The long-term sequelae of traumatic brain injury (TBI) in humans are linked with the development of convulsions and cognitive and emotional disorders and are also associated with acceleration of brain aging processes and the formation of hippocampal sclerosis (HS). The mechanisms of these complications remain incompletely understood and treatment is extremely difficult. Existing data obtained using experimental models in animals do not provide a clear assessment of these mechanisms. The present study clarifies the long-term histological, behavioral, and electrophysiological sequelae of TBI in rats. Six months after lateral hydrodynamic blows, animals displayed severe asymmetrical gliosis in hippocampal field CA3 and the dental gyrus in the form of fibrillary astrogliosis, with an increase in the number of glial cells and depletion of the pyramidal layer of field CA3 in the ipsilateral hemisphere (corresponding to type 3 HS in humans); sham-operated animals displayed only symmetrical gliosis (isolated gliosis in the human HS classification). The behavior of the rats six months after TBI and the sham procedure was characterized by decreases in motor activity, which some signs of increased anxiety. Behavioral impairments were more severe in rats after TBI, mainly due to decreases in exploratory activity. The long-term period of TBI was characterized on ECoG by prolonged spike-wave discharges in the cortex and asymmetry of epileptiform spikes in the hippocampus. Two rats in the late period demonstrated epileptic seizures. Intense brain aging processes in rats with TBI and the development of neurodegenerative changes in the hippocampus may be linked with chronic remote neuroinflammation, which plays an important role in the development of posttraumatic epilepsy and dementia.

The late period of traumatic brain injury (TBI) in humans is associated with the development of seizures, cognitive and emotional disturbances, accelerated brain aging and the formation of hippo- campal sclerosis (HS). The mechanisms of these complications remain elusive, and treatment is extremely difficult. Pronounced asymmetric gliosis in hippocampal CA3 fields and dentate gyrus and thinning of pyramidal layer of CA3 (type 3 HS) were observed in rats 6 months after lateral fluid percussion brain injury; symmetrical hippocampal gliosis was observed in sham-operated animals. Decrease in motor activity and signs of anxiety behaviour were observed in both sham and TBI groups and were more likely associated with aging. Behavioral changes were more pronounced in rats after head injury. Late posttraumatic period was characterized by the appearance of long-last- ing epileptiform discharges in cortex and asymmetry of spikes in hippocampus. In two rats in the late posttraumatic period epileptic seizures were found. Accelerated brain aging in rats with traumatic brain injury as well as neurodegenerative changes in hippocampus may be associated with chronic distant neuroinflammation in hippocampus. These mechanisms possibly play important role in the development of post-traumatic epilepsy and dementia.

Unprovoked seizures in the late period of traumatic brain injury (TBI) occur in almost 20% of humans and experimental animals, psychiatric comorbidities being common in both situations. The aim of the study was to evaluate epileptiform activity in the early period of TBI induced by lateral fluid percussion brain injury in adult male Srague-Dawley rats and to reveal potential behavioral and pathomorphological correlates of early electrophysiological alterations. One week after TBI the group of animals was remarkably heterogeneous regarding the incidence of bifrontal 7-Hz spikes and spike-wave discharges (SWDs). It consisted of 3 typical groups: a) rats with low baseline and high post-craniotomy SWD level; b)with constantly low both baseline and post-craniotomy SWD levels; c) constantly high both baseline and post-craniotomy SWD levels. Rats with augmented SWD occurrence after TBI demonstrated freezing episodes accompanying SWDs as well as increased anxiety-like behavior (difficulty of choosing). The discharges were definitely associated with sleep phases. The incidence of SWDs positively correlated with the area of glial activation in the neocortex but not in the hippocampus.The translational potential of the data is revealing new pathophysiological links between epileptiform activity appearance, direct cortical and distant hippocampal damage and anxiety-like behavior, putative early predictors of late posttraumatic pathology.

