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Connectivity is the coordinated activity of the neuronal networks responsible for brain functions; it is detected based on functional magnetic resonance imaging signals that depend on the oxygen level in the blood (blood oxygen level-dependent (BOLD) signals) supplying the brain. The BOLD signal is only indirectly related to the underlying neuronal activity; therefore, it remains an open question whether connectivity and changes in it are only manifestations of normal and pathological states of the brain or they are, to some extent, the causes of these states. The creation of chemogenetic receptors activated by synthetic drugs (designer receptors exclusively activated by designer drugs, DREADDs), which, depending on the receptor type, either facilitate or, on the contrary, inhibit the neuronal response to received physiological stimuli, makes it possible to assess brain connectivity in the light of controlled neuronal activity. Evidence suggests that connectivity is based on neuronal activity and is a manifestation of connections between brain regions that integrate sensory, cognitive, and motor functions. Chemogenetic modulation of the activity of various groups and types of neurons changes the connectivity of the brain and its complex functions. Chemogenetics can be useful in reconfiguring the pathological mechanisms of nervous and mental diseases. The initiated integration, based on the whole-brain connectome from molecular-cellular, neuronal, and synaptic processes to higher nervous activity and behavior, has the potential to significantly increase the fundamental and applied value of this branch of neuroscience.

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Abstract-Chemogenetic activation of glutamatergic neurons of the prefrontal cortex reduces the manifestations of psychoemotional anxiety during the juvenile period of ontogenesis. This result is the first evidence of feasibility of targeted chemogenetic control of neuronal activity during the early stages of brain development.

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Irradiation of a mixture of oligonucleotides with dextran resulted in the formation of a complex that is detected by a decelerated migration of an irradiated sample in electrophoretic gel compared to a non-irradiated one. When injected into the brain of neonatal rats, the formed complex penetrated into the cells 3 times easier compared to the original oligonucleotide, thus indicating that the use of radiation crosslinking of oligonucleotides with oligosaccharides is promising to enhance the efficiency of delivery of gene-targeted oligonucleotide drugs into cells.

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Doxycycline (Dox)-inducible transgenic approach is used to examine the neural mechanisms of anxiety and depression; however, its own effects on related behaviors are not clear. To address this, in the present study, we tested the anxiety- and depression-like behaviors in rats treated with Dox in drinking water (2 mg/ml) in the elevated plus-maze (EPM; on day 5) and forced swim (FST; on day 8) tests, respectively. In addition, the levels of mRNAs and proteins of brain-derived neurotrophic factor (BDNF) and anti-apoptotic protein Bcl-xL in the hippocampus (HIPP) and frontal cortex (FC) were also analyzed. Consumption of Dox for 4 days induced an anxiogenic-like phenotype that was manifested by the decreased percentages of open arm entries and time spent on the open arms of the EPM. After Dox for 7 days, animals demonstrated more active behavior in the FST than control rats as evidenced by the increase in climbing time. When assessed after the FST, expression of Bcl-xL was increased in the hippocampus of Dox-treated animals. Furthermore, hippocampal Bcl-xL content correlated positively with the duration of climbing in the test. This study is the first to find that Dox in treatment regime used to control transgene expression can affect anxiety- and depression-like behaviors in rats. Dox-induced increase in Bcl-xL expression in the hippocampus may be involved in the moderate activation of FST behavior.

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The antiapoptotic protein Bcl-xL is associated with several neuroplastic processes such as formation of synapses, regulation of spontaneous and evoked synaptic responses, and release of neurotransmitters. Dependence of expression on activity of neurons is characteristic for many proteins participating in regulation of neuroplasticity. Whether such property is exhibited by the Bcl-xL protein was analyzed using in vivo optogenetic stimulation of hippocampal glutamatergic neurons expressing channelrhodopsin ChR2H134 under CAMKIIa promoter in the adeno-associated viral vector, followed by immunohistochemical determination of the level of Bcl-xL protein in these neurons and surrounding cells. Increase in the level of early response c-Fos protein following illumination with blue light was indicative of activation of these hippocampal neurons. The optogenetic activation of hippocampus resulted in a significant increase in the level of antiapoptotic protein Bcl-xL in the photosensitive neurons as well as in the surrounding cells. The dependence of the level of expression of Bcl-xL protein on the activity of neurons indicates that this protein possesses one more important property that is essential for participation in neuroplastic processes in the brain.

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The antiapoptotic protein Bcl-xL is involved in development of neurobiological resilience to stress; hence, the possibility of use of psychotropic drugs to increase its expression in brain in response to stress is of considerable interest. Lithium is a neurotropic drug widely used in psychiatry. In work, we studied effects of lithium administration (for 2 or 7 days) on the expression of Bcl-xL mRNA and protein in the hippocampi and cortices of rats subjected to stress that induced depression-like behavior in the animals. In contrast to the brain-derived neurotrophic factor (BDNF), whose expression decreased in the hippocampus in response to acute stress, stress increased the level of Bcl-xL mRNA in the hippocampus, but decreased it in the frontal cortex. Treatment of stressed animals with lithium for 2 or 7 days increased Bcl-xL protein levels 1.5-fold in the hippocampus, but it decreased them in the cortex. Therefore, Bcl-xL expression in the brain can be modulated by both stress and psychotropic drugs, and the effects of these factors are brain region-specific: both stress exposure and lithium administration activated Bcl-xL expression in the hippocampus and suppressed it in the frontal cortex. The activation of Bcl-xL expression in the hippocampus by lithium, demonstrated for the first time in this study, suggests an important role of this protein in the therapeutic effects of lithium in the treatment of stress-induced psychoemotional disorders.

