Since the proposal of multiple classes of opiate receptors, much effort has been devoted to understanding the subtypes mediating specific opioid actions. Using the irreversible antagonist naloxozone, we have established a role for the high affinity (μ1) sites in analgesia. These sites also appear important in opiate catalepsy. Control rats showed dramatic catalepsy following a high dose of morphine sulfate (100 mg/kg, s.c.). Rats whose high affinity (μ1) sites had been blocked with naloxazone 24 h earlier, on the other hand, showed no evidence of catalepsy (P < 0.01). Accordingly, catalepsy appears to involve the same receptors as analgesia, the higher affinity (μ1) sites.
ASJC Scopus subject areas