Chronic stress is often a precursor to depression. Multiple brain mechanisms underlying the development of depression involve alterations in neurotrophin signaling. In the present study, male Wistar rats were exposed to chronic mild unpredictable stress (CMS), a well-known rodent model of depression, in order to investigate changes in BDNF content, BDNF mRNA expression, and BDNF receptor expression in different brain regions. After 8 weeks of CMS, anhedonia, a symptom of a depressive state, developed in 35% of stressed rats, while 65% remained resilient. The CMS treatment did not significantly affect the BDNF content as measured by ELISA in the frontal cortex, other neocortical regions, the hippocampus, and the medulla oblongata. The levels of exon I Bdnf mRNA decreased in the frontal cortex of both anhedonic and resilient rats. No changes were observed in exons IV, VI and IX in any of the studied brain structures, except for the hippocampus of anhedonic rats, where there was a tendency toward decreased exon IX Bdnf mRNA. The levels of Ntrk2 and Ngfr mRNAs did not significantly change in the brain after CMS. Therefore, the alterations in the expression of exon I Bdnf mRNA observed in this study were caused by chronic stress but were not associated with depression-like anhedonia.

Social isolation and loneliness can lead to an increased risk of cardiovascular disease, cognitive decline, and psychiatric disorders. In this study, we investigated the impact of chronic social isolation on the cognitive functions and structural-functional state of the brain in middle-aged rats. Ten-month-old male spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), and Wistar rats were housed individually for 15 weeks, while the control animals of respective strains were housed in groups. After 13 weeks, all the rats were trained to complete a spatial task in a Barnes maze. After the behavioral experiments, we analyzed the density of neurons, astrocytes, and microglia in the hippocampus. We also studied the expression of several genes in the hippocampus and frontal cortex, including Aqp4, Cx3cr1, Tnfa, Il1b, and Il6, using qPCR. We found that Wistar rats showed high resilience, maintaining stable physiological parameters and spatial learning abilities without significant neuroinflammatory or structural changes in the brain. In contrast, SHRs showed marked physiological vulnerability, characterized by a significant weight loss and severe memory impairments in the Barnes maze, accompanied by an elevated cytokine response in both brain regions studied. A different trajectory of neurobiological changes was observed in WKY rats. Although they had a high rate of hippocampal neurogenesis, which provided a compensatory effect on basic spatial learning and memory, they also showed decreased neuronal density and an elevated Il6 mRNA level, linked to impaired microglial Cx3cr1 mRNA expression. This study highlights the importance of genetic background in determining the outcome of brain aging in conditions of social isolation.

Genotypic characteristics may determine the body's response to stressful conditions as well as its susceptibility to cardiovascular diseases and stroke. Old age worsens the course of these diseases, and often concomitant hypertension can negatively affect brain function, especially in cases of social isolation. In this work, we studied how social isolation and hypertension affect the transcription activity of genes associated with glucocorticoid signaling in the rat brain. The study was performed on 10-month-old rats of the outbred Wistar stock (n = 48) and the inbred spontaneously hypertensive (SHR) strain (n = 28). The animals of each genotype were divided into groups, one of which was kept in home cages in groups of 3-4 individuals, and the other in single cages for 3 months. Physiological parameters and plasma corticosterone were controlled before the start and after 3 months of isolation. Each group was additionally divided into two subgroups: one subjected to 1 h of restraint stress, and changes in blood glucose and corticosterone levels were assessed. At the end, the levels of Nr3c1, Nr3c2, Hsd11b1, and Fkbp5 mRNAs were measured in the hippocampus and frontal cortex using the Q-PCR technique. After isolation, weight gain stopped in SHRs, although blood pressure did not change, and heart rate increased in rats of both genotypes. In response to restraint, there was practically no increase in corticosterone in isolated Wistar rats, whereas in SHRs, there were significant glucose and corticosterone responses. Significant disruptions in the system responsible for corticosterone-activated signaling cascades were found in the brains of SHR rats. The transcriptional activity of genes encoding corticosterone receptors and proteins regulating their action was reduced in the hippocampus and frontal cortex in SHRs compared to Wistar rats. However, neither isolation nor acute stress significantly affected the contents of transcripts studied. Meanwhile, after isolation, the relationships between the expression of these genes changed significantly, in different directions, in rats of the studied genotypes, both within and between brain structures. Thus, the SHR genotype is associated with persistent changes in the brain that affect the expression of glucocorticoid-associated genes. This indicates a more complex regulation of the stress response, not limited only by the feedback system within the hypothalamic-pituitary-adrenocortical or sympatho-adrenomedullary systems, but operated at the level of the limbic system and the cerebral cortex.

