Inhibition of the analgesia inhibitory system by D-phenylalanine and proglumide.

Stimulation of a nonacupuncture point (NAPS) does not normally produce analgesia in the same way that stimulation of an acupuncture point does. However, NAPS did produce dexamethasone reversible analgesia after intraperitoneal treatment with D-phenylalanine (DPA) or proglumide, or after microinjection of these compounds into such parts of the analgesia inhibitory system (AIS) as the lateral centromedian nucleus of the thalamus and part of the posterior hypothalamus. Inhibition of acupuncture analgesia (AA), or of morphine analgesia (MA) by 0.5 mg/kg, IP, which is equivalent to AA after AIS lesion, and of potentials in the lateral periaqueductal central gray evoked by repetitive NAPS or stimulation of the AIS, were antagonized by DPA. Disappearance of AA and MA in morphine tolerant acupuncture responder and nonresponder rats was reversed to reproduce the same magnitude of analgesia after proglumide application. The reproduced AA and MA were antagonized by dexamethasone. These results indicate that DPA and proglumide antagonized the AIS and unmasked the dexamethasone reversible AA and MA.