[Effects of morphine on muscarinic receptors in limbic system in acute adjuvant-induced arthritic rats].

To induce arthritis, the adjuvant with heat-killed Mycobacterium tuberculosis was injected into the ankle joint in rats. Local redness, swelling, hotness, pain, and motor dysfunction of the inflamed joint (as well as mental dullness) were observed 48 h after inoculation. At this time, the maximal binding capacity (Bmax) of muscarinic receptors in limbic system was increased, while the dissociation constant (Kd) was unchanged. Injection of morphine (5 mg.kg-1) 3 times within 48 h after the inoculation resulted in a decrease of Bmax and an increase of Kd of M-receptors, together with diminution of pain and disappearance of dullness.