Morphine self-administration in the rat during adjuvant-induced arthritis.
Rats injected with Freund's adjuvant develop a syndrome resembling human rheumatoid arthritis complete with paw swelling, edema and persistent pain. At the onset of pain, arthritic rats and their pain-free littermate controls (vehicle injection) were allowed to self-administer intravenous morphine (5.0 mg/kg/injection) in a 24 hr/day schedule. Self-injected morphine appeared to provide analgesia in arthritic rats as demonstrated by a decreased sensitivity to applied tail pressure. Arthritic rats self-inject significantly less morphine than pain-free animals. Injection of indomethacin, which alleviates the pain and inflammation of the adjuvant-induced disease, reduces, at least initially, morphine self-injection in the arthritic but not pain-free animals. As the adjuvant-induced inflammation and pain dissipated, arthritic rats rapidly began to increase opioid intake. The presence of persistent pain apparently reduces the addictive properties of morphine.
Lyness
W H
WH
Department of Pharmacology, Texas Tech University Health Sciences Center, Lubbock 79430.
Smith
F L
FL
Heavner
J E
JE
Iacono
C U
CU
Garvin
R D
RD
D000818:Animals; D001168:Arthritis / Q000503:physiopathology*; D001169:Arthritis, Experimental / Q000503:physiopathology*; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000627:therapeutic use; D010146:Pain / Q000188:drug therapy*; D051381:Rats; D011919:Rats, Inbred Strains; D012646:Self Administration
D009020:Morphine; D007213:Indomethacin