Objectives. To identify and analyze pathological activity in the acute period of craniocerebral trauma (CCT) and to seek possible morphological correlates of this activity in the cortex and hippocampus. Materials and methods. Studies were performed using Sprague–Dawley rats. CCT was modeled using lateral hydrodynamic blows to the sensorimotor cortex. Electrocorticograms were recorded one week before application of CCT and one week after CCT. Histological analysis was run one week after CCT. Sections were stained by the Nissl method and immunohistochemically for an astrocyte marker (GFAP) and microglia (isolectin B4). The extents of damage in the cortex and hippocampal were evaluated. Results and conclusions. Slowing of baseline activity was seen 1 and 6 h after CCT, and epileptiform activity appeared in 50% of the animals one week after CCT. The number of discharges correlated with the area of astrocyte gliosis in the cortex and the number of dark “ischemic” neurons in the hippocampus. Microglial activity in the hippocampus did not correlate with epileptiform activity. these data are important for understanding the early mechanisms of posttraumatic epileptogenesis.

To evaluate the consequences of traumatic brain injury (TBI), we used a model of lateral fluid percussion brain injury in freely moving male Wistar rats. The immediate response to TBI included development of motor excitation and tonic–clonic seizures. Morphological analysis was performed 7 day after TBI. To localize IgG in the brain, rat brain slices were double stained with antibodies against IgG and NeuN (neuronal marker). To evaluate the state of microglia, we performed staining with Isolectin B4 (a microglial marker). The number of neurons was measured in sections stained using the Nissl method. The results show the IgG accumulation in neurons adjacent to cortical focus of trauma. In the hippocampus, IgG was accumulated in the neurons of the ipsilateral hippocampal CA1 and CA2 fields and the dentate gyrus, while in the contralateral hemisphere IgG was accumulated in the neurons of the CA1 field. These changes were accompanied by activation of microglia in the hippocampus, as well as by a decrease in neuronal density in the dentate gyrus of the ipsilateral hippocampus. The results show that TBI leads to bilateral damage to the hippocampus.

The sequelae of craniocerebral trauma (CCT) were studied using a model based on severe (3–4 atm) lateral hydrodynamic percussion (liquid-percussive brain injury) in male Sprague–Dawley rats. With the aim of detecting the symptoms of anxiety states, the rats’ behavior was assessed in the dark-light box and the elevated plus maze test; sleep impairments were detected by recording the electrocorticogram (ECoG) before trauma and during the first week after trauma. The results provided evidence of the post-CCT development of signs of an anxiety state, accompanied by decreases in the proportion of REM sleep and decreases in the amplitude and frequency of the ECoG during this phase.

AIM:To analyze the pathological electrical activity during the acute period after traumatic brain injury (TBI) and to search for potential morphological correlates of this activity in the neocortex and hippocampus.MATERIAL AND METHODS:The study was performed on male Sprague Dawley rats. TBI was modeled using a lateral hydrodynamic impact in the sensorimotor cortex area. ECoG was continuously recorded one week before and one week after TBI. A histological analysis was performed one week after TBI. Brain slices were Nissl stained as well as immunohistochemically stained for astrocytes (GFAP) and microglia (Isolectin B4). The damage to the neocortex and hippocampus was evaluated.RESULTS AND CONCLUSION:The slowdown of the background activity one and six hours after TBI and appearance of epileptiform activity in a half of animals one week after TBI were shown. The number of discharges was correlated with the area of astrocyte gliosis in the neocortex and with the number of dark (ischemic-like) neurons in the hippocampus. Microglial activation did not correlate with the epileptiform activity. These data are important to understanding early mechanisms of post-trauma epileptogenesis.

To assess early consequences of severe traumatic brain injury (TBI) we used lateral fluid percussion model (3-4 atm) in male Sprague-Dawley rats. To evaluate symptoms of anxiety light-dark box and elevated plus-maze tests were used; to estimate global brain function and sleep disturbances electrocorticogramms (ECoG) were recorded prior TBI and during acute posttraumatic period (first week after injury). Our results suggest that during acute posttraumatic period rats demonstrate symptoms of anxiety associated with reduced percentage of REM-sleep as well as its decreased frequency and amplitude.

