receptor role and trigger intracellular signaling cascades. Interestingly, it is in the brain where the greatest diversity of Na⁺,K⁺-ATPase isoforms different in their affinity for compounds of this class is observed. Despite the abundance of data on the presence of endogenous CTS in mammalian organisms and the evolutionary prerequisites for their existence, the presence of specific compounds is being actively discussed in the scientific literature, and enzymes directly involved in the synthesis of these compounds have not been identified. This review describes currently established functions of cardiotonic steroids and gives a detailed description of currently existing prerequisites of the endogenous origin of CTS in mammals. Experimental evidence of the presence of specific CTS in the body is given and attention is paid to the methods based on which the structure of endogenous CTS is established or predicted. We discuss why CTS can be important endogenous regulators in the nervous system and why the problem of isolating endogenous CTS from the brain and establishing their structure is urgent.

We performed an analysis of the reciprocal influences of neurons involved in the rapid-eye-movement phase of sleep (REM sleep) under the conditions of changes in the concentrations of various neuromodulators that are characteristic of Alzheimer’s disease. Several approaches to the search for drugs for the weakening of disease symptoms have been proposed taking the results of this analysis into account. The antagonists of orexin receptors were recently suggested for the treatment of Alzheimer’s disease because the anomalously high concentration of orexin, which is specific for this pathology, results in impairment of REM sleep. However, our analysis shows that the treatment with the antagonists of orexin receptors is not appropriate because it may lead to depression of the excitation of cholinergic cells, an additional decrease in the cholinergic deficit, and aggravation of symptoms of the disease. For the same reason it is unlikely that one should apply the antagonists of histamine H1 receptors and the agonists of adenosine A1 receptors. Substances that can lead to reduced activity of orexinergic neurons may be helpful instead. These substances include melatonin and the agonists of melatonin M1 receptors. Administration of these substances should improve REM sleep because it decreases the efficacy of excitation of orexinergic and histaminergic cells. Melanin-concentrating hormone also should decrease the efficacy of excitation of orexinergic cells. Additionally, the antagonists of histamine H3 receptors may be used because they promote the increased efficacy of excitation of neurons that secrete the melanin-concentrating hormone. Experimental evidence exists that indicates the benefits of these substances for improvement of REM sleep and attenuation of cognitive impairments in Alzheimer’s disease. These drugs must be applied before nightfall and their action should not be prolonged because orexinergic cells must be active in the daytime.

It is known that mild hypobaric hypoxia preconditioning may prevent brain damage induced by ischemic stroke and other forms of hypoxia. Activation of the antioxidant systems is one of the key molecular mechanisms that protect cells from oxidative stress during and after severe hypoxia/ischemia. Specifically, the cytoplasmic protein antioxidant thioredoxin-1 efficiently protects neurons from oxidative stress and hypoxia-induced damage. It has been previously shown that preconditioning with triple mild hypobaric hypoxia treatment significantly increased the expression of some endogenous antioxidants, including thioredoxin- 1, in the rat brain after subsequent severe hypoxia. This increase correlated with prevention or at least substantial amelioration of behavioral disturbances and structural brain damage. However, triple preconditioning per se, that is, without or prior to beginning of the subsequent severe hypoxia, did not increase but even significantly decreased the expression of thioredoxin-1 and some other antioxidants. In the present study we estimated the effects of a six-time mild hypobaric hypoxia on the expression of thioredoxin-1 in various regions of the hippocampus and neocortex of rats. Using immunocytochemistry, we demonstrate that six-time treatment with mild hypoxia significantly increases the thioredoxin-1 expression in neurons of the hippocampus and neocortex of rats 24 h after the last hypoxia treatment.

