Brain self-stimulation and immunity: effect on humoral and cell-mediated immune responses

Intracranial self-stimulation-reward or immobilization-aversion had different effects on neurite extension and the ERK pathway in neurotransmitter-sensitive mutant PC12 cells

Various actions trigger pleasure (reward) or aversion (punishment) as emotional responses. Emotional factors that negatively affect brain neural control processes for long periods of time might cause various mental diseases by inducing neuronal changes. In the present study, newly developed PC12m12 cells which are　highly sensitivity to neurotransmitters such as acetylcholine (ACh), were used. Exposing the cells to plasma from rats that had been subjected to intracranial self-stimulation (ICSS) markedly upregulated neurite outgrowth. In addition, voluntary running in a wheel or forced on a rotating rod was used to induce behavioral excitation in rats, and examinations of their plasma confirmed that the ICSS-induced neurite outgrowth was not associated with the ICSS behavior itself. Furthermore, immunoblotting and treatment with U0126, an ERK (extracellular signal-regulated kinase) antagonist, showed that the ICSS-induced neurite outgrowth was related to neuronal ERK activity. Exposing the same cells to plasma from rats that had been subjected to immobilization (IMM) also increased neurite outgrowth. Although the degree of enhancement was not as great as that seen after the ICSS rat plasma treatment, it was less than that observed after treatment with ACh as a positive control. These results indicate that ICSS or IMM lead to varying degrees of morphological changes, such as enhanced neurite outgrowth, in PC12m12 cells, but the neuronal signal transduction pathways underlying these effects differ; i.e.,the former morphological change might involve the activation of the ERK pathway, whereas the latter changes might not. Using PC12m12 cells which exhibit sensitivity to neurotransmitters, it might be possible to clarify the pathogeneses of mental diseases at the neuronal level and search for therapeutic drugs.

Development and Characterization of an Allergic Asthma Rat Model for Interventional Studies

Allergic asthma is one of the most common chronic diseases of the airways, however it still remains underdiagnosed and hence undertreated. Therefore, an allergic asthma rat model would be useful to be applied in future therapeutic strategy studies. The aim of the present study was to develop an objective model of allergic asthma in atopic rats that allows the induction and quantification of anaphylactic shock with quantitative variables. Female Brown Norway rats were intraperitoneally sensitized with ovalbumin (OVA), alum and Bordetella pertussis toxin and boosted a week later with OVA in alum. At day 28, all rats received an intranasal challenge with OVA. Anaphylactic response was accurately assessed by changes in motor activity and body temperature. Leukotriene concentration was determined in the bronchoalveolar lavage fluid (BALF), and total and IgE anti-OVA antibodies were quantified in blood and BALF samples. The asthmatic animals' motility and body temperature were reduced after the shock for at least 20 h. The asthmatic animals developed anti-OVA IgE antibodies both in BALF and in serum. These results show an effective and relatively rapid model of allergic asthma in female Brown Norway rats that allows the quantification of the anaphylactic response.

Suppression of natural killer cell cytotoxicity following chronic electrical stimulation of the ventromedial hypothalamic nucleus in rats

In our previous study we found that chronic electrical stimulation of the lateral hypothalamus (LH) enhances and its lesion suppresses natural killer cell cytotoxicity (NKCC) and a large granular lymphocyte (LGL) number in conscious, freely behaving rats. Since the ventromedial nucleus of the hypothalamus (VMH) is regarded as behaviorally and physiologically opposite to LH, in our present study we investigated whether this antagonism also holds for the immune functions. Chronic electrical VMH stimulation effect on 1) immune parameters: both spleen and blood NKCC (chromium release assay and single-cell agarose assay) and the number of large granular lymphocytes (LGL; a morphological method), and 2) endocrine parameters: immunosuppressive-corticosterone (COR) and testosterone (TST) and immunostimulative-growth hormone (GH) and prolactin (PRL) plasma levels (RIA) was assessed. Twenty-one days of electrical stimulation of VMH caused significant decrease in both spleen and blood NKCC at the population level (chromium release assay) but not at the single cell level (agarose assay) with a simultaneous fall in the LGL number. Rats responding to the VMH stimulation with behavioral inactivation (BIN) showed a significantly lower depression of NKCC and LGL number than those responding with an aversive reaction (AVE). Depression of NKCC coexisted with various hormonal changes: increase of PRL, increase (AVE) or fall (BIN) of COR, decrease of GH (BIN), and increase of TST (VMH-stimulated and VMH-sham). There were significant differences in all measured plasma hormones between BIN and AVE groups. The results obtained indicate that VMH decreases cell-mediated immune response, represented by NK cell activity. The immunosuppressive effect is dependent on the behavioral outcome of VMH stimulation (BIN/AVE) rather than tested endocrine variables. Moreover, the present results indicate that the VMH and LH are antagonistically engaged in the regulation of NK cell cytotoxicity.

