Open AccessOlfactory Cues and Morphine-Induced Conditioned Analgesia in Rats
Author(s) -
Joanne M. Valone,
Christopher K. Randall,
Philipp J. Kraemer,
Michael T. Bardo
Publication year - 1998
Publication title -
pharmacology, biochemistry and behavior
Language(s) - English
Resource type - Journals
eISSN - 1873-5177
pISSN - 0091-3057
DOI - 10.1016/s0091-3057(97)00554-6
Subject(s) - morphine , odor , conditioning , classical conditioning , analgesic , saline , anesthesia , chemistry , medicine , mathematics , statistics , organic chemistry
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.