Distribution of agmatinase (AGM), an enzyme of agmatine metabolism, was studied in the spinal cord and dorsal root ganglia of rats with different levels of initial thermal pain sensitivity under normal conditions and during the development of inflammatory pain using immunohistochemistry. The initial type of pain threshold affects the specific pain response of an animal to pain so that the rats with a higher threshold exhibit a less-expressed behavioral pain response. We found a specific distribution and time course of activity of AGM in the brain regions of animals with different nociceptive thresholds. The animals with a lower threshold had a higher number of AGM-immunoreactive neurons in the ganglia and a lower density of fibers and neurons in the dorsal roots of the spinal cord compared to the animals with a higher threshold. The development of tonic pain was associated with differently directed changes of AGM activity in the studied structures and depended on the threshold of nociception. Our data suggest that the endogenous system of agmatine metabolism may be involved in the initial threshold of nociception, as well as in organization of the behavioral response to pain.

Exposure to stress during early postnatal development can cause neurological disorders in adulthood. The aim of this study was to evaluate changes in behavior, learning ability, and the content of the neurotrophic factor BDNF in rats that underwent neonatal stress. In addition, we studied the possibility of correction of the effects of neonatal stress by subsequent administration of an analog of the ACTH(4-10) fragment Semax. Neonatal isolation (NI) was used as a stress stimulus. Rat pups were separated from their mother and littermates for 5 h per day each day during the period from the 1st to the 14th day of life. The control animals were left in their nest in the first 2 weeks of life. From the 15th to 28th day of life, half of the rats subjected to NI were intranasally treated with Semax daily at a dose of 0.05 mg/kg. The remaining animals received intranasal injection of solvent at the same time. It has been shown that NI leads to an increase in the level of anxiety, a slight increase in depression, and impaired retention of the passive avoidance task in rats during the second month of life. At the age of 1 month, we observed an increase in the content of BDNF in the frontal cortex in the rats with NI; at the age of 2 months, a decrease occurred in the neurotrophin level in the hippocampus. Administration of Semax to rats subjected to NI decreased anxiety and depression, improved learning ability, and normalized the BDNF content in brain structures of animals. Therefore, chronic intranasal Semax administration after NI weakens the negative effects of neonatal stress.

We studied the influence of the neuroprotective dipeptide drug noopept on the state of the retina during thrombosis of its vessels in an experiment with male chinchilla rabbits. The pathology was modeled by intravenous injection of rose Bengal at a dose of 40 mg/kg followed by transpupillary focal illumination with white light of the temporal vascular arcade for 10 min. Noopept was administered intravenously immediately after modeling thrombosis at a dose of 0.5 mg/kg, and then three times per day per os at a dose of 10 mg/kg throughout the experiment. It was found that noopept improves the functional state of the retinal neurons according to electroretinography. At the 5–7th and 14th days, noopept reduced the glutamate content in the retina by 86.8% and 84.1% compared to the control animals (p < 0.05), decreased the concentration of products of reaction with thiobarbituric acid by 17.3% and 14.9% on the 3rd and 7th days (p < 0.05), and increased the activity of glutathione-S-transferase by 34.5% on the 1st day (p < 0.05).

Central nervous system (CNS) dysfunction caused by infection with neurovirulent viruses is of interest, and may play an important role in many neurodegenerative diseases. Since neuronal functions are believed to be partly regulated by cytokines produced by astrocytes, neuroinflammation and neurodegeneration caused by H5N1 influenza virus infection could be due to abnormal cytokine production of those infected astrocytes. In the present study, cytokine responses of murine astrocytes following H5N1 virus infection were investigated. Primary astrocytes from neonatal outbred ICR mice were isolated and used to investigate cytopathology upon infection with the H5N1 virus (A/Chicken/Thailand/CUK2/04). Thereafter, cell lysates at 6, 24, 48, and 72 hours-post infection (hpi) were collected and subjected to quantification of cytokine gene expression, including TNF-α, IL-1β, IL-2, IL-6 and IL-12β, by quantitative RT-PCR. The results revealed that infection with the H5N1 virus in primary murine astrocytes was restricted, and resulted in abortive virus infection. However, this abortive infection in the astrocytes was found to result in significant upregulation of IL-1β mRNA expression at 72 hpi compared with the mock-infected group, while the mRNA expression of IL-2 and IL-12β was observed to have undergone significant down-regulation at 6-72 hpi and 24-48 hpi, respectively. The results of the present study could support the role of astrocytes in neuroinflammation and neurodegeneration.

