Neuroimmunomodulation: potentiation of delayed hypersensitivity and antibody production by chronic electrical stimulation of the rat brain

Importance of immunological and inflammatory processes in the pathogenesis and therapy of Alzheimer's disease

The contribution of autoimmune processes or inflammatory components in the etiology and pathogenesis of Alzheimer's disease (AD) has been suspected for many years. The presence of antigen-presenting, HLA-DR-positive and other immunoregulatory cells, components of complement, inflammatory cytokines and acute phase reactants have been established in tissue of AD neuropathology. Although these data do not confirm the immune response as a primary cause of AD, they indicate involvement of immune processes at least as a secondary or tertiary reaction to the preexisting pathogen and point out its driving-force role in AD pathogenesis. These processes may contribute to systemic immune response. Thus, experimental and clinical studies indicate impairments in both humoral and cellular immunity in an animal model of AD as well as in AD patients. On the other hand, anti-inflammatory drugs applied for the treatment of some chronic inflammatory diseases have been shown to reduce risk of AD in these patients. Therefore, it seems that anti-inflammatory drugs and other substances which can control the activity of immunocompetent cells and the level of endogenous immune response can be valuable in the treatment of AD patients.

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.

Neuropeptides in the immunomodulation: substance P-induced stimulation of immune response in mice

The effects of substance P (SP) and its new structural analog EC-1 administered systemically to CBA mice on the immune responsiveness have been examined. Three main findings are presented in this study. First, the principal effect of SP and EC-1 on the immunity is a stimulatory one. It is shown that in the doses of 1, 10 and 100 mkg/kg of the body weight both neuropeptides significantly increased the number of plaque- and rosette-forming cells in the spleen of animals at the peak of the immune reactions. Second, the destruction of the pituitary stalk prevented the immune response stimulation caused by neuropeptides. Third, SP-induced immunostimulation was not observed after combination with the antagonist of the postsynaptic dopamine (DA) D-2 receptors haloperidol (2 mg/kg) suggesting the involvement of the DAergic system in the realization of this effect. Thus, these results demonstrate neurochemical DAergic mechanisms underlying the immunostimulating influence of tachykinins.

Humoral and cell-mediated immune responses following lesions of the nucleus basalis magnocellularis in the rat

The present study was undertaken to elucidate whether electrolytic lesions of nucleus basalis magnocellularis--NBM (an animal model of Alzheimer's disease--AD) may influence humoral and cellular immune responses in adult male Wistar rats. For this purpose intact control (IC), sham-operated (SO) and NBM-lesioned rats were divided into two main groups: (1) rats immunized with sheep red blood cells (SRBC) for plaque-forming cell (PFC) response and anti-SRBC agglutinins, and (2) rats immunized with bovine serum albumin in complete Freund's adjuvant (BSA-CFA) for anti-BSA antibody production, Arthus and delayed hypersensitivity skin reaction to BSA. PFC responses and anti-SRBC agglutinins as well as diameter and expression of edema/induration of Arthus/delayed skin reaction and titer of anti-BSA antibody were significantly lower in NBM lesioned rats (compared to IC and SO). The results showed that in NBM-lesioned rats both the humoral and cellular immune responses were suppressed.

Involvement of delta-opioid receptors in immunosuppression

The present experiments demonstrate that: (1) activation of delta-opioid receptors by a highly selective agonist DSLET leads to immunosuppression, whereas the blockade of these receptors by enkephalin analog ICI 174864 produces immunostimulation; (2) the immunomodulating effect of delta-opioid receptors is mediated by central mechanisms involving the hypothalamus-hypophysis complex; (3) the postsynaptic 5-HT (serotonin) receptors of 5-HT-2 type are involved in the immunoinhibitory action of DSLET. On the other hand, the immunostimulating effect of ICI 174864 is realized with the participation of D-2 postsynaptic DA (dopamine) receptors. It has also been shown that thymus is implicated in the immunostimulating influence of ICI 174864. The data obtained are explained as a result of the interaction of the neuromediator and opioid peptidergic systems in 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.

The role of brain-immune interactions in immunotoxicology

Certain xenobiotics (or the metabolites) can damage immunocompetence by directly interacting with one or more of the cells of the immune system and adversely affecting its function. It has also been proposed that xenobiotics may indirectly affect immune function by affecting other organ systems that will in turn affect immunocompetence. This review surveys evidence that supports the existence of a functional link between the brain and the immune system. In addition, we review data that support the concept that a xenobiotic-induced dysfunction in the neuroendocrine system may be associated with an immune dysfunction as well. Such chemicals do not necessarily interact directly with immunocompetent cells but would instead act to disrupt regulatory brain-immune interactions. This class of indirectly acting immunotoxic xenobiotics would not be detected in the typical in vitro screening assays.

