Level of Cytokines and C3 Complement in the Blood of Rats under Conditions of Chronic Unpredictable Stress of Different Durations.

The parameters of the cytokine profile and functional activity of the complement system in the blood of rats were studied during different time periods of chronic unpredictable mild stress using a model of sequentially alternating low-intensity stress effects for 1, 2, 3, and 4 weeks. In the dynamics of observation, a general tendency towards multidirectional fluctuations in the concentration of cytokines was revealed: an increase in IL-10, but a decrease in IL-4 in comparison with the control. Statistically significant changes in the level of IL-10 were noted after 2, 3, and 4 weeks, IL-4 - after 2 and 4 weeks of stress loads. The percentage of lysis of the C3 component in rats gradually increased by the 2nd week of chronic stress, but then decreased and practically did not differ from the control values (intact animals) by the end of the study. These results illustrate the specificity of changes in the indicators of the C component of the complement system and the cytokine profile of the blood reflecting activity of the cellular and humoral components of the immune response in rats exposed to repeated stress factors of different origins and duration.

Age and Sex Characteristics of the Blood Cytokine Profile in Rats Subjected to Prenatal Stress.

Parameters of blood cytokine profile in male and female rats subjected to prenatal stress on the model of swimming in cold water (10°C, 5 min, days 10-16 of gestation) were studied. Prenatal stress had no significant effects on the blood levels of IL-6 and IL-10 cytokines. The blood concentration of proinflammatory cytokine TNFα in 60-day-old rats was higher than in age-matched controls. Stress led to a lower level of anti-inflammatory IL-4 in the blood of 30-day-old males compared to controls. In female rats subjected to prenatal stress, the concentration of IL-4 decreased on day 21, but increased by day 60 of postnatal ontogeny. Specific effects of prenatal stress on the blood cytokine profile in male and female animals at different periods of ontogeny were revealed. Different and even opposite changes in blood cytokine levels could be largely mediated by sex- and age-specific features of immune functions after prenatal stress.

Behavior of In Utero Stressed Rats in the Elevated Plus Maze Test during Different Periods of Postnatal Ontogeny.

We studied the effect of prenatal stress (dams were forced to swim in cold water (10°C; 5 min) from day 10 to 16 of gestation) on the behavioral parameters of the offspring in an elevated plus maze on days 21, 30, and 60 of life (suckling, infantile, and juvenile ages, respectively). Females at the suckling age demonstrated suppressed orientation and exploratory activity and increased anxiety, which returned to normal by the infantile and juvenile periods. Prenatally stressed males in juvenile age were characterized by reduced anxiety (assessed by the time spent in the closed and open arms of the plus maze). Thus, the effect of prenatal stress on the behavioral parameters manifested differently depending on the sex and stage of postnatal ontogeny. The modulatory effects of prenatal stress on the analyzed behavioral parameters were more pronounced in females at early stages of postnatal ontogeny (suckling and infantile ages).

Effect of Repeated Stress Exposures on the Blood Cytokine Profile in Rats with Different Behavioral Parameters.

Changes in the blood cytokine profile were studied in rats with different behavioral patterns in the open-field test during chronic stress on the model of daily 4-h immobilization over 8 days. The level of proinflammatory cytokines IL-1α and IFNγ in behaviorally active and passive animals changed insignificantly under these experimental conditions. Repeated stress exposures were accompanied by a progressive decrease in the plasma level of IL-2 and IL-5 in passive rats; these changes were most pronounced on day 8 of the study. Active animals were characterized by a tendency toward reduction of IL-2 content, but significant decrease in IL-5 concentration on days 3 and 8 of restraint stress. Blood levels of IL-1ß and IL-6 in rats remained practically unchanged after single immobilization, but progressively increased during further stress exposures and reached maximum on day 8 of stress. The content of the anti-inflammatory cytokine IL-4 in rats was constant, but blood concentration of IL-10 increased during repeated stress exposures. These changes were most pronounced on day 8 in passive animals and on days 3 and 8 of restraint stress in active animals. These data indicate that the direction of variations in the blood cytokine profile of rats under conditions of chronic stress depends on the baseline parameters of behavior and frequency of stress exposures.

Lymphocyte Index of Peripheral Blood in Rats at Different Stages of the Post-Stress Period under Conditions of Antigenic Exposure and Injection of Lipopolysaccharide.