Hypertension is a serious disease characterized by a sustained or recurrent increase in blood pressure, which can lead to various complications. Here, we studied the effect of genetically determined arterial hypertension in rats on their adaptation to long-term isolation and subsequent response to acute restraint stress. Male SHR rats with spontaneous hypertension were maintained in individual cages for 14 weeks. The serum levels of corticosterone, glucose, and pro- and anti-inflammatory cytokines and salivary α-amylase activity were studied, and the expression of genes associated with the regulation of steroidogenesis in the adrenal glands was evaluated. There were no significant changes in the parameters of the hypothalamic–pituitary–adrenocortical and sympatho-adrenal systems after isolation. Nevertheless, the preliminary isolation significantly affected the response to moderate restraint stress, including the expression of the regulatory genes Fkbp5 and Star in the adrenal glands and the content of proinflammatory cytokines IL-1β and IL-6 in the blood, although the changes in these indices were relatively subtle. This may reflect the predisposition of animals in isolation to develop quite specific stress-related changes.

In our previous studies, we have found a suppressive effect of a single administration of pentylenetetrazole (PTZ) at a subconvulsive dose on cellular proliferation in the dentate gyrus. In the present work, we show that this decrease in proliferation develops after acute anxiogenic effect of PTZ and is present only in the posterior part of the hippocampus, where a decrease in the number of neuronal NO synthase expressing cells has been also found. These changes were also accompanied by a decrease in the level of nNOS protein in the hippocampus. Taken together, these observations may indicate the possible involvement of nNOS in the suppression of cellular proliferation in the dentate gyrus of the posterior hippocampus during the development of the anxiogenic effect of PTZ.

Aging is a complex process associated with multimorbidity. Hypertension, one of widespread states, is among main causes of age-related alterations in behavior, emotionality and sociability. We studied the effects of long-term isolated housing on anxiety, depressive-like and social behavior as well as changes in the adrenocortical and sympathetic systems in the aging normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Ten-month-old male rats of both strains were subjected to 90-day isolated or group housing. Surprisingly, social isolation induced only mild effect on anxiety without influencing other affective-related behaviors. No effects of isolated housing on sociability or social novelty preferences were revealed. Despite the adrenal gland hypertrophy in the SHRs, corticosterone levels remained stable within the period of isolation but the expression of nuclear glucocorticoid receptor (Nr3c1) mRNA in the adrenals was lower in the SHR as compared to WKY rats. Pre-existing hypertension, associated with SHR genotype, did not significantly contribute to the effects of social isolation. The data suggest that the aged WKY and SHR rats are relatively resilient to chronic social stress associated with isolated housing.

Simple, affordable, and reliable methods for assessing the maturation status of brain structures are vital for preclinical studies related to the effects of early-life stress. These methods make it possible to evaluate the effectiveness of specific therapies or the prevention of stress-related pathological changes. The morphology of astrocytes is one of the markers representing functional state of synapses and thus it is indicative of maturation state of neuronal networks. We performed the method for evaluating the morphological characteristics of astrocytes using epifluorescence microscopy and the ImageJ software. Application of the method to brain sections of rats on postnatal days 18 and 30 revealed the morphological changes in the astrocytes of the basolateral nucleus of the amygdala during normal ontogeny. The proposed method makes it possible to evaluate not only the density of the cell population, but also their morphological parameters associated with the degree of branching and the length of the astrocyte processes. The approach used revealed sexual dimorphism in the ontogeny: the length of the astrocytic processes increased during maturation from juvenile to pubertal period in the basolateral nucleus of the amygdala only in females but not in males.

Background/Objectives: Aging and chronic stress are regarded as the most important risk factors of cognitive decline. Aged spontaneously hypertensive rats (SHRs) represent a suitable model of age-related vascular brain diseases. The aim of this study was to explore the effects of chronic isolation stress in aging SHRs on their cognitive functions and response to acute stress, as well as the influence of the chronic oral intake of N-Pep-Zn, the Zn derivative of N-PEP-12. Methods: Nine-month-old SHRs were subjected to social isolation for 3 months (SHRiso group), and one group received N-pep-Zn orally (SHRisoP, 1.5 mg/100 g BW). SHRs housed in groups served as the control (SHRsoc). The behavioral study included the following tests: sucrose preference, open field, elevated plus maze, three-chamber sociability and social novelty and spatial learning and memory in a Barnes maze. Levels of corticosterone, glucose and proinflammatory cytokines in blood plasma as well as salivary amylase activity were measured. Restraint (60 min) was used to test acute stress response. Results: Isolation negatively affected the SHRs learning and memory in the Barnes maze, while the treatment of isolated rats with N-Pep-Zn improved their long-term memory and working memory impairments, making the SHRisoP comparable to the SHRsoc group. Acute stress induced a decrease in the relative thymus weight in the SHRiso group (but not SHRsoc), whereas treatment with N-Pep-Zn prevented thymus involution. N-pep-Zn mitigated the increment in blood cortisol and glucose levels induced by acute stress. Conclusions: N-pep-Zn enhanced the adaptive capabilities towards chronic (isolation) and acute (immobilization) stress in aged SHRs and prevented cognitive disturbances induced by chronic isolation, probably affecting the hypothalamo–pituitary–adrenal, sympathetic, and immune systems.

