The role of endogenous opioids in fear conditioning

Eippert, F., and Büchel, C.
Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf

The endogenous opioid system is involved in fear learning in rodents, as opioid agonists attenuate and opioid antagonists facilitate the acquisition of conditioned fear. To clarify whether blockade of endogenous opioid neurotransmission enhances acquisition of conditioned fear in humans, and to elucidate the neural underpinnings of such an effect, we used fMRI in combination with behavioral recordings and a double-blind pharmacological intervention. All subjects underwent a classical fear-conditioning paradigm, but subjects in the experimental group received the opioid antagonist naloxone during the experiment, in contrast to subjects in the control group, who received saline. Blocking endogenous opioid neurotransmission with naloxone led to more sustained responses to the unconditioned stimulus across trials, evident in both behavioral and BOLD responses in pain responsive cortical regions. Most importantly, naloxone enhanced the acquisition of fear on the behavioral level and changed the activation profile of the amygdala: whereas the control group showed rapidly decaying conditioned responses across trials, the naloxone group showed sustained conditioned responses in the amygdala.

Symposium 2: Neuronale Korrelate der Konditionierung
11.06.2009, 13:00-14:00
Seminarraum 10