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The ratio of the expression levels of the immediate early genes c-jun and c-fos that encode components of the AP-1 transcription complex determines the direction of changes in the expression of genes controlled by the complex, including changes induced by glucocorticoids. The aim of the present work was to assess the levels of mRNA encoded by genes c-jun and c-fos and the ratio of expression levels of these genes in various regions of the neonatal rat brain after the administration of dexamethasone, a selective ligand of the glucocorticoid receptor. The level of mRNA encoded by the immediate early gene c-fos in the hippocampus and prefrontal cortex of 3-day-old rat pups was elevated at 30, 60, and 120 min after dexamethasone administration. The basal level of c-fos gene expression in the brainstem was higher than in the cortex and hippocampus, and administration of the hormone was followed by a reduction in the amount of transcript detectable in the brainstem after 2 h. As a result, the ratio of c-jun to c-fos transcript levels in the brainstem of neonatal rats was doubled after dexamethasone administration. The dexamethasone-induced shift of the ratio of c-jun to c-fos transcript levels in the brainstem of neonatal rats towards a predominance of c-jun reported for the first time in the present work may induce the expression of genes that contain AP-1 response elements in the promoters, since the glucocorticoid receptor can be involved in protein-protein interactions with the Jun/Jun homodimer of the AP-1 complex.

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Lithium chloride (85, 255, or 255+127 µg/kg) or dexamethasone (0.2 or 2 mg/kg) were subcutaneously injected to 3-day-old rat pups, whose excretory system did not yet attain functional maturity. Both agents retarded the growth of rat pups and delayed the appearance of negative geotaxis. LD50 and therapeutic index of lithium chloride were 255 µg/kg and TI≤3, respectively. Thus, lithium salts even in low doses can be highly toxic for the developing organism.

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Optogenetics--new method which enables the control of selected cell type activity using light. This method significantly enhances the capabilities of modern neurobiology. In the review, the general concept of optogenetics and recent results and prospects of application of this approach in psycho-behavioral studies are discussed.

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In the developing brain, mature brain derived neurotrophic factor (mBDNF) and its precursor (proBDNF) exhibit prosurvival and proapoptotic functions, respectively. However, it is still unknown whether mBDNF or proBDNF is a major form of neurotrophin expressed in the immature brain, as well as if the level of active caspase-3 correlates with the levels of BDNF forms during normal brain development. Here we found that both proBDNF and mBDNF were expressed abundantly in the rat brainstem, hippocampus and cerebellum between embryonic day 20 and postnatal day 8. The levels of mature neurotrophin as well as mBDNF to proBDNF ratios negatively correlated with the expression of active caspase-3 across brain regions. The immature cortex was the only structure, in which proBDNF was the major product of bdnf gene, especially in the cortical layers 2-3. And only in the cortex, the expression of BDNF precursor positively correlated with the levels of active caspase-3. These findings suggest that proBDNF alone may play an important role in the regulation of naturally occurring cell death during cortical development.

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Triptorelin, a synthetic analogue of neurohormone gonadoliberin (gonadotropin-releasing hormone, GnRH) administered daily to rats on postnatal days 5-7 suppressed the expression of GnRH receptor in the pituitary gland, but did not change functioning of the pituitary-testicular complex. Administration of triptorelin on postnatal days 12-14 (i.e. during the formation of pulsatile pattern of GnRH secretion and increasing levels of its mRNA receptor in the pituitary gland) had no effect on receptor expression, but increased the levels of luteinizing hormone mRNA in the pituitary gland and the weight of testes. At that time, blood levels of testosterone were lowered, which indicated disturbed pulsatile pattern of GnRH secretion.

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Synthetic glucocorticoid dexamethasone decreased locomotor activity of neonatal rats 120 h after administration. Behavioral changes were associated with an increase in the content of active caspase-3 in the cerebellum. We found that expression of this apoptotic protease was similar to the control value when dexamethasone action was combined to hypoxic treatment to rats; however, the locomotor activity decreased to the hormone action did not recovered. We found that proapoptotic action of dexamethasone was blocked by hypoxic treatment; however, it was not sufficient for prevention of the effect of hormone on behavior.

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Here we review modern data on appearance and maintenance of depression at different levels of the body. We discuss a role of impairments of emotional and motivation mechanisms of adaptive behavior in genesis of depression. We demonstate an interaction of stress response and neuroinflammatory processes in pathogenesis of depression and analyze the effects of these molecular cascades on neurotrophic support of the central mechanisms of memory and neurogenesis.

