Olfactory cues and morphine-induced conditioned analgesia in rats.
In a Pavlovian conditioning procedure, rats were exposed to an odor conditioned stimulus (CS) and then were given morphine with its effect serving as the unconditioned stimulus (US). After four CS-US pairings, the CS was tested alone to assess the presence of an analgesic conditioned response (CR) using a hot-plate test. In Experiment 1a, two groups were conditioned by pairing either 10 mg/kg morphine or saline with an odor CS. In Experiment 1b, two groups were given an odor CS paired or unpaired with 10 mg/kg morphine. These results established that an odor cue can support a morphine-induced analgesic CR. Experiment 2 characterized the dose-effect curve (0, 3, 10, and 30 mg/kg morphine) using an odor conditioning procedure. The dose-effect curve showed an inverted U-shaped function, with the 10 mg/kg morphine group having significantly longer paw-lick latencies compared to all other groups. This finding contrasts with the monotonically ascending dose-effect curve for the analgesic unconditioned response (UR) to morphine.
Valone
J M
JM
Department of Psychology, University of Kentucky, Lexington 40506-0044, USA.
Randall
C K
CK
Kraemer
P J
PJ
Bardo
M T
MT
D000698:Analgesia; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009020:Morphine / Q000008:administration & dosage*; D009812:Odorants; D051381:Rats; D017207:Rats, Sprague-Dawley; D012903:Smell / Q000502:physiology*
D009020:Morphine