—Characteristics of small extracellular vesicles (sEVs) and sEVs composition are far from being well-studied for now, especially in the context of mental disorders. To elucidate the role of sEVs in disease we performed a quantitative analysis of the blood sEV in patients with focal epilepsy and patients with focal epilepsy with depression, psychogenic non-epileptic seizures with depression, pure depression, and bipolar affective disorder with the current depressive episode (cDE). Small EVs were isolated from the serum by gel filtration or PEG precipitation, and both methods showed very similar results. Subsequently, we precipitated neuronal sEVs and quantified it with several methods. Activity of lysosomal enzymes was determined in the sEVs fraction. The concentration of the blood sEVs in patients with depression, focal epilepsy, or depression with focal epilepsy was higher than in healthy controls. No difference was found between patients and controls in terms of neuronal sEVs concentration. Another finding of our study is that sEVs in the serum of patients contains various lysosomal enzymes. We suppose that the concentration of the blood sEVs in patients with depression or epilepsy is higher due to the sEVs secretion by the immune cells. Finding sEVs in the blood of patients with depression and focal epilepsy grants validity for future attempts to use sEVs as diagnostic tools for these disorders.

Brain aging is associated with a progressive decrease in learning abilities, memory, attention, decision making, and sensory perception. Age-related cognitive disturbances may be related to a decrease in the functional capacities of the hippocampus. This brain region is essential for learning and memory, and the lifelong neurogenesis occurring in the subgranular zone of the dentate gyrus may be a key event mediating the mnemonic functions of the hippocampus. In the present study, we investigated whether age-related changes in hippocampal neurogenesis are associated with learning and memory disturbances. Four- and 24-month-old rats were trained to find a hidden platform in a water maze. Though the older group showed higher latency to search the platform as compared to the younger group, both groups learned the task. However, the density of proliferating (PCNA-positive), differentiating (Dcx-positive), and new neurons (pre-labeled BrdU-positive) was significantly lower in the hippocampus of aged rats as compared to young ones. This inhibition of neurogenesis could be related to increased local production of nitric oxide since the density of neurons expressing neuronal NO-synthase was higher in the aged hippocampus. Thus, we can suggest that an age-related decrease in neurogenesis is not directly associated with place learning in aged rats.

Rodent models of deprivation of parental care are increasingly used to model depression-like disorders induced by early stress. The present study used a model of the consequences of mothers and offspring being kept in conditions of nesting material deficiency (NMD) for a prolonged period in early postnatal ontogeny in rats. The aim of this study was to determine whether the behavior of male rats exposed to stress due to being kept in conditions of NMD in the early postnatal period changes and whether any such changes are associated with impairments to the animals’ stress reactivity. Keeping of rats in conditions of NMD from postnatal day 2 to postnatal day 9 did not lead to any significant changes in measures of behavior pointing to anxiety and depressivity recorded in standard tests (open field test, elevated plus maze, sucrose solution preference) either in adolescence or adulthood. NMD in the early postnatal period produced an increase in social attachment (extent of socially oriented behavior manifest as the desire to spend more time in the presence of an unfamiliar individual in a novel context) in one-month-old but not adult animals. Keeping in conditions of NMD improved spatial learning but had no effect on long-term memory in adult rats on assessment of the ability of adults to learn to solve a spatial task in the Barnes maze. Changes in stress reactivity in animals (dynamics of release of corticosterone into the blood) were most marked in adult rats. Thus, NMD in the early postnatal period did not induce anxiety or depression-like behavior in male rats at ages 1 or 6 months but had transient effects on social attachment in young animals and altered stress reactivity on short-term exposure to a moderate stressor (restraint).

