The immunomodulating effects of specific opioid receptor antagonists after their intracerebroventricular application

The role of central opioid receptor types in the modulation of humoral immune response has not been investigated so far. Therefore, the aim of the present work was to investigate the possible role of these receptors in immunomodulation. For this purpose, male Wistar rats were intracerebroventricularly (icv) injected with opioid receptor specific antagonists. Control groups of rats were treated icv with physiological saline. Primary humoral immune response was determined by the "plaque-forming cell assay" (PFC response). ICI 174864, a selective δ opioid receptor antagonist, administered icv at doses of 0.01, 0.1, 1, 10, 20 and 50 μg/kg body weight (kg bw) caused a statistically significant immunosuppression. β-funaltrexamine (β-FNA), specific m opioid receptor antagonist, applied icv produced a significant immunosuppression only at lower doses of 0.01 and 0.1 mg/kg bw. Nor-binaltorphimine (nor-BNI), a selective κ opioid receptor antagonist administered icv, produced significant immunopotentiation at doses 0.1; 1; 10 and 50 μg/kg bw and not except at for the lowest dose of 0.01 μg/kg bw. Quaternary naltrexone (QNTx), which is a μ opioid antagonist at lower doses, but a nonselective opioid antagonist at higher doses, caused statistically significant potentiation on PFC response only when it was icv given at doses of 1 and 10 μg/kg bw. The results indicated differential involvment of central opioid receptor subtypes in immunomodulation.