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Conditioned opioid activity in the rat fetus
H M Arnold1, S R Robinson, N E Spear
1Department of Psychology, Binghamton University, New York 13902-6000.
Behavioral Neuroscience
|December 1, 1993
Summary
Rat fetuses can learn through classical conditioning, showing reduced facial responses after pairings of sucrose (conditioned stimulus) and milk (unconditioned stimulus). This in utero learning involves the endogenous opioid system.
Area of Science:
- Neuroscience
- Developmental Psychology
- Behavioral Biology
Background:
- Classical conditioning demonstrates associative learning.
- Fetal learning capabilities are increasingly recognized.
- The endogenous opioid system plays a role in reward and analgesia.
Purpose of the Study:
- To investigate classical conditioning in rat fetuses.
- To determine if fetuses can form associative learning in utero.
- To identify the neurobiological mechanisms underlying fetal learning.
Main Methods:
- Four experiments utilized rat fetuses on Embryonic Day 20.
- Classical conditioning involved pairing sucrose (CS) with milk (US).
- Perioral cutaneous responsiveness was measured using a facial wiping bioassay.
Main Results:
- Reexposure to sucrose reduced fetal facial wiping only in conditioned subjects.
- This effect was specific to paired CS-US presentations, excluding habituation or sensitization.
- Fetuses responded to the chemosensory, not tactile, properties of sucrose.
Conclusions:
- Rat fetuses exhibit classical conditioning in utero.
- Conditioned responses involve the endogenous opioid system and mu-opioid receptors.
- These findings confirm in utero learning and opioid-mediated responses in fetal rats.