Recently, we have shown the differences in the early response of corticosterone and inflammatory cytokines in the hippocampus and frontal cortex (FC) of rats with middle cerebral artery occlusion (MCAO), according to the methods of Longa et al. (LM) and Koizumi et al. (KM) which were used as alternatives in preclinical studies to induce stroke in rodents. In the present study, corticosterone and proinflammatory cytokines were assessed 3 months after MCAO. The most relevant changes detected during the first days after MCAO became even more obvious after 3 months. In particular, the MCAO-KM (but not the MCAO-LM) group showed significant accumulation of corticosterone and IL1β in both the ipsilateral and contralateral hippocampus and FC. An accumulation of TNFα was detected in the ipsilateral hippocampus and FC in the MCAO-KM group. Thus, unlike the MCAO-LM, the MCAO-KM may predispose the hippocampus and FC of rats to long-lasting bilateral corticosterone-dependent distant neuroinflammatory damage. Unexpectedly, only the MCAO-LM rats demonstrated some memory deficit in a one-trial step-through passive avoidance test. The differences between the two MCAO models, particularly associated with the long-lasting increase in glucocorticoid and proinflammatory cytokine accumulation in the limbic structures in the MCAO-KM, should be considered in the planning of preclinical experiments, and the interpretation and translation of received results.

Olfactory bulbectomy in rodents is widely used as a model of the symptoms of clinical depression and neurodegeneration, including cholinergic. Male C57BL/6 mice in the present study underwent olfactory bulbectomy. Formation of long-term nonassociative memory (habituation) and spatial memory were studied two and four weeks after surgery. The effect of bulbectomy on the state of neurons in the medial septal area was studied using immunohistochemical staining for choline acetyltransferase and NeuN at the end of the behavioral studies, i.e., four and seven weeks after surgery. Bulbectomy led to impaired habituation in terms of measures of motor activity in the open field test and impaired spatial learning, but not memory in a water maze at both time points. A decrease in the proportion of cholinergic cells in the medial septal area was seen at four but not seven weeks after surgery. There were no significant changes in the total number of neurons in this part of the brain. Thus, the occurrence of cognitive impairment after olfactory bulbectomy may be associated with the manifestations of transient cholinergic deficit at the early stages of the development of pathology.

Differential effect of the neonatal proinflammatory stress (NPS) on the development of neuroinflammation in the hippocampus and induction of the depressive-like behavior in juvenile and adult male and female rats was studied. NPS induction by bacterial lipopolysaccharide in the neonatal period upregulated expression of the Il6 and Tnf mRNAs accompanied by the development of depressive-like behavior in the adult male rats. NPS increased expression of the mRNAs for fractalkine and its receptor in the ventral hippocampus of the juvenile male rats, but did not affect expression of mRNAs for the proinflammatory cytokines and soluble form of fractalkine. NPS downregulated expression of fractalkine mRNA in the dorsal hippocampus of juvenile males. No significant effects of NPS were found in the female rats. Therefore, the NPS induces long-term changes in the expression of neuroinflammation-associated genes in different regions of the hippocampus, which ultimately leads to the induction of neuroinflammation and development of depressive-like behavior in male rats.

Neonatal proinflammatory challenge (NPC) may contribute to the development of psychiatric disorders in adults. A double exposure of neonatal rats to lipopolysaccharide, a component of cellular wall of gram-negative bacteria, on postnatal days 3 and 5 provokes the development of depressive- and anxiety-like behaviors. NPC impairs neuroplasticity and cognition in adult animals, significant modifications of neuroplasticity being evident even in adolescence. We studied effects of NPC on microglia and GABAergic neuronal population of the dorsal hippocampus in juvenile male and female rats using immunofluorescent histochemistry. The expression of glutamic acid decarboxylase-67 (GAD67) and calcium-binding proteins calretinin, calbindin, and parvalbumin were used as quantitative markers of GABAergic interneurons and their specific subpopulations, respectively. NPC induced changes of microglial morphology indicating inflammatory activation mostly expressed in CA3 field; the effect was similar in males and females. The number of GAD67 expressing neurons was similar in the dorsal hippocampus of females and males independently on the NPC. The portion of calbindin-immunoreactive GAD67-positive neurons significantly increased while the portion of calretinin-immunoreactive GAD67-positive neurons significantly decreased in the CA1 field of rats exposed to NPC independently on their sex. NPC did not affect the parvalbumin-positive subpopulation of GABAergic neurons in the hippocampus of rats of either sex. These data suggest that NPC-induced modification of GABAergic neuronal population composition under the proinflammatory conditions is involved in the maintenance of excitation/inhibition homeostatic balance in the hippocampus.