We studied the effect of chronic combined stress (model of experimental neurosis) on behavior of rats with different basal strategies of behavior in novelty conditions. Chronic stress resulted in decreases in the body weight and testosterone contents in the blood and neocortex in all animals. Animals with initially low orient- ing-exploratory response in the "open field" test did not exhibit substantial alterations of behavior during repeated testing in this test of the "dark-light chamber" test; however, the depression-like behavior was more expressed in the second forced swim test. Chronic combined stress did not significantly affect the behavior of this group of rats. Animals with initially high orienting-exploratory response in the "open field" test exhibited decreased locomotor and exploratory activity in the repeated "open field" tests. The decreases in the locomotor and exploratory activity were substantially less expressed in the repeated tests in these rats after chronic combined stress. The indices of depression-like behavior increased one month after the end of exposure to chronic combined stress. Our data demonstrate that different responses to novelty in the "open field" test do not allow predict with reasonable certainty the development of depression-like behavior after exposure to chronic combined stress.

Hippocampus is believed to be selectively vulnerable to stress. We hypothesized that this phenomenon may be mediated by relatively high vulnerability to neuroinflammation related to impairments of local glucocorticoid metabolism and signaling. We have evaluated inflammatory responses induced by acute or chronic combined stress in the cerebral cortex and hippocampus as well as circulating and brain corticosterone (CS) levels as well as expression of corticosterone target genes. The hippocampus showed higher stress-induced expression of the proinflammatory cytokine IL-1β as compared to the cerebral cortex. A month after the termination of the chronic stress, IL-1β mRNA in the cerebral cortex reached control level, while in the hippocampus it remained significantly increased. Under chronic stress, the maladaptive inflammatory response in hippocampus was accompanied by a significant increase in local CS levels, as compared to cerebral cortex. Under acute stress, the increased CS level induced changes in CS-regulated genes expression (CRF and IGF1), while this phenomenon was not observed after chronic stress. Thus, the hippocampus appears to be more vulnerable to stress-induced inflammation as compared to the neocortex and demonstrates persistent inflammatory response induced by chronic stress. Stress-induced maladaptive inflammatory response is associated with a selective increase in hippocampal CS accumulation and changes in CS signaling.

Depression is the most common form of mental disability in the world. Depressive episodes may be precipitated by severe acute stressful events or by mild chronic stressors. Studies on the mechanisms of depression require both appropriate experimental models (most of them based on the exposure of animals to chronic stressors), and appropriate tests for assessment of depressive states. In this study male Wistar rats were exposed to two different chronic stress paradigms: an eight-week chronic unpredictable mild stress or a two-week combined chronic stress. The behavioral effects of stress were evaluated using sucrose preference, forced swim and open field tests. After the exposure to chronic unpredictable mild stress, anhedonia was developed, activity in the open field increased, while no changes in the duration of passive floating could be detected. After chronic combined stress, anhedonia was also evident, whereas behavior in the open field and forced swim test did not change. The levels of corticosterone in the blood and brain structures involved in stress-response did not differ from control in both experiments. The absence of significant changes in corticosterone levels and passive floating may be indicative of the adaptation of animals to chronic stress. Anhedonia appears to be a more sensitive indicator of depressive-like behavioral effects of chronic stress as compared to behavior in the forced swim or open field tests.

Dosed lateral fluid percussion was used to model craniocerebral trauma (CCT) of moderate to severe intensity in one- and two-year-old rats. Brain sections were stained with cresyl violet by the Nissl method and with an immunochemical reaction for glial fibrillary acidic protein (GFAP) – a marker for astrocytes. The results provide evidence that zones of direct and remote injury formed in the side ipsilateral to the blow. The direct injury zone corresponded to the area of direct contact of the column of liquid with the dura mater, while the remote injury zone was positioned lateral and caudal to the direct injury zone. Morphological detection of trauma depended on the strength of the blow and was seen in both age groups as astrocytic gliosis, with thinning of layer I of the cortex due to death of neurons. Signs of ischemic changes to neurons were probably associated with local impairment to blood supply. Brain damage in one-year-old rats was local in nature but was more diffuse in two-year-olds, while gliosis was characterized by inhomogeneity. The reproducibility and appropriateness of the model allow it to be used for investigation of the molecular genetic mechanisms of the sequelae of CCT in humans and for identifying common mechanisms in the sequelae of CCT and the pathogenesis of major diseases comorbid with CCT, particularly depression and epilepsy.