In this study the authors compared the levels of glutamine synthetase (GS) enzymatic activities, as well as the levels of immunoreactive GS and GS-like protein (GSLP) in the readily soluble protein fraction of brain samples taken during autopsies of patients with schizophrenia and subjects from a control group. Enzymatic GS activity was measured and levels of immunoreactive GS and GSLP were determined in postmortem samples of the prefrontal, anterior, and posterior cingulate cortex (Brodmann areas 10, 24, and 23, respectively) and cerebellum cortex obtained from patients with schizophrenia (n = 8) and a control group (n = 9), matched according to age and postmortem interval. GS activity was evaluated in vitro in the “transferase” reaction by the formation of γ-glutamyl hydroxamate, and the levels of immunoreactive GS and GSLP were evaluated by ECL Western blotting using monoclonal and polyclonal antibodies. No differences in GS enzymatic activity were found in all of the studied brain structures. The level of immunoreactive GS in the prefrontal cortex was significantly decreased in patients with schizophrenia compared with the controls (at p < 0.001 according to the Mann–Whitney U-test); it was unchanged in the posterior cingulate cortex and significantly elevated in the anterior cingulate cortex and cerebellum (p < 0.001 and p < 0.004, respectively), whereas the level of immunoreactive GSLP was elevated in all studied brain areas (p < 0.004, p < 0.02, p < 0.04, and p < 0.006, respectively). The alteration of GS and GSLP levels in brains of patients with schizophrenia is one of the factors that disturb glutamate metabolism in these brain structures and is an important aspect of schizophrenia pathogenesis.

In this paper, the state of the body’s antioxidant defense was studied using the state of thiol groups in the albumin in patients with their first episode of schizophrenia (FES). We examined 21 patients with the first psychotic attack of schizophrenia; the average severity of the disorders was 75 ± 2 points on the PANSS scale. All patients were examined prior to initiation of the drug therapy. The control group consisted of ten healthy volunteers. The concentration and reactivity of the albumin SH groups was determined in the reaction with dithionitrobenzoic acid. As a result of the study, we found a 24% decrease in the average reactivity of albumin SH groups in the FES group compared with the control group (p = 0.02). Using two parameters, that is, the concentration and reactivity of albumin thiols, it was possible to separate the patient group and the control group, with the probability of a relationship of the patient to the respective group of 86%. Thus, patients with the first episode of schizophrenia before the start of treatment are characterized by significant disturbances in the concentration and reactivity of the albumin SH-groups involved in redox processes in the body.

It has been recently shown that insulin has a neuroprotective effect. Experimental studies and clinical trials have demonstrated that insulin is a promising drug for treatment of neurodegenerative and other diseases associated with brain damage. However, the mechanism of the neuroprotective effect of insulin is far from being elucidated. The aim of this study was to examine the dependence of the protective effect of insulin in cortical neurons on its concentration and the involvement of the modulation of the activity of extracellular signal-regulated kinase (ERK1/2) by insulin in neuronal survival. Using the MTT method, we found that the protective effect of insulin in neurons treated with hydrogen peroxide varied in the concentration range of 1–100 nm (1 nM < 10 nM < 100 nM). There were no significant differences between the effects of 100 nM or 1 nM insulin. The literature data on the effects of insulin on the activity of ERK1/2 in neurons are controversial. We studied the modulatory effect of insulin on the activity of ERK1/2 in cortical neurons during development of oxidative stress using the immunoblotting method at eight time points after prooxidant application. We found that insulin increased the basal activity of ERK1/2 and the activity of the enzyme at the early stage of action of hydrogen peroxide, that is, 5–30 min after its addition. This may improve the protective effect of insulin.