Interaction between dopamine D1 and D2 receptors in modulation of the immune response

The interaction between dopamine D1 and D2 receptors plays a role in immunomodulation. The results of thus interaction depends on the degree of receptor activation with selective agonists in different doses. Combined treatment with agonists of D1 and D2 receptors in high doses had a synergistic effect in the mechanisms of immunomodulation. Receptor agonists in low doses suppressed the immune response. Our results suggest that weak activation of one of these receptors is accompanied by inactivation of the other receptor type.

Involvement of dopamine D1 and D2 receptors in the rat nucleus accumbens in immunostimulation

Analysis of the nature of changes in the immune response in operated Wistar rats showed that electrolytic lesioning of the nucleus accumbens, the site of the greatest density of dopamine D1 and D2 receptors, led to suppression of the immune response in animals immunized with sheep erythrocytes. Administration of SKF 38393 (20 mg/kg) and quinpirol (1 mg/kg), selective agonists of dopamine D1 and D2 receptors respectively, to sham-operated rats induced significant increases in immune responses. However, no immunostimulation was seen on administration of the selective dopamine D2 agonist quinpirol to animals with lesions to the nucleus accumbens as compared with controls. At the same time, treatment of animals with nucleus accumbens lesions using the dopamine D1 receptor agonist SKF 38393 had no effect on the immune response as compared with that in sham-operated animals given the D1 receptor agonist. These data provide evidence that dopamine D2 receptors in the nucleus accumbens have a role in the mechanisms of immunostimulation, though D2 receptors in other brain structures may also make some contribution to this process; D1 receptors in the nucleus accumbens make no significant contribution to controlling the immune response.

Significance of initial emotional state for neuroimmunomodulation in conditions of activation and blockade of 5-HT1A receptors

Experiments performed on male CBA mice immunized with sheep erythrocytes at a dose of 5 x 10(8) cells showed that the selective agonist of serotonin 5-HT(1A) receptors 8-OH-DPAT (1 mg/kg) suppresses the immune response in aggressive animals. In mice demonstrating the submissive type of behavior, formed during 10 days of experience of defeats, activation of 5-HT(1A) receptors with 8-OH-DPAT had no effect on the immune response. However, treatment with the selective 5-HT(1A) receptor blocker WAY-100635 stimulated the immune response, but only in submissive mice. These data lead to the conclusion that activation and blockade of 5-HT(1A) receptors have different effects on the immune response in CBA mice depending on the initial emotional state of the animals, due to different activities of neurotransmitter systems, particularly the serotoninergic, in aggressive and submissive mice.

Stimulation of the Immune Response During Activation of the Dopaminergic System in Mice with Opposite Types of Behavior

Studies reported here demonstrated that activation of the dopaminergic system induces increases in the immune response regardless of the type of behavior in mice (line CBA), i.e., in aggressive mice, submissive mice, and mice lacking experience of victory or defeat (controls). Changes in the activity of the dopaminergic system were induced with SKF-38393, a selective agonist of dopamine D1 receptors, and with p-chlorophenylalanine (PCPA), which we have previously shown to activate D2 receptors. In the aggressive form of behavior, which was characterized by strong (compared with controls) immune responses, SKF-38393 and PCPA led to further increases in the immune response. In submissive mice, activation of the dopaminergic system altered the nature of the immune response, with immunostimulation, as in aggression. It is suggested that activation of the dopaminergic system in conditions of defined psychoemotional status fixed by acquisition of opposite types of behavior, induces the formation of a new neurochemical pattern--the dopaminergic set--which led to changes in the nature and intensity of the immune response.

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 the nucleus accumbens in stimulation of the immune response in rats after activation of opioid mu receptors with DAGO

The involvement of the nucleus accumbens in neuroimmunostimulation was demonstrated during activation of opioid mu receptors with the selective agonist DAGO (100 microg/kg); single doses of this agent to sham-operated (control) Wistar rats induced significant increases in the numbers of direct IgM antibody-forming and total rosette-forming cells after immunization with sheep erythrocytes. Bilateral electrolytic lesioning of the nucleus accumbens in rats led to sharp decreases in the intensity of immune responses; there was no immunostimulation after administration of DAGO to these animals. These data provide evidence for the involvement of the nucleus accumbens in the process of immunomodulation and for the importance of opioid mu receptors in the nucleus accumbens in the stimulation of immunogenesis.

Effects of type 1A serotonin receptor agonist 8-OH-DPAT on immune response

The selective agonist of type 1 A serotonin receptors 8-hydroxy-2-(di-n-propyl-amino)tetra-lin (8-OH-DPAT) suppressed the immune response. Intraperitoneal administration of 1 mg/kg 8-OH-DPAT to Wistar rats over 2 days after immunization decreased the count of plaque- and rosette-forming cells on day 5. Our results indicate that type 1A serotonin receptors are involved in the realization of the immunosuppressive effects of the serotoninergic system.

Involvement of the rat caudate nucleus in the immunostimulatory effect of DAGO

The involvement of the caudate nucleus, i.e., the terminal zone of the nigrostriatal dopaminergic system, in neuroimmunostimulation during the activation of mu opioid receptors by the highly specific agonist DAGO. Single doses of DAGO (100 microg/kg) in sham-operated control Wistar rats induced significant increases in the numbers of direct IgM-antibody-forming and total rosette-forming cells at the peak of the immune response after immunization with sheet red blood cells. The experiments showed that bilateral electrolytic lesioning of the caudate nucleus in rats suppressed the immune response, demonstrating its involvement in neuroimmunomodulation. Since the effect of immunostimulation induced by DAGO disappeared when given to animals with caudate nucleus lesions, it was concluded that this structure is involved in activatory immunogenesis via mu opioid mechanisms.

[Changes in the level of serotonin in the brain and immunocompetent organs during the formation of the immune response]

The serotonin content increased in adrenals within 20 min after immunization of rats with sheep red blood cells, and diminished in ventral part of the anterior hypothalamus, hippocampus and in thymus. The number of antigen--responsive cells was increased twofold in bone marrow after the 1000-fold increase of the antigen dose. On the 4-5th days, the dependence of antibody-forming cells and rosette-forming cells number on the antigen dose was still observed in the spleen. The correlation between the serotonin level in the above brain structures and immunocompetent organs and the intensity of immune responses is discussed.