Locus ceruleus and immunity. III. Compromised immune function (antibody production, hypersensitivity skin reactions and experimental allergic encephalomyelitis) in rats with lesioned locus ceruleus is restored by magnetic fields applied to the brain

This study deals with the relationship between the immunosuppression induced by electrolytic lesions placed into the nucleus locus cerules and the immunopotentiation produced by micromagnets implanted to the parietal area of the skull. The following groups of rats were set up: LC, rats with lesioned locus ceruleus; ShL, sham-lesioned animals bearing non-magnetic beads in the brain parietal region; M, rats with micromagnets of 60 mT influx density in the parietal part of the skull; LCM, animals with impaired locus ceruleus and magnetic beads placed in the parietal area of the skull; and IC, intact control rats. Animals of all groups were tested for plaque-forming cell response, circulating antibodies to sheep red blood cells and bovine serum albumin, Arthus and delayed hypersensitivity skin reactions to bovine serum albumin and old tuberculin, and experimental allergic encephalomyelitis. In LC-rats, humoral and cell-mediated immune reactions were compromised. On the other hand, immune responses in M-rats were significantly potentiated. In LCM-rats, however, the immunosuppression induced by destruction of the locus ceruleus was abrogated by prolonged exposure of the brain parietal region to the magnetic fields, i.e. immune reactivity of LCM-rats was quite similar to that of control IC- and ShL-animals. Several mechanisms may account for the immunomodulating effects produced by lesioning of the locus ceruleus and exposure of the brain to magnetic fields. Noradrenergic, serotoninergic, dopaminergic and peptidergic neurotransmitters, as well as growth hormones and immunopeptides, produced within the central nervous system or elsewhere, may be implicated as necessary for the interactions among the brain, immune apparatus and magnetic fields.

Modulation of non-specific immunity by hippocampal stimulation

Rats subjected to electrical stimulation of hippocampus (30 min/day for 4 days) showed an increase in the neutrophils in the peripheral blood when compared to sham (P < 0.01) and controls (P < 0.001). They also showed a significant decrease in lymphocytes, when compared to control rats (P < 0.001). Both sham and stimulated animals showed a significant decrease in total white blood cell count when compared to controls (P < 0.001). The phagocytic index of stimulated animals showed a significant increase from control (P < 0.001) and sham (P < 0.001). In addition, the stimulated animals showed a significant (P < 0.001) decrease in plasma corticosterone level when compared to sham and controls.

Enkephalins, brain and immunity: modulation of immune responses by methionine-enkephalin injected into the cerebral cavity

There is a large number of interactions at molecular and cellular levels between the nervous system and the immune system. It has been demonstrated that the opioid neuropentapeptide methionine-enkephalin (Met-Enk) is involved in humoral and cell-mediated immune reactions. Met-Enk injected peripherally produces a dual and dose-dependent immunomodulatory effect: high doses suppress, whereas low doses potentiate the immune reactivity. The present mini-review concerns the immunological activity of Met-Enk after its administration into the lateral ventricles of the rat brain, and describes the extraordinary capacity of centrally applied Met-Enk to regulate/modulate the immune function. This survey is composed of sections dealing with (a) the role of opioid peptides in the central nervous system (CNS); (b) the activity of opioid peptides in the immune system; (c) the application of Met-Enk into the cerebral cavity; (d) the influence of centrally administered Met-Enk on nonspecific local inflammatory reaction; (e) the effect of Met-Enk injected intracerebroventricularly (i.c.v.) on specific delayed hypersensitivity skin reaction, experimental allergic encephalomyelitis, anaphylactic shock, plaque-forming cell response, and hemagglutinin production; (f) the central antagonizing action of quaternary naltrexone, an opioid antagonist that does not cross the brain-blood barrier, on Met-Enk-induced immunomodulation; (g) the alteration of immune responsiveness by i.c.v. injection of enkephalinase-degrading enzymes; (h) the participation of the brain-blood/blood-brain barrier in the CNS-immune system interaction; and (i) the role of opioid receptors in immunological activity of Met-Enk. A hypothesis has been advanced for the reaction of Met-Enk and opioid receptor sitting on the cell membrane. This concept suggests that the constellation of chemical residues of enkephalin and receptor in the microenvironment determines the binding between the opioid partners. The plurality of conformational structures of enkephalins and receptors makes possible their involvement in a variety of processes which occur in different physiological systems, including the nervous system and the immune system, and intercommunications between the two systems.