μ- but not δ- and κ-opioid receptor mediates the nucleus submedius interferon-α-evoked antinociception in the rat

Previous studies have indicated that interferon-alpha (IFN-α) can bind to opioid receptors and exerts an antinociceptive effect in both peripheral and central nervous systems. The current study investigated the antinociceptive effect of IFN-α unilaterally microinjected into the thalamic nucleus submedius (Sm) of rats on noxious thermal stimulus, and the roles of different subtypes of opioid receptors in mediating the Sm IFN-α-evoked antinociception. The results indicated that unilateral microinjection of IFN-α (4, 8, 16 pmol) into the Sm dose-dependently increased the hind paw withdrawal latency from the noxious heat stimulus, and this effect was reversed by pretreatment with non-selective opioid receptor antagonist naloxone (200 pmol) and specific μ-opioid receptor antagonist β-FNA (1 nmol) into the same sites, whereas δ-opioid receptor antagonist ICI174,864 (1 nmol) and κ-opioid receptor antagonist nor-BNI (1 nmol) failed to alter the effect of IFN-α. These results suggest that Sm is involved in IFN-α-evoked antinociception and μ- but not δ- and κ-opioid receptor mediates the Sm IFN-α-evoked antinociception.