Проведено исследование морфологических изменений и экспрессии маркеров астроглии и микроглии в сенсомоторной коре и гиппокампе крыс, перенесших хроническое невротизирующее воздействие. Установлено, что адаптация к хроническому стрессу сопровождается возникновением большого числа поврежденных нейронов как в слое V сенсомоторной коры, так в пирамидном слое гиппокампа, причем наиболее выражены эти изменения в поле СА3. Неврозоподобное состояние у крыс характеризуется увеличением экспрессии маркеров микроглии в гиппокампе, которое сохраняется в течение месяца после окончания стрессорного воздействия. Экспрессия астроцитарного маркера GFAP снижается в поле СА3 гиппокампа. Введение производного пантотеновой кислоты – пантенола, способствует стабилизации глиального ответа на хронический стресс, но его эффекты не длительны и не могут предотвратить активацию микроглии в постстрессорный период.

We studied the morphological changes and expression of the astroglial and microglial markers in the sensorimotor cortex and hippocampus of rats that were subjected to chronic stress. Chronic neurotization was associated with the appearance of a large number of damaged neurons in layer V of the sensorimotor cortex and the pyramidal layer of the hippocampus. These changes were considerably expressed in the CA3 field. A neurosis-like state in rats was accompanied by an increased expression of microglial markers in the hippocampus and this effect was evident even 1 month after the end of stress. The expression of the astroglial marker GFAP decreased in the CA3 hippocampal field. Treatment of animals with the pantothenic acid derivative panthenol stabilized the glial response to chronic stress; however, its effects were not long-lasting and did not prevent activation of microglia during the period after stress.

Effects of a chronic combined unpredictable stress on activities of two cell death-related proteases, calpain and cathepsin B, were studied along with indices of nitrergic system in rat brain structures. Male Wistar rats were subjected to a 2-week-long combined stress (combination of unpaired flash light and moderate footshock associated with a white noise session). Stress resulted in a significant loss in the body and thymus weight and increased defecation in the open field test, though neither motor and exploratory activity, nor plasma corticosterone differed from the respective control levels. Decreased calpain activity and increased cathepsin B activity were demonstrated in the hippocampus of stressed rats (previously we have shown that caspase-3 activity was significantly suppressed in the brain of rats subjected to same type of stress). A significant reduction in the number of NOS-containing neurons was accompanied by a chronic stressinduced decline in NOS activity in the neocortex. Similar changes were observed in the hippocampus. However, levels of NO metabolites were elevated in both structures. Thus, stress-induced structural modifications in the brain may be mediated by disturbances in the nitrergic system and increased lysosomal proteolysis.

Behavioral changes and accompanying morphological neuron-glia reorganization in the rat brain were analyzed after long-term immobilization. Wistar rats (n = 23) were stressed by interruptive immobilization, which was carried out within three week daily for 7-8 h. Behavioral immobilization of rats was accompanied by a decrease in the locomotor and exploratory activity in "open field" test and increase in the number and duration of freezing episodes. The morphometric studies revealed a statistically significant threefold increase in the density of hypoxic neurons in the motor neocortex of both hemispheres and CA3 field of the hippocampus in the experimental animals as compared to control. The number of glia cells in the motor cortex did not change. The increase in the density ofglial cells and multi-nucleolar neurons in CA3 region of the hippocampus are indicative of the compensatory processes in the brain. The hypoxic changes in neurons were of the functional character.