Changes in the Shaganin lymphocyte index (ratio of the number of lymphocytes to segmented neutrophils) in the peripheral blood of rats after intraperitoneal administration of LPS (100 µg/kg) at the end of a single stress exposure in a model of 24-h restraint stress were studied. The lymphocyte index was analyzed 3 h later, on the 1st and 8th days after the stress load. Immobilization was accompanied by a decrease in this parameter 3 h after exposure. One day after the stress load, an increase in the lymphocyte index was noted, which remained on the 8th day of observation. LPS injection did not affect the changes in this parameter caused by 24-h immobilization on the 1st and 8th days of the study, but prevented a pronounced increase in the lymphocyte index on the 1st day after the stress load. The data obtained expand the existing scientific understanding of the specificity of the involvement of immunomodulatory substances in the implementation of adaptive-compensatory processes in mammals under conditions of emotional stress.

Correlation of Physiological Parameters in Rats after Stress Exposure under Conditions of Antigenic Stimulation with Lipopolysaccharide Administration.

We studied correlation dependences between physiological parameters in rats in 3 h, 1 day, and 8 days after administration of LPS (100 µg/kg) at the end of 24-h immobilization stress. In 3 h after LPS administration against the background of stress exposure, significant correlations of metabolic parameters with the relative weight of the adrenal glands and the perceptual component of nociception in rats were revealed. A direct relationship between the concentration of the proinflammatory cytokine TNFα and anti-inflammatory IL-4 was also found in these animals. On the first day after LPS injection, correlations were revealed, predominantly positive, only between the indicators of the cytokine blood profile. In the late post-stress period after antigenic exposure, no correlations between the studied physiological parameters were found. It can be hypothesized that immune modulation through systemic administration of LPS prevents persistent excessive stress of physiological functions at the later stages after stress exposure.

Spike Activity in the Ventromedial Nucleus of Rat Hypothalamus during Aging.

Spike activity of neurons in the ventromedial nucleus (VMN) of the hypothalamus in adult (6-8 months) and aged (2 years) male rats was studied by the in vivo extracellular method using stereotaxic insertion of microelectrodes. In all animals, firing frequency of most VMN neurons increased in response to glucose administration. However, in aged rats, the mean baseline and glucose-induced spike frequencies of VMN neurons were lower than in adult animals. These results support the hypothesis that aging is associated with a decrease in the functional activity of hypothalamic neurons.

Blood Cytokine Concentration in Rats during Antigenic Treatment after a Single Long-Term Stress Exposure.

We studied changes in the blood cytokine profile of rats 3 h, 1 day, and 8 days after acute stress on the model of 24-h immobilization followed by LPS administration (100 µg/kg intraperitoneally). The concentration of proinflammatory cytokines (particularly of IL-1ß and TNFα) significantly decreased at the early stage after stress exposure and physiological saline injection, but increased in the follow-up period and practically did not differ or even surpassed the control level by the end of observations. Under these conditions, the blood content of anti-inflammatory cytokine IL-10 increased most significantly on day 1 of the post-stress period. Restraint stress followed by LPS administration was accompanied by a decrease in the level of proinflammatory cytokines at the early (IFNγ and TNFα) and late stages (IL-1ß) of the experiment. Directed modulation of the immune status in animals after acute stress was followed by a significant increase in the content of IL-10 on days 1 and 8, as well as by a tendency toward elevation of IL-4 concentration by the end of the study. The directionality and degree of changes in the cytokine profile of mammalian tissues depend on the type of extreme exposure, duration of the post-stress period, and specific effects of exogenous pathogenic factors in the whole body.

State of Stress-Marker Organs in Rats after a Single Exposure to Long-Term Stress and Treatment with Lipopolysaccharide.

We studied the effect of LPS on the state of stress-marker organs in rats at various periods after a single exposure to long-term stress on the model of 24-h immobilization. The animals were intraperitoneally injected with LPS in a dose of 100 µg/kg immediately after the negative emotiogenic exposure. Changes in physiological parameters were evaluated 3 h, 1 day, and 8 days after immune stimulation. Acute stress was accompanied by a decrease in the weight of the thymus during all stages of the post-stress period. An increase in the relative weight of theadrenal glands in animals under these conditions was observed only on day 8 after restraint stress. The induction of immune reactions due to systemic treatment with LPS was shown to prevent involution of the spleen in the late stage after a single exposure to long-term stress (day 8). Hypertrophy of the adrenal glands, which serves as one of the typical reactions of mammals to negative emotiogenic factors, was not revealed during the post-stress period after antigenic stimulation. These data hold much promise for the development of new approaches to the use of immunoactive substances to prevent or reduce the severity of physiological changes after emotiogenic loads.

Blood Cytokine Profile in Rats with Different Behavioral Characteristics after Metabolic Stress.

Changes in the blood cytokine profile in rats with various parameters of behavior were studied under conditions of 5-day starvation not followed by the recovery period or with subsequent normalization of food intake. Metabolic stress had no effect on the content of most cytokines. The concentration of pro- and anti-inflammatory cytokines in blood plasma of rats was shown to increase significantly by the end of a 5-day recovery period after food deprivation. These changes in behaviorally passive specimens were more pronounced than in active animals. Therefore, differences in the strain of immune reactions in mammals with different prognostic resistance to extreme factors are most pronounced during the post-stress period. These data illustrate the necessity of an individual approach to studying the systemic organization of physiological functions under normal and pathological conditions.