Regional changes of brain serotonin and its metabolite 5-hydroxyindolacetic Acid and development of immunosuppression in submissive mice

The production of submissive behavior in C57BL/6J mice during 10 or 20 days of social confrontations resulted in increases in serotonin (5-HT) content in the amygdala, hippocampus, nucleus caudatus, Al1, A10, A9, and hypothalamus. The level of 5-hydroxyindolacetic acid (5-HIAA) was higher in most structures after 20 daily encounters compared to animals tested for 10 days. The ratio 5-HIAA/5-HT was increased in the nucleus raphe, accumbens, A9, and hypothalamus in mice displaying submission during 10 and 20 confrontations. The experience of defeats during 10 days accompanied with 5-HT system activation in a number of brain structures (nucleus raphe, accumbens, and A9) produced immunosuppression. With increasing number of confrontations the ratio 5-HIAA/5-HT was decreased in the same structures and a tendency to the immune response elevation appeared.

Chronic electric stimulation of the midbrain ventral tegmental area increases spleen but not blood natural killer cell cytotoxicity in rats

Previously we found that in conscious, freely behaving rats chronic electric stimulation of the lateral hypothalamus (LH) caused significant augmentation of natural killer cell cytotoxicity (NKCC) and a large granular lymphocyte (LGL) number more pronounced in the spleen than in the peripheral blood. The LH belongs to the so-called "brain reward system", a collection of the central structures whose activation produce positive emotions. The midbrain ventral tegmental area (VTA) is another prominent reward-relevant structure. In the present work, chronic electric stimulation of VTA (constant current 0.1 ms duration cathodal pulses delivered at frequency 50 Hz during 60 min daily session for 14 consecutive days) caused in rats an increase in the spleen but not in the peripheral blood NKCC (chromium release assay) without simultaneous effect on the number of large granular lymphocytes (LGL) (morphological method) and plasma level of prolactin (PRL), growth hormone (GH), corticosterone (COR), and testosterone (TST). This effect was anatomically specific as no influence of analogous thalamic stimulation on immune and endocrine response was found. The results obtained indicate that both reward-related areas VTA and LH enhance the cell-mediated immune response, represented by natural killer cytotoxicity, especially in the spleen. However, the effect pronounced by VTA is weaker than that of LH, possibly due to additional connections of LH with the hormonal and/or autonomic control systems.

The effects of lateral hypothalamic lesions on peripheral blood natural killer cell cytotoxicity in rats hyper- and hyporesponsive to novelty

Individual variability in the central control of the cellular immune responses is the main subject of the study. Previously, it was found that destruction of the lateral hypothalamus (LH) produced long-term depression of the cytotoxicity of NK cells (NKCC) and their number (LGL). In the present experiment we compared changes in the peripheral blood NKCC, LGL number, as well as leukocyte and lymphocyte number, their mitogenic activity and plasma corticosterone level evoked by electrolytic LH lesions in rats which were categorized as either high (HR) and low (LR) responders according to their locomotor response to a new environment. It was found that: (1) before the lesion NKCC (measured by 51Cr release assay) was higher in the HRs than in LRs; (2) LH damage caused a drop in NKCC and LGL number (21st postlesion day) preceded by a transient enhancement (5th postlesion day) significant for HRs only. As a result of a greater decrease in the HRs than LRs the baseline differences between groups disappeared by 21st postlesion day; (3) NKCC and LGL depression was not accompanied by changes in lytic activity of a single NK cell (agarose assay) which indicates that NKCC decrease concerned the population level and was dependent on LGL redistribution and/or recycling rate; (4) on the 21st postlesion day there was a significant leuko- and lymphopenia in the lesioned groups both HRs and LRs; (5) proliferative lymphocyte response to PWM (colorimetric assay) and plasma corticosterone level were not affected either by the motility level or by the lesion. The results emphasize the importance of individual differences in behavioral reactivity for NKCC regulation and a possible involvement of LH in the mechanism which connects high locomotor activity with stimulation of NKCC.

