Biochemistry (Moscow) (v.82, #3)

Biochemical processes in synapses and other neuronal compartments underlie neuroplasticity (functional and structural alterations in the brain enabling adaptation to the environment, learning, memory, as well as rehabilitation after brain injury). This basic molecular level of brain plasticity covers numerous specific proteins (enzymes, receptors, structural proteins, etc.) participating in many coordinated and interacting signal and metabolic processes, their modulation forming a molecular basis for brain plasticity. The articles in this issue are focused on different “hot points” in the research area of biochemical mechanisms supporting neuroplasticity.
Keywords: brain; neuroplasticity; synaptic plasticity; proteins; enzymes; receptors; biochemical mechanisms; signal transduction

Role of atypical protein kinases in maintenance of long-term memory and synaptic plasticity by A. A. Borodinova; A. B. Zuzina; P. M. Balaban (243-256).
Investigation of biochemical mechanisms underlying the long-term storage of information in nervous system is one of main problems of modern neurobiology. As a molecular basis of long-term memory, long-term changes in kinase activities, increase in the level and changes in the subunit composition of receptors in synaptic membranes, local activity of prion-like proteins, and epigenetic modifications of chromatin have been proposed. Perhaps a combination of all or of some of these factors underlies the storage of long-term memory in the brain. Many recent studies have shown an exclusively important role of atypical protein kinases (PKCζ, PKMζ, and PKCι/λ) in processes of learning, consolidation and maintenance of memory. The present review is devoted to consideration of mechanisms of transcriptional and translational control of atypical protein kinases and their roles in induction and maintenance of long-term synaptic plasticity and memory in vertebrates and invertebrates.
Keywords: protein kinase Mζ; atypical protein kinases; synaptic plasticity; memory; epigenetic regulation; histone acetylation; methylation

Mechanisms of long-term plasticity of hippocampal GABAergic synapses by A. V. Rozov; F. F. Valiullina; A. P. Bolshakov (257-263).
Long-term potentiation and depression of synaptic transmission have been considered as cellular mechanisms of memory in studies conducted in recent decades. These studies were predominantly focused on mechanisms underlying plasticity at excitatory synapses. Nevertheless, normal central nervous system functioning requires maintenance of a balance between inhibition and excitation, suggesting existence of similar modulation of glutamatergic and GABAergic synapses. Here we review the involvement of G-protein-coupled receptors in the generation of long-term changes in synaptic transmission of inhibitory synapses. We considered the role of endocannabinoid and glutamate systems, GABAB and opioid receptors in the induction of long-term potentiation and long-term depression in inhibitory synapses. The preand postsynaptic effects of activation of these receptors are also discussed.
Keywords: long-term synaptic plasticity; GABAergic synapses; endocannabinoids; GABAB receptor; G-protein-coupled receptors; hippocampus; opioid receptors

After accumulation of data showing that resident brain cells (neurons, astrocytes, and microglia) produce mediators of the immune system, such as cytokines and their receptors under normal physiological conditions, a critical need emerged for investigating the role of these mediators in cognitive processes. The major problem for understanding the functional role of cytokines in the mechanisms of synaptic plasticity, de novo neurogenesis, and learning and memory is the small number of investigated cytokines. Existing concepts are based on data from just three proinflammatory cytokines: interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha. The amount of information in the literature on the functional role of antiinflammatory cytokines in the mechanisms of synaptic plasticity and cognitive functions of mature mammalian brain is dismally low. However, they are of principle importance for understanding the mechanisms of local information processing in the brain, since they modulate the activity of individual cells and local neural networks, being able to reconstruct the processes of synaptic plasticity and intercellular communication, in general, depending on the local ratio of the levels of different cytokines in certain areas of the brain. Understanding the functional role of cytokines in cellular mechanisms of information processing and storage in the brain would allow developing preventive and therapeutic means for the treatment of neuropathologies related to impairment of these mechanisms.
Keywords: cytokines; synaptic plasticity; interleukin-1 beta; tumor necrosis factor-alpha; interleukin-6; interleukin-10; transforming growth factor

