Kappa receptors affecting

Mu and kappa receptor agonists have been shown to affect central dopaminergic activity in rodents in vivo and in vitro [78, 79]. This has been investigated with RP 60180 (51), which decreases dopamine (DA) utilization in rat prefrontal cortex and in the striatum (by 30—35 % and 10 % respectively at 1-2.5 mg/kg s.c.) whereas the mu agonist morphine causes a significant increase (90-150% and 30 40% respectively at 5 mg/kg), an effect which is abolished by RP 60180 (1 2.5 mg/kg) [80]. 

The direct effects opioid and opioidlike peptides exhibit on cells of the immune system is both varied and, in some instances, contradictory, depending on which receptor subtype is being studied. Mu and kappa receptors generally affect immunofunction in a suppressive manner, where delta receptors tend to express immunostimulation [82-85]. However, selected delta antagonists have shown to elicit suppressive effects on B-cell proliferation, NK cell activity, and T-helper cell cytokine production [86]. The alteration of leukocyte function via opioid receptors will be discussed highlighting specific cell subtype immunomodulation. Endorphin shows a inhibitory effect on splenocyte proliferation through central and peripheral autocrine/paracrine pathways [87]. 

Several opiate receptors have been identified on cells of the nervous systems of animals and humans, with mu (p), kappa (k), and gamma (y) subtypes being predominant. These classical opiate receptors are G- protein coupled 7-transmembrane molecules.27 Opiates predominantly affect immune responses directly by ligation of p, k, and y opiate receptors, as well as non-classical opiate-like receptors, on immune cells and indirectly by binding to receptors on CNS cells. Studies conducted in vitro with opiate-treated immune cells demonstrated receptor-mediated reduced phagocytosis, chemotaxis and cytokine and chemokine production. These effects are linked to modulation of host resistance to bacterial, protozoan, viral and fungal infections using animal models, cell lines and primary cells. 

Peckys D, Hurd YL. 2001. Prodynorphin and kappa opioid receptor mRNA expression in the cingulate and prefrontal cortices of subjects diagnosed with schizophrenia or affective disorders. Brain Res Bull 55 619-624. 

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