Opioid receptors in the midbrain periaqueductal gray regulate prediction errors during pavlovian fear conditioning

Behav Neurosci. 2006 Apr;120(2):313-23. doi: 10.1037/0735-7044.120.2.313.


The authors used a within-subject blocking design to study the role of ventrolateral periaqueductal gray (v1PAG) opioid receptors in regulating prediction errors during Pavlovian fear conditioning. In Stage I, the authors trained rats to fear conditioned stimulus (CS) A by pairing it with shock. In Stage II, CSA and CSB were co-presented and followed with shock. Two novel stimuli, CSC and CSD, were also co-presented and followed with shock in Stage II. CSA blocked fear from accruing to CSB. Blocking was prevented by systemic pretreatment with naloxone. Blocking was also prevented in a dose-dependent and neuroanatomically specific fashion by vlPAG infusions of the micro-opioid receptor antagonist CTAP. These experiments show that v1PAG micro-opioid receptors contribute to Pavlovian fear learning by regulating predictive error.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Behavior, Animal
  • Conditioning, Classical / drug effects
  • Conditioning, Classical / physiology*
  • Dose-Response Relationship, Drug
  • Electroshock / adverse effects
  • Fear*
  • Freezing Reaction, Cataleptic / drug effects
  • Freezing Reaction, Cataleptic / physiology
  • Freezing Reaction, Cataleptic / radiation effects
  • Male
  • Naloxone / pharmacology
  • Narcotic Antagonists / pharmacology
  • Peptide Fragments
  • Peptides / pharmacology
  • Periaqueductal Gray / drug effects
  • Periaqueductal Gray / physiology*
  • Photic Stimulation / methods
  • Rats
  • Rats, Wistar
  • Receptors, Opioid / metabolism*
  • Somatostatin


  • CTAP octapeptide
  • Narcotic Antagonists
  • Peptide Fragments
  • Peptides
  • Receptors, Opioid
  • Naloxone
  • Somatostatin