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Stress predisposes to depression by enhancing apoptosis and reducing neurogenesis in the brain. There are significant individual differences in resilience to the effects of stress on mood. These differences, at least in part, may be related to the expression of the anti-apoptotic protein Bcl-xL in the brain. Increased expression of this protein in the hippocampus may be an important factor of resilience to stress-induced depression. Expression of the Bcl-xL in the brainstem acquires the ability to respond to stress induction during the course of treatment with prozac concomitantly with the emergence of the therapeutic effect of this antidepressant on behavior. Processes linking stress and behavior in which the protein Bcl-xL is involved, are considered in this review.

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ACTH1-24(1 mg/kg) administered to 5-7-day-old rats reduced their locomotor activity and did not alter blood levels of corticosterone. ACTH administration on postnatal days 12-14 increased corticosterone levels, but had no effect on locomotor activity. Thus, the behavioral effect of ACTH is not due to corticotropic action of the hormone and is not associated with blood levels of glucocorticoids.

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The influence of corticosterone during the period of tyrosine hydroxylase gene expression (16th-18th days of rat embryogenesis), which is sensitive to hormonal induction, on the ontogenesis of presynaptic markers of the noradrenergic system has been studied. It has been found that hormone-induced changes in the level of noradrenaline and dopamine in the brain cortex and brainstem had a transitive character and were eliminated in adulthood. At the same time, the hormone increased the activity oftyrosine hydroxylase in the cortex of 7- to 16-day-old rat pups and in the cortex and brainstem of adult animals. It has been shown that the level of glucocorticoids is an important factor in development of the noradrenergic system of the brain, able during critical periods of ontogenesis to cause sustained changes of its functioning in subsequent periods of life.

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Natural glucocorticoid hydrocortisone was suggested as a potent substitution for dexamethasone in the treatment of bronchopulmonary dysplasia in neonates. The aim of this study was to investigate whether hydrocortisone is able to affect the expression of apoptotic genes and the intensity of naturally occurring cell death in the developing rat hippocampus. Hormone treatment decreased procaspase-3 and active caspase-3 levels as well as DNA fragmentation intensity in the hippocampal formation of one-week-old rats in 6 h after injection. These changes were accompanied by an upregulation of antiapoptotic protein Bcl-XL, while expression of proapoptotic protein Bax remained unchanged. The action of hydrocortisone was glucocorticoid receptor-independent, as the selective glucocorticoid receptor agonist dexamethasone did not affect either apoptotic protein levels or DNA fragmentation intensity in the hippocampal region. The data are the first evidences for in vivo antiapoptotic effects of hydrocortisone in the developing hippocampus.

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Dexamethasone increased the levels of active caspase-3 form in the brain cortex of neonatal rats 120 h after drug administration, but did not affect the expression of this key apoptotic protease in the brain 6 or 24 h postinjection. Increased expression of the active form of caspase-3 in the cerebral cortex was associated with earlier eye opening and delayed formation of startle-reflex in rats.

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Changes in gene expression of the brain serotonin (5-HT) 1A receptors may be important for the development and ameliorating depression, however identification of specific stimuli that activate or reduce the receptor transcriptional activity is far from complete. In the present study, the forced swim test (FST) exposure, the first stress session of which is already sufficient to induce behavioral despair in rats, significantly increased 5-HT1A receptor mRNA levels in the brainstem, frontal cortex, and hippocampus at 24 h. In the brainstem and frontal cortex, the elevation in the receptor gene expression after the second forced swim session was not affected following chronic administration of fluoxetine, while in the cortex, both control and FST values were significantly reduced in fluoxetine-treated rats. In contrast to untreated rats, no increase in hippocampal 5-HT1A receptor mRNA was observed in response to FST in rats chronically treated with fluoxetine. Metabolism of 5-HT (5-HIAA/5-HT) in the brainstem was significantly decreased by fluoxetine and further reduced by swim stress, showing a certain degree of independence of these changes on 5-HT1A receptor gene expression that was increased in this brain region only after the FST, but not after fluoxetine. FST exposure also decreased the brainstem dopamine metabolism, which was unexpectedly positively correlated with 5-HT1A receptor mRNA levels in the frontal cortex. Together, these data suggest that the effects of the forced swim stress as well as fluoxetine involve brain region-dependent alterations in 5-HT1A receptor gene transcription, some of which may be interrelated with concomitant changes in catecholamine metabolism.

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A single exposure of rats to the forced-swimming stress decreased BDNF mRNA levels in the cortex and increased Bcl-xl gene expression in the hippocampus and amygdala 24 h after the stress. The animals demonstrated a depressive-like behavior and elevated blood corticosterone level. There was a significant negative correlation between BDNF mRNA level in the cortex and immobility time during swimming. Repeated exposure to swimming stress caused the elevation of the hippocampal BDNF mRNA level assessed 24 h after the second swimming session. The data suggest that stress-induced down-regulation of cortical BDNF gene expression and behavioral despair in the forced-swimming test may be interrelated. The increase in the BDNF and Bcl-xl mRNA levels may contribute to the mechanisms protecting the brain against negative effects of stress.

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