Small-animal neuroimaging analysis of placebo analgesia

2016 Fiscal Year Final Research Report

• Project/Area Number: 15K14328
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Neurophysiology / General neuroscience
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: CUI Yilong 国立研究開発法人理化学研究所, ライフサイエンス技術基盤研究センター, ユニットリーダー (60312229)
• Co-Investigator(Renkei-kenkyūsha): Okauchi Takashi 国立研究開発法人理化学研究所, ライフサイエンス技術基盤研究センター, リサーチアソシエイト (80415405) ; Shingaki Tomotaka 国立研究開発法人理化学研究所, ライフサイエンス技術基盤研究センター, 研究員 (60643187)
• Project Period (FY): 2015-04-01 – 2017-03-31
• Keywords: Placebo / Pain / Neuroimaging / PET / Opioid

Outline of Final Research Achievements

Placebo analgesia is a kind of pain relief that follows the administration of an inert treatment and is thought to result from expectation and implication. However, the underlying neural and molecular mechanisms in detail are still poorly understood. To address this issue, we tried to establish an animal model of placebo analgesia in neuropathic pain rats using Pavlovian conditioning, in which neuropathic pain was caused by tight ligation of the lumber 5/6 spinal nerves and Pavlovian conditioning was established with a painkiller (gabapentin) as the unconditioned stimulus. We found that after a few trials of paired stimulation of gabapentin with conditioning stimulus, the inert treatment (saline, i.p.) alone also induced analgesia in some animals. Such placebo analgesia was completely blocked by naloxone, a mu-opioid receptor antagonist. Small-animal neuroimaging results also showed that regional brain activity in the mPFC, rACC, and vlPAG positive correlation with placebo score.

Free Research Field

脳科学