Neonatal proinflammatory stress induces accumulation of corticosterone and interleukin-6 in the hippocampus of juvenile rats: Potential mechanism of synaptic plasticity impairments by M. V. Onufriev; S. V. Freiman; D. I. Peregud; I. V. Kudryashova; A. O. Tishkina; M. Yu. Stepanichev; N. V. Gulyaeva (275-281).
Infectious diseases in early postnatal ontogenesis can induce neuroinflammation, disrupt normal central nervous system development, and contribute to pathogenesis of cerebral pathologies in adults. To study long-term consequences of such early stress, we induced neonatal proinflammatory stress (NPS) by injecting bacterial lipopolysaccharide into rat pups on postnatal days 3 and 5 and then assessed the levels of corticosterone, proinflammatory cytokines and their mRNAs, and neurotrophins and their mRNAs in the hippocampus and neocortex of the one-month-old animals. Long-term potentiation (LTP) was studied in hippocampal slices as an index of synaptic plasticity. NPS-induced impairments of LTP were accompanied by the accumulation of corticosterone and IL-6 in the hippocampus. In the neocortex, a decrease in exon IV BDNF mRNA was detected. We suggest that excessive corticosterone delivery to hippocampal receptors and proinflammatory changes persisting during brain maturation are among the principal molecular mechanisms responsible for NPSinduced neuroplasticity impairments.
Keywords: neonatal proinflammatory stress; lipopolysaccharide; corticosterone; proinflammatory cytokines; neurotrophins; long-term potentiation

Status epilepticus impairs synaptic plasticity in rat hippocampus and is followed by changes in expression of NMDA receptors by T. Y. Postnikova; O. E. Zubareva; A. A. Kovalenko; K. K. Kim; L. G. Magazanik; A. V. Zaitsev (282-290).
Cognitive deficits and memory loss are frequent in patients with temporal lobe epilepsy. Persistent changes in synaptic efficacy are considered as a cellular substrate underlying memory processes. Electrophysiological studies have shown that the properties of short-term and long-term synaptic plasticity in the cortex and hippocampus may undergo substantial changes after seizures. However, the neural mechanisms responsible for these changes are not clear. In this study, we investigated the properties of short-term and long-term synaptic plasticity in rat hippocampal slices 24 h after pentylenetetrazole (PTZ)-induced status epilepticus. We found that the induction of long-term potentiation (LTP) in CA1 pyramidal cells is reduced compared to the control, while short-term facilitation is increased. The experimental results do not support the hypothesis that status epilepticus leads to background potentiation of hippocampal synapses and further LTP induction becomes weaker due to occlusion, as the dependence of synaptic responses on the strength of input stimulation was not different in the control and experimental animals. The decrease in LTP can be caused by impairment of molecular mechanisms of neuronal plasticity, including those associated with NMDA receptors and/or changes in their subunit composition. Realtime PCR demonstrated significant increases in the expression of GluN1 and GluN2A subunits 3 h after PTZ-induced status epilepticus. The overexpression of obligate GluN1 subunit suggests an increase in the total number of NMDA receptors in the hippocampus. A 3-fold increase in the expression of the GluN2B subunit observed 24 h after PTZ-induced status epilepticus might be indicative of an increase in the proportion of GluN2B-containing NMDA receptors. Increased expression of the GluN2B subunit may be a cause for reducing the magnitude of LTP at hippocampal synapses after status epilepticus.
Keywords: long-term synaptic potentiation (LTP); CA1; epilepsy; NMDA receptors; GluN2B; GluN2A