Dynamics of Metabolic Parameters in Rats during Repeated Exposure to Modulated Low-Intensity UHF Radiation.

Metabolic parameters in rats were studied at various stages of repeated exposure to modulated low-intensity UHF radiation. The volume of O2 consumption and level of heat release were reduced by day 4 of intermittent irradiation and remained low over the next 2 days in the absence of a source for electromagnetic radiation. The amount of expired CO2 slightly increased over the first 3 sessions of irradiation, but significantly decreased in the recovery period on days 5 and 6. Changes in metabolic parameters were most significant on day 7 of the study. It was manifested in the decrease of O2 consumption, CO2 release, and intensity of heat exchange not only during irradiation, but also in the inter-exposure period. Electromagnetic radiation can induce a change of metabolic processes in mammals, which is most pronounced during repeated irradiation and persists even under physiological resting conditions.

Blood Cytokine Profile in Rats with Various Behavioral Characteristics after a Single Exposure to Long-Term Stress.

Changes in the blood cytokine profile of rats with different behavioral activity were evaluated in various periods after stress exposure on the model of 24-h immobilization. Behaviorally active animals exhibited only a tendency to a change in the concentration of study cytokines in the dynamics after experimental stress. Stress exposure in passive specimens was accompanied by a decrease in the content of pro- and anti-inflammatory cytokines. These changes were most pronounced at the early stages of the post-stress period and persisted until the end of observations. After a single exposure to long-term immobilization, cytokine level in the peripheral blood of behaviorally passive animals was much lower than in active rats. Variations in immune indexes of mammals depend on the initial parameters of their behavior and duration of the post-stress period. Differences in the blood cytokine profile during negative emotiogenic exposures in passive and active rats are probably related to the specifics of immune reactivity in specimens with various sensitivities to stress.

State of Stress-Marker Organs in Rats with Various Behavioral Characteristics during Repeated Stress Exposures.

Changes in the relative weight of stress-marker organs in rats with various behavioral patterns in the open-field test were studied after repeated stress exposures on the model of daily 4-h immobilization over 8 days. Involution of the thymus and spleen in behaviorally passive specimens was found after single stress, as well as under conditions of 3- and 8-fold immobilizations. The weight of these organs in active animals remained practically unchanged after acute stress, but decreased on day 3 and particularly on day 8 of repeated stress exposures. As differentiated from passive rats (open-field test), behaviorally active specimens were characterized by hypertrophy of the adrenal glands after single and 3-fold stress procedures. Our results complement the data on individual features of the peripheral and central mechanisms for the stress response in mammals. These data illustrate the importance of individual approach to studying systemic organization of physiological functions under normal conditions and during negative emotiogenic exposures.

Nociceptive Reactions in Rats during Repeated Stress Exposure.

Changes in nociceptive sensitivity of rats with various behavioral patterns in the open-field test were studied after repeated stress exposure on the model of daily 4-h immobilization for 8 days. The tail-flick latency in response to light-heat stimulation in passive and active specimens decreased most significantly on days 2 and 7, respectively. However, this parameter did not differ from the baseline on day 8 of observations. Vocalization threshold during electrocutaneous stimulation in behaviorally active animals did not change over the first 7 days of repeated stress exposure, but increased significantly on day 8 of the study. The emotional component of nociception in passive animals increased on day 3, but decreased on days 4 and 6 of the experiment. Therefore, repeated stress exposure in rats is mainly accompanied by an increase in the perceptual component of nociception. Variations in the emotional component of nociceptive sensitivity after stress loads are manifested in the initial increase and subsequent decrease in this parameter. The observed changes are more pronounced in behaviorally passive rats than in active animals. These data illustrate the specifics of stress-induced changes in nociception of specimens with various individual and typological characteristics. Our results hold much promise for the development of new individual approaches to modulation of pain sensitivity in humans under conditions of negative emotiogenic exposures.

Correlation dependencies between nociceptive sensitivity and cytokine level in biological fluids of rats after administration of lipopolysaccharide.

