CTAP reverses the Na
S-induced antinociception. Pre-treating rats with the selective μ opioid receptor antagonist CTAP (0.09 mg/kg i.c.v. thirty minutes before Na2S; panel C) abrogates the antinociceptive effect of Na2S (100 μMol/kg i.p.). In contrast, the selective δ opioid receptor antagonist NTI (4 μg/kg i.c.v. five minutes before Na2S, panel A) and the selective κ opioid receptor antagonist GNTI (0.08 μmg/kg i.c.v. three days before Na2S, panel B) do not inhibit the analgesic effect of Na2S, indicating that δ and κ opioid receptors have no effects on Na2S-induced antinociception. Data are mean ± SEM of 5 rats. *p < 0.05 versus CRD.