Role of nerve growth factor in plasticity of forebrain cholinergic neurons by N. K. Isaev; E. V. Stelmashook; E. E. Genrikhs (291-300).
Neuronal plastic rearrangements during the development and functioning of neurons are largely regulated by trophic factors, including nerve growth factor (NGF). NGF is also involved in the pathogenesis of Alzheimer’s disease. In the brain, NGF is produced in structures innervated by basal forebrain cholinergic neurons and retrogradely transported along the axons to the bodies of cholinergic neurons. NGF is essential for normal development and functioning of the basal forebrain; it affects formation of the dendritic tree and modulates the activities of choline acetyltransferase and acetylcholinesterase in basal forebrain neurons. The trophic effect of NGF is mediated through its interactions with TrkA and p75 receptors. Experimental and clinical studies have shown that brain levels of NGF are altered in various pathologies. However, the therapeutic use of NGF is limited by its poor ability to penetrate the blood–brain barrier, adverse side effects that are due to the pleiotropic action of this factor, and the possibility of immune response to NGF. For this reason, the development of gene therapy methods for treating NGF deficit-associated pathologies is of particular interest. Another approach is creation of low molecular weight NGF mimetics that would interact with the corresponding receptors and display high biological activity but be free of the unfavorable effects of NGF.
Keywords: nerve growth factor; cholinergic neurons; plasticity; Alzheimer’s disease

The excitatory neurotransmitter glutamate system and the brain-derived neurotrophic factor (BDNF) system are principally involved in phenomena of cellular and synaptic plasticity. These systems are interacting, and disclosing mechanisms of such interactions is critically important for understanding the machinery of neuroplasticity and its modulation in normal and pathological situations. The short state of evidence in this review addresses experimentally confirmed connections of these mechanisms and their potential relation to the pathogenesis of depression. The connections between the two systems are numerous and bidirectional, providing for mutual regulation of the glutamatergic and BDNF systems. The available data suggest that it is complex and well-coordinating nature of these connections that secures optimal synaptic and cellular plasticity in the normal brain. Both systems are associated with the pathogenesis of depression, and the disturbance of tight and well-balanced associations between them results in unfavorable changes in neuronal plasticity underlying depressive disorders and other mood diseases.
Keywords: BDNF; glutamate; TrkB; NMDA receptors; AMPA receptors; metabotropic glutamate receptors; neuronal plasticity; synaptic plasticity; depression

Neurotrophic factors (BDNF and GDNF) and the serotonergic system of the brain by N. K. Popova; T. V. Ilchibaeva; V. S. Naumenko (308-317).
Neurotrophic factors play a key role in development, differentiation, synaptogenesis, and survival of neurons in the brain as well as in the process of their adaptation to external influences. The serotonergic (5-HT) system is another major factor in the development and neuroplasticity of the brain. In the present review, the results of our own research as well as data provided in the corresponding literature on the interaction of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) with the 5-HT-system of the brain are considered. Attention is given to comparison of BDNF and GDNF, the latter belonging to a different family of neurotrophic factors and being mainly considered as a dopaminergic system controller. Data cited in this review show that: (i) BDNF and GDNF interact with the 5-HT-system of the brain through feedback mechanisms engaged in autoregulation of the complex involving 5-HT-system and neurotrophic factors; (ii) GDNF, as well as BDNF, stimulates the growth of 5-HT neurons and affects the expression of key genes of the brain 5-HT-system–those coding tryptophan hydroxylase-2 and 5-HT1A and 5-HT2A receptors. In turn, 5-HT affects the expression of genes that control BDNF and GDNF in brain structures; (iii) the difference between BDNF and GDNF is manifested in different levels and relative distribution of expression of these factors in brain structures (BDNF expression is highest in hippocampus and cortex, GDNF expression in the striatum), in varying reaction of 5-HT2A receptors on BDNF and GDNF administration, and in different effects on certain types of behavior.
Keywords: neurotrophic factors; serotonergic system; BDNF; GDNF; interaction between 5-HT-system and neurotrophic factors