Chronic electrical stimulation of the lateral hypothalamus increases natural killer cell cytotoxicity in rats

Previously, we found that in rats coagulation of the lateral hypothalamus (LH) caused depression of the peripheral blood natural killer cell cytotoxicity (NKCC) and the number of large granular lymphocytes (LGL). In the present work, we have tested the effects on both spleen and blood NKCC of acute (1 day) and chronic (21 days) electrical stimulation of LH, and LGL number in conscious, freely behaving animals. Five groups of male Wistar rats were used: LH stimulated (n=22), thalamic (Thal) stimulated control (n=4), operated but non-stimulated LH sham controls (n=7), non-operated normal control group (n=8) and spleen baseline group (n=10). Chronic stimulation of LH caused significant augmentation of NKCC (51Cr-release assay) and LGL number (a morphological method), more pronounced in the spleen than in the peripheral blood. Rats responding to LH stimulation with feeding showed a slightly greater effect than those responding with a locomotor reaction. The observed effects were anatomically specific as no influence of Thal stimulation or the sham procedure was found. The results are discussed in terms of the involvement of LH in reward phenomena and the hormonal control of the immune system.

Nature of the distribution of serotonin and a serotonin metabolite in brain structures and the development of immunosuppression in submissive mice

Studies of C57BL/6J mice with acquired submissive behavior in a sensory contact model demonstrated increases in serotonin (5-HT) levels in the amygdaloid complex, hippocampus, the dopaminergic nuclei A11, A10, and A9, and in the caudate nucleus and hypothalamus, compared with controls, after 10 and 20 days of confrontations. Levels of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) in most structures were significantly higher after 20 days of confrontations than after 10 days. Increases in the 5-HIAA/5-HT ratio in the cervical nuclei of the midbrain, nucleus accumbens, A9, and hypothalamus as compared with controls were seen in mice with 10 and 20 days of confrontations. Immunization of mice on days 10 and 20 of confrontations showed suppression of immune responses as compared with controls, while immune measures reached control values by 40 days of experience of defeat. Thus, experience of 10 days of defeat led to immunosuppression on a background of activation of the 5-HT system in a series of brain structures: the cervical nuclei of the midbrain, the nucleus accumbens, and A9. As confrontations continued, there were decreases in the 5-HIAA/5-HT ratio on these structures, along with a tendency for immune responses to increase.

Involvement of brain dopaminergic structures in neuroimmunomodulation

Bilateral electrolytic destruction of the brain areas containing dopamine (DA) cell bodies (nuclei A9 and A10) as well as terminal regions of the nigrostriatal and mesolimbic DAergic systems (nuclei caudatus and accumbens) resulted in a considerable decrease in the intensity of the immune response in rats immunized with sheep red blood cells (SRBC). Administration of SRBC (5 x 10(8) i.p.) to rats produced a marked rise in activity of central DAergic system at early stage of the immune response formation. The most pronounced elevation in the concentration of DA and its metabolites, measured by the method of high performance liquid chromatography with electrochemical detection, was observed in the terminal regions of the nigrostriatal and mesolimbic DAergic systems (nuclei caudatus and accumbens), hypothalamus, hippocampus, amygdala within 20 min following antigen inoculation. By 60 min after immunization DA metabolism has been retained at a high level in all brain regions examined. The concentration of DA returned to control level in the amygdala and hypothalamus 24 hours after antigen administration and had a tendency to reach control values in the rest of the structures. The present results indicate that nigrostriatal and mesolimbic DAergic systems and DAergic structures of the hypothalamus are involved in the mechanisms of neuroimmunomodulation.

Behavioral and immunological events induced by electrical stimulation of the rat midbrain periaqueductal gray region

We report here on the immunological and behavioral alterations induced by stimulation of the mesencephalic periaqueductal gray matter (PAG), a component of the brain aversive system. Male Wistar rats were implanted with stimulating electrodes in the caudal dorsolateral part of the PAG. After recovery, animals were screened for aversive behavior, characterized by running, jumping, vocalization or freezing reaction. Then, rats were subdivided to those which could control aversive stimulation (AS) by switch-off response (cAS group) and those which could not interrupt AS (uAS group). After sensitization with bovine serum albumin (BSA) in complete Freund's adjuvant, rats were stimulated 3 times/week for 40 days, each session lasting 30 min/rat. Immunological assessment included antibody production and hypersensitivity skin reactions to BSA 14 and 21 days after immunization. A behavioral profile of aversively stimulated animals was determined by a poststartle response, open field (OF) activity and two-way shuttle-box avoidance task. The results revealed elevated antibody production to BSA in cAS and lowered in uAS rats, compared to sham-stimulated and intact controls. Arthus and delayed hypersensitivity skin reactions increased in PAG-stimulated animals on day 14 but not on day 21 after immunization. Poststartle response was enhanced both in cAS and uAS rats. Along with immunopotentiation, administration of cAS produced hyperactivity in OF test and facilitation of the active avoidance learning, whereas uAS caused only moderate suppression of rearing in a novel OF environment. Physiological implications and possible mechanisms that may account for PAG-mediated immunobehavioral changes are outlined.