Correlation dependencies between nociceptive sensitivity and cytokine level in biological tissues of rats were studied on days 1 and 7 after antigenic stimulation due to intraperitoneal injection of LPS (30 µg/kg). No correlations were found between the nociceptive thresholds and cytokine contents in the dorsal hippocampus and anterior cingulate cortex of animals. Inverse correlations between the tail-flick latency in response to nociceptive stimulation and concentrations of an anti-inflammatory cytokine IL-10 and pro-inflammatory cytokine TNF-α in the peripheral blood of rats were revealed on day 7 after LPS injection. These animals were characterized by the following inverse correlations between the blood level of proinflammatory cytokines and baseline parameters of nociceptive sensitivity: IL-4 and latency of the tail-flick response; and IL-10 and vocalization threshold. The appearance of significant correlations between immune and nociceptive parameters in rats was shown to coincide with pronounced changes in the perceptual and emotional components of nociception in animals during antigenic stimulation. The formation of close interrelations between nociceptive sensitivity and immune processes in this period probably contributes to the systemic response to antigenic stimulation. Our results complement previous data on the relationship between individual immune reactivity and type of nociceptive reactions in mammals.

Dynamics of changes in nociceptive reactions of rats after peripheral administration of lipopolysaccharide.

The type of changes in nociceptive reactions of rats was studied at various time intervals after intraperitoneal injection of LPS in a dose of 30 µg/kg. The perceptual component of nociception in animals was evaluated from the tail-flick latency in response to light-heat stimulation. The emotional component of nociception in rats was determined from the vocalization threshold during electrocutaneous stimulation of the tail. The tail-flick latency of animals under conditions of light-heat stimulation was shown to decrease 1 day after peripheral administration of LPS, which illustrates an increase in the perceptual component of nociception at the relatively early stage of antigenic stimulation. A significant decrease in the tail-flick latency and vocalization threshold in rats in response to nociceptive stimulation was observed on day 7 after LPS injection. These changes demonstrate an increase in the perceptual and emotional components of nociception at the late period after antigen exposure. Our results indicate that antigenic stimulation due to peripheral administration of LPS is followed by the increase in nociceptive sensitivity of rats. LPS-induced variations in the emotional and perceptual components of nociception in animals suggest the existence of specific mechanisms for systemic regulation of pain. They probably depend on the period of study and type of immune reactions during antigenic stimulation.

Cytokine levels in rat blood and brain structures after administration of lipopolysaccharide.

We compared cytokine profile of rat serum and brain structures after immune status modulation by LPS (30 µg/kg intraperitoneally). The content of inflammatory (IL-1α, IL-1ß, IL-2, IL-6, IFN-γ, and TNF-α) and anti-inflammatory (IL-4 and IL-10) cytokines in biological samples of animals was measured on days 1 and 7 after antigenic stimulation. LPS administration reduced the levels of both inflammatory and anti-inflammatory cytokines in the peripheral blood of the rats, especially on the 1st day. LPS administration was also accompanied by specific changes in cytokine content in the dorsal hippocampus and anterior cingulate cortex. Antigenic stimulation increased the level of anti-inflammatory cytokines IL-4 and IL-10 in the examined brain tissues, the changes were most pronounced on day 1 after LPS injection. No significant changes in the levels of proinflammatory cytokines in the brain tissue of animals were found at the above terms after LPS injection. Thus, peripheral LPS administration to rats shifts the balance between the inflammatory and anti-inflammatory cytokines in the CNS structures towards the latter.

Nociceptive thresholds in rats in response to lipopolysaccharide injection into the specific nuclei of the thalamus of the brain.

Microinjections of LPS into the specific nuclei of rat thalamus (ventrobasal thalamic nuclei VPL and VPM) slightly increased perceptual component and significantly decreased emotional component of systemic nociceptive response.

Nociceptive sensitivity and lymphocytic index of peripheral blood in rats with different behavioral activity in model of inflammatory pain provoked by injection of freund's complete adjuvant and bovine serum albumin.

Nociceptive thresholds decreased in rats at the early stage of inflammatory reaction induced by subcutaneous injection of BSA and complete Freund's adjuvant. At the later stage of this reaction, there was a trend of restoring nociceptive parameters in behaviorally passive rats in contrast to active animals, which demonstrated further decrease in the nociceptive thresholds. During the late inflammatory period, the lymphocytic index (by Shaganin) changed unidirectionally in the rats with different behavioral parameters. Probably, the changes in nociceptive thresholds were not triggered by the shift in lymphocyte/segmented neutrophil ratio, but resulted from production of yet not established biologically active agents with proalgesic and analgesic nature.

Nociceptive thresholds of the response to lipopolysaccharide injection into the limbic structures of the brain in rats.

Microinjections of LPS into the limbic structures of rat brain (dorsal hippocampus and caudal compartment of the cingulate fascicle) caused opposite effects on the nociceptive thresholds: injection into the dorsal hippocampus enhanced perception and reduced the emotional affective perception of pain, while injection into the cingulate fascicle reduced the perceptual and enhanced the emotional components of the nociceptive reaction. These results indicated specific involvement of these limbic structures in nociception modulation during induction of the immune response in CNS.