Alzheimer’s disease (AD) is the most common type of age-related dementia. The development of neurodegeneration in AD is closely related to alterations in neurotrophic supplementation of the brain, which may be caused either by disorder of neurotrophin metabolism or by modification of its availability due to changes in the microenvironment of neurons. The underlying mechanisms are not fully understood. In this work, we used senescence-accelerated OXYS rats as a unique model of the sporadic form of AD to examine the relationship of development of AD signs and changes in neurotrophic supplementation of the cortex. Based on comparative analysis of the transcriptome of the frontal cerebral cortex of OXYS and Wistar (control) rats, genes of a neurotrophin signaling pathway with different mRNA levels in the period prior to the development of AD-like pathology in OXYS rats (20 days) and in the period of its active manifestation (5 months) and progression (18 months) were identified. The most significant changes in mRNA levels in the cortex of OXYS rats occurred in the period from 5 to 18 months of age. These genes were associated with neurogenesis, neuronal differentiation, synaptic plasticity, and immune response. The results were compared to changes in the levels of brain-derived neurotrophic factor (BDNF), its receptors TrkB and p75NTR, as well as with patterns of their colocalization, which reveal the balance of proneurotrophins and mature neurotrophins and their receptors. We found that alterations in neurotrophic balance indicating increased apoptosis precede the development of AD-like pathology in OXYS rats. Manifestation of AD-like pathology occurs against a background of activation of compensatory and regenerative processes including increased neurotrophic supplementation. Active progression of AD-like pathology in OXYS rats is accompanied by the suppression of activity of the neurotrophin system. Thus, the results confirm the importance of the neurotrophin system as a potential target for development of new approaches to slow age-related alterations in brain and AD development.
Keywords: neurotrophic factors; Alzheimer’s disease; OXYS rats

Brain mitochondrial subproteome of Rpn10-binding proteins and its changes induced by the neurotoxin MPTP and the neuroprotector isatin by A. E. Medvedev; O. A. Buneeva; A. T. Kopylov; O. V. Tikhonova; M. V. Medvedeva; L. N. Nerobkova; I. G. Kapitsa; V. G. Zgoda (330-339).
Mitochondria play an important role in molecular mechanisms of neuroplasticity, adaptive changes of the brain that occur in the structure and function of its cells in response to altered physiological conditions or development of pathological disorders. Mitochondria are a crucial target for actions of neurotoxins, causing symptoms of Parkinson’s disease in various experimental animal models, and also neuroprotectors. Good evidence exists in the literature that mitochondrial dysfunction induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) influences functioning of the ubiquitin-proteasomal system (UPS) responsible for selective proteolytic degradation of proteins from various intracellular compartments (including mitochondria), and neuroprotective effects of certain antiparkinsonian agents (monoamine oxidase inhibitors) may be associated with their effects on UPS. The 19S proteasomal Rpn10 subunit is considered as a ubiquitin receptor responsible for delivery of ubiquitinated proteins to the proteasome proteolytic machinery. In this study, we investigated proteomic profiles of mouse brain mitochondrial Rpn10-binding proteins, brain monoamine oxidase B (MAO B) activity, and their changes induced by a single-dose administration of the neurotoxin MPTP and the neuroprotector isatin. Administration of isatin to mice prevented MPTP-induced inactivation of MAO B and influenced the profile of brain mitochondrial Rpn10-binding proteins, in which two pools of proteins were clearly recognized. The constitutive pool was insensitive to neurotoxic/neuroprotective treatments, while the variable pool was specifically influenced by MPTP and the neuroprotector isatin. Taking into consideration that the neuroprotective dose of isatin used in this study can result in brain isatin concentrations that are proapoptotic for cells in vitro, the altered repertoire of mitochondrial Rpn10-binding proteins may thus represent a part of a switch mechanism from targeted elimination of individual (damaged) proteins to more efficient (“global”) elimination of damaged organelles and whole damaged cells.
Keywords: neuroplasticity; MPTP-induced parkinsonism; neuroprotection; isatin; Rpn10-binding proteins; brain mitochondrial fraction; subproteome

