Olfactory cues and morphine-induced conditioned analgesia in rats

Pharmacol Biochem Behav. 1998 May;60(1):115-8. doi: 10.1016/s0091-3057(97)00554-6.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analgesia*
  • Animals
  • Conditioning, Classical / physiology*
  • Male
  • Models, Biological
  • Morphine / administration & dosage*
  • Odorants
  • Rats
  • Rats, Sprague-Dawley
  • Smell / physiology*

Substances

  • Morphine