Pfaus J G, Pendleton N, Gorzalka B B
Pharmacol Biochem Behav. 1986 May;24(5):1461-4. doi: 10.1016/0091-3057(86)90211-x.
Intracerebroventricular (ICV) infusions of the selective mu receptor agonist morphiceptin produce a dual effect on lordosis behavior in ovariectomized, steroid-primed rats. Low doses of morphiceptin (20 ng) inhibit lordosis whereas higher doses (2000 ng) facilitate this behavior. The present experiment tested whether naloxone, an antagonist of both high- and low-affinity mu receptors, or the long-acting high-affinity mu receptor antagonist naloxazone could block the dual effect of morphiceptin on lordosis. Ovariectomized rats primed with estrogen and progesterone received naloxone, naloxazone, or a control solution prior to ICV infusions of either 0, 20, or 2000 ng of morphiceptin. Naloxone reversed both the inhibition and facilitation of lordosis produced by morphiceptin, but had no effect on lordosis when administered before control infusions. In contrast, naloxazone reversed the inhibition but not the facilitation of lordosis. These results indicate that the inhibitory effect of morphiceptin on lordosis reflects the activation of high-affinity mu receptors whereas the facilitatory effect reflects either the activation of low-affinity mu receptors or other opioid receptor subtypes. The failure of naloxone or naloxazone to affect lordosis in rats receiving control infusions of saline further suggests that endogenous opioid systems do not exert a tonic inhibitory or facilitatory action on lordosis behavior.
向去卵巢并用类固醇预处理的大鼠脑室内（ICV）注射选择性μ受体激动剂吗啡肽，对其脊柱前凸行为产生双重影响。低剂量吗啡肽（20纳克）抑制脊柱前凸，而高剂量（2000纳克）则促进这种行为。本实验测试了高亲和力和低亲和力μ受体的拮抗剂纳洛酮或长效高亲和力μ受体拮抗剂纳洛唑酮是否能阻断吗啡肽对脊柱前凸的双重影响。在向去卵巢并用雌激素和孕激素预处理的大鼠脑室内注射0、20或2000纳克吗啡肽之前，分别给予它们纳洛酮、纳洛唑酮或对照溶液。纳洛酮逆转了吗啡肽对脊柱前凸的抑制和促进作用，但在对照注射前给药时对脊柱前凸没有影响。相比之下，纳洛唑酮逆转了对脊柱前凸的抑制作用，但没有逆转促进作用。这些结果表明，吗啡肽对脊柱前凸的抑制作用反映了高亲和力μ受体的激活，而促进作用反映了低亲和力μ受体或其他阿片受体亚型的激活。纳洛酮或纳洛唑酮对接受生理盐水对照注射的大鼠的脊柱前凸没有影响，这进一步表明内源性阿片系统对脊柱前凸行为没有持续性的抑制或促进作用。