Optogenetic stimulation increases level of antiapoptotic protein Bcl-xL in Neurons by D. A. Lanshakov; U. S. Drozd; N. N. Dygalo (340-344).
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.
Keywords: protein Bcl-xL; protein c-Fos; AAV vector; optogenetics; hippocampal glutamatergic neuron; activity-dependent protein expression

Effects of short-term exposure to lithium on antiapoptotic Bcl-xL protein expression in cortex and hippocampus of rats after acute stress by N. N. Dygalo; A. V. Bannova; E. V. Sukhareva; G. T. Shishkina; K. A. Ayriyants; T. S. Kalinina (345-350).
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.
Keywords: Bcl-xL; BDNF; lithium chloride; stress; frontal cortex; hippocampus; gene expression

Mechanisms of brain glucocorticoid resistance in stress-induced psychopathologies by V. M. Merkulov; T. I. Merkulova; N. P. Bondar (351-365).
Exposure to stress activates the hypothalamic–pituitary–adrenal axis and leads to increased levels of glucocorticoid (GC) hormones. Prolonged elevation of GC levels causes neuronal dysfunction, decreases the density of synapses, and impairs neuronal plasticity. Decreased sensitivity to glucocorticoids (glucocorticoid resistance) that develops as a result of chronic stress is one of the characteristic features of stress-induced psychopathologies. In this article, we reviewed the published data on proposed molecular mechanisms that contribute to the development of glucocorticoid resistance in brain, including changes in the expression of the glucocorticoid receptor (GR) gene, biosynthesis of GR isoforms, and GR posttranslational modifications. We also present data on alterations in the expression of the FKBP5 gene encoding the main component of cell ultra-short negative feedback loop of GC signaling regulation. Recent discoveries on stressand GRinduced changes in epigenetic modification patterns as well as normalizing action of antidepressants are discussed. GR and FKBP5 gene polymorphisms associated with stress-induced psychopathologies are described, and their role in glucocorticoid resistance is discussed.
Keywords: glucocorticoid resistance; stress-induced psychopathologies; glucocorticoid receptor; FK506 binding protein 5 (FKBP5); epigenetic modifications

Cooperative synthesis of dopamine in rat mediobasal hypothalamus as a compensatory mechanism in hyperprolactinemia by A. U. Kurina; T. S. Pronina; L. K. Dilmukhametova; G. V. Maleev; M. V. Ugrumov (366-372).
Dopamine (DA), synthesized in the mediobasal hypothalamus by dopaminergic neurons containing two enzymes of DA synthesis–tyrosine hydroxylase and decarboxylase of aromatic L-amino acids, or by monoenzymatic non-dopaminergic neurons containing one DA synthesis enzyme in cooperation, is known to have an inhibitory effect on prolactin secretion. Deterioration of this inhibitory control leads to an increase in prolactin concentration in the blood and to the development of hyperprolactinemia syndrome. In a rat model of hyperprolactinemia induced by administration of a neurotoxin causing degeneration of dopaminergic and noradrenergic neurons, the level of DA first decreases, leading to an increase in prolactin level (decompensation stage), while later both levels are restored to normal (compensation stage). However, the mechanism of such compensation is still not clear. The aim of the present study was to analyze whether the increase in cooperative synthesis of DA by monoenzymatic neurons during hyperprolactinemia is a manifestation of a compensatory mechanism representing a particular case of neuroplasticity. The level of cooperative synthesis in the hyperprolactinemia model and in the control was estimated as the level of synthesis of DA and L-dihydroxyphenylalanine (L-DOPA)–an intermediate product of DA synthesis, when L-DOPA transfer from neurons containing tyrosine hydroxylase into neurons containing aromatic L-amino acid decarboxylase is inhibited. The level of DA synthesis during the decompensation stage was not changed, while during the compensation stage it was lower than the control. Along with a reduction in DA level, during the compensation stage an increase in the extracellular L-DOPA level in the medium was detected. Thus, the compensation of DA deficiency after degeneration of dopaminergic neurons in the mediobasal hypothalamus is due to the increase in cooperative synthesis of DA by monoenzymatic neurons containing one of the complementary enzymes of the DA synthesis pathway.
Keywords: mediobasal hypothalamus; neuroplasticity; dopamine; noradrenaline; L-dihydroxyphenylalanine; 6-hydroxydopamine; high-performance liquid chromatography

Plasticity of central and peripheral sources of noradrenaline in rats during ontogenesis by N. S. Bondarenko; L. K. Dilmukhametova; A. Yu. Kurina; A. R. Murtazina; A. Ya. Sapronova; A. P. Sysoeva; M. V. Ugrumov (373-379).
The morphogenesis of individual organs and the whole organism occurs under the control of intercellular chemical signals mainly during the perinatal period of ontogenesis in rodents. In this study, we tested our hypothesis that the biologically active concentration of noradrenaline (NA) in blood in perinatal ontogenesis of rats is maintained due to humoral interaction between its central and peripheral sources based on their plasticity. As one of the mechanisms of plasticity, we examined changes in the secretory activity (spontaneous and stimulated release of NA) of NA-producing organs under deficiency of its synthesis in the brain. The destruction of NA-ergic neurons was provoked by administration of a hybrid molecular complex–antibodies against dopamine-β-hydroxylase associated with the cytotoxin saporin–into the lateral cerebral ventricles of neonatal rats. We found that 72 h after the inhibition of NA synthesis in the brain, its spontaneous release from hypothalamus increased, which was most likely due to a compensatory increase of NA secretion from surviving neurons and can be considered as one of the mechanisms of neuroplasticity aimed at the maintenance of its physiological concentration in peripheral blood. Noradrenaline secretion from peripheral sources (adrenal glands and the organ of Zuckerkandl) also showed a compensatory increase in this model. Thus, during the critical period of morphogenesis, the brain is integrated into the system of NA-producing organs and participates in their reciprocal humoral regulation as manifested in compensatory enhancement of NA secretion in each of the studied sources of NA under specific inhibition of NA production in the brain.
Keywords: noradrenaline; brain; neuroplasticity; adrenal glands; organ of Zuckerkandl; neonatal; rats

In this review we summarize published data on the involvement of glial cells in molecular mechanisms underlying brain plastic reorganization in epilepsy. The role of astrocytes as glial elements in pathological plasticity in epilepsy is discussed. Data on the involvement of aquaporin-4 in epileptogenic plastic changes and on participation of microglia and extracellular matrix in dysregulation of synaptic transmission and plastic remodeling in epileptic brain tissue are reviewed.
Keywords: glial cells; neurons; epilepsy; plasticity

Cerebral mechanisms of hypoxic/ischemic postconditioning by O. V. Vetrovoy; E. A. Rybnikova; M. O. Samoilov (392-400).
This review analyzes recent data on mechanisms of cerebral hypoxia and the protective methods of hypoxic and ischemic postconditioning, as well as their interrelationship with the key mechanisms responsible for neuroprotection and neuroplasticity. Upregulation of expression of antiapoptotic factors and neurotrophins and modulation of activity of several protein kinases and transcription factors such as hypoxia-inducible factor-1 (HIF-1) are considered as the most important aspects in the neuroprotective potential of postconditioning. The presented information indicates substantial transformative promise of the noninvasive techniques of hypoxic postconditioning as well as significant similarity between the adaptive pathways activated by various postconditioning methods, which are far from being fully understood.
Keywords: hypoxia/ischemia; neuropathology; ischemic postconditioning; hypoxic postconditioning; neuroplasticity